Structural diversity and photocatalytic properties of Cd(ii) coordination polymers constructed by a flexible V-shaped bipyridyl benzene ligand and dicarboxylate derivatives

Abstract

Hydrothermal reactions of Cd(OAc)₂·2H₂O with a flexible V-shaped bipyridyl benzene ligand and five benzenedicarboxylic acid derivatives gave rise to five new coordination polymers i.e., [Cd(1,4-BDC)(bpmb)(H₂O)]_n (1), {[Cd(1,3-BDC)(bpmb)]·0.125H₂O}_n (2), [Cd₂(5-Me-1,3-BDC)₂(bpmb)₂]_n (3), [Cd(5-NO₂-1,3-BDC)(bpmb)(H₂O)]_n (4) and [Cd(5-OH-1,3-BDC)(bpmb)(H₂O)]_n (5) (bpmb = 1,3-bis(pyridine-3-ylmethoxy)benzene, 1,4-H₂BDC = 1,4-benzenedicarboxylic acid, 1,3-H₂BDC = 1,3-benzenedicarboxylic acid, 5-Me-1,3-H₂BDC = 5-methyl-1,3-benzenedicarboxylic acid, 5-NO₂-1,3-H₂BDC = 5-nitro-1,3-benzenedicarboxylic acid, 5-OH-1,3-H₂BDC = 5-hydroxy-1,3-benzenedicarboxylic acid). Their structures have been determined by single-crystal X-ray diffraction analyses, elemental analyses, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). Compound 1 is a two-fold interpenetrating network showing the coexistence of polyrotaxane and polycatenane characters. Compounds 2 and 3 exhibit similar 2D (3,5)-connected (4²·6⁷·8)(4²·6) nets in which the bpmb ligands work as lockers in interlocking 1D [Cd(1,3-BDC/5-Me-1,3-BDC)]_n chains. Compound 4 shows a 2D 4-connected (6⁶) sandwich-like structure with differently oriented [Cd(5-NO₂-1,3-BDC)]_n chains. Compound 5 is a 3D supramolecular pcu net based on a 1D ladder-shaped chain. These results suggest that the substituted positions of carboxylate groups and changes in substituted R groups in the 5-position of BDC ligands have significant effect on the final structures. These compounds exhibited relatively good photocatalytic activity towards the degradation of methylene blue (MB) in aqueous solution under UV irradiation. Moreover, solid-state photoluminescence properties of 1–5 were also investigated.