Crystal structures of two isomeric 2-aryl-3-phenyl-1,3-thia-zepan-4-ones

The crystal of 6-(3-nitro-phen-yl)-7-phenyl-5-thia-7-aza-spiro-[2.6]nonan-8-one (1), C₁₉H₁₈N₂O₃S, has monoclinic (P2₁/n) symmetry while that of its isomer 6-(4-nitro-phen-yl)-7-phenyl-5-thia-7-aza-spiro-[2.6]nonan-8-one (2), has ortho-rhom-bic (Pca2₁) symmetry: compound 1 has two mol-ecules, A and B, in the asymmetric unit while 2 has one. In all three mol-ecules, the seven-membered thia-zepan ring exhibits a chair conformation with Q2 and Q3 values (Å) of 0.521 (3), 0.735 (3) and 0.485 (3), 0.749 (3) in 1 and 0.517 (5), 0.699 (5) in 2. In each structure, the phenyl rings attached to adjacent atoms of the thia-zepan ring have inter-planar angles ranging between 41 and 47°. Except for the nitro groups, the three mol-ecules have similar conformations when overlayed in pairs. Both crystal structures are consolidated by C-H⋯O hydrogen bonds.