Syntheses and Structures of Two Series of Coordination Frameworks Based on the Assembly of 1,3,5-Benzenetriacetic Acid with Lanthanide Metal Salts

Two novel series of coordination frameworks [Ln(bta)(H2O)2]·nH2O·mEtOH (Ln = La 1a, n = 4.5, m
= 0; Ln = Ce 1b, n = 4, m = 0; Ln = Pr 1c, n = 2.88, m = 0.35) and [Ln2(bta)2(H2O)3]·nH2O (Ln = La 2a, n = 2.14;
Ln = Ce 2b, Pr 2c, n = 2) were synthesized by the reaction of 1,3,5-benzenetriacetic acid (H3bta) with the
corresponding lanthanide salts using different methods. X-ray diffraction analyses reveal that all six complexes
have 3D channel structures, but in the first series of complexes, each bta3- ligand adopts a cis, trans, trans
conformation and acts as a μ5-bridge linking five lanthanide atoms, while in the second series, the bta3- ligands
adopt cis, trans, trans and cis, cis, cis conformations and act as μ6- and μ5-bridges, respectively. Thus two series of
complexes have the same metal atoms and ligands but different structures. The results show that the flexible triacid
ligand is versatile and can adopt different conformations according to different reaction conditions. The variable-temperature magnetic susceptibility measurements of complexes 1c and 2c showed that both complexes exhibit
antiferromagnetic interactions between the Pr(III) ions.