Solvatochromism and Selective Sorption of Volatile Organic Solvents in Pyridylbenzoate Metal-Organic Frameworks

Abstract

Using cobalt(II) as a metal centre with different solvent systems afforded the crystallization of isomorphous metal-organic frameworks {[Co(34pba)(44pba)]·DMF} n (1) and {[Co(34pba)(44pba)]·(C 3 H 6 O)} n (2) from mixed 4-(4-pyridyl)benzoate (44pba) and 3-(4-pyridyl)benzoate (34pba) ligands. Zinc(II) under the same reaction conditions that led to the formation of 1 formed an isostructural {[Zn(34pba)(44pba)]·DMF} n framework (3). Crystal structures of all three MOFs were elucidated and their thermal stabilities were determined. The frameworks of 1, 2, and 3 were activated under vacuum to form the desolvated forms 1d, 2d, and 3d, respectively. PXRD results showed that 1d and 2d were identical, consequently, 1d and 3d were then investigated for sorption of volatile organic compounds (VOCs) containing either chloro or amine moieties. Thermogravimetric analysis (TGA) and nuclear magnetic resonance (NMR) were used to determine the sorption capacity and selectivity for the VOCs. Some sorption products of 1d with amines became amorphous, but the crystalline framework could be recovered on desorption of the amines. Investigation of the sorption of water (H 2 O) and ammonia (NH 3 ) in 1d gave rise to new phases identifiable by means of a colour change (solvatochromism). The kinetics of desorption of DMF, water and ammonia from frameworks 1d and 3d were studied using non-isothermal TGA. Activation energies for both cobalt(II) and zinc(II) frameworks are in the order NH 3 < H 2 O < DMF, with values for the 1d analogue always higher than those for 3d.

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

“…The molecular volumes of the VOCs were calculated using their liquid density according to equation ( 2 Single crystal data was obtainable for the inclusion of the chlorinated VOCs in Table 3 in the framework of 1d. These structures were previously reported 18 •••π interactions between chlorobenzene and the MOF walls (Figure 3). The crystallographic information for these structures is reproduced in the ESI, Table S1.…”

“…DMF} (2) were reported previously. 18 To obtain the activated phases 1d and 2d, they were heated at 210°C under vacuum for six hours. This protocol was selected to ensure complete desolvation but not decomposition of the MOFs.…”

“…DMF} (2) were reported previously. 18 These form frameworks where each side is comprised of a 34pba and a 44pba linker, giving a double-walled MOF of bcu topology. Hour-glass channels (ca.…”

“…These MOFs showed selective adsorption for the chlorinated VOCs dichloromethane, chloroform, and chlorobenzene. 18 Guest molecules could be removed with the retention of the framework. To further understand the robustness of this framework through the sorption of additional halogenated compounds, we now consider the use of [Co(34pba)(44pba)] n (1d) and [Zn(34pba)(44pba)] n (2d) (where 34pba is 3-(pyridin-4-yl)benzoate, 44pba is 4-(pyridin-4yl)benzoate, and d indicates the activated phase) as adsorbents for the bromo-and iodo-derivatives of the chloro-compounds studied previously.…”

Supramolecular Chemistry in the 3rd Millennium

“…This work nicely illustrates the potential for halogen bonding in the assembly of porous molecular solids. Bourne and coworkers report a series of cobalt-or zinc-based metal organic frameworks (MOFs) containing pyridylbenzoate linkers [15]. The three-dimensional assemblies comprise non-interpenetrated frameworks that retain their structure upon activation under vacuum, and the study extends to the sorption capacity of the assemblies and their selectivity for volatile organic compounds (VOCs).…”