Nickel complexes with rare pentagonal bipyramidal structures were synthesized via ligand-exchange reactions. The complexes were water- and acid-resistant. With the aid of theoretical calculations, the crystal structures showed that the pentagonal bipyramidal structures comprised electrostatic rings of cyclic pentapyridyls and threaded linear metal complexes.

Abstract

The coordination chemistries of transition metal complexes with pentagonal bipyramidal geometries were investigated, and the highly stable nature of a cyclic pentapyridyl ligand was disclosed. A NiCl₂ complex with the pentapyridyl ligand was found to be stable toward water and acidic conditions. The stable complex underwent ligand-exchange reactions with nucleophilic reagents, and a series of pentagonal bipyramidal complexes with different apical ligands was prepared. Crystallographic analyses with the aid of theoretical calculations revealed that the complexes were constructed by electrostatic threading of a divalent linear nickel complex into the ring of the neutral, cyclic pentapyridyl, which resulted in robust water- and acid-resistant complexes with unique pentagonal bipyramidal structures. A reductive metal exchange reaction was then discovered, which enabled “linear divalent metal + electrostatic ring” formulations with different metal atoms.