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.