Molecular complexes. Part XV. Crystal structure of the 1 : 1 molecular complex of pyrene and 1,2,4,5-tetracyanobenzene at 290 and 178 K

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Abstract
The crystal and molecular structure of the title complex has been determined at 290 and 178 K by three-dimensional X-ray diffraction methods. Crystals are monoclinic, unit cell dimensions (290 K)a= 7·27, b= 15·57, c= 8·44 Å, γ= 93·6°; (178 K)a= 7·27, b= 15·36, c= 8·38 Å, γ= 94·0°; space group P21/b, Z= 2. The structure was determined by Patterson and Fourier methods from visually estimated photographic data and refined by full matrix least-squares techniques to R 0·101 (290 K, 1367 independent reflections) and 0·110 (178 K, 767 independent reflections). In the crystal alternate pyrene and tetracyanobenzene molecules form stacks along the a axis. The mean separation of the molecular planes, which are inclined at an angle of 4·4°, is 3·50 Å at both temperatures. The relative orientation of the two molecules is not that predicted by MO calculations of charge-transfer interaction, and reflects the influence of lattice packing requirements and dipole–dipole interactions between tetracyanobenzene molecules. A detailed analysis of the anisotopic temperature factors suggests that there is a large in-plane angular oscillation of the pyrene molecule, together with a co-operative translational and rocking motion of the complex as a whole.

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