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

Four novel complexes, {[N(i)4(HEIDC)(4)(H2O)(8)] center dot 2H(2)O} (1), {[Mn(HEIDC)(4,4'-bipy)(0.5)(H2O)] center dot H2O}(n) (2), [Mn-6(EIDC)(4)(py)(H2O)(4)](n) (3), and {[Cd-2(EIDC)(H2EIDC)(4,4'-bipy)(1,5)] center dot 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 mu(2) or mu(3) modes. Compound 1 is a zero-dimensional (OD) symmetrical tetranuclear molecular square. Compound 2 exhibits a two-dimensional (20) 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 mu 3-EIDC3- and Mn(II) atoms. Compound 4 possesses a novel three-dimensional (3D) structure constructed from 2D layer motifs joined by mu(2)-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.