A series of three-dimensional architectures constructed from lanthanide-substituted polyoxometalosilicates and lanthanide cations or lanthanide–organic complexes as linkers

Abstract

Six 3D architectures based on lanthanide-substituted polyoxometalosilicates, KLn[(H₂O)₆Ln]₂[(H₂O)₄LnSiW₁₁O₃₉]₂·nH₂O (Ln = La 1, n = 42; Ce 2, n = 40), H[(H₂O)₆Nd]₂[(H₂O)₇Nd][(H₂O)₄NdSiW₁₁O₃₉][(H₂O)₃NdSiW₁₁O₃₉]·13H₂O (3), H₂K₂[(Hpic)(H₂O)₅Ln]₂[(H₂O)₄LnSiW₁₁O₃₉]₂·nH₂O (Ln = La 4, n = 18.5; Ce 5, n = 35; Nd 6, n = 36; Hpic = 4-picolinic acid), have been synthesized and characterized by elemental analysis, IR and UV-vis spectroscopy, TG analysis, powder X-ray diffraction and single crystal X-ray diffraction. Compounds 1 and 2 are isostructural, built up of lanthanide-substituted polyoxoanions [{(H₂O)₄Ln(SiW₁₁O₃₉)}₂]¹⁰⁻ linked by Ln³⁺ cations to form a 3D open framework with 1D channels. The polyoxoanion [{(H₂O)₄Ln(SiW₁₁O₃₉)}₂]¹⁰⁻ consists of two α₁-type mono-Ln-substituted Keggin anions. When Nd³⁺ ion was used instead of La³⁺ or Ce³⁺ ions, compound 3 with a different structure was obtained, containing two kinds of polyoxoanions [{(H₂O)₄Nd(SiW₁₁O₃₉)}₂]¹⁰⁻ and [{(H₂O)₃Nd(SiW₁₁O₃₉)}₂]¹⁰⁻ which are connected together by Nd³⁺ ions to yield a 3D framework. When 4-picolinic acid was added to the reaction system of 1–3, isostructural compounds 4–6 were obtained, constructed from the polyoxoanions [{(H₂O)₄Ln(SiW₁₁O₃₉)}₂]¹⁰⁻ linked by picolinate-chelated lanthanide centers to form a 3D channel framework. From a topological viewpoint, the 3D nets of 1, 2, 4, 5 and 6 exhibit a (3,6)-connected rutile topology, whereas the 3D structure of 3 possesses a rare (3,3,6,10)-connected topology. The magnetic properties of 2, 3, 5 and 6 have been studied by measuring their magnetic susceptibilities in the temperature range 2–300 K.