Gel self-assembly of lanthanum aminopolycarboxylates with skeleton structures and adsorptions of gases†
Abstract
Three lanthanum aminopolycarboxylates [La(Hida)2(H2O)2]n·nCl·4nH2O (1), K2n[La(nta)2]n·nH2O (2) and (H2en)n[La(edta)(H2O)]2n·10nH2O (3) (H2ida = iminodiacetic acid; H3nta = nitrilotriacetic acid; H4edta = 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 13C NMR spectra show that the coordinated β-CO2 groups give obvious downfield shifts compared with free β-CO2 groups. Interestingly, 3 possesses 5.8 Å diameter tunnels inside the crystals, which can selectively adsorb very small amounts of O2 at 5.49 mg g−1 and 29.9 bar, while no adsorption of H2, N2, CH4 and CO2 is observed. Compared with lanthanum 1,3-propylenediaminetetraacetate {La(H2O)4[La(1,3-pdta)(H2O)]3}n·11.25nH2O (4) with 10.0 Å diameter tunnels, the latter can adsorb CO2, O2 and N2 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.