Thermal behaviour of metal(II) isonicotinate tetrahydrates

Metal isonicotinate tetrahydrates with M = Mn, Fe, Co, Ni, Cu, Zn are analogous hexacoordinate complexes of the type trans-[M(NC 5 H 4 -p-CO 2 ) 2 (OH 2 ) 4 ], which form a robust 3-D supramolecular network in the solid state. Hydrogen bonds formed between OH 2 donors and CO 2 - acceptors strongly hold the water molecules and the isonicotinato ligands together with the metal ions to make these compounds quite stable in air at room temperature. Thermogravimetric analysis shows that these complexes lose weight in two well defined steps occurring in the 50-600 °C range. Thermogravimetric data on the compounds are found to follow metal-dependence close to expectations based on the Irving-Williams order for bivalent metal ions.