Abstract
Rhodium, a 4d transition metal and a lighter analogue of iridium, is known to exhibit its highest VIth oxidation state in RhF6 molecule. In this report, the stability and decomposition pathways of two species containing rhodium at a potentially formal +IX oxidation state, [RhO4]+ and RhNO3, have been investigated theoretically within the framework of the relativistic two-component Hamiltonian calculations. Possible rearrangement into isomers featuring lower formal oxidation numbers has been explored. We found that both species studied are metastable with respect to elimination of O2 or NO. However, the local minima containing Rh(IX) are protected by sufficient energy barriers on the decomposition pathway, and they could in principle be prepared. The analysis of a broader set of compounds containing group 8 and 9 metals in high formal oxidation states that correspond to the group number showed that, in contrast to a standard trend, the limits of formally attainable oxidation state correlate with high level of covalent bonding character in the complexes studied.
Highlights
The classical theory of 2-electron/2-center chemical bonding based on a molecular orbital picture, as taught to the chemistry students, puts accent on proper match of energy and “size” of atomic orbitals involved in chemical bonding
The computations with DKH2 approach were performed with ORCA 4.0.1 program [19], and the results by zeroorder regular approximation (ZORA) were obtained in ADF 2018 [20,21,22]
Abovementioned calculations based on density functional method (DFT) were used to perform geometry optimizations of stationary point structures (minimum energy ones and transition states (TS)) and relaxed surface scans, i.e. series of constrained geometry optimizations, with stretching or shortening of selected bond distances
Summary
The classical theory of 2-electron/2-center chemical bonding based on a molecular orbital picture, as taught to the chemistry students, puts accent on proper match of energy and “size” (i.e. spatial decay of electronic density) of atomic orbitals involved in chemical bonding. The better the match of energy and spatial distribution of orbitals (overlap), the stronger the chemical bond. In this simplified picture, the homonuclear diatomics best fulfil the criteria which favour strong bonding, albeit heteronuclear systems may still benefit. The well-known group 8 complexes are represented by stable yet largely covalent Os (VIII)O4 and the less stable and highly reactive Ru (VIII)O4 while related Fe (VIII)O4 has never been observed but it has been predicted to be metastable [4]. In group 9, only the observed [IrO4]+ cation and the recently predicted neutral molecule IrNO3 (nitride trioxide) [5] feature genuine nonavalent transition metal center. Similar to Fe (VIII)O4, Ir (IX)NO3 has been predicted to be mildly metastable with respect to (η2-NO)IrO2 and (η1NO)IrO2 but elimination of NO is predicted to be protected
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
