Investigations of Group 12 (IIB) Metal Halide/Pseudohalide-Bipy Systems: Syntheses, Structures, Properties, and TDDFT Calculations (Bipy = 2,2‘-bipyridine or 4,4‘-bipyridine)

Abstract

Ten compounds of the IIB metal halide/pseudohalide-bipy system, β-[ZnBr2(4,4‘-bipy)]n (1), [Cd2Br5(4,4‘-bipyH)2](CdBr3) (2), [Cd3Br6(4,4‘-bipy)]n (3), [CdI2(4,4‘-bipy)]n (4), (HgI2)2(4,4‘-bipy) (5), [Hg(CN)2(4,4‘-bipy)(H2O)2]n (6), HgCl2(2,2‘-bipy) (7), [HgCl2(2,2‘-bipy)]·2HgCl2 (8), [Hg3Br6(2,2‘-bipy)]·HgBr2 (9), and [HgI2(2,2‘-bipy)]·HgI2 (10), have been synthesized via hydro(solvo)thermal and solid-state reactions; except for 4, all the other compounds are reported for the first time. Compound 1 features a 1-D zigzag chain, based on tetrahedral zinc atoms bridged by 4,4‘-bipy molecules and terminally coordinated by two bromine atoms. The chains are linked by hydrogen bonds and π···π interactions to form a 2-D sheet. Compound 2 possesses dinuclear [Cd2Br5(4,4‘-bipyH)2]+ cations and CdBr3- anions. Compound 3 has a 2-D layered structure, constructed from novel triple chains and bridging 4,4‘-bipy ligands. The triple chains contain edge-shared CdBr6 and CdBr5N octahedra. In 4, the layers are formed by monochains and bridging 4,4‘-bipy molecules. The monochains contain edge-shared CdI4N2 octahedra. Compound 5 features a discrete structure with a 4,4‘-bipy ligand bridging two HgI2 moieties. Compound 6 has a 1-D zigzag chain, containing octahedral mercury atoms and bridging 4,4‘-bipy molecules. In 7 and 8, mercury atoms are tetrahedrally coordinated to two chlorine atoms and two nitrogen atoms. In 9, 2-, 3-, 4-, and 5-coordinated mercury atoms coexist, whereas in 10, the mercury atoms are only 2- and 4-coordinated. Photoluminescence investigations reveal that the compounds display strong emissions in the blue/green/yellow regions, which, in combination with the molecular orbital (MO) calculations of 1, 5, and 7, leads us to conclude that the emissions originate from a ligand-to-ligand charge-transfer (LLCT) transition. The solid-state diffuse reflectance spectra, IR, and TG-DTA are also presented.