INQUIMAE   12526
INSTITUTO DE QUIMICA, FISICA DE LOS MATERIALES, MEDIOAMBIENTE Y ENERGIA
Unidad Ejecutora - UE
artículos
Título:
Redox Properties of Ruthenium Nitrosyl Porphyrin Complexes with Different Axial Ligation: Structural, Spectroelectrochemical (IR, UV-VIS, EPR) and Theoretical Studies
Autor/es:
PRITI SINGH, ATANU KUMAR DAS, BIPRAQJIT SARKAR, MARK NIEMEYER, FEDERICO RONCAROLI, JOSÉ A. OLABE, JAN FIEDLER, STANISLAV ZALIS AND WOLFGANG KAIM
Revista:
INORGANIC CHEMISTRY
Editorial:
ACS
Referencias:
Lugar: Washington; Año: 2008 vol. 47 p. 7106 - 7106
ISSN:
0020-1669
Resumen:
Abstract. Experimental and computational results for different ruthenium nitrosyl porphyrin complexes [(Por)Ru(NO)(X)]n+, Por2- = tetraphenylporphyrin dianion (TPP2-) or octaethylporphyrin dianion (OEP2-),  X = H2O (n = 2, 1) or X = pyridine, 4-cyanopyridine or 4-N,N-dimethylaminopyridine (n = 1, 0), are reported with respect to their electron transfer behaviour. The structure of [(TPP)Ru(NO)(H2O)]BF4 is established as an {MNO}6 species with almost linear RuNO arrangement at 178.1(3)o. The compounds [(Por)Ru(NO)(H2O)]BF4 undergo two reversible one-electron oxidation processes. Spectroelectrochemical measurements (IR, UV-VIS-NIR and EPR) indicate that the first oxidation occurs on the porphyrin ring, as evident from the appearance of diagnostic porphyrin radical anion vibrational bands (1530 cm-1 for OEP·- and 1290 cm-1 for TPP·-), from the small shift of ~ 20 cm-1 for íNO, and from the EPR signal at giso ~ 2.00. The second oxidation as found electrochemically reversible for the OEP compound shows a 55 cm-1 shift of íNO, suggesting a metal-centered process. The compounds [(Por)Ru(NO)(X)]BF4, X = pyridines, undergo a reversible one-electron reduction, the site of which was determined by spectroelectrochemical studies as NO-centered with a ca. -300 cm-1 shift of íNO. The EPR response of the NO· complexes was essentially unaffected by the variation of the substituted pyridines X. DFT calculations support the interpretation of the experimental results as the HOMO of [(TPP)Ru(NO)(X)]+, X = H2O or pyridines, was calculated to be centered at the porphyrin p system whereas the LUMO of [(TPP)Ru(NO)(X)]+ has about 50% p*(NO) character, confirming that the (first) oxidation of [(Por)Ru(NO)(H2O)]+ occurs on the porphyrin ring while the reduction of [(Por)Ru(NO)(X)]+ is largely NO centered with the metal remaining in the low-spin ruthenium (II) state throughout. The 4% pyridine contribution to the LUMO of [(TPP)Ru(NO)(py)]+ is associated with the stabilization of the reduced form as opposed to that of the aqua complex.