Influence of mixed thiolate/thioether versus dithiolate coordination on the accessibility of the uncommon +I and +III oxidation states for the nickel ion: an experimental and computational study.

Sulfur-rich nickel metalloenzymes are capable of stabilizing Ni(I) and Ni(III) oxidation states in catalytically relevant species. In an effort to better understand the structural and electronic features that allow the stabilization of such species, we have investigated the electrochemical properties of two mononuclear N(2)S(2) Ni(II) complexes that differ in their sulfur environment. Complex 1 features aliphatic dithiolate coordination ([NiL], 1), and complex 2I is characterized by mixed thiolate/thioether coordination ([NiL(Me)]I, 2I).

Molecular and electronic structures of dinuclear iron complexes incorporating strongly electron-donating ligands: implications for the generation of the one- and two-electron oxidized forms.

The ligands (L(t-Bu(2)))(2-), (L(Me(2)))(2-), and (L(Cl(2)))(2-) have been employed for the synthesis of the dinuclear Fe(III) complexes [L(t-Bu(2))Fe(μ-O)FeL(t-Bu(2))], [L(Me(2))Fe(μ-O)FeL(Me(2))], and [L(Cl(2))Fe(μ-O)FeL(Cl(2))]. The strongly electron-donating groups (tert-amines and phenolates) were chosen to increase the electron density at the coordinated ferric ions and thus to facilitate the oxidation of the complexes, with the possibility of fine-tuning the electronic structures by variation of the remote substituents. Molecular structures established in the solid (by single-crystal X-ray diffraction) and in solution (by X-ray absorption spectroscopy) show that the Fe ions are five-coordinate in a square-pyramidal coordination environment with the ligand adopting a trans-conformation.

Highly oxidized diiron complexes: generation, spectroscopy, and stabilities.

Oxidation of the diferric complex [LFe(III)OFe(III)L] to the monoradical complex [LFe(III)OFe(III)L ](+) and the diradical complex [L Fe(III)OFe(III)L ](2+) is followed by a decay into monomeric complexes including a highly reactive putative [LFe(IV)[double bond, length as m-dash]O] complex.

Octahedral monodithiolene complexes of cobalt(III) and chromium(III). Spectroscopic and density functional theoretical characterization of S,S'-coordinated benzene-1,2-dithiolate(1-) pi radicals.

The reaction of [M(tren)Cl(2)]Cl (M = Co(III), Cr(III)) with benzene-1,2-dithiol, H(2)(bdt), and 3,6-bis(trimethylsilyl)benzene-1,2-dithiol, H(2)(tmsdt), in a water/methanol mixture in the presence of potassium tert-butoxide produced green crystals of [M(tren)(bdt)](PF(6))(1/2)(Cl)(1/2).H(2)O (1(PF(6))(1/2)(Cl)(1/2).H(2)O, M = Co; 2(PF(6))(1/2)(Cl)(1/2).

Targeted oxidase reactivity with a new redox-active ligand incorporating N2O2 donor atoms. Complexes of Cu(II), Ni(II), Pd(II), Fe(III), and V(V).

The coordination chemistry of the tetradentate ligand N,N'-bis(2-hydroxy-3,5-di-tert-butylphenyl)-2,2'-diaminobiphenyl H(4)L has been studied with the copper(II), nickel(II), palladium(II), iron(III), and vanadium(V) ions. The ligand is non-innocent in the sense that it is readily oxidized in the presence of air to its o-iminobenzosemiquinonato (L(**))(2-) radical form. The crystal structures of the diradical compounds, [Cu(II)(L(**))] 1, [Ni(II)(L(**))] 2, [Pd(II)(L(**))] 3, the monoradical high-spin compound [Fe(III)(HL(*))Cl] 4, and the di(mu-methoxo)divanadium(V) compound [L(2)V(2)(mu-OCH(3))(2)] 5 without a radical have been determined by X-ray crystallography at 100 K.

Ligand-derived oxidase activity. Catalytic aerial oxidation of alcohols (including methanol) by Cu(II)-diradical complexes.

Seven new bis(o-iminosemiquinonato)copper(II) complexes, 1- 5, 1a, 1b, derived from differently substituted N-phenyl-2-aminophenol-based ligands, are described. Their crystal structures were determined by X-ray diffraction, and their electronic structures were established by various physical methods including electron paramagnetic resonance and variable-temperature (2-290 K) susceptibility measurements. Like complex 6, which was reported recently by us, all complexes exhibit an S t = (1)/ 2 ground state, based on the "isolated" copper(II)-spin character resulting from the dominating antiferromagnetic spin coupling between the two radicals; the ground-state electronic configuration can thus be designated as (increasing, increasing, decreasing)[R-Cu-R].

Characterization of three members of the electron-transfer series [Fe(pda)2]n (n=2-, 1-, 0) by spectroscopy and density functional theoretical calculations [pda=redox non-innocent derivatives of N,N'-bis(pentafluorophenyl)-o-phenylenediamide(2-, 1.-, 0)].

The four-coordinate iron complexes, [Fe(III)(pda(2-))(pda(.-))] (1) and [AsPh(4)](2)[Fe(II)(pda(2-))(2)] (2) were synthesized and fully characterized; pda(2-) is the closed-shell ligand N,N'-bis(pentafluorophenyl)-o-phenylenediamido(2-), and pda(.-) represents its one-electron-oxidized pi-radical anion.

Molecular and electronic structures of mononuclear iron complexes using strongly electron-donating ligands and their oxidized forms.

The ligand L (2-) (H 2L = N, N'-dimethyl- N, N'-bis(3,5-di- t-butyl-2-hydroxybenzyl)-1,2-diaminoethane) has been employed for the synthesis of two mononuclear Fe (III) complexes, namely, [LFe(eta (2)-NO 3)] and [LFeCl]. L (2-) is comprised of four strongly electron-donating groups (two tert-amines and two phenolates) that increase the electron density at the coordinated ferric ions. This property should facilitate oxidation of the complexes, that is, stabilization of the oxidized species.

Neutral bis(alpha-iminopyridine)metal complexes of the first-row transition ions (Cr, Mn, Fe, Co, Ni, Zn) and their monocationic analogues: mixed valency involving a redox noninnocent ligand system.

A series of bis(alpha-iminopyridine)metal complexes featuring the first-row transition ions (Cr, Mn, Fe, Co, Ni, and Zn) is presented. It is shown that these ligands are redox noninnocent and their paramagnetic pi radical monoanionic forms can exist in coordination complexes. Based on spectroscopic and structural characterizations, the neutral complexes are best described as possessing a divalent metal center and two monoanionic pi radicals of the alpha-iminopyridine.

Oxidation of an o-iminobenzosemiquinone radical ligand by molecular bromine: structural, spectroscopic, and reactivity studies of a copper(II) o-iminobenzoquinone complex.

The bis(o-iminobenzosemiquinonato)copper(II) complex 1, containing the radical form [L(*)SQ](1-) arising from the aerial oxidation of the noninnocent ligand 2-anilino-4,6-di- tert-butylphenol, H2L, is readily oxidized by molecular bromine to a bis(o-iminobenzoquinone)copper(II) complex, 2. Thus, a ligand-based oxidative addition is reported for complex 1 containing an electron-rich Cu(II) d(9) metal ion. The crystal structure of the synthesized hexacoordinated complex [Cu(II)(LBQ)2Br2] (2) has been determined by X-ray crystallography at 100 K.

A tetracopper(II)-tetraradical cuboidal core and its reactivity as a functional model of phenoxazinone synthase.

The coordination chemistry of the tridentate ligand N-(2-hydroxy-3,5-di-tert-butylphenyl)-2-aminobenzylalcohol H3L has been studied with the copper(II) ion. The ligand is noninnocent in the sense that it is readily oxidized in the presence of air to its o-iminobenzosemiquinonato [L*]2- radical form. The crystal structure of the synthesized tetracopper(II)-tetraradical complex [CuII4(L*)4] (1), has been determined by X-ray crystallography at 100 K.

Trinuclear copper complexes with triplesalen ligands: geometric and electronic effects on ferromagnetic coupling via the spin-polarization mechanism.

A series of trinuclear Cu(II) complexes with the tris(tetradentate) triplesalen ligands H(6)talen, H(6)talen(tBu(2) ), and H(6)talen(NO(2) ), namely [(talen)Cu(II) (3)] (1), [(talen(tBu(2) ))Cu(II) (3)] (2), and [(talen(NO(2) ))Cu(II) (3)] (3), were synthesized and their molecular and electronic structures determined. These triplesalen ligands provide three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone. The structure of [(talen)Cu(II) (3)] (1) was communicated recently.

Insights into the nature of the hydrogen bonding of *Tyr272 in apo-galactose oxidase.

The synthesis and structure of an o-methylthio-phenol-imidazole, 2-(2'-(4'-tert-butyl-6'-methylsulfanyl)-hydroxyphenyl))-4,5-diphenyl-imidazole ((MeS)LH), is reported; X-ray crystallographic studies have shown that (MeS)LH involves an O-H...

Tridentate facial ligation of tris(pyridine-2-aldoximato)nickel(II) and tris(imidazole-2-aldoximato)nickel(II) To generate NiIIFeIIINiII, MnIIINiII, NiIINiII, and ZnIINiII and the electrooxidized MnIVNiII, NiIINiIII, and ZnIINiIII species: a magnetostructural, electrochemical, and EPR spectroscopic study.

Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), Mn(III)Ni(II) (2), Ni(II)Ni(II) (3a-c and 4), Zn(II)Ni(II) (5), and Zn(II)Zn(II) (6), are described. The tridentate ligation property of the metal complexes tris(pyridine-2-aldoximato)nickel(II) and tris(1-methylimidazole-2-aldoximato)nickel(II) with three facially disposed pendent oxime O atoms has been utilized to generate the said complexes. Complex 1 contains metal centers in a linear arrangement, as is revealed by X-ray diffraction.

Electronic structures of tris(dioxolene)chromium and tris(dithiolene)chromium complexes of the electron-transfer series [Cr(dioxolene)(3)](z) and [Cr(dithiolene)(3)](z) (z = 0, 1-, 2-, 3-). A combined experimental and density functional theoretical study.

From the reaction mixture of 3,6-di-tert-butylcatechol, H2[3,6L(cat)], [CrCl3(thf)3], and NEt3 in CH3CN in the presence of air, the neutral complex [CrIII(3,6L*(sq))3] (S = 0) (1) was isolated. Reduction of 1 with [Co(Cp)2] in CH2Cl2 yielded microcrystals of [Co(Cp)2][CrIII(3,6L*(sq))2(3,6L(cat))] (S = 1/2) (2) where (3,6L*(sq)(1-) is the pi-radical monoanionic o-semiquinonate of the catecholate dianion (3,6Lcat)(2-). Electrochemistry demonstrated that both species are members of the electron-transfer series [Cr(3,6LO,O)]z (z = 0, 1-, 2-, 3-).

The monoanionic pi-radical redox state of alpha-iminoketones in bis(ligand)metal complexes of nickel and cobalt.

The electronic structures of nickel and cobalt centers coordinated by two alpha-iminoketone ligands have been elucidated using density functional theory calculations and a host of physical methods such as X-ray crystallography, cyclic voltammetry, UV-vis spectroscopy, electron paramagnetic resonance spectroscopy, and magnetic susceptibility measurements. In principle, alpha-iminoketone ligands can exist in three oxidation levels: the closed-shell neutral form (L)0, the closed-shell dianion (L(red))(2-), and the open-shell monoanion (L*)(-). Herein, the monoanionic pi-radical form (L*)(-) of alpha-iminoketones is characterized in the compounds [(L*)2Ni] (1) and [(L*)2Co] (3), where (L*)(-) is the one-electron-reduced form of the neutral ligand (t-Bu)N=CH-C(Ph)=O.

Electronic structure of neutral and monoanionic tris(benzene-1,2-dithiolato)metal complexes of molybdenum and tungsten.

The reaction of 3 equiv of the ligand 2-mercapto-3,5-di-tert-butylaniline, H2[LN,S], or 3,5-di-tert-butyl-1,2-benzenedithiol, H2[LS,S], with 1 equiv of [MoO2(acac)2] or WCl6 (acac=acetonylacetate(1-)) in methanol or CCl4 afforded the diamagnetic neutral complexes [MoV(LN,S)2(L*N,S)]0 (1), [MoV(LS,S)2(L*S,S)] (2), and [WV(LS,S)2(L*S,S)] (3), where (L*N,S)- and (L*S,S)- represent monoanionic pi-radical ligands (Srad=1/2), which are the one-electron oxidized forms of the corresponding closed-shell dianions (LN,S)2- and (LS,S)2-. Complexes 1-3 are trigonal-prismatic members of the electron-transfer series [ML3]z (z=0, 1-, 2-). Reaction of 2 and 3 with [N(n-Bu)4](SH) in CH2Cl2 under anaerobic conditions afforded paramagnetic crystalline [N(n-Bu)4][MoV(LS,S)3] (4) and [N(n-Bu)4][WV(LS,S)3] (5).

The unusal redox centers of SoxXA, a novel c-type heme-enzyme essential for chemotrophic sulfur-oxidation of Paracoccus pantotrophus.

The heterodimeric hemoprotein SoxXA, essential for lithotrophic sulfur oxidation of the aerobic bacterium Paracoccus pantotrophus, was examined by a combination of spectroelectrochemistry and EPR spectroscopy. The EPR spectra for SoxXA showed contributions from three paramagnetic heme iron centers. One highly anisotropic low-spin (HALS) species (gmax = 3.

Dimerization processes of square planar [PtII(tbpy)(dithiolato*)]+ radicals.

The preparation and structural characterization of the neutral, square planar complexes [PtII(tbpy)(A)] (1), [PtII(tbpy)(B)] (2), and [PtII(PPh3)2(B)] (3) have been accomplished, where (tbpy) = 4,4'-di-tert-butylpyridine, (A)2- = 3,6-bis(trimethylsilyl)-1,2-benzenedithiolate(2-), and (B)2- = 1,2-bis(4-tert-butylphenyl)ethylene-1,2-dithiolate(2-) and (A*)1- and (B*)1- represent the corresponding monoanionic radicals. Electrochemical and chemical one-electron oxidation of 1 and 2 in CH2Cl2 solution affords the monomeric monocations [PtII(tbpy)(A*)]+ (1a) and [PtII(tbpy)(B*)]+ (2a), both of which possess an S = 1/2 ground state. The corresponding spin doublet monocationic dimers [PtII2(tbpy)2(A)(A*)]+ (1b) and [PtII2(tbpy)2(B)(B*)]+ (2b) were electrochemically generated in solution (50% oxidation) and identified by X-band EPR spectroscopy.

Iron complexes of new pentadentate ligands containing the 1,4,7-triazacyclononane-1,4-diacetate motif. spectroscopic, electro-, and photochemical studies.

Three new pentadentate, pendent arm macrocycles containing the 1,4,7-triazacyclononane-1,4-diacetate motif have been synthesized, and their coordination chemistry with Fe(III) has been investigated. Eight new octahedral Fe(III) complexes containing chloro, azido, or mu-oxo ligands have been synthesized, five of which have been characterized by X-ray crystallography. Spectroscopic characterization of these octahedral Fe(III) complexes by UV-vis, IR, electrochemistry, EPR, magnetic susceptibility, and zero-field Mössbauer measurements firmly establishes the high-spin state of the iron in all complexes.