Direct Single- and Double-Side Triol-Functionalization of the Mixed Type Anderson Polyoxotungstate [Cr(OH)₃W₆O₂₁]⁶

Since the first successful triol-functionalization of the Anderson polyoxometalates, the six protons of their central octahedron X(OH)₆ (X-heteroatom, p- or d-element) have been considered as a prerequisite for their functionalization with tripodal alcohols, and therefore, the functionalization of Anderson structures from the unprotonated sides have never been reported. Here, we describe the triol-functionalization of [Cr(OH)₃W₆O₂₁]^6- leading to the single-side grafted anions [Cr(OCH₂)₃CRW₆O₂₁]^6- (CrW₆-tris-R, R = -C₂H₅, -NH₂, -CH₂OH) and the unprecedented double-side functionalized anion [Cr((OCH₂)₃CC₂H₅)₂W₆O₁₈]^3- (CrW₆-(tris-C₂H₅)₂), despite the lack of protons in the parent anion in the solid state. CrW₆-(tris-C₂H₅)₂ demonstrates the first example of double-side functionalized Anderson POT with the partially one-side protonated corresponding parent anion. The new heteropolytungstates were characterized by single-crystal X-ray diffraction, elemental analysis, Fourier-transform infrared spectroscopy, thermal gravimetric analysis, cyclic voltammetry, and electrospray ionization mass spectrometry. Density functional theory calculations were performed to investigate and compare the stability among the different isomers of the parent anion [Cr(OH)₃W₆O₂₁]^6-.