A new family of 3D 3d–4f heterometallic frameworks comprising 1D inorganic lanthanide ladders and organic CuI-bipyridine chains

Abstract

A new family of the 3D heterometallic coordination polymers [{Ln₂(SO₄)₂(H₂O)₂(pydc)₂Cu₂ (bpy)₂·2(H₂O)}]_n (Ln = Sm (1), Eu (2), Gd (3), Tb (4) and Dy (5); pydc = 2,6-pyridine-dicarboxylate anion; bpy= 4,4′-bipyridine) have successfully been synthesized under solvothermal conditions (H₂O/ethanol). All the coordination polymers obtained were characterized by elemental analysis, FT-IR analysis, differential thermal analysis/thermogravimetry (DTA/TG), fluorescent spectra and single crystal X-ray diffraction analysis. The most intriguing structural feature is that all the compounds exhibit 3D frameworks with 1D inorganic lanthanide ladders and organic Cu^I-bipyridine chains, which represent two types of 3d/4f coordination polymers (form I: Ln = Sm and Eu; form II: Ln = Gd, Tb and Dy) as the result of a so-called “gadolinium break effect”. Additionally, compounds 2 and 4 showed the characteristic emission spectra of the Eu^III and Tb^III ions, respectively, and appeared to have good fluorescence properties, while 1, 3 and 5 emitted fluorescence resembling Cu^I complexes. To our knowledge, the investigation of the effect of mixed ligands on the assembly of Ln^III-Cu^I metal-based polymers has not been reported so far.