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-.

Bonding Insights from Structural and Spectroscopic Comparisons of {SnW5 } and {TiW5 } Alkoxido- and Aryloxido-Substituted Lindqvist Polyoxometalates.

Incorporation of {MX}n+ groups into polyoxometalates (POMs) provides the means not only to introduce reactivity and functionality but also to tune the electronic properties of the oxide framework by varying M, X and n. In order to elucidate the factors responsible for differences in reactivity between {TiW5 } and {SnW5 } Lindqvist-type hexametalates, a series of alkoxido- and aryloxido-tin substituted POMs (nBu4 N)3 [(RO)SnW5 O18 ] (R=Me, Et, iPr and tBu) and (nBu4 N)3 [(ArO)SnW5 O18 ] (Ar=C6 H5 , 4-MeC6 H5 , 4-tBuC6 H5 , 4-HOC6 H4 , 3-HOC6 H4 and 2-CHOC6 H4 ) has been structurally characterised and studied by multinuclear NMR (1 H, 13 C, 17 O, 119 Sn and 183 W) and FTIR spectroscopy. Spectroscopic and structural parameters were compared with those of titanium-substituted homologues and, when coupled with theoretical studies, indicated that Sn-OR and Sn-OAr bonds are ionic with little π-contribution, whereas Ti-OR and Ti-OAr bonds are more covalent with π-bonding that is more prevalent for Ti-OR than Ti-OAr. This experimental and theoretical analysis of bonding in a homologous series of reactive POMs is the most extensive and detailed to date, and reveals factors which account for significant differences in reactivity between tin and titanium congeners.

Synthesis, Structure, and Antibacterial Activity of a Thallium(III)-Containing Polyoxometalate, [Tl2{B-ß-SiW8O30(OH)}2]12.

We have synthesized and structurally characterized the first discrete thallium-containing polyoxometalate, [Tl2{B-ß-SiW8O30(OH)}2]12- (1). Polyanion 1 was characterized in the solid-state and shown to be solution-stable by 203/205Tl NMR, electrospray ionization mass spectrometry, and electrochemical studies. The antibacterial activity of 1 was also investigated.

Accurate calculation of (31)P NMR chemical shifts in polyoxometalates.

We search for the best density functional theory strategy for the determination of (31)P nuclear magnetic resonance (NMR) chemical shifts, δ((31)P), in polyoxometalates. Among the variables governing the quality of the quantum modelling, we tackle herein the influence of the functional and the basis set. The spin-orbit and solvent effects were routinely included. To do so we analysed the family of structures α-[P2W18-xMxO62](n-) with M = Mo(VI), V(V) or Nb(V); [P2W17O62(M'R)](n-) with M' = Sn(IV), Ge(IV) and Ru(II) and [PW12-xMxO40](n-) with M = Pd(IV), Nb(V) and Ti(IV). The main results suggest that, to date, the best procedure for the accurate calculation of δ((31)P) in polyoxometalates is the combination of TZP/PBE//TZ2P/OPBE (for NMR//optimization step). The hybrid functionals (PBE0, B3LYP) tested herein were applied to the NMR step, besides being more CPU-consuming, do not outperform pure GGA functionals. Although previous studies on (183)W NMR suggested that the use of very large basis sets like QZ4P were needed for geometry optimization, the present results indicate that TZ2P suffices if the functional is optimal. Moreover, scaling corrections were applied to the results providing low mean absolute errors below 1 ppm for δ((31)P), which is a step forward in order to confirm or predict chemical shifts in polyoxometalates. Finally, via a simplified molecular model, we establish how the small variations in δ((31)P) arise from energy changes in the occupied and virtual orbitals of the PO4 group.

A thirty-year old mystery solved: identification of a new heptatungstate from non-aqueous solutions.

A new isopolyoxotungstate has been characterised, thirty years since the first spectroscopic evidence of its existence. The heptatungstate [W7O24H]5-, containing a {W5} lacunary Lindqvist unit fused to a ditungstate fragment, has significant stability and is only the third isopolytungstate structure to be obtained from non-aqueous systems.

Protonation and water exchange kinetics in sandwich polyoxometalates.

Density functional theory is used to explore the locus and consequences of protonation in [Zn4(HO)2(PW9O34)2]10-. The results are used to explain recent observations regarding the contrasting pH effects on the water-ligand exchange in [Mn4(H2O)2(P2W15O56)2]16- and [Co4(H2O)2(P2W15O56)2]16-, and the general effect of protonation on solvent exchange in metal oxides is discussed.