Structural and NMR spectroscopic investigations of chair and twist conformers of the P2Se8(2-) anion.

Four new salts of the P2Se8(2-) anion have been prepared, starting from easily available reagents using different reaction strategies including reaction of the elements, oxidation of P4Se3 with alkalimetal diselenides and elemental selenium, and the use of an ionic liquid as a reaction medium. Multinuclear NMR investigations show the presence of both chair-P2Se8(2-) and twist-P2Se8(2-) in solution, with twist-P2Se8(2-) being the predominant conformer. The interconversion between the two conformers is slow on the NMR time scale. Structural investigations of the new salts by single-crystal X-ray diffraction show that chair-P2Se8(2-) is the conformer mostly found in the solid state. A first structural characterization of twist-P2Se8(2-) is reported. The bonding situation in the P2Se8(2-) anion as well as the relative stability of the chair, twist, and boat conformers was elucidated by quantum chemical calculations.