A three-dimensional network of H-bonding nickel (II) hexamethylenetetramine complex has been synthesized and characterised and its structure determined by single crystal X-ray diffraction studies which show that [Ni(H2O)6](HMTA)2Cl32.4H2O crystallizes in the triclinic crystal system with space group PĪ, a = 9.2955(4), b = 9.3187(2), c = 9.3996 Ǻ, α = 119.4160(10), β = 94.4940(10), ɣ = 100.8680(10)º, V =682.47(4) Å3 and z = 1. The nickel atoms are each bonded to six aquo ligands giving an octahedral geometry. The ligand hexamethylenetetramine (HMTA) and chloride ions are bonded to water molecules through hydrogen bonding. Thermal studies show a decomposition pattern corresponding to the loss of the coordinated and uncoordinated water molecules, chloride ions and HMTA ligand in the form of a mixture of gases