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

Novel Cu^II complexes CuLCl₂ (L = 1−4) 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 Cu^II 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 1−3 in that three nitrogens direct their lone pairs to one side of the folded tetracycle, with adjacent nitrogen atoms coordinated to Cu^II. This difference is probably caused by the presence of the more flexible seven-membered ring rather than the five- to six-membered rings in 1−3. Air oxidation of Cu^I 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.