Interchanged Hysteresis for Carbon Dioxide and Water Vapor Sorption in a Pair of Water-Stable, Breathing, Isoreticular, 2-Periodic, Zn(II)-Based Mixed-Ligand Metal-Organic Frameworks.

Abstract

We report the synthesis of two isoreticular mixed-ligand metal-organic frameworks (MOFs), namely, [Zn(μ2-ia)(μ2-bpe)] n· nDMF (1) and [Zn(μ2-mia)(μ2-bpe)] n· nDMF (2), where ia = isophthalate, mia = 5-methoxyisophthalate, bpe = 1,2-bis(4-pyridyl)ethane, and DMF = N, N'-dimethylformamide. Single-crystal X-ray diffraction studies revealed that the structures of 1 and 2 consist of a 2-periodic, layer sql motif. Structures exhibit entanglement through interpenetration of neighboring frameworks to form a two-dimensional bilayer. Variable-temperature powder X-ray diffraction studies confirmed both structures retain crystallinity upon desolvation up to ∼500 K. Although structurally similar, activated samples of 1 and 2 showed differing gas and vapor sorption capabilities. Despite activated 2 having the higher actual void space, activated 1 showed significantly higher sorption for carbon dioxide at 195 K, as well as significant hysteresis upon desorption. Empirical evidence points toward weaker bilayer···bilayer interactions, which allow the separation of the bilayers, illustrating that small changes in functional groups within an isoreticular pair of MOFs may have a large tuning effect on sorption properties.