Exposing elusive cationic magnesium–chloro aggregates in aluminate complexes through donor control

Abstract

The cationic magnesium moiety of magnesium organohaloaluminate complexes, relevant to rechargeable Mg battery electrolytes, typically takes the thermodynamically favourable dinuclear [Mg₂Cl₃]⁺ form in the solid-state. We now report that judicious choice of Lewis donor allows the deliberate synthesis and isolation of the hitherto only postulated mononuclear [MgCl]⁺ and trinuclear [Mg₃Cl₅]⁺ modifications, forming a comparable series with a common aluminate anion [(Dipp)(Me₃Si)NAlCl₃]⁻. By pre-forming the Al–N bond prior to introduction of the Mg source, a consistently reproducible protocol is reported. Usage of the green solvent 2-methyltetrahydrofuran in place of THF in the context of Mg/Al battery electrolyte type complexes is also promoted.