Keith F. White

Hysteretic carbon dioxide sorption in a novel copper(II)-indazole-carboxylate porous coordination polymer

The synthesis, structural and gas sorption studies of a porous Cu(II) coordination polymer featuring 1H-indazole-5-carboxylic acid (H(2)L) are presented. [Cu(HL)(2)] is a thermally and hydrolytically robust 4-connected 3D coordination polymer of NbO topology and is replete with 1D channels that permit selective and hysteretic sorption of CO(2).

Solid state gas adsorption studies with discrete palladium(II) [Pd2(L)4]4+ cages

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.

Structural chemistry and selective CO2 uptake of a piperazine-derived porous coordination polymer

A new piperazine-derived ligand has been prepared and used to synthesise a porous coordination polymer which displays selective carbon dioxide uptake after solvent exchange and thermal activation. The ligand N,N′-bis(4-carboxyphenylmethylene)piperazine H2L1 was prepared from piperazine in three steps and good yield. A structure containing the deprotonated form K2L1·2H2O was determined and consists of a three-dimensional coordination polymer containing inorganic K2(COO)2(OH2) layers separated by the long organic bridging linker. The free compound H2L1 displays a one-dimensional hydrogen-bonded polymeric structure in the solid state with hydrogen bonding interactions between carboxylic acids and piperazine groups tightly linking molecules together. The two-dimensional polymeric complex [Zn3(L1)2(OH)2]·2DMF·0.5H2O 1 was prepared and analysed in the solid state to reveal tubular one-dimensional channels which, when activated by solvent exchange and evacuation, displayed selective affinity for CO2 over N2 and H2.

Guest-induced Assembly of Bis(thiosemicarbazonato) Zinc(II) Coordination Nanotubes

A ZnII complex of the dianionic tetradentate ligand formed by deprotonation of glyoxal-bis(4-phenyl-3-thiosemicarbazone) (H2 gtsp) is a [3+3] trinuclear triangular prism. Recrystallization of this complex in the presence of either CO2 , CS2 , or CH3 CN leads to the formation of [4+4] open-ended charge-neutral tetranuclear coordination nanotubes, approximately 2 nm in length and with internal dimensions large enough to accommodate linear guest molecules, which serve to template their formation. Upon removal of the templating molecules the nanotubes demonstrated reversible sorption of CO2 with an isosteric enthalpy of sorption of 28 kJ mol-1 at low loading.

Copper(II) coordination polymers of imdc− (H2imdc+ = the 1,3-bis(carboxymethyl)imidazolium cation): unusual sheet interpenetration and an unexpected single crystal-to-single crystal transformation

The monoanion of 1,3-bis(carboxymethyl)imidazolium (H2imdc+) combines with Cu(II) to produce an undulating 2D coordination polymer of composition [Cu2(imdc)2(CH3OH)2](BF4)2·(CH3OH)(H2O) (1) in which copper acetate-like dimers, linked by imdc− ligands, act as 4-connecting centres. Cationic sheets stack on top of each other in an A, B, A, B… fashion and produce a structure that contains channels running parallel to the plane of network. Tetrafluoroborate anions are located in channels between sheets. Upon removal of coordinated and non-coordinated solvent molecules a single crystal-to-single crystal transformation occurs to yield a similar compound but with BF4− anions now coordinated. CO2 isotherms measured at 258 and 273 K show only modest uptake of CO2 but provide an indication that the sheets move apart at elevated pressures in order to accommodate the guest molecules. A compound of composition [Cu3(OH)2(imdc)2]·SiF6·2H2O·2MeOH (3), which possesses a 3D network, is formed by the combination of copper(II) acetate, copper(II) hexafluorosilicate and Himdc. In this structure infinite parallel Cu3(OH)2 chains are linked by bridging imdc− ligands to form channels that have an approximately triangular cross-section. These channels are occupied by SiF62− anions in addition to solvent molecules. When copper(II) acetate is combined with Himdc in the appropriate ratio, a 1D coordination polymer of composition Cu(imdc)2 (4) is formed in which pairs of imdc− anions bridge Cu(II) centres. When the reaction is performed in the presence of NaBF4 a minor crystalline product with tetragonal symmetry is isolated in addition to the 1D coordination polymer. This compound of composition Cu2(imdc)4NaBF4·7H2O (5) consists of 2D Cu(imdc)2 networks and features an unusual mode of interpenetration.

Tunable Porous Coordination Polymers for the Capture, Recovery and Storage of Inhalation Anesthetics

The uptake of inhalation anesthetics by three topologically identical frameworks is described. The 3D network materials, which possess square channels of different dimensions, are formed from the relatively simple combination of ZnII centres and dianionic ligands that contain a phenolate and a carboxylate group at opposite ends. All three framework materials are able to adsorb N2 O, Xe and isoflurane. Whereas the framework with the widest channels is able to adsorb large quantities of the various guests from the gas phase, the frameworks with the narrower channels have superior binding enthalpies and exhibit higher levels of retention. The use of ligands in which substituents are bound to the aromatic rings of the bridging ligands offers great scope for tuning the adsorption properties of the framework materials.