Template-assisted self-assembly: Synthesis, structures, and magnetic properties of lanthanide(III)-cobalt(II) coordination complexes constructed with deprotonated 3,5-pyridinedicarboxylic acid ligand

Two new 3d-4f complexes, [LnCo(3,5-pdc)2(3,5-Hpdc) (H2O)7]·H2O (Ln = Gd 2, La 3; 3,5-pdcH2 = pyridine-3,5-dicarboxylic acid), have been synthesized by the self-assembly of Ln(III) oxides, 3,5-pdcH2 and the template molecule [Co(3,5-pdc)(H2O)5]·H2O (1) under hydrothermal conditions. Heterometallic complexes 2 and 3 are isostructural with supracyclic units containing four Ln(III) ions and two Co(II) ions, in which Co(II) and Ln(III) are linked by the deprotonated 3,5-pdcH2 ligands in three kinds of bridging modes. The weak antiferromagnetic coupling of complex 2 and 3 imply that the large 3,5-pdc bridges with the greater separation ( > 7 Å) cannot lead to long range magnetic ordering, the strength of dn-fn exchange coupling increasing with decreases the size of the lanthanide ion.