CRYSTAL-STRUCTURE OF ((S)-MALATO)TETRAAQUAMAGNESIUM(II) HYDRATE - VERSATILITY OF (S)-MALATE-METAL ION BINDING

The crystal structure of ((S)-malato)tetraaquamagnesium(II) hydrate, [Mg(S-C4O5)(H2O)] -H2O, has been determined from three-dimensional single-crystal X-ray diffraction data collected by counter methods on a computer-automated diffractometer. The compound crystallizes in the orthorhombic space group D24-P212121 with unit cell dimensions a = 11.403 (9) A, b = 15.486 (10) Å, c = 5.954 (4) Å, and Z = 4. The structure was solved by direct methods and refined by a full-matrix least-squares procedure to a conventional R index of 0.081 for 1248 reflections. The bidentate (S)-malate ligand chelates the magnesium(II) ion with an α-carboxylate oxygen atom and the hydroxyl oxygen forming a planar five-membered chelate ring. The irregular octahedral coordination polyhedron around the metal ion is completed by four water molecules. The β-carboxylate group is not bound directly to Mg(II) which differs from (S)-malate binding observed in all other 1:1 metal (S)-malate compounds. However, the β-carboxylate group is indirectly attached to the Mg(II) in an outer-sphere fashion through an intramolecular hydrogen bond from a coordinated water molecule. The conformation of the (S)-malate ligand is synclinal, and the range in Mg-O bond lengths is 2.045 (5)-2.125 (5) Å. © 1979, American Chemical Society. All rights reserved.