title: Surface activity and molecular organization of metallacarboranes at the air-water interface revealed by nonlinear optics.
abstract: Because of their amphiphilic structure, surfactants adsorb at the water-air interface with their hydrophobic tails pointing out of the water and their polar heads plunging into the liquid phase. Unlike classical surfactants, metallabisdicarbollides (MCs) do not have a well-defined amphiphilic structure. They are nanometer-sized inorganic anions with an ellipsoidal shape composed of two carborane semicages sandwiching a metal ion. However, MCs have been shown to share many properties with surfactants, such as self-assembly in water (formation of micelles and vesicles), formation of lamellar lyotropic phases, and surface activity. By combining second harmonic generation and surface tension measurement, we show here that cobaltabis(dicarbollide) anion {[(C2B9H11)2Co](-) also named [COSAN](-)} with H(+) as a counterion, the most representative metallacarborane, adsorbs vertically at the water surface with its long axis normal to the surface. This vertical molecular orientation facilitates the formation of intermolecular and nonconventional dihydrogen bonds such as the B-H(δ-)···(δ+)H-C bond that has recently been proven to be at the origin of the self-assembly of MCs in water. Therefore, it appears here that lateral dihydrogen bonds are also involved in the surface activity of MCs.
authors: Institut de Chimie Séparative de Marcoule, UMR 5257 (CEA-CNRS-UM-ENSCM) , B.P. 17171, 30207 Bagnols sur Cèze Cedex, France.
authors: Pierre-Marie
authors: PM
authors: Gassin
authors: Luc
authors: L
authors: Girard
authors: Gaelle
authors: G
authors: Martin-Gassin
authors: Damien
authors: D
authors: Brusselle
authors: Alban
authors: A
authors: Jonchère
authors: Olivier
authors: O
authors: Diat
authors: Clara
authors: C
authors: Viñas
authors: Francesc
authors: F
authors: Teixidor
authors: Pierre
authors: P
authors: Bauduin
mesh_terms: D000388:Air; D001896:Boron Compounds / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010316:Particle Size; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D001896:Boron Compounds; D009942:Organometallic Compounds; D014867:Water; D003035:Cobalt