The title compound, C(5)H(5)Cl(5)N(5)P(3), crystallizes as a zwitterion in which the pyridine N atom is protonated. An S(6) ring motif is formed via an intra-molecular C-H⋯N hydrogen bond. The triaza-triphosphinine ring adopts an envelope conformation, with one N atom displaced by 0.145 (1) Å from the other atoms. In the crystal, N-H⋯N and C-H⋯N hydrogen bonds link the mol-ecules into centrosymmetric dimers containing one R(2) (2)(7) ring motif and two R(2) (2)(8) ring motifs.