Positively charged

Main-group atoms often occur in small clusters, which can be neutral, negative or positive charged. The best known neutral cluster-tetrahedron is white phosphorus (P₄), but other tetrahedra can also be isolated. They are four-atom molecules whose spatial arrangement corresponds to a tetrahedron of equilateral triangles. Up to now, scientists only knew of at least six neutral versions, such as As₄ and AsP₃, and a large number of negatively charged tetrahedra like In₂Sb₂^2– - but no cationic or positively charged variants. Now, a team led by Prof. Dr. Ingo Krossing from the Institute of Inorganic and Analytical Chemistry at the University of Freiburg has succeeded in producing positively charged tetrahedra: three of them, to be precise: P₃E⁺ (E = S, Se, Te), were studied in solution. The Freiburg researchers have presented their results in the current edition of Chemical Science, and a highlight of their study came out in Nature Chemistry Reviews.

The Freiburg chemists were able to produce the tetrahedra in mixtures in the condensed phase. The analysis by NMR spectroscopy and MS spectrometry was clear, explains Krossing, and left no doubt that the compounds were P₃E⁺, with E being S, Se and Te. By reacting the P₄ tetrahedron with the cations ECl₃⁺ (E = S, Se, Te), the researchers were able to obtain P₃E⁺ salts with very good, weakly coordinating anions. And for the first time, this provided access to very Lewis-acidic ECl₃⁺ salts that can be easily dissolved in organic solvents and thus are ideally suited for follow-up chemistry.

The team is now looking for more synthetic possibilities: "We have ideas to continue and work with, but that will take some time," Krossing says.

Publication:
Weis, P., Röhner, D.C., Prediger, R., Butschke, B., Scherer, H., Weber, S., Krossing, I. (2019): First Experimental Evidence for the Elusive Tetrahedral Cations [EP₃]⁺ (E = S, Se, Te) in the Condensed Phase. In: Chemical Science. DOI: 10.1039/C9SC03915E

Highlight in Nature Reviews Chemistry:
DOI: 10.1038/s41570-019-0145-8