y 2-Picolinate-Decorated Iron-Lanthanide Heterometallic Germanotungstates Including an S-Shaped [Ge2W20O72](16-) Segment

摘要

A series of neoteric 2-picolinate (pic)-decorated iron-lanthanide (Ln)-embedded germanotungstates (GTs), [Ln(III)(H2O)(8)](2)H-2[Fe-4(H2O)(4)v(pic)(4)Ge2W20O72]center dot 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)](2)H-2[Fe-4(H2O)(4)(pic)(4)Ge2W20O72]center dot 36H(2)O (10; Hpic = picolinic acid), were hydrothermally prepared. The polyoxoanions of 110 possess a quadri-Fe-III-inserted [Fe-4(H2O)(4)(pic)(4)Ge2W20O72](8-) subunit with bisupporting [Ln(H2O)(8)](3+) cations. The quadri-Fe-III-inserted [Fe-4(H2O)(4) (pic)(4)Ge2W20O72](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 Ln(3+) 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.