Investigation into aroylhydrazones as chelating agents. Part 8. Synthesis and spectroscopic characterization of complexes of Co, Ni, Cu, Zn, and Cd with 2,6-diacetylpyridine bis(salicyloylhydrazone); X-ray crystal structure of dichloro[(2,6-diacetylpyridine bis(salicyloylhydrazone)]cadmium(II)-chloroform methanol (1/1/1)