Enrique Gutiérrez-Puebla

Reversible Breaking and Forming of Metal–Ligand Coordination Bonds: Temperature‐Triggered Single‐Crystal to Single‐Crystal Transformation in a Metal–Organic Framework

Yb(C(4)H(4)O(4))(1.5)] undergoes a temperature-triggered single-crystal to single-crystal transformation. Thermal X-ray single-crystal studies showed a reversibly orchestrated rearrangement of the atoms generated by the breaking/formation of coordination bonds, in which the stoichiometry of the compound remains unchanged. The transformation occurs on heating the crystal at approximately 130 degrees C. This uncommon behavior was also studied by thermal methods, FTIR spectroscopy, and thermodiffractometry. Both polymorphs, alpha (room-temperature form) and beta (high-temperature form), are proven to be active heterogeneous catalysts; the higher catalytic activity of beta is owed to a decrease in the Yb coordination number. A mechanism based on spectroscopic evidence and involving formation of the active species Yb-O-OH is proposed for the sulfide oxidation.

Lanthanide Metal–Organic Frameworks: Searching for Efficient Solvent-Free Catalysts

Three Ln-based 2D metal-organic frameworks with the formula [Ln(3,5-DSB)(Phen)] (Ln = La, Pr, Nd; 3,5-DSB = 3,5-disulfobenzoate; Phen = 1,10-phenathroline) were hydrothermally synthesized. They belong to two 2D structural types, and their nets own different topologies. The isostructural La and Pr compounds possess a uninodal 5-connected SP 2-periodic net (6,3). The Nd compound has a binodal 3- and 6-connected kgd net. The novel compounds exhibit excellent catalytic activities toward the cyanosilylation reaction under solvent-free conditions.

Multimetal rare earth MOFs for lighting and thermometry: tailoring color and optimal temperature range through enhanced disulfobenzoic triplet phosphorescence

New isostructural compounds [Ln7(3,5-DSB)4(OH)9(H2O)15]·4H2O (Ln = Eu, Gd and Tb) (DSB = 3,5-disulfobenzoate), with excellent optical properties, have been obtained and studied. By combining the lanthanide cations with the DSB ligand the formation of a singular heptanuclear [Ln7(OH)9]+12 metallic core secondary building unit (SBU) has been promoted. This core is defined as a bi-capped dicubane SBU, and is a 4-connected node in a bidimensional net with (44·62) topology. The highly efficient emission from the triplet state of the disulfobenzoic ligand in the Gd-MOF and the exponential temperature dependence of ITriplet/ILn = Io exp(−EA/kBT) allow the design of thermometers with different color ranges through the adequate multimetal combination that cover almost the whole visible spectrum and are useful in a wide temperature range (10–300 K) with unprecedented sensitivities up to 32% K−1. The Eu-DSB and Tb-DSB MOFs present an optimum antenna effect, a temperature independent f–f emission temporal decay and, in spite of the close packing of the Ln ions inside the MOF, no concentration quenching. The external efficiency is drastically increased in MOFs with a combination of a few percent of Eu and/or Tb with Gd by means of radiative and non-radiative energy transfers from the Gd ions and Gd connected ligands.

Tunable Catalytic Activity of Solid Solution Metal–Organic Frameworks in One-Pot Multicomponent Reactions

The aim of this research is to establish how metal-organic frameworks (MOFs) composed of more than one metal in equivalent crystallographic sites (solid solution MOFs) exhibit catalytic activity, which is tunable by virtue of the metal ions ratio. New MOFs with general formula [InxGa1-x(O2C2H4)0.5(hfipbb)] were prepared by the combination of Ga and In. They are isostructural with their monometal counterparts, synthesized with Al, Ga, and In. Differences in their behavior as heterogeneous catalysts in the three-component, one pot Strecker reaction illustrate the potential of solid solution MOFs to provide the ability to address the various stages involved in the reaction mechanism.

Synthesis, Characterization, Molecular Structure and Theoretical Studies of Axially Fluoro-Substituted Subazaporphyrins

A new and general synthetic method for the preparation of fluoro-substituted subazaporphyrins is reported that involves the treatment of the corresponding chloro- or aryloxy-substituted subazaporphyrins (SubAPs) with BF(3).OEt(2). The strategy has been applied to both subphthalocyanines (SubPcs) and subporphyrazines (SubPzs). The yields were high for the latter, although low yields were obtained for the benzo derivatives. In contrast to the corresponding chloro derivatives, fluorosubazaporphyrins are quite robust towards hydrolysis. All of the new compounds were characterized by several spectroscopic techniques, which included (1)H, (13)C, (19)F, (15)N, and (11)B NMR spectroscopy, IR spectroscopy, UV/Vis spectrophotometry, and mass spectrometry (both high and low resolution). In addition, DFT calculations provided theoretical NMR spectroscopy values that are in good agreement with the experimental ones. The high dipole moments exhibited by the fluorosubazaporphyrins as a result of the presence of a fluorine atom in an axial position are responsible for the spontaneous and singular supramolecular aggregation of the macrocycles in the crystalline state. The molecular and crystal structures of two one-dimensional fluorine SubAPs, namely, a SubPc and a SubPz, are discussed. Molecules of the same class stack in alternating configurations along the c axis, which gives rise to columns that contain large numbers of monomers. SubPz 3 c forms aggregates with the macrocycles arranged in a parallel fashion with the B-F bonds perfectly aligned within a column, whereas with SubPc 3 b the neighboring columns cause a commensurate sinusoidal distortion along the columns in the c direction, which prevents the alignment of the B-F bonds. However, the most remarkable feature, common to both crystalline architectures, is the extremely short and unusual intermolecular F...N distances of the contiguous molecules, which are shorter than the sum of the corresponding van der Waals radii. Theoretical calculations have shown that these short distances can be explained by the existence of a cooperativity effect as the number of monomers included in the cluster increases.

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.

C−H Bond Activation of Benzene and Cyclic Ethers by TpIrIII Species

An unusual Fischer carbene derivative that, in addition, contains an alkyl and a hydride ligand is obtained by C−H bond activation of THF by the hydride–vinyl species [TpMe2IrH(CHCH2) (C2H4)]. This complex is also capable of activating the C−H bonds of benzene to give remarkably stable IrIII–N2 complexes (see illustration).

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.

(NH4)2Ge7O15: A Microporous Material Containing GeO4 and GeO6 Polyhedra in Nine‐Rings

GeO4tetrahedra and GeO6octahedra, which form nine-rings (see sketch on the right), feature in the unprecedented structure of the microporous solid, (NH4)2Ge7O15. This compound provides the first evidence that in the GeO2/NH4+ system the cubic (NH4)3HGe7O16⋅n H2O is not the only existing phase, but depending on the GeO6/GeO4 ratio, differently charged frameworks can be generated.

Heterogeneous Catalysis with Alkaline-Earth Metal-Based MOFs: A Green Calcium Catalyst

A new class of hydrogenation catalysts is required to develop cheaper and environmentally friendly alternatives, in order to avoid the loss of the huge quantities of precious metals, such as Pd, Pt, Rh, Ir, Re, which are widely used to perform traditional heterogeneous hydrogenation for the needs of pharmaceutical, petrochemical, food, soap and detergent, or plasticizer industries. Soluble rhodium and iridium complexes, such as Wilkinson’s and Crabtree’s catalysts, are elegant examples of homogeneous catalysts for these reactions. However, the complicated recovering and recycling processes of homogeneous catalysts have prevented many of them from being commercialized. In this context, metal–organic frameworks (MOFs) can be expected to provide interesting alternatives. These materials are known to possess the capability for several important functionalities, including gas storage, catalysis, and optical properties. Usually, transition metals or rare earths are used to synthesize MOF materials, yet, in spite of the similarities between rare-earth and alkaline-earth complexes, the use of the latter to build MOFs has been much less studied. However, the high Lewis acidity of the alkalineearth metal ions can provide catalysts with very active sites for alkene hydrogenation; strontium and calcium complexes have recently been used as homogeneous catalysts, both for hydrogenation and polymerization of alkenes. Taking into account these considerations, we present herein the synthesis and studies of the properties of a new MOF based on calcium, one of the most abundant and cheap elements. This environmentally friendly material could provide an alternative to traditional precious metal-based hydrogenation catalysts, owing to its low cost, easy fabrication, thermal stability, and robust framework. Previously, we have reported heterogeneous catalysts based on Ln, In, and Zn cations with 4,4’-(hexafluoroisopropylidene)bis(benzoic acid) (H2hfipbb) as a ligand. [8] MOFs of H2hfipbb with transition metals such as Cu and Co have also been studied. Solvothermal reaction of Ca(CH3CO2)2·H2O and H2hfipbb in a water/acetone mixture resulted in the formation of a new MOF with the formula [Ca(hfipbb)(H2hfipbb)0.5(H2O)]·0.7 C3H6O, AEPF-1 (AEPF = alkaline earth polymeric framework) in approximately 70 % yield. In AEPF-1 calcium atoms are heptacoordinated to form monocapped octahedra, whose vertices are occupied by five oxygen atoms from completely deprotonated hfipbb ligands, one from a protonated H2hfipbb ligand, and one water molecule (Figure 1). For every Ca + cation there is one