AsCl3:: From the crystalline to the liquid state.: XRD (176<T (K)<250) and WAXS (295 k) studies

This paper presents structural studies on crystalline and liquid AsCl3, performed using X-ray diffraction (XRD) and wide-angle X-ray scattering (WAXS) in the 176-250 K temperature range and at 295 K for the crystalline and liquid samples, respectively. The XRD results, collected using a single-crystal diffractometer, show that AsCl3 crystallizes in the orthorhombic system with P2(1)2(1)2(1) space group and the unit cell parameters a = 9.475(3) Angstrom, b = 11.331(2) Angstrom, and c = 4.2964(8) Angstrom at 221 K. This structure is stable in the temperature range 176-243 K. Above the melting point, at 257 K, transition to the liquid state is observed. The WAXS data were recorded up to a maximum scattering vector K-max = 16 Angstrom(-1) and then converted to real space by the sine Fourier transform, yielding to the reduced radial distribution function (RRDF). For a series of models, based on the crystalline AsCl3 structure, the intensity and RRDF functions have been computed and compared with the experimental data. These simulations indicate that the model consisting of six AsCl3 molecules, arranged along the gamma axis, accounts satisfactorily for the experimental observation. The results of the structure analysis in both crystalline and liquid states are discussed in relation to the influence of the As lone electron pair.