Helicity controlled by the chirality of amino acid: two novel enantiopure chiral 3D architectures containing fivefold interwoven helices

Abstract

Two novel three-dimensional (3D) chiral coordination polymers, namely [Zn₄(btc)₂(Hbtc)(L-His)₂(H₂O)₄]·1.5H₂O (L-1) and [Zn₄(btc)₂(Hbtc)(D-His)₂(H₂O)₄]·1.5H₂O (D-1), have been assembled from zinc salt with mixed ligands 1,3,5-benzenetricarboxylic acid (H₃btc) and chiral histidine (His). Their structures were determined by single-crystal X-ray diffraction analyses, elemental analyses, infrared (IR) spectra, X-ray powder diffraction, circular dichroism (CD) spectra, and thermogravimetric (TG) analysis. Compounds L-1 and D-1 are enantiomers and exhibit unique 3D chiral frameworks containing fivefold interwoven helices, which represent the first examples of chiral metal–amino acid complexes containing n-fold interwoven helices. Furthermore, the helices in L-1 are left-handed, while those in D-1 are right-handed, which indicate that the handedness of helices can be controlled by the chirality of His bound to the metal. More wonderfully, the 3D framework can be simplified to a (3,4)-connected chiral net with an unprecedented (4·9²)(4·9⁴·11) topology. Moreover, the luminescent properties of compound L-1 are discussed.