Cs[H2NB2(C6F5)6] Featuring an Unequivocal 16-Coordinate Cation

Cesium bis(perfluoro-triphenylborane)amide, Cs[H2NB2(C6F5)(6)] (1), has been prepared by the reaction of sodium salt and CsF in dichloromethane add water. The compound is exceptional for a [H2NB2(C6F5)(6)]- salt in that it contains a monatomic solute-free cation. Determination of the molecular structure revealed a novel C-2 symmetrical conformation of the weakly coordinating [H2NB2(C6F5)(6)]- anion, which gives rise to an unprecedented 16-coordinate (CN 16) Cs+ cation in a likewise unprecedented tetracosahedral arrangement of F atoms. The poor solubility of 1 allows nearly quantitative separation of Cs+ from water, which suggests potential applications as an effective Cs-134/137 remover from nuclear waste solutions, administration as an antidote for Cs-134/137 poisoning, and use for Cs-131/137 radiotherapy (brachytherapy). Rb[H2NB2(C6F5)(6)].CH2Cl2 (2) has also been characterized, featuring two inequivalent Rb+ cations having CN 10, one of which involves Rb+(eta(Cl2CH2)-Cl-2)(2) coordination.