Three zinc iodide complexes based on phosphane ligands: syntheses, structures, optical properties and TD-DFT calculations.

Three zinc iodide complexes based on phosphane ligands, namely diiodidobis(triphenylphosphane-κP)zinc(II), [ZnI2(C18H15P2)2], (1), diiodidobis[tris(4-methylphenyl)phosphane-κP]zinc(II), [ZnI2(C21H21P2)2], (2), and [bis(diphenylphosphoryl)methane-κ2O,O']zinc(II) tetraiodidozinc(II), [Zn(C25H22O2P2)3][ZnI4], (3), have been synthesized and characterized. Single-crystal X-ray diffraction revealed that the structures of (1) and (2) are both mononuclear four-coordinated ZnI2 complexes containing two monodentate phosphane ligands, respectively. Surprisingly, (2) spontaneously forms an acentric structure, suggesting it might be a potential second-order NLO material. The crystal structure of complex (3) is composed of two parts, namely a [Zn(dppmO2)3]2+ cation [dppmO2 is bis(diphenylphosphoryl)methane] and a [ZnI4]2- anion. The UV-Vis absorption spectra, thermal stabilities and photoluminescence spectra of the title complexes have also been studied. Time-dependent density functional theory (TD-DFT) calculations reveal that the low-energy UV absorption and the corresponding light emission both result from halide-ligand charge-transfer (XLCT) excited states.