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Physical Chemistry

Oxidation state +10 a possibility

Should chemists be able to prepare it, the platinum oxide [PtO4]2+ would set a new standard for highest oxidation state in a compound

by Stephen K. Ritter
June 20, 2016 | A version of this story appeared in Volume 94, Issue 25

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The most stable form of [PtO4]2+ is predicted to have tetrahedral geometry and four terminal Pt=O bonds.
A list of iridium compounds with oxidation states ranging from -3 to +9.
The most stable form of [PtO4]2+ is predicted to have tetrahedral geometry and four terminal Pt=O bonds.
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Prior to 2014, the highest observed oxidation state of an atom in a molecule had been +8, which occurs in only a few tetroxide compounds—RuO4, OsO4, IrO4, and XeO4. Then researchers unveiled [IrO4]+, an iridium +9 compound—iridium perhaps shows the widest range of oxidation states of any element, as noted here. The new [PtO4]2+, should it be made, would stretch out the range of oxidation states to +10.
A table showing various oxidation states of Ir in various compounds.
Prior to 2014, the highest observed oxidation state of an atom in a molecule had been +8, which occurs in only a few tetroxide compounds—RuO4, OsO4, IrO4, and XeO4. Then researchers unveiled [IrO4]+, an iridium +9 compound—iridium perhaps shows the widest range of oxidation states of any element, as noted here. The new [PtO4]2+, should it be made, would stretch out the range of oxidation states to +10.

The oxidation state of an atom in a molecule is an important means of electron bookkeeping and determining structure and bonding, so the question of just how high oxidation states can go is a curiosity to chemists. Researchers have prepared compounds containing oxidation states that stretch from –4 to +9, with +9 being the latest addition to the list in 2014 when [IrO] was reported. Haoyu S. Yu and Donald G. Truhlar of the University of Minnesota, Twin Cities, have now made a new offer for the highest oxidation state: They have predicted that the +10 state should exist in the platinum oxide [PtO4]2+ (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201604670). Using density functional theory, the team explored the electronic structure of palladium, platinum, and darmstadtium compounds and found several plausible +10 platinum and palladium compounds. Like [IrO4]+, these are molecules in which the central metal atom has plenty of valence electrons to give away and the resulting high charge can be stabilized by small, highly electronegative ligands such as fluorine or oxygen. After calculating the decomposition pathways for the +10 candidates, they found that [PtO4]2+ is the most stable and potentially could be synthesized. It has tetrahedral geometry and four terminal Pt=O bonds, similar to [IrO4]+, and could possibly be made the same way, by blasting a metal target with a pulsed laser with O2 present.

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