The title compound (C6H5)(C4H8NO)[N(C6H 11)2]P=N-S3N3 crystallizes in a triclinic crystal system with unit cell parameters a = 9.8884(4) Å, b = 10.6075(1) Å, c = 14.2276(2) Å, α = 78.14(3)°, β = 79.31(1)°, γ = 65.42(2)°, V = 1319.44(6) Å3, Z = 2, and space group P1̄. The cyclotrithiazene ring adopts a "distorted chair" conformation with a deviation of 0.682(7) Å for the tricoordinated sulfur atom. Remarkably, a short exocyclic S-N bond length 1.489(4) Å along with a large P-N-S angle 136.2(3)° are observed with the iminophosphorus moiety. © 2003 MAIK "Nauka/Interperiodica".