The crystal structures of m-xylene and p-xylene, C₈D₁₀, at 4.5 K

The crystal structures of perdeuterated m-xylene, space group Pbca, a = 10.1550(1), b = 7.4649(1), c = 16.8814(1) Å, V = 1279.72(2) ų, Z = 8, ρ(calc) = 1.1021(1) g cm^-3 and perdeuterated p-xylene, space group P2₁/n, a = 5.7337(1), b = 4.9485(1), c = 11.1385(1) Å, β = 100.7130(1)°, V = 310.52(2) ų, Z = 2, ρ(calc) = 1.2431(1) g cm^-3 at 4.5 K have been refined against high-resolution neutron powder diffraction data. The previously unknown structure of m-xylene was solved from the neutron powder diffraction data utilising a simulated annealing method and verified by a conventional Direct Methods solution using X-ray single crystal data. The inter-molecular contacts determined in the structures of the meta and para compounds are closely related. (C) 2000 Elsevier Science B.V.