Establishing the NO oxidation state in complexes [Cl<sub>5</sub>(NO)M]<sup>n−</sup>, M = Ru or Ir, through experiments and DFT calculations

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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 A. 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*-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*. 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 Ir-N-O moiety is partially bent and tilted.

“…This conclusion is based on XANES experimental evidence, which demonstrates that the formal oxidation state for iridium in PPh 4 -…”

Section: (No)]mentioning

confidence: 85%

Section: A C H T U N G T R E N N U N G [Ircl 5 (No)]mentioning

confidence: 98%

Section: (No)]mentioning

confidence: 99%

Section: A C H T U N G T R E N N U N G [Ircl 5 (No)] Is + 4 As Compamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Salvo

Escola

Scherlis

et al. 2007

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Spectroelectrochemical Evidence for the Nitrosyl Redox Siblings NO⁺, NO^., and NO⁻ Coordinated to a Strongly Electron‐Accepting Fe^II Porphyrin: DFT Calculations Suggest the Presence of High‐Spin States after Reduction of the Fe^II–NO⁻ Complex

Pellegrino

Hübner

Doctorovich

et al. 2011

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Experimental and computational results for the electron-deficient porphyrin complex [Fe(NO)(TFPPBr(8))] (1; TFPPBr(8)=2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(pentafluorophenyl)porphyrin) are reported with respect to its electron-transfer behavior. Complex 1 undergoes three one-electron processes: two reversible reductions and one irreversible oxidation. Spectroelectrochemical measurements (IR and UV/Vis/NIR spectroscopy) of (14)NO- and (15)NO-containing material indicate that the first reduction to 1(-) occurs largely on the NO ligand to produce nitroxyl anion (NO(-)) character, as evident from the considerable change in ν(NO) from 1715 to around 1550 cm(-1). The second reduction to 1(2)(-) does not result in a further shift of ν(NO) to lower frequencies, but to a surprising high-energy shift to 1590 cm(-1). This and the notable changes of the characteristic porphyrin vibrations as well as significant changes of the UV/Vis absorptions indicate a porphyrin-centered process; DFT calculations predict the shift of ν(NO) to higher frequencies for the intermediate- and high-spin states of 1(2-). The oxidation of 1 is irreversible on the voltammetry timescale, but chemically reversible in spectroelectrochemical experiments, suggesting that the cationic form dissociates to the corresponding ferric porphyrin and NO. DFT calculations support the interpretation of the experimental results.

Near‐Infrared‐Absorbing Organometallic Diruthenium Complex Intermediates: Evidence for Bridging Anthrasemiquinone Formation and against Mixed Valency

Kamatchi

Mondal

Scherer

et al. 2017

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The new redox-active complexes [RuH(CO)(EPh ) (μ-Q )RuH(CO)(EPh ) ], E=P (1) and E=As (2) with the bis-chelate bridging ligand Q =1,4-dioxido-9,10-anthraquinone were prepared and characterised. The related compound [RuCl(CO)(PPh ) (μ-Q )RuCl(CO)(PPh ) ] (4) with E=P and Q =5,8-dioxido-1,4-naphthoquinone 4 revealed trans-positioned PPh groups. The electrogenerated one-electron oxidised states 1 and 2 were examined using spectroelectrochemical techniques (EPR, IR and UV/Vis/NIR). In situ EPR studies gave spectra with P or As hyperfine splitting of about 16 Gauss, small Ru coupling and small g-anisotropy in the frozen solution state. The P and As hyperfine values reflect axial positioning of the four Ru-E bonds relative to the plane of an anthrasemiquinone bridge. Single CO stretching bands around 1910 cm of the precursors 1 and 2 shift by about 25 cm to higher energies on oxidation. The direction, uniformity and the extent of the shifts confirm ligand bridge-based oxidation. Absorbance by the cations in the near infrared region is thus assigned to intra-ligand transitions of ruthenium(II)-bonded anthrasemiquinones and not to intervalence charge transfer of mixed-valent species. Ruthenium(II) stabilisation by CO and EPh is made responsible for the anthrasemiquinone formation instead of metal-centered oxidation.