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)(3)W6O21](6-) leading to the single-side grafted anions [Cr(OCH2)(3)CRW6O21](6-)(CrW6-tris-R, R = -C2H5, -NH2, CH2OH) and the unprecedented double-side functionalized anion [Cr(OCH2)(3)CC2H5)(2)W6O18](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)(3)W6O21](6-).