| Abstract | Reactions between alumina and sodium hydroxide in ethylene glycol result in the formation of aluminoglycolate anions. 27Al NMR studies have been carried out to assist in their characterization, and aluminum species in tetra-, penta-, and hexacoordinate geometries have been detected. X-ray diffraction studies of crystalline products confirm the formation of pentacoordinate dianions; two crystalline forms of a 2:1 Na:Al complex have been isolated, containing different amounts of solvent molecules. The compound Na2Al(OCH2CH2O)2OCH 2CH2-OH·4HOCH2CH2OH (1) crystallizes in space group P1, with a = 8.062(2) Å, b = 8.660(2) Å, c = 17.257(3) Å; α = 99.78(3)°, β = 97.61(3)°, γ = 97.08(3)°, Z = 2 at 130 K; Na2Al(OCH2CH2O)2OCH 2CH2OH·5HOCH2CH2OH) (2) crystallizes in space group P1, with a = 8.479(3)°, b = 19.557(5)°, c = 16.641(5) Å; a = 90.48(3)°, β = 96.68(2)°, γ = 89.22(2)°, and Z = 4 at 291 K. A third complex isolated has a 1:1 Na:Al ratio and contains a trimeric aluminum species consisting of two pentacoordinate and one hexacoordinate aluminum geometries: Na3Al3(OCH2CH2O) 5(OCH2CH2OH)2.6HOCH 2CH2OH (3) crystallizes in space group P21/c, with a = 9.531(2) Å, b = 21.490(4) Å, c = 22.298(4) Å, β = 99.41(3)°, and Z = 4 at 130 K. The intermolecular binding in the three structures involves extensive hydrogen bonding between coordinated and free glycolate molecules coupled with close cation⋯O ionic contacts. The Al-O bond distance for the monobasic glycolates is significantly shorter than the fully coordinated bond distances (means 1.783(9), 1.846(28) Å), though ionic contacts also perturb the coordination geometries. © 1995 American Chemical Society. |
