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 = 6.114;(2) and 7.114;(1)°]. The C-C bond distances along the heptadienyl chain vary in the narrow range 1.38214;(2)-1.39414;(2)14;Å, 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 antiparallel chains stack along the [110] direction with alternating separations between the neighboring anions in stacks of 3.291 and 3.50414;Å. The C-H..N short contacts and stacking interactions combine to link the anions into layers parallel to the (01) plane and separated by columns of tetramethylammonium cations.