Copper(II)-Promoted Reactions of α-Pyridoin Oxime: A Dodecanuclear Cluster and a 2D Coordination Polymer

Abstract

The reaction of CuCl2∙2H2O, (E)-2-hydroxy-1,2-di(pyridin-2-yl)ethanone oxime (α-pyroxH2) and Et3N in refluxing MeOH gave complex [Cu12Cl12(mpydol)4(pydox)2(MeOH)4] (1), where mpydol2− is the dianion of 1,2-dimethoxy-1,2-di(pyridin-2-yl)ethane-1,2-diol and pydox2− is the dianion of (E,E)-1,2-di(pyridin-2-yl)ethanedione dioxime. “Blind” experiments have proven that the transformation of α-pyroxH2 is copper(II)-assisted. By changing the solvent from MeOH to MeCN, the polymeric compound {[Cu4Cl4(pic)4]}n (2) was isolated; pic− is the pyridine-2-carboxylato(-1) ligand. The observed α-pyroxH2 → pic− transformation is also copper(II)-assisted. The topology of the metal ions in 1 can be described as consisting of four consecutive isosceles triangles in a zigzag configuration. Complex 2 is a 2D coordination polymer consisting of CuII4 squares. Complete mechanistic views for the α-pyroxH2 → mpydol2−, pydox2− and pic− transformations are critically discussed. In 1, the six CuII ions of the “central” triangles seem to be strongly antiferromagnetically coupled, thus cancelling out their spins (SCu6 = 0). The two local spins of S = 1/2 for each of the antiferromagnetically coupled “terminal” CuII3 triangles result in an overall S = 1 ground state spin value for 1. In 2, the four CuII ions within each tetrameric unit are practically isolated and ferromagnetic interactions occur between these units through CuII–(μ-Cl)–CuII bridges.

Keywords

• coordination chemistry
• copper(II) clusters
• copper(II) coordination polymers
• magnetic studies
• reactivity of coordinated α-pyridoin oxime mediated by copper(II)
• structural characterization