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 and 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 C2 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 (134/137)Cs remover from nuclear waste solutions, administration as an antidote for (134/137)Cs poisoning, and use for (131/137)Cs 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(+)(η(2)-Cl2CH2)2 coordination.