Syntheses and Crystal Structures of a Series of Novel Helical Coordination Polymers Constructed from Flexible Bis(imidazole) Ligands and Metal Salts

This paper reports eight novel one-dimensional (1D) helical chain polymers consisting of metal salts and flexible bis(imidazole) ligands, formulated as [Co(L 1 ) 2 (bimb)] ( 1 ), [Cu 2 (bimb) 2 Cl 2 ] ( 2 ), [Co(L 2 ) 2 (bimb)] ( 3 ), [Co(L 3 )(bix)Cl] ( 4 ), [Co(L 4 ) 2 (bix)] ( 5 ), [Co(L 5 ) 2 (bimb)] ( 6 ), [Ni(L 6 ) 2 (bimb)] ( 7 ), and [Ni(L 7 ) 2 (bimb)] ( 8 ) (bimb = 1,4-bis(imidazol-1-yl)-butane, bix = 1,4-bis(imidazol-1-yl-methylene)-benzene, HL 1 = 3,5-dinitrobenzoic acid, HL 2 = 4-methoxylbenzoic acid, HL 3 = benzoic acid, HL 4 = 4-methylbenzoic acid, HL 5 = 3-nitrobenzoic acid, HL 6 = 4-nitrobenzoic acid and HL 7 = 4-chlorobenzoic acid), which have been obtained via hydrothermal reaction and characterized by single-crystal X-ray diffraction, elemental analysis, IR and thermogravimetric analyses. 1 consists of chiral polymer chains assembled from achiral components due to the presence of left-handed helices. 2 is a very unusual racemic compound based on perpendicular left- and right-handed helical chains. 3 contains two distinct types of helical chains, one with an almost flat, zigzag type geometry and the other showing a distinct tubular motif. 4 is also a racemic compound with tubes larger than those in 3 . 5 − 8 show rare meso -helical structures. This series of complexes provides new examples of 1D infinite helical structures for flexible bis(imidazole) ligands.