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–.
A post-functionalization protocol was used for the synthesis of two new tris-hybrid Al-centred Anderson-type polyoxomolybdates with indometacin or cinnamic acid.
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