American Chemical Society
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Lanthanide Complexes of 3-Diphenylamino-4-hydroxycyclobut-3-ene-1,2-dione (Diphenylaminosquarate)

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posted on 1999-07-30, 00:00 authored by Bert D. Alleyne, Leonard St. Bernard, Hema Jaggernauth, Lincoln A. Hall, Ian Baxter, Andrew J. P. White, David J. Williams
Complexation of the ligand 3-diphenylamino-4-hydroxycyclobut-3-ene-1,2-dione (diphenylaminosquarate) with metal salts of La, Eu, Gd and Tb produced the first set of lanthanide complexes with a monosubstituted aminosquarate ligand. The lanthanum complex La[(C6H5)2NC4O3]3(H2O)6·5H2O (1) is monomeric and crystallizes in the triclinic space group P1̄, with a nine-coordinate La center bonded to three pendant diphenylaminosquarate groups and six aqua ligands. The Eu, Gd, and Tb complexes [M(μ-(C6H5)2NC4O3)((C6H5)2NC4O3)(NO3)(OH2)4]2·4H2O (24) are isomorphous (also P1̄), each metal atom being nine-coordinate and bridged to its neighbor by two diphenylaminosquarate ligands in a μ-1,2- fashion; the coordination polyhedron around each metal is completed by a pendant diphenylaminosquarate ligand, four aqua ligands, and a chelating nitrate ion. The resistance of the diphenylamino substituent to hydrolysis, vis-à-vis the hydrolysis of dialkylamino substituents, is discussed.