Synthesis and Characterization of Copper Complexes with Cu<sup>I</sup>Cu<sup>I</sup>, Cu<sup>1.5</sup>Cu<sup>1.5</sup>m and Cu<sup>II</sup>Cu<sup>II</sup> 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 [Cu<sub>2</sub>(2pcp)<sub>2</sub>] (<b>1a</b>) and {Na­[(Cu<sub>2</sub>(2pcp)<sub>2</sub>)<sub>2</sub>]­PF<sub>6</sub>}<sub><i>n</i></sub> (<b>1b</b>). The X-ray crystal structures of both complexes feature Cu<sup>I</sup>Cu<sup>I</sup> cores with close Cu···Cu interactions. Electrochemical studies of <b>1a</b> showed a reversible one-electron oxidation wave in CH<sub>2</sub>Cl<sub>2</sub>. On the basis of the work on <b>1a</b>, we began studying the mixed-valence copper species supported by this ligand. The reaction of H2pcp with Cu­(OAc)<sub>2</sub> and CuCl in different stoichiometries yielded [Cu<sub>2</sub>(2pcp)<sub>2</sub>Cl] (<b>2</b>) and [Cu<sub>3</sub>(2pcp)<sub>2</sub>Cl<sub>2</sub>] (<b>3</b>). X-ray crystallography and spectroscopic characterization suggested delocalized Cu<sup>1.5</sup>Cu<sup>1.5</sup> core structures of both compounds. These results further inspired us to explore the coordination properties of H2pcp toward Cu<sup>II</sup> ions. The complexes [HNEt<sub>3</sub>]­[Cu<sub>2</sub>(2pcp)<sub>3</sub>(ClO<sub>4</sub>)]­(ClO<sub>4</sub>) (<b>4a</b>), [Cu<sub>2</sub>(2pcp)<sub>3</sub>(NO<sub>3</sub>)] (<b>4b</b>), and [Cu<sub>2</sub>(2pcp)<sub>3</sub>(H<sub>2</sub>O)]­BF<sub>4</sub> (<b>4c</b>) featuring dinuclear Cu<sup>II</sup>Cu<sup>II</sup> cores were prepared and characterized by X-ray crystallography and spectroscopic methods. Structural analysis of these complexes implied that the accommodation of Cu<sup>I</sup>Cu<sup>I</sup>, Cu<sup>1.5</sup>Cu<sup>1.5</sup>, and Cu<sup>II</sup>Cu<sup>II</sup> is attributed to the structural flexibility of the ligand H2pcp. Complexes <b>1a</b>, <b>2</b>, <b>3</b>, and <b>4a</b> 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.