Search

A combined experimental and theoretical study of H

Nanothreads are one-dimensional nanomaterials composed of a primarily sp

Strategies to improve the catalytic efficiency of the hydrogen evolution reaction (HER), an integral electrochemical reaction in solar-to-hydrogen technologies, frequently include the use of porous...

We demonstrate a simple and generalizable method for the one pot, in situ formation of bimetallic metal–organic framework (MOF) materials decorated with crystallographically defined, low-valent metal sites. Solvothermal reactions between poly(carboxylated) aryl(phosphine) ligands and mixtures of higher- and lower-valent metal precursors achieves concomitant P–M complexation and MOF formation via metal–carboxylate network bonding. This method is demonstrated in the preparation of two new phosphine coordination materials, PCM-107 and PCM-74, which feature Ar3P–AuX (X = Cl, Br) and chelated PN–Cu2I2–PN units as the MOF building blocks, respectively. PCM-107 is an active catalyst for alkyne hydroaddition, while PCM-74 shows promise for the crystallization of MOFs bearing kinetically favored isomers.

A new terthiophene-based imidazole luminophore 5,5’-(1H-thieno[3,4-d]imidazole-4,6-diyl)bis(thiophene-2-carboxylic acid) (TIBTCH2, 5) was synthesized in one step from previously reported 4,6-di(thiophen-2-yl)-1H-thieno[3,4-d]imidazole (DTTI, 4), and their photophysical properties were studied and compared accordingly. Under solvothermal conditions, reacting 5 with Mn(OAc)2 yielded a new three-dimensional metal-organic framework (MOF, 6) which was structurally defined by single-crystal X-ray diffraction. In 6, all Mn(II) ions octahedrally bind to carboxylate-O atoms to form a linear Mn3 secondary building unit (SBU) that contains three distinct coordination modes. Importantly, 6 exhibits dual functional properties of ligand-based emission and metal-based magnetic behaviors.

The tetrahedral zwitterion of tetrakis(p-carboxyphenyl) phosphonium is structurally analogous to a family of ligands with C or Si cores that have found great utility in the preparation of stable MOFs. However, the central P(V)+ core in this molecule reduces the formal ligand charge, resulting in a PR43− tetra(carboxylate) species. This new strategy allows for the formation of lighter MOFs by incorporation of less metal, which cannot be accessed using conventional ligands. The phosphonium zwitterion is stable under hydrothermal synthesis conditions; it spontaneously crystallizes from hot DMF to give a metal-free and infinitely porous ionic hydrogen-bonded organic framework, which is stable in water and organic solvents. We demonstrate how direct hydrothermal treatment of the ionic framework in the presence of In(NO3)3 yields a new charge-neutral In(III) MOF with diamondoid topology. By comparison, solvothermal reaction in the presence of Mg(NO3)2 yields a chemically-robust MOF with permanent 3D porosity. The Mg(II)-based MOF displays water adsorption properties with an estimated ΔHads of −63.5 kJ mol−1 and a maximum uptake of 38.9 wt% at 30 °C. This exceptionally stable material also showed highly reversible H2S sorption with a capacity of ∼8 mmol g−1, and solvent-triggered H2S release.

A large-pore version of Mg-CUK-1, a water-stable metal-organic framework (MOF) with 1-D channels, was synthesized in basic water. Mg-CUK-1L has a BET surface area of 2896 m2 g-1 and shows stark selectivity for CO2 sorption over N2, O2, H2, and CH4. It displays reversible, multistep gated sorption of CO2 below 0.33 atm. The dehydrated single-crystal structure of Mg-CUK-1L confirms retention of the open-channel structure. The MOF can be loaded with organic molecules by immersion in hot melts, providing single crystals suitable for X-ray diffraction. trans-Azobenzene fills the channels in a 2 × 2 arrangement. Solid-state UV-vis spectroscopy reveals that azobenzene molecules undergo reversible trans-cis isomerization, despite being close-packed; this surprising result is confirmed by DFT-simulated UV-vis spectra.

We present the synthesis of Ag–Ir alloys in the form of solid-solution nanoparticles (NPs). Ag and Ir are classically immiscible in the bulk and therefore the physical properties of Ag–Ir alloys are unknown. A convenient microwave-assisted, solution-phase method that employs readily available Ag(NO3) and IrCl3 precursors enables the preparation of small (2.5–5.5 nm) Ag–IrNPs with alloyed structures. AgxIr(100–x)NPs can be obtained by this method between x = 6–31. The Ag–IrNPs resist dealloying upon heating up to 300 °C. Ir-rich Ag–IrNPs dispersed on amorphous silica are significantly more active gas-phase alkene hydrogenation catalysts than pure IrNPs. Density functional theory (DFT) and theoretical modeling studies reveal that the Ag–IrNPs—which are consistently larger than monometallic IrNPs prepared under the same conditions—have comparatively fewer strong H-binding edge sites. This promotes faster H atom transfer to coadsorbed alkenes. Ag–IrNPs supported on amorphous Co3O4 show a linear composition de...

PCM-101 is a phosphine coordination material comprised of tris(p-carboxylato)triphenylphosphine and secondary pillaring groups coordinated to [M3 (OH)]5+ nodes (M=Co, Ni). PCM-101 has a unique topology in which R3 P: sites are arranged directly trans to one another, with a P⋅⋅⋅P separation distance dictated by the pillars. Post-synthetic coordination of soft metals to the P: sites proceeds at room temperature to provide X-ray quality crystals that permit full structural resolution. Addition of AuCl groups forces a large distortion of the parent framework. In contrast, CuBr undergoes insertion directly between the trans-P sites to form dimers that mimic solution-phase complexes, but that are geometrically strained due to steric pressure exerted by the MOF scaffold. The metalated materials are active in heterogeneous hydroaddition catalysis under mild conditions, yielding different major products compared to their molecular counterparts.

Ancillary functionalization of a PCP pincer ligand with para -carboxylic acids provides a simple route to the subsequent preparation of crystalline coordination polymers using pre -cyclometallated complexes as polymer building blocks. This synthetic strategy is demonstrated here using air- and moisture-stable PCP-PdCl metalloligands to prepare new coordination polymers with both 1-D (chain) and 2-D (sheet) networks, named PCM-29 and PCM-30, respectively. The single crystal X-ray structures and solid-state gas sorption properties of both materials are presented. The Brunauer-Emmett-Teller (BET) surface area of PCM-30 was found to be 302 m 2 g −1 using CO 2 as the probe gas, indicating permanent porosity and reversible small molecule diffusion between the 2-D sheets.

Controlled partial decomposition of 2-selenonicotinic acid in the presence of Co2+ or Ni2+ resulted in the in situ formation of an unusual MOF based on triselenane ligands (RSeSeSeR) coordinated to M2+ centers as NSeN-pincers. Post-synthetic oxidation by treatment with aqueous H2O2 facilitates its solid-state conversion into a RSeO2− molecular coordination complex, which was tracked via powder X-ray diffraction studies and by single-crystal structural resolution of the final product.

ACM-1 is the first example of an organoarsine metal–organic framework (MOF), prepared using a new pyridyl-functionalized triarylarsine ligand coordinated to Ni(II) nodes. ACM-1 has micropores that are decorated with cis-diarsine coordination pockets. Postsynthetic metalation of ACM-1 with AuCl under facile conditions studied by single-crystal X-ray diffraction reveals the installation of dimeric Au2Cl2 complexes via the formation of As–Au bonds. The Au(I) dimers display exceptionally short aurophilic bonds (2.76 A) induced by the rigidity of the MOF, which acts as a unique solid-state ligand.

PCM-22, a metal-organic framework material comprising triphenylphosphine and Ln3+ ions (Ln = Pr–Yb), exhibits solid-state luminescence at room temperature. Mixed-metal versions of PCM-22 that contain controlled amounts of Eu3+, Gd3+, and Tb3+ function as highly sensitive, broad-scope solid-state sensors that can rapidly identify unknown solvents by providing a unique “eight-factor” fingerprint. The sensors allow for immediate solvent identification via color changes that are obvious to the naked eye and also permit quantitative chemical analysis by uncomplicated spectrophotometry. These same materials achieve quantitative detection of H2O in D2O from 10 to 120,000 ppm. The detection of trace H2O is also demonstrated in a range of common solvents, including those incompatible with conventional laboratory titration methods. A series of luminescent phosphine coordination materials show diverse sensing capabilities. These solid-state sensor materials can detect trace H2O impurities in D2O from 10 to 120,000 ppm and can rapidly identify unknown solvents.

A tetra(carboxylated) PCP pincer ligand has been synthesized as a building block for porous coordination polymers (PCPs). The air- and moisture-stable PCP metalloligands are rigid tetratopic linkers that are geometrically akin to ligands used in the synthesis of robust metal-organic frameworks (MOFs). Here, the design principle is demonstrated by cyclometalation with Pd(II) Cl and subsequent use of the metalloligand to prepare a crystalline 3D MOF by direct reaction with Co(II) ions and structural resolution by single crystal X-ray diffraction. The Pd-Cl groups inside the pores are accessible to post-synthetic modifications that facilitate chemical reactions previously unobserved in MOFs: a Pd-CH3 activated material undergoes rapid insertion of CO2 gas to give Pd-OC(O)CH3 at 1 atm and 298 K. However, since the material is highly selective for the adsorption of CO2 over CO, a Pd-N3 modified version resists CO insertion under the same conditions.