Structural diversity and chemical trends in hybrid inorganic-organic framework materials

Hybrid framework compounds, including both metal-organic coordination polymers and systems that contain extended inorganic connectivity (extended inorganic hybrids), have recently developed into an important new class of solid-state materials. We examine the diversity of this complex class of materials, propose a simple but systematic classification, and explore the chemical and geometrical factors that influence their formation. We also discuss the growing evidence that many hybrid frameworks tend to form under thermodynamic rather than kinetic control when the synthesis is carried out under hydrothermal conditions. Finally, we explore the potential applications of hybrid frameworks in areas such as gas separations and storage, heterogeneous catalysis, and photoluminescence.     

Interactions between Eu ions in inorganic-organic hybrid materials

The optical properties of two-dimensional lanthanide dicarboxylates EuBDC or Eu₂(H₂O)₂(O₂C-C₆H₄-CO₂)₃ and EuCDC (denoted also MIL94) or Eu₂(H₂O)₄(O₂C-C₆H₁₀-CO₂)₃.2H₂O are reported. The structures are built up from dimers of corner-sharing polyhedra and 1,3-benzenedicarboxylate (BDC) for EuBDC and from dimers of edge-sharing polyhedra and 1,3-benzenedicarboxylate (CDC) for EuCDC. The high Eu³⁺ concentration and the weak luminescence quenching allow the study of Eu³⁺ interactions. Anti-Stokes spectra from ⁵D₁ are observed with excitation in ⁵D₀. These results are very unusual for Eu³⁺ ions and reflect strong interactions between ions within a dimer. Excitation spectrum of the Eu³⁺ luminescence strongly differs in both compounds in the UV range. In case of EuBDC, an efficient sensitization of the luminescence due to the ligand is observed between 250 and 350 nm while only 4f-4f transitions are recorded on the Eu³⁺ excitation spectrum in EuCDC. The efficiency of the sensitization of the rare earth by the host is discussed by taking into account the geometrical arrangement and the electronic delocalization of the ligands.     

New lead inorganic-organic hybrid microporous and layered materials: synthesis,properties, and crystal structures

Two new lead(II) phosphonates, namely, Pb2[PMIDA]*1.5H2O (1) (H4PMIDA = H2O3PCH2N(CH2CO2H)2) and Pb(H2L) (2) (H4L = CH3N(CH2PO3H2)2), have been synthesized by hydrothermal reactions at 150 degrees C. Complex 1 crystallized in tetragonal P42/n with cell dimensions of a = 17.317(7) and c = 7.507(5) A and Z = 8. In complex 1, Pb(1) is 6-coordinated by chelation in a tetradentate fashion by a PMIDA ligand (3 O, 1 N) and two phosphonate oxygen atoms from neighboring Pb(PMIDA) units in a severely distorted octahedral geometry, whereas Pb(2) is 6-coordinated by 4 carboxylate and 2 phosphonate oxygen atoms also with a severely distorted octahedral environment. These two different types of Pb(II) ions are interconnected through bridging carboxylate and phosphonate groups, resulting in a 3D network with micropores, whose cavity is filled by lattice water molecules interlinked via hydrogen bonds. Each PMIDA ligand bridges with 8 Pb(II) ions (3 Pb(1) and 5 Pb(2)). Complex 2 is orthorhombic, P2(1)2(1)2(1), with a = 7.382(5), b = 7.440(6), and c = 30.75(2) A and Z = 8. The structure of 2 features a 2D double lead(II) phosphonate layer along the ab plane. Each lead(II) ion is 5-coordinated by five phosphonate oxygen atoms from four ligands in a distorted trigonal bipyramid geometry. These double layers are further interconnected via hydrogen bonds between the protonated and uncoordinated phosphonate oxygens along the c-axis.     

Microwave synthesis of hybrid inorganic-organic porous materials: phase-selective and rapid crystallization

Microwave synthesis of two porous nickel glutarates was compared with conventional hydrothermal synthesis. The cubic nickel glutarate, [Ni20(C5H6O4)20(H2O)8] x 40 H2O (1), was synthesized by conventional electrical heating in several hours or days, depending on synthesis temperature. Crystallization was greatly accelerated by microwave irradiation, in which more stable, tetragonal nickel glutarate, [Ni22(C5H6O4)20(OH)4(H2O)10] x 38 H2O (2), was formed within a few minutes, suggesting the efficiency of the microwave technique in the synthesis of porous hybrid materials. The cubic phase 1 is formed preferentially at low pH, low temperature, and especially under conventional electrical heating. In contrast, the tetragonal phase 2 is obtained favorably at high pH, high temperature, and especially with microwave irradiation. This work demonstrates that the microwave method provides not only the very fast synthesis of a hybrid material, but also the possibility to discover a new porous hybrid material not yet identified by conventional hydrothermal synthesis. The hydrothermal formation of metal-organic hybrid materials in a matter of minutes is an important step towards developing commercially viable routes for producing this valuable class of materials.     

Two inorganic-organic hybrid materials based on polyoxometalate anions and methylene blue: Preparations, crystal structures and properties

Two novel inorganic-organic hybrid materials based on an organic dye cation methylene blue (MB) and Lindqvist-type POM polyanions, [C₂₂H₁₈N₃S]₂Mo₆O₁₉ 2DMF (1) and [C₂₂H₁₈N₃S]₂W₆O₁₉ 2DMF (2) were synthesized under ambient conditions and characterized by CV, IR spectroscopy, solid diffuse reflectance spectrum, UV-vis spectra in DMF solution, luminescent spectrum and single crystal X-ray diffraction. Crystallographic data reveal that compounds 1 and 2 are isostructural and both crystallize in the triclinic space group P1¯. Their crystal structures present that the layers of organic molecules and inorganic anions array alternatively, and there exist strong π···π stacking interactions between dimeric MB cations and near distance interactions among organic dye cations, Lindqvist-type POM polyanions and DMF molecules. The solid diffuse reflectance spectra and UV-vis spectra in DMF solution appear new absorption bands ascribed to the charge-transfer transition between the cationic MB donor and the POM acceptors. Studies of the photoluminescent properties show that the formation of 1 and 2 lead to the fluorescence quenching of starting materials.     

Order-disorder antiferroelectric phase transition in a hybrid inorganic-organic framework with the perovskite architecture

[(CH3)2NH2]Zn(HCOO)3, 1, adopts a structure that is analogous to that of a traditional perovskite, ABX3, with A = [(CH3)2NH2], B = Zn, and X = HCOO. The hydrogen atoms of the dimethyl ammonium cation, which hydrogen bond to oxygen atoms of the formate framework, are disordered at room temperature. X-ray powder diffraction, dielectric constant, and specific heat data show that 1 undergoes an order-disorder phase transition on cooling below 156 K. We present evidence that this is a classical paraelectric to antiferroelectric phase transition that is driven by ordering of the hydrogen atoms. This sort of electrical ordering associated with order-disorder phase transition is unprecedented in hybrid frameworks and opens up an exciting new direction in rational synthetic strategies to create extended hybrid networks for applications in ferroic-related fields.     

Study of interface properties in CuPc based hybrid inorganic-organic solar cells

Metal-substituted phthalocyanine thin films such as copper-phthalocyanine (CuPc) are often used as photo-active and hole transporting layers (HTLs) in fully organic photovoltaic devices. In this work, CuPc is vacuum sublimated on an electron acceptor layer of mesoporous titania (TiO(2)) for the formation of hybrid TiO(2):CuPc solar cell devices. The performance of these hybrid solar cell devices was demonstrated without and with dye sensitization at the TiO(2):CuPc interface. The charge separation and photocurrent contribution at the interfaces in these multilayer hybrid devices was studied by using a variety of optoelectrical and photophysical characterization techniques. It is important to understand the fundamental interface properties of these multilayer hybrid solar cell devices for optimized performance.     

Impact of regularity in structure-property relationships

The regular evolution of properties with structural modification is quantitatively formulated. It is defined in a structural space which is exhaustive, ordered, flexible and explicit. It is detected along the ordered pathways of structural filiations by inference tools, which take into account the experimental precision and proceed by a heuristic modulation of the initial representation space. The introduction of nuances in the quantitative formulation of regularity leads to diverse tools for setting up and exploiting the relationships. These latter constitute a prediction law, which is both simple and as precise as the measurements. The detected regularities make for a generalization of certain structural effects and suggest a fruitful interpretation. Zeroth- and first-order regularities, characteristic of strongly linear variation, are used to safely extrapolate the prediction range and to orient experimental planning.     

Solvothermal synthesis and photoluminescent properties of ZnS/cyclohexylamine: inorganic-organic hybrid semiconductor nanowires

An inorganic-organic hybrid semiconductor, ZnS/CHA (CHA = cyclohexylamine) nanocomposites was successfully synthesized via a solvothermal method using CHA as solvent, which yielded uniform and ultralong nanowires with widths of 100-1000 nm and lengths of 5-20 microm. Changing the reaction conditions could alter the morphology and optical properties of the nanocomposites. The periodic layer subnanometer structures were identified by high-resolution transmission electron microscopy (HR-TEM) images, with thickness of approximately 2 nm. The composites exhibited a very large blue-shift in their optical absorption edge as well as an exciton excitation band due to a strong quantum confinement effect caused by the internal subnanometer-scale structures. The pure hexagonal wurtzite ZnS nanowires were also obtained by extracting the ZnS/CHA nanocomposites with dimethyl formamide (DMF). In addition, the luminescent properties of exciton and defect-related transitions in different samples of ZnS/CHA were discussed in detail.     

含氮多齿配体构筑的无机-有机杂化材料及其光催化研究进展

综述了金属离子与多齿含氮配体构筑的无机-有机杂化材料,并概述了这些材料在光催化降解亚甲基蓝(MB)方面的研究进展.为此类材料在光催化降解染料方面的研究提供了理论和实验基础.     

Charge transport properties in discotic liquid crystals: a quantum-chemical insight into structure-property relationships

We describe at the quantum-chemical level the main parameters that control charge transport at the molecular scale in discotic liquid crystals. The focus is on stacks made of triphenylene, hexaazatriphenylene, hexaazatrinaphthylene, and hexabenzocoronene molecules and derivatives thereof. It is found that a subtle interplay between the chemical structure of the molecules and their relative positions within the stacks determines the charge transport properties; the molecular features required to promote high charge mobilities in discotic materials are established on the basis of the calculated structure-property relationships. We predict a significant increase in the charge mobility when going from triphenylene to hexaazatrinaphthylene; this finding has been confirmed by measurements carried out with the pulse-radiolysis time-resolved microwave conductivity technique.     

The role of temperature in the synthesis of hybrid inorganic-organic materials: the example of cobalt succinates

Five different cobalt succinate materials synthesized from an identical starting mixture using temperature as the only independent variable show increasing condensation and density at higher synthesis temperatures.     

Fabrication and characterization of nanostructured titania films with integrated function from inorganic-organic hybrid materials

Nanostructured titania films are of growing interest due to their application in future photovoltaic technologies. Therefore, a lot of effort has been put into the controlled fabrication and tailoring of titania nanostructures. The controlled sol-gel synthesis of titania, in particular in combination with block copolymer templates, is very promising because of its high control on the nanostructure, easy application and cheap processing possibilities. This tutorial review gives a short overview of the structural control of titania films gained by using templated sol-gel chemistry and shows how this approach is extended by the addition of further functionality to the films. Different expansions of the sol-gel templating are possible by the fabrication of gradient samples, by the addition of a homopolymer, by the combination with micro-fluidics and also by the application of novel precursors for low-temperature processing. Moreover, hierarchically structured titania films can be fabricated via the subsequent application of several sol-gel steps or via the inclusion of colloidal templates in a one-step process. Integrated function in the block copolymer used in the sol-gel synthesis allows for the fabrication of an integrated blocking layer or an integrated hole-conductor. Both approaches grant a one-step fabrication of two components of a working solar cell, which make them very promising towards a cheap solar cell production route. Looking to the complete solar cell, the top contact is also of great importance as it influences the function of the whole solar cell. Thus, the mechanisms acting in the top contact formation are also reviewed. For all these aspects, characterization techniques that allow for a structural investigation of nanostructures inside the active layers are important. Therefore, the characterization techniques that are used in real space as well as in reciprocal space are explained shortly as well.     

Effect of inorganic cores on dye properties of inorganic-organic hybrid pigments yellow 12

Some inorganic-organic hybrid pigments were fabricated by depositing pigment yellow 12(P.Y.12) on the surface of three inorganic cores with different particle size (white carbon black,microsilica,palygorskite). Effect of inorganic cores on the morphology and structure of the hybrid pigments were systematically investigated by nanoparticle analyzer, Fourier transforms infrared spectroscopy, and X-ray diffraction. Results showed that all three inorganic cores were encapsulated by the organic pigment. The particle size of hybrid pigments was all smaller and had narrower diameter scatter than the original pigment. The water dispersion and flow ability of these fabricated pigments were slightly improved. Thermal and UV-Vis analyses showed that the hybrid pigments had better thermo- and photo-stabilities. Additionally, the properties of the hybrid pigments including color strength, lightness, and yellow hue index were also improved and the modified pigment with white carbon black had the best coloring performance and better heat resistance than original P.Y.12.     

Synthesis and structure-property relationships of amphiphilic organogelators

A series of low-molecular-weight amphiphilic molecules was synthesized and investigated for their ability to gel organic solvents. These amphiphilic molecules are composed of a head-group moiety capable of forming intermolecular associations through hydrogen bonds and n-alkyl chains of various lengths. This paper describes the continuation of recently published work, in which this class of gelators was presented for the first time. Here, the focus addresses systematically three different structural variations of the head-group moiety: 1) the rigidity, 2) the type and strength of the hydrogen-bond-forming units, and 3) the reduction of the intermolecular interaction by incorporating a lateral substituent. The gelation behavior was investigated in p-xylene and in several polar solvents. The aim was to establish structure-property relationships and to provide organogelators capable of forming gels at low concentrations with adjustable sol-gel transition temperatures and good optical quality. For some individual compounds of the series this property profile was achieved. For the investigated solvents, with particular compounds, sol-gel transition temperatures above 100 degrees C with a reasonable concentration of gelator are obtainable.     

Diphenylamino end-capped oligofluorenes with enhanced functional properties for blue light emission: synthesis and structure-property relationships

A novel series of monodisperse asymmetrically and symmetrically substituted diphenylamino end-capped oligofluorenes, OF(2)-NPhR, R = H or An (An = 9-anthryl) and OF(n)-NPh, n = 2-4, has been synthesized by a convergent approach using palladium-catalyzed Suzuki cross-coupling. End-capping of oligofluorenes with diphenylamino group(s) has been shown to offer advantages in terms of lowering their first ionization potentials, enhancing thermal stability, and inducing good amorphous morphological stability. By tuning the number of diphenylamino end-caps and the chain length, the optimal conjugated length for optical and luminescence properties has been determined. Of all the hitherto reported oligofluorenes capable of serving as non-doped blue emitters, OF(3)-NPh, with an optimal conjugated length, exhibits some of the best hole-transport and blue-emitting properties. A maximum luminance of 7500 cd m(-2) and a luminance efficiency up to 1.8 cd A(-1) have been achieved.     

Microgel particles: The structure-property relationships and their biomedical applications

Microgels are crosslinked soft particles with a three-dimensional network structure that are swollen in a good solvent. They have frequently been termed “smart materials” since the size, softness, and interaction forces between particles are tunable by external stimuli such as temperature, pH, or magnetic and electric fields. It is this unique feature that has captured the interest of many scientists across a wide range of disciplines. This brief review covers the basic aspects of the relationships between the network structure and gel properties of the thermally sensitive poly(N-isopropylacrylamide) (pNIPAM) microgels including the phase transition process, the internal structure of microgels, and the phase behavior. Additionally, we highlight the impacts of microgels on the biomedical applications, especially in the gene delivery, cell matrix and differentiation of stem cells. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2995–3003     

Polyfunctional inorganic-organic hybrid materials: an unusual kind of NLO active layered mixed metal oxalates with tunable magnetic properties and very large second harmonic generation

Mixed M(II)/M(III) metal oxalates, as "stripes" connected through strong hydrogen bonding by para-dimethylaminobenzaldeide (DAMBA) and water, form an organic-inorganic 2D network that enables segregation in layers of the cationic organic NLO-phore trans-4-(4-dimethylaminostyryl)-1-methylpyridinium, [DAMS+]. The crystalline hybrid materials obtained have the general formula [DAMS]4[M2M'(C2O4)6].2DAMBA.2H2O (M = Rh, Fe, Cr; M' = Mn, Zn), and their overall three-dimensional packing is non-centrosymmetric and polar, therefore suitable for second harmonic generation (SHG). All the compounds investigated are characterized by an exceptional SHG activity, due both to the large molecular quadratic hyperpolarizability of [DAMS+] and to the efficiency of the crystalline network which organizes [DAMS+] into head-to-tail arranged J-type aggregates. The tunability of the pairs of metal ions allows exploiting also the magnetic functionality of the materials. Examples containing antiferro-, ferro-, and ferri-magnetic interactions (mediated by oxalato bridges) are obtained by coupling proper M(III) ions (Fe, Cr, Rh) with M(II) (Mn, Zn). This shed light on the role of weak next-nearest-neighbor interactions and main nearest-neighbor couplings along "stripes" of mixed M(II)/M(III) metal oxalates of the organic-inorganic 2D network, thus suggesting that these hybrid materials may display isotropic 1D magnetic properties along the mixed M(II)/M(III) metal oxalates "stripes".     

Preparation and nonlinear optical properties of inorganic-organic hybrid films with various substituents on chromophores

Four kinds of hydroxy-ended azobenzene-type chromophores containing different substituent groups as electron donor or electron acceptor were synthesized and further reacted with 3-isocyanatopropyltriethoxysilane (ICTES) to give alkoxysilane dyes via a urethane reaction. Following a sol-gel process of the alkoxysilane dyes, the inorganic-organic hybrid nonlinear optical (NLO) films were successfully prepared. Molecular structures of the resultant films were confirmed by elemental analysis, FTIR, and 1H NMR. The betaCT mu(g) values of the chromophores were evaluated by a solvatochromic method, and the second harmonic coefficients (d33) of the hybrid films were measured by in situ second harmonic generation (SHG) measurement. The hybrid films exhibited large optical nonlinearity and full transparency in the visible range. The effects of substituent group and position on betaCT mu(g) values of the chromophores and d33 values of the films were also discussed.