= Solution
\b[Amine <nitrogen> binds the <carbon> end of CO$_2$; Mg$^{2+}$ binds through <oxygen>.] The polarized C=O bonds make <carbon> electrophilic and <oxygen> electron rich. An amine <nitrogen> <lone pair> therefore donates toward <carbon>, potentially giving a carbamate-like adduct after <proton transfer>. The hard <Lewis acid> Mg$^{2+}$ accepts an <oxygen> <lone pair>, either from coordinated CO$_2$ or from an <oxygen> of a captured <carbamate> species. Simply reversing these assignments because <nitrogen> and <oxygen> both have <lone pairs> would put two electron-pair donors together without accounting for the electrophilic site.
The local binding pattern does not by itself determine the full proton-transfer state or whether cooperative chains form; those depend on the framework and amine arrangement. A documented diamine-appended framework shows cooperative carbon-dioxide insertion and <ammonium carbamate chain> formation, illustrating one possible implementation.<Cooperative insertion of CO2 in diamine-appended metal-organic frameworks by Thomas M. McDonald and others>[Adsorption mechanism and ammonium-carbamate-chain assignment]{ref}
To regenerate the material, lower the CO$_2$ <chemical potential> using reduced <pressure> or a CO$_2$-free purge, and, where binding is exothermic, <heat> the framework to favour <desorption>. The <temperature> must remain compatible with framework stability. This reverses <adsorption> or reversible <chemisorption>; it does not require permanently destroying the <metal–organic framework>.
Back to article page
