Design and constructions of three novel metal–organic frameworks based on pillared-layer motifs

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Three novel 3D metal–organic frameworks, [Co2(butca)(o-bix)2·8H2O]n (1), [Co2(butca)(m-bix)2·2H2O]n (2) and [Co2(butca)(p-bix)2·3H2O]n (3) (butca = 1,2,3,4-butane-tetracarboxylic acid; o-bix = 1,2-bis(imidazol-1-ylmethyl)-benzene; m-bix = 1,3-bis(imidazol-1-ylmethyl)-benzene; and p-bix = 1,4-bis(imidazol-1-ylmethyl)-benzene), have been successfully synthesized from a 2D layer compound [Co2(butca)(H2O)5·2H2O]n (0) employing a three isomer pillars insertion reaction, and their structures were determined by single-crystal X-ray diffraction studies. Complexes 1 and 2 are isostructural. Interestingly, there exist metal-bix double-helical chains in these two 3D frameworks, which are arranged left- and right-handed alternately. Different from 1 and 2 which have only one coordination model, Co atoms in 3 have two types of different coordination enviroments. The Co1 ions are exclusively bridged by cis-bix ligands to give one 26-number ring through spontaneous resolution. At the same time, the Co2 ions are wholely connected with tran-bix ligands to form a 1-D zigzag chain. Moreover, the relationship between a 2D layer structure and 3D metal–organic frameworks based on the pillared-layer motifs is discussed. This work has significant potential for the study of crystal engineering of transition metal coordination networks.