Chemistry of polydentate ligands. Part 9. Preparation and properties of Group 2B cation complexes with multidentate ligands based on 2,2′-bipyridyl

Abstract

Complexes of Group 2B metal ions with 6,6′-di-(1-methylhydrazino)-2,2′-bipyridyl and with the quinquedentate macrocycle prepared by condensation of this compound with 2,6-diacetylpyridine are reported. Infrared spectra are consistent with the linear ligand adopting either a cis-α or cis-β conformation in octahedral complexes. The cavity of the macrocycle is of sufficient size to incorporate a Zn^II ion bound to two axial ligands, but the larger Cd^II ion gives a six-co-ordinate complex with a chloride ion occupying the axial site in a pentagonal pyramid. Hydrogen-1 n.m.r. spectral parameters for the complexes are presented : signals from two of the bipyridyl hydrogens move downfield in passing from the linear to the cyclic ligands, while the third resonanceshifts upfield. This behaviour is discussed in terms of a change in the dihedral angle about the 2,2′ bond and an alteration in the extent of π conjugation in the two ligands.