Copper(II) and cobalt(II) coordination polymers with bridging 1,2,4,5-benzenetetracarboxylate and N-methylimidazole: coordination number-determined sheet topology

Two new coordination polymers were synthesized under ambient conditions in water by combining a cobalt(II) or copper(II) metal salt with 1,2,4,5-benzenetetracarboxylate (BTEC) and N-methylimidazole (Meim), forming Co2(BTEC)(Meim)4(H2O)4·H2O (1) and Cu2(BTEC)(Meim)4 (2). Compounds 1 and 2 were characterized by X-ray crystallography, powder X-ray diffraction, TGA, FT-IR and elemental analysis. The crystal structures and 2D polymeric structures of compounds 1 and 2 are reported. Coordination polymer 1 crystallizes in the monoclinic space group C2/c. Coordination polymer 2 crystallizes in the triclinic space group P. Both 1 and 2 are made up of infinite sheets of BTEC ligands and metal ions. The sheets in 1 are puckered, giving an offset zigzag sheet topology, while the sheets in 2 are flat. Significant π–π stacking between Meim rings on adjacent sheets contributes to inter-sheet interactions in both 1 and 2. While hydrogen bonding does not play a role in 2, significant hydrogen bonding between sheets in 1 also stabilizes inter-sheet interactions.