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. 2022 Sep 19;61(38):e202207688.
doi: 10.1002/anie.202207688. Epub 2022 Aug 10.

The Highest Oxidation State of Rhodium: Rhodium(VII) in [RhO3 ]

Mayara da Silva Santos  1   2 , Tony Stüker  3 , Max Flach  1   2 , Olesya S Ablyasova  1   2 , Martin Timm  2 , Bernd von Issendorff  1 , Konstantin Hirsch  2 , Vicente Zamudio-Bayer  2 , Sebastian Riedel  3 , J Tobias Lau  1   2
Affiliations

The Highest Oxidation State of Rhodium: Rhodium(VII) in [RhO3 ]

Mayara da Silva Santos et al. Angew Chem Int Ed Engl. .

Abstract

Although the highest possible oxidation states of all transition elements are rare, they are not only of fundamental interest but also relevant as potentially strong oxidizing agents. In general, the highest oxidation states are found in the electron-rich late transition elements of groups 7-9 of the periodic table. Rhodium is the first element of the 4d transition metal series for which the highest known oxidation state does not equal its group number of 9, but reaches only a significantly lower value of +6 in exceptional cases. Higher oxidation states of rhodium have remained elusive so far. In a combined mass spectrometry, X-ray absorption spectroscopy, and quantum-chemical study of gas-phase R h O n + (n=1-4), we identify R h O 3 + as the 1 A 1 ' trioxidorhodium(VII) cation, the first chemical species to contain rhodium in the +7 oxidation state, which is the third-highest oxidation state experimentally verified among all elements in the periodic table.

Keywords: Gas Phase; Oxidation State; Oxides; Rhodium; X-Ray Absorption Spectroscopy.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Experimental ion yield spectrum (solid red line) and computational TD‐DFT X‐ray absorption spectrum for the 1A1' ground state (dashed black line) of RhO3+ , at the oxygen K‐edge, with very good agreement for the transitions below 542 eV.
Figure 2
Figure 2
Frontier natural molecular orbital plot at 0.1 e Bohr−3 (state‐specific CASSCF(15,20)/aug‐cc‐pVTZ‐DK) for the 1A1' electronic ground state in D 3h point group symmetry of RhO3+ spanning the rhodium valence d orbital space, a 1′, e′′ and e′, as well as the oxygen ligand centered a 1′′ orbital. Arrows indicate the electron distribution of the leading configuration, while fractional numbers show the natural occupations. The fully (1.99 electrons) occupied, non‐bonding a 1′ (4d2) orbital indicates rhodium in the formal +7 oxidation state.
Figure 3
Figure 3
Ion yield spectra at the oxygen K edge of the RhOn+ (n=0–4) series. The absence of any oxygen‐oxygen σ* resonance for n=1–3 indicates purely oxido rhodium cations, while the presence of an oxygen‐oxygen σ* resonance for RhO4+ indicates the presence of at least one oxygen–oxygen bond.
Figure 4
Figure 4
Median values, calculated from the integrated intensity of the rhodium M3 edge of RhOn+ (n=0–3) species, plotted as a function of the formal oxidation state of the rhodium center, with a linear fit shown as a red line. The formal occupation of the (non‐bonding) rhodium 4d atomic orbitals is indicated in the figure. Cf. Table 1 for numerical values.
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