The weakly coordinating binary macropolyhedral anion closo,closo-[B21H18]- (B21; D3h symmetry) has been synthesized using a simplified strategy compared to that in the literature. While gas-phase complexes of B21 with β- and γ-cyclodextrin (CD) were detected using ESI FT-ICR spectrometric measurements, α-CD did not bind to the B21 guest. This spectroscopic evidence has been interpreted using quantum-chemical computations, showing that β- and γ-CD are able to interact with B21 due to their larger cavities, in contrast to the smaller α-CD. The hydridic B-H vectors of the B21 anion interact with K+ counterions and, via dihydrogen bonding, also with the partially positively charged hydrogens of the CD sugar units in the modeled β- and γ-CD complexes. In summary, it has been shown by combined spectrometric/computational analysis that macropolyhedral boron hydride anions with two counterions can form stable complexes with β- and γ-CD in the gas phase, offering a new perspective for the future investigation of this remarkable anion in the areas of supramolecular and medicinal chemistries.

Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences Flemingovo nam 2 CZ 16610 Prague 6 Czech Republic

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Face-Fusion of Icosahedral Boron Hydride Increases Affinity to γ-Cyclodextrin: closo,closo-[B21 H18 ]- as an Anion with Very Low Free Energy of Dehydration