Katarzyna Grubel - Synthesis, Characterization, and Ligand Exchange Reactivity of a Series of First Row Divalent Metal 3-Hydroxyflavonolate Complexes

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  Grubel K.; Rudzka, K.; Arif, A. M.; Klotz, K. L.; Halfen, J. A.;   Berreau, L. M. Inorganic Chemistry  2010, 49, 82-96; DOI:  10.1021/ic901405h


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  A series of divalent metal flavonolate complexes of the general   formula [(6-Ph2TPA)M(3-Hfl)]X (1−5-X;   X = OTf or ClO4;   6-Ph2TPA =   N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine;   M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II); 3-Hfl =   3-hydroxyflavonolate) were prepared and characterized by X-ray   crystallography, elemental analysis, FTIR, UV−vis, 1H   NMR or EPR, and cyclic voltammetry. All of the complexes have a   bidentate coordinated flavonolate ligand. The difference in M−O   distances (ΔM−O) involving this ligand varies through   the series, with the asymmetry of flavonolate coordination   increasing in the order Mn(II)   Ni(II) < Cu(II) < Zn(II) < Co(II). The hypsochromic   shift of the absorption band I (π→π*) of the coordinated   flavonolate ligand in 1−5-OTf (relative to that   in free anion) increases in the order Ni(II) < Mn(II) <   Cu(II) < Zn(II), Co(II). Previously reported 3-Hfl complexes   of divalent metals fit well with this ordering. 1H NMR   studies indicate that the 3-Hfl complexes of Co(II), Ni(II), and   Zn(II) exhibit a pseudo-octahedral geometry in solution. EPR   studies suggest that the Mn(II) complex 1-OTf  may form binuclear structures in solution. The mononuclear Cu(II)   complex 4-OTf has a distorted square pyramidal   geometry. The oxidation potential of the flavonolate ligand   depends on the metal ion present and/or the solution structure of   the complex, with the Mn(II) complex 1-OTf  exhibiting the lowest potential, followed by the   pseudo-octahedral Ni(II) and Zn(II) 3-Hfl complexes, and the   distorted square pyramidal Cu(II) complex 4-OTf.   The Mn(II) complex [(6-Ph2TPA)Mn(3-Hfl)]OTf   (1-OTf) is unique in the series in undergoing   ligand exchange reactions in the presence of   M(ClO4)2·6H2O (M = Co, Ni, Zn)   in CD3CN to produce   [(6-Ph2TPA)M(CD3CN)n](X)2,   [Mn(3-Hfl)2·0.5H2O], and MnX2 (X   = OTf or ClO4). Under similar   conditions, the 3-Hfl complexes of Co(II), Ni(II), and Cu(II)   undergo flavonolate ligand exchange to produce   [(6-Ph2TPA)M(CD3CN)n](X)2  (M = Co, Ni, Cu; n = 1 or 2) and   [Zn(3-Hfl)2·2H2O]. An Fe(II) complex of   3-Hfl, [(6-Ph2TPA)Fe(3-Hfl)]ClO4  (8), was isolated and characterized by elemental   analysis, FTIR, UV−vis, 1H NMR, cyclic voltammetry,   and a magnetic moment measurement. This complex reacts with   O2 to produce the diiron(III) μ-oxo compound   [(6-Ph2TPAFe(3Hfl))2(μ-O)](ClO4)2  (6).

  Address (URL): http://pubs.acs.org/doi/abs/10.1021/ic901405h?