Halide ion directed templation effect of quadruple-stranded helicates

Abstract

The allosteric effect, described as biological enzymes’ conformation change to accommodate specific substrates, plays an important role in metabolic regulation. However, well-organized aggregation of synthetic receptors into high-order supramolecular structures with different conformations and functions in response to a variety of external stimuli presents a formidable challenge. Herein, a series of quadruple-stranded helicates are created through the templation effect of halide ions in a library of metallo-macrocycles. Single-crystal X-ray diffraction unambiguously confirms that the four intertwined strands are bridged with halide ions via eight robust C–H···X¯ hydrogen bonds, four anion-π interactions, and two electrostatic contacts. The binding of I¯ results in a D2-symmetric helicate, while the Br¯ or Cl¯ adducts display asymmetric infrastructures. Furthermore, the templation effect exhibits non-thermodynamically controlled, high selectivity toward I¯ due to its nucleophilicity toward breaking up partial coordination bonds.