Molecular complexes. Part XVI. Crystal structure of the 1 : 1 molecular complex of pyrene and 7,7,8,8-tetracyanoquinodimethane

Abstract

The crystal and molecular structure of the title π complex has been determined by three-dimensional X-ray diffraction methods. Crystals are monoclinic, a= 7·14, b= 14·73, c= 10·01 Å, γ= 102·5°, space group P2₁/b, Z= 2. Two determinations of the structure were made: from 1084 visually estimated photographic data by the symbolic addition method, and from 1068 diffractometer data by Patterson and Fourier methods; each was refined by least-squares methods to R 0·136 and 0·137, respectively. In the crystal alternate pyrene and tetracyanoquinodi-methane molecules form stacks along the a axis. The mean separation of the molecular planes, which are inclined at an angle of 6·3°, is 3·50 Å. The relative orientation of the two molecules is not that predicted by MO calculations of charge-transfer interactions, and reflects the influence of lattice packing requirements and dipole–dipole interactions. In both determinations the molecular dimensions found for tetracyanoquinodimethane are in good agreement with known values, whereas those found for pyrene are not. Thermal vibration parameters suggest that the pyrene molecule is disordered.