Hayley S. Scott

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’.

Highly Selective Separation of C2H2 from CO2 by a New Dichromate-Based Hybrid Ultramicroporous Material

A new hybrid ultramicroporous material, [Ni(1,4-di(pyridine-2-yl)benzene)2(Cr2O7)]n (DICRO-4-Ni-i), has been prepared and structurally characterized. Pure gas sorption isotherms and molecular modeling of sorbate-sorbent interactions imply strong selectivity for C2H2 over CO2 (SAC). Dynamic gas breakthrough coupled with temperature-programmed desorption experiments were conducted on DICRO-4-Ni-i and two other porous materials reported to exhibit high SAC, TIFSIX-2-Cu-i and MIL-100(Fe), using a C2H2/CO2/He (10:5:85) gas mixture. Whereas CO2/C2H2 coadsorption by MIL-100(Fe) mitigated the purity of trapped C2H2, negligible coadsorption and high SAC were observed for DICRO-4-Ni-i and TIFSIX-2-Cu-i.

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.

Iron(II) Mononuclear Materials Containing Functionalised Dipyridylamino-Substituted Triazine Ligands: Structure, Magnetism and Spin Crossover

The spin crossover effect in iron(II) materials containing the di-2-pyridylamine functional group has been investigated for the new nitrile-functionalised ligand DTAC (2,2′,2″,2″′-((6-(di(pyridin-2-yl)amino)-1,3,5-triazine-2,4 diyl)bis(azanetriyl))tetra acetonitrile). This ligand has successfully been incorporated into a family of materials of the general formula trans-[Fe(DTAC)2(anion)2], wherein we have systematically varied the trans-nitrogen donor anion from NCS, NCSe, N(CN)2 (dca; dicyanamide) to NCBH3 – thus forming the four mononuclear materials trans-[Fe(DTAC)2(NCS)2]·6MeCN (1), trans-[Fe(DTAC)2(NCSe)2]·6MeCN (2), trans-[Fe(DTAC)2(N(CN)2)2] (3) and trans-[Fe(DTAC)2 (NCBH3)2]·3MeCN (4)). We find that the materials with a weaker crystal field strength anion remain high spin over all temperatures (1 and 2) whereas the materials containing stronger crystal field strength anions undergo a thermally induced spin crossover (3 and 4). Structural analysis revealed that the packing interactions in the solid state and the degree of solvation also play a large role in the observed magnetic behaviour. Indeed, aged or rapidly precipitated samples of 2 show a spin transition above room temperature.

2,2′-Dipyridylamino-based ligands with substituted alkyl chain groups and their mononuclear-M(II) spin crossover complexes

Four new alkyl chain appended dipyridylamino-substituted-s-triazine ligands have been incorporated into seven new, mononuclear MII compounds of type [MII(NCX)2(L)2] (where NCX = NCS− or NCSe−, L = dipyridylamino-substituted-s-triazine-based ligand and MII = Fe or Co). These complexes have been structurally and magnetically characterised. The magnetic consequence of varying the alkyl chain length has been investigated in terms of intermolecular interactions and crystallographic packing arrangements. For selected complexes photomagnetic LIESST (Light-Induced Excited Spin State Trapping) measurements have been performed revealing reversible photo-induced spin-state switching.