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A series of eight new materials based on the ionic association between 1-methyl-3-alkylimidazolium cations and the nanometric anionic Keplerate [Mo132O372(CH3COO)30(H2O)72]42− has been prepared and characterized in the solid state. The liquid crystal properties of these materials were investigated by the combination of Polarized Optical Microscopy, Differential Scanning Calorimetry and Small-angle X-Ray Diffraction showing a self-organization in lamellar (L) mesophases for the major part of them. From the interlamellar spacing h and the intercluster distance ahex, we demonstrated that the cations are not randomly organized around the anionic cluster and that the alkyl chains of the cations are certainly folded, which limits the van der Waals interactions between the cations within the liquid crystal phase and therefore harms the quality of the mesophases.

A series of six hybrid polymers based on the mixed-valent {ε-PMoV 8MoVI 4O40Zn4} (εZn) Keggin unit have been synthesized under hydrothermal conditions using tritopic (1,3,5-benzenetricarboxylate (trim) or 1,3,5-benzenetribenzoate (BTB)) or ditopic (4,4'-biphenyldicarboxylate (biphen)) linkers and [M(bpy)3]2+ (M = Co, Ru) complexes as charge-compensating cations. (TBA)2[Co(C10H8N2)3][PMo12O37(OH)3Zn4](C27H15O6)4/3·1.5C27H18O6·24H2O (Co-ε(BTB) 4/3 ) has a three-dimensional (3D) framework with two interpenetrated networks and is isostructural to (TBA)4[PMo12O37(OH)3Zn4](C27H15O6)4/3·1.5C27H18O6·8H2O (ε(BTB) 4/3 ). In Co-ε(BTB) 4/3 , two tetrabutylammonium (TBA+) cations over the four present in ε(BTB) 4/3 are replaced by one [Co(bpy)3]2+ complex. [Co(C10H8N2)3][PMo12O37(OH)3Zn4](C9H3O6)Co(C10H8N2)4(H2O)·16H2O (Co-ε(trim) (bpy) 2 ) is a 1D coordination polymer with two types of CoII-containing complexes, one covalently attached to the 1D chains and the other located in the voids as the counterion. [Ru(C10H8N2)3]4[PMo12O38(OH)2Zn4]2(C9H3O6)2·42H2O (Ru-ε 2 (trim) 2 ) and [Ru(C10H8N2)3]3[PMo12O37(OH)3Zn4Cl]2(C14H8O4)2·24H2O (Ru-ε 2 (biphen) 2 ) contain dimeric (εZn)2 units linked by dicarboxylate linkers, and both have [Ru(bpy)3]2+ countercations. Ru-ε 2 (trim) 2 has a 3D framework, while Ru-ε 2 (biphen) 2 is only 2D because of the presence of chloride ions on one-fourth of the ZnII ions. [P(C6H5)4]6[PMo12O37(OH)3Zn4]2(C9H3O6)2·18H2O (PPh 4 -ε 2 (trim) 2 ) is isostructural to Ru-ε 2 (trim) 2 . These insoluble compounds entrapped in carbon-paste electrodes exhibit electrocatalytic activity for the hydrogen evolution reaction. The effects of their structure and the nature of the counterions on the activity have been studied. For the first time, different POM-based coordination polymers are compared for catalytic H2 production using controlled-potential electrolysis. This study shows that the nature of the countercation has a strong effect on the electrocatalytic activity of the compound. [ABSTRACT FROM AUTHOR]

The chemically and structurally highly stable polyoxometalate (POM) single-molecule magnet (SMM) [(FeW9O34)2Fe4(H2O)2]10− (Fe6W18) has been incorporated by direct or post-synthetic approaches into a biopolymer gelatin (Gel) matrix and two crystalline metal-organic frameworks (MOFs), including one diamagnetic (UiO-67) and one magnetic (MIL-101(Cr)). Integrity of the POM in the Fe6W18@Gel, Fe6W18@UiO-67 and Fe6W18@MIL-101(Cr) composites was confirmed by a set of complementary techniques. Magnetic studies indicate that the POMs are magnetically well isolated. Remarkably, in Fe6W18@Gel, the SMM properties of the embedded molecules are close to those of the crystals, with clear quantum tunneling steps in the hysteresis loops. For the Fe6W18@UiO-67 composite, the molecules retain their SMM properties, the energy barrier being slightly reduced in comparison to the crystalline material and the molecules exhibiting a tunneling rate of magnetization significantly faster than for Fe6W18@Gel. When Fe6W18 is introduced into MIL-101(Cr), the width of the hysteresis loops is drastically reduced and the quantum tunneling steps are smeared out because of the magnetic interactions between the antiferromagnetic matrix and the SMM guest molecules. [ABSTRACT FROM AUTHOR]

The encapsulation of polyoxometalates within the large pores of the Zr(IV) biphenyldicarboxylate UiO-67 metal–organic framework has been achieved, for the first time, by direct solvothermal synthesis. The resulting POM@UiO-67 composite materials were fully characterized by XRPD, IR, MAS NMR, N2 porosimetry measurements and cyclic voltammetry. [ABSTRACT FROM AUTHOR]

The encapsulation of three different cobalt substituted polyoxometalates (POMs) within the mesoporous chromium(III) terephthalate MIL-101(Cr) metal-organic framework (MOF) was studied by a simple and green impregnation method using water. The POM@MIL composite materials were fully characterized by EDX, XRPD, IR, MAS NMR and N2 porosimetry measurements. The encapsulated POMs were then extracted by an exchange procedure using a LiCl solution. 31P NMR spectroscopy is the key experiment which indicates that the monosubstituted Keggin anion [PW11CoO39(H2O)]5- (PW11Co) and the sandwichtype anion [(PW9O34)2Co4(H2O)2]10- (P2W18Co4) can be encapsulated and extracted without degradation, neither of the POM nor of the MOF, while the hybrid sandwich-type POM [(PW9O34)2Co7(OH)2- (H2O)4(O3PC(O)(C3H6NH3)PO3)2]14- (Co7-Ale) evolves into P2W18Co4 inside the cavities of the mesoporous material. The PW11Co Keggin anion is the most quantitatively uploaded and the most easily extracted anion. 31P MAS-NMR spectroscopy further suggests that this anion is more mobile inside the cavities of the MOF than the P2W18Co4 POM. [ABSTRACT FROM AUTHOR]

Inorganic molecular oxides—also called polyoxometalates (POMs)—possess a high thermal and chemical stability, a major advantage for the further processing of these species. This feature has been exploited for the incorporation of single‐molecule magnet POMs in supports with very different characteristics (amorphous vs. crystalline; diamagnetic vs. paramagnetic). It is shown that with a judicious choice of the matrix, the single‐molecule magnet properties of the embedded and well‐isolated molecules are very close to those of a crystal. More information can be found in the Full Paper by T. Mallah, W. Wernsdorfer, P. Mialane et al. on page 6564 ff. [ABSTRACT FROM AUTHOR]

Three compounds associating for the first time polyoxotungstates, bisphosphonates, and copper ions were structurally characterized. They consist in heteropolyanionic monodimensional materials where [Cu6(Ale)4(H2O)4]4- (Ale = alendronate = [O3PC(O)(C3H6NH3)PO3]4-) complexes alternate with polyoxometalate (POM) units. In Na12[{SiW9O34Cu3(Ale)(H2O)}{Cu6(Ale)4(H2O)4}]•50H2O (SiW9CuAle), the polyoxometalate core consists in a {SiW9Cu3} monomer capped by a pentacoordinated Ale ligand, while sandwich-type Keggin {(SbW9O33)2Cu3(H2O)2.5Cl0.5} and Dawson {(P2W15O56)2Cu4(H2O)2} complexes are found in Na8Li29[{(SbW9O33)2Cu3(H2O)2.5Cl0.5}2{Cu6(Ale)4(H2O)4}3]•163H2O (SbW9CuAle) and Na20[{(P2W15O56)2Cu4(H2O)2}{Cu6(Ale)4(H2O)4}]•50H2O (P2W15CuAle), respectively. A comparative magnetic study of the SiW9CuAle and SbW9CuAle compounds enabled full quantification of the CuII superexchange interactions both for the POM and non-POM subunits, evidencing that, while the paramagnetic centers are anti-ferromagnetically coupled in the polyoxometalate units, both anti-ferromagnetic and ferromagnetic interactions coexist in the {Cu6(Ale)4(H2O)4} cluster. All the studied compounds present a good efficiency upon the reduction of HNO2 or NO2-, the POM acting as a catalyst. However, it has been found that SbW9CuAle is inactive toward the reduction of nitrates, highlighting that both the {(SbW9O33)2Cu3} unit and the {Cu6(Ale)4(H2O)4} cluster do not act as electrocatalysts for this reaction. In contrast, SiW9CuAle and P2W15CuAle have shown a significant activity upon the reduction of NO3- and thus both at pH 1 and pH 5, evidencing that the chemical nature of the polyoxometalate is a crucial parameter even if it acts as precatalyst. Moreover, comparison of the activities of P2W15CuAle and [(P2W15O56)2Cu4(H2O)2]16- evidenced that if the [Cu6(Ale)4(H2O)4]4- cluster does not act as electrocatalyst, it acts as a cofactor, significantly enhancing the catalytic efficiency of the active POM. [ABSTRACT FROM AUTHOR]

Five molecular one-, two-, or three-dimensional(1D, 2D, or 3D)organic–inorganic hybrid polyoxometalates (POMs) based on the{ε-PMoV8MoVI4O40Zn4} (εZn) Keggin unit have been synthesizedunder hydrothermal conditions using a mixture of O- and N-donor ligands.(TBA)6[PMoV8MoVI4O37(OH)3Zn4]2(C14H8O4)3·6H2O (ε2(biphen)3) is a 3D materialwith two interpenetrated networks built from dimeric (εZn)2POMs linked by 4,4′-biphenyldicarboxylate (biphen) ligands. (TBA)2[PMoV8MoVI4O38(OH)2Zn4](C7H6N2)3(C14H8O4)1/2·H2O (ε(bim)3(biphen)1/2), (TBA)3[PMoV8MoVI4O38(OH)2Zn4](C7H6N2)2(C8H4O4)·6H2O (ε(bim)2(isop)), (TBA)7/3[PMoV8MoVI4O38(OH)2Zn4](C7H6N2)8/3(C8H4O4)2/3(ε(bim)8/3(bdc)2/3), and (TBA)3[PMoV8MoVI4O38(OH)2Zn4](C7H6N2)2(C9H3O6)2/3·6H2O (ε(bim)2(trim)2/3) allconsist of monomeric εZn units bound to two types of organicligands: benzimidazole (bim) and one of the followingcarboxylate ligands: biphen, 1,3-benzenedicarboxylate(isop), 1,4-benzenedicarboxylate (bdc),or 1,3,5-benzenetricarboxylate (trim) ligands. While ε(bim)3(biphen)1/2is a molecular complex, ε(bim)2(isop)and ε(bim)8/3(bdc)2/3adopt a chain arrangement, and ε(bim)2(trim)2/3is a 2D compound. In these materials, the limitation of the dimensionalityis a direct consequence of the protonation of the nitrogen atom ofthe bimligands. The electrocatalytic activity for thehydrogen evolution reaction (HER) of these five new POM-based coordinationpolymers has been studied, showing that their performance dependsmainly on the presence of the εZn Keggin units but also on theirstructure. Modified electrodes fabricated with ε(bim)2(trim)2/3entrapped in a carbon paste revealed that this hybrid is themost efficient electrocatalyst of the series, being stable and catalyzingthe HER in the pH 1–5 range. [ABSTRACT FROM AUTHOR]