STRUCTURE AND CRYSTAL PACKING OF 4-AMINOBENZONITRILES AND 4-AMINO-3,5-DIMETHYLBENZONITIRLES AT VARIOUS TEMPERATURES

The amino N atom in 4-aminobenzonitrile (ABN) and 4-(dimethylamino)benzonitrile (DMABN) has a pyramidal character, with values of 34 (3) and 11.9 (3)-degrees, respectively, for the angle between the planes of the amino group and the phenyl ring. In 3,5-dimethyl-4-(dimethylamino)benzonitrile (MMD) at 173 K, the dimethylamino group is twisted over an angle of 59.3(2)-degrees with respect to the phenyl plane. In addition, the amino N(1) atom is not located in the plane of the phenyl ring, with an out-of-plane displacement of 0.117(5) angstrom. The N phenyl bond length in MMD of 1.414 (3) angstrom is larger that that in the four other aminobenzonitriles, for which an average bond length of 1.367 angstrom is found. With DMABN, the crystal structure consists of stacks with an alternating orientation of the molecules. In the crystals of ABN. 3,5-dimethyl-4-(methylamino)benzonitrile (MHD) and 4-amino-3,5-dimethylbenzonitrile (HHD), hydrogen bonding is an important structural element. In ABN and MHD, hydrogen bonds are formed between an amino H atom and the cyano N atom of adjacent molecules. In HHD. each H atom is linked to a cyano N atom of two different neighbouring molecules, in a layered structure consisting of squares and octagons. Temperature-dependent solid-solid phase transitions are observed with all five aminobenzonitriles studied here. Crystals of the low-temperature phase could only be obtained from ABN, with lattice constants which are considerably different from those observed at room temperature.