From Bowls to Capsules: Assembly of Hexanuclear Ni^II Rings Tailored by Alkali Cations

An anionic hexanuclear Ni^II 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=Li^I and Na^I ) to {Ni₆ -M} bowls (M=K^I and Cs^I ). 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.