Electronic Perturbation in a Molecular Nanowire of [IrCl5(NO)]– Units

FLORENCIA DI SALVO, NATALIA ESCOLA, DAMIÁN A. SCHERLIS, DARÍO A. ESTRIN, CARLOS BONDÍA, DANIEL MURGIDA, JOSÉ M. RAMALLO–LÓPEZ, FÉLIX G. REQUEJO, LINDA SHIMON, AND FABIO DOCTOROVICH

CHEMISTRY-A EUROPEAN JOURNAL

Wiley InterScience

Lugar: Weinheim; 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 NO moiety of one anion and the trans chloride of the upper one nearby is only 2.83 Å. For the same complex [IrCl5(NO)]- but with a different counterion, Na[IrCl5(NO)], he 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 IrIII–NO+, as expected for any d6 third row transition metal complex. However, in PPh4[IrCl5(NO)] an unprecedented electronic perturbation takes place, probably due to NO-Cl, acceptor- donor interactions among a large number of [IrCl5(NO)]-units, favoring a different electronic distribution, namely the open-shell electronic structure IrIV - NO·. 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(NO)]. 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 pi - pi stacking interactions among the phenyl rings in PPh4+. Experimental and theoretical data indicate that in PPh4[IrCl5(NO)] the IrNO moiety is partially bent and tilted.