First lanthanide coordination polymers with N,N-dimethylformamide hydrolysis induced formate ligands

A series of isostructural lanthanide organic frameworks with composition [Ln(tpa)(fa)] (Ln = Eu, Gd, Tb; H2tpa = terephthalic acid, i.e. 1,4-benzenedicarboxylic acid; Hfa = formic acid, i.e. methanoic acid) has been synthesized through reaction of the corresponding lanthanide nitrates with H2tpa in DMF/H2O mixed solvent under solvothermal conditions (DMF = N,N-dimethylformamide). The formate ligand is in situ generated by hydrolysis of DMF. The dilanthanide-diformate subunits build two-dimensional layers which are shored up by terephthalates, leading to a three-dimensional pillar-layer network. These are the first examples of lanthanide complexes containing the formate ligand originated from hydrolysis of DMF. The dilanthanide-diformate subunit is also the first ever reported. The Eu and Tb complexes emit strong ligand sensitized f–f luminescence. Temperature variable magnetic susceptibility analysis reveals that the Gd(III) atoms are antiferromagnetically coupled (J = −0.0048 cm−1, Ĥ = −2JŜGd1·ŜGd2).