Three d10 metal coordination compounds based on pyrazole-3-carboxylic acid showing mixed-ligand characteristic: Syntheses, crystal structures, and photoluminescent properties

Abstract

Solvothermal reaction of pyrazole-3-carboxylic acid (H2pac) and different d10 metal salt with or without auxiliary organic ligand afforded three new coordination compounds: [Cd(Hpac)(H2O)Cl]n (1), [Cd(Hpac)(phen)2]ClO4 (2, phen=1,10-phenanthroline) and [Zn(pac)(2,2′-bipy)(H2O)]2·2H2O (3, 2,2′-bipy=2,2′-bipyridine). Compounds 1–3 all feature mixed-ligand characteristic. 1 consists of a two-dimensional (2-D) layer structure containing (4,4) networks. 2 is composed of a mononuclear [Cd(Hpac)(phen)2]+ cation and a perchlorate anion. 3 contains a binuclear [Zn(pac)(2,2′-bipy)(H2O)]2 cluster and water molecules. Through abundant hydrogen bonds and/or offset π⋯π stacking interactions, the molecules of 2 and 3 assemble into 2-D and 3-D supramolecular frameworks, respectively. The Hpac− or pac2− ligands in 1–3 display three different coordination modes. Photoluminescence studies in the solid state reveal that 1–3 exhibit interesting luminescent behaviors, and the relevant density of states (DOS) calculation results show that their photoluminescence mainly originates from the Hpac− ligand-centered charge transition mixing with Cl−–Hpac− charge transition for 1, mixed organic ligand–organic ligand charge transition and ClO4−–phen charge transition for 2, and mixed organic ligand–organic ligand charge transition for 3.