Crystal structures, Hirshfeld surface analysis and interaction energies of ( <i>Z</i> )-2-(4-methylbenzylidene)- and ( <i>Z</i> )-2-(furfurylidene)-2 <i>H</i> -benzo[ <i>b</i> ][1,4]thiazin-3(4 <i>H</i> )-one

Two new 2-aryl-methyl-idene derivatives of benzo-1,4-thia-zin-3-one, namely, (<i>Z</i>)-2-(4-methyl-benzyl-idene)-2<i>H</i>-benzo[<i>b</i>][1,4]thia-zin-3(4<i>H</i>)-one, C₁₆H₁₃NOS, <b>1</b>, and (<i>Z</i>)-2-(furan-2-yl-methyl-idene)-2<i>H</i>-benzo[<i>b</i>][1,4]thia-zin-3(4<i>H</i>)-one, C₁₃H₉NO₂S, <b>2</b>, 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 <b>1</b>; 2.881 (3) Å for <b>2</b>]. 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 <b>2</b>, 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 <b>1</b> to <b>2</b>, 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 <b>2</b>. 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 <b>1</b> and <b>2</b>, 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.