A dinuclear extension to constrained heteroleptic Cu(I) systems

This article reports the synthesis and optical properties of three dinuclear, cationic copper complexes [Cu(2)(μ-dppm)(2)(μ-L)](NO(3))(2) (dppm diphenyldiphosphinomethane, L: L(A) 3,6-bis(2-pyridyl)-4,5-diphenyl-pyridazine, L(B) 3,6-bis(2-pyridyl)-4,5-di(4-pyridyl)-pyridazine and L(C) 3,6-bis(2-pyridyl)-8,9-diazafluoranthene). These were formed on the reaction of [Cu(μ-dppm)(NO(3))](2) with a series of N-donor (bppn) ligands L. The single crystal X-ray structures of [Cu(2)(μ-dppm)(2)(μ-L)](NO(3))(2)·CH(2)Cl(2) were determined and revealed that in both, the two copper atoms are held by three bridging ligands, two dppm ligands and one bppn ligand acting as a tetradentate bridge. The absorption spectra of the complexes present a MLCT [Cu → π*(N(∧)N)] band in the λ 370-425 nm region. These new complexes exhibit red-orange MLCT-based emission in the solid-state with lifetimes in the microsecond range. In oxygen-free dichloromethane solution, the complex [Cu(2)(μ-dppm)(2)(μ-L(C))](2+) has a long lifetime of 22.8 μs. The long emission lifetimes are attributed to a rigid conformation that precludes the possible distortion of the copper in the excited state.