Modular Molecules: Site‐Selective Metal Substitution, Photoreduction, and Chirality in Polyoxometalate Hybrids

Abstract

The first members of a promising new family of hybrid amino acid-polyoxometalates have emerged from a search for modular functional molecules. Incorporation of glycine (Gly) or norleucine (Nle) ligands into an yttrium-tungstoarsenate structural backbone, followed by crystallization with p-methylbenzylammonium (p-MeBzNH3(+)) cations, affords (p-MeBzNH3)6K2(GlyH)[As(III)4(Y(III)W(VI)3)W(VI)44Y(III)4O159(Gly)8(H2O)14]⋅47 H2O (1) and enantiomorphs (p-MeBzNH3)15(NleH)3[As(III)4(Mo(V)2Mo(VI)2)W(VI)44Y(III)4O160(Nle)9(H2O)11][As(III)4(Mo(VI)2W(VI)2)W(VI)44Y(III)4O160(Nle)9(H2O)11] (generically designated 2: L-Nle, 2 a; D-Nle, 2 b). An intensive structural, spectroscopic, electrochemical, magnetochemical and theoretical investigation has allowed the elucidation of site-selective metal substitution and photoreduction of the tetranuclear core of the hybrid polyanions. In the solid state, markedly different crystal packing is evident for the compounds, which indicates the role of noncovalent interactions involving the amino acid ligands. In solution, mass spectrometric and small-angle X-ray scattering studies confirm maintenance of the structure of the polyanions of 2, while circular dichroism demonstrates that the chirality is also maintained. The combination of all of these features in a single modular family emphasizes the potential of such hybrid polyoxometalates to provide nanoscale molecular materials with tunable properties.

Structural Transformation from Dimerization to Tetramerization of Serine‐Decorated Rare‐Earth‐Incorporated Arsenotungstates Induced by the Usage of Rare‐Earth Salts

“…It is obvious that there are very few reports on amino acid‐containing RECATs, which provides us an excellent opportunity and a great possibility to explore this research realm further. Moreover, amino acid ligands with flexible carboxyl and amino coordination sites allow these ligands to utilize multifunctional coordination modes to combine various metal centers, thus giving rise to unique metal–oxo cluster aggregates with novel structures and interesting properties.…”

Synthesis and Characterization of 8-Yttrium(III)-Containing 81-Tungsto-8-Arsenate(III), [Y8(CH3COO)(H2O)18(As2W19O68)4(W2O6)2(WO4)]43−

“…In fact, 1 could not be isolated in the absence of cesium ions, and a sufficient amount was needed to induce precipitation, before filtration and crystallization of the product salt. On the other hand, CsNa-1 proved to be only slightly soluble in D2O, and hence our solution studies by 183 , respectively, should also be mentioned here [38]. Thermogravimetric Analysis.…”

Addition of Metalated 3‐Alkyl‐Substituted Alkoxyallenes to Imines: Preparation of Tetrasubstituted 2,5‐Dihydropyrroles, Pyrrolidin‐3‐ones, and Pyrroles

“…Neither the addition of extra tungstate to the solution, nor reducing the amount of yttrium nitrate, affords compounds with a homometallic {W 4 } core. [22,23] All compounds are insoluble in both aqueous solutions and organic solvents and all subsequent characterization has been performed in the solid state. This is in direct contrast to the blue coloration due to photoreduction observed for analogous solutions that also contain molybdate.…”

“…[22,23] This electron shuttling would give rise to a larger than usual electron-hole separation in the photoinduced LMCT state and correspondingly long lifetimes of the photoreduced POM. With lifetimes of many hours to days, the photoinduced states of compounds 1 and 2 are relatively long-lived.…”

“…[20,21] In general, the photochromic response of both POM salts with organic cations and covalently functionalized hybrid organic POMs can be characterized by the kinetics of color change, the excitation energy, the stability of the photoinduced state, the fading rate, and the cyclability. [22][23][24] Herein, we present an exploration of the photocoloration properties observed for some salts of the hybrid POMs of formula [As 4 {YW 3 }W 44 Y 4 O 159 (Gly) 8 (H 2 O) 14 ] 9with different countercations (Figure 1), including primary ammonium moieties, glycinium (GlyH), benzylammonium (BAH), and 4methylbenzylammonium (MBAH), and the quaternary ammonium benzyltriethylammonium (BTEA). Neither of the two mechanisms (Scheme S1) proposed to explain photoinduced coloration have been definitively demonstrated experimentally, although DFT calculations support the Dessapt mechanism of hydrogen-atom transfer.…”