The incommensurately modulated structure of the triclinic form of N,N-di­methylmorpholinium di-7,7,8,8-tetra­cyano-p-quinodimethanide; DMM(TCNQ)2(II) at 99 K

The triclinic form of DMM(TCNQ)2, space group P1 at room temperature, transforms below 207 K to an incommensurately modulated phase. Its
crystal structure has been determined at 99K: C6H14NO+.2_CIEH4N~ f2-, Mr = 524.6, superspace group PP-~ [-0.046 (4), 0.465 (5), 0.385 (3)],
a = 16.452 (3), b = 12.838 (3), c = 6.592 (2) A, a = 103"18 (2), /3 =98.79 (2), y= 103"25 (2) °, V= 1288 ~3, Z = 2, Dx = 1.352 Mg m -a, Mo Kff, A = 0.71069 A, /z = 0.095 mm -~, F(000) = 546, wR(F) =0.037 for 12 291 independent reflections [wR(F) =0.122 for the 4790 satellite reflections of first order]. At room temperature, the DMM molecules, in chair conformations, are randomly disordered. At 99 K, the DMM groups are almost completely ordered in an incommensurate way and are accommodated in the channels formed by the TCNQ stacks by a small displacive modulation of the latter. Some physical implications of the structural changes are discussed.