This is the first experimental evidence that both self-assembly and surface activity are common features of all water-soluble boron cluster compounds. The solution behavior of anionic polyhedral boranes (sodium decaborate, sodium dodecaborate, and sodium mercaptododecaborate), carboranes (potassium 1-carba-dodecaborate), and metallacarboranes {sodium [cobalt bis(1,2-dicarbollide)]} was extensively studied, and it is evident that all the anionic boron clusters form multimolecular aggregates in water. However, the mechanism of aggregation is dependent on size and polarity. The series of studied clusters spans from a small hydrophilic decaborate-resembling hydrotrope to a bulky hydrophobic cobalt bis(dicarbollide) behaving like a classical surfactant. Despite their pristine structure resembling Platonic solids, the nature of anionic boron cluster compounds is inherently amphiphilic-they are stealth amphiphiles.

Aalto University Department of Applied Physics Nanotalo Puumiehenkuja 2 FI 02150 Espoo Finland

Institute of Macromolecular Chemistry v v i Academy of Sciences of the Czech Republic Heyrovský Sq 2 16206 Prague 6 Czech Republic

Institute of Organic Chemistry and Biochemistry v v i Academy of Sciences of the Czech Republic Flemingovo nam 2 166 10 Prague 6 Czech Republic

Stranski Laboratorium für Physikalische Chemie und Theoretische Chemie Institut für Chemie Sekr TC 7 Technische Universität Berlin Strasse des 17 Juni 124 D 10623 Berlin Germany

References provided by Crossref.org

Carbon-Substituted Amines of the Cobalt Bis(dicarbollide) Ion: Stereochemistry and Acid-Base Properties

Chemistry of Carbon-Substituted Derivatives of Cobalt Bis(dicarbollide)(1-) Ion and Recent Progress in Boron Substitution

Metallacarborane Cluster Anions of the Cobalt Bisdicarbollide-Type as Chaotropic Carriers for Transmembrane and Intracellular Delivery of Cationic Peptides

Electrochemistry of Cobalta Bis(dicarbollide) Ions Substituted at Carbon Atoms with Hydrophilic Alkylhydroxy and Carboxy Groups

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