Fig. 1. Structures determined by single-crystal X-ray diffraction. (Left) A portion of the crystal structure of Co₂(dobdc) (dobdc^4– = 2,5-dioxido-1,4-benzenedicarboxylate) at 296 K viewed along the c axis. (Right) First coordination spheres for Co^II in the structures of CO, CO₂,²⁹ N₂, O₂, CH₄, Ar, and P₄ in Co₂(dobdc) (at 150 K for CO₂; at 100 K for N₂, O₂, CH₄, and P₄; at 90 K for CO and Ar); purple, red, gray, blue, light blue, light orange, and white spheres represent Co, O, C, N, Ar, P, and H atoms, respectively. Note that the O₂ molecules bound to the Co^II sites in Co₂(dobdc)·5.9O₂ were found to be disordered over two orientations with relative occupancies of 73(3)% and 27(3)% (Fig. S8†), but only one of these orientations (73(3)% occupancy) is shown for clarity. The structure of Co₂(dobdc)·2.9CO₂ has been reported previously²⁹ and is shown here to facilitate comparisons.