M. Ángeles Monge

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.

3D scandium and yttrium arenedisulfonate MOF materials as highly thermally stable bifunctional heterogeneous catalysts

Three new 3D metal-organic frameworks (MOFs), namely scandium and yttrium naphthalenedisulfonates (nds), have been obtained and their crystal structures have been determined by single crystal X-ray diffraction. The 1,5- and 2,6-nds scandium compounds (RPF-12 and RPF-13, respectively), both with the formula [Sc2(nds)(OH)4]n, and the yttrium naphthalenedisulfonate [Y(1,5-nds)(OH)(H2O)]n, RPF-14, were synthesised under hydrothermal conditions. The frameworks can be described as pillared layered motifs where sheets of sulfonate bridged polyhedra are connected by naphthalene units. The scandium disulfonate [Sc2(2,6-nds)(OH)4]n is the first obtained rare-earth 2,6-nds MOF with the same stoichiometry and arrangement as its 1,5-nds counterpart. The new MOFs, with high thermal stability, act as active and selective bifunctional heterogeneous catalysts in the epoxidation of linalool and oxidation of sulfides.

Mixed lanthanide succinate–sulfate 3D MOFs: catalysts in nitroaromatic reduction reactions and emitting materials

The first series of mixed succinate/sulfate/Ln MOFs, [Ln22(C22H44C22O44)22(SO44)(H22O)22] (RPF-16), where Ln = La, Pr, Nd, and Sm, were hydrothermally obtained and their structures determined by X-ray single crystal diffraction. The crystalline products are a series of isostructural 3D polymeric compounds that crystallise in the monoclinic space group P2(1)/n. Their framework comprises infinite crossing chains of LnO9 sharing edges polyhedra, kept together by succinate and sulfate anions. Topological simplification gives rise to a 3D uninodal six connected net of type pcu alpha-Po primitive cubic. These well-defined compounds show high chemoselectivity towards reduction of the nitro group and present bifunctional activity for the one-pot reductive amination of heptanal at near-complete conversion of the substrates. A general overview of the room-temperature luminescence behavior in the new RPF-16 Ln materials is also reported.

A Mesoporous Indium Metal–Organic Framework: Remarkable Advances in Catalytic Activity for Strecker Reaction of Ketones

With the aim of developing new highly porous, heterogeneous Lewis acid catalysts for multicomponent reactions, a new mesoporous metal-organic framework, InPF-110 ([In3O(btb)2(HCOO)(L)], (H3btb = 1,3,5-tris(4-carboxyphenyl)benzene acid, L = methanol, water, or ethanol), has been prepared with indium as the metal center. It exhibits a Langmuir surface area of 1470 m(2) g(-1), and its structure consists of hexagonal pores with a 2.8 nm aperture, which allows the diffusion of multiple substrates. This material presents a large density of active metal sites resulting in outstanding catalytic activity in the formation of substituted α-aminonitriles through the one-pot Strecker reaction of ketones. In this respect, InPF-110 stands out compared to other catalysts for this reaction due to the small catalyst loadings required, and without the need for heat or solvents. Furthermore, X-ray single crystal diffraction studies clearly show the framework-substrate interaction through coordination to the accessible indium sites.

H3O2 Bridging Ligand in a Metal–Organic Framework. Insight into the Aqua-Hydroxo↔Hydroxyl Equilibrium: A Combined Experimental and Theoretical Study

A metal-organic framework (MOF) bearing the aqua-hydroxo species (O2H3)(-) in the framework, as well as the processes that govern the equilibrium aqua-hydroxo (O2H3)(-)↔hydroxyl (OH) in Sc-MOFs, are studied experimentally and theoretically. Computational studies were employed to determine the relative energies for the two compounds that coexist under certain hydrothermal conditions at pH < 2.8. The thermodynamically more stable [Sc3(3,5-DSB)2(μ-O2H3)(μ-OH)2(H2O)2] (from now on, (O2H3)Sc-MOF; 3,5-DSB = 3,5-disulfobenzoic acid) was obtained as a pure and stable phase. It was impossible to isolate [Sc3(3,5-DSB)2(μ-OH)3(H2O)4] as a pure phase, as it turned out to be the precursor of (O2H3)Sc-MOF. Additionally, a third compound that appears at pH between 3.5 and 4, [Sc3(3,5-DSB)(μ-OH)6(H2O)] and a fourth, [Sc(3,5-DSB)(Phen)(H2O)](H2O), in whose formula neither OH groups nor H3O2(-) anions appear, are reported for comparative purposes. A study of the (O2H3)Sc-MOF electronic structure, and some heterogeneous catalytic tests in cyanosilylation of aldehydes reactions, are also reported.

A Germanium Zeotype Containing Intratunnel Transition Metal Complexes

A new zeolite-type structure is adopted by (NH(4))(+)[M(NH(3))(2)](+)(Ge(9)O(19))(2-) (M=Cu, Ag; shown in the picture). These compounds are the first microporous germanates containing a transition metal complex inside their tunnels. The large separation between the metal centers and the unhindered access of reactants to these active sites through uniformly sized channels make these materials a good point of departure for designing new catalysts.

Indium metal–organic frameworks as catalysts in solvent-free cyanosilylation reaction

Two new Indium MOFs with the bending multicarboxylate ligand H2dpmda as a linker and different N-donor ancillary ligands were obtained; the two compounds are isoreticular with 2D-hcb uninodal 3-connected nets. Comparison of their activity in cyanosilylation reactions with another eight In-MOFs is also reported. Eight out of the ten resulted in being good catalysts under mild and environmentally friendly conditions. Correlations between indium coordination number (CN), framework topology and catalytic activity are made and discussed, demonstrating that among the studied MOFs, the indium material named InPF-6 with the formula [In2(dpa)3(1,10-phen)2]·H2O is the most effective catalyst. A possible catalytic mechanism is discussed.