Chiral Recognition between Metallohelicates via Strong H Bonds: Homochiral Bishelical Coupling and Mesohelical Polymerization

A rigid, one-dimensional, and monotopic ligand containing both a proton donor and a proton acceptor, 2-[(1H-imidazol-2-yl)­methyleneamino]­phenol (H₂L), has been used to attain three hierarchically assembled supramolecular polymers. The handedness of these hydrogen-bonded metallo-supramolecular structures is modulated by a selective coupling, via strong H bonds with significant covalent character. Thus, alternate Δ and Λ enantiomers of Cd­(HL)₂ form a one-dimensional supramolecular polymer via mutual strong N–H···O interactions (2.58 Å), which are associated with a hydrogen bond energy value of ∼11.5 kcal mol^–1. In contrast, homochiral self-recognition of enantiomers of M­(HL)₂ and [M­(H₂L)₂]²⁺ (M = Cu^II and Ni^II) gives rise to dinuclear bishelicates, whose metallohelical units are held together by two strong O–H···O bonds (2.41–2.44 Å), which are associated with hydrogen bond energies in the range of 25–35 kcal mol^–1.