Luminescent dimeric polyoxotungstate [Ho(C4H2O6)(α-PW11O39)]216- with magnetism and reversible photochromism

A new organic-inorganic hybrid dimeric phosphotungstate, [N(CH3)(4)](6)K3H7[Ho(C4H2O6)(alpha-PW11O39)](2)center dot 27H(2)O (1), was obtained by the reaction of [P2W19O69(H2O)](14-) precursor with Ho3+ ions in the tartaric acid aqueous medium, which was characterized by IR spectrum, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDX), elemental analyses, Uv-Vis spectroscopy and single-crystal X-ray diffraction. The polyanion [Ho(C4H2O6)(alpha-PW11O39)](2)(16-) contains two mono-Ho substituted Keggin-type fragments linked together by two tartaric acid groups. This photoreactive compound exhibits reversible photochromism which can change from light pink to blue upon UV irradiation. The solid-state photoluminescence spectra of 1 at room temperature displays the characteristic Ho3+ ions emission patterns of S-5(2)/F-5(4)-> I-5(8) and F-5(5)-> I-5(8). Simultaneously, the CIE chromaticity diagram has been acquired according to corresponding emission spectra of 1.