Synthesis, crystal structures and magnetic behavior of polymeric lanthanide complexes with benzenehexacarboxylic acid (mellitic acid)

Three lanthanide complexes with mellitic acid, [Ce-2{C-6(COO)(6)}(H2O)(8)]. H2O (1), [Eu-2{C-6(COO)(6)}(H2O)(8)]. H2O (2) and [Yb-2{C-6(COO)(6)}(H2O)(10)]. 2H(2)O (3), have been synthesized and structurally characterized by X-ray crystallography and magnetic properties. The three compounds crystallize in the monoclinic space group P2(1)/n, with unit cell, dimensions of: a = 8.627(2), b = 13.218(2), c = 9.650(1) Angstrom, beta = 95.93(1)degrees and Z = 2 for 1; a = 8.505(2), b = 13.145(1), c = 9.536(2) Angstrom, beta = 94.73(2)degrees and Z = 2 for 2; a = 8.420(1), b = 9.224(4), c = 16.229(1) Angstrom, beta = 100.267(9)degrees and Z = 2 for 3. All three structures consist of an extended network of metal ions, coordinated to mellitate anions and water molecules linked by a complex hydrogen bonding. 1 and 2 are isomorphous with near isostructural [M(2){C-6(COO)6}(H2O)(8)] units in which the metal ion is coordinated by four water molecules and five oxygen atoms of the mellitate anions, and each mellitate group involves a tetrakis(bidentate) and bis(unidentate) coordination mode bridging six metal ions forming a threedimensional framework. In 3 the ytterbium atom is bound with five water molecules and three oxygen atoms of the mellitate anion, and each mellitate moiety bridges four dodecahedral Yb(III) ions yielding a two-dimensional sheet structure. The magnetic susceptibility of 1 and 3 as a function of temperature (5.0-300 K) exhibits a sharp maximum at 6.0 K for both compounds.