Interchain-Solvent-Induced Chirality Change of 1D Helical Chains:  From Achiral to Chiral Crystallization

Three helical supramolecular stereoisomers of meso-2, Δ-2, and Δ-3 with the formula of cis-[Ni(f-rac-L)][Ni(CN)₄] were successfully constructed based on the [Ni(f-rac-L)²⁺ and [Ni(CN)₄]^2- building blocks (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane). In all three supramolecular stereoisomers, cis-[Ni(f-rac-L)]²⁺ cations are alternately bridged by [Ni(CN)₄]^2- anions through two cis (in meso-2 and Δ-2) or trans (in Δ-3) cyano groups to form one-dimensional (1D) helical chains of cis-[Ni(f-rac-L)][Ni(CN)₄]. In meso-2, the right/left-handed chirality of the originally formed chain is transferred oppositely to adjacent chains through the interchain hydrogen-bonding interactions of hexameric water clusters, leading to the formation of meso-2 with a central symmetrical space group, P2₁/n, in which the 1D helical chains are packed in an alternating right- and left-handed chirality. In Δ-2 and Δ-3, the right/left-handed chirality of the original chain is transferred uniformly to adjacent chains through the zipper-like interchain hydrophobic interactions, resulting in the formation of Δ-2 and Δ-3 with chiral space groups of P2₁2₁2₁ and P3₁21, respectively, in which all of the 1D helical chains are arranged in the same right/left-handed chirality.