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Pentacene, C(22)H(14), crystallizes in different morphologies characterized by their d(001)-spacings of 14.1, 14.5, 15.0 and 15.4 A. We have studied the crystal structure of the 14.1 and 14.5 A d-spacing morphologies grown by vapour transport and from solution. We find a close correspondence between the 14.1 A structure reported by Holmes, Kumaraswamy, Matzeger & Vollhardt Chem. Eur. J. (1999), 5, 3399-3412 and the 14.5 A structure reported by Campbell, Monteath Robertson & Trotter Acta Cryst. (1961), 14, 705-711. Single crystals commonly adopt the 14.1 A d-spacing morphology with an inversion centre on both molecules in the unit cell. Thin films grown on SiO(2) substrates above 350 K preferentially adopt the 14.5 A d-spacing morphology, with a slightly smaller unit-cell volume.
Mattheus et al. (Thu,) studied this question.