Crystal structure of tetramethylammonium 1,1,7,7-tetracyanohepta-2,4,6-trienide

Abstract

The title compound, C4H12N+·C11H5N4 −, contains one tetramethylammonium cation and one 1,1,7,7-tetracyanohepta-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 dinitrile moieties are slightly twisted from the polymethine main chain to which they are attached [C(CN)2/C5 dihedral angles = 6.1 (2) and 7.1 (1)°]. The C—C bond distances along the heptadienyl chain vary in the narrow range 1.382 (2)–1.394 (2) Å, thus indicating the significant degree of conjugation. In the crystal, the anions are linked into zigzag chains along the [10\overline{1}] direction by C—H...N(nitrile) short contacts. The antiparallel chains stack along the [110] direction with alternating separations between the neighboring anions in stacks of 3.291 and 3.504 Å. The C—H...N short contacts and stacking interactions combine to link the anions into layers parallel to the (\overline{1}01) plane and separated by columns of tetramethylammonium cations.