Effects of substituent groups on the structures and luminescence properties of 2D/3D CdII complexes with mixed rigid and flexible carboxylate ligands

Three new Cd(II) complexes, [Cd(bic)(adp)(0.5)] (1), [Cd(mbic)(adp)(0.5)]center dot H2O (2) and [Cd(hbic)(adp)(0.5)]center dot H2O (3) (Hbic = 1H-benzoimidazole-5-carboxylic acid, Hmbic = 2-methyl-1H-benzoimidazole-5-carboxylic acid, Hhbic = 2-hydroxyethyl-1H-benzoimidazole-5-carboxylic acid, H(2)adp = adipic acid), have been prepared by the hydrothermal reaction of adp(2-) with Cd(II) ions in the presence of different benzimidazole carboxylic acids. 1 exhibits a 3D framework constructed from 1D infinite [Cd(COO)](n) units which are connected by adp in a trans-(kappa(2)-kappa(1))-(kappa(2)-kappa(1))-mu(4) mode and bic in a novel trans-(kappa(1)-kappa(1))-(kappa(1))-mu(3) mode. 2 features an unusual [Cd-2(COO)(4)] paddle-wheel dinuclear secondary building unit (SBU), which is bridged into a 2D sheet by adp in a (kappa(1)-kappa(1))-(kappa(1)-kappa(1))-mu(4) mode and mbic in a cis-(kappa(1)-kappa(1))-(kappa(1))-mu(3) mode. For 3, the metal centre is connected into a 1D double chain by hbic in a (kappa(1))-(kappa(1)-kappa(1))-mu(2) mode, which is further linked by the trans (kappa(2)-kappa(1))-(kappa(2)-kappa(1))-mu(4) adp to form a 2D layer architecture. The luminescence properties in the solid state at room temperature of compound 1-3 are almost the same as the free ligand.