Syntheses, structures and photophysical properties of binuclear copper(I) complexes bridged by diphosphine ligands

Reaction of [Cu(NCCH3)4]ClO4 with 5,5′-dibromo-2,2′-bipyridine (BrbpyBr) and diphosphine ligands Ph2P(CH2)xPPh2 (x = 1, 4, 5, 6) in dichloromethane gives good yields of a series of binuclear copper(I) complexes [Cu2(BrbpyBr)2(Ph2P(CH2)xPPh2)2](ClO4)2, where x is 1, 4, 5 and 6 in complexes 1–4, respectively. The crystallographic data and the space-filling drawings of complexes 1 and 3 show that the Cu(I) centers, N atom centers and P atoms centers are well protected by the close contact of BrbpyBr and diphosphine ligands, which may be the reasons why complexes 1–4 are so stable to air and moisture in the solid state. The ESI-MS result through changing the collision cell energy from 0 to 15 eV suggests that the binding energies between Cu(I) ions and Ph2P(CH2)xPPh2 ligands are much larger than that between Cu(I) and BrbpyBr ligand in the [Cu2(BrbpyBr)2(Ph2P(CH2)xPPh2)2]2+ cations, confirming that the corresponding [Cu2(Ph2P(CH2)xPPh2)2]2+ cations are the thermodynamically stable products in DCM solutions. All the complexes 1–4 display good phosphorescent emission in the solid state.