Hydrogen bonding in C-methylated nitroanilines:: three triclinic examples with Z′=2 or 4

4-Methyl-2-nitroaniline, (I), C7H8N2O2, crystallizes with two molecules in the asymmetric unit. The molecules both form intramolecular N-H . . .O hydrogen bonds and they are linked into hydrogen-bonded C-2(2)(12) chains in which the two independent molecules alternate. 4,5-Dimethyl-2-nitroaniline, (II), C8H10N2O2, also has Z' = 2 and the two independent molecules each form hydrogen-bonded C(6) chains. In 4-methyl-3-nitroaniline, (III), C7H8N2O2, there are four molecules in the asymmetric unit. Molecules of two of these types are linked by N-H . . .O hydrogen bonds into molecular ladders containing R-4(3)(18) rings and the other two types independently form single C(7) chains.