Alizarin
crystals: An extreme case of solvent induced morphology change
R.E. Algra, W.S. Graswinckel, W.J.P.van Enckevort, and E. Vlieg
Journal of Crystal Growth, Volume 285, Pages 168-177
Abstract
The organic compound alizarin (1,2-dihydroxy-9,10-anthraquinone)
normally crystallizes as very long needles. However, if alcohol is used
as solvent, a completely different, triangular shape is obtained. Due
to disorder and twinning of the crystals single crystal X-ray
diffraction could not be used to establish a possible difference in
crystal structure. Differential scanning calorimetry, IR and Raman
spectroscopy and powder X-ray diffraction show that the two forms of
alizarin are isostructural. From this it follows that solvent influence
rather than polymorphism causes the difference in crystal habit.
Surface examination, using optical, scanning electron and atomic force
microscopy provides information on the mechanism of habit change, which
is introduced by the blocking of growth of specific crystal faces in
the alcohol solutions.