CRYSTAL STRUCTURE OF BENZENE-2 AT 25-KILOBARS

Crystals of a high-pressure form of benzene (benzene II) were grown in the diamond-anvil pressure cell at elevated temperature and pressure from the transition of solid I to solid II. X-ray precession data were obtained from a single-crystal in the high-pressure cell. At 21°C and about 25 kilobars, benzene II crystallizes in the monoclinic system with a = 5.477±0.005 angstroms (S.D.), b = 5.376±0.079 angstroms, c = 7.532±0.007 angstroms, β = 110.00°±0.08°, space group P21/c, pc = 1.26 grams per cubic centimeter. The crystal structure was solved by generating all possible molecular packing configurations and calculating structure factors, reliability factors, and packing energies for each configuration. This procedure produced a unique solution for the molecular packing of benzene II.