Fig. 1. (a) Structure of the metal–organic framework Mg₂(dobpdc) (dobpdc^4– = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate). Green, grey, and red spheres correspond to Mg, C, and O, respectively. (b) Addition of alkylethylenediamines to the methanol-solvated framework yields adsorbents with diamines appended to the open Mg²⁺ sites. (c) Upon CO₂ adsorption, ammonium carbamate chains form along the c-axis, illustrated by the single crystal X-ray diffraction structure of i-2–Zn₂(dobpdc)–CO₂.14b Light blue, grey, red, dark blue, and white spheres correspond to Zn, C, O, N, and H, respectively. (d) The bulky linear and branched primary,secondary (1°,2°) alkylethylenediamines studied in this work.