INDIAN J. CHEM., VOL. 21A. MAY 1982

TABLE 2 - ESR PARAMETERS FOR CHel3 SoLUTIONS OF THECoMPLEXES

Parameter VO(SaI-H)2

1.9611.994l.98017l.465.3

100.5

VO(van-H).

l.9631.993l.983173.564.7

10l.0

gngJ.goAll (G)Ai (G)Ao (G)

~tudy l~e quite close to these straight lines. TheIsotropIc contact. term, K, is dependent upon thed-orbltal population for the unpaired electron andis given by K::::: (~~)2 Ko. Boucher et af.8 havedisc.ussedthe variation of K with (~; )2 for a varietyof Iigands, Lowenng of the (~t )2 value indicatesincreasing covalent bonding which arises from the~elocalisation of. the electron onto the ligand viain-plane rr-bonding of the d"l1 orbital with theIt-orbitals of the basal ligands.

The value of the in-plane a-bonding coefficient(~!)2 generally follows the a-donor strength ofthe ligands, i.e., (M)2 decreases as the covalentbonding increases.. From this criterion, van appearsto be a stronger ligand as compared to sal, Un )2valu~s art: 0.614 and 0.675 respectively. A linearrelationship between K and (~!)2 has earlier beendemonstrated by Boucher et al», Data on thepresent co~plexes too obey this linearity (Fig. 3b).

Also, K IS dependent on the a-bonding effect of4s.. The. energ~ separation of the bonding andantibonding orbitals for the 4s-ligand interaction isinversely proportional'' to the indirect 4s. contri-bution to K. This energy separation should be afunction of the in-plane ligand, reflected in/:::,El (2B2 ~ 2B1) in the electronic absorption

spectra. A plot of /:::,IEl vs K for a variety of

l~gands i~ linear. The data points for the presentligands he quite close to .this line (Fig. 3).

(e~ )2, the bonding coefficient for the d.,z anddl/z orbitals, measures the covalency of the V=Obond. It also indirectly shows the strength of thein-plane ligands, since, stronger the in-plane donoratom, less covalent is the v=o bond. The value ofthis parameter for VO(van-H)2 is much smaller thanthat for VO(acac), suggesting stronger covalentcharacter ofV=O and weaker in-plane ligand fieldin the former.

References1. JARSKI, M. A. & LINGAFELTER, E. C., Acta Crystallogr., 17

(1964),1109.2. SRIVASTAVA, R. C., LINGAFELTER, E. C. & JAIN, P. C.,

Acta Crystallog; 22 (1967),922.3. BURGER, K: & EGYED, I., J inorg : nucl.Chem., 27 (1965),

2361.4. MERRITT, L. L., GAURE, C. & LESSOR, A. E., Acta Crystal-

logr.,9 (1956), 253.5. PFLUGER, C. E., HARLOW, R. L. & SIMONSEN, S. M.,

Acta Crystallogr-, B26 (1970), 163l.6. CONE. H. & SHARPLESS, N. E., J. chem. Phys" 42 (1965),

906 ; 70 (1966), 105.

504

7. ~~~5~ER, L. i.,& Fu. YEN, TBH., 1.00"8. Chemi, 7 (1968),

8. BoU.CHER, L. J., Tynan, E. C. & Fu. Y~N,Teh., Electronspin resonance 0/ metal complexes, edited by Teh, Fu.Yen, (Plenum Press, New York), (1969),111.

9. MCGARVEY,B. R., J. chem. Phys., 41 (1964), 3743:

Effect of Hydration on Annealing of ChemicalRadiation Damage in Cadmium Nitrate

S. M. K. NAIR* & C. JAMESDepartment of Chemistry, University of Calicut,

Kerala 673 635

Received 21 September 1981; accepted 16 November 1981

The effect of hydration on the annealing of chemical radiationdamage in anhydrous cadmium nitrate has been investigated.Rehydration induces direct recovery of damage and the rehydratedsalt is susceptible to thermal annealing but the extent of annealingis small compared to the anhydrous salt. The direct recoveryis due to enhanced lattice mobility on rehydration.

p~ASE trans~ormations, in irradiated crystalsInduce rapid rec?mb.inati?l'l of damage frag-

ments and the recombination virtually ceases oncethe phase t~ans~ormation has taken place>". Theeffect of lattice re~rr~ngement accompanying loss ofwat~r .of crystalhsa~lOn on annealing of chemicalradiation damage In calcium bromate monohy-drate-anh~drous systems"has also been investigated.It was ?f interest therefore, to investigate the effectof lattice rearr~ng~ment. accompanying regain ofwat~r .ofcrystalhs~tlOnon the annealing of chemicalradiation damage in solid substances. The cadmiumnitrate anhydrous-tetrahydrate system has beenchosen for this investigation because the regain ofwater by the anhydrous nitrate takes place at roomtemperature and more over the kinetics of thermalannealing of chemical radiation damage in thissystem ~as bet:n investigated in detail recently",

Cadmium nitrate (AR) was dried to a constant,,:eight at 250aC and stored over phosphorus pento-xide. The loss of weight on heating agreed with theloss of four molecules of water of crystallisation.Samples of anhrdro~s salt sealed in Vacuo in glassampoules were irradiated at room temperature with52Mrad lOCO y-rays at a dose rate of 0.2 Mrad hr-1

The irradiated samples were also preserved ove~phosphorus pentoxide. Due to highly hygroscopicnature of anhydrous cadmium nitrate it was always "handled in a dry box.

T~e .e!fect.of.regain of water of crystallisation onthe 1~ltIal ~Itflte content in y-irradiated anhydrousca~mlUm mtrate. wa~ studied by keeping knownweights of the irradiated material in a constanthumidity-controlled atmosphere? of relative humidity93.9% for various time intervals from 0-240 hr atroom temperature and determining the NO; presentat the end of each time interval spectrophotometri-cally=". The weight of the irradiated salt after ex-posure to moisture for 240hr agreed with the uptake

of four molecules of water indicating that completerehydration has occurred. Isothermal annealing runswere made at 180"± O.5"C with samples of y-irradia-ted anhydrous cadmium nitrate, the irradiated samplerehydrated for 240 hr at room temprature and alsowith the sample desiccated after rehydration..The damage induced in anhydrous cadmium nitrate

by 52 Mrad 60COy-rays was 1365 ppm of nitrite.There was progressive diminution of NO~ contentduring rehydration. Typical plots of the nitrite con-centration versus the time of rehydration are givenin Fig. 1. The plots are linear which implies a mono-molecular recombination process. The velocity cons-tant of the process is 2.32 x 10-3hr-+.

The thermal annealing characteristic for anhyd-rous cadmium nitrate is shown in Fig. 2 along withthat for the rehydrated sample. Uptake of water ofcrystaIIisation by irradiated anhydrous cadmiumnitrate at room temperature to form the tetrahydrateresults in considerable recovery of damage, to theextent of ,p = 0.505 (Fig. 2) but subsequent thermalannealing behaviour of the material below thedehydration temperature is quite normal althoughthe extent of annealing is smaller than that for theirradiated anhydrous salt. Desication of the

.-,'N 2.95oz'--''" 2.90o-'

2.85

TIME OF RE HYDRATION, Hr

Fig. 1 - Annealing of chemical radiation damage in" anhydrouscadmium nitrate on rehydration ..

1.0

~"\

0W..J<{WZZ<{

0.4zS?....u<{

'"u,

NOTES

rehydrated samples produces an additional recoveryof 0.047 but the annealing characteristic forthe desiccated sample is the same as that of therehydrated one.

In the model of annealing developed by Maddockand Mohanty-? it has been proposed that the recombi-nation of the damage fragments (NO; and 0 in thecase of nitrates) occurs without appreciable energyof activation and that the energy input to the systemis only utilised for the release and migration of thedamage oxygen. The annealing on rehydration of theanhydrous salt and subsequent thermal annealingof the rehydrated salt can therefore be explainedas follows; The rehydration of the anhydrous saltresults in phase change. The lattice mobility duringthe phase change liberates the damage oxygen and aproportion of these combine with the nitrite to givenitrate ions. This results in the annealing observedon rehydration. However, according to Bolton andMcCallumll a small portion of the fragments couldsurvive the lattice rearrangement. These fragmentsanneal back to nitrate on heating. Since the propor-tion of these fragments is s~ll the extent of thermalannealing after rehydration is very small asobserved.

Grateful thanks of the authors are due to MisWestern India Plywoods, Baliapattam, Kerala forirradiations.

References1. MADDOCK, A. G. & MOHANTY, S. R., Radiochim. Acta,

1 (1963), &5.2. MOHANTY, S. R. & UPADHYAY, S. R., Indian J. Chem.,

3 (1965), 2&5.3. CHANDUNNl, B. & NAIR, S. M. K., Radiochim. Acta. 26

(1979), 177.4. CHANDUNNl, E. & NAIR, S. M. K., Rad. Ejf. Lett., 58

(1981), 5.5. KHARE, M. & MOHANTY, S. R., J. inorg. nucl., Chem.,

29 (1967), &53. .6. NAIR, S. M. K. & JAMESt. C., Rad. Eff.. (communicated):7. CHANDUNNI, E., KRISHNAN, M. S. & NAIR, S. M. K.,

J. Indian chem. Soc .• 55( 197&), 574.8. SHlNN, M. G., Ind. Engng' Chern. (Anal. Edn), 13 (1941),

33.

100

TIME OF HEATING) Hr

Fig, ~ - The effect of rehydration and subsequent desiccation on thermal annealing of anhydrous cadmium nitrate [(0)Irradiated anhydrous cadmium nitrate; (6) irradiated anhydrous cadmium nitrate rehydrated; (D) irradiated anhydrous

cadmium nitrate desiccated after rehydration]

505

INDIAN J. CHEM .. VOL. 21A, MAY 1982

9. KERSHAW, N. F. & CHAMBERLIN, N. S., Irtd. Ertgrtg.Chern. (Anal. Edn) , 14 (1942), 312.

10. MADDOCK, A. G. & MOHANTY, S. R., Disc. Faraday Soc.,31 (1961), 193.

II. BoLTON, 1. R. & MCCALLUM K. 1., Cart. J. Chern. 35(I957), 761.

Crystallographic Study of the System La2Cul-xNixO.

K. V. RAMANUJACHARY & C. S. SWAMY*Department of Chemistry, Indian Institute of Technology,

Madras 600 036

Received 20 August 19&1; revised and accepted 9 November19&1

A series or solid solutions or the formula La.Cu,_x-Nix-O.possessing K.NiF. like structure have been syntbesised. Theunit cell parameters or the solid solutions have been evaluatedfrom X-ray studies. A change in crystal symmetry from or-thorhombic to tetragonal is observed when x=O.5 in the solidsolution series.

THE structure of the system K2NiF. is closely. related to perovskite structure with space group14/mmm and represented by a general formulaA2BO.. The B-site has a coordination number six,while the A-ion experiences a coordination numbernine. Compounds having substitutional pairs ofcations at A-site of the type, AA'BO. are wellknownv". However, very few compounds havingsubstitutional pairs at B-sites are reported in lite-rature=",

La2Cu04 and La2NiO. crystallizing in K2NiF.structure have been synthesised by Foex-", Thesecompounds are known to exhibit interesting solidstate properties-v'" and their catalytic activity hasalso been evaluated-=!". It is well known that theB-site ion plays a dominant role in determiningelectrical, magnetic and catalytic properties of thesecompounds.

In the present work, we report the preparation ofcompounds belonging to a new solid solution serieshaving the composition La2Cu1-xNixO. (O~x~l)with a view to establishing the effect of nature ofB-ion in the octahedral sites on its structural pro-perties.

The members of the title series were prepared fromthe oxalates of copper and lanthanum, and nickel

dimethylglyoxime. Stoichiometric amounts ofstarting materials were thoroughly mixed in an agatemortor and fired in a platinum crucible at 960°C for28 to 30 hr, with intermediate grindings, Theformation of single phase in each compound waschecked by recording the X-ray powder diffractionpattern in a Phillips diffractometer employing CuKIIradiation. The lattice parameters of the variouscompounds were evaluated from the d-spacingsusing standard computer programmes. The tolerancefactor values were calculated from the standardexpression :

t = tr»: + 'O)/'"(2(rB + ro),

The cell constants, volume of the unit cell andtolerance factor values for the individual membersof the solid solution series are given in Table 1.The cell parameters reported here are refined to theextent of 0.001 A using an iterative procedure.A change in symmetry from orthorhombic to tetra-gonal around x = 0.5 is evident from the data inTable 1.

La2CuO. is reported to have orthorhombic dis-tortion in K2NiF. structure below 270"C due to co-operative Jahn-Teller distortion, produced by Cu2+ions in oxygen octahedra-". On the other handLa2NiO 4 crystallizes in tetragonal phase at all tem-peratures. In perovskite structures of the typeABB'03 having mixed ions at B-sites, completeordering among the B-site ions is possible as theB-B' interactions overcome entropy considera-tionsl7.l8. However, in the K2NiF. structure therock salt type of layers interposed between the per-ovskitic layers prevent any charge interactions totake place between the B-site ions and this leads torandom distribution of ions at B-sites.

Extending the above mentioned ideas to the presentsystem it becomes clear that as Cu2+ ions are intro-duced into the La2Ni04 lattice, the distribution atthe B-site becomes random. Consequently, the dis-tortion due to individual Cu2+ ions is not reflectedin the total symmetry. Further, at relatively higherCu2+ concentration (say x<O.5) it is reasonable toconceive a cooperative Jahn-Teller effect playing apredominent role, thus altering the symmetry ofthe system from tetragonal to orthombic,

It is also clear from the data presented in Table 1that the volume of the unit cell ineither symmetryremains almost constant and this is reasonable to

TABLE 1 - CRYSTAL STRUCTURE PARAMETERS FOR THE SOUD SOLUTION SERIES La.Cu,_xNix-O •.

Composition System a .b .c Volume clax (X) (A) (A) (.-\)"

0.0 0 5.3fi? 5.407 13.169 381.9 0.&63 2.4560.2 0 5.393 5.427 13.110 3&3.7 0.866 2.4300.4 0 5.406 5.419 12.995 380.6 0.&6& 2.4030.5 T 3.813 13.040 1&9.6 0.&69 3.4190.6 T 3.&36 13.017 191.5 0.&70 3.3930.& T 3.&51 12.&3& 190.4 0.&73 3.3331.0 T 3.&65 12.660 1&9.5 0.&75 3.275

o = Orthorhombic; T = Tetragonal

506