A comparison of 2,7-di­hydro-2,2,7,7-tetra­methyl-3,6-di­phenyl-1,4,5-thiadiazepine and the corresponding 1,1-­dioxide

The structures of the highly substituted title heterocycles, C₂₀H₂₂N₂S and C₂₀H₂₂N₂O₂S, have been determined at 123 (1) K. Both mol­ecules possess exact C₂ symmetry and the seven-membered rings have very similar twist-boat conformations. The magnitudes of the C—S—C bond angles, 107.13 (6) and 108.27 (7)°, respectively, are influenced significantly by the four substituent methyl groups on the seven-membered rings.