Helix is an important structural motif in nature. Dinuclear triple-stranded [M₂L₃] complexes, as simple models for more complex natural structures of biological molecules, have been of much interest.

Researchers from Lanzhou Institute of Chemical Physics (LICP) of the Chinese Academy of Sciences (CAS), and University of Glasgow, have successfully synthesized a series of highly charged, dinuclear triple-stranded cagelike [M₂L₃]⁷⁺ complexes by employing an imidazolium-bridged bis(2,2′-bipyridine) ligand (L) and a FeII or CuII ion.

Interestingly, the complex can accommodate an anion in the cage, and the size and/or shape of the encapsulated anion is the key factor that determines the stereochemistry of the product. In the presence of the larger tetrahedral anions such as BF₄⁻, SO₄²⁻, and ClO₄⁻, the meso complexes are favored. In contrast, the smaller trigonal-planar(NO₃⁻) or spherical (Br⁻) anions lead to helicates. Moreover, spontaneous resolution of the P helices occurred during crystallization of the helicates and. The conformational change of the ligand upon encapsulation of the anion may be responsible for the anion-dependent formation of the helicates versus mesocates.

The work has received support from the National Natural Science Foundation of China. The findings have been published in Inorg. Chem. (Inorg. Chem. 2012, 51, 179−187).

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