Non-oxo 5-coordinate and 6-coordinate vanadium(IV) complexes with their precursor [LV(III)(CH3OH)](0), where L = a trianionic aminetris(phenolate)-[N,O,O,O] donor ligand: a magnetostructural and EPR study.

Ligating properties of a tripodal, potentially tetradentate aminetris(phenol) ligand, tris(2-hydroxy-3,5-di-tert-butylbenzyl)amine, H(3)L, containing [N,O,O,O] donor atoms toward the vanadium ions in +III and IV oxidation states have been studied. The structures of complexes 1 [LV(III)(CH(3)OH)](0), 2 [LV(IV)(OCH(3))](0) and 3 [LV(IV)(acac)](0) were determined by X-ray diffraction methods as having five-coordinate V(III), 1, five-coordinate non-oxo-vanadium(IV), 2, and six-coordinate non-oxo-vanadium(iv) 3, respectively. Compounds 1-3 were also studied with electrochemical methods, variable-temperature (2-295 K) magnetic susceptibility measurements and X-band electron paramagnetic resonance (EPR) spectroscopy.

A star-shaped heteronuclear Cr(III)Mn(II)3 species and its precise electronic and magnetic structure: spin frustration studied by X-ray spectroscopic, magnetic, and theoretical methods.

Molecular magnets incorporate transition-metal ions with organic groups providing a bridge to mediate magnetic exchange interactions between the ions. Among them are star-shaped molecules in which antiferromagnetic couplings between the central and peripheral atoms are predominantly present. Those configurations lead to an appreciable spin moment in the nonfrustrated ground state.

Metal-complexes as ligands to generate asymmetric homo- and heterodinuclear M(A)(III)M(B)(II) species: a magneto-structural and spectroscopic comparison of imidazole-N versus pyridine-N.

Ten hetero- and homodinuclear M(A)(III)M(B)(III) complexes, 1-10, containing the metal centers Fe(III)Zn(II) (1), Fe(III)Cu(II) (2), Fe(III)Ni(II) (3), Fe(III)Fe(II) (4), Fe(III)Mn(II) (5), Cr(III)Ni(II) (6), Cr(III)Zn(II) (7), Ga(III)Ni(II) (8), Co(III)Fe(II) (9), and Mn(III)Mn(II) (10) are described. The tridentate ligation property of the divalent metal complexes tris(1-methylimidazole-2-aldoximato)metal(II) with three facially disposed pendent oxime O-atoms has been utilized to generate the said complexes. Complexes were characterized by various physical methods including MS, IR, UV-vis, Mossbauer and EPR spectroscopy, cyclic voltammetry (CV), variable-temperature (2-290 K) magnetic susceptibility, and X-ray diffraction techniques.

Polynuclear nickel(II) complexes: a magnetostructural study of Ni(II)4, Ni(II)6, and Ni(II)9 species with oxime ligands.

Syntheses, crystal structures, and magnetic properties are reported for a tetrametallic (complex 1), a nonametallic (complex 2), and two hexametallic (complexes 3 and 4) nickel(II) clusters, namely, [Ni(4)(HL(1))(2)(mu-OAc)(2)(MeOH)] (1), [Ni(9)(L(2))(10)(mu(3)-OH) (2) (mu-OH) (2) (mu-OH (2))(2)(OH(2))(6)](ClO(4)) (4) (2), [Ni(6)(L(2))(9)(L(2)H)(MeOH)(H(2)O)(2)](ClO(4))(3) (3), and [Ni(6)(L(3))(3)(mu(3)-O)(2)](ClO(4))(2) (4), where H(4)L(1) represents N,N'-dimethyl-N,N'-ethylene-bis(5-bromo-3-formyloxime-2-hydroxybenzylamine); HL(2), 1-methylimidazole-2-aldoxime; and H(2)L(3), N,N'-bis(2,3-butanedionemonoxime-2-ene)-3(aminomethyl)benzylamine. The structure of 1 can be considered as two face-sharing bioctahedral units of [Ni(2)(mu-O(phen))(2)(mu-OAc)] bridged by a two-atom (-N-O-) oximate linker. The Ni(II).

A nonanuclear copper(II) cluster incorporating endogenous alkoxo- and exogenous hydroxo bridges containing [Cu3(micro3-OH)] cores.

A remarkable nonanuclear copper(II) complex, , with the composition [Cu9(L)4(micro3-OH)4(MeOH)2](ClO4)2, in which L is a pentadentate trianionic Schiff-base ligand with N2O3 donor atoms, has been characterized by analytical, structural and magnetochemical methods. The structure consists of four dinuclear [Cu2L]+ units linked covalently to a central copper atom by four micro3-OH, thus yielding the nonacopper core. Variable-temperature (2-290 K) magnetic susceptibility data of , have been analyzed by a "three-J" exchange coupling model (H=-2JSi.

A magneto-structural study of a hexanuclear (V(IV)=O)6-complex and a tetranuclear mixed-valent [V(III)2V(IV)2] species.

Syntheses, crystal structures, and magnetic properties are reported for a hexametallic and a mixed-valent tetrametallic vanadium cluster, namely [Na(L(1))(6)(V(IV)=O)(6)]ClO(4) (1) and [(L(2))(2)V(III)(2)V(IV)(2)(mu-Cl)(6)Cl(4)] (2), where H(2)L(1) represents N-methyldiethanolamine and H(2)L(2) N'N'-di(3,5-di-tert-butyl-salicylidene)-1,3-diaminobenzene. The structure of the cation in 1 is comprised of a hexagon of six (V(IV)=O) units, in which a sodium ion is encapsulated in the center of the hexagon. Thus, the hexametalate ring contains six d(1) ions, each of which is in an octahedral environment of O(5)N atoms.

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.

An oximate-based hexanuclear mixed-valence Mn(III)4Mn(II)2 edge-sharing bitetrahedral core with an St = 5 spin ground state.

The synthesis, structures and magnetic properties of two hexanuclear Mn6 clusters are reported: Mn6(mu4-O)2(dapdo)2(dapdoH)4(mu2-OH)2](ClO4)(2).6MeCN (1.6MeCN) and [Mn6(mu4-O)2(dapdo)2(dapdoH)4(mu2-OCH3)2](ClO4)(2).

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].

Radical-ligand-derived C-N coupling, Ga(III)-radical vs low-spin Co(III)-radical reactivity.

The redox-active ligand 2-(3,5-dimethoxyanilino)-4,6-di- tert-butylphenol, H 2L (OCH3), results in, as expected, a trisradical complex with a low-spin Co(III) center, [Co (III)(L (OCH3) (*)) 3] ( 1), whereas the Ga(III) center yields a coordinated new hexadentate monoradical ligand, [Ga (III)L (*) 1] ( 2), presumably due to the ligand-derived redox activity involving C-H activation.

Star-shaped molecule of MnII4O6 core with an St=10 high-spin state. A theoretical and experimental study with XPS, XMCD, and other magnetic methods.

We report a comprehensive study of the electronic and magnetic properties of a star-shaped molecule comprising a MnII4O6 core. One feature of this compound is weak magnetic coupling constants compared to other similar polyoxo compounds. This leads to complicated low-lying magnetic states in which the ground state is not well separated from the upper-lying states, yielding a high-spin molecule with a giant magnetic moment of up to 20 microB/formula unit.

Effect of the substituents on the spin coupling between iminosemiquinone pi-radicals mediated by diamagnetic metal ions: l.s. Co(III) vs Ga(III).

Exchange coupling between the radical iminosemiquinone ligands changes from ferromagnetic to antiferromagnetic in l.s. Co(III) complexes, whereas the same coupling in Ga(III) complexes is always antiferromagnetic.

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.

Rational synthesis of a heterotetranuclear CrIII2CuII2 species using a metaloximate as a building block. A magnetostructural study.

The reaction of [Cu(DapdoH(2))2](2+) ions with [Cr(III)L(MeOH)2Br](2+) ions (L = 1,4,7-trimethyl-1,4,7-triazacyclononane; DapdoH(2) = 2,6-diacetylpyridine dioxime) produced in situ in methanol, yielded, in the presence of triethylamine, the complex [L(2)Cr(III)(2)(Dapdo)2(OH)2Cu(II)(2)Br(2)](ClO(4))2. It has been characterized on the basis of elemental analysis, IR spectroscopy and variable-temperature (2-298 K) magnetic susceptibility measurements. The molecular structure established by X-ray diffraction consists of a [Cr(III)(2)(micro-NO)4(micro-OH)2Cu(II)(2)](4+)-core, which can be considered as two edge-sharing triangular CrCu(2)-units.

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.

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.

Ferromagnetic vs antiferromagnetic coupling in bis(mu-phenoxo)dicopper(II) complexes. Tuning of the nature of exchange coupling by remote ligand substituents.

Two bis(mu-phenoxo)dicopper(II) complexes, [(L(CH3))(2)Cu(2)] (1) and [(L(t-Bu))(2)Cu(2)] (2), where L(CH3) and L(t-Bu) represent the dianions of (methylamino)-N,N-bis(2-methylene-4,6-dimethylphenol) and of (methylamino)-N,N-bis(2-methylene-4,6-di-tert-butylphenol), respectively, are reported to demonstrate the effect of remote substituents on the nature of exchange coupling interactions between the copper(II) centers. In contrast to 1, which is as usual antiferromagnetically coupled, complex 2 is a rare example of a ferromagnetically coupled diphenoxodicopper(II) complex.

A one-pot synthesis of a paramagnetic high-nuclearity nickel(II) cluster: an octadecanuclear Ni(II)16Na(I)2 metal aggregate.

An unusual Ni(II)(16)Na(I)(2) cluster which features formate as a bridging clamp between two octanuclear nickel cages is reported; preliminary magnetic studies exhibit paramagnetic low-lying states resulting from dominating antiferromagnetic interactions between the nickel(II) centers.

A spin-frustrated star-shaped heterotetranuclear CrIIIMnII3 species and its magnetic and HF-EPR measurements.

A tetranuclear complex [Cr(III)Mn(II)(3)(PyA)(6)Cl(3)] 1 containing pyridine-2-aldoximato monoanion, PyA, has been structurally and magnetochemically characterized. The compound is a rare example of a tetranuclear star-shaped metal topology containing pyridine-2-aldoximato ligands. Static magnetic studies have demonstrated very weak antiferromagnetic exchange interactions between the paramagnetic centers (S(Cr) = 3/2 and S(Mn) = 5/2) resulting in closely spaced low-lying levels, which undergo splitting and crossing.

Molecular and electronic structure of square planar complexes [PdII(tbpy)(L N,O IP)]0, [PdII(tbpy)(LN,O ISQ)](PF6), and [PdII(tbpy)(L N,O IBQ)](PF6)(BF4).2CH2Cl2: an o-iminophenolato based ligand centered, three-membered redox series.

Three Pd(II) complexes which are members of the same electron-transfer series have been synthesized. Refluxing of the reaction mixture containing equimolar amounts of PdCl(2), 2-(2-trifluoromethyl)anilino-4,6-di-tert-butylphenol (H(2)L(N,O)), 4,4'-di-tert-butyl-2,2'-dipyridyl ((t)bpy), and 3 equiv of triethylamine in MeOH under an argon atmosphere followed by exposure to air and addition of KPF(6) after cooling to room temperature yields reddish brown crystals of paramagnetic (S = 1/2) [Pd(L(N,O)(ISQ))((t)bpy)](PF6) (2). Reaction of 2 with one equiv of [CoCp2] in dry and degassed CH(2)Cl(2) using anaerobic conditions gives diamagnetic [Pd(L(N,O)(IP))((t)bpy)] (1), which is the one-electron reduced form of 2.

Ferromagnetic vs. antiferromagnetic coupling in bis(mu2-1,1-azido)dinickel(II) complexes with syn- and anti-conformations of the end-on azide bridges.

Reaction of a 1 : 1 : 1 molar ratio of NiCl(2), NaN(3) and H(2)L, a tetradentate ligand N-(2-pyridyl)methyl)-N,N-bis(2'-hydroxy-3',5'-dimethylbenzyl)amine in methanol in presence of Et(3)N results in a turquoise precipitate, which affords deep green crystals of [Ni(2)(HL)(2)(N(3))(2)]*1.5CH(2)Cl(2) (1) and [Ni(2)(HL)(2)(N(3))(2)]*H(2)O (2) upon crystallization from CH(2)Cl(2)-MeOH or THF-MeOH, respectively. Both complexes reveal distorted octahedral NiN(4)O(2) coordination environments around the Ni(ii) centers with bis(micro-1,1-azido) bridging ligands.

Deliberate synthesis for magnetostructural study of linear tetranuclear complexes BIIIMnIIMnIIBIII, MnIIIMnIIMnIIMnIII, MnIVMnIIMnIIMnIV, FeIIIMnIIMnIIFeIII, and CrIIIMnIIMnIICrIII. Influence of terminal ions on the exchange coupling.

As part of an ongoing effort to deliberate synthesis of polynuclear heterometal complexes, we are exploring synthetic routes to high-nuclearity complexes using "metal oximates" as building blocks. Series of tetranuclear linear complex ions of the general types M(A)M(B)M(B)M(A), where M(A) is a trivalent or tetravalent metal ion and M(B) is a divalent metal ion, e.g.

A trinuclear complex containing MnII MnIII MnIV, radicals, quinone and chloride ligands potentially relevant to PS II.

Reaction of MnCl2 with a non-innocent ligand H3L results in an unprecedented mixed-valence trinuclear complex [MnII MnIII MnIV (L)(L*)2(L(IQ))Cl] whose structural and magnetic properties are described.

Photoinduced intramolecular proton transfer of phenol-containing ligands and their zinc complexes.

N,N'-Bis(salicylidene)hydrazine (L(I)), a bis-2-hydroxybenzene-type ligand H2L, its tert-butyl derivative (L(II)), and the corresponding Zn2+ complexes of the type Zn2(LH)2L (Zn-I and Zn-II) were synthesized. The molecular structure of Zn-II was determined by X-ray crystallography at -170 degrees C. The photoreactions of the four compounds in solution were studied by time-resolved UV-vis spectroscopy using nanosecond laser pulses.

Self-assembly of a nonanuclear nickel(II) complex and its magnetic properties.

A nonanuclear nickel(II) complex [Ni9(PyA)(10)(mu3-OH)2(mu2-OH)2(mu2-OH2)2(H2O)6](ClO4)4.12H2O, containing pyridine-2-aldoximato monoanion, PyA, has been structurally and magnetochemically characterized. The nickel(II) ions, linked together via several bi- or trifurcated oximato, hydroxo, and water bridges, are antiferromagnetically coupled with the coupling constants J1 = -26.