Cadmium(ii) terephthalates based on trinuclear units {Cd3(bdc)3}: control of coordination structure dimensionality and luminescence properties

Two metal-organic coordination polymers based on cadmium(ii) ions and terephthalic (1,4-benzenedicarboxylic) acid were synthesized in dimethylformamide or a mixture of dimethylformamide and methanol: [Cd3(bdc)3(dmf)4] (1, bdc is 1,4-benzenedicarboxylate, dmf is N,N´-dimethylformamide) and [Cd3(bdc)3(dmf)2] (2), respectively. According to the single-crystal X-ray diffraction data, both compounds are built up by the trinuclear carboxylate units {Cd3(O2CR)6}. Compound 1 has a layered structure, whereas compound 2 has a three-dimensional structure due to the presence of additional coordination interactions between adjacent trinuclear units and the formation of polymer chains {Cd3(dmf)2(μ2-O2CR-κ1,κ1)2(μ2-O2CR-κ2,κ1)4(O2CR-κ1)2}. The synthesized compounds were characterized by IR spectroscopy, thermogravimetric analysis, elemental analysis, and powder X-ray diffrac- tion. The luminescence properties of these compounds provide evidence for the existence of both intraligand and charge-transfer transitions. The luminescence quantum yields for both compounds are 10%.