Matteo Lusi

Direct Air Capture of CO2 by Physisorbent Materials

Sequestration of CO2, either from gas mixtures or directly from air (direct air capture, DAC), could mitigate carbon emissions. Here five materials are investigated for their ability to adsorb CO2 directly from air and other gas mixtures. The sorbents studied are benchmark materials that encompass four types of porous material, one chemisorbent, TEPA-SBA-15 (amine-modified mesoporous silica) and four physisorbents: Zeolite 13X (inorganic); HKUST-1 and Mg-MOF-74/Mg-dobdc (metal-organic frameworks, MOFs); SIFSIX-3-Ni, (hybrid ultramicroporous material). Temperature-programmed desorption (TPD) experiments afforded information about the contents of each sorbent under equilibrium conditions and their ease of recycling. Accelerated stability tests addressed projected shelf-life of the five sorbents. The four physisorbents were found to be capable of carbon capture from CO2-rich gas mixtures, but competition and reaction with atmospheric moisture significantly reduced their DAC performance.

Solid state synthesis of coordination compounds from basic metal salts

The preparation of the complex salts [H2im]2[MCl4] (H2im = imidazolium, M = Co, 1; Zn, 2; Cu, 3) and coordination compounds [MCl2(Him)2] (M = Co, 4; Zn, 5; Cu, 6) by a range of solid-state and solid-gas reactions is reported. Compounds 4–6 and the related [{MCl2(4,4′-bipy)}n] (M = Co, 7; Zn, 8) were prepared by the solid state reactions of metal hydroxide or carbonate salts (or their equivalent) with the hydrochloride salt of the appropriate ligand (imidazole or 4,4′-bipy).

Crystal engineering of lattice metrics of perhalometallate salts and MOFs.

The synthesis of the salt 3 and metallo-organic framework (MOF) [{(4,4′-bipy)CoBr2}n] 4 by a range of solid state (mechanochemical and thermochemical) and solution methods is reported; they are isostructural with their respective chloride analogues 1 and 2. 3 and 4 can be interconverted by means of HBr elimination and absorption. Single phases of controlled composition and general formula [4,4′-H2bipy][CoBr4-xClx] 5x may be prepared from 2 and 4 by solid—gas reactions involving HBr or HCl respectively. Crystalline single phase samples of 5x and [{(4,4′-bipy)CoBr2-xClx}n] 6x were prepared by solid-state mechanochemical routes, allowing fine control over the composition and unit cell volume of the product. Collectively these methods enable continuous variation of the unit cell dimensions of the salts [4,4′-H2bipy][CoBr4-xClx] (5x) and the MOFs [{(4,4′-bipy)CoBr2-xClx}n] (6x) by varying the bromide to chloride ratio and establish a means of controlling MOF composition and the lattice metrics, and so the physical and chemical properties that derive from it.

Practical and Highly Selective Sulfur Ylide-Mediated Asymmetric Epoxidations and Aziridinations Using a Cheap and Readily Available Chiral Sulfide: Extensive Studies To Map Out Scope, Limitations, and Rationalization of Diastereo- and Enantioselectivities

The chiral sulfide, isothiocineole, has been synthesized in one step from elemental sulfur, γ-terpinene, and limonene in 61% yield. A mechanism involving radical intermediates for this reaction is proposed based on experimental evidence. The application of isothiocineole to the asymmetric epoxidation of aldehydes and the aziridination of imines is described. Excellent enantioselectivities and diastereoselectivities have been obtained over a wide range of aromatic, aliphatic, and α,β-unsaturated aldehydes using simple protocols. In aziridinations, excellent enantioselectivities and good diastereoselectivities were obtained for a wide range of imines. Mechanistic models have been put forward to rationalize the high selectivities observed, which should enable the sulfide to be used with confidence in synthesis. In epoxidations, the degree of reversibility in betaine formation dominates both the diastereoselectivity and the enantioselectivity. Appropriate tuning of reaction conditions based on understanding the reaction mechanism enables high selectivities to be obtained in most cases. In aziridinations, betaine formation is nonreversible with semistabilized ylides and diastereoselectivities are determined in the betaine forming step and are more variable as a result.

Hydrophobic pillared square grids for selective removal of CO2 from simulated flue gas

Capture of CO2 from flue gas is considered to be a feasible approach to mitigate the effects of anthropogenic emission of CO2. Herein we report that an isostructural family of metal organic materials (MOMs) of general formula [M(linker)2(pillar)], linker = pyrazine, pillar = hexaflourosilicate and M = Zn, Cu, Ni and Co exhibits highly selective removal of CO2 from dry and wet simulated flue gas. Two members of the family, M = Ni and Co, SIFSIX-3-Ni and SIFSIX-3-Co, respectively, are reported for the first time and compared with the previously reported Zn and Cu analogs.

Towards polymorphism control in coordination networks and metallo-organic salts

[{(4,4′-bipy)ZnCl2}n] (4) is known in three different polymorphs, in the space groups C2/c (4a), Pnma (4b) and Pban (4c). Solution synthesis produces a mixture of 4a and 4b, but solid-state synthesis, either by grinding together 4,4′-bipy and ZnCl2 or by heating [4,4′-H2bipy][ZnCl4] 3 to thermally eliminate HCl, generates only the 4b form, demonstrating that solid-state synthesis can exert control over polymorph formation; other solid-state preparations of 4 such as reaction of basic zinc carbonate with [4,4′-H2bipy]Cl2 or reaction of [4,4′-H2bipy][ZnCl4] 3 with KOH also increase the amount of 4b generated relative to the solution synthesis. It is also possible to form the mixed-metal phases [{(4,4′-bipy)Co1−xZnxCl2}n] 4x as effectively homogeneous solid-solutions by the same techniques, and when x 0.5, the amount of this polymorph is still greater than would be expected for a predominantly zinc-containing phase.

Crystal synthesis of 1,4-phenylenediamine salts and coordination networks

para-Phenylenediamine (ppda) may be ground together with metal chloride salts MCl2 to produce the coordination network compounds [{(ppda)MCl2}n] {M = Zn (2), Cd (4), Cu (6)}. Its dihydrochloride salt [H2ppda]Cl2 can be ground with MCl2 to produce the layered salt structures [H2ppda][MCl4] {M = Zn (1), Cd (3), Cu (5)}, which (when M = Zn or Cd) may then be converted into 2 or 4 respectively by grinding with solid KOH. Alternatively, [H2ppda][MCl4] will react directly with appropriate basic metal compounds (hydroxides and/or carbonates) to give 2 or 4, which can then be converted back to the salts by reaction with gaseous HCl. The interconversion of 5 and 6 is more complicated, with different combinations of starting material giving different products. The crystal structure of 2 has been solved ab initio from the powder-diffraction data, and is shown to consist of zigzag polymeric chains containing alternating ppda and MCl2 units.

Viologen-Based Conjugated Covalent Organic Networks via Zincke Reaction

Morphology influences the functionality of covalent organic networks and determines potential applications. Here, we report for the first time the use of Zincke reaction to fabricate, under either solvothermal or microwave conditions, a viologen-linked covalent organic network in the form of hollow particles or nanosheets. The synthesized materials are stable in acidic, neutral, and basic aqueous solutions. Under basic conditions, the neutral network assumes radical cationic character without decomposing or changing structure. Solvent polarity and heating method determine product morphology. Depending upon solvent polarity, the resulting polymeric network forms either uniform self-templated hollow spheres (HS) or hollow tubes (HT). The spheres develop via an inside-out Ostwald ripening mechanism. Interestingly, microwave conditions and certain solvent polarities result in the formation of a robust covalent organic gel framework (COGF) that is organized in nanosheets stacked several layers thick. In the gel phase, the nanosheets are crystalline and form honeycomb lattices. The use of the Zincke reaction has previously been limited to the synthesis of small viologen molecules and conjugated viologen oligomers. Its application here expands the repertoire of tools for the fabrication of covalent organic networks (which are usually prepared by dynamic covalent chemistry) and for the synthesis of viologen-based materials. All three materials-HT, HS, and COGF-serve as efficient adsorbents of iodine due to the presence of the cationic viologen linker and, in the cases of HT and HS, permanent porosity.

Flue-gas and direct-air capture of CO2 by porous metal-organic materials.

Sequestration of CO2, either from gas mixtures or directly from air (direct air capture), is a technological goal important to large-scale industrial processes such as gas purification and the mitigation of carbon emissions. Previously, we investigated five porous materials, three porous metal–organic materials (MOMs), a benchmark inorganic material, Zeolite 13X and a chemisorbent, TEPA-SBA-15, for their ability to adsorb CO2 directly from air and from simulated flue-gas. In this contribution, a further 10 physisorbent materials that exhibit strong interactions with CO2 have been evaluated by temperature-programmed desorption for their potential utility in carbon capture applications: four hybrid ultramicroporous materials, SIFSIX-3-Cu, DICRO-3-Ni-i, SIFSIX-2-Cu-i and MOOFOUR-1-Ni; five microporous MOMs, DMOF-1, ZIF-8, MIL-101, UiO-66 and UiO-66-NH2; an ultramicroporous MOM, Ni-4-PyC. The performance of these MOMs was found to be negatively impacted by moisture. Overall, we demonstrate that the incorporation of strong electrostatics from inorganic moieties combined with ultramicropores offers improved CO2 capture performance from even moist gas mixtures but not enough to compete with chemisorbents. This article is part of the themed issue ‘Coordination polymers and metal–organic frameworks: materials by design’.

Towards an understanding of the propensity for crystalline hydrate formation by molecular compounds

The propensity for crystalline hydrate formation by molecular compounds that are devoid of strong hydrogen-bond donors has been analyzed and rationalized through a Cambridge Structural Database (CSD) survey, systematic hydrate screening experiments and computational studies.