The C-H center dot center dot O hydrogen bond in (dicyanomethyl)ammonium p-toluenesulfonate

C-H . . . O hydrogen bonds are known to have a very wide range of geometrie s and strengths. With highly polar C-H groups, such as in CHCl3, C=C-H, CH( NO2) etc., C- H . . . O interactions may have similar geometries to convent ionalO/N-H . . .O hydrogen bonds. On the other hand, with weakly polar meth yl groups, C-H . . . interactions have long contact distances and are only slightly directional. All intermediate situations exist between these extre mes (see, e.g., Steiner, 1997; Steiner & Desiraju, 1998; Desiraju & Steiner , 1999). When studying the stronger kinds of C-H . . . O interactions, meth yl groups which carry two or even three strongly electron-withdrawing subst ituents are of interest (Pedireddi & Desiraju, 1992). In this context, the (dicyanomethyl)ammonium cation is of obvious interest. In the p-toluenesulf onate salt, (I), formation of a short C-H . . .O hydrogen bond may be expec ted.