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Synthesis & thermal studies on some polyvanadate and polymolybdate complexes containing Zn++ and Ni++ cations

Uma Shankar Upadhyay, Rajesh Kumar, R.R.Jha

Two new polyvanadate and polymolybdate containing Zn++ and Ni++ cations have been prepared in dilute acetic acid mediumPH 4.4- 4.6 at reflux temperature. The Polyvanadate product obtained is dull yellowin appearance which gradually losses associated water molecules at roomtemperature yielding the final product containing only two water molecules as water of hydration. The Polymolybdate residue obtained posses light brown colour. The polyvanadate and polymolybdate both are paramagnetic at roomtemperature havingmagneticmoment value 3.02 BM&3.78 BM. These magnetic moment values of triheteropoly complexes suggest the six co-ordinated octahedral around Ni (II) environment in weak field. The I.R. Spectrum of the products suggest the presence of NH4 +, M = O, M–O- MÂÂ’ and hydrogen bonded H2O group in the Complexes whereM=V or Mo and MÂÂ’=Zn or / and Ni. The TG and DTA curve of Polyvanadate show it decomposition in two major steps while the decomposition of polymolybdate in multi steps process. The Polymolybdate starts losing weight at 30oC and it losses 4.079% water with endothermic steps with DTA peak Maxima at 51.22OC, which correspond to 3H2O weight loss. After that the other TG and DTAsteps of Polymolybdate exhibit multistep elimination and decomposition of the residue whichwas entirely different from the polyvanadate product. On the basis of analytical results thermogravimetric studies, i.r. spectral, bond position, thermal stability and thermodynamic, parameter results of the isolated products the composition of the Polyvanadate and polymolybdate are assigned as:- (NH4)2[Zn.NiV6O18]. 2H2Oand (NH4)4 [Zn.NiMo6O22]. 10H2Orespectively.