Electrophilic and nucleophilic gas phase reactivity of the Janus cluster-based anions [{Mo 6 Cl 8 }Cl 5 □] - (□ = lacuna).

The lacunary monocharged anion [{Mo 6 Cli8}Cla5□ a ] - presents concomitantly a strongly electrophilic site and a nucleophilic one. This Janus character in terms of reactivity is confirmed by its gas phase reaction with [Br 6 Cs 4 K] - to form [{Mo 6 Cli8}Cla5Br a ] 2- and by its unusual self-reactivity leading to [{Mo 6 Cli8}Cla6] 2- dianions.