Pentacene, C22H14, crystallizes in different morphologies characterized by
their d(001)-spacings of 14.1, 14.5, 15.0 and 15.4 Angstrom. We have studie
d the crystal structure of the 14.1 and 14.5 Angstrom d-spacing morphologie
s grown by vapour transport and from solution. We rnd a close correspondenc
e between the 14.1 Angstrom structure reported by Holmes, Kumaraswamy, Matz
eger & Vollhardt [Chem. Eur. J. (1999), 5, 3399-3412] and the 14.5 Angstrom
structure reported by Campbell, Monteath Robertson & Trotter [Acta Cryst.
(1961), 14, 705-711]. Single crystals commonly adopt the 14.1 Angstrom d-sp
acing morphology with an inversion centre on both molecules in the unit cel
l. Thin films grown on SiO2 substrates above 350 K preferentially adopt the
14.5 Angstrom d-spacing morphology, with a slightly smaller unit-cell volu
me.