Salts of the 1-cyanocarba-closo-dodecaborate anions [1-NC-closo-1-CB11X11]- (X = H, F, Cl, Br, I)

The caesium and tetraethylammonium salts of the 1-cyanocarba-closo-dodecaborate anions [1-NC-closo-1-CB11X11](-) (X = H, F, Cl, Br, I) were synthesized from CsLi[closo-1-CB11X11] and phenylcyanate. All anions are stable against aqueous acids and bases, except for the fluorinated anion [1-NC-closo-1-CB11F11](-) that immediately reacts with water. The Cs+ and [Et4N](+) salts of the anions were characterized by IR, Raman and multinuclear NMR spectroscopy as well as by MALDI and ESI mass spectrometry. The thermal properties of the Cs[1-NC-closo-1-CB11X11] (X= H, Cl, Br, I) and of some of their tetraethylammonium salts were studied by differential scanning calorimetry. The crystal structures of [Et4N][1-NC-closo-1-CB11H11] and Cs[1-NC-closo-1-CB11Cl11] were determined and the discussion of the structural and spectroscopic properties is supported by density functional and (RI)-MP2 calculations. A first insight into the hydrolysis of the [1-NC-closo-1-CB11F11]-anion is presented and its reactions with water are compared to those of other undecafluorinated carba-closo-dodecaborate anions. The reduced hydrolytic stability of the [1-NC-closo-1-CB11F11](-) anion in comparison to its homologues is related to differences in the carbon-boron and boron-boron bond lengths of the {closo-1-CB11} cage and to different partial charges of the cluster atoms.