M(ii) effect on encapsulation of guests into a series of M3L2 chiral cages: enantio-recognition

Abstract

Self-assembly of M(ClO₄)₂ (M²⁺ = Ni²⁺, Cu²⁺, and Zn²⁺) with (1S,1′S,1′′S,2R,2′R,2′′R)-(benzenetricarbonyltris(azanediyl))tris(2,3-dihydro-1H-indene-2,1-diyl) trinicotinate (s,r-L) and the corresponding enantiomer (r,s-L) as a pair of chiral tridentate donors gives rise to the chiral cage pairs [M₃(s,r- and r,s-L)₂](ClO₄)₆. For the two pairs of [(Me₂CO)(H₂O)@M₃(r,-s and s,r-L)₂](ClO₄)₆ (M²⁺ = Ni²⁺ and Zn²⁺), the inner cavity is occupied by both an acetone and a single water molecule, whereas for the copper(II) pair of [Me₂CO@Cu₃(r,s- and s,r-L)₂](ClO₄)₆ under the same conditions, the cavity is filled by only one acetone molecule. Thus, the encapsulation of guest molecules into the cages during self-assembly shows significant metal(II) ion effects. These chiral cages are effective for the enantio-recognition of chiral (S)-2-butanol and (R)-2-butanol via the shifts of the electrochemical oxidation potentials obtained by the linear sweep voltammetry (LSV) technique, density functional theory (DFT) calculations, and the chiral 2-butanol adsorption in the single-crystal-to-single-crystal (SCSC) mode.