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(L1)2(bimb)] (1), [Cu2(bimb)2Cl2] (2), [Co(L2)2(bimb)] (3), [Co(L3)(bix)Cl] (4), [Co(L4)2(bix)] (5), [Co(L5)2(bimb)] (6), [Ni(L6)2(bimb)] (7), and [Ni(L7)2(bimb)] (8) (bimb = 1,4-bis(imidazol-1-yl)-butane, bix = 1,4-bis(imidazol-1-yl-methylene)-benzene, HL1 = 3,5-dinitrobenzoic acid, HL2 = 4-methoxylbenzoic acid, HL3 = benzoic acid, HL4 = 4-methylbenzoic acid, HL5 = 3-nitrobenzoic acid, HL6 = 4-nitrobenzoic acid and HL7 = 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.