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

Abstract

Three microporous coordination polymers, [NiL]₃[(NiL)(H₂O)₂][(NiL)(TATAB)₂]₂·46H₂O (1), [(NiL)₃(TATAB)₂]·5DMF (2) and [(NiL)₃(BTCMT)₂]·DMF·16H₂O (3) (L = 1,3,6,9,11,14-hexaazatricyclo[12.2.1.1^6,9]octadecane, H₃TATAB = 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 6³ 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.