Carbonate and phosphite encaged in frameworks constructed from square lanthanum aminopolycarboxylates and sodium chloride

Abstract

Novel additives of lanthanum aminopolycarboxylates with inorganic anions, Na_12n[La(edta)L]_4n·8nNaCl·4nH₂O (1: L = HPO₃²⁻; 2: L = CO₃²⁻) and K_12n[La(cdta)(CO₃)]_4n·35nH₂O (3) (H₄edta = ethylenediaminetetraacetic acid; H₄cdta = cyclohexanediaminetetraacetic acid), were obtained in alkaline solution. Structural analyses reveal that 1 and 2 are isomorphous and contain interesting square structures. HPO₃²⁻ (CO₃²⁻) was encaged in the constructed tetranuclear frameworks. Tetranuclear lanthanum ethylenediaminetetraacetate was further encaged in superstructures of sodium chloride. 3 has a similar square structure, in which edta is replaced by cdta. All complexes are fully characterized via elemental, FT-IR, NMR, thermogravimetric and structural analyses. Solution ¹³C NMR spectra show that 1 and 2 dissociate into mononuclear units in water. Interestingly, 2 possesses 3.7 Å diameter holes inside its crystals, which can adsorb a small amount of O₂ or CO₂ selectively. The amounts of O₂ and CO₂ adsorbed increase gradually from 0.32 and 0.38 mg g⁻¹ at 0.4 bar to 15.90 and 10.54 mg g⁻¹ at 29.9 bar, respectively.