Mandal, N. G.

Sengupta, A. K.

English

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The trend observed in T6,St versus cr curve canbe explained by considering the solvation of theactivated complex. The activated complex is morepolar in the case of 2-ethylfluorene resulting in alarge decrease in entropy. The electron withdraw-ing substituents render the molecule a dipole result-ing in the solvation of the ground state. Thus,a smaller change in ~st is effected.One of the authors (S.N.) thanks the CSIl{, NewDelhi for financial assistance.References1. NARASIMHAN, S. & VENKATASUBRAMANIAN, N., Int. J.chem, Kin., accepted for publication.2. JACQUES-EMILE DUBOIS & :MAY MARIE DE FICQUEDIONT-LOIZOS, Tetrahedron Leti., (1976). 635.3. DE LA }IARE, 1'. B. D., HALL, D. :\1., HARRIS, M. M. &HASSAN, 1\1., Cheniy Ind., (1958), 1086oxopen tafluoronio bates(V)A. K. SENGUPTA & N. G. MANDALDepartment of Chemistry, Kalyani UniversityKalyani 741235Received 17 February 1976; accepted 16 September 1976The oxopentafluoroniobates (V) of the type [(CH3).N][HNbOF5] and [M(py).][NbOF5], where M ~ Cu, Ni,Zn, Cd, Co and py = pyridine, have been prepared.The IR spectra and TGA data for the above compoundsare reported.A LARGE number of oxoperitafluoroniobates+" areknown. In the present paper several newoxopentafluoroniobates of (CHa)4N+ and [M(PY)4F+,where M=Cu, Ni, Zn , Cd, Co, and py=pyridine,are reported. The compounds are studied throughthermogravimetry and infrared spectroscopy.Niobium pent oxide (purity about 99'9%) obtainedfrom the BARC was utilized in the present work.Methods for determining Nb, F and N in thecompounds were as before", For estimating niobiumin the fluoroniobates containing Ni2+, Cu-" or Co2+ion the sample was fumed with H2S04, diluted andtartaric acid added. From the solution Ni2+, Cu~+or C02+were precipitated by standard methods andestimated, whilst from the filtrate niobium wasprecipitated as its cupferronate and estimated asNb20s. The presence of Zn and Cd along withNb does not interfere in the precipitation of niobiumas its cupferronate from the acidic oxalate solution.For determining fluorine as PbCIF it was separatedfrom Nb and the other metals by fusing the sampleswith K2C03 and extracting with water.NOTESPreparation of oxopentafluoroniobates - Tetra-methylammonium compound was prepared asfollows: Nb O, (2 g) was dissolved in minimumvolume of HF (40%) and to it [(CH3)4NJOH (1·4 g)acidified with HF (10%) was added. The mixturewas evaporated on a water-bath to crystallization.The colourless crystals were filtered, pressed be-tween filter papers and dried to constant weightin vacuo over H2S04 and KOH and analysed. Thecompound was highly soluble in water and hydrolyseon boiling, The PH of its aqueous solution is ca. 3.The molar conductivity of its aqueous solution atdifferent dilutions also indicate progressive dissocia-tion of the complex ion with dilution.Tetrapyridinemetal(II) oxopentafiuoroniobaics :-:Copper compound was prepared as follows: Nb-O,(2 g) was dissolved in a minimum amount of HF(40%) and then excess pyridine was added to it.Copper carbonate (1·9 g) was suspended in pyridine(5 g) and HF (3M) was added till copper carbonatedissolved almost completely. The solution wasfiltered and then added to the niobium solution withstirring when immediately deep blue precipitateappeared. The precipitate was filtered, washedwith water, filter-pressed and dried in vacuo overfused CaCI~; yield 7·3 g.Light blue nickel compound was prepared asabove starting from its carbonate (1,8 g), Nb20s(2 g), pyridine and HF; yield 6·6 g. The cadmiumcompound (white polyhedra) was obtained as aboveby adding a solution of tetrapyridinecadmiumnitrate [prepared by dissolving cadmium carbonate(2·6 g) in minimum amount of HNOa(2N), andadding pyridine (5 g)] to a solution prepared bydissolving Nb.O, (2 g) in HF (10%) and then neutra-lizing with pyridine. The zinc and cobalt com-pounds were prepared in a similar manner as thecadmium compound starting from their respectivecarbonates.The analytical data are given in Table 1. Theabove compounds hydrolyse in water with thegeneration of pyridine and are insoluble in commonorganic solvents.The strong bands for Nb=O in the IR spectra werefound to occur at 892-952, 918, 930-960, 935-958,and 918 crrr ' for the Cu, Ni, Zn, Cd and Co com-pounds respectively. Thus it is observed thatvNb=O appears in the region, as observed! in thecase of MIINbOFs, nH20 (M=Cu2+, Mn2+, etc.).The data suggest that in the above tetrapyridine-metal compounds the NbOF~- anion remains un-altered. Due to the limitations of the instrumentbands below 700 ern? could not be recorded. InTABLE 1 - ANALYTICAL DATA OF OXOPENTAFLUORONIOBATESCompound Found (%) Calc. (%)M(Il) N Nb F M(II) N Nb F[(CH3).N]EHNbOF5] 4·96 33·92 34·86 5·02 33·32 34·06ECu(py).]ENbOF5J 10·75 9·51 16·18 16·36 10·89 9·6 15·92 16·29ENi(py).]ENbOF5] 9·66 9·78 16·38 16·55 10·15 9-68 16·05 16·42[Zn(py).]ENbOF5] 9·33 16·09 15·80 9·57 15·87 16·23[Cd(py).][NbOF5] 8·81 14·94 15·45 8·86 14·69 15·05[Co (py).J [NbOFsl 10·32 9-62 16·39 16·17 10·18 9·68 16·05 16·42357INDIAN J. CHEM., VOL. 15A, APRIL 1977TABLE 2 - THERMAL BEHAVroUR OFOXOPENTAFLUORONIOBATESCompound Decomp.temp.(0C)Range Lossof max. (%)decomp. observed(0C) at 500°Theore-ticalloss (%)for thegenera-tion of='l"b205andMilO[Cu(py).][NbOF5l[Ni(py).] [NbOF5][Zn(py).] [NbOF5][Cd(py).][NbOF.][Co(py).][NbOF5]140-250170-30080-230120-230150-24064·1365·8063·8058·7863·2163·5964·4263·3658·6964·135040304040the case of [N(CH~).lJ[HNbOFsJ strong bands appear-ed at 930 and 955-965 crrr'.The compounds were studied thermogravimetri-cally as before! in the region 30-500° in a manuallyoperated therrnobalance. The thermal behaviourof [MII(pY)4JNbOF 5 showed that loss of pyridineand fluorine took place simultaneously. The forma-tion of MIlNbOF:; also could not be observed.The residues obtained at 5000 consisted of a mixtureof Nb20s and metal oxide. The salient featuresof the thermal data are given in Table 2. Thepyrolysis of [N(CH~)4J[HNbOF5J was slow from90° to 300°, thereafter the compound underwentvery rapid decomposition and ultimately at 450°generated pure niobium pentoxide.The authors thank the Department of AtomicEnergy, Government of India, for the award ofa junior research fellowship to one of them (N.G.M.).References1. FAIRBROTHER, F., The chemistry of niobium and tantalum(Elsevier, Amsterdam), 1967, 80.2. DAVIDOVICH, R. L., LEVCHISHINA, T. F., KAIDALOVA,T. A. & SERGIENKO, V.!., J. less-com.mon .'I,Ietals, 27(1972), 35.3. SENGUPTA, A. K. & "IANDAL, N. G., J. Indian chem, Soc.,51 (1974), 479.4. SENGUPTA, A. K. & NANDI, A. K., J. Indian chem, Soc.,52 (1975), 797.HeteropoJy-niobates, -tantaJates & -vanadatesSALIL KUMAR RoyDepartment of Chemistry, Ranchi UniversityRanchi 834008Received 31 March 1976; accepted 23 August 1976Heteropolyniobates, -tantalates and -vanadates ofthe compositions K1oH[VNb\20'8.]20H,O, KgH,[VTaI2038].26H20 and (NH,)z[MoV.01,,].12H20 havebeen prepared. Analytical data agree well with theproposed molecular formulae. Cell constants and spacegroups have been determined from X-ray studies.REPORTS on heter<?poly salts of niobium, tan-talum and vanadium are very fewl-3. Thepresent note deals with the preparation and charac-terization of some new heteropoly salts, viz. potas-sium vanadoniobate, potassium vanadotantalateand ammonium molybdovanadate.358Aqueous solutions of freshly prepared- potassiumhexaniobate, K7HNb6019.13H20, and potassiummetavanadate were mixed in the molar ratio of12: 1 and refluxed for 4 hr. The resulting solutionwas kept under atmospheric conditions for threedays and finally crystallization induced by keepingin vacuo when small needle-shaped crystals separatedwhich were recrystallized thrice from hot water(Found: K, 15·32; V, 1'97; Nb, 44·27; H, 1·59.KlOH[VNb12038].20H20 requires K, 15·44; V, 2·01;Nb, 44·15; H, 1·61%). The formations KlOH[VNb12-038J.20H20 is in accord with that suggested byLindqvist" for complex heteroanicn of the type[XH+Nb1203s] (16- n) - •The corresponding heteropoly tantalate has alsobeen prepared as above starting from potassiumvanadate and freshly prepared potassium hexatan-talatc". Light yellow crystals of potassium vanado-tantalate obtained, were crystallized from hot water(Found: K, 8·50; V, 1·35; Ta, 60·15, H, 1'49; KsH3[VTa1203s].26H"0 requires K, 8·63; V, 1'41; Ta,60·08; H, 1·52%). The formulation of the compoundis in agreement with that suggested by Lindqvist/for heteroanion of the type [Xn+Tal~038](16-n) -.Hete-opoly molybdovanadate has been preparedsimilarly starting from ammonium metavana-date (0'2M) and molybdic acid (O'OSM) solutions.Small fibrous, silky yellowish crystals of ammo-nium molybdovanadat e obtained were crystallizedfrom hot water (Found: N, 2·88; H, 3·29; Mo,10·25; V, 31·50. (NH4) [MOV6019].12HP requiresN, 2·92; H, 3·34; Mo, 10·01; V, 31'92%). Theformulation is in accord with that suggested byKeggin6 for complex anion of the type [V6019J8-.The results of the X-ray crystal diffraction studiesof the compounds are given below:(a) K1oH[VNb 2038].20H20: a=15·66, b=26·10,c=8·40 A and (X.=~=Y=90°. The system isorthorhombic. Volume per unit cell = 3433°29A.3. The space group is DkPnnn' Number ofmolecules per unit cell = 2. The observed density=2·46 gl-1.(b) KsH3[VTa1203s].26H20: a=16'56, b=35·12,c=14·72 A and (X.=~=Y=90°. The system isorthorhombic. Volume per unit cell = 8560·96 A.3.The space group is 141/a. Number of moleculesper unit cell = 4. The observed density = 2·79 gl-l.(c) (NH,,)2[MoV6019].12HP: a=9·62±0·02, b=16·25±0·02, c=6·24±0·02 A., (X.=~=Y=90°. Thesystem is orthorhombic. Volume per unit cell =975·46 A.3. The space group is D~h-Pnnn. Numberof molecules per unit cell = 2. The observed den-sity = 3·240 gcel against the calculated density of3·259 gcc-I•References1. DALE, W. B., BUCKLEY, J. M. & POPE, M. T., J. chem,Soc., 2A (1969), 301.2. Roy, SALIL KUMAR & BHATTACHARY, G. C., J. Indianchem, Soc., 52 (1975), 1151.3. GIBBS, O. W., J. Am. chem. Soc., 5 (1884), 374.4. MILLER, G. L., M etallurgy of rare earth metals - Tantalumand niobium, Vol. VI (Butterworths, London), 1959.5. LINDQVIST, I., Chem. Abstr., 47 (1953), 728a; 48 (1954),9782i.6. DURRANT, P. J. & DURRANT, B., Introduction to advancedinorganic chemistry (Longmans Green, London), 1962976. '

Oxopentafluoroniobates(V)

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Oxopentafluoroniobates(V)

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