Syntheses, crystal structure, electrochemistry and luminescence properties of lanthano–germanotungstates

Abstract

A series of sandwich-type early lanthanoid substituted complexes: [Ln(α-GeW₁₁O₃₉)₂]¹³⁻ [Ln = La^III (La-1) and Ce^III (Ce-2)] and acetate-bridged hybrid dimeric complexes: [{Ln(μ-CH₃COO)GeW₁₁O₃₉(H₂O)}₂]¹²⁻ [Ln = Pr^III (Pr-3), Nd^III (Nd-4) and Sm^III (Sm-5)] were synthesized by the interaction of a trilacunary Na₁₀[GeW₉O₃₄]·18H₂O precursor with Ln(NO₃)₃·nH₂O in a potassium acetate buffer at pH 4.7. All these compounds were isolated as mixed sodium/potassium salts and structurally characterised by various analytical techniques such as single-crystal X-ray diffraction, FT-IR, ICP-AES, UV/vis, photoluminescence spectroscopy, thermogravimetric analysis, ¹³C and ¹H NMR spectroscopy, magnetism and electrochemistry. The FT-IR spectra suggest that compounds (La-1a and Ce-2a) and (Pr-3a–Sm-5a) are isomorphous. We also synthesized analogous acetate-bridged dimeric complexes (Pr-3a to Sm-5a) with mid and late lanthanoid ions (Ln = Eu^III, Gd^III, Tb^III, Dy^III, Ho^III, Er^III, Tm^III and Yb^III) using a procedure published elsewhere and also investigated other features such as electrochemistry and magnetic and photochromic properties. The molecular complexes Pr-3a, Sm-5a, Eu-6a, Tb-8a, Dy-9a, Ho-10a, Er-11a and Tm-12a show good photochromic behaviour at room temperature. Magnetic studies of La-1a, Ce-2a, Pr-3a, Nd-4a and Sm-5a were performed at room temperature and the molecular complexes were found to exhibit ferromagnetic behaviour.