+10 Oxidation state, Exist or Not Exist?
Chemical physicist and spectroscopist C. K. Jørgensen once said that one of the major goals of inorganic chemistry is to prepare compounds of elements in unusual oxidation states. In 2009, the range of oxidation states produced from chemical reaction was -4 to +8, and in 2010 Himmel's group showed that Ir compound with +9 oxidation state, [IrO4]+, exists by electronic structure calculations. In 2014, Wang's group confirmed the existence of the Ir(IX) by matrix-isolation experiments. From these ideas, can it be stretched further? Let say oxidation state +10?
Truhlar's group from University of Minnesota took up the challenge by studying group 10 compounds (Pd, Pt, and Ds) and it was found that Pt is more likely to have an oxidation state of +10. From this information, six compounds of Pd and Pt with +10 oxidation state ([PdO4]2+, [PtO4]2+, [PtO3F2]2+, [PtO4OH]+, [PtO5], and [PtO4SH]2+) were studied.
From the calculate energies, ΔE, ΔH, and ΔG, all the six compounds are not thermodynamically stable due to at least one of decomposition reaction gives negative ΔE, ΔH, and ΔG.
Interestingly, for [PtO4,]2+ all the possible reactions give positive energies except reaction (3). Further investigation on this reaction was conducted and the energy profile of this reaction is shown below.
The decomposition reaction of [PtO4]2+ happens via transformation from Td to C2v structure, then it goes to Cs through TS3 to give the decomposition product. The calculated energy barrier for the decomposition reaction as 30.7 kcal mol-1 with the transition state theory rate constant gives unimolecular lifetime of 312.5 dayss. From these values, it can be concluded that [PtO4]2+ is kinetically stable.
It is noteworthy that [PtO4]2+ is isoelectronic with Ir(IX) [IrO4]+ and Os(VIII) OsO4. Besides that, the orbitals of [PtO4]2+ is similar with to those in [IrO4]+ with HOMO in Pt compound is lower than is Ir compound.
Further investigation in charge distribution of this high oxidation state was done using CM5 and Hirshfeld charge analysis. These calculations show that both compounds give the highest positive charge on the metal with the charge on Pt is about 0.2 atomic units higher than Ir compound.
In short, oxidation state of +10 could exist in form of Td structure of [PtO4]2+. The energy profile of [PtO4]2+ shows the decomposition reaction needs to overcome a high energy barrier with lifetime of 312.5 days; hence it is kinetically stable. Furthermore, [PtO4]2+ shows similar charge distribution and electron densities with [IrO4]+, but the partial atomic charge on the metal is 20% units higher.
References
H. S. Yu and D. G. Truhlar, Angew. Chem. Int. Ed., 2016, 55, 9004 - 9006.
Truhlar's group from University of Minnesota took up the challenge by studying group 10 compounds (Pd, Pt, and Ds) and it was found that Pt is more likely to have an oxidation state of +10. From this information, six compounds of Pd and Pt with +10 oxidation state ([PdO4]2+, [PtO4]2+, [PtO3F2]2+, [PtO4OH]+, [PtO5], and [PtO4SH]2+) were studied.
From the calculate energies, ΔE, ΔH, and ΔG, all the six compounds are not thermodynamically stable due to at least one of decomposition reaction gives negative ΔE, ΔH, and ΔG.
 |
| The energy profile of decomposition reaction of [PtO4]2+ |
It is noteworthy that [PtO4]2+ is isoelectronic with Ir(IX) [IrO4]+ and Os(VIII) OsO4. Besides that, the orbitals of [PtO4]2+ is similar with to those in [IrO4]+ with HOMO in Pt compound is lower than is Ir compound.
 |
| HOMO of [IrO4]+ (left) and [PtO4]2+ (right) |
In short, oxidation state of +10 could exist in form of Td structure of [PtO4]2+. The energy profile of [PtO4]2+ shows the decomposition reaction needs to overcome a high energy barrier with lifetime of 312.5 days; hence it is kinetically stable. Furthermore, [PtO4]2+ shows similar charge distribution and electron densities with [IrO4]+, but the partial atomic charge on the metal is 20% units higher.
References
H. S. Yu and D. G. Truhlar, Angew. Chem. Int. Ed., 2016, 55, 9004 - 9006.
Comments