Journal of Applied Crystallography

Volume 40, Part 6 (December 2007)

research papers

J. Appl. Cryst. (2007). 40, 1039-1043 [ doi:10.1107/S0021889807048236 ]

Temperature dependence of the crystal structure of -AgSCN by powder neutron diffraction

D. J. Williams, L. L. Daemen, S. C. Vogel and Th. Proffen

Abstract: A structural study of [alpha] -AgSCN was carried out using the neutron powder diffractometer HIPPO (high-pressure preferred orientation powder) at ten different temperatures between 25 and 275 K. The structure of [alpha] -AgSCN was refined using the Rietveld method and the symmetry elements for the material were found to be: space group No. 15, C2/c, a = 8.7210 (8) Å, b = 7.9318 (8) Å, c = 12.3329 (5) Å, [beta] = 138.750 (3)°, volume = 562.497 (9) Å³ and Z = 8. The Ag⁺ cation has tetrahedral coordination and is surrounded by three -SCN thiocyanate ligands and one isothiocyanate -NCS ligand down to 25 K, with no structural changes. The bond lengths at 275 K are Ag-S1 = 2.749 (10), Ag-S2 = 2.995 (11), Ag-S3 = 2.411 (11), Ag-N = 2.150 (5), S-C = 1.783 (11) and C-N = 1.1447 (35) Å. The bond lengths at 25 K are Ag-S1 = 2.782 (5), Ag-S2 = 2.941 (5), Ag-S3 = 2.431 (5), Ag-N = 2.1526 (26), S-C = 1.749 (5) and C-N = 1.140 (2) Å.

Keywords: silver thiocyanate; disorder; order; thermal expansion; pseudohalides.