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A remarkably flexible, multifunctional, 2D coordination polymer exhibiting an unprecedented mode of reversible mechanical motion, enabling pores to open and close, is reported. Such multifunctional materials are highly sought after, owing to the potential to exploit coexisting electronic and mechanical functionalities that underpin useful technological applications such as actuators and ultrasensitive detectors. The coordination polymer, of composition Mn(F4TCNQ)(py)2(F4TCNQ = 2,3,5,6-tetrafluoro-7,7,8,8-tetracycanoquinodimethane; py = pyridine), consists of Mn(II) centers bridged by F4TCNQ dianions and coordinated by py molecules that extend above and below the 2D network. Exposure of Mn(F4TCNQ)(py)2, in its collapsed state, to carbon dioxide results in a pore-opening process at a threshold pressure for a given temperature. In addition to carbon dioxide, a variety of volatile guests may be incorporated into the pores, which are lined with electron-rich F4TCNQ dianions. The inclusion of electron-deficient guests such as 1,4-benzoquinone, nitrobenzene, maleic anhydride, and iodine into the pores is accompanied by a striking color change associated with a new host–guest charge-transfer interaction and an improvement in the semiconductor behavior, with the iodine adduct showing an increase in conductivity of almost 5 orders of magnitude. Experimental and density functional theory calculations on this remarkable multifunctional material demonstrate a reduction in the optical band gap with increasing electron affinity of the guest.

An investigation of the adsorption properties of two structurally related, 3D coordination polymers of composition Zn(2-Mehba) and Zn(2,6-Me2hba) (2-Mehba = the dianion of 2-methyl-4-hydroxybenzoic acid and 2,6-Me2hba = the dianion of 2,6-dimethyl-4-hydroxybenzoic acid) is presented. A common feature of these structures are parallel channels that are able to accommodate appropriately sized guest molecules. The structures differ with respect to the steric congestion within the channels arising from methyl groups appended to the bridging ligands of the network. The host network, Zn(2-Mehba), is able to take up appreciable quantities of H2(77 K) and CO2and CH4(298 K) in a reversible manner. In regard to the adsorption of N2by Zn(2-Mehba), there appears to be an unusual temperature dependence for the uptake of the gas such that when the temperature is increased from 77 to 298 K the uptake of N2increases. The relatively narrow channels of Zn(2,6-Me2hba) are too small to allow the uptake of N2and CH4, but H2molecules can be adsorbed. A pronounced step at elevated pressures in CO2and N2O isotherms for Zn(2,6-Me2hba) is noted. Calculations indicate that rotation of phenolate rings leads to a change in the available intraframework space during CO2dosing.

A new divergent homopiperazine-derived ligand N,N′-bis(4-carboxyphenyl)-1,4-diazacycloheptane H2Lhas been prepared, containing a semirigid saturated heterocyclic core which is capable of providing multiple distinct bridging geometries. Reaction of H2Lwith zinc acetate in DMSO gives a two-dimensional parallel interpenetrated polyrotaxane structure 1in which the loops and rods are formed by the bent cis-(eq,ax) twist boat and trans-(ax,ax) twist chair conformers, respectively. By matching the distances between the solvated metal sites in the structure of 1, a related material 2can be prepared incorporating the pillaring ligand trans-1,2-bis(4-pyridyl)ethylene bpe. Compound 2displays a similar polyrotaxane interpenetration mode, permitted by the presence of both cisand transligand conformers, but displays a three-dimensional 2.69topology related to the diadiamondoid network. The guest exchange and gas adsorption properties of both materials were investigated; while compound 1displays poor stability to guest exchange and negligible gas uptake, the higher connectivity microporous compound 2shows facile guest exchange and a surprisingly high CO2capacity of 12 wt % at 1 bar and 273 K, and a zero-loading enthalpy of adsorption of −32 kJ mol–1. High-pressure adsorption isotherms also show moderate physisorption of H2and CH4within the material.