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The interaction among topological defects can induce novel phenomena such as disclination pairs in liquid crystals and super-conducting vortex lattices. Nanoscale topological vortices with swirling ferroelectric, magnetic, and structural antiphase relationships were found in multiferroic h-YMn[O.sub.3]. Herein, we report the discovery of intriguing, but seemingly irregular configurations of a zoo of topological vortices and antivortices. These configurations can be neatly analyzed in terms of graph theory and reflect the nature of self-organized criticality in complexity phenomena. External stimuli such as chemistry-driven or electric poling can induce the condensation and eventual annihilation of topological vortex--antivortex pairs. doi/ 10.1073/pnas.1011380107

The synthesis and two-step spin crossover behavior of Fe[(bpp).sub.2]][Pt[(ox).sub.2]].[H.sub.2]O where bpp is 2,6-bis(pyrazol-3-yl)-pyridine and ox is oxalate, is described. The complex and unique transitional behavioral changes over many cycles are discussed.

The metal-to-ligand charge transfer (MLCT) and ligand-to-metal CT (LMCT) excited states are used to study the ultrafast dynamics of Fe[(acetylacetonate).sub.3] and monitor the transient behavior of the system by infrared (IR) spectroscopy. The observation has showed that both excitation wavelengths have led to efficient bleach of the ground state molecule on a time scale limited by instrumental response time.

The N-N bond of dinitrogen at the FeMo cofactor is studied on the basis of density functional calculations. The strongly exothermic cleavage of the dinitrogen bond occurs, while a single nitrogen atom bridges the Fe atoms.

Polarized optical microscopy, differential scanning calorimetry and powder X-ray analysis are used to characterize the physical properties and synthesize the iron(II) compounds. It is found that the iron(II) compounds can undergo spin-crossover and photoinduced spin transition as well as have liquid-crystal properties all in a single molecule.

X-ray emission spectra of [Fe.sup.III], [Fe.sup.II] and [Co.sup.II] spin-crossover compounds in their high-spin and low-spin forms are described. It is shown that all X-ray emission features are sensitive to the spin state and they reveal the details of the redistribution of electrons on the three-dimensional levels associated with the spin-state change revealing features at the X-ray absorption preedge.

Density functional methods (DFT) are used to investigate Fe(III) hydrolysis in aqueous solution and the solvation energy is estimated by using the united atoms Hartree-Fock/polarizable continuum (UAHF-PCM) model. The stepwise hydrolysis equilibrium constants are estimated and compared with the available experimental values.

The migration of H atoms over S and Fe atoms in the reaction domain of FeMo-co, the active site of nitrogenase is described and used to explain mechanistic data on the catalyzed reductions of [N.sub.2] and [C.sub.2][H.sub.2]. The positions of H atoms influence the binding of substrates [N.sub.2] and [C.sub.2][H.sub.2] and the bound substrate blocks further migration of H atoms past the binding site.

An attempt is made to study the function of the histidine that ligates the distal [4Fe4S] cluster in Df NiFe hydrogenase (H184), and so, it was exchanged for a cysteine or a glycine. The results suggest that the short distance between FeS clusters in biological redox chains might not always be sufficient to allow rapid intramolecular electron transfer (ET).

A organically templated material based on the Fe(super III) cations and the (HPO3)(super 2-) phosphite oxoanions is prepared under solvothermal conditions in the form of single crystals and the crystal structure shows the existence of triangular spin ladder chains, without M-O,F-M covalent bonding. The J-exchange parameter for the (C2N2H10)[M(HPO3)F3] compounds, M(super III) = Fe, Cr, and V, are also calculated by fitting the experimental magnetic data.

The exchange bias of CoFe/CrPt films is greatly enhanced through interfacial Mn addition while its high stability is sustained. A system with extra large exchange bias along with superior stability are demonstrated.

Metastable FeB(sub 49) phase evolved during nonequilibrium laser surface engineering was investigated with FeB, Fe(sub 2)B and Fe(sub 3)B phases. Theoretical X-ray diffraction showed that metastable FeB(sub 49) was crystalline in nature while high resolution transmission electron microscopy (HRTEM) showed smooth interface transition between Fe(sub 3)B and FeB(sub 49) dictating the integrity between the two metastable phases.

A detailed structural, electronic and magnetic characterization of nanoparticles composed of iron and carbon was performed by various methods. The atomic arrangement in the as-prepared particles was strongly affected and stabilized by excess carbon.

A planar structure of an anion cluster I(super -).(H(sub 2)O)(sub 6) in a 3D supramolecular complex [Ru(bpy)(sub 3)](sub 2)[I.(H(sub 2)O)(sub 6)Fe(CN)(sub 6).H(sub 2)O] was determined by single crystal X-ray analysis. In the supramolecule, the anion cluster I(super -).(H(sub 2)O)(sub 6), together with the anion [Fe(CN)(sub 6).H(sub 2)O](super 2-) acts as a 3D crystal host, and the [Ru(bpy)(sub 3)](super 2+) cations, as the guest molecule, occupy the vacancies of the 3D host framework.

Kinetics of the reaction of chromium(VI) with tris(1,10-phenanthroline)iron(II) ions in acidic solutions were studied. It was found that the rate of the reaction is directly proportional to [Fe(phen)(sub 3)(super 2+)] in a triflic acid-lithium triflate medium whereas a faster and nonlinear dependence was seen in perchloric acid-lithium perchlorate solutions.

Three new iron(III) complexes with the ligand N,N'-bis(2-hydroxybenzyl)-N-N'-bis(pyridine-2-ylmethyl)ethylenediamine, H9sub 2)bbpen, containing electron-donating and withdrawing groups (me, Br, NO(sub 2) in the 5-position of phenol rings were synthesized and characterized. The redox potentials Fe(super III)/Fe(super II) and the energies of the charge transfer process of these complexes were found to be linearly correlated with the Hammett parameter.

The use of dinuclear cyano-bridged Co(super III)-Fe(super II) complexes as precursors for mixed-valence compounds of higher nuclearity is demonstrated. The complexes show optical and electrochemical characteristics that correspond to the existence of two equivalent and fully independent cyanide-bridged {Co(super III)-NC-Fe(super II)} mixed-valence units.

Density functional theory calculations represent a complementary approach for investigating the electronic and spectroscopic properties of the active-site metal center. The results provide insight on how the unusual low-spin preference and spectroscopic properties of the Fe(III) center depend on the posttranslationally oxidized cysteine residues and deprotonated backbone amides that constitute the ligand field of the metal.

An glassy states is observed from the dc and ac susceptibility measurements in LaMn(sub 0.5)Fe(sub 0.5)O3. The large field-cooled effect and frequency-dependent results indicate a glassy state between T(sub g) and T(sub p') while the relaxation dynamics does not show cooperative relaxation without aging, suggesting the existence of noninteracting clusters of frozen spin.

The di-mixed-valence complex [{(eta(super 5)-C5H5)Fe(eta(super 5)-C5H4)}4(eta(super 4)-C(super 4))Co(eta(super 5)-C5H5)](super 2+), 1(super 2+) is evaluated as a molecular four-dot cell for the quantum cellular automata paradigm for electronic devices. In the solid state 1(super 2+) is a valence-trapped Robin and Day class II compound on the 10(super -12)s infrared time-scale, the fastest technique used, while an unambiguous evidence for two Fe(super II) and two Fe(super III) sites is observed.

A study of the stability of amorphous FeSi2 and their transition to a crystalline phase as a function of deposition or annealing temperature is presented. Stoichiometric FeSi2 films were deposited on Si substrates by co-sputtering of Fe and Si.

The most common contaminants in silicon, its coexisting defect configurations, interstitial iron (FE(sub i)) and iron-boron pairs (FeB) are investigated on an intentionally iron-contaminated silicon sample by means of temperature-dependent lifetime spectroscopy (TDLS) and injection-dependent lifetime spectroscopy (IDLS). As the most sensitive technique to detect and determine an iron contamination in silicon heavily relies on the Fe(sub i) and Fe(sub B) defect parameters, the spectroscopic results are of special practical importance.

The pressure dependence of the geometry and tao-point phonons of FeS2 pyrite up to 150 GPa using the plane-wave density functional calculations was investigated. The Raman-active modes were excellent agreement with the experimental data available up to 50 GPa, and predicted the evolution with the pressure of the infrared-active modes for which no high-pressure spectroscopic data were reported.

The thermal stability and the atomic ordering of single-crystal Heusler alloy Co2FeSi layers grown by molecular beam epitaxy (MBE) on GaAs(001) are studied. It was seen that the Co2FeSi layers have a long-range atomic order and crystallize in a partly disordered L2(sub 1) structure in the low growth temperature (T(sub G)) regime.

Electronic structures of [Fe2S2(SCH3)4](super 2-, 3-) in DMSO solution are calculated using reference interaction site model complete active space self-consistent field (RISM-CASSCF)/multireference second-order Moller-Plesset perturbation theory (MRMP) method. The effect of solvent environment and its fluctuation is crucial in describing the redox processes of Fe2S2 clusters.

The syntheses, structures, and physical properties of intramolecular donor/acceptor systems containing naphthalene donors and antiferromagnetically coupled diiron(III) cores as acceptors are described. It is found that photoexcitation of the naphthalene chromophore resulted in intramolecular electronic energy transfer to the Fe(super III)(sub 2) core from both the lowest-lying singlet and triplet excited states of naphthalene.

Density functional theory (DFT) based theoretical calculations are performed to identify the ground-state geometries, the spin multiplicities, and the relevant energetics of neutral and positively charged Fe-corannulene complexes. Calculations reveal that the on-top site of the six-membered ring of corannulene molecule is the most preferred binding site for both Fe atom and Fe(super +) ion.

Forty states of the diatomic iron carbide cation FeC(super +) are studied by multireference methods coupled with relatively large basis sets. The ground state is of (super2)delta symmetry, with the first excited state [a(super 4)sigma(super -)] lying 18 kcal/mol higher.

Absorption, photoluminescence, and time-resolved photoluminescence spectroscopies are used to study the properties of polycrystalline ZnSe diffusion doped with Fe or Co or codoped with both Fe and Co. Energy transfer between Co(super 2+) and Fe(super 2+) ions gives rise to modified behaviors of optical transitions near 3 mum.

The characteristic association time constant describing the formation of iron-acceptor pairs in crystalline silicon is measured for samples of various p-type dopant concentrations and species near room temperature. The results reveal that the dopant species has no impact on the pairing kinetics, suggesting that the pairing process is entirely limited by iron diffusion.

The measured Fe vibrational density of states in deoxy-myoglobin, obtained from nuclear resonance vibrational spectroscopy is compared to results from a normal-mode analysis using an all-atom empirical potential. A Green function technique is developed to calculate the iron vibrational spectrum of deoxymyoglobin by coupling the independently calculated heme and globin normal modes, nonbonded interactions between the heme molecule and the protein are essential for a good fit to the measurements.

The synthesis and X-ray structure of the-low coordinate, high-spin Fe(I) compound LFe(HCCPh) (L=HC(C[(super t)Bu]N-[2,6-diisopropylphenyl])2)](super -) are reported. Low temperature Mossbauer and electron paramagnetic resonance (ERP) spectroscopies reveal that the electronic ground state is a Kramers doublet with uniaxial magnetic properties that is well isolated from the excited states.

The operation of the solid-state Pd/Fe/GaAs spin detector throughout a wide energy band, ranging from a few eV up to a few keV, is analyzed on the basis of the available experimental data. Keys for the practical development of spin filters in the keV range is provided from the proposed spin-dependent transport scheme.

Density functional theory calculation was carried out for hydrogen adsorption on the (001), (110), and (100) surfaces of Fe(sub 5)C(sub 2) and found that the most stable hydrogen species is C(sub S)H at 1/3 and 2/3 monolayer (ML) on (001). On the metallic Fe(Sub 5)C(sub 2)(100) surface which lacks surface carbon atoms on the surface monolayer, dissociated hydrogen is found at 1/2 ML, while both dissociated hydrogen and activated H(sub 2) are found at 1 ML.

The structural properties of beta- and alpha-FeSi(sub 2) were examined by high-pressure x-ray diffraction at room temperature. The experimental values of B(sub 0) are compared with the values estimated by various first-principles calculations, where the characteristics tendency is shown.

A FePt nanoparticle assembly on MgO(110) with a new type of self-organized groove structure is fabricated. The magnetic properties of the FePt nanoparticle assembly well reflected such c-axis distribution, and their switching behavior almost followed the Stoner-Wohlfarth model.

Magnetic susceptibility, heat capacity, and neutron diffraction studies of Fe[C(CN)3]2 reveal the existence of two magnetic phase transitions at T(sub N,I) = 2.45 K and T(sub N,II) = 1.85 K. It was found that between 1.85 and 2.45 K, the magnetic ordering is incommensurate with a temperature-dependent propagation vector (k(sub I,x)0 0), k(sub I, x) = 0.525-0.540.

The intermediates formed during reduction of Fe2(mu-PPh2)(sub 2)(CO)(sub 6) in the presence of protons are identified by spectroelectrochemical, continuous-flow, and interrupted-flow techniques. The presence of the Fe-Fe bond for both 1H(super -)w and [Fe2(mu-PPh2)(mu-CO)(CO)(sub 6)](super -) is a key aspect of the proposed structures and this supports the deductions based on spectroscopic evidence.

The inhomogeneity of the zero field splitting (ZFS) interaction is reported. Details of the multifrequency continuous wave electron paramagnetic resonance (CW-EPR) study of Fe(III)-doped MFI zeolite is provided to establish the inhomogeneity of ZFS interaction.

(super 129)Xe-NMR is employed, with different iron loadings, in the characterization of the activation of two irons of two iron silicates. For monitoring the state of iron species, (super 129)Xe-NMR can be considered as an excellent tool.

The investigation revealed the results of wave length-dependent mass-selected ion signals which where the outcome by supersonic-cooled ferrocene irradicated with nanosecond laser pulses in the region of the 3d(sub z)(super 2)->R4p(sub x,y) transition (40 000-42 000 cm(super -1)). The report stated that Rydberg transition 'works' in both processes of multiphoton dissociation and ionization of ferrocene.

Electroabsorption (Stark) spectroscopy is used to study the dye sensitized interfacial electron transfer in Fe(super II)(CN)(sub 6)(super 4-) donor complex bound to a TiO2 nanoparticle. The average charge-transfer distance determined from the Stark spectra is 5.3 angstrom.

The study conducted shows that air oxidation of ferrous complexes containing aminothiophenolato ligands yields ferric species with N,S-coordinated o-iminothionebenzosemiquinonate(1-) pi radical ligands. The techniques used in this study include, crystallography, electron paramagnetic resonance, UV-vis and Mossabauer spectroscopies.

The three catalysts for the electroreduction of oxygen are prepared by pyrolyzing between 400 and 1000 degree Celsius two iron precursors, Fe acetate or Fe porphyrin, adsorbed on a synthetic carbon made from the pyrolysis of PTCDA (perylene tetracarboxylic dianhydride).

The structural analysis of low-energy ion scattering spectroscopy shows that Cu-phthalocyanine (CuPc) molecules adsorb on the Fe (100) surface with their planes parallel to the surface when the film thickness is one monolayer. The adsorption of oxygen on Fe prior to the CuPc deposition is found to induce a remarkable difference in the polarization of the CuPc orbitals.

A study is conducted on the corrosive nature of iron-zinc alloys which are electroplated on mild steel, in aerated and deaerated quadrupuly distilled water using valence band x-ray photoelectron spectroscopy. Results indicate that the 17% iron alloy forms a protective zinc oxide surface.

The structure of iron pentacarbonyl, Fe(CO)(sub 5) is reinvestigated by gas-phase electron diffraction using an experimental rotational constant as a constraint on the structural parameters. The results confirm that the equatorial Fe-C bonds are longer than the axial ones, an important difference with the structure in the crystal where the equatorial Fe-C bonds are the shorter.

Room-temperature thermal rate constants for quenching and energy transfer are determined for the individual fine-structure levels of z(super 5)D(sub j)(super o) term of the FE atom in collisions with He, Ar, and several molecular gases (N2, O2, H2 and CH4). The results reveal that the intramultiplet rate constants for He summed over all final fine-structure levels roughly equaled the total removal rate constants, while they were ~10% of the total removal constants for O2.

Exchange coupling is studied in NiO/CoFe(sub 2) and CoFe(sub 2)O(sub 4)/CoFe(sub 2) systems grown by pulsed laser deposition. An exchange coupling of 0.06 and 0.05 erg/cm(super 2) is obtained for NiO/CoFe(sub 2) and CoFe(sub 2)/CoFe(sub 2)O(sub 4) systems, respectively; no coupling is observed when NiO is integrated in the top hard electrode but coupling is observed when a CoFe(sub 2)O(sub 4) layer is used.

Five-coordinate complexes of iron(III) and gallium(II) were obtained and characterized by crystallographic, electrochemical and electron paramagnetic resonance methods. The complexes showed enhanced formation of phenoxyl radicals and an improved reversibility of the ligand-centered redox processes was observed suggesting that unusual magnetic interaction between metal and radicals may take place.