Tudy L~Equite Close to These Straight Lines. the Isotropic Contact

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

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

TABLE 2 - ESR PARAMETERS FOR CHel3 SoLUTIONS OF THE CoMPLEXES 8. BoU.CHER, L. J., Tynan, E. C. & Fu. Y~N,Teh., Electron spin resonance 0/ metal complexes, edited by Teh, Fu. Parameter VO(SaI-H)2 VO(van-H). Yen, (Plenum Press, New York), (1969),111. 9. MCGARVEY,B. R., J. chem. Phys., 41 (1964), 3743: gn 1.961 l.963 gJ. 1.994 1.993 go l.980 l.983 All (G) 17l.4 173.5 Ai (G) 65.3 64.7 Effect of Hydration on Annealing of Chemical 100.5 Ao (G) 10l.0 Radiation Damage in Cadmium Nitrate

~tudy l~e quite close to these straight lines. The S. M. K. NAIR* & C. JAMES IsotropIc contact. term, K, is dependent upon the Department of Chemistry, University of Calicut, d-orbltal population for the unpaired electron and Kerala 673 635 is given by K::::: (~~)2 Ko. Boucher et af.8 have Received 21 September 1981; accepted 16 November 1981 disc.ussedthe variation of K with (~; )2 for a variety of Iigands, Lowenng of the (~t )2 value indicates The effect of hydration on the annealing of chemical radiation increasing covalent bonding which arises from the damage in anhydrous cadmium nitrate has been investigated. ~elocalisation of. the electron onto the ligand via Rehydration induces direct recovery of damage and the rehydrated in-plane rr-bonding of the d"l1 orbital with the It-orbitals of the basal ligands. salt is susceptible to thermal annealing but the extent of annealing The value of the in-plane a-bonding coefficient is small compared to the anhydrous salt. The direct recovery (~!)2 generally follows the a-donor strength of is due to enhanced lattice mobility on rehydration. the ligands, i.e., (M)2 decreases as the covalent bonding increases.. From this criterion, van appears p~ASE trans~ormations, in irradiated crystals to be a stronger ligand as compared to sal, Un )2 Induce rapid rec?mb.inati?l'l of damage frag- valu~s art: 0.614 and 0.675 respectively. A linear ments and the recombination virtually ceases once relationship between K and (~!)2 has earlier been the phase t~ans~ormation has taken place>". The demonstrated by Boucher et al», Data on the effect of lattice re~rr~ngement accompanying loss of present co~plexes too obey this linearity (Fig. 3b). wat~r .of crystalhsa~lOn on annealing of chemical K Also, IS dependent on the a-bonding effect of radiation damage In calcium bromate monohy- 4s.. The. energ~ separation of the bonding and drate-anh~drous systems"has also been investigated. antibonding orbitals for the 4s-ligand interaction is It was ?f interest therefore, to investigate the effect inversely proportional'' to the indirect 4s. contri- of lattice rearr~ng~ment. accompanying regain of bution to K. This energy separation should be a wat~r .ofcrystalhs~tlOnon the annealing of chemical function of the in-plane ligand, reflected in radiation damage in solid substances. The cadmium /:::,El (2B2 ~ 2B1) in the electronic absorption nitrate anhydrous-tetrahydrate system has been chosen for this investigation because the regain of spectra. A plot of /:::,IEl vs K for a variety of water by the anhydrous nitrate takes place at room temperature and more over the kinetics of thermal l~gands i~ linear. The data points for the present annealing of chemical radiation damage in this ligands he quite close to .this line (Fig. 3). system ~as bet:n investigated in detail recently", (e~ )2, the bonding coefficient for the d.,z and Cadmium nitrate (AR) was dried to a constant dl/z orbitals, measures the covalency of the V=O ,,:eight at 250aC and stored over phosphorus pento- bond. It also indirectly shows the strength of the xide. The loss of weight on heating agreed with the in-plane ligands, since, stronger the in-plane donor loss of four molecules of water of crystallisation. atom, less covalent is the v=o bond. The value of Samples of anhrdro~s salt sealed in Vacuo in glass this parameter for VO(van-H)2 is much smaller than ampoules were irradiated at room temperature with that for VO(acac), suggesting stronger covalent 52 Mrad lOCO y-rays at a dose rate of 0.2 Mrad hr-1 character ofV=O and weaker in-plane ligand field The irradiated samples were also preserved ove~ in the former. phosphorus pentoxide. Due to highly hygroscopic nature of anhydrous cadmium nitrate it was always " References handled in a dry box. 1. JARSKI, M. A. & LINGAFELTER, E. C., Acta Crystallogr., 17 T~e .e!fect.of.regain of water of crystallisation on (1964),1109. the 1~ltIal ~Itflte content in y-irradiated anhydrous 2. SRIVASTAVA, R. C., LINGAFELTER, E. C. & JAIN, P. C., Acta Crystallog; 22 (1967),922. ca~mlUm mtrate. wa~ studied by keeping known 3. BURGER, K: & EGYED, I., J inorg : nucl.Chem., 27 (1965), weights of the irradiated material in a constant 2361. humidity-controlled atmosphere? of relative humidity 4. MERRITT, L. L., GAURE, C. & LESSOR, A. E., Acta Crystal- 93.9% for various time intervals from 0-240 hr at logr.,9 (1956), 253. room temperature and determining the NO; present 5. PFLUGER, C. E., HARLOW, R. L. & SIMONSEN, S. M., at the end of each time interval spectrophotometri- Acta Crystallogr-, B26 (1970), 163l. 6. CONE. H. & SHARPLESS, N. E., J. chem. Phys" 42 (1965), cally=". The weight of the irradiated salt after ex- 906 ; 70 (1966), 105. posure to moisture for 240 hr agreed with the uptake

504 NOTES of four molecules of water indicating that complete rehydrated samples produces an additional recovery rehydration has occurred. Isothermal annealing runs of 0.047 but the annealing characteristic for were made at 180"± O.5"C with samples of y-irradia- the desiccated sample is the same as that of the ted anhydrous cadmium nitrate, the irradiated sample rehydrated one. rehydrated for 240 hr at room temprature and also In the model of annealing developed by Maddock with the sample desiccated after rehydration. and Mohanty-? it has been proposed that the recombi- .The damage induced in anhydrous cadmium nitrate nation of the damage fragments (NO; and 0 in the by 52 Mrad 60COy-rays was 1365 ppm of nitrite. case of nitrates) occurs without appreciable energy There was progressive diminution of NO~ content of activation and that the energy input to the system during rehydration. Typical plots of the nitrite con- is only utilised for the release and migration of the centration versus the time of rehydration are given damage oxygen. The annealing on rehydration of the in Fig. 1. The plots are linear which implies a mono- anhydrous salt and subsequent thermal annealing molecular recombination process. The velocity cons- of the rehydrated salt can therefore be explained tant of the process is 2.32 x 10-3 hr-+. as follows; The rehydration of the anhydrous salt The thermal annealing characteristic for anhyd- results in phase change. The lattice mobility during rous cadmium nitrate is shown in Fig. 2 along with the phase change liberates the damage oxygen and a that for the rehydrated sample. Uptake of water of proportion of these combine with the nitrite to give crystaIIisation by irradiated anhydrous cadmium nitrate ions. This results in the annealing observed nitrate at room temperature to form the tetrahydrate on rehydration. However, according to Bolton and results in considerable recovery of damage, to the McCallumll a small portion of the fragments could extent of ,p = 0.505 (Fig. 2) but subsequent thermal survive the lattice rearrangement. These fragments annealing behaviour of the material below the anneal back to nitrate on heating. Since the propor- dehydration temperature is quite normal although tion of these fragments is s~ll the extent of thermal the extent of annealing is smaller than that for the annealing after rehydration is very small as irradiated anhydrous salt. Desication of the observed. Grateful thanks of the authors are due to Mis Western India Plywoods, Baliapattam, Kerala for irradiations.

References .-, 'N 2.95 1. MADDOCK, A. G. & MOHANTY, S. R., Radiochim. Acta, o 1 (1963), &5. z 2. MOHANTY, S. R. & UPADHYAY, S. R., Indian J. Chem., '--' 3 (1965), 2&5. o'" 2.90 -' 3. CHANDUNNl, B. & NAIR, S. M. K., Radiochim. Acta. 26 (1979), 177. 2.85 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): TIME OF RE HYDRATION, Hr 7. CHANDUNNI, E., KRISHNAN, M. S. & NAIR, S. M. K., J. Indian chem. Soc .• 55( 197&), 574. Fig. 1 - Annealing of chemical radiation damage in" anhydrous 8. SHlNN, M. G., Ind. Engng' Chern. (Anal. Edn), 13 (1941), cadmium nitrate on rehydration .. 33.

1.0

~ "\ 0 W ..J <{ W Z Z <{ 0.4 z ....S? u <{ '"u,

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. dimethylglyoxime. Stoichiometric amounts of Chern. (Anal. Edn) , 14 (1942), 312. starting materials were thoroughly mixed in an agate 10. MADDOCK, A. G. & MOHANTY, S. R., Disc. Faraday Soc., 31 (1961), 193. mortor and fired in a platinum crucible at 960°C for II. BoLTON, 1. R. & MCCALLUM K. 1., Cart. J. Chern. 35 28 to 30 hr, with intermediate grindings, The (I957), 761. formation of single phase in each compound was checked by recording the X-ray powder diffraction pattern in a Phillips diffractometer employing CuKII radiation. The lattice parameters of the various Crystallographic Study of the System La2Cul-xNixO. compounds were evaluated from the d-spacings using standard computer programmes. The tolerance K. V. RAMANUJACHARY & C. S. SWAMY* factor values were calculated from the standard Department of Chemistry, Indian Institute of Technology, expression : Madras 600 036 t = tr»: + 'O)/'"(2(rB + ro), Received 20 August 19&1; revised and accepted 9 November 19&1 The cell constants, volume of the unit cell and A series or solid solutions or the formula La.Cu,_x-Nix-O. tolerance factor values for the individual members possessing K.NiF. like structure have been syntbesised. The of the solid solution series are given in Table 1. unit cell parameters or the solid solutions have been evaluated The cell parameters reported here are refined to the extent of 0.001 A using an iterative procedure. from X-ray studies. A change in crystal symmetry from or- A change in symmetry from orthorhombic to tetra- thorhombic to tetragonal is observed when x=O.5 in the solid gonal around x = 0.5 is evident from the data in solution series. Table 1.

La2CuO. is reported to have orthorhombic dis- THE structure of the system K2NiF. is closely tortion in K2NiF. structure below 270"C due to co- . related to perovskite structure with space group operative Jahn-Teller distortion, produced by Cu2+ 14/mmm and represented by a general formula ions in oxygen octahedra-". On the other hand A2BO.. The B-site has a coordination number six, La2NiO 4 crystallizes in tetragonal phase at all tem- while the A-ion experiences a coordination number peratures. In perovskite structures of the type nine. Compounds having substitutional pairs of ABB'03 having mixed ions at B-sites, complete cations at A-site of the type, AA'BO. are well ordering among the B-site ions is possible as the knownv". However, very few compounds having B-B' interactions overcome entropy considera- l substitutional pairs at B-sites are reported in lite- tions 7.l8. However, in the K2NiF. structure the rature=", rock salt type of layers interposed between the per- La2Cu04 and La2NiO. crystallizing in K2NiF. ovskitic layers prevent any charge interactions to structure have been synthesised by Foex-", These take place between the B-site ions and this leads to compounds are known to exhibit interesting solid random distribution of ions at B-sites. state properties-v'" and their catalytic activity has Extending the above mentioned ideas to the present also been evaluated-=!". It is well known that the system it becomes clear that as Cu2+ ions are intro-

B-site ion plays a dominant role in determining duced into the La2Ni04 lattice, the distribution at electrical, magnetic and catalytic properties of these the B-site becomes random. Consequently, the dis- compounds. tortion due to individual Cu2+ ions is not reflected In the present work, we report the preparation of in the total symmetry. Further, at relatively higher compounds belonging to a new solid solution series Cu2+ concentration (say x

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

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

0.0 0 5.3fi? 5.407 13.169 381.9 0.&63 2.456 0.2 0 5.393 5.427 13.110 3&3.7 0.866 2.430 0.4 0 5.406 5.419 12.995 380.6 0.&6& 2.403 0.5 T 3.813 13.040 1&9.6 0.&69 3.419 0.6 T 3.&36 13.017 191.5 0.&70 3.393 0.& T 3.&51 12.&3& 190.4 0.&73 3.333 1.0 T 3.&65 12.660 1&9.5 0.&75 3.275

o = Orthorhombic; T = Tetragonal

506