A Metal-Organic Framework with Highly Polar Pore Surfaces: Selective CO2 Adsorption and Guest-Dependent On/Off Emission Properties

作者：Kanoo Prakash; Ghosh Ashta Chandra; Cyriac Soumya T; Maji Tapas Kumar^*

来源：Chemistry - A European Journal, 2012, 18(1): 237-244.

DOI：10.1002/chem.201101183

• adsorption
• host-guest systems
• metal-organic frameworks
• microporous materials
• zinc

A 3D porous ZnII metalorganic framework {[Zn2(H2dht)(dht)0.5(azpy)0.5(H2O)]center dot 4?H2O} (1; H2dht=dihydroxyterphthalate, azpy=4,4%26apos;-azobipyridine) has been synthesised by employing 2,5-dihydroxyterephthalic acid (H4dht), a multidentate ligand and 4,4%26apos;-azobipyridine by solvent-diffusion techniques at room temperature. The as-synthesised framework furnishes two different types of channels: one calyx-shaped along the [001] direction and another rectangle-shaped along the [101] direction occupied by guest water molecules. The dehydrated framework, {[Zn2(H2dht)(dht)0.5(azpy)0.5]} (1%26apos;) provides 52.7?% void volume to the total unit-cell volume. The pore surfaces of 1%26apos; are decorated with unsaturated ZnII sites and pendant hydroxyl groups of H2dht linker, thereby resulting in a highly polar pore surface. The dehydrated framework 1%26apos; shows highly selective adsorption of CO2 over other gases, such as N2, H2, O2 and Ar, at 195 K. Photoluminescence studies revealed that compound 1 exhibits green emission (lambda max approximate to 530 nm) on the basis of the excited-state intramolecular proton-transfer (ESIPT) process of the H2dht linker; no emission was observed in dehydrated solid 1%26apos;. Such guest-induced on/off emission has been correlated to the structural transformation and concomitant breaking and reforming of the OH center dot center dot center dot OCO hydrogen-bonding interaction in the H2dht linker in 1%26apos;/1.

• 出版日期2012-1