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

Crystal structure and optical properties of new 0D-hybrid hydroxyfluorotitanates

International audienceNew 0D hybrid organic-inorganic hydroxyfluorotitanates result from the microwave assisted reactions in autoclaves of TiF4 with organic amines (3-5 diamino-1,2,4,triazol (guaz), ethylenediamine (en) and diethylenetriamine (dien)) and concentrated aqueous HF in ethanol at 190 °C for 1 h. Four compounds, [Hguaz]2*(TiF4.9(OH)1.1) (I), [H2guaz]*(TiF4.8(OH)1.2) (II), [H2en]*(TiF4.3(OH)1.7) (III) and [H2dien]*(Ti(F,OH)6)*2H2O (IV) are prepared and characterized. All structures are built up from isolated (Ti(F,OH)6)2− anions interacting with mono- or di-protonated amines which local symmetry dictates the long range stacking of the Ti(F,OH)6 octahedra. Insertion of crystallized water molecules is only observed for IV. The experimental optical gaps of I, II and III have been measured at about 3.4 eV and compare well with the theoretical values estimated from the examination of density of state diagrams. The optical thresholds are mainly due to O(2p) → Ti(3d) electronic transitions, the F(2p) → Ti(3d) charge transfers occurring at higher energy

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

Kinetics of Coloration in Photochromic Organoammonium Polyoxomolybdates

International audienceThe excellent photochromic properties of (H(2)DABCO)(2)(HDMA)(0.5)Na-0.75(H3O)(0.75)[Mo8O27]center dot 3H(2)O (4), a new member of the (H(2)DABCO)(2)(A)(x)[Mo8O27]center dot nH(2)O series, are compared with those of (H(2)DABCO)(2)(NH4)(2)[Mo8O27]center dot 4H(2)O (1), (H(2)DABCO)(2)(H(2)pipz)[Mo8O27] (2), and (H(2)pipz)(3)[Mo8O27] (3). All these powdered materials turn from white to purple under illumination at 365 nm, which is associated with photoreduction of Mo6+ cations into Mo5+ cations. We show that the rates of coloration, which increase in the order 1 < 3, 2 < 4, are related to the decrease in the concentration of reducible Mo6+ centers with irradiation time and follow a second-order reaction law because the event of light absorption at a reducible Mos+ site does not necessarily coincide with that of the N+-H bond breaking in the N+-H center dot center dot center dot O hydrogen bond associated with the Mo6+ site. First-principles density functional electronic structure calculations were carried out to find that this trend correlates with the homolytic dissociation energies of the N+-H bonds in the organic cations HDMA(+), H(2)pipz(2+), H(2)DABCO(2+), and NH4+. This observation is consistent with a photochromic mechanism based on the homolytic cleavage of N+-H bonds rather than on the heterolytic cleavage of N+-H bonds

Modulation of Defects in Semiconductors by Facile and Controllable Reduction: The Case of p-type CuCrO 2 Nanoparticles

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