IFLP   13074
INSTITUTO DE FISICA LA PLATA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Linear vs. Tilted / Bent Nitrosyl Paradox: a NEXAFS and XANES study to determine the nature of Spin Isomers.
Autor/es:
F. DI SALVO; J.M. RAMALLO-LÓPEZ; F. G. REQUEJO; F. DOCTOROVICH
Lugar:
Campinas, Brasil
Reunión:
Workshop; 18ª Reunião Anual de Usuários (RAU).; 2008
Institución organizadora:
Laboratorio Nacional de Luz Síncrotron
Resumen:
A linear vs. tilted/bent metal-nitrosyl isomerism is observed for pentachloronitrosyliridate(III) ([IrCl5(NO)]–) by EXAFS. While its Na+ and K+ salts comprise octahedral anions with linear Ir–NO moieties, the crystal structure of PPh4[IrCl5(NO)] shows a nitrosyl with an off-axis tilting. A multiple scattering EXAFS fitting was used to determine the alignement of the Ir-N-O atoms. The pentachloronitrosyliridate(III) anions are spatially distributed in a curious arrangement in which one is over the other forming an infinite “cable”, with a short distance between the N-O moiety of one anion and the trans-chloride of the nearby upper one. In addition XANES data shows that the oxidation state for PPh4[IrCl5(NO)] is notably higher than that for K[Ir(III)Cl5(NO)]. This results as well as DFT calculations suggest an unprecedented spin isomerism for this third row transition metal complex, IrIII–NO+ ↔ IrIV–NO●, in contrast to the Na+ and K+ salts. The spin isomerism could be seen as an electron promotion from a metal-chloride orbital to a metal-NO one due to the small HOMO-LUMO gap in PPh4[IrCl5(NO)]. This is probably induced by electrostatic interactions acting as a result of the closeness and “cable-like” spatial arrangement of the Ir metal centers, imposed by lattice forces due to π–π stacking interactions among the phenyl rings.
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