X-Ray Diffraction Study of the Low Temperature Phase of Rubidium Cyanide

Abstract

Crystal structure of RbCN has been investigated on single crystals by X-ray precession photographic method at temperatures ranging from 300 to 85, K. At about 125, K, the crystal transforms from the cubic NaCl-type phase into a low-temperature phase in which a monoclinic and a triclinic forms coexist. Both the forms are related with the specific crystallographic orientation to the cubic lattice. The lattice constants of the monoclinic form are a_M=4.81(1), b_M=4.87(1), c_M=7.92(1), Å, β =122.7(1)° at 85, K, and the structure is A-base-centered with the space group A2/m. The lattice constants of the triclinic form are a_T=9.79(1), b_T=4.62(1), c_T=4.88(1), Å, α =121.1(1)°, β =119.4(1)°, γ =90.0(1)° at 85, K. Crystallographic relationships between these forms and the cubic form are presented. The results are compared with the findings in the related compound KCN.