The chemistry of hydrazine derivatives—thermal behavior and characterisation of hydrazinium salts and metal hydrazine complexes of 4,5-imidazoledicarboxylic acid

New hydrazinium hydrogen-4,5-imidazoledicarboxylate (N2H5Himdc), its monohydrate, N2H5Himdc·H2O, (H2imdc=4,5-imidazoledicarboxylic acid) and the metal complexes of the type M(imdc)0.5N2H4·H2O, where M=Mn,Co or Cd and M(imdc)N2H4·H2O, where M=Ni or Zn have been prepared. The compounds have been characterised by analytical, electronic and IR spectral and thermal studies. Electronic spectral data suggest that the Co and Ni complexes are of spin-free (high spin) type with octahedral geometry. The IR absorption bands of NN stretching in the range 970–960 cm−1 unambiguously prove the bidentate bridging nature of the N2H4 ligands. IR spectra also confirm the unidentate coordination behaviour of carboxylate (νasy=1570 cm−1 and νsym=1390 cm−1) groups of the imidazoledicarboxylate dianion. Simultaneous TG and DTA of the free acid show a single-step complete endothermic (281 °C) decomposition whereas its anhydrous and hydrated hydrazinium salts show endotherm followed by exotherm decomposition. All the metal complexes undergo endothermic decomposition around 100 °C with the loss of hydrazine and water, via the metal 4,5-imidazoledicarboxylate which further decomposes exothermically in the range 110–560 °C to give the respective metal oxide as the end product.