Two cobalt coordination polymers based on an asymmetric dicarboxylate: structural diversity tuned by auxiliary ligands

Two 1-D cobalt coordination polymers, [Co(mbtx)(hpht)(H2O)] (n) (1) and [Co(mbix)(hpht)] (n) (2) (mbtx=1,3-bis(1,2,4-triazol-1-ylmethyl)benzene, mbix=1,3-bis(imidazol-1-ylmethyl)benzene, H(2)hpht=homophthalic acid), were synthesized by hydrothermal reactions and characterized by elemental analyzes, IR spectroscopy, thermogravimetry, and single-crystal X-ray diffraction. Complex 1 is a 1-D heterostranded double-helical chain as a result of bridging hpht and mbtx, and the 1-D chains are further self-assembled into a 2-D layer structure through hydrogen bonds. Complex 2 shows a 1-D molecular ladder structure, linked through C-H interactions to give a 2-D layer structure, which is further linked through C-HO hydrogen bonds to form a 3-D framework. The mbtx adopts cis-conformation in 1, while for 2, mbix has trans-conformation. Factors causing the differences between 1 and 2 are discussed.