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

Three dinuclear Cu(I) complexes, [Cu 2 (pnd)(PPh 3 ) 4 ](BF 4 ) 2 (1) , [Cu 2 (pnd)(dppp) 2 ] (BF 4 ) 2 (2) , and [Cu 2 (pnd)(DPEphos) 2 ](BF 4 ) 2 (3) (PPh 3  =  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, 1 H NMR, 31 P NMR, 13 C 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.