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

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[(C 6 H 5 ) 2 NC 4 O 3 ] 3 (H 2 O) 6 ·5H 2 O ( 1 ) is monomeric and crystallizes in the triclinic space group P 1̄, with a nine-coordinate La center bonded to three pendant diphenylaminosquarate groups and six aqua ligands. The Eu, Gd, and Tb complexes [M(μ-(C 6 H 5 ) 2 NC 4 O 3 )((C 6 H 5 ) 2 NC 4 O 3 )(NO 3 )(OH 2 ) 4 ] 2 ·4H 2 O ( 2 − 4 ) are isomorphous (also P 1̄), 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.