Syntheses, steric hindrance effects, luminescent properties and TD-DFT calculations for a series of copper(I) iodide coordination complexes

A series of copper(I) coordination complexes, CuI(Phen)[2-(Dpp)bp] (1) (Phen = phenanthroline, 2-(Dpp)bp = 2-(Diphenylphosphino)-biphenyl), Cu2I2(Phen)[2-(Dpp)bp] (2), CuI(2-PBI)[2-(Dpp)bp] (3) and (2-PBI = 2-(pyridin-2-yl)-1H-benzo[d]imidazole) and CuI(Bipy)[2-(Dpp)bp] (Bipy = 2,2'-bipyridine) (4) have been synthesized. X-ray crystal structure studies revealed that complexes 1, 3 and 4 showed mononuclear structures with the copper atoms coordinated by iodide, a chelating nitrogen-donor ligand, and a monodentate phosphine ligand. However, the coordination centers display different distortions of their tetrahedral geometries, according to the steric hindrance of the bulky phosphine ligands. Complex 2 has a dinuclear structure, with trigonal and tetrahedral coordination centers. Variations in the aromatic system of the N-heterocyclic ligands result in different luminescence properties. Thus, the emission maxima for these complexes range from 580 to 642 nm, with lifetimes of tau = 0.6-0.9 and 1.6-4.2 mu s. TD-DFT calculations reveal the origin of the luminescence to be metal-ligand charge transfer, as well as halogen-ligand charge transfer. The optical absorption spectra and thermal stabilities of the complexes have also been studied.