Synthesis and X-ray Crystal Structure Determination of the First Copper(II) Complexes of Tetraazamacrocycle−Glyoxal Condensates

Novel CuII complexes CuLCl2 (L = 14) have been synthesized containing the metal bound to a well-known type of tetracyclic bisaminal formed from the condensation of glyoxal and tetraazamacrocycles (1 = cyclam−glyoxal condensate, 2 = [13]aneN4−glyoxal condensate, 3 = cyclen−glyoxal condensate, 4 = isocyclam−glyoxal condensate). The four-coordinate complexes were characterized by X-ray crystallography, electronic spectroscopy, solid-state magnetic moments, and electron spin resonance spectroscopy. The tetracyclic bisaminals, although having four potential donor atoms, are bound in a cis-bidentate fashion to CuII with two additional cis-chloride donors. The ligands take up folded conformations, and with the exception of ligand 4, only nonadjacent nitrogen atoms coordinate. As expected, ligand 2 in Cu(2)Cl2 has a folded structure similar to those of the previously characterized 1 and 3. The conformation of 4 in the complex Cu(4)Cl2 differs from 13 in that three nitrogens direct their lone pairs to one side of the folded tetracycle, with adjacent nitrogen atoms coordinated to CuII. This difference is probably caused by the presence of the more flexible seven-membered ring rather than the five- to six-membered rings in 13. Air oxidation of CuI in the presence of 1 or 3 results in bis(μ-hydroxo) dimers as characterized by X-ray crystal structures, suggesting dioxygen binding, followed by O−O bond splitting to give the Cu2O2 diamond core.