The Solid State Structures of Potassium and Rubidium Salicylate by High Resolution X-Ray Powder Diffraction

We report the ab initio structure solution of rubidiumsalicylate C₇H₅O₃Rb and the crystal packing of potassium-salicylate C₇H₅O₃K by high resolution X-ray powder diffraction. The compounds are of interest for the understanding of the mechanism of Kolbe-Schmitt type reactions. C₇H₅O₃Rb (I) crystallizes in space group P2₁/n, Z = 4, with unit cell parameters a = 7.2110(1) Å, b = 26.5258(3) Å, c = 4.23110(6) Å, β = 106.843(1)?, and V = 774.60(2) ų. C₇H₅O₃K (II) crystallizes in space group P&1macr;, Z = 2, with unit cell parameters a = 7.3575(2), b = 13.6399(3), c = 3.8622(1) Å, α = 95.955(4)?, β = 103.326(2)?, γ = 92.994(4)?, and V = 373.95(2) ų. Both compounds exhibit similar crystal packing schemes and consist of layers of distorted RbO₈ resp. KO₇ polyhedra perpendicular to the b-axis and phenol rings almost perpendicular to the layers pointing up and down. The molecular structure is held together by van der Waals forces between the phenyl groups of different layers. The sample of C₇H₅O₃K shows extremely anisotropic peak broadening and stacking faults which could not be satisfactory modeled by the available models.