Dehydration and rehydration behavior of a trinodal topological 3-D framework of Cd(II) benzimidazole-5,6-dicarboxylate

Abstract

A hydrothermal reaction of benzimidazole-5,6-dicarboxylic acid (H₃BimDc) with Cd(NO₃)₂·4H₂O in an aqueous solution in the presence of NH₃·H₂O yielded a 3-D coordination framework [Cd_1.5(BimDc)(H₂O)₂]·2H₂O (1). Complex 1 shows a (3,4,5)-connected net topology in which the ligand BimDc³⁻ acts as five-connecting node, and two independent Cd(II) centres act as three-connecting node and four-connecting node, respectively. The Schläfli symbol of this trinodal network can be described as (4·6·8)₂(4²·6²·8²) (4²·6⁵·8³)₂. The dehydration and rehydration behavior of 1 has been studied by means of thermogravimetric analysis (TG), variable temperature (VT) X-ray powder diffraction patterns (XPRD), as well as single-crystal X-ray diffraction methods. It was found that the two lattice water molecules and one of the two coordinative water molecules can be reversibly dehydrated and rehydrated through a single-crystal-to-single-crystal procedure for the loss of the first water molecule, and two crystal-to-crystal procedures for the loss of the second and third water molecules. The coordination framework decomposes along with the loss of the last water molecule. The luminescence property of 1 has also been investigated.