Structural characterization, DFT studies and luminescent properties of dinuclear copper(I)-diimine complexes with the S-shape configurations

Abstract

Three dinuclear Cu(I) complexes, [Cu2(pnd)(PPh3)4](BF4)2(1), [Cu2(pnd)(dppp)2] (BF4)2(2), and [Cu2(pnd)(DPEphos)2](BF4)2(3) (PPh3 = triphenylphosphine, dppp = 1, 3-bis (diphenylphosphino)propane, DPEphos = bis(2-diphenylphosphinophenyl)ether, pnd = N, N’-bis (pyridin-2-ylmethylene)naphthyl-1, 5-diimine), have been prepared and characterized by IR, 1H NMR, 31P NMR, 13C NMR, XRD, elemental analysis and X-ray crystal structure analysis. The structural analysis reveals that the flexible pnd in 1–3 acts in a trans bridging coordination mode to connect two Cu+ ions, forming a S-shape conformation, while each of Cu (I) ion is four-coordinate N2P2, adopting a distorted-tetrahedral geometry. DFT calculations show that the HOMOs of complexes 1–3 are primarily located on the copper d-orbital and the phosphine ligand, together with a specific contribution of pnd, while LUMOs are mostly composed of pnd with admixed Cu(I) d-orbital character. Corresponding calculations of atomic charges indicate that the charge of the copper atom in complexes 1–3 is below + 1, while the total charges of the coordinated atoms are 0.743–0.786. Moreover, the solid-state emission spectra of complexes 1–3 show the existence of broad emission bands at 350–550 nm.