Porous coordination polymers based on azamacrocyclic complex: syntheses, solvent-induced reversible crystal-to-crystal transformation and gas sorption properties

Three microporous coordination polymers, [NiL](3)[(NiL)(H2O)(2)][(NiL)(TATAB)(2)](2)center dot 46H(2)O (1), [(NiL)(3)(TATAB)(2)]center dot 5DMF (2) and [(NiL)(3)(BTCMT)(2)]center dot DMF center dot 16H(2)O (3) (L = 1,3,6,9,11,14-hexaazatricyclo[12.2.1.1(6,9)]octadecane, H(3)TATAB = 4,4',4 ''-triazine-1,3,5-triyltriaminobenzoic acid and H3BTCMT = 4,4',4 ''-[1,3,5-benzenetriyltris(carbonylimino)]-trisbenzoic acid), were constructed from two tripodal carboxylic ligands and an azamacrocyclic complex. The solvent-mediated, reversible, crystal-to-crystal transformation between 1 and 2 was achieved by immersing the crystalline samples in the corresponding solvent (H2O or DMF). Furthermore, during the fast bidirectional transformation, solvatochromic behavior was observed and confirmed. The comparison between 2 and 3 indicates that the degree of 6(3) monolayer corrugation has a significant effect on the formation and porous stability of an overall 2D or 3D network. Both 2 and 3 consist of large solvent accessible voids, but only compound 3 possesses permanent porosity, as confirmed by gas adsorption measurements and X-ray powder diffraction. In particular, compound 3 shows a high selective adsorption for CO2.