Tuning the gate-opening pressure in a switching pcu coordination network, X-pcu-5-Zn, by pillar ligand substitution.

Abstract

Coordination networks that reversibly switch between closed and open phases are of topical interest since their stepped isotherms can offer higher working capacity for gas storage applications than related rigid porous coordination networks. In order to be of practical utility, the pressures at which switching occurs, the gate-opening and gate-closing pressures. Here we study the effect of linker substitution to fine-tune gate-opening and gate-closing pressure. Specifically, three variants of a previously reported pcu topology MOF, X-pcu-5-Zn , have been prepared. X-pcu-6-Zn , 6 = 1,2-bis(4-pyridyl)ethane (bpe), X-pcu-7-Zn , 7 = 1,2-bis(4-pyridyl)acetylene (bpa) and X-pcu-8-Zn , 8 = 4,4 -azopyridine (apy), each exhibited switching isotherms but at different gate-opening pressures. The N 2 , CO 2 , C 2 H 2 and C 2 H 4 adsorption isotherms consistently indicated that the most flexible dipyridyl organic linker, 6 , afforded lower gate-opening and gate-closing pressures. This simple design principle enables rational control of the switching behaviour in adsorbent materials.