From Bowls to Capsules: Assembly of Hexanuclear NiII Rings Tailored by Alkali Cations

Chemistry. 2020 Sep 1;26(49):11158-11169. doi: 10.1002/chem.202001900. Epub 2020 Jul 29.

Abstract

An anionic hexanuclear NiII metallamacrocycle with endo and exo linking sites has been employed as a building block to generate a series of capsules and bowls of nanometric size. The supramolecular arrangement of the {Ni6 } rings was tailored by the size of the alkali cations, showing the transition from {Ni6 -M2 -Ni6 } capsules (M=LiI and NaI ) to {Ni6 -M} bowls (M=KI and CsI ). The alkyl co-cations are determinant to stabilize the assemblies by means of CH⋅⋅⋅π interactions on the exo side of the metallamacrocycles. The effect on the topology of the supramolecular assemblies of the cation size, cation charge, Et3 NH+ or Me4 N+ counter cations has been analyzed. Magnetic measurements reveal the presence of ferromagnetic and antiferromagnetic interactions inside the rings that allow a S=0 ground state.

Keywords: capsules; magnetism; metallamacrocycles; nickel; self-assembly.