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IntroduetlonC19H15C1 is trigonal, space group P3, with a = 13.998 (2), c = 13.202 (4)/k, V = 2240.2 A 3, Z = 6, Dm= 1.26, D x = 1.240 Mg m -3, F(000) = 876,/~ = 0.225 mm-k The final R and R w, based on 905 reflections, are 0.038 and 0.025 respectively. The molecules lie in special positions on the crystallographic threefold axes. They are associated in pairs and form two distinct Ph3C-C1...CI-CPh 3 head-to-head arrangements characterized by long C-C1 bonds and short C1... CI contacts. The shortest C1... C1 distance (3.210 A) is about 0.3/k smaller than the sum of the van der Waals radii. For the sake of comparison, the lattice energy was computed using two different sets of Buckingham potential functions. The effects of including electrostatic terms were also investigated. These calculations account satisfactorily for all the salient features of the crystal packing. Analysis of the thermal motion showed that the rigid-body approximation holds reasonably well for the triphenylchloromethane molecule.

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