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3d-and 4d-metal(II) complexes of a tris(pyridyl)ethane-derived N-4 ligand – a structural study and reactivity remarks

Wiedemann, Dennis; Grohmann, Andreas

A series of complexes of the new N-4 chelate ligand L (L = 1-{6-[1,1-bis(pyridin-2-yl) ethyl] pyridin-2-yl}-N, N-dimethylmethanamine) with intermediate to late divalent transition metal ions M was obtained by the reaction between L and the respective chloride salt or similar precursor in methanol: [MCl2L] (M = Mn, Fe, Co, Ni, Zn; Ru) and [CuClL]Cl. The stereochemical characteristics of the chelate ligand were studied by means of single-crystal X-ray diffraction, and quantified on the basis of several geometric parameters, including the tetragonal distortion Sigma and the continuous symmetry measure S(O-h). The overall distortion of the coordination environment is predomi-nantly determined by the steric demand of the central ion, while electronic or other subtler influences essentially contribute to the distortion of the ligand L. Unlike similar complexes, [(MnCl2L)-Cl-II] cannot be oxidized to a manganese(III) complex by dioxygen, hydrogen peroxide, or iodosylbenzene. In [(RuCl2L)-Cl-II], one chlorido ligand can be exchanged against small p-accepting molecules such as acetonitrile or dinitrogen. L offers an environment ideal for small metal ions (0.4-0.6 angstrom), such as low-spin iron(II), which rationalizes the late onset of thermal spin crossover in the complex [(FeL)-L-II(NCS)(2)].
Published in: Zeitschrift für anorganische und allgemeine Chemie, 10.1002/zaac.201400047, Wiley-VCH