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.