Dimeric complexes of rare-earth substituted Keggin-type silicotungstates: syntheses, crystal structure and solid state properties

Abstract

A series of rare-earth substituted dimeric complexes of Keggin-type silicotungstates: [{Ln(α-SiW₁₁O₃₉)(H₂O)}₂(μ-CH₃COO)₂]¹²⁻ [Ln = Eu^III (Eu-1), Gd^III (Gd-2), Tb^III (Tb-3), Dy^III (Dy-4), Ho^III (Ho-5), Er^III (Er-6) and Tm^III (Tm-7)] and [Ln(α-SiW₁₁O₃₉)₂]¹³⁻ [Ln = Pr^III (Pr-8), Nd^III (Nd-9), Sm^III (Sm-10)] were synthesized by a single step reaction of Na₁₀[α-SiW₉O₃₄]·16H₂O with Ln(NO₃)₃·nH₂O in potassium acetate buffer at pH 4.5. All these compounds were structurally characterized by single-crystal X-ray diffraction, and other analytical techniques including FT-IR, ICP-AES, UV/vis, photoluminescence spectroscopy, thermogravimetric analysis, ¹³C and ¹H NMR spectroscopy and vibrating sample magnetometry (VSM). The single-crystal X-ray diffraction and FT-IR studies suggest that the compounds Na₄K₈[{Ln(α-SiW₁₁O₃₉)(H₂O)}2(μ-CH₃COO)₂]·xH₂O (Ln = Eu − Tm) (Eu-1a–Tm-7a), and K₆Na₇[Ln(SiW₁₁O₃₉)₂]·xH₂O (Ln = Pr, Nd, Sm) (Pr-8a–Sm-10a) are isostructural. The photoluminescence properties of Eu-1a, Tb-3a, Dy-4a and Sm-10a were studied at room temperature. VSM studies of Gd-2a, Tb-3a, Dy-4a, Ho-5a, Er-6a and Tm-7a were carried out at room temperature, and they showed paramagnetic behaviour.