New Hybrid Layered Molybdates Based on ²/_∞[Mo_<i>n</i>O_3<i>n</i>+1]^2– Units (<i>n</i> = 7, 9) with Systematic Organic–Inorganic Interfaces

Two new hybrid organic–inorganic molybdates based on layered ²/_∞[Mo_<i>n</i>O_3<i>n</i>+1]^2– blocks and organoammonium cations ⁺(Me_<i>x</i>H_3–<i>x</i>N)­(CH₂)₆(NH_3–<i>x</i>Me_<i>x</i>)⁺ (<i>x</i> = 0–1), namely, (H₃N­(CH₂)₆NH₃)­[Mo₇O₂₂]·H₂O (<b>1</b>) and (MeH₂N­(CH₂)₆NH₂Me)­[Mo₉O₂₈] (<b>2</b>), have been synthesized under hydrothermal conditions. The ²/_∞[Mo₉O₂₈]^2– unit in <b>2</b> is an unprecedented member of the ²/_∞[Mo_<i>n</i>O_3<i>n</i>+1]^2– family with the <i>n</i> value extended to 9. The structural filiation between the ²/_∞[Mo_<i>n</i>O_3<i>n</i>+1]^2– (<i>n</i> = 5, 7, 9) blocks is well established, and their structural similarity with the ²/_∞[MoO₃] slabs in α-MoO₃ is also discussed. Single-crystal X-ray analyses show that the ²/_∞[Mo_<i>n</i>O_3<i>n</i>+1]^2– layers in <b>1</b> and <b>2</b> are pillared in the three-dimensional networks by the organic cations with a similar connection at the organic–inorganic interface. In addition, a correlation between the topology of the ²/_∞[Mo_<i>n</i>O_3<i>n</i>+1]^2– blocks in <b>1</b> and <b>2</b> and the overall sizes of the associated organic cations is pointed out. Finally, the efficiency of Fourier transform Raman spectroscopy to easily discriminate the different ²/_∞[Mo_<i>n</i>O_3<i>n</i>+1]^2– blocks (<i>n</i> = 5, 7, 9) in hybrid organic–inorganic layered molybdate materials is clearly evidenced

New Hybrid Layered Molybdates Based on ²/_∞[Mo_<i>n</i>O_3<i>n</i>+1]^2– Units (<i>n</i> = 7, 9) with Systematic Organic–Inorganic Interfaces

Two new hybrid organic–inorganic molybdates based on layered ²/_∞[Mo_<i>n</i>O_3<i>n</i>+1]^2– blocks and organoammonium cations ⁺(Me_<i>x</i>H_3–<i>x</i>N)­(CH₂)₆(NH_3–<i>x</i>Me_<i>x</i>)⁺ (<i>x</i> = 0–1), namely, (H₃N­(CH₂)₆NH₃)­[Mo₇O₂₂]·H₂O (<b>1</b>) and (MeH₂N­(CH₂)₆NH₂Me)­[Mo₉O₂₈] (<b>2</b>), have been synthesized under hydrothermal conditions. The ²/_∞[Mo₉O₂₈]^2– unit in <b>2</b> is an unprecedented member of the ²/_∞[Mo_<i>n</i>O_3<i>n</i>+1]^2– family with the <i>n</i> value extended to 9. The structural filiation between the ²/_∞[Mo_<i>n</i>O_3<i>n</i>+1]^2– (<i>n</i> = 5, 7, 9) blocks is well established, and their structural similarity with the ²/_∞[MoO₃] slabs in α-MoO₃ is also discussed. Single-crystal X-ray analyses show that the ²/_∞[Mo_<i>n</i>O_3<i>n</i>+1]^2– layers in <b>1</b> and <b>2</b> are pillared in the three-dimensional networks by the organic cations with a similar connection at the organic–inorganic interface. In addition, a correlation between the topology of the ²/_∞[Mo_<i>n</i>O_3<i>n</i>+1]^2– blocks in <b>1</b> and <b>2</b> and the overall sizes of the associated organic cations is pointed out. Finally, the efficiency of Fourier transform Raman spectroscopy to easily discriminate the different ²/_∞[Mo_<i>n</i>O_3<i>n</i>+1]^2– blocks (<i>n</i> = 5, 7, 9) in hybrid organic–inorganic layered molybdate materials is clearly evidenced

Luminescence Properties of Al₂O₃:Ti in the Blue and Red Regions: A Combined Theoretical and Experimental Study

Using jointly experimental results and first-principles calculations, we unambiguously assign the underlying mechanisms behind two commonly observed luminescence bands for the Al2O3 material. Indeed, we show that the red band is associated with a Ti3+ d–d transition as expected, while the blue band is the combination of the Ti3+ + O– → Ti4+ + O2– and VO•+e– → VO× de-excitation processes. Thanks to our recent developments, which take into account the vibrational contributions to the electronic transitions in solids, we were able to simulate the luminescence spectra for the different signatures. The excellent agreement with the experiment demonstrates that it should be possible to predict the color of the material with a CIE chromaticity diagram. We also anticipated the luminescence signature of Al2O3:Ti,Ca and Al2O3:Ti,Be that were confirmed by experiment

Tuning the Photochromic Properties of Molybdenum Bisphosphonate Polyoxometalates

Seven hybrid organic–inorganic bisphosphonate molybdenum­(VI) polyoxometalate complexes with the general formula [(Mo₃O₈)₄(O₃PC­(C_<i>m</i>H_2<i>m</i>NRR′R″)­(O)­PO₃)₄]^8– (<i>m</i> = 3; R, R′, and R″ = H or CH₃) and [(Mo₃O₈)₂(O)­(O₃PC­(C_<i>m</i>H_2<i>m</i>NRR′R″)­(O)­PO₃)₂]^6– (<i>m</i> = 3 or 4; R, R′, and R″ = H or CH₃) have been synthesized and their structures solved using single-crystal X-ray diffraction. These compounds are made of a {Mo₁₂} or a {Mo₆} inorganic core functionalized by various alkylammonium bisphosphonates, with these ligands differing by the length of their alkyl chains and the number of methyl groups grafted on the N atom. The nature of the counter-cations (Na⁺, K⁺, Rb⁺, Cs⁺, and/or NH₄⁺) constituting these materials has also been modulated. ³¹P NMR spectroscopic studies in aqueous media have shown that all the dodecanuclear complexes reported here are stable in solution, whereas for the hexanuclear compounds, a dynamic equilibrium between two isomers has been evidenced, and the corresponding standard thermodynamic parameters determined for one of them. The electrochemical properties of six representative compounds of this family have been investigated. It has been found that the Mo⁶⁺/Mo⁵⁺ reduction potential is similar for all the polyoxometalates studied. Besides, it is shown that electrochemical cycling is an efficient method for the deposition of these compounds on a surface. The photochromic properties of all the complexes reported herein have been studied in the solid state. Under irradiation in the near ultraviolet (UV), the {Mo₁₂} systems shift from white to reddish-brown, while the {Mo₆} compounds develop a purple coloration. The coloration kinetics has been systematically quantified and the optical band gaps, the salient coloration kinetic parameters and the coloration kinetic half-life times have been determined. This has evidenced that several of these materials develop very strong and rapid UV-induced color changes, with remarkable coloration contrasts. Finally, the optical properties of these systems are discussed in light of several salient parameters as the POM topology, the nature of the grafted bisphosphonate ligand, and the design of the hydrogen-bonding network at the organic–inorganic interface

Persistent Type-II Multiferroicity in Nanostructured MnWO₄ Ceramics

Persistent Type-II Multiferroicity in Nanostructured MnWO₄ Ceramic

Incorporation of Jahn–Teller Cu²⁺ Ions into Magnetoelectric Multiferroic MnWO₄: Structural, Magnetic, and Dielectric Permittivity Properties of Mn_1–<i>x</i>Cu_<i>x</i>WO₄ (<i>x</i> ≤ 0.25)

Polycrystalline samples of Mn_1–<i>x</i>Cu_<i>x</i>WO₄ (<i>x</i> ≤ 0.5) have been prepared by a solid-state synthesis as well as from a citrate synthesis at moderate temperature (850 °C). The goal is to study changes in the structural, magnetic, and dielectric properties of magnetoelectric type-II multiferroic MnWO₄ caused by replacing Jahn–Teller-inactive Mn²⁺ (d⁵, <i>S</i> = 5/2) ions with Jahn–Teller-active Cu²⁺ (d⁹, <i>S</i> = 1/2) ions. Combination of techniques including scanning electron microscopy, powder X-ray and neutron diffraction, and Raman spectroscopy demonstrates that the polycrystalline samples with low copper content 0 ≤ <i>x</i> ≤ 0.25 are solid solution that forms in the monoclinic <i>P</i>2/c space group. Rietveld analyses indicate that Cu atoms substitutes for Mn atoms at the Mn crystallographic site of the MnWO₄ structure and suggest random distributions of Jahn–Teller-distorted CuO₆ octahedra in the solid solution. Magnetic susceptibility reveals that only 5% of Cu substitution suppresses the nonpolar collinear AF1 antiferromagnetic structure observed in pure MnWO₄. Type-II multiferroicity survives a weak Cu substitution rate (<i>x</i> < 0.15). Multiferroic transition temperature and Néel temperature increase as the amount of Cu increases. New trends in some of the magnetic properties and in dielectric behaviors are observed for <i>x</i> = 0.20 and 0.25. Careful analysis of the magnetic susceptibility reveals that the incorporation of Cu into MnWO₄ strengthens the overall antiferromagnetic interaction and reduces the magnetic frustration

Pair Distribution Function and Density Functional Theory Analyses of Hydrogen Trapping by γ‑MnO₂

In the presence of “Ag₂O” as a promoter, γ-MnO₂ traps dihydrogen in its (2 × 1) and (1 × 1) tunnels. The course of this reaction was examined by analyzing the X-ray diffraction patterns of the H_<i>x</i>MnO₂/“Ag₂O” system (0 ≤ <i>x</i> < 1) on the basis of pair distribution function and density functional theory (DFT) analyses. Hydrogen trapping occurs preferentially in the (2 × 1) tunnels of γ-MnO₂, which is then followed by that in the (1 × 1) tunnels. Our DFT analysis shows that this process is thermodynamically favorable

Photochromic Properties of Polyoxotungstates with Grafted Spiropyran Molecules

The first systems associating in a single molecule polyoxotungstates (POTs) and photochromic organic groups have been elaborated. Using the (TBA)₄­[PW₁₁O₃₉­{Sn­(C₆H₄I)}] precursor, two hybrid organic–inorganic species where a spiropyran derivative (SP) has been covalently grafted onto a {PW₁₁Sn} fragment via a Sonogashira coupling have been successfully obtained. Alternatively, a complex containing a silicotungstate {PW₁₁Si₂} unit connected to two spiropyran entities has been characterized. The purity of these species has been assessed using several techniques, including ¹H and ³¹P NMR spectroscopy, mass spectrometry, and electrochemical measurements. The optical properties of the hybrid materials have been investigated both in solution and in the solid state. These studies reveal that the grafting of SPs onto POTs does not significantly alter the photochromic behavior of the organic chromophore in solution. In contrast, these novel hybrid SP–POT materials display highly effective solid-state photochromism from neutral SP molecules initially nonphotochromic in the crystalline state. The photoresponses of the SP–POT systems in the solid state strongly depend on the nature and the number of grafted SP groups

Photochromic Properties of Polyoxotungstates with Grafted Spiropyran Molecules

The first systems associating in a single molecule polyoxotungstates (POTs) and photochromic organic groups have been elaborated. Using the (TBA)₄­[PW₁₁O₃₉­{Sn­(C₆H₄I)}] precursor, two hybrid organic–inorganic species where a spiropyran derivative (SP) has been covalently grafted onto a {PW₁₁Sn} fragment via a Sonogashira coupling have been successfully obtained. Alternatively, a complex containing a silicotungstate {PW₁₁Si₂} unit connected to two spiropyran entities has been characterized. The purity of these species has been assessed using several techniques, including ¹H and ³¹P NMR spectroscopy, mass spectrometry, and electrochemical measurements. The optical properties of the hybrid materials have been investigated both in solution and in the solid state. These studies reveal that the grafting of SPs onto POTs does not significantly alter the photochromic behavior of the organic chromophore in solution. In contrast, these novel hybrid SP–POT materials display highly effective solid-state photochromism from neutral SP molecules initially nonphotochromic in the crystalline state. The photoresponses of the SP–POT systems in the solid state strongly depend on the nature and the number of grafted SP groups

Novel Soft-Chemistry Route of Ag₂Mo₃O₁₀·2H₂O Nanowires and in Situ Photogeneration of a Ag@Ag₂Mo₃O₁₀·2H₂O Plasmonic Heterostructure

Ultrathin Ag₂Mo₃O₁₀·2H₂O nanowires (NWs) were synthesized by soft chemistry under atmospheric pressure from a hybrid organic–inorganic polyoxometalate (CH₃NH₃)₂[Mo₇O₂₂] and characterized by powder X-ray diffraction, DSC/TGA analyses, FT-IR and FT-Raman spectroscopies, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Their diameters are a few tens of nanometers and hence much thinner than that found for silver molybdates commonly obtained under hydrothermal conditions. The optical properties of Ag₂Mo₃O₁₀·2H₂O NWs before and after UV irradiation were investigated by UV–vis–NIR diffuse reflectance spectroscopy revealing, in addition to photoreduction of Mo⁶⁺ to Mo⁵⁺ cations, in situ photogeneration of well-dispersed silver Ag⁰ nanoparticles on the surface of the NWs. The resulting Ag@Ag₂Mo₃O₁₀·2H₂O heterostructure was confirmed by electron energy-loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS), and Auger spectroscopy. Concomitant reduction of Mo⁶⁺ and Ag⁺ cations under UV excitation was discussed on the basis of electronic band structure calculations. The Ag@Ag₂Mo₃O₁₀·2H₂O nanocomposite is an efficient visible-light-driven plasmonic photocatalyst for degradation of Rhodamine B dye in aqueous solution