The electronic structure of a series of metallacyclopentadienyl diiron complexes, containing a chelating 4e-donor 1,4-diaza-l,3-butadiene (R-DAB) ligand in different structural arrangements, is discussed by using SCF-first-principle discrete variational (DV)-Xa calculations and gas-phase UV-photoelectron (PE), solid-state X-ray PE (XPS), and Mossbauer spectroscopies. Comparison of the obtained theoretical results with those relative to the isoelectronic unsubstituted diiron metallacyclopentadienyl complex (Fe2(CO)6(C4H4)) indicates that, even though the substitution of two terminal CO ligands with R-DAB mainly affects molecular orbitals localized on the metal atom R-DAB is bonded to, the overall bonding scheme is significantly influenced by the coordination site of R-DAB. When compared to two carbonyls, R-DAB causes a higher amount of electronic density on the metal atom to which it is directly bonded. Moreover, the involvement of n+ and n- nitrogen lone-pair combinations in the metal-nitrogen interaction is computed to be definitely stronger than in complexes where R-DAB acts as a bridging 8e donor. Remarkable differences in structural data of the investigated series are discussed and clarified on the basis of the reported theoretical results. Transition-state ionization energies reproduce very well the experimental UV-PE pattern, allowing us to be confident about the main features of the bonding scheme. Furthermore, the computed different electronic charge distributions for the two nonequivalent iron sites along the series are well in tune with both Mossbauer experimental data and binding energy values obtained by XPS.
Theoretical, UV-PES, XPS, and Moessbauer investigation of the electronic structure of dinuclear metal carbonyl diimine complexes with a metallacyclopentadienyl system
DAL COLLE, Maurizio;
1989
Abstract
The electronic structure of a series of metallacyclopentadienyl diiron complexes, containing a chelating 4e-donor 1,4-diaza-l,3-butadiene (R-DAB) ligand in different structural arrangements, is discussed by using SCF-first-principle discrete variational (DV)-Xa calculations and gas-phase UV-photoelectron (PE), solid-state X-ray PE (XPS), and Mossbauer spectroscopies. Comparison of the obtained theoretical results with those relative to the isoelectronic unsubstituted diiron metallacyclopentadienyl complex (Fe2(CO)6(C4H4)) indicates that, even though the substitution of two terminal CO ligands with R-DAB mainly affects molecular orbitals localized on the metal atom R-DAB is bonded to, the overall bonding scheme is significantly influenced by the coordination site of R-DAB. When compared to two carbonyls, R-DAB causes a higher amount of electronic density on the metal atom to which it is directly bonded. Moreover, the involvement of n+ and n- nitrogen lone-pair combinations in the metal-nitrogen interaction is computed to be definitely stronger than in complexes where R-DAB acts as a bridging 8e donor. Remarkable differences in structural data of the investigated series are discussed and clarified on the basis of the reported theoretical results. Transition-state ionization energies reproduce very well the experimental UV-PE pattern, allowing us to be confident about the main features of the bonding scheme. Furthermore, the computed different electronic charge distributions for the two nonequivalent iron sites along the series are well in tune with both Mossbauer experimental data and binding energy values obtained by XPS.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
