Elisa M. Baggio-Saitovitch

On the photofragmentation of Fe(CO)5. II. Molecular orbital studies of Fe(CO)n, 1≥n≥5

Self‐consistent molecular orbital calculations were performed for Fe(CO)5 and its photofragments Fe(CO)n, 1≤n<5. The discrete variational method was employed, with the Xα local approximation for the exchange interaction. In the case of Fe(CO)5, photoelectron and optical spectra are analyzed, and photochemical behavior is discussed. The Mossbauer isomer shifts and quadrupole splittings are investigated. In the case of Fe(CO)5 and Fe(CO)4, the values derived for these hyperfine interactions are compared to experimental measurements reported in a polyethylene matrix.

On the photofragmentation of Fe(CO)5. I. Infrared and Mössbauer evidence for the formation of Fe(CO)4 in polymer matrices

Pentacarbonyliron sorbed in low density polyethylene (LDPE) or polytetrafluorethylene (PTFE) and irradiated with UV light has been studied by infrared and Mossbauer spectroscopies. The main photofragment reacts with the residual pentacarbonyliron leading to the formation of Fe2(CO)9. This reaction, plus the information obtained from infrared and Mossbauer spectra, suggest that the new species could be assigned as tetracarbonyliron Fe(CO)4 and tricarbonyliron Fe(CO)3. We have proved that molecules sorbed in a polymer matrix can be used as Mossbauer absorbers at low temperature. The polymer matrix allowed the isolation of otherwise unstable species: The high permeability of LDPE to gaseous carbon monoxide precludes the reformation of pentacarbonyliron molecules, thus excluding the ‘‘cage effect’’ observed in frozen gas matrices.

Electronic and Mössbauer spectroscopy studies of iron(II) complexes with tridentate unsaturated nitrogen containing ligands

Abstract The effect of the fusion of a further N-donor coordination site to a diimine giving tridentate unsaturat- ed chelate ligands in iron(II) complexes was investigated by using electronic and 57Fe Mossbauer spectroscopy. The electronic spectra, measured at 77 °K, showed that the tridentate ligands produce with iron(II) complexes, [Fe(ligand)2]++, having characteristic spectral features connected with the structure of the complex ion. The Mossbauer spectra taken at 295 and 4.2 °K, showed a variation of the isomer shift and quadrupole splitting In the series of complexes. The spectra taken with a external magnet- ic field showed for all complexes a negative sign for the principal component of the EFG tensor (Vzz). The results are discussed the basis of a strong σ-bonding along a unique axis, considering the D2d point group symmetry.

Effect of magnetism on superconductivity in rare-earth compounds RENi2B2C

Abstract Spin-polarized first-principles density-functional electronic structure calculations were performed for 73-atoms embedded clusters representing antiferromagnetic RENi 2 B 2 C (RE = Pr, Nd, Sm, Gd, Ho, Tm). A substantial difference in the extent of the exchange polarization of the conduction electrons between early and late rare-earth compounds is revealed due to the reduced coupling between RE 4f and 5d electrons with increasing Z. This result is relevant to observed phenomena of coexistence of superconductivity and magnetism in these compounds.

Spin and magnetism of rare-earth intermetallic nickel borocarbides: RENi2B2C

Abstract The spin and magnetism in quaternary intermetalic borocarbides RENi2B2C, REPr, Nd, Sm, Gd, Ho, Tm are determined by first-principles density functional theory, using the embedded cluster formalism. Spin polarization of the lattice by the RE moments is examined in detail, and related to observed magnetic ordering phenomena. The observed superconductivity and regions of coexistence with antiferromagnetism are discussed in terms of the lattice polarization, magnitude of moments, and differences in interatomic distances.