Robust pyridylbenzoate metal–organic frameworks as sorbents for volatile solvents and gases

Abstract

Two activated isostructural porous compounds, [Co(34pba)(44pba)]_n (1d) and [Zn(34pba)(44pba)]_n (2d) (where 34pba is 3-(pyridin-4-yl)benzoate, 44pba is 4-(pyridin-4-yl)benzoate, and d indicates the activated phase) were used for the adsorption of halogenated volatile organic compounds (VOCs), iodine, carbon dioxide (CO₂), and hydrogen. Elucidation of single-crystal structures found that the desolvated phases 1d and 2d show rotational disorder of one ring on each linker. The crystal structure of {[Co(34pba)(44pba)]·1.6 I₂}_n (1dI₂) was obtained by vapour sorption of iodine into 1d, and this could be desolvated to a phase isostructural with 1d. Thus the MOF is robust to cycling through sorption/desorption processes with an accompanying order/disorder phase transition. Activation energies for the desorption of dichloromethane, dibromomethane, and iodine were measured as 70, 60, and 77 kJ mol⁻¹ respectively. Both activated compounds were tested as gas sorbents, with 1d showing higher adsorption capacity than 2d for both carbon dioxide and hydrogen.