Synthesis and Characterization of Copper Complexes with Cu^ICu^I, Cu^1.5Cu^1.5m and Cu^IICu^II Core Structures Supported by a Flexible Dipyridylamide Ligand

A series of copper complexes supported by a simple dipyridylamide ligand (H2pcp) were isolated and characterized. Treatment of H2pcp with NaH and copper­(I) salts led to the formation of [Cu₂(2pcp)₂] (1a) and {Na­[(Cu₂(2pcp)₂)₂]­PF₆}_n (1b). The X-ray crystal structures of both complexes feature Cu^ICu^I cores with close Cu···Cu interactions. Electrochemical studies of 1a showed a reversible one-electron oxidation wave in CH₂Cl₂. On the basis of the work on 1a, we began studying the mixed-valence copper species supported by this ligand. The reaction of H2pcp with Cu­(OAc)₂ and CuCl in different stoichiometries yielded [Cu₂(2pcp)₂Cl] (2) and [Cu₃(2pcp)₂Cl₂] (3). X-ray crystallography and spectroscopic characterization suggested delocalized Cu^1.5Cu^1.5 core structures of both compounds. These results further inspired us to explore the coordination properties of H2pcp toward Cu^II ions. The complexes [HNEt₃]­[Cu₂(2pcp)₃(ClO₄)]­(ClO₄) (4a), [Cu₂(2pcp)₃(NO₃)] (4b), and [Cu₂(2pcp)₃(H₂O)]­BF₄ (4c) featuring dinuclear Cu^IICu^II cores were prepared and characterized by X-ray crystallography and spectroscopic methods. Structural analysis of these complexes implied that the accommodation of Cu^ICu^I, Cu^1.5Cu^1.5, and Cu^IICu^II is attributed to the structural flexibility of the ligand H2pcp. Complexes 1a, 2, 3, and 4a were examined by X-ray photoelectron spectroscopy, which confirmed the oxidation state assignments. Computational studies were also performed to provide insight into the electronic structures of these complexes.