A Family of Flexible Lanthanide Bipyridinedicarboxylate Metal–Organic Frameworks Showing Reversible Single-Crystal to Single-Crystal Transformations

A family of flexible lanthanide metal–organic frameworks, [Ln2(bpydc)3(H2O)3]·nDMF (denoted as SUMOF-6-Ln; Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er, H2bpydc =2,2′-bipyridine-5,5′-dicarboxylic acid), was synthesized and characterized. SUMOF-6-Ln has a monoclinic space group P21/c. The three-dimensional framework contains chains of LnOn (n = 7–8) polyhedra connected through the bpydc linkers forming 1D rhombic channels along the c-axis. SUMOF-6-Ln showed reversible breathing phenomenon upon desorption/adsorption of the solvent, with up to 27% changes of the unit cell dimensions and 23% changes of the unit cell volume. Single crystal X-ray diffraction (XRD) revealed that the desolvation and resolvation of SUMOF-6-Ln occurred via single-crystal to single-crystal transformations. The thermal behavior of SUMOF-6-Sm was also examined. SUMOF-6-Eu and SUMOF-6-Tb showed solid-state luminescent properties.