Apical Ligand Substitution, Shape Recognition, Vapor-Adsorption Phenomenon, and Microcalorimetry for a Pillared Bilayer Porous Framework That Shrinks or Expands in Crystal-to-Crystal Manners upon Change in the Cobalt(II) Coordination Environment

A 2D pillared bilayer coordination polymer, [Co(5-NH2-bdc)(bpy)0.5(H2O)]·2H2O (1; 5-NH2-bdc = 5-aminoisophthalate; bpy = 4,4′-bipyridine) has been hydrothermally synthesized and shows a novel microporous host framework with 1D channels and high thermal stability (∼400 °C). The framework of 1 exhibits reversible single-crystal-to-single-crystal transformations upon removing and rebinding the coordinated waters as well as replacing them with MeOH and EtOH from the solvent. X-ray crystallography reveals that the coordination geometry of Co(II) changes from octahedron to square pyramid, as well as the shrinkage/expansion of pore deformation in respect to the subsequent shear motion of bpy pillars and vice versa. The dehydrated form 2 exhibits a shape recognition ability, which can accommodate linear molecules, such as MeCN and 2-propynyl alcohol, and interesting storage capabilities for oversized MeOH, EtOH, and benzene molecules, concomitant with spongelike dynamic transformation. The microcalorimetric study indicates that the crystalline state−liquid guest exchange and guest inclusion processes (1 ⊃ MeOH or EtOH, 2 ⊃ MeOH, EtOH or MeCN) are feasibly endothermic reactions with the values of molar enthalpy, ΔHθm, of +21.38(96), +12.68(85), +25.92(86), +17.03(57), and +14.93(75) kJ mol−1, respectively.