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

Abstract

The need for effective CO 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 [Pd (L) ] 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 CO . The best performing cage reversibly sorbed 1.4 mol CO per mol cage at 298 K, and 2.3 mol CO per mol cage at 258 K (1 bar). The enthalpy of binding was calculated to be 25-35 kJ mol , across the number of equivalents bound, while DFT calculations on the CO binding in the cage gave ΔE for the cage-CO interaction of 23-28 kJ mol , across the same range. DFT modelling suggested that the binding mode is a hydrogen bond between the carbonyl oxygen of CO and the internally directed hydrogen atoms of the cage.

A Rotaxane‐like Cage‐in‐Ring Structural Motif for a Metallosupramolecular Pd6L12 Aggregate

“…Banana‐shaped bridging ligands carrying 3‐pyridyl coordination groups usually self‐assemble into Pd II 2 L 4 cages upon treatment with Pd II ions and these cages have found wide applications in, e.g., host–guest chemistry, sensors, and drug delivery . Recently, there have also been a few reports where chromophores were integrated into palladium organic assemblies in an unique spatial orientation which gives rise to some exciting optical properties .…”

Metal‐Organic Frameworks and Metal‐Organic Cages – A Perspective

“…When working with MOCs in the solid state it is important to consider whether they exhibit the same binding properties (and even have the same structure) as in solution. Recently an M 14 L 24 rhombic dodecahedral MOC was shown to encapsulate the important greenhouse gas CO 2 both in solution and in the solid state, [88] and other MOCs are known to encapsulate CO 2 [89] and H 2 [90] in the solid state. It is crucial to consider not only the internal cavities of MOCs in the solid state, but also the external cavities formed due to solid-state packing, as this may be where binding occurs.…”

Conformational control of Pd2L4 assemblies with unsymmetrical ligands

“…6 Since their rst report by McMorran and Steel over two decades ago, 7 Pd 2 L 4 molecular cages 8 assembled from ditopic ligands and "naked" palladium(II) ionshave been examined for a range of functions, including biomedical applications, 9 catalysis 10 and gas storage. 11 Recently several examples have emerged in which two different ligands have been incorporated into cage structures in a controlled manner, resulting in heteroleptic complexes, 12 either as a result of steric interactions, 13 or through geometric design. 14 This approach enables the preparation of cages with cavities that deviate from the standard approximately spherical shape generally associated with these complexes, and could potentially allow different segments of the cage to contain separate functionalities.…”