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

F. DI SALVO; N. ESCOLA; D.A. SCHERLIS; D.A. ESTRIN; C. BONDIA; D.H. MURGIDA; J.M. RAMALLO LOPEZ; F.G. REQUEJO; L. SHIMON; F. DOCTOROVICH

Chemistry: a european journal

Wiley-VCH Verlag

Año: 2007 vol. 13 p. 8428 - 8433

0947-6539

            The nitrosyl in [IrCl5(NO)]– is probably the mostelectrophilic known to date. This fact is reflected by theextremely high IR frequency in solid state, itselectrochemical behavior and remarkable reactivity insolution. PPh4[IrCl5(NO)] forms a crystal structure in whichthe [IrCl5(NO)]– anions are placed in a curious wire-likelinear arrangement, with a short distance between the N–Omoiety of one anion and the trans-chloride of the nearbyupper one (2.8 ). For the same complex [IrCl5(NO)]– butwith a different counterion, Na[IrCl5(NO)], the anions arestacked one over the other in a “side by side” arrangement. Inthis last case the electronic distribution can be depicted as theclosed shell electronic structure IrIII–NO+, as expected for anyd6 third row transition metal complex. However, inPPh4[IrCl5(NO)] an unprecedented electronic perturbationtakes place, probably due to NO+–Cl– acceptor-donorinteractions among a large number of [IrCl5(NO)]– units,favoring a different electronic distribution, namely the openshell electronic structure IrIV–NO . This conclusion is basedon XANES experimental evidence, which demonstrates thatthe formal oxidation state for PPh4[IrCl5(NO)] is +4 ascompared to +3 in K[IrCl5(NO)]. In agreement with theabove, solid state DFT calculations show that the groundstate for [IrCl5(NO)]– in the PPh4+ salt is comprised by anopen shell singlet with an electronic structure thatencompasses half of the spin density mainly localized on ametal-centered orbital, and the other half on an NO-basedorbital. The electronic perturbation could be seen as anelectron promotion from a metal-chloride orbital to a metal-NO one due to the small HOMO-LUMO gap inPPh4[IrCl5(NO)]. This is probably induced by electrostaticinteractions acting as a result of the closeness and wire-likespatial arrangement of the Ir metal centers, imposed by latticeforces due to – stacking interactions among the phenylrings in PPh4+. Regarding the geometry of the Ir-N-O moiety,experimental and theoretical data indicate that inPPh4[IrCl5(NO)] it shows a partially bent/tilted conformation.