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%.