Electronic perturbation in a molecular nanowire of [IrCl5(NO)](-) units

DI SALVO F , ESCOLA N , SCHERLIS DA , ESTRIN DA, BONDIA C , MURGIDA D , RAMALLO-LOPEZ JM, REQUEJO FG , SHIMON L, DOCTOROVICH F

CHEMISTRY-A EUROPEAN JOURNAL

WILEY-V C H VERLAG GMBH

Año: 2007 vol. 13 p. 8428 - 8436

0947-6539

The nitrosyl in [IrCl5(NO)](-) is probably the most electrophilic known to date. This fact is reflected by its extremely high IR frequency in the solid state, electrochemical behavior, and remarkable reactivity in solution. PPh4[IrCl5(NO)] forms a crystal in which the [IrCl5(NO)]- anions are in a curious wire-like linear arrangement, in which the distance between the N-O moiety of one anion and the trans chloride of the upper one nearby is only 2.8 angstrom. For the same complex [IrCl5(NO)]- but with a different counterion, Na[IrCl5(NO)], the anions are stacked one over the other in a side-by-side arrangement. In this case the electronic distribution can be depicted as the closed-shell electronic structure Ir-III-NO+, as expected for any d(6) third-row transition metal complex. However, in PPh4[IrCl5(NO)] an unprecedented electronic perturbation takes place, probably due to NO center dot-Cl- acceptor-donor interactions among a large number of [IrCl5(NO)](-) units, favoring a different electronic distribution, namely the open-shell electronic structure Ir-IV-NO center dot. This conclusion is based on XANES experimental evidence, which demonstrates that the formal oxidation state for iridium in PPh4- [IrCl5(NO)] is +4, as compared with +3 in K[IrCl5(NO)]. In agreement, solid-state DFT calculations show that the ground state for [IrCl5(NO)]- in the PPh4+ salt comprises an open-shell singlet with an electronic structure which encompasses half of the spin density mainly localized on a metal-centered orbital, and the other half on an NO-based orbital. The electronic perturbation could be seen as an electron promotion from a metal-chloride to a metal-NO orbital, due to the small HOMO-LUMO gap in PPh4- [IrCl5(ANO)]. This is probably induced by electrostatic interactions acting as a result of the closeness and wire-like spatial arrangement of the Ir metal centers, imposed by lattice forces due to YE-YE stacking interactions among the phenyl rings in PPh4+. Experimental and theoretical data indicate that in PPh4[IrCl5(NO)] the Ir-N-O moiety is partially bent and tilted.