Cis-trans isomerism in mononuclear nickel(ii) β-ketoenamine complexes

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Solution NMR and X-ray crystallographic structural studies of square-planar nickel(II) Schiff base complexes are reported. In contrast to recently prepared cofacial binuclear complexes derived from bis(β-ketoenamines), which have the cis arrangement of O and NH donors about each metal atom, two representative mononuclear complexes, Ni(acim)2(acimH = 4-amino-3-penten-2-one) and Ni- (bzacim)2(bzacimH = 3-amino-l-phenyl-2-buten-l-one), are produced as trans isomers. Ni(acim)2 (NiC10H16N2O2) is orthorhombic, space group Ccca, a = 16.770(2), b = 15.054(2), c = 13.494(1) A, Z = 12, R = 0.055, Rw= 0.042 for 143 parameters and 1748 reflections with I > lσ(l). Ni(bzacim)2(NiC20H20N2O2) is monoclinic, space group P21/c, a = 5.9186(8), b = 13.694(2), c = 11.944(4) A, β = 112.18(2)°, Z = 2, R = 0.038, Rw= 0.037 for 156 parameters and 1589 reflections with I > 2σ(I). Crystals of Ni(bzacim)2 contain centrosymmetric, nearly planar trans molecules. The structure of Ni(acim)2 contains independent molecules with 2 and 222 symmetry, but both of these are disordered, so that whether the cis or trans isomer is present cannot be determined. However, solution 1H NOE and lanthanide shift measurements indicate that the trans isomer predominates for both compounds. © 1989, Taylor & Francis Group, LLC. All rights reserved.

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Journal of Coordination Chemistry

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