Coordination assemblies of the CdII–BDC/bpt mixed-ligand system: positional isomeric effect, structural diversification and luminescent properties

Abstract

To further systematically investigate the influence of the positional isomeric ligands on the structures and properties of transition metal complexes, we synthesized six Cd(II) complexes with three positional isomeric dipyridyl ligands (4,4′-bpt, 3,4′-bpt and 3,3′-bpt) and three positional isomeric phenyl dicarboxylate anions (p-BDC, m-BDC and o-BDC), namely, [Cd₃(p-BDC)₃(4,4′-bpt)₂(H₂O)₅]·H₂O (1), [Cd(p-HBDC)(p-BDC)_0.5(3,4′-bpt)] (2), [Cd₄(p-BDC)₄(3,3′-bpt)₄]·9H₂O (3), [Cd(m-BDC)(3,3′-bpt)(H₂O)]·2H₂O (4), [Cd(o-BDC)(3,3′-bpt)(H₂O)]·(3,3′-bpt)·4H₂O (5), [Cd(o-BDC)(3,4′-bpt)(H₂O)]·H₂O (6). Structural analysis reveals that 1 is composed of a three dimensional (3D) 4-connected net giving an interesting 3-fold interpenetrating architecture. 2 and 3 possess a similar two dimensional (2D) layer structures. 4 presents an infinite one dimensional (1D) tubular-like chain. 5 displays a 2D honeycomb structure consisting of a 1D metal–organic helical chain. 6 exhibits a 2D wave-like layer structure with a (4⁴)-sql network. Structural diversities indicate that the nature of isomeric benzene–dicarboxylates and bpt ligands plays crucial roles in modulating structures of these complexes. Intermolecular forces have important effects on the formation and strengthening of the supra-molecular architecture in these complexes. Moreover, the luminescent properties of them have been briefly investigated.