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 (2−4) 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.

The synthesis and characterization by single-crystal X-ray crystallography of a series of monomeric first-row transition-metal complexes with the 1-methoxycyclobutenedionate(1-) ligand are described. The isomorphous compounds [M(CH(3)OC(4)O(3))(2)(H(2)O)(4)] (M = Mn, Co, Ni, Zn) are C(2) symmetric and crystallize in the monoclinic space group C2/c. The metal atom in each of these complexes is six-coordinate with two cis 1-methoxycyclobutenedionate(1-) ligands, the methoxy substituent being oriented cis with respect to the ligating oxygen atom. The remaining coordination sites are filled by four aqua ligands. Monomers are linked by O-H.O hydrogen bonds to form arrays of stepped tapes. Hydrolysis of the methoxy group on the ligand occurs during the formation of the copper complex and {[Cu(C(4)O(4))(H(2)O)(2)].0.25H(2)O}(n)() is produced. This complex crystallizes in the tetragonal space group P4/n and has a structure similar to, but differing significantly from, those of a series of 3-dimensional cage squarates which have been reported previously.

Reaction of 1-methylcyclobutenedione with M(NO 3 ) 2 ‚xH 2 O [M ) Co (1) and Ni (2)] produces isomorphous polymeric complexes of formula M(CH 3 C 4 O 3 )(NO 3 )(H 2 O) 4 ‚2H 2 O that crystallize in the monoclinic space group P2 1 /m (No. 11) with, for 1, a ) 6.409(5) Å, b ) 14.717(10) Å, c ) 7.259(6) Å, ) 114.73(4)°, and Z ) 2 (the metal atom being positioned on a center of symmetry). In both cases, adjacent metal centers are bridged µ-1,3 by the 1-methylcyclobutenedione ligand, which exhibits distinct multiple bond localization. The positive charges on the polymer chains are in each case balanced by nitrate ions. The metal atoms are six-coordinate with transoriented 1-methylcyclobutenedione ligands, and with four aqua ligands completing the coordination sphere. Reduction of the crystallization temperature, however, resulted, with Co, in the formation of the monomeric complex Co(CH 3 C 4 O 3 ) 2 ‚4H 2 O (4). Isomorphous Mn (3), Cu (5), and Zn (6) analogues have also been synthesized. These crystallize in the monoclinic space group P2 1 /n (No. 14) with, for 3, a ) 8.8258(8) Å, b ) 16.1527 (14) Å, c ) 9.9084(8) Å, ) 93.230(7)°, and Z ) 4. The central metal atom in each of these compounds is sixcoordinate, being bound to two trans-oriented 1-methylcyclobutenedione ligands and four aqua ligands, the former coordinating in a monodentate fashion via the oxygen atom trans to the methyl substituent. In both the polymeric and monomeric complexes extensive three-dimensional hydrogen-bonded networks are formed in the solid state.

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