2-Amino-5-trifluoromethyl-1,3,4-thiadiazole and a redetermination of 2-amino-1,3,4-thiadiazole, both at 120 K: chains of edge-fused R(2)(2)(8) and R(4)(4)(10) rings, and sheets of R(2)(2)(8) and R(6)(6)(20) rings.

Molecules of 2-amino-5-trifluoromethyl-1,3,4-thiadiazole, C3H2F3N3S, are linked by two independent N-H...N hydrogen bonds into sheets of alternating R(2)(2)(8) and R(6)(6)(20) rings, while the molecules of the unsubstituted 2-amino-1,3,4-thiadiazole, C2H3N3S, are linked, again by two independent N-H...N hydrogen bonds, but into chains of edge-fused R(2)(2)(8) and R(4)(4)(10) rings.