Phase transition to the modulated structure in hemimellitic acid compound
J. Kusz1, M. Zubko2, P. Kuś3
1Institute of Physics, University
of Silesia, Uniwersytecka 4, 40-007 Katowice, Poland
2Institute of Materials Science, University of Silesia,75 Pułku Piechoty
1a, 41-500 Chorzów, Poland
3Institute of Chemistry, University of Silesia, Szkolna 9, 40-007
Katowice, Poland
joachim.kusz@us.edu.pl
1,2,3-Benzenetricarboxylic acid (hemimellitic acid) is rather uncommon tricarboxylic acids with three carboxylic units close together in 1,2,3 positions of benzene ring. The studied compound is a inhibitor of the citrate carriers in liver mitochondria and inhibitor of pyruvate carboxylation in small animals like rat, mice and rabbit [1]. It is also used in cosmetology.
Studied compound was obtained in oxidation reaction of 1,5 dimethylnaphthalene with KMnO4 in water suspension at boiling temperature. The reaction is an interesting example of the disintegration of the aromatic ring (naphthalene) in a fairly mild conditions for this type of reaction. In the literature there are similar reactions, but they occurred in more drastic conditions (high temperature, high pressure). The crystals were prepared from a solution of D2O directly in a test tube for performing NMR measurements. The H1 NMR spectrum is consistent with the invention and expectations.
Good quality single crystals were preselected under stereoscopic polarization Zeiss microscope and mounted on quartz glass capillary. X-ray diffraction measurements were performed using Agilent Technologies SuperNova 4-circle Kappa diffractometer using both Cu and Mo radiation. X-ray diffractometer was equipped with Atlas CCD camera and Cryostream 700 low temperature attachment. Studied compound crystallizes in the monoclinic crystal system in C2/c space group. There are 8 hemimellitic acid molecules per average unit cell.
Figure 1. a) Cuts thru reciprocal space showing temperature evolution of satellite reflections and diffuse scattering. b) Cuts thru reciprocal space in logarithmic scale.
At 240 K phase transition is observed from structure with diffuse scattering to the two dimensional modulated structure. Analysis of the modulated structure and short range order has been performed.