Crystal structure of tetra-methyl-ammonium 1,1,7,7-tetra-cyano-hepta-2,4,6-trienide.

The title compound, C(4)H(12)N(+)·C(11)H(5)N(4) (-), contains one tetra-methyl-ammonium cation and one 1,1,7,7-tetra-cyano-hepta-2,4,6-trienide anion in the asymmetric unit. The anion is in an all-trans conjugated C=C bonds conformation. Two terminal C(CN)(2) di-nitrile moieties are slightly twisted from the polymethine main chain to which they are attached [C(CN)(2)/C(5) dihedral angles = 6.1†(2) and 7.1†(1)°]. The C-C bond distances along the hepta-dienyl chain vary in the narrow range 1.382†(2)-1.394†(2)†à , thus indicating the significant degree of conjugation. In the crystal, the anions are linked into zigzag chains along the [10] direction by C-H⋯N(nitrile) short contacts. The anti-parallel chains stack along the [110] direction with alternating separations between the neighboring anions in stacks of 3.291 and 3.504†à . The C-H⋯N short contacts and stacking inter-actions combine to link the anions into layers parallel to the (01) plane and separated by columns of tetra-methyl-ammonium cations.