Inner transition elements or d-block elements
The elements from Ce to Lu and from Th to Lr are called inner transition elements have been shown at a separate pkace at the bottom of the periodic table.
The first series of 14 elements lies between La and Hf ib 6th period while the other series of 14 elements lies between Ac and Ku in 7th period . Both the sreies are present in IIIB (3) group.
The element of 1st series are called lanthanides or lanthanones while those of second series are called actindes or actinones. The name lanthanide and actinides has been given since these element follow La and Ac respectively with which these elements show close similarties .
Chemistry ofLanthanides
F block elements
Lanthanides series
elements are also called fblock elements. Thus the last electron enters (n 2) f subshell in inner-transition elements.
Valence shell electronic conjiguration of the atoms of f block elements can be represented as (n2)]"‘“ (n1)d"‘2 us 2which shows that in these elements the intermost three shells are partially-filled while the remaining inner shells are E ' partially filled.
.Classification of f-Block Elements '1Inner transition elements (f-block elements) have been classified into the following two series.
(i) Lanthanide series (CeEB to Lu ). The 14 elements from Ce t0 Lu are the members 0f this series, i. e 14 elements7 from Ce“ to L 1.,1 are called lanthanides. or elements are called lanthanides, since these elements are placed after
lanthamum (Lam) 1n group 3 and period 6 of the periodic table (See Fig. 9.1) and how close similarities with La“.
Since lanthanides are present Ln 6th period (n: 6) of the periodic table, these elements have six shells 1n their electronic configurationthe last electron in these elements enters (6-2) f or 4f subshell Thus lanthanides are als'o called 4f ?%lock elements, 1. e. lanthanides are a series of 14 elements (Ce5 ate Lu“) m which the last electron goes to 4f subshell or to f sub shell of 4th shell. ‘
It has been observed that all the 15 elements from La to Lu71 have similar properties. Hence the study of lanthanides consists of the study all the 15 elements om La to Lu together. La57 is the prototype of lanthanides.
Lanthanides are also called lanthanones or rare earths. The name are earth
Elements given to them because they were originally extracted from oxides for which “ancient name was earth and which were considered to rare. The term rare earth was avoided now because manv of these elements are no longer rare but are abudant nn ---
Position of lanthanides
Production of Lanthanide Metals
position of Lanthanides in the Periodic Table
All the fifteen lanthanides atomic numbers have atomic weights between those of barium( atomic number Z= 56 and hafnium Z= 72 ) and, therefore, must be placed between these two elements as was also proved by Moseley.
Production of Lanthanides Metals
The following methods may used for this purpose: »
1. Electrolysis of fused chlorides. This method is similar to that used the metallurgy of Ca by the electrolysis of CaCl2.
2. Reduction of anhydrous chlorides with Na. Lighter lanthanides such a.‘ La, Ce and Gd can easily be prepared by the reduction of their anhydrous chloride With Na at 100°C.
LaCla + 3Na i‘E-a La + 3NaCl f}
3. Reduction of anhydrous iiuorides and chlorides with Mg or C5;
Hence lanthanides such as Lu are prepared when their anhydrous fluorides chlorides are reduced by Ca or Mg metals at a temperature above 1000°C, sing: the fluorides are less volatile than the chlorides and consequently the loss cause by evaporation in case of fluorides 18 small. * -.
Properties of Lanthanides
1.Electronic Configurations
Electronic configurations of lanthanum (La) and fourteen Ianthanides (Ceto Lu) are given in Table 9.1. Valence shell electronic configurations (V. S. E C. )these elements are also given in the same Table. 33
After the completion of 6S orbital at Ba [Ba = [Xe} in La according to Aufbau principle must enter according to Aufbuu principle, must 4f orbitals to give configuration to La but in La , the energy“ 5d orbitals IS lower than that 4f orbitals as shown 1n Fig 9. 3. Consequently 5th electron 1n La enters 5d orbitals instead of 4f orbitals. Thus the electronic configuration of La Xe 4f 5d 6s is 1X91“ 4f"5d‘632 and not [Xe],N f" 1°65 as predicted by aufbau principle
Excepting Gd“ and Lu, other lanthanides have empty 5d orbitals (5d° configuration). Electronic configurtion of Eu 1s [Xe] 4f75d°65and that of Gd [Xe154f’ 5d‘ 6532 Both these configurations are stable due to the presence of stable halftilled 4f orbitals (4f’ configuration) in them. Electronic configuration of wa 41‘“ 5d° Gs2 and that of Lu711s [Xe]5 4f“ 5d‘ Gs2. Both these configurations are
stable due tobthe presence of stable of these elements can be written as: ‘
)
the experimental fact that Sm ion has a tendency to get reducedd to Ce ion in aqueous solution.
28m" + 2H20 ---» 28m" + 0n + "2 (RA) (H +1) (H I 0) Ce"+ Fem ~-> Ce" + F0" ‘ Prue ,
Thus sm" is a good RA and Ce is a good OA In aqueous solution. Pr‘ ‘and Tb" are ex on more powerful oxithsing agents
3. Atomic and Ionic Radii: Lanthnnide Contraction
Atomic radIi of Ln atoms and ionic radii of Ln" are given below In Table 9. It may be seen that as we move along lanthanide series. there is a stead decrease In the value of radii.
The steady decrease in atomic and ionic radii of lanthanide elements with increasing atomic number is called lanthanum contraction. ,
Cause of Lanthanide Cohtraction ~
'1
‘We know that as we proceed from one element to the next one in lanthanide series, the nuclear charge (Le., atemic number) increases by +1 at each element . Thus as we move from Ce to Lu, the attraction between the nucleus aIl in the outermost shell electron Increases gradually at each step. It Is also known th 7 as we move from Ce to Lu, the addition of extra electron takes place to 4f orbitals
Since 4 orbitals have ve diffused shape. the electrons In these orbitals are” not to shield (decrease) attraction between the nucleus and the outerMost shell in the 4 ‘ outermost 3 el as 1e atomIc number of lanthanides only du to the Increase. In tITYIuclcnrcharge I..e, mcmasemte attraction between nucleus and the outer-most shell electrons) that the size of the lanthanide atoms’ and M" Ions decreases gradually with atomic number The above discussion shows * He: that it is due to the poor shielding effect of 4felectrons and gradual Increase in nuclear charge that the lanthanide contraction takes place among lanthanides.
Consequences of Lanthanide Contraction
Lanthanide contraction plays an important role In determining the chemistry end heavier transition series elements. Some important oonsequen 0 La on are discussed below:(V nic radii of the two in pairs an the same. The above discussion shows that its due to the poor shielding effect of 4f electron and gradual increase in the nuclear charge that the lanthanide contraction takes place among lanthanides.
.x
2nd and 3rd transition series are given in Table 9 4. This table shows that the atomic radius of La (element of 3rd transition series) 15 greater than that of Y On thebasis of trend the atomic radii of the two elements present in each of the pairs viz ZrHf NbTa, M0 W
Ku should be in the order Hf> Zr Ta > Nb W > Mo etc, but the atomic radii of the element is due to the lanthanide contraction seen in lanthanides which lies between La and Hf. Thus we can say that due to lanthanide cnntraclmn the atomic radius 0f 3rd transition series following La is nearly the same ac that of the 11 responding element lying in the same group
Lanthanide contraction
(ii) Similarity in properties of the two elements in the pairs viz Zr-Hf, .-Ta, Mo-W etc,
We have said above that, due to lanthanide contraction, the atomic size of the two elements present in the pairs mz Zr-H.f, NbTa Mo'W etc.are almost the same. Due to similarity in their atomic size, the properties of the f1 elements in each of the above pairs are very sunilar.
(iii) Difficulty in the separation of lanthanides. We know that the
1 properties of metal ion is determined by their size and charge. Now since, on proceeding Erom Ce to Lu the change. In the size of Ln ion is very small and these ions have the same charge (= +3) chemical properties of lanthanides are
most identical. Due to identical properties. the separation of lanthanides from one another' in the pure state is ditiicult.
(iv) Comparison between the densities of the elements of 2nd and transition series.
The densities of d-block elements are given in Table 9 5. it may be seen from the table that the densities of elements belonging to the same sub-group icreases on moving down the sub-group .The densities of the d block elements transition series are only slightly higher than those of the corresponding elements of lst transition series while these values for the transition elements from Hf to Hg“ (elements of 3rd transitmn series) are almost double these values T0 the elements from Zr 0 to Cd“ respectively (elements of 2nd transition series ) 1 Note that the density of La (= 6.“17)' 15 not double that of the value for Y (= 4. 47).
The variation of densities oftransition series element' 1.11 the given subgrous as discussed above, can be explained as follows on the basis of lanthanide contraction.
because of lanthanide contraction occurring in lanthanides, the atomic sizes Elements (f ,d transition series coming after La. Consequently the packing off, the atoms in their metallic crystals become so much compact that their densities become very high.
(v) Basic character of hydroxides, M(OH)3 decreases from La(OH) t‘ 'Lu(OH).
Due to lanthanide contraction, the size of +3 lanthanide 1on3 (M3 ions ) decreases regularly with increase in atomic number. As a result of this decrease in size the covalent character between M3‘ ion and OH‘ mus increases from La(0H). (Fajan ’3 rules). Therefore, the basic character of the hydroxides decrease a with increase in atomic number. Consequently, La(OH.)3 is most basic while Lu(0 IE: _ is the least basic. i: '
hydroxides of lanthanides are stronger bases than Al(OH) but weaker th.
‘ Ca(OH) 1' L . 4. Colour of Tripositive Lanthanide Ions (M Ions) Most of the trivalent cations of lanthanide elements are coloured in the 501i as well as in aqueous solution while only a few 1on 5 are colourless. (See Fig. 9 4) . f It may be seen from Fig. 9. 4 that the colour depends on the number of electron present' 1n 4f orbitals The elements having n electrons' in 4f orh1tals has the same colou Tr as the which has (14n) electrons 1n 4f orbitals For example La (4P) which has no electron in its 4f orbitals (n: 0) 1s colourless and Lu3* ion (4)“) which has (140): 14 electrons 1n 4f orb1tals 18 also colourless.Similar1y P1“ 1011 (4F) Which has two electrons' 1n its 4f orbitals (n: 2) and Tm“ 10!] MI“) which has (142): .5; 12 electrons 1n its 4f orbitals have the same colour (green). (See Fig. 9. 3).
Origin of colour.
Colour of lanthanide tripositive ions is due to f f transitin .The absorption bands in the visible region of electronic spectra of the 1ons in their compounds arise due to the absorption of light in the visible range. This results in the transition of the electrons of the ions from the lower energy 4f-orbitals to their higher energy 4f-orbitals. Thus lanthanide ions have colour which is complement to the colour of the absorbed light. This type of electronic transition, which takes place due to absorption of light, is called f-f transition. Evidently absorption bands seen in the electronic spectra arise due to electronic transition within 4f orbitals ‘3’} f-f transitions of lanthanides are more forbidden than dd transition of metal ion because 4f electrons of lanthanide ions are much less affected}; a liganad elecrons than the electrons in d-orbitals of transition metal ions groups the selection rules are more strictly followed for transitionin the compounds of lanthanides than in the compounds or f transition metals.
5. Magnetic Properties of Tripositive Lanthanide
M ions)
We known that in Lais empty and that Lu ion is completely filled (4 coniiguration). Thus since all the eléctrons present p 4f orbitals 1n Lu are paired, La shows diamagnetic character. Due the absence of any electron in 4f orbitals of La. This is also diamagnet. The remaining M are paramagnetic, since 4f orbitals in the remaining ions are partly filled.
To Calculate the value of amu for M" ions.
In-M3" ions, since 4f orbitals are Well shielded from the surroundings by the overlapping 5s and 5p orbitals electric field of ligands surrounding M3+ ions does not restrict (destroy 01' quench the orbital motion of electrons present in partly filled 4f orbitals of M3+ ions. Thus M ions, in addition to spin motion, orbital motion of electrons also contribu to the value of pm of M? ions, 1'. e. both types of motion of electrons contribute to 1 Value of pm of M3" 10118. 4felectrons are free to undergo L and S coupling to g? overall (tota1)angular momentum quantum number, which decides the value of for W 10118. um fer Ma? ions is thus represented as which amu given by
It may be seen from Table 9. 6 that the calculated values of amu of some M3 are in good agreement With the experimental values.
In Fig. 9. 5 experimental value of magnetic moments (in BM) of M3 are plotted against the number of unpaired electrons (n) m 4]" orbitals. From figure it may be seen that Laa+ ion (4f°) IS diamagnetic (p: 0), since it has electron 4f orbitals. Pm value increases upto Nd3+ ion and then decrease. It starts rising again and becomes maximum at about
10.5 BM for Dy“. It again starts decreasing and becomes zero (diamagnetic) at ion due to 4 1‘ configuration
The type of paramagnetism which is found in M3” ions is that in which the energy difference (AE) between the lowest energy J level of the metal ion. and the adjascent excited state is larger than thermal energy (kT) at room temperature . Thus since the excited states are much above the ground state, it is only the lowest energy state which is occupied by metal ions. Other states are not occupied by metals ions. Note that a magnetic field of strength H, each J level is split into 2J +'f‘ states in which each levels separated from its neighbours by BH. In case of su, metal ions the value of u frist given by equation (12).
Equation (1') IS not applicable for Sm3+ and Eu3’“ ions, since the lowest state (ground state) 1s close to the j excited state and hence the energy separation (AE)= kT. In such cases, calculated by taking J of the ground state only will not give the correct value oftenE for Sm3+ and Eu8+ lons.
The value of Per calculated from equation (i) for Sm3+ and Eu“ ions are; 0.86 BM and 0.0 BM F respectively (See Table 9. 6). In the calculation of these values W .1 l: have used J: 5/2 fors Sm3” and J: -0 for Eu3+ Total values of J for these ions are as.
Experimental values of amu for Sm" and Eu” ions are 16 BM and 3. 60 BM :respectively. These values show that Physical Properties
All the lanthanides are soft, malleable and ductile, and have low tensile.They are not good conductors of heat and electricity In general the atomic numbers and densities of these elements increase with the increases in atomic number. : Lanthanides have high melting and boiling points. However, they donot exhibit 3 regular trend with rise in atomic number. Lanthanides have low ionization
energy which compare well with those of the alkaline earth metals particularly Calcium
properties Dependent on Standard Oxidation Potential Values
The standard oxidation potentials (E values) of lanthanides (M) for the oxidation half-reaction,
M(s)‘ -> M3' (aq) + 3e
are given below.
' ' 1‘ ---------EZ, values involts decrease --------> .
15-12“:La-252 Ce'=2.48, Pr=2.46, Nd: 2.43, Pm: 2.42 Sm: 2.41,Eu= 2.40,
I
5i." .3" =2.39 Tb: 2.39, Dy: 2.,35 H0: 232, Er: 230, Tm: 2.28 Yb: 2.2:7Lu 2.25
g‘ These E“ values explain the following properties of lanthanides:
E: (1') Reducing property.
Since lanthanides have positive E" values these elements (M) have a strong tendency to lose their three electrons hence act as strong reducing agents. Due to the decrease of E" values from La If Lu, the reducing power of lenthanides also decreases from La to Lu.
h(11') Electropositive character.
Since E" values are high, lanthanides can readily lose their electrons and hence show strong electropositive (or metallic) character With the decrease of E" values from La to Lu, the electropositive
. Solubility of Compounds of Lanthanides
_ The nitrates, chlorides, sulphates, perchlorates and salts of oxy acids of lanthanides are soluble but the oxalates, carbonates and fluorides are insoluble 1n
é ,Water. Note that the sulphates of the elements of group 2 are insoluble in water.
Fnrmation of Double Salts
Lanthanides form a number of double salts.1mportant double salts formed by given below (M 15 the lanthanide element) (1) Cdrbonates, e..g K2
nitrates, e.g. 31 Mg(NO )2. 2M(N0). 24H,O (111) Sulphates, gr Ni1SO Mi so”) 8 water.
10. Chemical Reactivity
Lanthunides differ from one number only in the number of 4f electrons. Since those elements (are very effectively shielded from Interaction with other elements by the overlying 5S, 5p and 6:5 Neutrons they show very little difference in tthe chemical reactivity. Some of the chemical properties of lanthunides are given below
(ii Lauthanides are highly reactive, silverywhite metals. These meta1s ta . Tu readily on exposure to air In the finely divided state, these metals burn in form sesquioxide (MO ). Ce forms CeO. Ytterbium (Yb) resists the action of even at 1000 due to the formation of a protective coating of its oxide.
(ii) Lanthanides combine with H on heating. The hydrides formed are of MH2 and MH3 type. These hydrides are stable.
(iii) Lanthanides react with non metals like S, X2, P N2, C and Si to form corresponding compounds .
(1v) Lanthanides decompose H2O to evolve H2. Evolution of H2 takes Place slowly in cold and rapidly on heating.
Formation of Complexes
Although tripositive lanthanide cations have a high charge equal to +3 on them, yet their size is so large that their chargeto-radius ratio becomes so sm that these 1on 5 have very poor tendency to form complexes Common ligands which M3 was form stable complexes are: (1') chelating oxygen containing liga like EDTA citric acid, oxalic acid. acetylacetone, (ii) nitrogen containing liga like ethylenediamine, NCS, etc.
Bonding between M3+ mas and the coordinating ligands mainly depends the electronegativity of the bonding atom of the ligands The following order of bond formation of mouodentate ligands has been observed: F< OH‘ < HZO < [9 < C1 etc.
Complex formation in aqueous solution is possible only With those ligating which bind to metal through O-atoms. For example carboxylate anions (RCOO )
13-diketones are such type of ligands. Due to the resonating structures, the chel 21.: ring is stabilised to such extent that it cannot be replaced by OH‘ or 1-120 But fcomplexes m which the ligands are bonded to the metal through N and S dissocia in aqueous solution. Hence such complexes are prepared 1n non-aqueous solutimii ’ ‘~ 1
Generally coordination number (C. N. ) of lanthanide mus in their complexgé ranges from 6 to 9. Maximum C. N of lanthanide ions in complexes formed v. monodentate ligands like F', H201 Cl etc. is 9 Bidentate hgands form complex in which C N. of lanthanide Ions is generallyS, 7 and 8. :3»? Complexes formed by lanthanides 111 +4, +3 and +2 oxidation states 3 discussed below.
(i) Complexes of lanthanides in +4 oxidation state.
Ce is the lanthanide which forms complexes in +4 oxidation state. Pr Nd and Dy form some flouro complexes like Na ”[PrF], Cs HINdF ] and C53 [Dy F 71. Carrie ammonia!” i 1' nitrate 0le(NH)621 and cerric ammonium sulphate,7,(NH1{Ce (SO )1 5f inportant compiexes of Ce. These compounds are soluble in water. Iodates, beta di kitone so form stable complexes having Ce m +4 oxidation state Ce“ £15“ ‘ form: complex ions like [CeF 8]“ [CeF 6:12[CeCl 612etc.
1:. (ii) Complexes of lanthanides in +3 oxidation state. Since +3 is the most oxidation state of lanthanides, lanthanides form the maximum number of complexes having lanthanides in +3 oxidatidn state. All the lanthanides form a complex cation, [M(H20)"]3+ where n is generally 8 or 9.
M3+ ions form complex ions with various organic and inorganic anions as like state, citrate tartrate, nitrate and sulphate In all these complexes C. N. of M3“ -. is quite high. For example C N. of C9 ion in [Ge (NO 3);?" and [Ge(NO ) 613" Is Fa "d 6 respectively. Diketonate anion (RCOCHCOR) reacts With M3*1ons to form {M (L3 diketo13‘) l [M (Bdiketonato)a L] (L: H2 0, pyridine etc )and M (Bdiketonato). These
complexes are more stable than all other types of M3*-complexes.. [EDTA anions
:3 1') forms complex anions of [M(EDTA). 3H 2'0] type with all M ions.
Although nitrogen containing monodentate ligands do not form stable complex with M1“ ions, bidentate ligands having two donor N-atoms form stable chelates.
For example, ethylene diamine (en) forms complex cation, [M( en )13‘ With ions in polar organic solvents
' (iii) Complexes of lanthanides' m +2 oxidation state Complexes having thamdes 111 +2 oxidation state are rare.
Compounds of Lanthanides in +2 Oxidation State
5 Compounds of Sm”, Eu2+ and Yb“ have been characterised. Compounds of “ese ions are obtained by (i) the reduction of fused trihalides or oxides with the esponding metal (ii) electrolytic reduction of Eu” and Yb” in aqueous solution ‘ ) by thermal decomposition of anhydrous trihalides (2M}(: --> 2MX:+ X2) Of the valent compounds of lanthamdes those ofEu2" are the most stable All c‘ompounds M2+ IODS decompose in H O with evolution of H2.
2M2+ eee+ 2H 0 ~~~> 2M3“ + 220B“ + H2
Compounds of Sm” Eu and Yb” lODS exist in solution. These ions are oxidised M“ ions in aqueous solution
SmWaq) ---> Sm3*(aq) +e‘, E3, 2 1.55V
1 Eu2*(aq) ~-) Eu3*(aq) + e’, ng = 0.43 V 0.
Yb” (aq) --> Yb3+ (aq) +e*. E3, = 1.15 V
E values given above show that reducing strength of M ions in the order:
Sm◀Yb◀Eu
Dalides
These compound are obtained by the reaction between molten MX and elemental lanthanides . Difluoride of all lanthanides are iso structure with each other .
Divalent Chalco genides
These compound have been prepared for all Ianthanides except for Pm, most by direct Combination Thesecompounds are almost black with the exception; :51 I SmZ, EuZ. YbZ, 'I‘mSIand. They have high metallic conductivity. CrystaI of these compounda have cubic NaCI type structure.
M0 oxides
MO oxides are obtained by the reduction of M2 0 oxides with the metal at ;, elevated temperature.
Compounds of Lanthanides in +3 Oxidation State
Nearly all known anions form the compounds with M3‘ cation These compound; are stable In solid as well as in solution state Compounds of M3“ cation With th: anions such as OH‘, COJ'J', 8043', C204}, NOa‘ etc. decompose on heating, give fir; “ basic salts and finally oxides. Hydrated salts that contain thermally stable anion such as F, Cl‘, Br, PO 3” etc. also give similar products on heating because of .: hydrolysis. 1.
Compounds of M“ cation with the anions Cl, Br, I, NOJ‘, CH 3'C00 ,,B0 7‘ :2: are generally soluble In water while those with F, 0H, 02‘, C :0 1’ ,COf‘ ,CrO 1' PO"? etc. are generally insoluble. ‘
1. Trihalides, MX
Fluorides are precipitated by the addition ofHF or a soluble fluoride to a M" I salts solution. The fluorides particularly of heavier lanthauides, are sparingly soluble 5' ‘ in HF due to the formation of Iiuoto complexes. ' The anhydrous chlorides can be prepared by the direct combination of the M elements on heating. These are best prepared by heating the oxides (M203) with The
carbonyl chloride (COCIZ) or NH ‘Cl. and
M20a + 300012 --> 2MC13 + 3002 s N D};
M203 + 6NH4CI JOEL, mm, + 3H20 + 6NH3
'The anhydrous chlorides cannot be obtained from the hydrated chlorides, sinc aque IhI-se lose HCI on heating to give the oxychlorides (MOCI) more easily.
Excepting CeO and TbO other oxides are obtaIned by burning lanthanides in O(ii) igniting carbonates, nitrates and salts containing anions (e g CO3a CO ’r so 2 etc. ) In air
2M+302 --) M303
M2(CO3)3 -> M303+CO3
4M(NO33) -> 2M330 +2NO +30
. M2 03 oxides are strongly basic and their basic character decreases as atomic (sumber Increases. For example Lu is strongly basic while Lu is least basic. ~m’des are soluble In H2O and form M(OH)3. Oxides dissolve In aqueous acids to ,Jve solution which contains [M (H2 0) 3‘ Ion. 3M(OH) can be prepared by prolonged ,3 geatment of M2 03 with cone NaOH at high temperature and pressure.
‘ . Trivalent chalcogenides, M3Z 3(ZS, Se, Te)
LIE 7“: M283, M2 Se3 and M 33Te have been obtained for most of lantham'des. These .I‘ Impounds arze obtained by (i) the direct combination of elements (ii) the reaction of Is .113" z: or H2 Se on lanthanide metals (iii) by the reduction of 0x0 salts In general these of lid compounds are stable m dry air but are hydrolysed In presence of mmsture Ifheated ‘;_,In air, they (especially sulphides) are oxidised to basic salts of the corresponding anion and they are attacked by acids With the evolution of H3Z.
. 4. Nitrides
Nitrides are prepared by direct combination of elements at about 1200°C or 3ij the action of N2 or N H on hydrides of lanthamdes.
13 5. Carbonates, M3(CO3)3
The normal carbonates can be prepared by passing CO2 into an aqueous solution be ofM(OH)3. They can also be prepared by adding N 213003 solution to M“ saltsolution.
.th The carbonates are insoluble in H30, but dissolvein acids with liberation of CO2 and Forming Ma’ salts.
Nitrates, M(NO )
The hydrated nitrates, M(NO 3) 6H3 O are obtained by the evaporation of aqueous solutions These compounds are soluble m H O, alcohols, ketones and esters
Phosphates and Oxalate
These compounds are insoluble' In water. All lanthanides are quantatively precipitated as oxalales from M" solution containing CO ion. The precipitate on
dring and ignition gives MO
Double Salts
Lamhunide salts form a large number of dauble salts. The most importing ‘ double salts are:
(i) Double nitrates such as 2M(NO) 3(N03): . 24H20 (15!" 1 Mg. Zn. Ni: Mn) and “(310, ). 2N}! N0. 4!! 0. ‘1
r (ii) Double sulphates such as M (SO «3) .3M‘SQ 12HO (alkali metal) .The double sulphates. M (SO ). 3N3 “SO .12H :0 where \l = LaEu are on); sparingly soluble ln Na ”SO IN MI: those where M: Gd Lu are appreciably soluble; Time a separation of lanthanides Into two groups: Cerium group having L8,.-;Eu lnnthanidcs and Yttrium group having Gd “-Lu. lanthanides Is possible. Since the double salts crystallisc well. these are sued to separate the ramanhs from one another. In the above description M represents lanthanide atom.
Compounds of Lanthanides in +4 Oxidation State '
Chemistry of compounds in +4 oxidation state is mainly the chemistry o§ Co (IV) compounds Double salts like Ge(NO ). 2N}! ”NO and Ce(SO )2 SO 2H 0 have also been prepared.
The standard oxidation potentials at 25'C. in acid solution. of Ce“ and Pr: ions are given as under:
. 7i’).,
Ce" = Ce" 4» e". EL: +1.74 v
Pr“ = Pr“+e.E;-+2.86V
E vaues show that Co (Ni and Pr (IV) are strong oxidising agents. the latter being further stronger of the two CeiSO ). is generally used In volumetric analysis.Ce" ion is mutually reduced to ion. The tetravalentm ions of Ce are stable In the solId state as well as In solution Pr", Nd“. Tb" and D)“ are stable only In solution.
Uses of Lanthanides
Linthnnides are used In metallothermic reactions due to their extraordnairy reducing property (Co is a stronger reducing agent than All Lanthanido thermic process can yield sufficiently pure Nb. Zr. Fe, Co. NI. Mn. Y. W. L'. B and 5‘.
Those metals are also used as de-oxidising agents particularly in the manufacture of (Eu and its alloys.
Use of lanthanides. Alloys of lanthanides are known as rnIsh-mewl: The major constituents of mish~metals are Ce (45-50%). La (25% . Nd 5%) IL.“ 'cmll qunnunes of other lanthanide metals and F e and Ca impurities.
mish metal are used for the production of different brands of steel like heat and Instrumental steels. The addition of 0.75% of mish-metals
i M steel raises its yield point and its working in heated state and improves its resistance to oxidation mIisch metal is an excellant scanvengers for absorping oxygen and sulphur 1n metallurgy.
: 1 1': Mg-allops containing about 30% misch metal and 1% Zr are useful in making
y m of Jet engine When 11110} ed with 30% iron, it is sumciently pvrophoric to be
" _ éseful 111 lighter flints.
-' 595 of the Lanthanide Compounds
‘3. The uses of the compounds of lanthanides can broadly be classifled as follows; 1. Nonnuclear applications. The following uses are important
,. (1:) )Ceramic applications. CeOZ. Lagos, Nd203 and 131303 are widely used for ecolorising glass Approximately 1% CeO is used in the manufacture ofprotectiv e ', ansparent glass blocks to be used In nuclear technology because these blocks are ‘ ot affected b) pro-longed exposure to radiations Because Ianthanjde oxides can .gibsorb ultTa-violet rays, these are used as additives in glasses for special purposes, :35 g. for making (1) sun-glasses (by adding, NdZOS) (ii) goggles for glass blowing and :weldmg work 11:11:03 + P1203) (iii) glasses protecting eyes h'orn neutron radiation 4:11:03 + 5:11:03) etc. 5‘1: The addition of more than 1% CeO2 to glass gives it a brown colour. NdEOS and £31203 give respectively red and green colours. (Nd203 + Pr203) gives a blue colour. E“; (b) Refractories. C138 (11:. pt = 2000°C) is used in the manufacture of a special 5: ye of crucibles which are used for melting metals m a reducing atmosphere at Wfémperatures upto 1800°C Borides, carbides and nitrides of lanthanides are also gused as refractories
K1:
1-.“ (c) Abrasives. Lantham'de oxides are used as abrasi ves for polishing glasses, gig. the mixture of oxides, CeO2 (47%), LaZO. + Nd20 + Pr 0 (51%) + 3102,0210,
1Ee_0 etc (= 2%) which is callezd poljrite has been used for polishing glassezs.
(d) Paints. Lanthanide compounds are used 111 the manufacture oflakes, dyes {and paints for porcelain, e.g. cerium molybdate gives light yellow colour, cerium isiungstate gives gTeenjsh blue colour and salts of Nd give red colour.
(e) In textiles and leather industries. Ceric salts are used for dying in "textile industries and as tanning agents in leather industries. Ge(NOJ)‘ is used as a mordant for alizarin dyes. Chlorides and acetates oflanthanjdes make the fabrics Waterproof and acid resistant
(f) In medicine and agriculture.
DimaJs which are salicylates of Pr and Nd iare used as germicides. Cerium salts are used for the treatment of vomiting and Sea sickness. Salts of Er and Ce increase the red-blood corpuscles and haemoglobin content of blood.
In agriculture lantham'de compotmds are used as insecto-fungicides and as trace elements in fertilizers.
In lamps
Salts of La, Ce, Eu and Sm are used as activators ofluminophores 1): 0' ed 11. .h: manufacture of gas mantles in the coatings of luminescent 101 paunting 1r5 the screens of cathode-ray tubes.
"‘ In analytical chemistry_ Ge(SO‘)2 is used as an oxidising agent, in voImetric titrations.
F block elements
Lanthanides series
elements are also called fblock elements. Thus the last electron enters (n 2) f subshell in inner-transition elements.
Valence shell electronic conjiguration of the atoms of f block elements can be represented as (n2)]"‘“ (n1)d"‘2 us 2which shows that in these elements the intermost three shells are partially-filled while the remaining inner shells are E ' partially filled.
.Classification of f-Block Elements '1Inner transition elements (f-block elements) have been classified into the following two series.
(i) Lanthanide series (CeEB to Lu ). The 14 elements from Ce t0 Lu are the members 0f this series, i. e 14 elements7 from Ce“ to L 1.,1 are called lanthanides. or elements are called lanthanides, since these elements are placed after
lanthamum (Lam) 1n group 3 and period 6 of the periodic table (See Fig. 9.1) and how close similarities with La“.
Since lanthanides are present Ln 6th period (n: 6) of the periodic table, these elements have six shells 1n their electronic configurationthe last electron in these elements enters (6-2) f or 4f subshell Thus lanthanides are als'o called 4f ?%lock elements, 1. e. lanthanides are a series of 14 elements (Ce5 ate Lu“) m which the last electron goes to 4f subshell or to f sub shell of 4th shell. ‘
It has been observed that all the 15 elements from La to Lu71 have similar properties. Hence the study of lanthanides consists of the study all the 15 elements om La to Lu together. La57 is the prototype of lanthanides.
Lanthanides are also called lanthanones or rare earths. The name are earth
Elements given to them because they were originally extracted from oxides for which “ancient name was earth and which were considered to rare. The term rare earth was avoided now because manv of these elements are no longer rare but are abudant nn ---
Position of lanthanides
Production of Lanthanide Metals
position of Lanthanides in the Periodic Table
All the fifteen lanthanides atomic numbers have atomic weights between those of barium( atomic number Z= 56 and hafnium Z= 72 ) and, therefore, must be placed between these two elements as was also proved by Moseley.
Production of Lanthanides Metals
The following methods may used for this purpose: »
1. Electrolysis of fused chlorides. This method is similar to that used the metallurgy of Ca by the electrolysis of CaCl2.
2. Reduction of anhydrous chlorides with Na. Lighter lanthanides such a.‘ La, Ce and Gd can easily be prepared by the reduction of their anhydrous chloride With Na at 100°C.
LaCla + 3Na i‘E-a La + 3NaCl f}
3. Reduction of anhydrous iiuorides and chlorides with Mg or C5;
Hence lanthanides such as Lu are prepared when their anhydrous fluorides chlorides are reduced by Ca or Mg metals at a temperature above 1000°C, sing: the fluorides are less volatile than the chlorides and consequently the loss cause by evaporation in case of fluorides 18 small. * -.
Properties of Lanthanides
1.Electronic Configurations
Electronic configurations of lanthanum (La) and fourteen Ianthanides (Ceto Lu) are given in Table 9.1. Valence shell electronic configurations (V. S. E C. )these elements are also given in the same Table. 33
After the completion of 6S orbital at Ba [Ba = [Xe} in La according to Aufbau principle must enter according to Aufbuu principle, must 4f orbitals to give configuration to La but in La , the energy“ 5d orbitals IS lower than that 4f orbitals as shown 1n Fig 9. 3. Consequently 5th electron 1n La enters 5d orbitals instead of 4f orbitals. Thus the electronic configuration of La Xe 4f 5d 6s is 1X91“ 4f"5d‘632 and not [Xe],N f" 1°65 as predicted by aufbau principle
Excepting Gd“ and Lu, other lanthanides have empty 5d orbitals (5d° configuration). Electronic configurtion of Eu 1s [Xe] 4f75d°65and that of Gd [Xe154f’ 5d‘ 6532 Both these configurations are stable due to the presence of stable halftilled 4f orbitals (4f’ configuration) in them. Electronic configuration of wa 41‘“ 5d° Gs2 and that of Lu711s [Xe]5 4f“ 5d‘ Gs2. Both these configurations are
stable due tobthe presence of stable of these elements can be written as: ‘
)
the experimental fact that Sm ion has a tendency to get reducedd to Ce ion in aqueous solution.
28m" + 2H20 ---» 28m" + 0n + "2 (RA) (H +1) (H I 0) Ce"+ Fem ~-> Ce" + F0" ‘ Prue ,
Thus sm" is a good RA and Ce is a good OA In aqueous solution. Pr‘ ‘and Tb" are ex on more powerful oxithsing agents
3. Atomic and Ionic Radii: Lanthnnide Contraction
Atomic radIi of Ln atoms and ionic radii of Ln" are given below In Table 9. It may be seen that as we move along lanthanide series. there is a stead decrease In the value of radii.
The steady decrease in atomic and ionic radii of lanthanide elements with increasing atomic number is called lanthanum contraction. ,
Cause of Lanthanide Cohtraction ~
'1
‘We know that as we proceed from one element to the next one in lanthanide series, the nuclear charge (Le., atemic number) increases by +1 at each element . Thus as we move from Ce to Lu, the attraction between the nucleus aIl in the outermost shell electron Increases gradually at each step. It Is also known th 7 as we move from Ce to Lu, the addition of extra electron takes place to 4f orbitals
Since 4 orbitals have ve diffused shape. the electrons In these orbitals are” not to shield (decrease) attraction between the nucleus and the outerMost shell in the 4 ‘ outermost 3 el as 1e atomIc number of lanthanides only du to the Increase. In tITYIuclcnrcharge I..e, mcmasemte attraction between nucleus and the outer-most shell electrons) that the size of the lanthanide atoms’ and M" Ions decreases gradually with atomic number The above discussion shows * He: that it is due to the poor shielding effect of 4felectrons and gradual Increase in nuclear charge that the lanthanide contraction takes place among lanthanides.
Consequences of Lanthanide Contraction
Lanthanide contraction plays an important role In determining the chemistry end heavier transition series elements. Some important oonsequen 0 La on are discussed below:(V nic radii of the two in pairs an the same. The above discussion shows that its due to the poor shielding effect of 4f electron and gradual increase in the nuclear charge that the lanthanide contraction takes place among lanthanides.
.x
2nd and 3rd transition series are given in Table 9 4. This table shows that the atomic radius of La (element of 3rd transition series) 15 greater than that of Y On thebasis of trend the atomic radii of the two elements present in each of the pairs viz ZrHf NbTa, M0 W
Ku should be in the order Hf> Zr Ta > Nb W > Mo etc, but the atomic radii of the element is due to the lanthanide contraction seen in lanthanides which lies between La and Hf. Thus we can say that due to lanthanide cnntraclmn the atomic radius 0f 3rd transition series following La is nearly the same ac that of the 11 responding element lying in the same group
Lanthanide contraction
(ii) Similarity in properties of the two elements in the pairs viz Zr-Hf, .-Ta, Mo-W etc,
We have said above that, due to lanthanide contraction, the atomic size of the two elements present in the pairs mz Zr-H.f, NbTa Mo'W etc.are almost the same. Due to similarity in their atomic size, the properties of the f1 elements in each of the above pairs are very sunilar.
(iii) Difficulty in the separation of lanthanides. We know that the
1 properties of metal ion is determined by their size and charge. Now since, on proceeding Erom Ce to Lu the change. In the size of Ln ion is very small and these ions have the same charge (= +3) chemical properties of lanthanides are
most identical. Due to identical properties. the separation of lanthanides from one another' in the pure state is ditiicult.
(iv) Comparison between the densities of the elements of 2nd and transition series.
The densities of d-block elements are given in Table 9 5. it may be seen from the table that the densities of elements belonging to the same sub-group icreases on moving down the sub-group .The densities of the d block elements transition series are only slightly higher than those of the corresponding elements of lst transition series while these values for the transition elements from Hf to Hg“ (elements of 3rd transitmn series) are almost double these values T0 the elements from Zr 0 to Cd“ respectively (elements of 2nd transition series ) 1 Note that the density of La (= 6.“17)' 15 not double that of the value for Y (= 4. 47).
The variation of densities oftransition series element' 1.11 the given subgrous as discussed above, can be explained as follows on the basis of lanthanide contraction.
because of lanthanide contraction occurring in lanthanides, the atomic sizes Elements (f ,d transition series coming after La. Consequently the packing off, the atoms in their metallic crystals become so much compact that their densities become very high.
(v) Basic character of hydroxides, M(OH)3 decreases from La(OH) t‘ 'Lu(OH).
Due to lanthanide contraction, the size of +3 lanthanide 1on3 (M3 ions ) decreases regularly with increase in atomic number. As a result of this decrease in size the covalent character between M3‘ ion and OH‘ mus increases from La(0H). (Fajan ’3 rules). Therefore, the basic character of the hydroxides decrease a with increase in atomic number. Consequently, La(OH.)3 is most basic while Lu(0 IE: _ is the least basic. i: '
hydroxides of lanthanides are stronger bases than Al(OH) but weaker th.
‘ Ca(OH) 1' L . 4. Colour of Tripositive Lanthanide Ions (M Ions) Most of the trivalent cations of lanthanide elements are coloured in the 501i as well as in aqueous solution while only a few 1on 5 are colourless. (See Fig. 9 4) . f It may be seen from Fig. 9. 4 that the colour depends on the number of electron present' 1n 4f orbitals The elements having n electrons' in 4f orh1tals has the same colou Tr as the which has (14n) electrons 1n 4f orbitals For example La (4P) which has no electron in its 4f orbitals (n: 0) 1s colourless and Lu3* ion (4)“) which has (140): 14 electrons 1n 4f orb1tals 18 also colourless.Similar1y P1“ 1011 (4F) Which has two electrons' 1n its 4f orbitals (n: 2) and Tm“ 10!] MI“) which has (142): .5; 12 electrons 1n its 4f orbitals have the same colour (green). (See Fig. 9. 3).
Origin of colour.
Colour of lanthanide tripositive ions is due to f f transitin .The absorption bands in the visible region of electronic spectra of the 1ons in their compounds arise due to the absorption of light in the visible range. This results in the transition of the electrons of the ions from the lower energy 4f-orbitals to their higher energy 4f-orbitals. Thus lanthanide ions have colour which is complement to the colour of the absorbed light. This type of electronic transition, which takes place due to absorption of light, is called f-f transition. Evidently absorption bands seen in the electronic spectra arise due to electronic transition within 4f orbitals ‘3’} f-f transitions of lanthanides are more forbidden than dd transition of metal ion because 4f electrons of lanthanide ions are much less affected}; a liganad elecrons than the electrons in d-orbitals of transition metal ions groups the selection rules are more strictly followed for transitionin the compounds of lanthanides than in the compounds or f transition metals.
5. Magnetic Properties of Tripositive Lanthanide
M ions)
We known that in Lais empty and that Lu ion is completely filled (4 coniiguration). Thus since all the eléctrons present p 4f orbitals 1n Lu are paired, La shows diamagnetic character. Due the absence of any electron in 4f orbitals of La. This is also diamagnet. The remaining M are paramagnetic, since 4f orbitals in the remaining ions are partly filled.
To Calculate the value of amu for M" ions.
In-M3" ions, since 4f orbitals are Well shielded from the surroundings by the overlapping 5s and 5p orbitals electric field of ligands surrounding M3+ ions does not restrict (destroy 01' quench the orbital motion of electrons present in partly filled 4f orbitals of M3+ ions. Thus M ions, in addition to spin motion, orbital motion of electrons also contribu to the value of pm of M? ions, 1'. e. both types of motion of electrons contribute to 1 Value of pm of M3" 10118. 4felectrons are free to undergo L and S coupling to g? overall (tota1)angular momentum quantum number, which decides the value of for W 10118. um fer Ma? ions is thus represented as which amu given by
It may be seen from Table 9. 6 that the calculated values of amu of some M3 are in good agreement With the experimental values.
In Fig. 9. 5 experimental value of magnetic moments (in BM) of M3 are plotted against the number of unpaired electrons (n) m 4]" orbitals. From figure it may be seen that Laa+ ion (4f°) IS diamagnetic (p: 0), since it has electron 4f orbitals. Pm value increases upto Nd3+ ion and then decrease. It starts rising again and becomes maximum at about
10.5 BM for Dy“. It again starts decreasing and becomes zero (diamagnetic) at ion due to 4 1‘ configuration
The type of paramagnetism which is found in M3” ions is that in which the energy difference (AE) between the lowest energy J level of the metal ion. and the adjascent excited state is larger than thermal energy (kT) at room temperature . Thus since the excited states are much above the ground state, it is only the lowest energy state which is occupied by metal ions. Other states are not occupied by metals ions. Note that a magnetic field of strength H, each J level is split into 2J +'f‘ states in which each levels separated from its neighbours by BH. In case of su, metal ions the value of u frist given by equation (12).
Equation (1') IS not applicable for Sm3+ and Eu3’“ ions, since the lowest state (ground state) 1s close to the j excited state and hence the energy separation (AE)= kT. In such cases, calculated by taking J of the ground state only will not give the correct value oftenE for Sm3+ and Eu8+ lons.
The value of Per calculated from equation (i) for Sm3+ and Eu“ ions are; 0.86 BM and 0.0 BM F respectively (See Table 9. 6). In the calculation of these values W .1 l: have used J: 5/2 fors Sm3” and J: -0 for Eu3+ Total values of J for these ions are as.
Experimental values of amu for Sm" and Eu” ions are 16 BM and 3. 60 BM :respectively. These values show that Physical Properties
All the lanthanides are soft, malleable and ductile, and have low tensile.They are not good conductors of heat and electricity In general the atomic numbers and densities of these elements increase with the increases in atomic number. : Lanthanides have high melting and boiling points. However, they donot exhibit 3 regular trend with rise in atomic number. Lanthanides have low ionization
energy which compare well with those of the alkaline earth metals particularly Calcium
properties Dependent on Standard Oxidation Potential Values
The standard oxidation potentials (E values) of lanthanides (M) for the oxidation half-reaction,
M(s)‘ -> M3' (aq) + 3e
are given below.
' ' 1‘ ---------EZ, values involts decrease --------> .
15-12“:La-252 Ce'=2.48, Pr=2.46, Nd: 2.43, Pm: 2.42 Sm: 2.41,Eu= 2.40,
I
5i." .3" =2.39 Tb: 2.39, Dy: 2.,35 H0: 232, Er: 230, Tm: 2.28 Yb: 2.2:7Lu 2.25
g‘ These E“ values explain the following properties of lanthanides:
E: (1') Reducing property.
Since lanthanides have positive E" values these elements (M) have a strong tendency to lose their three electrons hence act as strong reducing agents. Due to the decrease of E" values from La If Lu, the reducing power of lenthanides also decreases from La to Lu.
h(11') Electropositive character.
Since E" values are high, lanthanides can readily lose their electrons and hence show strong electropositive (or metallic) character With the decrease of E" values from La to Lu, the electropositive
. Solubility of Compounds of Lanthanides
_ The nitrates, chlorides, sulphates, perchlorates and salts of oxy acids of lanthanides are soluble but the oxalates, carbonates and fluorides are insoluble 1n
é ,Water. Note that the sulphates of the elements of group 2 are insoluble in water.
Fnrmation of Double Salts
Lanthanides form a number of double salts.1mportant double salts formed by given below (M 15 the lanthanide element) (1) Cdrbonates, e..g K2
nitrates, e.g. 31 Mg(NO )2. 2M(N0). 24H,O (111) Sulphates, gr Ni1SO Mi so”) 8 water.
10. Chemical Reactivity
Lanthunides differ from one number only in the number of 4f electrons. Since those elements (are very effectively shielded from Interaction with other elements by the overlying 5S, 5p and 6:5 Neutrons they show very little difference in tthe chemical reactivity. Some of the chemical properties of lanthunides are given below
(ii Lauthanides are highly reactive, silverywhite metals. These meta1s ta . Tu readily on exposure to air In the finely divided state, these metals burn in form sesquioxide (MO ). Ce forms CeO. Ytterbium (Yb) resists the action of even at 1000 due to the formation of a protective coating of its oxide.
(ii) Lanthanides combine with H on heating. The hydrides formed are of MH2 and MH3 type. These hydrides are stable.
(iii) Lanthanides react with non metals like S, X2, P N2, C and Si to form corresponding compounds .
(1v) Lanthanides decompose H2O to evolve H2. Evolution of H2 takes Place slowly in cold and rapidly on heating.
Formation of Complexes
Although tripositive lanthanide cations have a high charge equal to +3 on them, yet their size is so large that their chargeto-radius ratio becomes so sm that these 1on 5 have very poor tendency to form complexes Common ligands which M3 was form stable complexes are: (1') chelating oxygen containing liga like EDTA citric acid, oxalic acid. acetylacetone, (ii) nitrogen containing liga like ethylenediamine, NCS, etc.
Bonding between M3+ mas and the coordinating ligands mainly depends the electronegativity of the bonding atom of the ligands The following order of bond formation of mouodentate ligands has been observed: F< OH‘ < HZO < [9 < C1 etc.
Complex formation in aqueous solution is possible only With those ligating which bind to metal through O-atoms. For example carboxylate anions (RCOO )
13-diketones are such type of ligands. Due to the resonating structures, the chel 21.: ring is stabilised to such extent that it cannot be replaced by OH‘ or 1-120 But fcomplexes m which the ligands are bonded to the metal through N and S dissocia in aqueous solution. Hence such complexes are prepared 1n non-aqueous solutimii ’ ‘~ 1
Generally coordination number (C. N. ) of lanthanide mus in their complexgé ranges from 6 to 9. Maximum C. N of lanthanide ions in complexes formed v. monodentate ligands like F', H201 Cl etc. is 9 Bidentate hgands form complex in which C N. of lanthanide Ions is generallyS, 7 and 8. :3»? Complexes formed by lanthanides 111 +4, +3 and +2 oxidation states 3 discussed below.
(i) Complexes of lanthanides in +4 oxidation state.
Ce is the lanthanide which forms complexes in +4 oxidation state. Pr Nd and Dy form some flouro complexes like Na ”[PrF], Cs HINdF ] and C53 [Dy F 71. Carrie ammonia!” i 1' nitrate 0le(NH)621 and cerric ammonium sulphate,7,(NH1{Ce (SO )1 5f inportant compiexes of Ce. These compounds are soluble in water. Iodates, beta di kitone so form stable complexes having Ce m +4 oxidation state Ce“ £15“ ‘ form: complex ions like [CeF 8]“ [CeF 6:12[CeCl 612etc.
1:. (ii) Complexes of lanthanides in +3 oxidation state. Since +3 is the most oxidation state of lanthanides, lanthanides form the maximum number of complexes having lanthanides in +3 oxidatidn state. All the lanthanides form a complex cation, [M(H20)"]3+ where n is generally 8 or 9.
M3+ ions form complex ions with various organic and inorganic anions as like state, citrate tartrate, nitrate and sulphate In all these complexes C. N. of M3“ -. is quite high. For example C N. of C9 ion in [Ge (NO 3);?" and [Ge(NO ) 613" Is Fa "d 6 respectively. Diketonate anion (RCOCHCOR) reacts With M3*1ons to form {M (L3 diketo13‘) l [M (Bdiketonato)a L] (L: H2 0, pyridine etc )and M (Bdiketonato). These
complexes are more stable than all other types of M3*-complexes.. [EDTA anions
:3 1') forms complex anions of [M(EDTA). 3H 2'0] type with all M ions.
Although nitrogen containing monodentate ligands do not form stable complex with M1“ ions, bidentate ligands having two donor N-atoms form stable chelates.
For example, ethylene diamine (en) forms complex cation, [M( en )13‘ With ions in polar organic solvents
' (iii) Complexes of lanthanides' m +2 oxidation state Complexes having thamdes 111 +2 oxidation state are rare.
Compounds of Lanthanides in +2 Oxidation State
5 Compounds of Sm”, Eu2+ and Yb“ have been characterised. Compounds of “ese ions are obtained by (i) the reduction of fused trihalides or oxides with the esponding metal (ii) electrolytic reduction of Eu” and Yb” in aqueous solution ‘ ) by thermal decomposition of anhydrous trihalides (2M}(: --> 2MX:+ X2) Of the valent compounds of lanthamdes those ofEu2" are the most stable All c‘ompounds M2+ IODS decompose in H O with evolution of H2.
2M2+ eee+ 2H 0 ~~~> 2M3“ + 220B“ + H2
Compounds of Sm” Eu and Yb” lODS exist in solution. These ions are oxidised M“ ions in aqueous solution
SmWaq) ---> Sm3*(aq) +e‘, E3, 2 1.55V
1 Eu2*(aq) ~-) Eu3*(aq) + e’, ng = 0.43 V 0.
Yb” (aq) --> Yb3+ (aq) +e*. E3, = 1.15 V
E values given above show that reducing strength of M ions in the order:
Sm◀Yb◀Eu
Dalides
These compound are obtained by the reaction between molten MX and elemental lanthanides . Difluoride of all lanthanides are iso structure with each other .
Divalent Chalco genides
These compound have been prepared for all Ianthanides except for Pm, most by direct Combination Thesecompounds are almost black with the exception; :51 I SmZ, EuZ. YbZ, 'I‘mSIand. They have high metallic conductivity. CrystaI of these compounda have cubic NaCI type structure.
M0 oxides
MO oxides are obtained by the reduction of M2 0 oxides with the metal at ;, elevated temperature.
Compounds of Lanthanides in +3 Oxidation State
Nearly all known anions form the compounds with M3‘ cation These compound; are stable In solid as well as in solution state Compounds of M3“ cation With th: anions such as OH‘, COJ'J', 8043', C204}, NOa‘ etc. decompose on heating, give fir; “ basic salts and finally oxides. Hydrated salts that contain thermally stable anion such as F, Cl‘, Br, PO 3” etc. also give similar products on heating because of .: hydrolysis. 1.
Compounds of M“ cation with the anions Cl, Br, I, NOJ‘, CH 3'C00 ,,B0 7‘ :2: are generally soluble In water while those with F, 0H, 02‘, C :0 1’ ,COf‘ ,CrO 1' PO"? etc. are generally insoluble. ‘
1. Trihalides, MX
Fluorides are precipitated by the addition ofHF or a soluble fluoride to a M" I salts solution. The fluorides particularly of heavier lanthauides, are sparingly soluble 5' ‘ in HF due to the formation of Iiuoto complexes. ' The anhydrous chlorides can be prepared by the direct combination of the M elements on heating. These are best prepared by heating the oxides (M203) with The
carbonyl chloride (COCIZ) or NH ‘Cl. and
M20a + 300012 --> 2MC13 + 3002 s N D};
M203 + 6NH4CI JOEL, mm, + 3H20 + 6NH3
'The anhydrous chlorides cannot be obtained from the hydrated chlorides, sinc aque IhI-se lose HCI on heating to give the oxychlorides (MOCI) more easily.
Excepting CeO and TbO other oxides are obtaIned by burning lanthanides in O(ii) igniting carbonates, nitrates and salts containing anions (e g CO3a CO ’r so 2 etc. ) In air
2M+302 --) M303
M2(CO3)3 -> M303+CO3
4M(NO33) -> 2M330 +2NO +30
. M2 03 oxides are strongly basic and their basic character decreases as atomic (sumber Increases. For example Lu is strongly basic while Lu is least basic. ~m’des are soluble In H2O and form M(OH)3. Oxides dissolve In aqueous acids to ,Jve solution which contains [M (H2 0) 3‘ Ion. 3M(OH) can be prepared by prolonged ,3 geatment of M2 03 with cone NaOH at high temperature and pressure.
‘ . Trivalent chalcogenides, M3Z 3(ZS, Se, Te)
LIE 7“: M283, M2 Se3 and M 33Te have been obtained for most of lantham'des. These .I‘ Impounds arze obtained by (i) the direct combination of elements (ii) the reaction of Is .113" z: or H2 Se on lanthanide metals (iii) by the reduction of 0x0 salts In general these of lid compounds are stable m dry air but are hydrolysed In presence of mmsture Ifheated ‘;_,In air, they (especially sulphides) are oxidised to basic salts of the corresponding anion and they are attacked by acids With the evolution of H3Z.
. 4. Nitrides
Nitrides are prepared by direct combination of elements at about 1200°C or 3ij the action of N2 or N H on hydrides of lanthamdes.
13 5. Carbonates, M3(CO3)3
The normal carbonates can be prepared by passing CO2 into an aqueous solution be ofM(OH)3. They can also be prepared by adding N 213003 solution to M“ saltsolution.
.th The carbonates are insoluble in H30, but dissolvein acids with liberation of CO2 and Forming Ma’ salts.
Nitrates, M(NO )
The hydrated nitrates, M(NO 3) 6H3 O are obtained by the evaporation of aqueous solutions These compounds are soluble m H O, alcohols, ketones and esters
Phosphates and Oxalate
These compounds are insoluble' In water. All lanthanides are quantatively precipitated as oxalales from M" solution containing CO ion. The precipitate on
dring and ignition gives MO
Double Salts
Lamhunide salts form a large number of dauble salts. The most importing ‘ double salts are:
(i) Double nitrates such as 2M(NO) 3(N03): . 24H20 (15!" 1 Mg. Zn. Ni: Mn) and “(310, ). 2N}! N0. 4!! 0. ‘1
r (ii) Double sulphates such as M (SO «3) .3M‘SQ 12HO (alkali metal) .The double sulphates. M (SO ). 3N3 “SO .12H :0 where \l = LaEu are on); sparingly soluble ln Na ”SO IN MI: those where M: Gd Lu are appreciably soluble; Time a separation of lanthanides Into two groups: Cerium group having L8,.-;Eu lnnthanidcs and Yttrium group having Gd “-Lu. lanthanides Is possible. Since the double salts crystallisc well. these are sued to separate the ramanhs from one another. In the above description M represents lanthanide atom.
Compounds of Lanthanides in +4 Oxidation State '
Chemistry of compounds in +4 oxidation state is mainly the chemistry o§ Co (IV) compounds Double salts like Ge(NO ). 2N}! ”NO and Ce(SO )2 SO 2H 0 have also been prepared.
The standard oxidation potentials at 25'C. in acid solution. of Ce“ and Pr: ions are given as under:
. 7i’).,
Ce" = Ce" 4» e". EL: +1.74 v
Pr“ = Pr“+e.E;-+2.86V
E vaues show that Co (Ni and Pr (IV) are strong oxidising agents. the latter being further stronger of the two CeiSO ). is generally used In volumetric analysis.Ce" ion is mutually reduced to ion. The tetravalentm ions of Ce are stable In the solId state as well as In solution Pr", Nd“. Tb" and D)“ are stable only In solution.
Uses of Lanthanides
Linthnnides are used In metallothermic reactions due to their extraordnairy reducing property (Co is a stronger reducing agent than All Lanthanido thermic process can yield sufficiently pure Nb. Zr. Fe, Co. NI. Mn. Y. W. L'. B and 5‘.
Those metals are also used as de-oxidising agents particularly in the manufacture of (Eu and its alloys.
Use of lanthanides. Alloys of lanthanides are known as rnIsh-mewl: The major constituents of mish~metals are Ce (45-50%). La (25% . Nd 5%) IL.“ 'cmll qunnunes of other lanthanide metals and F e and Ca impurities.
mish metal are used for the production of different brands of steel like heat and Instrumental steels. The addition of 0.75% of mish-metals
i M steel raises its yield point and its working in heated state and improves its resistance to oxidation mIisch metal is an excellant scanvengers for absorping oxygen and sulphur 1n metallurgy.
: 1 1': Mg-allops containing about 30% misch metal and 1% Zr are useful in making
y m of Jet engine When 11110} ed with 30% iron, it is sumciently pvrophoric to be
" _ éseful 111 lighter flints.
-' 595 of the Lanthanide Compounds
‘3. The uses of the compounds of lanthanides can broadly be classifled as follows; 1. Nonnuclear applications. The following uses are important
,. (1:) )Ceramic applications. CeOZ. Lagos, Nd203 and 131303 are widely used for ecolorising glass Approximately 1% CeO is used in the manufacture ofprotectiv e ', ansparent glass blocks to be used In nuclear technology because these blocks are ‘ ot affected b) pro-longed exposure to radiations Because Ianthanjde oxides can .gibsorb ultTa-violet rays, these are used as additives in glasses for special purposes, :35 g. for making (1) sun-glasses (by adding, NdZOS) (ii) goggles for glass blowing and :weldmg work 11:11:03 + P1203) (iii) glasses protecting eyes h'orn neutron radiation 4:11:03 + 5:11:03) etc. 5‘1: The addition of more than 1% CeO2 to glass gives it a brown colour. NdEOS and £31203 give respectively red and green colours. (Nd203 + Pr203) gives a blue colour. E“; (b) Refractories. C138 (11:. pt = 2000°C) is used in the manufacture of a special 5: ye of crucibles which are used for melting metals m a reducing atmosphere at Wfémperatures upto 1800°C Borides, carbides and nitrides of lanthanides are also gused as refractories
K1:
1-.“ (c) Abrasives. Lantham'de oxides are used as abrasi ves for polishing glasses, gig. the mixture of oxides, CeO2 (47%), LaZO. + Nd20 + Pr 0 (51%) + 3102,0210,
1Ee_0 etc (= 2%) which is callezd poljrite has been used for polishing glassezs.
(d) Paints. Lanthanide compounds are used 111 the manufacture oflakes, dyes {and paints for porcelain, e.g. cerium molybdate gives light yellow colour, cerium isiungstate gives gTeenjsh blue colour and salts of Nd give red colour.
(e) In textiles and leather industries. Ceric salts are used for dying in "textile industries and as tanning agents in leather industries. Ge(NOJ)‘ is used as a mordant for alizarin dyes. Chlorides and acetates oflanthanjdes make the fabrics Waterproof and acid resistant
(f) In medicine and agriculture.
DimaJs which are salicylates of Pr and Nd iare used as germicides. Cerium salts are used for the treatment of vomiting and Sea sickness. Salts of Er and Ce increase the red-blood corpuscles and haemoglobin content of blood.
In agriculture lantham'de compotmds are used as insecto-fungicides and as trace elements in fertilizers.
In lamps
Salts of La, Ce, Eu and Sm are used as activators ofluminophores 1): 0' ed 11. .h: manufacture of gas mantles in the coatings of luminescent 101 paunting 1r5 the screens of cathode-ray tubes.
"‘ In analytical chemistry_ Ge(SO‘)2 is used as an oxidising agent, in voImetric titrations.
