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Electronic Perturbation in a Molecular Nanowire of [IrCl 5 (NO)] − Units
Author(s) -
Di Salvo Florencia,
Escola Natalia,
Scherlis Damián A.,
Estrin Darío A.,
Bondía Carlos,
Murgida Daniel,
RamalloLópez José M.,
Requejo Félix G.,
Shimon Linda,
Doctorovich Fabio
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200601761
Subject(s) - iridium , chemistry , electronic structure , electrophile , moiety , acceptor , open shell , singlet state , crystallography , counterion , ground state , ion , computational chemistry , stereochemistry , atomic physics , catalysis , excited state , physics , biochemistry , organic chemistry , condensed matter physics
The nitrosyl in [IrCl 5 (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. PPh 4 [IrCl 5 (NO)] forms a crystal in which the [IrCl 5 (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 2.8 Å. For the same complex [IrCl 5 (NO)] − but with a different counterion, Na[IrCl 5 (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 PPh 4 [IrCl 5 (NO)] an unprecedented electronic perturbation takes place, probably due to NO . –Cl − acceptor–donor interactions among a large number of [IrCl 5 (NO)] − units, favoring a different electronic distribution, namely the open‐shell electronic structure Ir IV NO . . This conclusion is based on XANES experimental evidence, which demonstrates that the formal oxidation state for iridium in PPh 4 [IrCl 5 (NO)] is +4, as compared with +3 in K[IrCl 5 (NO)]. In agreement, solid‐state DFT calculations show that the ground state for [IrCl 5 (NO)] − in the PPh 4 + 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 PPh 4 [IrCl 5 (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 π–π stacking interactions among the phenyl rings in PPh 4 + . Experimental and theoretical data indicate that in PPh 4 [IrCl 5 (NO)] the IrNO moiety is partially bent and tilted.