Synthesis, characterization and thermal behaviour of cadmium (II) complexes of photosubstituted octacyano-molybdate(IV) and -tungstate(IV) with ethylenediamine

Photosubstituted ethylenediamine complexes of M(CN)84- [where M =Mo(IV) or W(IV)] with cadmium (II) chloride have been synthesized and characterized by infrared (IR), thermogravimetric (TG) and differential scanning calorimetry (DSC). Both Mo(IV) and W(IV) show similar stoichiometric as well as thermal decomposition behaviour. The assigned general formula is Cd[M(CN)3(OH)(C2H8N2)2](C2H8N2) Cl2XH2O [where M = Mo(IV) for which X = 1(I) and M = W(IV) for which X = 2 (II)]. The presence of CN-, OH- and C2H8N2 has been shown by observed characteristic IR peaks. The extra absorption bands appearing in complex (II) are due to librational modes of water which show the formation of hydrogen bonding, which is also supported by TG analysis. The loss of these absorption bands rules out this type of bonding in (I). Both the complexes decompose in three steps up to 650 degC after which there is no change. DSC of the complexes also shows three transitions, two exothermic and one endothermic. On the basis of TG and DSC thermograms, mechanism for the decomposition of each step has been shown. Kinetic parameters like activation energy (Ea), frequency factor (A) and entropy of activation (ΔS) have been calculated using different integral methods. (author)