Unprecedented ferromagnetic interaction in an erbium(III)–copper(II) coordination polymer

Two 3D Ln(III)–Cu(II) coordination polymers [Er2Cu3(pydc)6(H2O)6]n (1) and [Tb2Cu3(pydc)6(H2O)6]n (2) were hydrothermally prepared from pyridine-2,4-dicarboxylic acid (H2pydc) and characterized by single-crystal X-ray diffraction analysis. The magnetic studies show that an unexpected ferromagnetic interaction between metal centers exists in 1 while 2 behaves as an antiferromagnet.