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

Abstract

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–.

Polyoxometalates in solution: speciation under spotlight

“…262 All these examples show the importance of speciation analysis in physiological systems in the presence of biomacromolecules. The double-side trisfunctionalized [Cr III ((OCH 2 ) 3 CC 2 H 5 ) 2 W VI 6 O 18 ] 3À is a predominant species in neutral pH between 5.7 and 7 almost without decomposition fragments, which was shown by ESI-MS. 265…”

Synthesis and characterization of the Anderson–Evans tungstoantimonate [Na5(H2O)18{(HOCH2)2CHNH3}2][SbW6O24]

“…Ni II or Co II ) (Blazevic & Rompel, 2016). The third group, called 'mixed type', is a combination of the two types mentioned above, as it has protonated 3 -O ions only on one side (Gumerova et al, 2019). Therefore, it is referred to as one-side protonated with one known polyoxotungstate example, [Cr III (OH) 3 W VI 6 O 21 ] 6-, so far (Gumerova et al, 2019).…”

“…The third group, called 'mixed type', is a combination of the two types mentioned above, as it has protonated 3 -O ions only on one side (Gumerova et al, 2019). Therefore, it is referred to as one-side protonated with one known polyoxotungstate example, [Cr III (OH) 3 W VI 6 O 21 ] 6-, so far (Gumerova et al, 2019). Interestingly, there are some platinum-based compounds, with the general formula [H n Pt IV M VI 6 O 24 ] (8-n)À (M = W or Mo, where 1 < n < 6; Lee et al, 2004), which exhibit protonation degrees of their 3 -O ions ranging from 1 to 6 and n is not necessarily an integer.…”

The Smallest Polyoxotungstate Retained by TRIS-Stabilization

“…Tris­(hydroxymethyl)­aminomethane ((HOCH 2 ) 3 CNH 2 , TRIS) has been recently utilized to stabilize and isolate elusive heptavanadate . While in biochemistry, TRIS (p K a 8.06) is used as pH buffer between 7.0 and 9.2, in POM chemistry, TRIS is usually used for covalent organic functionalization via alkoxo-groups −CH 2 OH attachment to the POM, − and −NH 2 plays the key role for postfunctionalization through amide bond formation. − Recently, we expanded the role of TRIS by showing that TRIS, as part of a buffer solution that is normally considered unimportant, plays a defining role in the formation of a new member of the Keggin family . In POM chemistry, TRIS has never acted as a primary amine by replacing oxo-ligands and thus as a protective ligand to prevent the formation of POTs with a higher nuclearity.…”