Solid-State Gas Adsorption Studies with Discrete Palladium(II) [Pd2(L)4]4+ Cages

5 years ago

Solid-State Gas Adsorption Studies with Discrete Palladium(II) [Pd2(L)4]4+ Cages

Roan A. S. Vasdev, James D. Crowley, James E. M. Lewis, Keith F. White, Dan Preston, Brendan F. Abrahams

The need for effective CO2 capture systems remains high, and due to their tunability, metallosupramolecular architectures are an attractive option for gas sorption. While the use of extended metal organic frameworks for gas adsorption has been extensively explored, the exploitation of discrete metallocage architectures to bind gases remains in its infancy. Herein the solid state gas adsorption properties of a series of [Pd2(L)4]4+ lantern shaped coordination cages (L = variants of 2,6-bis(pyridin-3-ylethynyl)pyridine), which had solvent accessible internal cavities suitable for gas binding, have been investigated. The cages showed little interaction with dinitrogen gas but were able to take up CO2. The best performing cage reversibly sorbed 1.4 mol CO2 per mol cage at 298 K, and 2.3 mol CO2 per mol cage at 258 K (1 bar). The enthalpy of binding was calculated to be 25–35 kJ mol−1, across the number of equivalents bound, while DFT calculations on the CO2 binding in the cage gave ΔE for the cage–CO2 interaction of 23–28 kJ mol−1, across the same range. DFT modelling suggested that the binding mode is a hydrogen bond between the carbonyl oxygen of CO2 and the internally directed hydrogen atoms of the cage. Cage trap: Discrete metallosupramolecular palladium(II) [Pd2(L)4]4+ cages are shown to selectively adsorb CO2 over N2. The NMR and DFT studies indicate that the CO2 guests are bound within the cavity of the cages and interact mainly through hydrogen bonding.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701477