Crystal structure determination of 2-oxo-3-benzoyloxazolo[3,Z-a]pyridine from X-ray powder data

The crystal structure of the mesoionic compound 2-oxo-3-benzoyloxazolo[3,2- a]pyridine (C14H9NO3) has been determined from X-ray powder data using the grid search procedure. The crystal symmetry is orthorhombic (space group Pn a2(1), a = 7.940(1) Angstrom, b = 24.562(3) Angstrom, c = 5.402(1) Angstrom ). The results of Rietveld refinement (R-wp = 11.9%; R-exp = 3.7%) with gra dually relaxed bond restrains show that the delocalization of positive char ge does not involve the entire pyridine fragment and occurs along the triad N-C-O, whereas the negative charge is localized on the carbon atom.