Amine-templated polymeric lanthanide formates: synthesis, characterization and applications in luminescence and magnetism.

The novel polymeric formates of general formula [(Fmd)LnIII(HCOO)4]n (Fmd+ = NH2-CH+-NH2; Ln = Eu (1), Gd (2), Tb (3), Dy (4)] were synthesized through solvothermal methods in formamide solutions. The compounds are isotructural; they crystallize in the orthorhombic C2221 chiral space group. The coordination geometry at the metal centers is square anti-prismatic (coordination number eight), with each formate ligand bridging adjacent lanthanide ions. The overall negative 3D framework charge is balanced by the formamidinium cations sitting inside the channels along the a axis, forming extensive N-H---O hydrogen bonding with the surrounding cage. All the compounds have been characterized through single-crystal / powder X-ray diffraction, IR spectroscopy and TG-MS analysis. Finally, their luminescence and magnetic properties have been assessed, leading to remarkable emission intensities, especially for the Tb(III) compound (phi = 0.83), with corresponding lifetime decays in the micro (Dy) and millisecond (Tb, Eu) timescale. A weak but sizeable antiferromagnetic interaction has been observed for the Gd(III) derivative.