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

Abstract

The caesium and tetraethylammonium salts of the 1-cyanocarba-closo-dodecaborate anions [1-NC-closo-1-CB(11)X(11)](-) (X = H, F, Cl, Br, I) were synthesized from CsLi[closo-1-CB(11)X(11)] and phenylcyanate. All anions are stable against aqueous acids and bases, except for the fluorinated anion [1-NC-closo-1-CB(11)F(11)](-) that immediately reacts with water. The Cs(+) and [Et(4)N](+) 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-CB(11)X(11)] (X = H, Cl, Br, I) and of some of their tetraethylammonium salts were studied by differential scanning calorimetry. The crystal structures of [Et(4)N][1-NC-closo-1-CB(11)H(11)] and Cs[1-NC-closo-1-CB(11)Cl(11)] 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-CB(11)F(11)](-) 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-CB(11)F(11)](-) anion in comparison to its homologues is related to differences in the carbon-boron and boron-boron bond lengths of the {closo-1-CB(11)} cage and to different partial charges of the cluster atoms.