The synthesis, variable temperature NMR spectra, and crystal structures of two crystalline forms, 2a and 2b, of the enamine 1-(N,N-diethylamino)-2,2-bis(2-nitrophenylthio)ethene have been obtained. Both forms crystallize in the monoclinic space group P21/a. The two phases have similar molecular structures but possess different intermolecular C–H······O hydrogen bonding interactions. Both forms exhibit disorder within the NEt2 fragment at 298 K: sufficient disorder persisted with 2a (orange needles) down to 100 K to make the geometric parameters pertaining to the enamine fragment unreliable. The disorder was effectively eliminated on cooling 2b down (red colored blocks) to 150 K. Cell dimensions for the 2a-phase are at 100 K: a = 11.1030(4) A, b = 15.1325(7) A, c = 12.4504(7) A, β = 114.606(3)°, while for the 2b-phase at 150 K, a = 15.5206(4) A, b = 7.6958(2) A, c = 15.7137(3) A, β = 92.580(7)°. The C–N bond length in the β-form at 150 K of 1.335(3) A indicates considerable double bond character: the rotational barrier of the C–N bond in CDCl3 was calculated to be 52.4 kJ mol−1.