Publication Details (including relevant citation information):
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
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?