Self-assembly of three cadmium(II) complexes based on 5-methylisophthalic acid and flexible bis(imidazole) ligands with different spacer lengths

Three different cadmium(II) coordination polymers, [Cd2(mip)2(1,2-bie)] (1), [Cd(mip)(1,3-bip)] (2), {[Cd(mip)(1,4-bib)(H2O)]·H2O}2 (3), where H2mip = 5-methylisophthalic acid, 1,2-bie = 1,2-bis(imidazole)ethane, 1,3-bip = 1,3-bis(imidazole)propane and 1,4-bib = 1,4-bis(imidazole)butane, were synthesized under hydrothermal conditions. Their structures have been characterized by elemental analysis, IR and single-crystal X-ray crystallography. Complex 1 displays a 3D network with a (4,5)-connected (42.74)(42.62.76) topology. Complex 2 features a 2D layer structure with a (3,5)-connected (42.6)(42.67.8) topology. Complex 3 has two crystallographically distinct 2D (4,4) polymeric motifs, which are further extended by hydrogen-bonding interactions to form a 2D double layer. These structural analyses indicate that the flexible bis(imidazole) ligands with different spacer lengths play important roles in the formation of the final structures. In addition, the photoluminescent properties of 1–3 in the solid state have been investigated.