Valence Tautomerism of the Heptaheteronortricycles [P7 − xAsx]3−

Abstract
Solutions of the mixed crystals Rb3[P7−xAsx] in ethylenediamine contain almost the entire series of the heptaheteronortricycle anions P7−xAsx, as has been demonstrated by 31P‐NMR spectroscopy; only [PAs6]3‐ could not be detected with certainty. [P6As]3− and [P5As2]3− are preferentially formed, but not [P4As3]3− as would be expected on the basis of the concept of topological charge stabilization. Very suprisingly, exchange reactions do not take place.