Supramolecular nanotubes constructed from 3d–4f heterometallic sandwiched polyoxotungstate dimers

Abstract

By the hydrothermal technique, a series of organic–inorganic hybrid polyoxometalates (POMs) H_x(H₂en)_y [Fe₂Ln(β-PW₁₀O₃₇)₂(Tart)]·nH₂O (Ln = La³⁺, (x, y, n) = (5, 3, 9) for 1; Ln = Ce³⁺, (x, y, n) = (5, 3, 7) for 2; Ln = Sm³⁺, (x, y, n) = (3, 4, 25) for 3; Ln = Tb³⁺, (x, y, n) = (3, 4, 21) for 4; H₂Tart = tartaric acid) have been obtained and structurally characterized by elemental analyses, IR spectroscopy, thermogravimetric analyses and single-crystal X-ray diffraction. The common structural characteristics of 1–4 consist of a [Fe₂Ln(β-PW₁₀O₃₇)₂(Tart)]⁹⁻ unit, in which transition metal and lanthanide ions co-exist in the vacant site of divacant [β-PW₁₀O₃₇]⁹⁻ with the assistance of Tart ligands. It should be pointed out that 1–4 represent the first 3d–4f heterometallic cluster sandwiched phosphotungstate dimers, [Fe₂Ln(β-PW₁₀O₃₇)₂(Tart)]⁹⁻, linked by Fe–O–Ln–O–Fe bonds. Furthermore, 3 and 4 exist as rare supramolecular nanotubes built from the organic–inorganic hybrid 3d–4f POM units. Also, the photochromism and optical properties of 1–4 have been studied.