Synthesis of a chiral rod-like metal–organic framework from a preformed amino acid-based hexanuclear wheel

Abstract

We report the two-step synthesis of a chiral rod-like metal-organic framework (MOF). The chemical approach consists on the use of a previously prepared oxamato-based homochiral hexanuclear wheel, the ligand being a derivative of the natural amino acid l-alanine, with formula (Me4N)6{CuII6[(S)-alama])6}·10H2O (1) [where (S)-alama=(S)-N-(ethyl oxoacetate)alanine]. The anionic hexacopper(II) wheels, stabilized by the presence of templating tetramethylammonium counter-cations, disassemble in the presence of cationic square-planar [Ni(cyclam)]2+ complexes to yield, after a supramolecular reorganization process that involves axial coordination of the [Ni(cyclam)]2+ cations through the free carbonyl groups of the copper(II) moieties, a neutral chiral rod-like, three-dimensional (3D) MOF with formula [Ni(cyclam)][Cu(S)-alama]2·16H2O (2). The resulting MOF constitutes one of the few examples where such a high-nuclearity metal complex is used as precursor for the construction of rod-like MOFs.