Structural, electronic and computational studies of heteroleptic Cu(I) complexes of 6,6′-dimesityl-2,2′-bipyridine with sulfur-substituted dipyridophenazine ligands

A series of stable heteroleptic Cu(I) complexes of 6,6'-dimesityl-2,2'-bipyridine with three sulfur-substituted dipyridophenazine ligands, and unsubstituted dppz are synthesized and studied. The X-ray crystal structures of the complexes display coordinative flexibility of the Cu(I) metal ion and display strong intramolecular pi-pi stacking interactions. The coordination geometries of the Cu(I) metal centers are characterized by the tau(4) parameter, and range from 0.626 for [Cu(bpy(Mes)(2))(dppz(Sdec)(2)]BF4 to 0.757 for [Cu(bpy(Mes)(2))(dppzS(2)CS)]BF4. Cyclic voltammetry reveals Cu(I)/Cu(II) oxidation potentials around 0.83 V for all the complexes studied, consistent with a similar coordination environment of the complexes in solution. The ligand-based reduction potentials are consistent with the electronic nature of the sulfur substituent. Resonance Raman spectroscopy and TD-DFT calculations reveal the presence of an MLCT -> bipyridine transition with 488 and 514.5 nm excitation, and dppz-type chromophores ranging from UV (351 nm) to the visible (457 nm) excitation wavelengths. For [Cu(bpy(Mes)(2))(dppzS(2)CS)]BF4 and [Cu(bpy(Mes)(2))(dppz(Sdec)(2)]BF4 the most intense optical transition at 434 and 442 nm respectively are assigned as intraligand (IL)/MLCT transitions. (C) 2012 Elsevier Ltd. All rights reserved.