Crystal engineering of a rectangular sql coordination network to enable xylenes selectivity over ethylbenzene

Abstract

Separation of the C8 aromatic isomers,p-xylene (PX),m-xylene (MX),o-xylene (OX) and ethylbenzene (EB), is relevant thanks to their widespread application as chemical feedstocks but challenging because of their similar boiling points and close molecular dimensions. Physisorptive separation could offer an energy-efficient solution to this challenge but sorbents which exhibit strong selectivity for one of the isomers remain a largely unmet challenge despite recent reports of OX or PX selective sorbents with high uptake capacity. For example, the square lattice,sql, topology coordination network[Co(bipy)(2)(NCS)(2)](n)(sql-1-Co-NCS)exhibits the rare combination of high OX selectivity and high uptake capacity. Herein we report that a crystal engineering approach enabled isolation of the mixed-linkersqlcoordination network[Co(bipy)(bptz)(NCS)(2)](n)(sql-1,3-Co-NCS, bipy = 4,4 '-bipyridine, bptz = 4,4 '-bis(4-pyridyl)tetrazine) and study of its C8 vapour and liquid sorption properties.sql-1,3-Co-NCSwas found to exhibit high adsorption capacity from liquid xylenes (similar to 37 wt%) and is to our knowledge the first sorbent to exhibit high selectivity for each of xylene isomer over EB (S-OX/EB,S-MX/EB,S-PX/EB> 5). Insights into the performance ofsql-1,3-Co-NCSare gained from structural studies which reveal stacking interactions between electron-deficient bptz linkers and the respective xylenes.sql-1,3-Co-NCSis the first N-donor mixed-linkersqlcoordination network studied for its gas/vapour sorption properties and represents a large and diverse class of understudied coordination networks.