Synthesis and crystal structures of terephthalato-bridged macrocyclic nickel(II) complexes with cis configurations

Three dinuclear terephthalato-bridged nickel(II) complexes [Ni(rac-L)]2(μ-TPA)(ClO4)2 (1), [Ni(RR-L)]2(μ-TPA)(ClO4)2 (2), and [Ni(SS-L)]2(μ-TPA)(ClO4)2 (3) (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, TPA = terephthalic acid) have been synthesized and characterized. Single-crystal X-ray diffraction analyses revealed that the Ni(II) atoms have six-coordinated distorted octahedral environments, and the terephthalato ligand bridges two Ni(II) centres in a bis bidentate fashion to form dimers in all three complexes. The monomers of {[Ni(RR-L)]2(μ-TPA)}2+ and {[Ni(SS-L)]2(μ-TPA)}2+ are connected through intermolecular hydrogen bonds to generate 1D right-handed and left-handed helical chains, respectively. The racemic character of 1 and the homochiral natures of 2 and 3 are confirmed by the results of CD spectroscopy.