Fábio Souza Nunes

Novel double alkoxides of titanium(IV) and iron(II)/(III): synthetic, structural and spectroscopic studies

The first structurally characterised titanium and iron polynuclear isopropoxides [FeCl{Ti2(OPri)9}], 1, and [Ti3(OMe)2(OPri)9][Fe4TiCl4(O)(OPri)9], 2, have been prepared from 2 : 1 : 1 mixtures of [Ti(OPri)4], K(OPri) and FeCl2. Their identity was confirmed by a number of chemical and physical methods including X-ray diffractometry. Semiempirical quantum mechanical calculations were consistent with an S = 2 ground state for 1. Structural and spectroscopic data support a mixed-valence formulation for the unique {Fe4Ti} anion in 2.

Synthesis and crystal structure of a novel tetraiminediphenolate iron(II) macrocyclic complex: A six-coordinate iron-protein model

A novel tetraiminediphenolate iron(II) macrocyclic complex [Fe(tidf)(CH3OH)2](NO3)2(1) has been prepared and characterized by microanalysis, X-ray crystallography, FTIR spectroscopy, and mass spectrometry. The crystal structure (monoclinic, space group C2/c, Z=8, a = 26.8573(6) Å, b = 10.6551(4) Å, c = 23.5371(7) Å, β = 107.450(2)°) shows that the iron(II) occupies a distorted octahedral geometry with two methanol molecules bound axially. The macrocyclic ligand is very flexible and adopts a butterfly conformation with a dihedral angle of 112°.

The synthesis of triangulo-trimetal complexes containing both iron(II) and vanadium(II)

Abstract Reactions between a variety of vanadium(II) and iron(II) starting materials in tetrahydrofuran (thf) solution afforded di-, tri-, and tetra-nuclear complexes containing thf or N,N,N′,N′-tetramethylethylenediamine (tmen) as ligands. Most products were ionic and contained the two metals in different structural units, cation or anion. Trinuclear clusters formulated as [V3−xFexCl5(tmen)3][BPh4](x=0–3) were obtained and characterised by C, H, N and metal analyses, 1H NMR, Mossbauer, and positive ion FAB and electrospray mass spectroscopies, and magnetic moment measurements in solution. We characterised fully by low-temperature single-crystal X-ray diffraction analysis the mixed-metal triangulo-complex salt [V2Fe(μ-Cl)3(μ3-Cl)2(tmen)3][BPh4].

Preparation, crystallography and spectroscopic properties of the polymeric {(1-(E)-2-pyridinylmethylidene)semicarbazone)(aqua)copper(II)} sulphate dihydrate complex: Evidence of dynamic Jahn–Teller effect

Pyridine-2-carbaldehyde semicarbazone ligand (HL) reacts with copper(II) sulphate in water solution to yield the coordination polymer [{Cu(II)(HL)(H(2)O)(SO(4))}(n)] (1). The crystals are triclinic with space group P(-1) and the metal ion is occupying a distorted octahedral geometry. EPR results show that a dynamic Jahn-Teller (J-T) effect is operative in water solutions and also support the stability of the polymeric chains as they continue to show a characteristic half-field Δm(S)=±2 transitions. UV-visible spectrum analysis allowed access to the J-T stabilization energy of 5995 cm(-1) in water. Thermogravimetric/differential thermal analysis curves showed a step-by-step decomposition of complex 1 with loss of water, release of SO(3) and oxidation of the semicarbazone ligand in the 30-422°C range.

ISOTHIOCYANATE COPPER(II) TETRAAZA-IMINOOXIME MACROCYCLIC COMPLEX: AN EXAMPLE OF LINKAGE ISOMERISM. PART I — SYNTHESIS, INFRARED SPECTROSCOPY AND CRYSTAL STRUCTURE

Abstract The isothiocyanate complex [Cu(DOHPN)(NCS)] (DOHPN = 3, 3′-trimethylenedinitrilobis-(2-butanone oxime)) has been prepared and characterized by infrared spectroscopy and X-ray crystallography as the isomer of the thiocyanate complex whose crystal structure is found in the literature. The formula unit of the title compound, is [Cu(DOHPN)(NCS)]2[Cu(DOHPN)-(H2O)](ClO4) corresponding to C35H59ClCu3N14O11S2- The crystal is triclinic, space group P-1, Z = 2, and has the following lattice constants: a = 7.460(l) A, b = 11.541(2)A, c = 29.149(6)A, a = 97.44(3)°, β = 91.32(3)°, γ = 96.68(3)°. In each of the three complexes which compose the formula unit, the copper(II) lies in a square pyramidal environment made of an axial ligand and four nitrogen atoms of the tetraaza ligand. The stronger the interaction between copper(II) and the axial ligand, the more the DOHPN bends resulting in a “butterfly-like” geometry. Formation of the thiocyanate isomer is kineti-cally favored over the thermodynamically more sta...

A new pentanuclear cyano-bridged complex [{FeII(tetraazamacrocycle)}3{μ-NC-FeIII(CN)5}2]: Synthesis, spectroscopic and magnetic characterization

Hexacyanoferrate(III) reacts with [FeII(meso)(CH3CN)2](ClO4)2.2CH3CN (meso=5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) in acetonitrile/water mixture producing the title complex, where three [Fe(meso)]2+ units are connected by two [Fe(CN)6](3-) anions. Molecular modeling (MM+) shows a fairly linear molecule and Mössbauer data are consistent with two terminal pentacoordinated low spin iron(II)-meso units linked to one hexacoordinated low spin iron(II)-meso through two hexacoordinated low spin iron(III) units. Spectroscopic characterization showed a typical mixed-valence charge transfer band and the degree of electron coupling was calculated to be H(AB)=678 cm(-1). Magnetic properties exhibited an antiferromagnetic exchange interaction between the iron(III) ions with a coupling constant J= -44 cm(-1).

Fixação de nitrogênio: estrutura, função e modelagem bioinorgânica das nitrogenases

Biological nitrogen fixation, catalyzed by nitrogenases, contributes about half of the nitrogen needed to global agriculture. For forty years synthetic chemists and theoreticians have tried to understand and model the structure and function of this important metalloenzyme. Ten years after the first report on the crystal structure of the MoFe protein, scientists still have not been able to synthesize a chemical equivalent of the FeMo cofactor nor the structure knowledge revealed the key to its catalytic activity. This paper with 104 references presents a review of the most relevant advances in chemical nitrogen fixation and their relation with the nitrogenases.

2-Mercaptobenzoxazole pentacyanoferrate(II/III) complexes: UV-Visible, Mössbauer, electron paramagnetic resonance, electrochemistry and molecular modeling

2-Mercaptobenzoxazole pentacyanoferrate(II/III) complexes, [FeII/III(CN)5(bzoxs)]3-/2- , were prepared in MeOH/H2O 75:25% solutions and characterized by spectroscopic UV-Vis, Mossbauer, electron paramagnetic resonance (epr) and electrochemical-cyclic voltammetry- techniques. UV-Vis and epr spectra along with the electrochemical behavior suggested the coordination of the multi-functional N,S,O- donor ligand, bzoxs, to iron(III) through the sulfur atom. The crystal field parameters, DqL and Dt, calculated for the iron(II) complex, in addition to the reversible redox process FeIII-bzoxs + e- ® FeII-bzoxs also pointed to coordination via the sulfur atom. The results were compared with the chemical properties of pentacyanoferrate complexes containing other monodentate N-, S- and O-donor ligands. Ab initio calculations revealed the composition of the frontier orbitals of bzoxs and are in agreement with the mode of coordination proposed from the experimental data.

(Imidazole)(3,3′-trimethylenedinitrilo bis (2-butanone oximate)) copper(II) perchlorate: Synthesis and crystal structure of a five-coordinate copper-protein model complex

The synthesis and crystal structure of the novel pentacoordinated complex [Cu(DOHPN)(IMI-DAZOLE)] (ClO4), (DOHPN=(3,3′-trimethylenedinitrilo bis 2-butanone oxime) are reported. The X-ray crystal structure (space groupP21/n, a=11.349(2) Å,b=14.241(3) Å,c= 12.635(3) Å; α=90°, β=100.21 (3)°, γ=90°) shows that the copper(II) ion occupies a distorted square-pyramidal geometry with the imidazole ligand occupying the axial position. The copper(II)-(N)imidazole distance is 2.125(3) Å and the copper(II)-tetraaza plane distance is 0.385/Å. The tetraaza ligand DOHPN adopts a “butterfly-like” geometry with a dihedral angle of 149.69°. The title complex is the first structurally characterized compound of the series [Cu(DOHPN)(axial ligand)]n+ where the axial ligand is a neutral N-heterocycle with known biological relevance. A comparison of the structural parameters with those observed when the axial ligand is H2O or NCS− (N-bonded) gives the following series with increasing metal-ligand interaction: H2O>IMIDAZOLE>NCS− (N-bonded).

Spectroscopic, electrochemical, magnetic and structural investigations of dimanganese-(II/II) and mixed-valence-(II/III)-tetraiminodiphenolate complexes

Synthesis, spectroscopic [electron paramagnetic resonance (EPR), UV-Vis and Fourier transform infrared spectroscopy (FTIR)], magnetic and spectroeletrochemical properties of [MnII2(tidf)(OAc)(ClO4)(MeOH)] (tidf = a Robson type macrocyclic ligand obtained through condensation of 2,6-diformyl-4-methylphenol and 1,3-diaminopropane) are reported. Compound [MnII2(tidf)(OAc)(ClO4)(MeOH)] shows a weak antiferromagnetic behavior with exchange coupling constant J = -1.59(1) cm-1. UV-Vis and EPR spectroelectrochemical response after oxidation of complex [MnII2(tidf)(OAc)(ClO4)(MeOH)] detected the stabilization of mixed-valence Mn2(II/III) species in solution showing spectral features similar to the ones of the isolated mixedvalence [MnIIMnIII(tidf)Br3(H2O)2] compound. Crystallization of [MnII2(tidf)(OAc)(ClO4)(MeOH)] surprisingly produced the trimanganese complex [Mn3III/II/III(tidf)2(µ-OAc)2](ClO4)2, not observed in solution. It contains two pentacoordinated [MnIII(tidf)]+ units, each one connected to a central hexacoordinated MnII ion through one µ-phenolate and one µ-acetate bridge.