Layered Quaternary Compounds in the Cu2S-In2S3-Ga2S3 system.

Several new materials with four structure-types (e.g., Cu0.32In1.74Ga0.84S4 (CIGS4), Cu0.65In1.75Ga1.4S5 (CIGS5), Cu1.44In2.77Ga0.76S6 (CIGS6), and Cu1.1In2.49Ga1.8S7 (CIGS7)) have been evidenced in the Cu2S-In2S3-Ga2S3 pseudo-ternary system. All of them present a 2D structure built upon infinite 2/∞[InS2] layers ((InS6) octahedra sharing edges) on which condense on both sides mono-, bi-, or tri-2/∞[MS] layers ((MS4) tetrahedra (M = Cu, In, Ga) sharing corners). (M(Td))n-2(In(Oh))Sn slabs are separated from each other by a van der Waals gap, and subscript n refers to the number of sulfur layers within the building block. These compounds have the propensity to display stacking faults but also polymorphic forms. Their optical gap (ca. 1.7 eV) is quite similar to the one of the Cu(In0.7Ga0.3)S2 chalcopyrite absorbers used in tandem solar cells, and the major charge carriers are holes. This suggests that they might be very attractive for photovoltaic applications in thin film devices but also for photocatalysis.

A p-Type Zinc-Based Metal-Organic Framework.

An original concept for the property tuning of semiconductors is demonstrated by the synthesis of a p-type zinc oxide (ZnO)-like metal-organic framework (MOF), (ZnC2O3H2)n, which can be regarded as a possible alternative for ZnO, a natural n-type semiconductor. When small oxygen-rich organic linkers are introduced to the Zn-O system, oxygen vacancies and a deep valence-band maximum, the two obstacles for generating p-type behavior in ZnO, are restrained and raised, respectively. Further studies of this material on the doping and photoluminescence behaviors confirm its resemblance to metal oxides (MOs). This result answers the challenges of generating p-type behavior in an n-type-like system. This concept reveals that a new category of hybrid materials, with an embedded continuous metal-oxygen network, lies between the MOs and MOFs. It provides concrete support for the development of p-type hybrid semiconductors in the near future and, more importantly, the enrichment of tuning possibilities in inorganic semiconductors.

Modulation of Defects in Semiconductors by Facile and Controllable Reduction: The Case of p-type CuCrO2 Nanoparticles.

Optical and electrical characteristics of solid materials are well-known to be intimately related to the presence of intrinsic or extrinsic defects. Hence, the control of defects in semiconductors is of great importance to achieve specific properties, for example, transparency and conductivity. Herein, a facile and controllable reduction method for modulating the defects is proposed and used for the case of p-type delafossite CuCrO2 nanoparticles. The optical absorption in the infrared region of the CuCrO2 material can then be fine-tuned via the continuous reduction of nonstoichiometric Cu(II), naturally stabilized in small amounts. This reduction modifies the concentration of positive charge carriers in the material, and thus the conductive and reflective properties, as well as the flat band potential. Indeed, this controllable reduction methodology provides a novel strategy to modulate the (opto-) electronic characteristics of semiconductors.

New hybrid layered molybdates based on (2/∞)[Mo(n)O(3n+1)]2- units (n = 7, 9) with systematic organic-inorganic interfaces.

Two new hybrid organic-inorganic molybdates based on layered (2/∞)[Mo(n)O(3n+1)](2-) blocks and organoammonium cations (+)(Me(x)H(3-x)N)(CH(2))(6)(NH(3-x)Me(x))(+) (x = 0-1), namely, (H(3)N(CH(2))(6)NH(3))[Mo(7)O(22)]·H(2)O (1) and (MeH(2)N(CH(2))(6)NH(2)Me)[Mo(9)O(28)] (2), have been synthesized under hydrothermal conditions. The (2/∞)[Mo(9)O(28)](2-) unit in 2 is an unprecedented member of the (2/∞)[Mo(n)O(3n+1)](2-) family with the n value extended to 9. The structural filiation between the (2/∞)[Mo(n)O(3n+1)](2-) (n = 5, 7, 9) blocks is well established, and their structural similarity with the (2/∞)[MoO(3)] slabs in α-MoO(3) is also discussed. Single-crystal X-ray analyses show that the (2/∞)[Mo(n)O(3n+1)](2-) layers in 1 and 2 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(n)O(3n+1)](2-) blocks in 1 and 2 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(n)O(3n+1)](2-) blocks (n = 5, 7, 9) in hybrid organic-inorganic layered molybdate materials is clearly evidenced.

Smart heterostructures for tailoring the optical properties of photochromic hybrid organic-inorganic polyoxometalates.

A new concept of photoresponsive composites has been elaborated by intimately connecting a Photochromic Phase (PP), (H(2)DABCO)(2)(HDMA)(0.5)Na(0.75)(H(3)O)(0.75)[Mo(8)O(27)]·3H(2)O (1), with a second hybrid organic-inorganic molybdate material, (H(2)DABCO)(HDABCO)[Fe(OH)(6)Mo(6)O(18)]·4H(2)O (2) acting as an Oxidation Catalytic Phase (OCP) toward the former once photoexcited. The association of both the PP and the OCP in the composite drastically improves the bleaching process of the PP alone because of efficient electronic transfers through the OCP-PP interface without affecting significantly its photoinduced color change characteristic. Two OCP-PP composites with different PP weight percents have been obtained by associating 1 with 2. The optical properties of these composites before and after UV irradiation have been investigated by Diffuse Reflectance Spectroscopy, and the strong impact of the OCP on the fading kinetics of the PP has been clearly highlighted.

How does the synthesis temperature impact hybrid organic-inorganic molybdate material design?

We investigate the reactivity of MoO(4)(2-) toward six organoammonium cations (+)(Me(3-x)H(x)N)(CH(2))(2)(NH(y)Me(3-y))(+) (x, y = 1-3) at different synthesis temperatures ranging from 70 to 180 °C. A total of 16 hybrid organic-inorganic materials have been synthesized at an initial pH of 2, via ambient pressure and hydrothermal routes, namely, (H(2)en)[Mo(3)O(10)]·H(2)O (1), (H(2)en)[Mo(3)O(10)] (2), (H(2)en)[Mo(5)O(16)] (3), (H(2)MED)(2)[Mo(8)O(26)]·2H(2)O (4), (H(2)MED)[Mo(5)O(16)] (5), (N,N-H(2)DMED)(2)[Mo(8)O(26)]·2H(2)O (6), (N,N-H(2)DMED)(2)[Mo(8)O(26)]·2H(2)O (7), (N,N'-H(2)DMED)(2)[Mo(8)O(26)] (8), (N,N'-H(2)DMED)[Mo(5)O(16)] (9), (H(2)TriMED)(2)[Mo(8)O(26)]·4H(2)O (10), (H(2)TriMED)(2)[Mo(8)O(26)]·2H(2)O (11), (H(2)TriMED)[Mo(7)O(22)] (12), (H(2)TMED)(2)[Mo(8)O(26)]·2H(2)O (13), (H(2)TMED)(2)[Mo(8)O(26)] (14), (H(2)TMED)(2)[Mo(8)O(26)] (15), and (H(2)TMED)[Mo(7)O(22)] (16). All of these compounds contain different polyoxomolybdate (Mo-POM) blocks, i.e., discrete ß-[Mo(8)O(26)](4-) blocks in 6, 10, 13, 14, (1)/(∞)[Mo(3)O(10)](2-), and (1)/(∞)[Mo(8)O(26)](4-) polymeric chains in 1, 2, 4, 7, 8, and 15, respectively, and (2)/(∞)[Mo(5)O(16)](2-) and (2)/(∞)[Mo(7)O(22)](2-) layers in 3, 5, 9, 12, and 16, respectively. The structures of 5, 9, and 14 have been resolved by single-crystal X-ray analyses. The characterization of the different Mo-POM blocks in 1-16 by Fourier transform Raman spectroscopy is reported. The impact of the synthesis temperature on both the composition and topology of the Mo-POM blocks is highlighted.

Kinetics of coloration in photochromic organoammonium polyoxomolybdates.

The excellent photochromic properties of (H(2)DABCO)(2)(HDMA)(0.5)Na(0.75)(H(3)O)(0.75)[Mo(8)O(27)] x 3 H(2)O (4), a new member of the (H(2)DABCO)(2)(A)(x)[Mo(8)O(27)] x n H(2)O series, are compared with those of (H(2)DABCO)(2)(NH(4))(2)[Mo(8)O(27)] x 4 H(2)O (1), (H(2)DABCO)(2)(H(2)pipz)[Mo(8)O(27)] (2), and (H(2)pipz)(3)[Mo(8)O(27)] (3). All these powdered materials turn from white to purple under illumination at 365 nm, which is associated with photoreduction of Mo(6+) cations into Mo(5+) 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 Mo(6+) centers with irradiation time and follow a second-order reaction law because the event of light absorption at a reducible Mo(6+) site does not necessarily coincide with that of the N(+)-H bond breaking in the N(+)-H...O hydrogen bond associated with the Mo(6+) 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 NH(4)(+). 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.

Synthesis, characterization, and photochromic properties of hybrid organic-inorganic materials based on molybdate, DABCO, and piperazine.

Prompted by our interest in new photochromic organic-inorganic hybrid materials, the reactivity of [Mo7O24]6- toward a structure-directing reagent diamine such as 1,4-diazabicyclo[2.2.2]octane (DABCO) and piperazine (pipz) has been investigated, and three new molybdenum(VI)-containing compounds, namely, (H2DABCO)3[Mo7O24].4H2O (1), (H2DABCO)[Mo3O10].H2O (2), and (H2DABCO)2(NH4)2[Mo8O27].4H2O (3), have been synthesized and characterized. New synthetic routes to achieve the known compounds (H2DABCO)2(H2pipz)[Mo8O27] (4), (H2pipz)3[Mo8O27] (5), and (H2DABCO)2[Mo8O26].4H2O (6) are also reported. All of these compounds contain different poly(oxomolybdate) clusters, i.e., discrete [Mo7O24]6- blocks in 1, infinite polymeric chains 1/infinity[Mo3O10]2- in 2, 1/infinity[Mo8O27]6- in 3-5, and 1/infinity[Mo8O26]4- in 6, associated in a tridimensional assembly by hydrogen bonds with H2DABCO2+ and/or H2pipz2+ cations. Interconversion pathways and chemical factors affecting the stabilization of the different species are highlighted and discussed. At the opposite of 6, compounds 1-5 show photochromic behavior under UV excitation. Namely, compounds 1-5 shift from white or pale yellow to pale pink, reddish brown, or purple under UV illumination depending on the chemical nature of the mineral framework, with the kinetics of the color change being dictated by the nature of the organic component and by the organic-inorganic interface.

Commensurate (C6H14N2)2[Mo8O26] * 4H2O and incommensurate (C6H14N2)2[Mo8O26] * 4.66H2O: a structural versatility linked to solvent content.

The syntheses and structure determinations by means of single-crystal X-ray diffraction of commensurate (C(6)H(14)N(2))(2)[Mo(8)O(26)] * 4H(2)O and incommensurate (C(6)H(14)N(2))(2)[Mo(8)O(26)] * 4.66H(2)O, two new organic-inorganic hybrid compounds based on polyoxomolybdates and differing in their solvent content, are reported. Given the important disorder observed in the latter compound, only a combination of non-harmonic waves, crenel functions and TLS tensors offered a good modelling of the structure. (C(6)H(14)N(2))(2)[Mo(8)O(26)] * nH(2)O results from the self-assembly of [Mo(8)O(26)](4-) anionic chains, C(6)H(14)N(2)(2+) (H(2)DABCO(2+)) cations and water molecules. The [Mo(8)O(26)](4-) chain is built from gamma-[Mo(8)O(28)](8-) octamolybdate clusters, connected to each other through corner sharing. In both compounds, the [Mo(8)O(26)](4-) chains are separated, in a similar way, by the H(2)DABCO(2+) subunits, acting as charge-compensating cations, and by the water molecules. The orientation of the H(2)DABCO(2+) cations is shown to be different from what has been observed previously in monoclinic (H(2)DABCO)(2)[Mo(8)O(26)] * 4H(2)O, and therefore to give a different network of hydrogen bonds.

Synthesis and X-ray Powder Structure of a New Pillared Layered Cadmium Phosphonate, Giving Evidence that the Intercalation of Alkylamines into Cd(O(3)PR).H(2)O Is Topotactic.

A new pillared layered phosphonate, cadmium 2-aminoethylphosphonate, Cd(O(3)PC(2)H(4)NH(2)) (1), has been synthesized, and its structure was solved ab initio from X-ray powder diffraction data and refined by Rietveld methods. Compound 1 is orthorhombic: space group Pna2(1), a = 15.4643(2) Å, b = 5.16512(7) Å, c = 6.27650(8) Å, and Z = 4. Its layer arrangement is similar to that in Cd(O(3)PR).H(2)O, except that the water molecule coordinated to cadmium in Cd(O(3)PR).H(2)O is replaced by the nitrogen atom from the amino ends of the ethyl chains borne by phosphorus of the upper and lower layers. The strong similarity of the IR, (31)P, and (113)Cd NMR data for Cd(O(3)PC(2)H(4)NH(2)) and Cd(O(3)PCH(3)).n-NH(2)C(4)H(9) clearly shows the topotactic character of the intercalation of n-alkylamines in the dehydrated form of Cd(O(3)PR).H(2)O to yield Cd(O(3)PR).n-NH(2)R'.

Syntheses and Crystal Structures of the New Zinc Phosphonates Zn(O(3)PCH(2)P(O)(R)(C(6)H(5))).xH(2)O, Based on Mixed Phosphonic Acid-Phosphine Oxide Building Blocks.

The two new zinc(II) phosphonates Zn(O(3)PCH(2)P(O)(C(6)H(5))(2)) (monoclinic P2(1)/c (No. 14), a = 9.961(2) Å, b = 5.838(1) Å, c = 24.608(5) Å, beta = 101.48(3) degrees, Z = 4) and Zn(O(3)PCH(2)P(O)(CH(3))(C(6)H(5))).0.67H(2)O (monoclinic P2(1)/c (No. 14), a = 15.879(5) Å, b = 7.383(2) Å, c = 10.475(3) Å, beta = 105.01(5) degrees, Z = 4) were prepared by reaction of zinc nitrate, (R)(C(6)H(5))P(O)CH(2)PO(3)H(2) [R = C(6)H(5), CH(3)], and sodium hydroxide in water in an autoclave. For the first compound, a unidimensional arrangement is observed, while for the second, a layered structure is obtained, in relation to the size of the substituents present on the phosphine oxide moiety.