Investigation of the Zinc Chloride / Methyl(2-pyridyl)ketone Oxime Reaction System: A Mononuclear Complex and an Inverse 12-Metallacrown-4 Cluster

Abstract

The reactions of methyl(2-pyridyl)ketone oxime, (py)C(Me)NOH, with zinc chloride have been investigated. An excess of the ligand in EtOH/MeCN affords the mononuclear complex [ZnCl2{(py)C(Me)NOH}2] (1) in moderate yield. The metal ion is coordinated by two chloro ligands and two N,N′- chelating (py)C(Me)NOH molecules. The six-coordinate molecule is the ciscis- trans isomer considering the positions of the coordinated chlorine, pyridyl and oxime nitrogen atoms, respectively. The reaction between equimolar quantities of ZnCl2, (py)C(Me)NOH and LiOH·H2O in EtOH/MeCN leads to the tetranuclear cluster [Zn4(OH)2Cl2{(py)C(Me)NO}4] (2) in high yield. The molecule lies on a crystallographic inversion center and has an inverse 12-metallacrown- 4 topology. Two triply bridging hydroxides are accommodated within the metallacrown ring. Each (py)C(Me)NO− ligand adopts the 2.111 coordination mode (Harris notation), chelating one ZnII ion and bridging a ZnII 2 pair. Two metal ions are in a distorted O2N4 octahedral environment, whereas the other two are in a severely distorted tetrahedral O3Cl environment. Complex 2 joins a small family of structurally characterized zinc(II) metallacrown complexes. The IR data are discussed in terms of the nature of bonding and the structures of the two complexes.