N. V. Bausk

Electronic and spatial structure of spin transition iron(II) tris(4-amino-1,2,4-triazole) nitrate and perchlorate complexes

Electronic and spatial structure of polynuclear iron(II) complexes Fe(ATr)3(ClO4)2, Fe(ATr)3(NO3)2, and Fe0.34Zn0.66(ATr)3(NO3)2 (where ATr is 4-amino-1,2,4-triazole) is investigated using EXAFS and XANES spectroscopy and X-ray fluorescent spectroscopy. Changes in the distances to the first four coordination spheres of Fe and Zn atoms upon spin transitions induced by variations of the anion or temperature are analyzed. It is shown that in polynuclear complexes the spin transition (from S=2 to S=0) is accompanied by pronounced variations in the electronic and spatial structure. A mutual effect of Fe and Zn atoms was found which alters the local environment of the low-spin Fe atoms in a magnetically diluted complex as compared to the initial one.

EXAFS study of spin transition effect on the spatial and electronic structure of Fe(II) complexes with triazoles

EXAFS spectroscopy is used to investigate the characteristic features of the spatial and electronic structure of the polynuclear Fe(II) complexes Fe(ATR)3A2 (where A is the NO3−, BF4−, Br−, or ClO4− anion and ATR is 4-amino-1,2,4-triazole) and their magnetically diluted phases FexZn1−x(ATR)3(NO3)2. The absolute distances from Fe and Zn to the surrounding atoms are determined at temperatures higher and lower than the spin transition point. In all complexes, the spin transition is accompanied by significant changes in the local environment of Fe atoms, while in the magnetically diluted phases the surrounding of zinc remains unchanged. It is shown that addition of Zn atoms distorts the triazole rings in the low-spin state of the complexes. No localized anions were revealed within 3.3 Å from the Fe and Zn atoms. It is shown that a decrease in the spin transition temperature correlates with an increase in Fe−N distances in the low-spin complexes due to magnetic dilution and substitution of anions in the series NO3−, BF4−, Br−, ClO4− of ATR-containing complexes.

Relation between electronic and spatial structure and spin-transition parameters in chain-like Fe(II) compounds

Abstract EXAFS spectroscopy is used to investigate the characteristic features of the spatial and electronic structure of the polynuclear iron(II) complexes with 1,2,4-triazoles and various anions. The spin transition has been found to be accompanied by drastic changes in spatial structure. The increase in spin transition temperature for the complexes with variable anions ClO4−, I−, Br−, BF4−, NO3− was found to correlate with changes in the FeN distances and changes in bond covalence determined from the chemical shifts in Mossbauer spectra.

Structure of palladium chloride complexes with organic sulfides in solutions

EXAFS spectroscopy was used to study the influence of various factors on the structure of PdCl2 complexes with organic sulfides in organic solvents. Absolute interatomic distances in the first coordination sphere of Pd were determined for the complexes [PdCl2·2(C6H13)2S] (I), [PdCl2·(C6H13)2S]2 (II), [PdCl2·2(C6H5)2S] (III), and [PdCl2·(C4H9)S(C4H7)] (IV) and for their solutions in some organic solvents. Our hypothesis that aromatic solvent molecules are coordinated to palladium atoms through weak π-bonds, which was proposed for complex (I) in benzene, is supported fror benzene and pseudocumene solutions of complexes (I), (II), and (III). It is shown that the characteristic features of the specific solvation of the complexes under study are determined by the electron properties and spatial structures of the molecules as well as by the donating abilities of the solvents.

Influence of the electronic and spatial structure parameters on the spin-transition temperature in unusual chain iron(II) complexes

Abstract Using EXAFS, XANES and X-ray fluorescence spectroscopy it has been established that the sharp spin crossover in a series of polynuclear complexes of iron(II) with triazole and aminotriazole is accompanied by considerable changes in the spatial and electronic structure. The effect of electronic and structural parameters on the spin crossover temperature in compounds of iron(II) with aminotriazoles upon change of anion and upon magnetic dilution with zinc is discussed.

X-Ray Investigation of the Structure of Metal Chelate Dithiocarbamate Complexes in Solution

The spatial and electronic structure of some transition metal chelate complexes was studied in solution by EXAFS and XANES spectroscopy using synchrotron radiation. Structural data were obtained for the Co(III), Ni(II), Cu(II), Zn(II), and Cd(II) metal complexes with dithiocarbamate ligands. The electronic structure of the complexes in various solvents is discussed.

Geometry and orientation of molecules in a graphite fluoride matrix

Polarization dependences of the EXAFS and XANES spectra of graphite fluoride intercalation compounds C2Fx·yA (x ≈ 1, A=Br2, Fe(AA)3, FeCl3, SnCl4; AA=acetylacetonate) synthesized by diffusion from solution were measured. The measurements were carried out in the FeK-, BrK-, and SnK-edge of absorption spectral regions using synchrotron radiation of the VEPP-3 storage ring (Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences). The polarization dependences of effective coordination numbers and edge σ-resonance intensity are analyzed, and parameters of the local surroundings of atoms (coordination numbers, interatomic distances, Debye-Waller factors σ2) are determined. For the Br2 intercalates, the orientation angle with respect to the matrix layers is 64±1.5°, and the interatomic distances are close to those in the gas phase. The FeCl3 molecule forms dimers in the matrix as it does in the gas phase, and the iron atoms have tetrahedral surroundings. For the Fe(AA)3 molecules intercalated into the matrix, the iron atoms have significantly distorted octahedral environments. For the SnCl4 intercalates, the lowering of temperature does not cause additional coordination of Sn atoms, and structural disorder of SnCl4 makes the major contribution to σ2.

Determining the orientations of BrF3 and FeBr3 molecules in graphite fluoride matrices using the XANES and EXAFS polarization dependences

Synchrotron radiation was used to measure the EXAFS and XANES polarization dependences for intercalation compounds of graphite fluoride. An approach is developed which allows one to analyze the orientation of molecules of arbitrary shapes using XANES and EXAFS data. Analyzing the orientation dependences of BrK XANES spectra for the T-shaped BrF3 molecules, we determined possible combinations and admissible ranges of angles between the normal to the graphite fluoride matrix planes and the Br−F bond directions (α=52–90°, β=27–82°) and between the normal to the matrix planes and the molecular planes (γ=27–53°). The average orientation angles obtained by the combined analysis of the EXAFS and XANES data are as follows: α=62±1.5°, β=58±1.5°, γ=45±1.5°. The interatomic distances Br−F, Br−Br, and Fe−Br are determined. It is established that thermal treatment, which recovers the X-ray diffraction pattern from the unfilled matrix, does not affect the predominant orientation of the BrF3 molecules. This suggests that the thermally treated graphite fluoride matrix contains thin layers of ordered molecules. The absence of the polarization dependence of the spectra of FeBr3 in graphite fluoride allows the assumption that the molecular planes are oriented with respect to the normal to the matrix planes at a “magic” angle of 35°.

Spatial structure of transition metal complexes in solution determined by EXAFS spectroscopy

Abstract CdK EXAFS, ZnK and CuK EXAFS and XANES spectra were measured for solutions of cadmium, zinc and copper dialkyldithiocarbamates in organic solvents with varying donating abilities: tributylphosphine, methylene chloride, benzene, dibutylsulfide, pyridine, dimethylsulfoxide and for some model compounds. The parameters of the local surroundings of the Cd, Zn and Cu atoms for complex forms in solutions were determined using EXAFS spectroscopy. Spatial structure models of the complex forms in a metal chelate – nonaqueous solvent system are suggested.

Microscopic Parameters of Heterostructures with Ge Nanoclusters and Thin Films in a Si Matrix

Microstructural parameters (interatomic distances, coordination numbers, and their anisotropy) of heterostructures with Ge nanoclusters and thin films were determined by EXAFS spectroscopy. The variation of these parameters is correlated to the morphology of the germanium quantum points on Si(001), and adequate structural models are suggested. It is found that the pseudomorphic four-monolayer germanium films buried in a Si matrix contain up to 50% Si atoms. The pyramidal germanium islands (lateral size ∼15 nm, height ∼1.5 nm) formed during further Stranski–Krastanov heteroepitaxial growth have a thinner Ge–Si intermediate boundary layer near two monolayers and Ge–Ge interatomic distances 0.04 Å shorter than those in pure germanium in agreement with the results of bond length calculations in the framework of the valence force field (VFF) model.