True symmetry or pseudosymmetry: 5-amino-1-(4-methylphenylsulfonyl)-4-pyrazolin-3-one and a comparison with its 1-phenylsulfonyl analogue

The title compound, C10H11N3O3S, (I), crystallizes as the NH tautomer. The two rings subtend an interplanar angle of 72.54(4)degrees. An intramolecular hydrogen bond is formed from the NH2 group to a sulfonyl O atom. The molecular packing involves layers of molecules parallel to the bc plane at x similar or equal to 0, 1 etc., with two classical linear hydrogen bonds (aminosulfonyl and pyrazolinecarbonyl NH...O) and a further interaction (aminosulfonyl NH...O) completing a three-centre system with the intramolecular contact. The analogous phenyl derivative, (II) [Elgemeie, Hanfy, Hopf & Jones (1998). Acta Cryst. C54, 136138], crystallizes with essentially the same unit cell and packing pattern, but with two independent molecules that differ significantly in the orientation of the phenyl groups. The space group is P21/c for (I) but P21 for (II), which is thus a pseudosymmetric counterpart of (I).