Novel Alkali-Metal Coordination in Phenoxides: Powder Diffraction Results on C(6)H(5)OM (M = Li, Na, K, Rb, Cs)

We report the ab initio structure solutions of C(6)H(5)OM (M = K, Rb, Cs) by high-resolution powder X-ray diffraction. The compounds, which are of interest for reactions of the Kolbe-Schmitt type, are isostructural. The crystal structures are orthorhombic, space group Pna2(1), Z = 12, with lattice parameters (a, b, c in Å) 14.1003(1), 17.9121(1), and 7.16475(1) for the K compound, 14.4166(2), 18.2028(2), and 7.4009(1) for the Rb compound, and 14.8448(2), 18.5070(2), and 7.6306(1) for the Cs compound. They have a chain structure [M([6])] along the crystallographic c axis. This is a very unusual arrangement in which two different alkali-metal coordination spheres are observed: a distorted octahedron and a 3-fold oxygen coordination. In the latter, the 3-fold-coordinated unsaturated alkali metals additionally show weak interactions with phenyl rings. We also give powder patterns for the compounds with M = Li, Na. The former crystallizes in the monoclinic space group P2(1)/a with lattice parameters a = 22.594 Å, b = 4.7459 Å, c= 10.053 Å, and beta = 97.82 degrees with Z = 8, but no structure solution was possible. The powder pattern for the Na phenolate is in agreement with the earlier single-crystal structure.