Crystal structures, Hirshfeld surface analysis and inter-action energies of (Z)-2-(4-methyl-benzylidene)- and (Z)-2-(furfuryl-idene)-2H-benzo[b][1,4]thia-zin-3(4H)-one.

Two new 2-aryl-methyl-idene derivatives of benzo-1,4-thia-zin-3-one, namely, (Z)-2-(4-methyl-benzyl-idene)-2H-benzo[b][1,4]thia-zin-3(4H)-one, C16H13NOS, 1, and (Z)-2-(furan-2-yl-methyl-idene)-2H-benzo[b][1,4]thia-zin-3(4H)-one, C13H9NO2S, 2, are rare examples of a nearly planar structure of the 1,4-thia-zin-3-one core stabilized by conjugation. Their supra-molecular structures are very similar, being dominated by assembly of inversion dimers through highly directional reciprocal N-H⋯O bonds [N⋯O = 2.822 (2) Å for 1; 2.881 (3) Å for 2]. Weaker forces are represented by C-H⋯O, C-H⋯π and stacking inter-actions, with more inter-actions in the case of furfuryl-idene 2, and they are important for consolidation of the structures. This is consistent with the results of Hirshfeld surface analysis and calculated inter-action energies. Doubling the number of O atoms, when moving from 1 to 2, results in even larger increase in fractions of O⋯H/H⋯O contacts [7.6 to 18.6%] due to extensive inter-actions with the furyl-O acceptor and this contributes to higher packing index in the case of 2. The far superior energetics in the structures are related with the formation of hydrogen-bonded dimers [-73.3 and -72.9 kJ mol-1, for 1 and 2, respectively], followed by dispersion forces and weak C-H⋯O bonding. Identification of reliable 1,4-thia-zin-3-one based supra-molecular synthons is important for selective targeting for biomedical applications.