Alkyl substituents introduced into novel d10-metalimidazole-4,5-dicarboxylate frameworks: synthesis, structure diversities and photoluminescence properties

Abstract

Seven novel d10-metal–imidazole-4,5-dicarboxylate compounds namely [Zn(H2EIMDC)2(H2O)2]·2.25H2O (1), [Ag2(HPIMDC)(HPIM)2] (2), [Zn(HPIMDC)(H2O)]n (3), {[Cd(H2PIMDC)2]}n (4), {(H3O)[Cd(MIMDC)]}n (5), {(H3O)[Cd(EIMDC)]}n (6) and {(H3O)[Cd2(PIMDC)(HPIMDC)]}n (7), (H3MIMDC = 2-methyl-1H-imidazole-4,5-dicarboxylic acid, H3EIMDC = 2-ethyl-1H-imidazole-4,5-dicarboxylic acid, and H3PIMDC = 2-propyl-1H-imidazole-4,5-dicarboxylic acid, HPIM = 2-propyl-1H-imidazole), have been synthesized by careful control of the synthetic conditions such as the solvent, pH value and the metal-to-ligand molar ratios. X-ray single-crystal structural analyses reveal that the change of alkyl groups on the 2-position of the ligand leads to the diversity of their structures, which range from discrete compounds (1 and 2), one-dimensional chain (3), two-dimensional layer (4) to three-dimensional frameworks (5, 6 and 7). Specially, under the same reaction conditions, the extending of the 2-position alkyl substitutents gradually reduces the symmetry of the ultimate 3D frameworks, which vary from tetragonal I4/mmm (5), tetragonal P42/nmc (6) to orthorhombic Pbam (7) space groups. Alkyl-substituted imidazole-4,5-dicarboxylate ligands exhibit either singly, doubly, or triply deprotonated fashion, and coordinate to Zn(II), Cd(II) or Ag(I) ions in terminal μ2-, μ3- or μ4-modes. Compounds 1–7 have also been characterized by means of elemental analyses, X-ray powder diffractions, FT-IR, TGA and gas-adsorption. Furthermore, solid-state photoluminescence measurements show that all these d10-metal compounds produce strong blue emissions at room temperature.