Saddle-Shaped Cyclic Indole Tetramers: 3D Electroactive Molecules.

We present a joint theoretical and experimental study of a series of cyclic indole tetramers aimed at understanding the fundamental electronic properties of this 3D platform and evaluating its potential in the construction of new semiconductors. To this end, we combined absorption and Raman spectroscopy, cyclic voltammetry, and spectroelectrochemistry with DFT calculations. Our results suggest that this platform can be easily and reversibly oxidized. Additionally, it has a HOMO that matches very well with the workfunction of gold, therefore charge injection from a gold electrode is expected to occur without significant barriers. Interestingly, the cyclic tetraindoles allow for good electron delocalization in spite of their saddle-shaped structures. The steric constraints introduced by N-substitution significantly inhibits ring inversion of the central cyclooctatetraene unit, whereas it only barely affects the optical and electrochemical properties (a slightly higher oxidation potential and a blueshifted absorption upon alkylation are observed).

An anthraquinone-based bismuth-iron metal-organic framework as an efficient photoanode in photoelectrochemical cells.

Metal-organic frameworks (MOFs) are appealing candidate materials to design new photoelectrodes for use in solar energy conversion because of their modular nature and chemical versatility. However, to date there are few examples of MOFs that can be directly used as photoelectrodes, for which they must be able to afford charge separation upon light absorption, and promote the catalytic dissociation of water molecules, while maintaining structural integrity. Here, we have explored the use of the organic linker anthraquinone-2, 6-disulfonate (2, 6-AQDS) for the preparation of MOFs to be used as photoanodes. Thus, the reaction of 2, 6-AQDS with Bi(iii) or a combination of Bi(iii) and Fe(iii) resulted in two new MOFs, BiPF-10 and BiFePF-15, respectively. They display similar structural features, where the metal elements are disposed in inorganic-layer building units, which are pillared by the organic linkers by coordination bonds through the sulfonic acid groups. We show that the introduction of iron in the structure plays a crucial role for the practical use of the MOFs as a robust photoelectrode in a photoelectrochemical cell, producing as much as 1.23 mmol H2 cm-2 with the use of BiFePF-15 as photoanode. By means of time-resolved and electrochemical impedance spectroscopic studies we have been able to unravel the charge transfer mechanism, which involves the formation of a radical intermediate species, exhibiting a longer-lived lifetime by the presence of the iron-oxo clusters in BiFePF-15 to reduce the charge transfer resistance.

Insight into Lewis acid catalysis with alkaline-earth MOFs: the role of polyhedral symmetry distortions.

We propose a multidisciplinary approach to face the interpretation of heterogeneous catalysis with alkaline-earth metal-organic frameworks (MOFs). Their oxygen-based polyhedra, which do not exhibit regular geometries, do act as very active Lewis acid sites. Four novel alkaline-earth MOFs that belong to three different structural types-Mg-AEPF-11, Mg-APF-12, Ca-AEPF-13 and Sr-APF-13-are reported, together with their net topologies, and a study of the symmetry distortions around the alkaline-earth metal polyhedra by using a continuous shape mapping (CShM) description. These MOFs are good catalysts in the selective hydrogenation of styrene. Even more, Sr-AEPF-13 shows the best conversions ever published with alkaline-earth MOFs for the hydrogenation of activated alkenes under mild conditions. A combination of crystallographic and topological analysis and theoretical calculations, together with experimental catalytic results, has been applied to understand the catalytic activity of these four novel alkaline-earth MOFs. This work demonstrates that the presence of symmetry-distorted alkaline-earth polyhedra gives rise to highly catalytic-active MOFs in the hydrogenation of activated alkenes.

Insight into the SBU condensation in mg coordination and supramolecular frameworks: a combined experimental and theoretical study.

This work is to emphasize the influence of the synthetic procedures in the isolation of different coordination polymers that coexist under hydro-/solvothermal conditions. An experimental and theoretical study in the Mg(2+):4,4'-(hexafluoroisopropylidene)bis(benzoic acid):1,10-phenantroline system has been carried out. Computational studies have determined the relative energies for those compounds that coexist under certain hydrothermal conditions, and have helped to identify the driving forces for the formation of the different phases. The five new compounds belong to five different structural types: AEPF-14, which presents two polymorphs (α- and ß-) ([Mg(H(2)O)(4)(phen)(2)]L), AEPF-15 ([Mg(HL)(2)(phen)]) and AEPF-16 ([Mg(H(2)O)(2)(L)(phen)]) are both 1D MOFs (AEPF-16 with a helical structure), and AEPF-17 ([Mg(H(2)O)(L)(phen)]) with a 2D structure. Hydrogen bond interactions found in the five compounds have been taken into account to study the topology of their supramolecular nets. Finally, dehydration studies performed on AEPF-14 (α- and ß-) and AEPF-16 have shown that the topological type of their supramolecular networks determines the structural changes that take place during the dehydration processes of these Mg compounds.

In situ transformation of TON silica zeolite into the less dense ITW: structure-direction overcoming framework instability in the synthesis of SiO2 zeolites.

Under specific synthesis conditions the crystallization of a dense silica zeolite (TON) is followed by its in situ transformation into a less dense and, in the absence of occluded species, less stable zeolite (ITW). Periodic ab initio calculations including energy corrections for van der Waals interactions as well as zero-point and thermal effects are used first to assess the relative stability of both SiO(2) (calcined) phases and then to investigate host-guest interactions in the as-made zeolites, as well as their relative stability. The less dense SiO(2)-ITW is less stable than SiO(2)-TON, with an energy difference that is significantly larger than expected from their difference in molar volume. This extra destabilization is ascribed to the strained double 4-ring units of silica tetrahedra (D4R). Regarding the as-made materials, the organic cation fills in more efficiently the zeolitic voids in ITW than in TON, bringing about a larger stabilization in the former owing to the extension of the long-range addition of dispersion force contributions. On the other hand, fluoride induces a polarization of the silica framework that is highly localized in TON (showing pentacoordinated [SiO(4/2)F](-) units) but has a large global character in ITW (where fluoride is encapsulated into D4R units). We argue that the structure-directing role toward D4R materials that has been proposed for fluoride consists fundamentally in the ability to induce a global polarization of the silica framework that allows relaxation of the strain associated with these units. In this sense, fluoride stabilizes the otherwise strained D4R-SiO(2) frameworks making them reachable for crystallization. This work documents a case in which the structure directing agents "choose" a structure not kinetically but through stabilization.

Dynamic calcium metal-organic framework acts as a selective organic solvent sponge.

Herein, we present a Ca-based metal-organic framework named AEPF-1, which is an active and selective catalyst in olefin hydrogenation reactions. AEPF-1 exhibits a phase transition upon desorption of guest molecules. This structural transformation takes place by a crystal to crystal transformation accompanied by the loss of single-crystal integrity. Powder diffraction methods and computational studies were applied to determine the structure of the guest-free phase. This work also presents data on the exceptional adsorption behavior of this material, which is shown to be capable of separating polar from nonpolar organic solvents, and is a good candidate for selective solvent adsorption under mild conditions.

Self-assembly of C3-symmetrical hexaaryltriindoles driven by solvophobic and CH-pi interactions.

The synthesis and aggregation properties of a series of differently substituted star-shaped hexaaryltriindoles both in solution and in the solid state are being reported. While these molecules do not show any significant intermolecular aggregation in CDCl(3), it has been possible to induce aggregation by increasing the polarity of the solvent and therefore facilitating the occurrence of solvophobic forces. A study of the influence of the electronic character of peripheral substituents on the self-association behavior in solution has shown that increasing the electron-donor character of the substituents facilitates self-association while derivatives substituted with electron-acceptor substituents do not self-assemble. The electronic nature of the substituents also has an influence in the geometry of the stacking of these derivatives observed in the solid state. While unsubstituted hexaphenyl triindole self-assemble in a staggered face-to-face arrangement, attaching six cyano functional groups results in an offset stacking. The influence of the substituents in the strength and geometry of the stacking tendency contrasts with the trend expected for an aggregation induced solely by pi-pi interactions, but can be explained considering an important contribution of multiple cooperative CH-pi interactions.

Structural analysis of zincocenes with substituted cyclopentadienyl rings.

New zincocenes [ZnCp'(2)] (2-5) with substituted cyclopentadienyl ligands C(5)Me(4)H, C(5)Me(4)tBu, C(5)Me(4)SiMe(2)tBu and C(5)Me(4)SiMe(3), respectively, have been prepared by the reaction of ZnCl(2) with the appropriate Cp'-transfer reagent. For a comparative structural study, the known [Zn(C(5)H(4)SiMe(3))(2)] (1), has also been investigated, along with the mixed-ring zincocenes [Zn(C(5)Me(5))(C(5)Me(4)SiMe(3))] (6) and [Zn(C(5)Me(5))(C(5)H(4)SiMe(3))] (7), the last two obtained by conproportionation of [Zn(C(5)Me(5))(2)] with 5 or 1, as appropriate. All new compounds were characterised by NMR spectroscopy, and by X-ray methods, with the exception of 7, which yields a side-product (C) upon attempted crystallisation. Compounds 5 and 6 were also investigated by (13)C CPMAS NMR spectroscopy. Zincocenes 1 and 2 have infinite chain structures with bridging Cp' ligands, while 3 and 4 exhibit slipped-sandwich geometries. Compounds 5 and 6 have rigid, eta(5)/eta(1)(sigma) structures, in which the monohapto C(5)Me(4)SiMe(3) ligand is bound to zinc through the silyl-bearing carbon atom, forming a Zn--C bond of comparable strength to the Zn--Me bond in ZnMe(2). Zincocene 5 has dynamic behaviour in solution, but a rigid eta(5)/eta(1)(sigma) structure in the solid state, as revealed by (13)C CPMAS NMR studies, whereas for 6 the different nature of the Cp' ligands and of the ring substituents of the eta(1)-Cp' group (Me and SiMe(3)) have permitted observation for the first time of the rigid eta(5)/eta(1) solution structure. Iminoacyl compounds of composition [Zn(eta(5)-C(5)Me(4)R)(eta(1)-C(NXyl)C(5)Me(4)R)] resulting from the reactions of some of the above zincocenes and CNXyl (Xyl=2,6-dimethylphenylisocyanide) have also been obtained and characterised.

A new scandium metal organic framework built up from octadecasil zeolitic cages as heterogeneous catalyst.

Zeolitic cages of the AST type are found in the novel scandium-squarate MOF, and the joining of them gives rise to a new binodal network with a unique topology; this new material is an efficient heterogeneous Lewis acid catalyst.

Angstrom-Resolved Metal-Organic Framework-Liquid Interfaces.

Metal-organic frameworks (MOFs) are a class of crystalline materials with a variety of applications in gas storage, catalysis, drug delivery or light harvesting. The optimization of those applications requires the characterization of MOF structure in the relevant environment. Dynamic force microscopy has been applied to follow dynamic processes of metal-organic-framework material. We provide images with spatial and time resolutions, respectively, of angstrom and seconds that show that Ce-RPF-8 surfaces immersed in water and glycerol experience a surface reconstruction process that is characterized by the diffusion of the molecular species along the step edges of the open terraces. The rate of the surface reconstruction process depends on the liquid. In water it happens spontaneously while in glycerol is triggered by applying an external force.

Addressed realization of multication complex arrangements in metal-organic frameworks.

The preparation of materials with structures composed of multiple metal cations that occupy specific sites is challenging owing to the difficulty of simultaneously addressing the incorporation of different elements at desired precise positions. We report how it is possible to use a metal-organic framework (MOF) built with a rod-shaped inorganic secondary building unit (SBU) to combine multiple metal elements at specific positions in a manner that is controllable at atomic and mesoscopic scales. Through the combination of four different metal elements at judiciously selected molar ratios, 20 MOFs of different compositions and the same topology have been prepared and characterized. The use of diffraction techniques, supported by density functional theory calculations, has led us to determine various possible atomic arrangements of the metal cations within the SBUs. In addition, seven of the compounds combine multiple types of atomic arrangements, which are mesoscopically distributed along the crystals. Given the large diversity and importance of rod-based MOFs, we believe that these findings offer a new general strategy to produce complex materials with required compositions and controllable arrangements of the metal cations for desired applications.

One teflon-like channelled nanoporous polymer with a chiral and new uninodal 4-connected net: sorption and catalytic properties.

Zn(C17H8F6O4) is the first example of a fluoro-lined nanotube organo-inorganic 3D polymeric chiral structure, which possesses two different types of isolated channels, one of them being laid out with a double spiral of CF3-groups from the ligand molecule; the structure is a new uninodal 4-connected net that only exists when bent ligands connect the centres, and the compound exhibits selective sorption and catalytic chiral recognition properties.

Synthesis and Characterization of (2,4,6-Trimethylphenylimido)molybdenum Complexes. X-ray Crystal Structures of (L(OEt))Mo(Nmes)(2)Cl, (L(OEt))Mo(Nmes)Cl(2), and MoCl(3)(Nmes)(depe) (mes = 2,4,6-Trimethylphenyl, L(OEt) = (eta-C(5)H(5))Co{P(O)(OEt)(2)}(3), depe = Et(2)PCH(2)CH(2)PEt(2)).

The bis(imido) complex MoCl(2)(Nmes)(2)(dme) (1) (mes = 2,4,6-trimethylphenyl, dme = 1,2-dimethoxyethane) has been used as the starting material for the preparation of the compounds (L(OEt))Mo(Nmes)(2)Cl (2) (L(OEt) = (eta-C(5)H(5))Co{P(O)(OEt)(2)}(3)) and Mo(Nmes)(2)(acac)(2) (5), as well as for the synthesis of the mixed oxo-imido MoCl(2)(Nmes)(O)(dme) (6), the latter reaction involving conproportionation of 1 and MoCl(2)(O)(2)(dme). Similarly, the paramagnetic mono(imido) species Mo(Nmes)Cl(3)(dme) (11) can also be obtained from 1 by interaction with MoCl(4)(THF)(2) (THF = tetrahydrofuran) in refluxing dme. Compounds 6 and 11 are suitable sources for the synthesis of other diamagnetic mixed oxo-imido and paramagnetic mono(imido) compounds, respectively. Three of the newly synthesized complexes, namely, (L(OEt))Mo(Nmes)(2)Cl (2), (L(OEt))Mo(Nmes)Cl(2) (12), and MoCl(3)(Nmes)(depe) (14) (depe = Et(2)PCH(2)CH(2)PEt(2)) have been characterized by X-ray crystallography.

Synthesis, Structural Characterization, and MO Calculations of Vanadium Imido Complexes Containing Bidentate Phosphine Coligands.

Treatment of complex V(N-2,6-(i)Pr(2)C(6)H(3))Cl(3) with 1,2-dimethoxyethane (dme) gives in quasi-quantitative yield the adduct V(N-2,6-(i)Pr(2)C(6)H(3))Cl(3)(dme) (1). Interaction of 1 with bidentate phosphines gives V(N-2,6-(i)Pr(2)C(6)H(3))Cl(3)(P-P) (P-P = depe, 2a; dppe, 2b) compounds. An X-ray analysis (monoclinic, space group P2(1)/c, a = 14.7387(14) Å, b = 10.6738(10) Å, c = 16.999(3) Å, beta = 90.954(2) degrees, Z = 4, R = 0.0544), carried out on complex 2a, shows a mer arrangement of the chloride ligands and a nonsymmetrical coordination of the diphosphine ligand. One of the phosphorus atoms occupies the trans position with respect to the organoimido ligand. MO calculations on the models V(NR)Cl(3)(H(2)PCH(2)CH(2)PH(2)) (R = H, C(6)H(5)) of complex 2a were performed. The mer isomer, which is more stable than the fac isomer, shows good agreement with the experimental data.

Synthesis of Enantiopure α-Alkoxy-α-Trifluoromethyl Aldehydes and Carboxylic Acids from Trifluoromethyl Ketones.

Formaldehyde dialkylhydrazones behave as neutral d1 synthons in their uncatalyzed reaction with trifluoromethyl ketones (see reaction). Both racemic and optically pure 1,2-adducts were obtained in good yields. Efficient deprotection of the hydrazone moiety afforded interesting fluorinated quaternary compounds such as 1 and 2.

Development of homogeneous and heterogenized rhodium(I) and palladium(II) complexes with ligands based on a chiral proton sponge building block and their application as catalysts.

Chiral compounds prepared from proton sponge building block 8-((2R,5R)-2,5-dimethylpyrrolidin-1-yl)naphthalen-1-amine were found to be effective chiral ligands for obtaining complexes of rhodium(I) and palladium(II) by reaction with [RhCl(cod)](2), PdCl(2)(cod) or Pd(OAc)(2). The complexes bearing triethoxysilane groups were immobilized on mesoporous MCM-41 in order to obtain new heterogeneous catalysts. Both materials are active in the hydrogenation of alkenes and could be recycled without loss of activity or enantioselectivity.

Isolation of enantiomerically pure organometallic palladium compounds: synthesis of the triangles prepared from enantiopure [cis-Pd2(C6H4PPh2)2(NCCH3)4]2+.

Reaction of the racemic [Pd(C(6)H(4)PPh(2))Br](4) () with the silver salt of 1R-(1alpha,2beta,3alpha)]-3-methyl-2-(nitromethyl)-5-oxocyclopentaneacetate, (R)-AgO(2)CR*, results in the formation of a mixture of diastereoisomers (RRR)- and (SRR)- of the formula Pd(2)(C(6)H(4)PPh(2))(2)(O(2)CR*)(2) that were separated by standard chromatographic methods. Each diastereoisomer was readily converted into the tetrametallic stereoisomers (SS)- and (RR)-, of the formula [Pd(C(6)H(4)PPh(2))Br](4) that were isolated and characterized by X-ray crystallography. The R enantiomer of the solvated cationic species [cis-Pd(2)(C(6)H(4)PPh(2))(2)(NCCH(3))(4)](2+), obtained from (RR)-, was reacted with ammonium terephthalate yielding RRR-[Pd(2)(C(6)H(4)PPh(2))(2)](3)(O(2)CC(6)H(4)CO(2))(3), (RRR)-. The reaction of ammonium diphenyldicarboxylate with the S enantiomer of the solvated species, gave SSS-[Pd(2)(C(6)H(4)PPh(2))(2)](3)(O(2)CC(6)H(4)C(6)H(4)CO(2))(3), (SSS)-. Compounds and have been crystallographically characterized. Reactions performed with racemic [Pd(2)(C(6)H(4)PPh(2))(2)(CH(3)CN)(4)](2+), have also been studied and the relative chiralities of the triangles have been determined by (31)P NMR spectroscopy.

Synthesis and preferred all-syn conformation of C3-symmetrical N-(hetero)arylmethyl triindoles.

A new series of C(3)-symmetrical N-(hetero)arylmethyl triindoles has been synthesized in a straightforward procedure. The structure and conformation in the solid state have been determined for three derivatives (3, 4, and 6) by X-ray crystallographic analysis. In all three cases, the molecules adopt a tripodal conformation with all of the flexible arms directed towards the same side, thereby delimiting an inner cavity. Compound 6 crystallizes and forms C(3)-symmetric dimeric cagelike complexes. Guest molecules of chloroform and water are confined within the resulting cavities with stabilization by different intermolecular interactions; this highlights the potential of these compounds in the construction of supramolecular systems. A computational analysis has been performed to predict the most stable conformers. As a general trend, a preference for a conformation with all branches directed to the same side has been predicted. Comparison between theoretical and experimental results indicates that the computational level selected for the present study, B3LYP/6-31G*, is able to reproduce both the minimum energy conformations and the rotation barriers about the N--CH(2) bond.