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

Abstract

Lanthanum microporous frameworks (Hdma) 2n [La 2 (1,3-pdta) 2 (H 2 O) 2 ] n ·5nH 2 O ( 1 , dma = dimethylamine, 1,3-pdta = 1,3-propanediaminetetraacetic acid) and (H 2 pn) n [La 2 (1,3-pdta) 2 (H 2 O) 2 ] n ·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 (H 2 O) 4 ]·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 °C based on TG and XRD analyses. Gas adsorptions demonstrate that MOFs 1 and 2 are amicable for O 2 and CO 2 , while no adsorption has been observed for CH 4 , N 2 or H 2 respectively. The amounts of encapsulated CO 2 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 13 C NMR spectroscopies, along with clear red shifts in FT-IR spectra compared with free species. Moreover, captured CO 2 inside 1 can be quantized by NMR measurements and IR spectroscopies under ambient condition. These all reflect the confinement effects of nano-environments. • Synergistic and confined effects in lanthanide MOFs with gases are quantized and discussed. • An interesting precursor is obtained when the synthetic template is 1,4-butanediamine. • CO 2 uptake and conversion in the hydrophobic channels can also be spectroscopic characterized.