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

The cationic magnesium moiety of magnesium organohalo aluminate 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.