The crystal structure of γ-P4, a low temperature modification of white phosphorus

Abstract

Abstract The crystal structure of γ-P4, one of three modifications hitherto reported on white phosphorus, was determined from X-ray powder diffraction data collected at T = 123 K on a Guinier-Simon camera equipped with a cold gas blower and an image plate detector. Crystallographic data at T = 123 K are: space group C2/m, a = 9.1709(5) Å, b = 8.3385(5) Å, c = 5.4336(2) Å, and β = 90.311(3)°, V = 415.51(6) Å3, Z = 4. The crystal structure of γ-P4 was solved by the method of simulated annealing. The subsequent Rietveld refinement in the range 12° < 2θ < 92° employing rigid-body constraints on the P4 molecule converged at Rp = 3.8, wRp = 5.0, and RF 2 = 14.0%. The asymmetric unit of γ-P4 contains three P atoms; two P atoms in a molecule are related by a mirror plane which bisects the molecule. The centers of gravity of these P4 molecules show a distorted body-centered cubic arrangement. The four apices of the P4 tetrahedron point to the largest possible voids formed by neighbor molecules. The difference to the crystal structures of SiF4 and GeF4 with an exact bcc arrangement of tetrahedral molecules is discussed as well as, in terms of layer stackings, the similarity of the structures of γ- and β-P4.