Synthesis, structure and characterization of novel nickel(II) and iron(II) complexes with a 5,5′-bis[2-(2,2′-bipyridin-6-yl)-ethyl]-2,2′-bipyridine ligand

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Abstract
A new tris-bipyridine ligand 5,5′-bis[2-(2,2′-bipyridin-6-yl)-ethyl]-2,2′-bipyridine (L) was synthesized, and complexes [ML3][PF6]2·2EtOH·0.5H2O [M = Ni(II), 1 M = Fe(II), 2] were obtained by reaction of the ligand L with Ni(II) and Fe(II) ions, respectively. X-Ray data of complex 1 show that the central 5,5′-disubstituted 2,2′-bipyridine units of each ligand L coordinate to the Ni(II) ion to give a distorted octahedral environment, while all the terminal 6-monosubstituted 2,2′-bipyridine groups of the ligand keep free of coordination. Complex 2 is isomorphic to 1. The solution behavior of complex 2 was investigated by 1H NMR spectroscopy. Complexes 1 and 2 were also characterized by ES-MS spectrometry and cyclic voltammetry. The ES-MS spectral data indicate that only the mononuclear complexes formed in the reaction mixtures of the ligand L and M(ClO4)2 (M = Fe and Ni) even in the presence of excess metal ion. The results illustrate that the central 5,5′-disubstituted 2,2′-bipyridine moiety of each ligand L is selectively coordinated by octahedral geometric metal ions, whereas the 6-substituted 2,2′-bipyridine unit does not participate in any metal ion coordination.
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