Gel self-assembly of lanthanum aminopolycarboxylates with skeleton structures and adsorptions of gases

Three lanthanum aminopolycarboxylates [La(Hida)(2)(H2O)(2)](n)center dot nCl center dot 4nH(2)O (1), K-2n[La(nta)(2)](n)center dot nH(2)O (2) and (H(2)en)(n)[La(edta)(H2O)](2n)center dot 10nH(2)O (3) (H(2)ida = iminodiacetic acid; H(3)nta = nitrilotriacetic acid; H(4)edta = ethylenediaminetetraacetic acid; en = ethylenediamine, NH2CH2CH2NH2) were isolated by gel self-assembly and were fully characterized. Structural analyses reveal that 1-3 have infinite 2D and 3D structures with different coordination modes. Topological analyses of 1-3 were also performed. Solid state C-13 NMR spectra show that the coordinated beta-CO2 groups give obvious downfield shifts compared with free beta-CO2 groups. Interestingly, 3 possesses 5.8 angstrom diameter tunnels inside the crystals, which can selectively adsorb very small amounts of O-2 at 5.49 mg g(-1) and 29.9 bar, while no adsorption of H-2, N-2, CH4 and CO2 is observed. Compared with lanthanum 1,3-propylenediaminetetraacetate {La(H2O)(4)[La(1,3-pdta)(H2O)](3)}(n)center dot 11.25nH(2)O (4) with 10.0 angstrom diameter tunnels, the latter can adsorb CO2, O-2 and N-2 at 55.33, 18.01 and 4.41 mg g(-1) and 29.9 bar, respectively. This shows that smaller diameter tunnels have better selectivity towards the adsorption of specific gases. When the diameter of the tunnels increases, the adsorption amounts of numerous gases increase significantly with a decrease in selectivity.

Automated summary

The three lanthanum aminopolycarboxylates exhibit infinite 2D and 3D structures with different coordination modes, and solid state C-13 NMR spectra show distinct shifts in coordinated beta-CO2 groups. Compound 3 has tunnels with a 5.8 angstrom diameter that selectively adsorb small amounts of O-2, while compound 4 with larger tunnels exhibits adsorption of CO2, O-2, and N-2. Smaller tunnel diameters provide better selectivity for gas adsorption.