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2‑Picolinate-Decorated Iron–Lanthanide Heterometallic Germanotungstates Including an S‑Shaped [Ge2W20O72]16– Segment

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journal contribution
posted on 14.11.2019, 16:42 by Jun Jiang, Yanhong Chen, Lulu Liu, Lijuan Chen, Junwei Zhao
A series of neoteric 2-picolinate (pic)-decorated iron–lanthanide (Ln)-embedded germanotungstates (GTs), [LnIII(H2O)8]2H2­[Fe4­(H2O)4v­(pic)4­Ge2­W20­O72]·34 H2O [Ln = La (1), Ce (2), Nd (3), Sm (4), Gd (5), Tb (6), Dy (7), Er (8), Tm (9)] and [Eu­(H2O)8]2H2[Fe4(H2O)4(pic)4Ge2W20O72]·36H2O (10; Hpic = picolinic acid), were hydrothermally prepared. The polyoxoanions of 110 possess a quadri-FeIII-inserted [Fe4(H2O)4(pic)4Ge2W20O72]8– subunit with bisupporting [Ln­(H2O)8]3+ cations. The quadri-FeIII-inserted [Fe4(H2O)4 (pic)4Ge2W20O72]8– subunit can be described as a particular S-shaped [Ge2W20O72]16– segment functionalized by four [Fe­(H2O)­(pic)]2+ cations. It should be pointed out that the carboxyl O and pyridine N atoms on pic ligands simultaneously coordinate with Fe3+ cations in a five-membered heterocyclic mode, which can enhance the stability of the structures. Moreover, fluorescent measurements of 3, 4, 6, and 10 were made, manifesting that fluorescent emissions primarily stem from Ln3+ ions. With regard to 10, energy transfer (ET) from GT and pic groups to Eu3+ centers was intensively studied. In addition, the magnetic susceptibility properties of 7 and 10 were studied.