SPECTROSCOPIC AND THERMAL STUDIES ON THE DIPEROXO-CITRATO COMPLEX K2{[}MOO(O2)2(O7C6H6)].1/2H2O2.3H2O

The i.r. spectrum of the diperoxo-citrato complex K2{[}MoO(O2)2(O7C6H6)] - 1/2 H2O2 . 3H2O has been recorded and the observed bands are assigned on the basis that the ion (MoO(O2)(O7C6H6))2- has C1 symmetry while the oxo-diperoxo unit, MoO(O2)2, has local symmetry C2. The nu(s) (O-O) and nu(as)(O-O) frequencies are observed to be 910 and 875 cm-1, respectively, while nu(as)(Mo-O) and nu(s) (Mo-O) (O of O2(2-)) are assigned at 585 and 560 cm-1, respectively. The corresponding nu(Mo-O) for the O of the citrate group are assigned at 520 and 498 cm-1, and nu(Mo=O) is observed at 945 cm-1. The electronic absorption spectrum of the diperoxo-citrato complex shows one band at 320 nm assigned to a charge-transfer of the type O2(2-) -> Mo6+. Thermogravimetric (TG) and differential thermal analysis (DTA) measurements on the complex were also carried out. The data obtained agree quite well with its expected structure and show that the complex finally decomposes to form K2MoO4. A detailed mechanism for the complex thermal decomposition is given and the activation energies for the bonds are calculated.