A refinement of the crystal structure of quinolinic acid at 100 K with neutron diffraction data

The crystal structure of quinolinic acid (pyridine-2,3-dicarboxylic acid: CTHsNO4) has been refined, based upon neutron diffraction data measured at 100 K. Crystal data: space group P2ffc; a = 7.415 (5), b -12.396 (9), c = 7.826 (6) .A, fl = 117.05 (4) °, Z = 4. The final unweighted R value based on F 2 is 0.048 for all 1643 unique reflections, and bond distances have been determined with precision better than 0-003 ,/~. The major temperature dependence in the cell constants is observed for the b axis, which is perpendicular to the molecular planes. Rigid-body analyses of the thermal parameters determined here at 100 K and those found in a prior study at 297 K indicate that the translational motion changes with temperature more along the b axis than in other directions. Significant differences between the structure at 100 and 297 K are observed in the intramolecular O . . . H . . . O hydrogen bond, where the H atom shifts towards the midpoint of the bond when the crystal is cooled. This temperature effect is discussed in the light of results of the rigid-body thermalmotion analyses. 1149