Ilich A. Ibarra

Highly porous and robust scandium-based metal–organic frameworks for hydrogen storage

The metal-organic frameworks NOTT-400 and NOTT-401, based on a binuclear [Sc(2)(μ(2)-OH)(O(2)CR)(4)] building block, have been synthesised and characterised; the desolvated framework NOTT-401a shows a BET surface area of 1514 m(2) g(-1) with a total H(2) uptake of 4.44 wt% at 77 K and 20 bar.

Synthesis of metal-organic frameworks by continuous flow

A continuous flow process for the synthesis of a metal–organic framework using only water as the reaction medium and requiring only short residence times is described. This affords a new route to scale-up of materials incorporating many of the principles of Green Chemistry. The process is demonstrated by the synthesis MIL-53(Al) via continuous flow reaction requiring only 5–6 minutes with a space time yield of 1300 kg m−3 d−1. We have demonstrated the synthesis of 500 g of MIL-53(Al) using this process, which can be scaled-up further by simply feeding further solutions of metal salt and ligand through the reactor. The product has a higher surface area and a better colour than a commercially produced sample of this MOF. In addition, a new and effective method for the extraction of terephthalic acid from within the pores of MIL-53(Al) using supercritical ethanol has been developed, representing a new methodology for activation and removal of substrates from porous hosts.

Rational design of porous coordination polymers based on bis(phosphine)MCl2 complexes that exhibit high-temperature H2 sorption and chemical reactivity.

MCl2 complexes of a new p-carboxylated 1,2-bis(diphenylphosphino)benzene ligand are effectively utilized as tetratopic building blocks to prepare isostructural porous coordination polymers with accessible reactive metal sites (M = Pd, Pt). The crystalline materials exhibit unusual and fully reversible H2 sorption at 150 °C. Post-synthetic reactivity is also possible, in which Pt-Cl bonds can be activated to provide organometallic species in the pores.

Structures and H2 Adsorption Properties of Porous Scandium Metal-Organic Frameworks

Two new three-dimensional Sc(III) metal-organic frameworks {[Sc(3)O(L(1))(3)(H(2)O)(3)]·Cl(0.5)(OH)(0.5)(DMF)(4)(H(2)O)(3)}(∞) (1) (H(2)L(1)=1,4-benzene-dicarboxylic acid) and {[Sc(3)O(L(2))(2)(H(2)O)(3)](OH)(H(2)O)(5)(DMF)}(∞) (2) (H(3)L(2)=1,3,5-tris(4-carboxyphenyl)benzene) have been synthesised and characterised. The structures of both 1 and 2 incorporate the trinuclear trigonal planar [Sc(3)(O)(O(2)CR)(6)] building block featuring three Sc(III) centres joined by a central μ(3)-O(2-) donor. Each Sc(III) centre is further bound by four oxygen donors from four different bridging carboxylate anions, and a molecule of water located trans to the μ(3)-O(2-) donor completes the six coordination at the metal centre. Frameworks 1 and 2 show high thermal stability with retention of crystallinity up to 350 °C. The desolvated materials 1a and 2a, in which the solvent has been removed from the pores but with water or hydroxide remaining coordinated to Sc(III), show BET surface areas based upon N(2) uptake of 634 and 1233 m(2) g(-1), respectively, and pore volumes calculated from the maximum N(2) adsorption of 0.25 cm(3) g(-1) and 0.62 cm(3) g(-1), respectively. At 20 bar and 78 K, the H(2) isotherms for desolvated 1a and 2a confirm 2.48 and 1.99 wt% total H(2) uptake, respectively. The isosteric heats of adsorption were estimated to be 5.25 and 2.59 kJ mol(-1) at zero surface coverage for 1a and 2a, respectively. Treatment of 2 with acetone followed by thermal desolvation in vacuo generated free metal coordination sites in a new material 2b. Framework 2b shows an enhanced BET surface area of 1511 m(2) g(-1) and a pore volume of 0.76 cm(3) g(-1), with improved H(2) uptake capacity and a higher heat of H(2) adsorption. At 20 bar, H(2) capacity increases from 1.99 wt% in 2a to 2.64 wt% for 2b, and the H(2) adsorption enthalpy rises markedly from 2.59 to 6.90 kJ mol(-1).

Near-critical water, a cleaner solvent for the synthesis of a metal-organic framework

The microporous metal–organic framework {[Zn2(L)]·(H2O)3}∞ (H4L = 1,2,4,5-tetrakis(4-carboxyphenyl)benzene) has been synthesised using near-critical water (300 °C) as a cleaner alternative to toxic organic solvents. A single crystal X-ray structure determination confirms that the complex incorporates tetrahedral Zn(II) centres bridged through the carboxylate anions to form a binuclear building block, which extends into a one dimensional chain along the c axis. Four L4− ligands bind to each Zn(II) centre and cross-link the one dimensional chains along both a and b axes to afford a three dimensional network structure incorporating pores of ca. 4.3 A in diameter. The complex shows high thermal stability up to 425 °C by gravimetric thermal analysis, and on desolvation, displays a high adsorption enthalpy of 11.0 kJ mol−1 for H2 uptake at zero coverage, consistent with the narrow pore diameter for the framework.

Molecular sensing and discrimination by a luminescent terbium–phosphine oxide coordination material

PCM-15 is a robust and recyclable sensor for the effective discrimination of a wide range of small molecules. Sensing is achieved by direct attenuation of the luminescence intensity of Tb(III) ions within the material. A competition study involving trace amounts of NH3 in H2 gas shows that PCM-15 can be used to quantitatively detect trace analytes.

Organic Vapor Sorption in a High Surface Area Dysprosium(III)–Phosphine Oxide Coordination Material

PCM-16 is a phosphine coordination material comprised of Dy(III) and triphenylphosphine oxide, which displays the highest reported CO2 BET surface area for a Ln(III) coordination polymer of 1511 m(2) g(-1). PCM-16 also adsorbs 2.7 wt % H2 and 65.1 wt % O2 at 77 K and 0.97 bar. The adsorption-desorption behavior of a series of organic vapors has been studied in PCM-16 to probe the nature of certain host-guest interactions in the pores. Aromatic and polar guest species showed high uptakes and marked adsorption/desorption hysteresis, while aliphatic vapors were less easily adsorbed. The surface area of PCM-16 could be increased significantly (to 1814 m(2) g(-1)) via exchange of Me2NH2(+) cations in the pores with smaller NH4(+) groups.

Catalytic activity of HKUST-1 in the oxidation of trans-ferulic acid to vanillin

HKUST-1 was used as a catalyst in the conversion of trans-ferulic acid to vanillin. The generation of unsaturated metal sites within HKUST-1 is the fundamental step in the catalytic process. When activated under vacuum, the catalyst gives complete conversion in only 1 h with a significant average reaction yield of 95%.

High surface area mesoporous Co3O4 from a direct soft template route

Mesoporous Co3O4 with hexagonally ordered cylindrical channels has been synthesized by a single-step method using Pluronic soft micellar templates. The resulting material has been directly compared to isomorphous Co3O4 that was obtained via an established but laborious five-step nanocasting method. The soft template route employs only surfactant templates and a decane additive, which yields directly mesoporous Co3O4 by a gelling process in a carefully controlled basic (pH = 12.7) alcohol solution at 35 °C. The method is significantly faster and more economical than conventional nanocasting, and has similar overall reproducibility to the conventional multi-step route. The soft templated Co3O4 displays long-range ordered cylindrical microchannels with crystalline walls. Most importantly, it exhibits an unparalleled N2 BET surface area of 367 m2 g−1.

Tuning the Host–Guest Interactions in a Phosphine Coordination Polymer through Different Types of post-Synthetic Modification

The porous Phosphine Coordination Material, PCM-10 contains abundant free P(III) donor sites that can be subjected to a variety of post-synthetic modifications. The diverse P(III)/P(V) organic reactivity and coordination chemistry available to aryl phosphines have been exploited to decorate the pores of PCM-10, allowing for an extensive structure-function study. Polar P═O moieties, charged P(+)-CH3 phosphonium species with exchangeable coanions (I(-), F(-), BF4(-), and PF6(-)) and P-AuCl groups have been successfully post-synthetically incorporated. These modifications directly affect the strength of the resulting host-guest interactions, as demonstrated by comparative sorption studies of CO2, H2, and other gases in the solid-state. Broad tunability of the enthalpy of CO2 adsorption is observed: incorporation of BF4(-) ions inside the pores of PCM-10 results in 24% enhancement of the isosteric adsorption enthalpy of CO2 compared to the parent material, while F(-) anions induce a 36% reduction. Meanwhile, AuCl-decorated PCM-10 shows a high H2 sorption capacity of 4.72 wt % at 77 K and 1.0 bar, versus only 0.63 wt % in the unmodified material.