Homochiral three-dimensional noncentrosymmetric lanthanide coordination polymers directed by chiral linkers: syntheses, crystal structures, and optical properties

Abstract

Crystals of six enantiomorphic lanthanide–organic coordination polymers, [Ln₂((R,R)-TBA)₂((R,R)-HTBA)₂(H₂O)₂]·7H₂O [Ln(R)] and Ln₂((S,S)-TBA)₂((S,S)-HTBA)₂(H₂O)₂]·7H₂O [Ln(S)] (Ln = La, Ce, and Pr; TBA = 1,3,5-triazin-2(1H)-one-4,6-bis(alanyl)), have been grown through solvothermal reactions. The chirality of compounds Ln(R) and Ln(S) turns out to be directed by that of the respective chiral TBA ligands. The structures of the reported compounds crystallizing in the noncentrosymmetric (NCS) polar space group, C2, consist of two types of polyhedra, namely, Ln(1)O₈ and Ln(2)O₁₀, and TBA linkers. Each Ln(1)O₈ polyhedron is connected through TBA ligands forming unidimensional (1D) chains. The 1D chains composed of Ln(1)O₈ polyhedra are further connected to La(2)O₁₀ polyhedra completing a three-dimensional framework. The chiral structures derived from the chiral organic TBA ligands not only absorb circularly polarized light, but also reveal second-harmonic generation signals originating from the macroscopic NCS structures. The reported chiral coordination polymers are further characterized by spectroscopic, thermal, and elemental analyses.