The crystal structure (at five temperatures) and anisotropic thermal expansion of anthraquinone

Abstract

The structure analysis of the monoclinic single crystals of anthraquinone has been carried out at room temperature and four lower temperatures, independently. This gives molecular reorientation and the change of anisotropic thermal vibrations. Double and treble Weissenberg photographs on single films have given the anisotropic thermal-expansion figures. Over the range +20 ° to-170 °C the principal values are ex1=56"4; 0(22 = 125"0; ~33 =-8"6 (allx 106. °C-I). 0(33, which lies very nearly along c, varies with temperature, becoming positive near to and above-12 °C. An explanation of the large expansion along the unique axis is given in terms of the large independent out-of-plane vibration of the oxygen atoms. The positive and negative el l and 0~33 , and their respective magnitudes, are shown to be related to this large expansion along [010], to the molecular reorientation and thermal vibration, and to the directions of the stronger intermolecular bonds. The change of sign of 0~33 is due to the increasing effect of thermal vibration.