Syntheses and crystal structures of 2-( p -tol-yl)-1 H -perimidine hemihydrate and 1-methyl-2-( p -tol-yl)-1 H -perimidine.

The title compounds, 2-(4-methylphenyl)-1 H -perimidine hemihydrate ( 1 , C 18 H 14 N 2 ·0.5H 2 O) and 1-methyl-2-(4-methylphenyl)-1 H -perimidine ( 2 , C 19 H 16 N 2 ), were prepared and characterized by 1 H NMR and single-crystal X-ray diffraction. The organic mol-ecule of the hemihydrate lies on a twofold rotation axis while the water mol-ecule lies on the inter-section of three twofold rotation axes (point group symmetry 222). As a consequence, the hydrogen atoms that are part of the N-H group and the water mol-ecule as well as the CH 3 group of the p -tolyl ring are disordered over two positions. In compound 1 , the perimidine and the 2-aryl rings are slightly twisted while its N -methyl-ated derivative 2 has a more distorted conformation because of the steric repulsion between the N -methyl group and the 2-aryl ring. In the crystal structures, mol-ecules of perimidine 2 are held together only by C-H⋯π contacts while the parent perimidine 1 does not exhibit this type of inter-action. Its crystal packing is established by inter-molecular N-H⋯O hydrogen bonds with the solvent water mol-ecules and additionally stabilized by π-π stacking.