Sequestered Aerial CO₂ and Phosphate-Assisted Formation of 2D Nanosheets

Two new 4,4'-methylenedianiline (MDA)-based neutral bis-amide-bis-urea receptors (L1, L2) are reported, where L1 and L2 feature a para-NO₂ and meta-CF₃ group, respectively, at the terminal ring. Notably, in the solid state, L1 forms a 2D sheet upon binding with phosphate and atmospheric carbon dioxide (CO₂) as a bicarbonate (HCO₃^-); however, L2 does not show any such 2D network formation with such anions. The formation of 2D nanosheets in the case of L1 with phosphate and bicarbonate is confirmed by both SCXRD and FESEM studies, where FESEM analysis shows 2D sheets, with size in the nano- to micrometer range. Although other oxyanions show binding affinity with both receptors in solution, they fail to form a 2D network in the solid state, as observed in the cases of L1 with phosphate and bicarbonate.