Adsorption and Separation of Reactive Aromatic Isomers and Generation and Stabilization of Their Radicals within Cadmium(II)-Triazole Metal-Organic Confined Space in a Single-Crystal-to-Single-Crystal Fashion

A series of reactive group functionalized aromatics, namely 2-furaldehyde, 3-furaldehyde, 2-thenaldehyde, 3-thenaldehyde, o-toluidine, m-toluidine, p-toluidine, and aniline, can be absorbed by a CdL2 (1; L = 4-amino-3,5-bis(4-pyridyl-3-phenyl)-1,2,4-triazole) porous framework in both vapor and liquid phases to generate new G(n)subset of CdL2 (n = 1, 2) host guest complexes. In addition, the CdL2 framework can be a shield to protect the active functional group (-CHO and -NH2) substituted guests from reaction with the outside medium containing their reaction partners. That is, aldehyde-substituted guests within the CdL2 host become stable in the aniline phase and vice versa. Moreover, 1 displays a very strict selectivity for these reactive group substituted aromatic isomers and can completely separate these guest isomers under mild conditions (i.e., 2-furaldehyde vs 3-furaldehyde, 2-thenaldehyde vs 3-thenaldehyde, and o-toluidine vs m-toluidine vs p-toluidine). All adsorptions and separations are directly performed on the single crystals of 1. More interestingly, these reactive group substituted aromatics readily transform to the corresponding radicals within the CdL2 host upon ambient light or UV light (355 nm) irradiation. Furthermore, the generated organic radicals are alive for 1 month within the interior cavity in air under ambient conditions. Simple organic radicals are highly reactive short-lived species, and they cannot be generally isolated and conserved under ambient conditions. Thus, the CdL2 host herein could be considered as a radical generator and storage vessel.