NOVEL ALKALI-METAL COORDINATION IN PHENOXIDES - POWDER DIFFRACTION RESULTS ON C6H5OM (M=LI, NA, K, RB, CS)

We report the ab initio structure solutions of C6H5OM (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 Angstrom) 14.1003(1), 17.9121(1) , and 7.16475(1) for the K compound, 14.4166(2), 18.2028(2), and 7.400 9(1) for the Rb compound, and 14.8448(2), 18.5070(2), and 7.6306(1) fo r the Cs compound. They have a chain structure (1)(infinity)[(MM2O3[2] )-M-[6]-O-[3]] along the crystallographic c axis. This is a very unusu al arrangement in which two different alkali-metal coordination sphere s are observed: a distorted octahedron and a 3-fold oxygen coordinatio n. Tn the latter, the 3-fold-coordinated unsaturated alkali metals add itionally show weak interactions with phenyl rings. We also give powde r patterns for the compounds with M = Li, Na. The former crystallizes in the monoclinic space group P2(1)/a with lattice parameters a = 22.5 94 Angstrom, b = 4.7459 Angstrom, c = 10.053 Angstrom, and beta = 97.8 2 degrees with Z = 8, but no structure solution was possible. The powd er pattern for the Na phenolate is in agreement with the earlier singl e-crystal structure.