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

DI SALVO, F.; ESCOLA, N.; SCHERLIS,* D. A.; ESTRIN, D. A.; BONDÍA, C.; MURGIDA, D.; RAMALLO-LÓPEZ, J. M.; REQUEJO, F. G.; SHIMON, L.; DOCTOROVICH,* F.

Chem. Eur. J.

Año: 2007 vol. 13 p. 8428 - 8436

Abstract: 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. PPh4ACHTUNGTRENUNG[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 3. For the same complex [IrCl5(NO)]
but with a different counterion, NaACHTUNGTRENUNG[IrCl5(NO)], the anions are stacked one over the other in a sideby- side arrangement. In this case the electronic distribution can be depicted as the closed-shell electronic structure IrIII
NO+, as expected for any d6 thirdrow transition metal complex. However, in PPh4ACHTUNGTRENUNG[IrCl5(NO)] an unprecedented electronic perturbation takes place, probably due to NOC–Cl
acceptor–donor interactions among a large number of [IrCl5(NO)]
units, favoring a different electronic distribution, namely the open-shell electronic structure IrIV
NOC. This conclusion is based on XANES experimental evidence, which demonstrates that the formal oxidationstate for iridium in PPh4- ACHTUNGTRENUNG[IrCl5(NO)] is +4, as compared with +3 in KACHTUNGTRENUNG[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 metalcentered 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 thesmall HOMO–LUMO gap in PPh4-ACHTUNGTRENUNG[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 p–p stacking interactions among the phenyl rings in PPh4+. Experimental and theoretical data indicate that in PPh4ACHTUNGTRENUNG[IrCl5(NO)] the Ir
N
O moiety is partially bent and tilted.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. PPh4ACHTUNGTRENUNG[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 3. For the same complex [IrCl5(NO)]
but with a different counterion, NaACHTUNGTRENUNG[IrCl5(NO)], the anions are stacked one over the other in a sideby- side arrangement. In this case the electronic distribution can be depicted as the closed-shell electronic structure IrIII
NO+, as expected for any d6 thirdrow transition metal complex. However, in PPh4ACHTUNGTRENUNG[IrCl5(NO)] an unprecedented electronic perturbation takes place, probably due to NOC–Cl
acceptor–donor interactions among a large number of [IrCl5(NO)]
units, favoring a different electronic distribution, namely the open-shell electronic structure IrIV
NOC. This conclusion is based on XANES experimental evidence, which demonstrates that the formal oxidationstate for iridium in PPh4- ACHTUNGTRENUNG[IrCl5(NO)] is +4, as compared with +3 in KACHTUNGTRENUNG[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 metalcentered 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 thesmall HOMO–LUMO gap in PPh4-ACHTUNGTRENUNG[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 p–p stacking interactions among the phenyl rings in PPh4+. Experimental and theoretical data indicate that in PPh4ACHTUNGTRENUNG[IrCl5(NO)] the Ir
N
O moiety is partially bent and tilted.