Ln[(μ2-H)(H-mpdc)2](H-mpdc)2: Lanthanide infinite architectures with symmetric OHO hydrogen bonds (mpdc = 2,6-dimethylpyridine-3,5-dicarboxylate)

Three isostructural lanthanide coordination polymers LnIII[(μ2-H)(H-mpdc)2](H-mpdc)2, (mpdc=2,6-dimethylpyridine-3,5-dicarboxylate, Ln=Nd(1), Eu(2) and Ce(3)) were synthesized from lanthanide nitrates and H2dmpdc under solvothermal conditions. H2dmpdc is a new multifunctional ligand. Of particular interest is that there are the strongest types of OHO hydrogen bonds with a symmetric character (O⋯O, 2.487–2.493Å; OH, 1.247–1.257Å and OHO, 165–180°) in these polymeric compounds revealed by X-ray crystal diffraction analyses. The symmetric OHO hydrogen bonding in infinite polymeric architectures provides a new proof of proton transfer. Moreover, 3-D supramolecular architectures were self-assembled from 2-D grids with symmetric OHO hydrogen bonds.