The novel coordination polymers [Cu(Hoxonic)(H2O)](n) (1) and [Cu(Hoxonic)(bpy)(0.5)](n)*1.5n H2O (2*H2O) (H3oxonic: 4,6-dihydroxy-1,3,5-triazine-2-carboxylic acid; bpy: 4,4'-bipyridine) have been isolated and structurally characterised by ab initio X-ray powder diffraction. The dense phase 1 contains 1D zig-zag chains in which Hoxonic dianions bridge square-pyramidal copper(II) ions, apically coordinated by water molecules. On the contrary 2*H2O, prepared by solution and solventless methods, is based on 2D layers of octahedral copper(II) ions bridoed by Hoxonic ligands, further pillared by bpy spacers. The resulting pro-porous 3D network possesses small hydrated cavities. The reactivity, thermal, magnetic and adsorptive properties of these materials have been investigated. Notably, the adsorption studies on 2 show that this material possesses unusual adsorption behaviour. Indeed, guest uptake is facilitated by increasing the thermal energy of both the guest and the framework. Thus, neither N2 at 77 K nor CO2 at 195 K are incorporated, and CH4 is only minimally adsorbed at 273 K and high pressures (0.5 mmol/g at 2500 kPa). By contrast, CO is readily incorporated at 273 K (up to 2.5 mmol/g at 2500 kPa). The selectivity of 2 towards CO2 over CH4 has been investigated by means of variable-temperature zero coverage adsorption experiments and measurement of breakthrough curves of CO2/CH4 mixtures. The results show the highly selective incorporation of CO2 in 2, which can be rationalised on the basis of the framework flexibility and polar nature of its voids.

A flexible pro-porous coordination polymer: non-conventional synthesis and separation properties towards CO2/CH4 mixtures

GALLI, SIMONA;MASCIOCCHI, NORBERTO;
2010

Abstract

The novel coordination polymers [Cu(Hoxonic)(H2O)](n) (1) and [Cu(Hoxonic)(bpy)(0.5)](n)*1.5n H2O (2*H2O) (H3oxonic: 4,6-dihydroxy-1,3,5-triazine-2-carboxylic acid; bpy: 4,4'-bipyridine) have been isolated and structurally characterised by ab initio X-ray powder diffraction. The dense phase 1 contains 1D zig-zag chains in which Hoxonic dianions bridge square-pyramidal copper(II) ions, apically coordinated by water molecules. On the contrary 2*H2O, prepared by solution and solventless methods, is based on 2D layers of octahedral copper(II) ions bridoed by Hoxonic ligands, further pillared by bpy spacers. The resulting pro-porous 3D network possesses small hydrated cavities. The reactivity, thermal, magnetic and adsorptive properties of these materials have been investigated. Notably, the adsorption studies on 2 show that this material possesses unusual adsorption behaviour. Indeed, guest uptake is facilitated by increasing the thermal energy of both the guest and the framework. Thus, neither N2 at 77 K nor CO2 at 195 K are incorporated, and CH4 is only minimally adsorbed at 273 K and high pressures (0.5 mmol/g at 2500 kPa). By contrast, CO is readily incorporated at 273 K (up to 2.5 mmol/g at 2500 kPa). The selectivity of 2 towards CO2 over CH4 has been investigated by means of variable-temperature zero coverage adsorption experiments and measurement of breakthrough curves of CO2/CH4 mixtures. The results show the highly selective incorporation of CO2 in 2, which can be rationalised on the basis of the framework flexibility and polar nature of its voids.
carbon dioxide capture; gas separation; metal-organic frameworks; methane purification; thermochemistry
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11383/1715674
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