Alkali metal ion directed self-assembled Ni(ii) molecular clusters

Abstract

A series of Ni²⁺ complexes of N-(7-hydroxy-4-methyl-8-coumarinyl)-glycine (H₂mugly) and N-(7-hydroxy-4-methyl-8-coumarinyl)-L-alanine (H₂muala) has been prepared by self-assembly of Ni(CH₃COO)₂·4H₂O with ligands in the presence of alkali metal ions. The complexes have been characterized by elemental analysis, thermogravimetry, IR and ESI-MS studies, and several of these complexes have also been structurally characterized by X-ray crystallography. Interestingly, the alkali metal ions have been found to direct the self-assembly processes and facilitate the formation of oligonuclear structures. Structural investigations showed that the molecular clusters displayed intriguing architectures including heptanickel metallocrowns with highly symmetrical hexagonal shapes, a heterobimetallic molecular cage and a pentanickel cluster with a nanobasket shape. The diversity of the coordination geometries and the cluster structures are discussed in detail.