The title compound (NC4H8NCH3)(C 6H5)[N(C6H11)2]P=N-S 3N3 crystallizes in the triclinic crystal system with unit cell dimensions: a = 9.7572(2), b = 10.6845(1), c = 16.9381(3) Å, α = 71.75(1)°, β = 80.65(2)°, γ = 65.93(1)°, and Z = 2. The tricoordinated sulfur atom (S1) in the cyclotrithiazene deviates from the mean plane of the other five atoms by 0.716(6) Å, which is the highest among the known phosphiniminocyclotrithiazene structures. In the exocyclic P=N4-S1 moiety, the two bond distances are short: 1.585(6) and 1.527(6) Å; but the bond angle is large 135.3(4)°. The S1 displacement is highly correlated with the endocyclic angle at the nitrogen atom (diagonally opposite to S1), but the nature of correlation is bimodal (R = 1.0 + or -1.0) for the cyclic and acyclic substituents (R) in the (R)(C6H 5)[N(C6H11)2]P=N-S3N 3 series. On the other hand, the S1-N4 bond distances are negatively correlated (R = -0.94) with the P=N4-S1 bond angle in the above series. © 2005 Springer Science+Business Media, Inc.