Four Novel Frameworks Built by Imidazole-Based Dicarboxylate Ligands: Hydro(Solvo)thermal Synthesis, Crystal Structures, and Properties

Four novel complexes, {[Ni4(HEIDC)4(H2O)8]·2H2O} (1), {[Mn(HEIDC)(4,4′-bipy)0.5(H2O)]·H2O}n (2), [Mn6(EIDC)4(py)(H2O)4]n (3), and {[Cd2(EIDC)(H2EIDC)(4,4′-bipy)1.5]·H2O}n (4) (H3EIDC = 2-ethyl-1H-imidazole-4,5-dicarboxylic acid, 4,4′-bipy = 4,4′-bipyridine, and py = pyridine) have been hydro(solvo)thermally synthesized by fine control over synthetic conditions, such as solvent and pH value, and structurally characterized. It is shown through single-crystal X-ray diffractions that the ligands H3EIDC can be either singly, doubly, or triply deprotonated and can coordinate to Ni(II), Mn(II) or Cd(II) ions in μ2 or μ3 modes. Compound 1 is a zero-dimensional (0D) symmetrical tetranuclear molecular square. Compound 2 exhibits a two-dimensional (2D) sheet, in which alternate left- and right-handed helical chains are bridged by 4,4′-bipy linkages. Compound 3 assumes a 2D honeycomb-like sheet built up from μ3-EIDC3− and Mn(II) atoms. Compound 4 possesses a novel three-dimensional (3D) structure constructed from 2D layer motifs joined by μ2-HEIDC2− and 4,4′-bipy bridges. The thermal properties of complexes 1−4 have been determined as well. Also, it is discovered that there exists antiferromagnetic coupling between the Ni(II) or Mn(II) ions in 1 or 2 (3); the best fittings to the experimental magnetic susceptibilities gave J = −10.83 cm−1 and g = 2.19 for 1, and J = −0.025 cm−1, zJ′ = −0.02 cm−1 and g = 2.0 for 2.