Ahmad, Md Faiz

Prasad, Rajendra

Thakur, Lambodar

English

NOPR

35273272-211IV1285€284If)oz~2'63a.If)a:.:( 2·82z~~"~Ir---~~--~----~----~----~----~~a.:::i 356I-z355353II3·953·9439T E MPERATUREoC ~1_~2.?...._:_...J l, ~ L_. .L.__.-J ...L£.00 "iOO 600 700 800 900 1000Fig. 1 - Variation of d-spa.cings with temperature for fourstrong reflections in X-ray pattern of barium pyrophosphatebarium pyrophosphate is not yet known, it isnot possible to give a conclusive explanation forthis phenomenon. However, if its structure consistsof P04 tetrahedra linked together to form P207groups, then the decrease in the cell dimensionscould perhaps be explained on the basis of thetilting theory", because tilting is probable in struc-tures where polyhedra are linked by their cornersonly.The peculiar behaviour of barium pyrophosphateas well as its diffraction pattern suggest that thissubstance is not isomorphous with calcium andstrontium pyrophosphates, This is in agreementwith the observations of Ranby ct aU who havementioned that the o-form has no isomorphs at all.Therefore, the general statement that barium pyro-phosphate is -isomorphous with strontium andcalcium pyrophosphates- is not wholly correct.NOTESTABLE 1 - INDEXED X-RAY POWDER PATTERN OF BARIUMPYROPHOSPHATEd in A I 1Ikl d in A I hkl5·331 6 001 2·153 31 0424·334 3 210 2·108 27 1613·915 100 121 2·037 4 3023·529 25 040 1·956 11 0523·354 6 211 1·909 4 1523·254 6 131 1'865 8 332. 3603·223 3 230 1·832 4 5003'(l70 11 300 1·805 4 0033·011 3 310 1·769 4 080, 3612·')67 4 041 1·722 5 1232·828 55 050 1·668 4 2132·708 39 002 1·586 7 233, 1432·351 5 202. 060 1·538 6 6002·318 27 340 1·482 9 5512·265 11 410 1·411 12 4132·219 18 222 1·402 7 516. 4801·354 8 004The powder pattern of barium pyrophosphatehas been indexed and is given in Table 1. Thesystem is orthorhombic with Pmmm, Pmm2 or P222as the probable space group. The crystal datais as follows:a = 9·200 A, b = 14·120 A, c = 5·420 A, z = 4and Pm=4·45 g crrr".The authors thank Drs E. R. Saxena and RaziaFarooqi for the sample of barium hydrogen phos-phate, Dr V. S. Subrahmanyam for measuring thedensity and to the Director, RRL, Hyderabad,for his keen interest in the work.References1. RANBY. 1'. W., MASH. D. H. & HENDERSON. S. T .• Brit.f. appl. Phys., Supplement 4 (1955), 18.2. KIRCHNER, H. P., MERZ, K. M. & BROWN, W. R., f. Am.ceram. Soc .• 40 (1963). 137.3. MEGAW. H. D .• Mat. Res. Bull .• 6 (1971), 1007.4. PLUMIER, R, Bull. Classe. Sci. A cad. ray Belg, (1957).43.Thermochemical Studies ofDiaquodiacetatodioxouranium(VI)LAMBODAR THAKUR*. MD FAIZ AHMAD & RAJENDRA PRASADtDepartment of Chemistry. Bhagalpur UniversityBhagalpur 812007Received 23 August 1976; accepted 13 April 1977The heats of solution of anhydrous diacetatodioxo-uranium(VI) and diaquodiacetatodioxouranium(VI) inwater and 2N acetic acid at 300oK, are -1l·3±0·6,-22'4±0'5; 22·6±0·4, and 10·7±0'2 KJ mol-! respec-tively. The standard heat of formation of anhydrousU02Ac2 is -1991·9 KJ mol-t, The gas phase enthalpyof reaction between U02Ac2 and one mole of wateris -60·6 KJ mol-I, commensurate with the dativeuranium-oxygen bond strength.ANHYDROUS diacetatodioxouranium(VI) in thecrystalline state, dissolves in water or in aqueousacetic acid giving a clear yellow solution which on*To whom all correspondence should be addressed.[Present address: A. N. S. College. Barh (MagadhUniversity).821INDIAN J. CHEM., VOL. 15A, SEPTEMBER 1977crystallization under vacuum at room temperature(> lO°C) leads to the formation of diaquodiacetato-dioxouranium(VI) [U02Ac2·2H20(c)J1• In the pre-sent study, the heat of reaction of water solvatewith anhydrous diacdatodioxouranium(VI) has beendetermined calorimetrically and some related thermaldata calculated.Diaquodiacetatodioxouranium(VI) (BDH, AR) wasrecrystallized from dilute acetic acid solution.Anhydrous diacetatodioxouranium(VI) was preparedby heating the above sample at 115-20°C for 6-8 hrand stored in a desiccator (Found: IT, 60·9. Calc.for U02Ac2: U, 61·3%»).The calorimeter was designed as before- andcalibrated electrically by means of a 1O·6201-oh11lmanganin heater. The current through the heaterwas measured by the potential drop across a stan-dard one-ohm resistor connected in series. Thecalorimeter stirrer was a multi-paddled glass roddriven by a synchronous motor. Samples weresealed in fragile glass ampoules and mixing waseffected by rupturing on a pointed spike. Thecalorimeter was immersed completely in a well-stirred thermostat ed water-bath. On attainingthermal equilibrium, the time-temperature (resis-tance) change was noted for the fore-period, thereaction-period, and the after-period. Followingan earlier procedure", the correct temperaturechange was estimated. The calorimeter was checkedby measuring the heat of solution of potassiumchloride in water (Found: 17·60 KJ 11101-1; lit.417·30 KJ mor ').Heat of reaction and heat of formation - The heatof reaction can be obtained from the thermochemicalEqs. (1-3).U02Ac2(c) + excess H.O(l) = UO.Ac.(soln); MIl'" (1)UO.Ac2.2H.o(c)+excess H.O(I) = UO.Ac.(soln); t1H•... (2)UO.Ac2(c)+2H.O(I) = UO.Ac.,2H20(c); t1H3 ... (3)Following Sacconi et al»t1H3= t1Hl-t1H2andt1H; UO.Ac. (c)= t1H' UO.Ac •. 2H.O(c) - 2t1H;H20(l)-t1H3 ... (4)The mean values of ~Hl for diacetatodio xoura-nium(VI) in water and 2N acetic acid are -11·3 ± 0·6and -22·4 ± 0·5 KJ mol".tlH2 values in water and acetic aciel are 22·6 ± 0·4and 10·7 ± 0·2 KJ mol+. The average values of~H3 in water and 2N acetic acid are -33,9 and-33,1 KJ mol? respectively. In calculation, themean of the two values i.e. --33·5 KJ mol'", hasbeen used. A dilute acetic acid solution was usedto suppress the remote possibility of hydrolysisof the uranyl acetate in solution at the room tempe-rature. The aqueous solutions were found freefrom hydrolysis in either case.The heat of formation of U02Ac2 (=--~-1991·9KJ mol+) has been obtained from Eq. (4) by com-puting tlH;U02Ac2,2H20(c) (= -2597·0 KJ mol")from Lange6 and ~H;H20(l) (= -285·8 KJ mol'")from Wagman et aU.The heat of formation of U02Ac2·2H20(aq.) fromour results is -2003·2 KJ mol+, which comparesclosely with the value -2004·6 KJ mol= reportedby Lange6•822Uranium-oxygen bond strength - In the diaquo-diacetatodioxouranium(VI), the two water moleculesare coordinated to the UO~+ ion forming a distortedhexagonal bipyramid''. The uranium-oxygen bondstrength is the energy of gas-phase reaction betweenaqua-oxygen and uranyl ion. This can be obtainedby considering the well-knownv-w thermochemicalsteps (5-10).UO.Ac,(c) +2H.O(I) = U02Ac2·2H20(c); t1H3UO.Ac a- 2H,O(c) = UO.Ac2.2H20(g); Ml;UO,Ac2(c) = U02Ac2(g); Ml;2H.o(I) = 2H20(g); 2M!,;U02Ac2(g)+2H20(g) 0-' U02Ac2.2H20(g); MIMI = t1l!3-1-Ml;-Ml;-·2Miv... (5)... (6)... (7)... (8)... (9)... (10)where t:J.H;, t:J.H; are the heats of sublimation ofdiaquo and anhydrous uranyl acetates respectively.tlHv is the heat of vaporization of liquid waterwhich is known from the literature", The heatsof sublimation data are not known and it has beenassumed here that t:J.H.;,= sit; Hence, su =~H3-2~Hv =-121·3 KJ mol'<. The uranium-oxygen hand strength, E(H20- UO~+)= ~H/2=-,60·65 KJ mol'".The resulting bond energy has an element ofuncertainty due to our assumption that the heatsof sublimation of the diaquo and anhydrous com-plexes are identical. In spite of this uncertaintyit is apparent that the uranium-oxygen bond strengthin diaquodiacctatoclioxouranium(VI) is of the sameorder of magnitude as the dative bond formedbetween oxygen donors and the uranyl ion for anumber of uranyl complexes reported earlicr-". Italso compares Iavourably with the bond strengthbetween UCl4 and alcoholic oxygen!'.The authors wish to thank the UGC, New Delhi,for the award of a JRF to one of them (M.F.A.),to Dr B. C. Smith, Birkbcck College, Universityof London, for the gift of a pair of thermistors andto Prof. A. B. Lal for laboratory facilities.References1. CHERNYAEV, 1. 1., Complex compounds of uranium,translated by Israel Program for Scientific Translations,Jerusalem, 1966, 92.2. SMITH, B. c., THAKUR, L. & ROCH, D. P., Cherny Ind.(1965), 1787.3. ROSSINI, F. D., Experimental thermochemistry (Inter-science, New York), 1950, 297.4. PARKER, V. B., Thermal properties of aqueous uni-univalentelectrolytes (US Deptt of Commerce, NBS, Washington),1965, 66.S. SACCONI, L. & PAOLETTI, P., J. chem. Soc. (1961). 4250.6. LANGE, N. A., Handbook of chemistry, 11th edn (McGrawHill. New York). 1974, 9.7. \VAGMAN, D. D., EVANS, \V. u.. HALOW, 1., PARKER,V. D., BAILY, S. M. & SCHUMM. R. H., Setected values ojchemical thermodynamic properties, Technical Note 270-1(NBS, Washington), 1965, 13.8. ZACHARIASEN, \V. H. 8: PLATTINGER, M. A., Acta Crysl e ,12 (1959), 526.9. \VENDLANDT, W. \V., BEAR, J. L. & HORTON, G. R.,J. phys. Chem., 64 (1960). i289.10. ASHCROFT, S. J. & MORTIMER, c. T., Thermochemistry oftransition metal complexes (Academic Press, London).1970, 410-414.11. SMITH, B. C., THAKUR, L. & WASSEF, M. A., Indian J.Chem., 7 (1969), 1157.

Thermochemical Studies of Diaquodiacetatodioxouranium(VI)

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Thermochemical Studies of Diaquodiacetatodioxouranium(VI)

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