The 2-chloro-1,3,2-dithiaphospholane anion has been trapped in an X-irradiated single crystal of 1. The anion has been identified by comparing its 31P and 35Cl hyperfine tensors with the corresponding couplings obtained from ab initio calculations on H2PCl−. and PCl3−.. The structure of R2PCl− is discussed. Increasing the temperature causes the dissociation reaction to occur, and the phosphinyl radical has been observed after annealing at 220 K.