Showing papers by "Hongyu Chen published in 2005"
TL;DR: The use of Mn(II)LCl2 precursors leads to higher product purity of the Mn dimers while achieving the 1:1 ligand to Mn stoichiometry appropriate for catalytic activity assay.
Abstract: A series of complexes with the formula [MnIII/IV2(μ-O)2(L)2(X)2]3+ have been prepared in situ from MnIILCl2 precursors by a general preparative method (L = terpy, Cl-terpy, Br-terpy, Ph-terpy, tolyl-terpy, mesityl-terpy, t Bu3-terpy, EtO-terpy, py-phen, dpya, Me2N-terpy, or HO-terpy, and X = a labile ligand such as water, chloride, or sulfate). The parent complex, where L = terpy and X = water, is a functional model for the oxygen-evolving complex of photosystem II (Limburg, et al. J. Am. Chem. Soc. 2001, 123, 423−430). Crystals of MnII(dpya)Cl2, MnII(Ph-terpy)Cl2, MnII(mesityl-terpy)Cl2, and an organic-soluble di-μ-oxo di-aqua dimanganese complex, [MnIII/IV2(μ-O)2(mesityl-terpy)2(OH2)2](NO3)3, were obtained and characterized by X-ray crystallography. Solutions of the in situ-formed di-μ-oxo dimanganese complexes were characterized by electrospray mass spectrometry, EPR spectroscopy, and UV−visible spectroscopy, and the rates of catalytic oxygen-evolving activity were assayed. The use of MnIILCl2 precurso...
96 citations
TL;DR: This complex is the first example of a compound where a MnIV ion is coordinated by all three types of water-derived ligands: oxo, hydroxo, and aqua, and the absence of an EPR signal for this complex, even at high temperature.
Abstract: An unprecedented atom connectivity, MnIV(μ-O)MnIV(μ-O)2MnIV(μ-O)MnIV, is found in the complex [MnIV4O4(EtO-terpy)4(OH)2(OH2)2](ClO4)6·8H2O (EtO-terpy = 4‘-ethoxyl-2,2‘:6‘,2‘ ‘-terpyridine), which has been characterized by X-ray crystallography, X-ray powder diffraction, EPR spectroscopy, and magnetic studies. This complex is the first example of a compound where a MnIV ion is coordinated by all three types of water-derived ligands: oxo, hydroxo, and aqua. Bond distances and angles for this complex are consistent with a MnIV4 oxidation state assignment. The di-μ-oxo- and mono-μ-oxo-bridged Mn−Mn distances are 2.80 and 3.51 A, respectively. The variable-temperature magnetic susceptibility data for this complex, in the range of 10−300 K, are consistent with an S = 0 ground state and were fit using the spin Hamiltonian ĤHDvV = −J1Ŝ2Ŝ1 − J2Ŝ1Ŝ1A − J1Ŝ1AŜ2A (S1 = S1A = S2 = S2A = 3/2) with J1 = −432 cm-1 and J2 = −164 cm-1 (where J1 and J2 are exchange constants through the mono-μ-oxo and the di-μ-oxo bridges,...
46 citations
TL;DR: This study confirms the previous results and shows that: i) the sign of D is correlated with the nature of the tetragonal distortion; ii) the magnitude ofD is not sensitive to thenature of the anions in the authors' series of rhombic complexes, contrary to the porphyrinic systems; iii) the E term increases when the ligand-field strength of the equatorial ligands decreases.
Abstract: The isolation, structural characterization, and electronic properties of two six-coordinated chloromanganese (III) complexes, [Mn(terpy)(Cl) 3 ] (1) and [Mn(Phterpy)(Cl) 3 ] (2), are reported (terpy=2,2':6'2-terpyridine, Phterpy=4'-phenyl-'22':6',2-terpyridine). These complexes complement a series of monomuclear azide and fluoride Mn(III) complexes synthesized with neutral N-tridentate ligands, [Mn(L)(X) 3 ] (X= F or N 3 - and L=terpy or bpea [N,N-bis(2-pyridylmethyl)-ethylamine)], previously described. Similar to these previous complexes, 1 and 2 exhibit a Jahn-Teller distortion of the octahedron, characteristic of a high-spin Mn(III) complex (S=2). The analysis of the crystallographic data shows that, in both cases, the manganese ion lies in the center of a distorted octahedron characterized by an elongation along the tetragonal axis. Their electronic properties were investigated by multifrequency EPR (190-475 GHz) performed in the solid state at different temperatures (5-15 K), This study confirms our previous results and further shows that: i) the sign of D is correlated with the nature of the tetragonal distortion; ii) the magnitude of D is not sensitive to the nature of the anions in our series of rhombic complexes, contrary to the polphyrinic systems; iii) the |E/D| values (0.124 for 1 and 0.085 for 2) are smaller compared to those found for the [Mn(L)(X) 3 ] complexes (in the range of 0.146 to 0.234); and iv) the E term increases when the ligand-field strength of the equatorial ligands decreases.
24 citations