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

Abstract

Three new Cd(II) complexes, [Cd(bic)(adp)_0.5] (1), [Cd(mbic)(adp)_0.5]·H₂O (2) and [Cd(hbic)(adp)_0.5]·H₂O (3) (Hbic = 1H-benzoimidazole-5-carboxylic acid, Hmbic = 2-methyl-1H-benzoimidazole-5-carboxylic acid, Hhbic = 2-hydroxyethyl-1H-benzoimidazole-5-carboxylic acid, H₂adp = adipic acid), have been prepared by the hydrothermal reaction of adp²⁻ 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-(κ²-κ¹)-(κ²-κ¹)-μ₄ mode and bic in a novel trans-(κ¹-κ¹)-(κ¹)-μ₃ mode. 2 features an unusual [Cd₂(COO)₄] paddle-wheel dinuclear secondary building unit (SBU), which is bridged into a 2D sheet by adp in a (κ¹-κ¹)-(κ¹-κ¹)-μ₄ mode and mbic in a cis-(κ¹-κ¹)-(κ¹)-μ₃ mode. For 3, the metal centre is connected into a 1D double chain by hbic in a (κ¹)-(κ¹-κ¹)-μ₂ mode, which is further linked by the trans-(κ²-κ¹)-(κ²-κ¹)-μ₄ 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.