Search

The synthesis, magnetic, electrochemical, spectroscopic, and physical studies of group of homo- and heterometal complexes is reported. The complexes were generated by using the metal complex [Ni.sup.II][(oximato).sub.3] monoanions as tridentate ligands.

Several studies are conducted to explain the monoanionic [pi]-radical redox state observed in various [alpha]-iminoketones in bis(ligand)metal complexes of nickel and cobalt. These complexes are shown to consist of a high-spin divalent metal center that is strongly coupled to two ligand radicals.

The preparation and full characterization of the mononuclear neutral complexes [P[t.sup.II]([super t]bpy)(A)] and [P[t.sup.II]([super t]bpy)(B)] (where bpy = 4,4'-di-tert-butylbipyridine, (A) = 3,6-bis(trimethylsilyl)benzene-1,2-(dithiolate(2-) and (B) = 1,2-bis(4-tert-butylphenyl)ethylene-1,2-dithiolate(2-)) is described. The cations are shown to dimerize in C[H.sub.2]C[l.sub.2] solution affording diamagnetic dimers.

Electron-transfer series are described for three ferric complexes of the pentadentate ligand 4,8,11-trimethyl-1,4,7,11-tetraazacyclotetradecane-1-acetate ([Me.sub.3]cyclam-acetate) with axial chloride, fluoride and azide ligands. The Fe(II), Fe(III) and Fe(IV) species are studied spectroscopically and their UV vis, Mossbauer, EPR, and IR spectra are presented.

A synthesis of a series of mononuclear square-based pyramidal complexes of iron having two 1,2-diaryl-ethylene-1,2-dithiolate ligands in various oxidation levels is conducted. This showed that redox noninnocent ligands exist in at least two oxidation levels, namely, the diamagnetic closed-shell dianionic form and paramagnetic open-shell monoanionic form.

Fourier transform infrared spectroscopy is used to study the different redox intermediates of [NiFe] hydrogenase of Desulfovibrio vulgaris Miyazaki F. It is shown that the Fe carries one carbon monoxide molecule and two [CN.sup.-] molecules as ligands as found for D. gigas and A. vinosum hydrogenase, indicating high degree of similarity among these three enzymes.

Dinickel(II) complexes of the ligands N,N'-di-p-anisylformamidinate (DAniF) and N,N',N'-tripheynlguanidinate (TPG) are synthesized and crystallographically characterized, along with their one-electron oxidized analogues. In both systems, the Ni-Ni distances become shorter by ~0.1 A upon oxidation and it is proposed that this species contains a [Ni.sub.2.sup.6+] core with a single Ni-Ni sigma bond.

The electronic structure of [Ni(super II)(L(sub N)(super ISQ))2] and of [Pt(super II)-(L(sub O)(super ISQ))2] is calculated by density functional theoretical and correlated ab initio methods. Electronic and resonance spectra is reported, and the electronic structures of all members of this electron-transfer series is established.

Ligating properties of four potentially tridentate bisphenol ligands containing [O, X, O] donor atoms (X = S, Se, P, or P=O) toward the vanadium ions in +IV or +V oxidation states are studied. A combination of density functional theory calculations and experimental electron paramagnetic resonance (EPR) investigations indicates a dramatic effect of the heteroatoms on the electronic structure of (X = S, Se, P, or P=O) with consequent reordering of the energy levels.

The {Fe(super IV)(Mu-O)(Mu-caboxylato)2Fe(super III)}(super 3+) core represents an important new structural motif in the coordination chemistry of high valent non-heme diiron compounds. Through the successful calculation of the spectroscopic parameters of 4(super ox) and 5(super ox), it is claimed that the calculated structures of these species are realistic and their electronic structure is described qualitatively by the DFT methods.

Research has been conducted on the octahedral complexes with (cis-cyclam)iron(III) moiety and O,N-coordinated o-iminosemiquinonate(1-) pi radical anion. The synthesis of these complexes and their characterization via the use of X-ray crystallography are described.

Research has been conducted on the diamagnetic blue-green palladium and platinum neutral complexes. The preparation and characterization of these complexes have been carried out and the details are reported.

Results from X-ray crystallography coupled with spectroscopy unambiguously assign the oxidation level of the ligands and metal ion in any given octahedral complexes of o-aminophenolato and o-iminobenzosemiquinonato complexes with transition metal ions V(V), Cr(III), Fe(III), and Co(III).

Synthesis of tetra- to nonanuclear transition metal complexes has been carried out. Results include the arrangement of redox-active photoactive components along the photosystem II pathway.

Research has been conducted on the mononuclear blue complex [Ru (super)III L] where L is a trianion. The synthesis of the complex has been carried out in the presence of air.

The pendant arm macrocycles of 1,4,7-tris(2-hydroxybenzyl)-1,4,7-triazzacyclononane from stable octahedral complexes with zinc(II) were studied. The research utilized electron pragmatic resonance, resonance Raman and UV-vis spectrocopy to determine their spectroscopic features. Results show that oxidation of coordinated phenol pendant arms occurs at significantly higher potentials and is irreversible.

The preparation of seven new bis(o-iminosemiquinonato)copper(II) complexes from differently substituted N-phenyl-2-aminophenol-based ligands are described. The copper(II) complexes containing redox-active ligands exhibit oxidase-like reactivity based on a primarily ligand-derived redox mechanism.

The strongly electron-donating ligand composed of two tert-amines and two phenolate donor groups were utilized to prepare two mononuclear [Fe.sup.III] complexes [LFe([[eta].sup.2]-N[O.sub.3]) and [LFeCl]. The results showed that the ligand could be adopt a cis and a trans conformation to oxidize [LFeCl] at moderate potentials to yield the monophenoxyl-radical complex [[LFeCl].sup.+] and the bisphenonoxyl-radical complex [[LFeCl].sup.2+].

An example of a hexacoordinated bis(o-iminobenzoquinone)copper(II) complex (complex 2) with [Cu.sup.II]-iminobenzoquinone bonds is prepared by oxidizing a square-planar bis(iminobenzosemiquinone)copper(II) compound with molecular bromine. Electrochemical measurements have shown two successive one-electron reductions of the ligand and the reactivity of the complex 2 as an oxidizing agent toward ethanol and triethylamine is examined.

A series of bis([alpha]-iminopyridine)metal complexes featuring the first-row transition ions (Cr, Mn, Fe, Co, Ni and Zn) is analyzed. The analysis has shown that these ligands are redox noninnocent and their paramagnetic [pi] radical monoanionic forms have existed in coordination complexes.

The synthesis and the coordination chemistry of a tetracopper(II)-tetraradical cuboidal core are described. The analysis reveals that the complex can also be easily be used to study the synthesis of phenoxazinone.

A combination of experimental, as well as density functional theoretical study is employed to analyze the electronic structures of the tris(dioxolene)chromium and tris(dithiolene)chromium complexes of the electron-transfer series [[Cr[(dioxolene).sub.3]].sup.z] (z = 0, 1-, 2-, 3-).

A combination of spectroelectrochemistry and EPR spectroscopy is used for examining the heterodimeric hemoprotein SoxXA, which is essential for lithographic sulfur oxidation of the aerobic bacterium Paracoccus pantotrophus. It is shown that heme 2 has participated in the catalysis and that the cysteine persulfide ligation has led to the unusually low redox potential, which might be due to deprotonation of the Arg247 residue located in the active site.

The electronic structure of [Pd.sub.2.sup.5+]-formamidinate paddlewheel compounds was studied by combination techniques such as X-ray crystallography, electrochemistry and EPR spectroscopy. It was shown that the unpaired electron is located in mainly metal-based molecular orbital and the uncommon [Pd.sub.2.sup.5+] has a Pd-Pd bond order of 1/2.

The isolation of four members of the electron-transfer series [[Fe(NO)[(L).sub.2].sop's] (z = 1+, 0, 1-, 2-) as solid materials (R = p-tolyl) is presented. The results show that the monocationic, neutral, and monoanionic species possess an [{FeNO}.sup.6] (S = 0) moiety where the redox chemistry is sulfur ligand-based.

The synthesis of [Ni([.sup.3.L.sup.ISQ])2], [Pd([.sup.3.L.sup.ISQ])2], and [Co([.sup.3.L])2], where [([.sup.3.L]).sup.R] represents the o-phenylenediimide (n = 2-), the corresponding radical (n = 1-), and the diimine (n = 0) derivative of the bulky ligand N,N'-bis(3,5-di-tert-butylphenyl)-1,2-phenylenediamine, H2[[.sup.3.L].sub.PD1] is reported. The electro- and spectroelectrochemistry of the tetrahedral complexes [Ni([.sup.3.L.sup.ISQ])2] and [Co([.sup.3.L])2] are compared with those of nearly square planar [Pd([.sup.3.L.sup.ISQ])2] and the electronic structure of tetrahedral 1 is elucidated by broken symmetry (BS) density functional theory (DFT) calculations.

Imido complexes with the tridentate Schiff base N-salicylidene-2-aminophenol (sapH2) were synthesized using Ni(NAr)2Cl2(dme) (NAr = 2,6-dimethyl phenylimido, 2,4,6-trimethylphenylimido, 2-tert-butyl-phenylimido). The intermediate Mo(NAr)(sap) (OCH3)2 formed during the synthesis of such compounds can be reacted with bidentate aromatic ligands to form complexes in which, the bidentate ligand occupies an equatorial and axial position.

Oxidative cyclodehydrogenation is an important process in the formation of the new graphene, N-1/2HSB, which results from the FeCl3-catalyzed oxidative cyclodehydrogenation of 1,2-dipyrimidyl-3,4,5,6-tetra-(4-tert-butylphenyl)benzene. The new ligand N-1/2HSB, its Ru(II) complexes and also the half-cyclized N-1/2HSB are characterized by (super 1)H, NMR, infra-red (IR), ESI-MS, and accurate aromatic ligands.

A series of new S-methyl-1-pehnyl-isothiosemicarbazones H2[L(super 2)], H2[L(super 3) is synthesized. and different ligand oxidative products of the ligands H2[L(super 5)] and H2(L(super 6)] are characterized and isolated. The density functional theoretical (DFT) and correlated ab initio calculations are also presented.

A series of isostructural dimeric manganese complexes of the type [(Me4dtne)Mn2(Mu-O)2(Mu-R)](super 2+)[X(super -)](sub 2) are prepared and characterized. The dimanganese cores of the complexes are rigidly held together by the hexadentate ligand Me4dtne (Me4dtne = 1,2-bis(4,7-dimethyl-1,4,7-triazacyclonon-1-yl)ethane).

The synthesis of the tetradentate ligand N, N' -bis(3,5-di-tert-butyl-2-hydroxyphenyl)ethylenediamine, H4[L(super 1)], and its unsaturated counterpart glyoxal-bis(2-hydroxy-3,5-di-tert-butylanil), H2[L(super 2)] is described.

A detailed experiment and theoretical study of the series [Fe (NO) (cyclam-ac)] (super 2+/+/0) is described. The findings provide strong evidence for ligand-centered reduction steps with consequences for the reactivity of the bound NO ligand.

Two series of square planar, diamagnetic, neutral complexes of nickel(II), palladium(II), and platinum(II) containing two N,N-coordinated o-diiminobenzosemiquinonate(1-) pai radical ligands are synthesized and characterized by UV-vis and (Super 1)H NMR spectroscopy. Both complexes possesses a weak M...M bond and the ligands adopt an eclipsed configuration due to weak bonding interactions via pai stacking.

A series of mononuclear, octahedral first-row transition metal ion complexes mer-[M(super II)L(super 0)-(sub 2)]PF9sub 6) containing the tridentate ligand 2,6-bis[1-(4-methoxyphenylimino)ethyl]pyridine (L-(super 0) and a divalent Mn, Fe, Co, Ni, Cu, Zn ion have been synthesized and characterized by X-ray crystallography. The ligand is noninnocent and can be reduced by one-electron (L(super 1))(super 1-).

The modification of the macrocyclic ligand cyclam-acetate (I) is described, in which three N-methyl groups are introduced, namely, Me3cyclam-acetate (II), are presented. The results show that due to N-methylation of the ligand II, the resulting iron(II) complex (1red) is stabilized and is high spin, its iron(III) analogue (1) is high spin at room temperature, but a significant amount of the compound is low spin at lower temperatures and the iron(IV) species is stable at -25 degree C for at least few hours.

The synthesis of phenylthiyl radical complexes of Gallium(III), iron(III) and cobalt(III) is described and they are compared with their phenoxyl analogues.

Methods to establish physical oxidation states in transition-metal complexes containing radical ligands are discussed.

The reaction of [M(tren)Cl[sub2]]Cl(M=Co(III), Cr(III)) with benzene-1,2-dithiol, H[sub2](dbt), and 3,6-bis(trimethylsilyl)benzene-1,2-dithiol, H[sub2](tmsdt), in a water/methanol mixture in the presence of potassium tert-butoxide produced green crystals of [M(tren)(bdt)](PF[sub6])[sub½](Cl)[sub½]∙H[sub2]O (1(PF[sub6])[sub½](Cl)[sub½]∙H[sub2]O, M = Co; 2(PF[sub6])[sub½]](Cl)[sub½]∙H[sub2]O, M = Cr) and [M(tren)(tmsdt)](PF[sub6])[sub½](CI)[sub½]∙H[sub2]O (1a(PF[sub6])[sub½](Cl)[sub½]∙H[sub2]O, M = Co; 2a(PF[sub6])[sub½](Cl)[sub½]∙H[sub2]O, M = Cr), respectively, upon addition of KPH[sub6]. The structures of 1(PF[sub6])[sub½](CI)[sub½]∙H[sub2]O and 2(PF[sub6])[sub½](CI)[sub½]∙H[sub2]O have been determined by X-ray crystallography. Octahedral 1 and 1a are diamagnetic whereas 2 and 2a possess an S=¾ ground state. Cyclic voltammetry of 1a and 2a in CH[sub2]Cl[sub2] solution established that both species undergo a reversible one-electron oxidation generating the stable dications [Co[supII](tren)(tmsdt[sup∙])][sup2+] (S=½) and [Cr[supIII](tren)(tmsdt[sup∙])][sup2+] (S=1) where (tmsdt[sup∙])[sup1-] represents the π radical monoanion of oxidized (tmsdt)[sup2-]. The electrochemical oxidations are ligand centered processes. These dictations have been investigated by UV-vis and EPR spectroscopy an d density functional calculations using the B3LYP functional. The S,S'-coordinated benzene-1,2-dithiolate(1-) radical has been identified and ambiguously characterized. Comparison with the corresponding o-benzosemiquinonate(1-) complexes shows that the S,S'-coordinated benzene-1,2-dithiolate(1-) radical is a sulfur centered radical whereas its oxygen containing analogue carries ∼65% of the spin density on the six-membered ring. [ABSTRACT FROM AUTHOR]

From the reaction mixture of 3,6-di-tert-butylcatechol, H2[3,6Lcat], [CrCI3(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 CH2CI2 yielded microcrystals of [Co(Cp)2)[CrIII(3,6L·sq)2(3,6Lcat)] (S = 1/2) (2) where (3,6L·sq)1- is the π-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 corresponding tris(benzo-1,2-dithiolato)chromium complex [N(n-Bu)4][CrIII(3,5L·s,s)2(3,5LS,S)] (S = 1/2) (3) has also been isolated; (3,5LS,S)2- represents the closed-shell dianion 3,5-di-tert-butylbenzene-1,2-dithiolate(2-), and (3,5L·S,S)1- is its monoanionic < radical. Complex 3 is a member of the electron-transfer series [Cr(3,5LS,S)3]z (z = 0, 1-, 2-, 3-). It is shown by Cr K-edge and S K-edge X-ray absorption, UV-vis, and EPR spectroscopies, as well as X-ray crystallography, of 1 and 3 that the oxidation state of the central Cr ion in each member of both electron-transfer series remains the same (+III) and that all redox processes are ligand-based. These experimental results have been corroborated by broken symmetry density functional theoretical calculations by using the B3LYP functional. [ABSTRACT FROM AUTHOR]

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 WCI6 (acac = acetonylacetate(1-)) in methanol or CCI4 afforded the diamagnetic neutral complexes [MoV(LN,S)2(L*N,S)]0 (1), [MoV(LS,S)2(L*S,S)1 (2), and (WV(LS,S)2(L*S,S)] (3), where (L*N,S)- and (L*S,S)- represent monoanionic π-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). Complexes 1-5 have been characterized by X-ray crystallography. S K-edge X-ray absorption and infrared spectroscopy prove that a π-radical ligand (L*S,S)- is present in neutral 2 and 3, whereas the monoanions [MV(LS,S)3]- contain only closed-shell dianionic ligands. These neutral species have previously been incorrectly described as [MVI(L)3)0 complexes with a MoVI or WVI (d0) central metal ion; they are, in fact MV (d¹) (M = Mo, W) species: [MoV(LS,S)2(L*S,S)] and [WV(LS,S)2(L*S,S)] with a diamagnetic ground state St = 0, which is generated by intramolecular, antiferromagnetic coupling between the MV (d¹) central ion (SM = 1/2) and a ligand π radical (L*S,S) (Srad = 1/2). [ABSTRACT FROM AUTHOR]