Confined and synergistic effects between protonated amines and gases in the frameworks of lanthanum 1,3-propanediaminetetraacetates

Lanthanum microporous frameworks (Hdma)(2n)[La-2(1,3-pdta)(2)(H2O)(2)] n center dot 5nH(2)O (1, dma = dimethylamine, 1,3-pdta = 1,3-propanediaminetetraacetic acid) and (H(2)pn)n[La-2(1,3-pdta)(2)(H2O)(2)] n center dot 5nH(2)O (2, pn = 1,3-propanediamine) with double channels have been template-synthesized by protonated dimethylamines and 1,3-propanediamines, respectively. While bulky product (H(2)bn)[La-2(1,3-pdta)2(H2O)(4)]center dot 10H(2)O (3, bn = 1,4-butanediamine) is isolated as a dinuclear species with tetrahydrates, whose main anion can be served as a precursor for 1 and 2. Materials 1-3 are able to maintain their chemical and thermal stabilities to 200 degrees C based on TG and XRD analyses. Gas adsorptions demonstrate that MOFs 1 and 2 are amicable for O-2 and CO2, while no adsorption has been observed for CH4, N-2 or H-2 respectively. The amounts of encapsulated CO2 in hydrophobic pores are dependent on the alkalinities of the diamines in the next confined hydrophilic holes, showing synergistic effects between double channels. For protonated dimethylamines and 1,3-propanediamines in 1 and 2, obvious downfield shifts have been found by solid-state C-13 NMR spectroscopies, along with clear red shifts in FT-IR spectra compared with free species. Moreover, captured CO2 inside 1 can be quantized by NMR measurements and IR spectroscopies under ambient condition. These all reflect the confinement effects of nanoenvironments.

Automated summary

In this study, lanthanum microporous frameworks 1 and 2 with double channels were successfully synthesized using protonated dimethylamines and 1,3-propanediamines as templates. The materials exhibited good chemical and thermal stabilities up to 200 degrees C. Gas adsorption experiments showed that MOFs 1 and 2 had affinity for O-2 and CO2, but no adsorption of CH4, N-2, or H-2 was observed. Quantitative measurements of captured CO2 inside material 1 were achieved using NMR and IR spectroscopies. These findings highlight the confinement effects of nanoenvironments on material properties.