Different nuclearities of M(II) nitrate complexes (M = Co, Ni, Cu and Cd) with a tetrapyridyl pendant-armed hexaazamacrocyclic ligand

Abstract

A new series of nitrate M(II) (M = Co, Ni, Cu and Cd) complexes with a tetrapyridyl pendant-armed hexaazamacrocyclic ligand (L) has been synthesized. The complexes have been characterized by microanalysis, FAB-MS, conductivity measurements, IR, UV–Vis, 1H NMR spectroscopy and magnetic measurements at room temperature. In all cases, complexes with 1:1 and 2:1 metal:ligand molar ratios were obtained depending on the stoichiometry. Crystal structures of [Co 2L(NO 3) 4] · 2H 2O, [Cu 2L(H 2O) 2](NO 3) 4, [Cd 2L(NO 3) 2](NO 3) 2 · 5H 2O · CH 3CN and [CdL](NO 3) 2 · 6H 2O have been determined. The X-ray studies show that in [Co 2L(NO 3) 4] · 2H 2O and [Cu 2L(H 2O) 4](NO 3) 4, the metal atoms are exocyclically coordinated to the pyridine pendant arms and the tertiary amine nitrogen atoms in a distorted square pyramid [N4O] and distorted octahedral geometry [N4O2], respectively. In both cases, the pyridine rings of the macrocyclic backbone (bridgehead) are not coordinated. In contrast, in [Cd 2L(NO 3) 2](NO 3) 2 · 5H 2O · CH 3CN the metal atoms are coordinated by both types of pyridine group (bridgehead and pendant arm) and the tertiary amine with an [N5O2] core in a distorted capped octahedral geometry. Finally, the structure of the 1:1 cadmium complex [CdL](NO 3) 2 · 6H 2O was also resolved and this showed the metal centre in a distorted octahedral geometry [N6] with the metal coordinated by both types of pyridine group and the tertiary amine.