• Carborates;
  • Polyatomic main group cations;
  • Nitrosyl cation;
  • Phosphorus;
  • Weakly coordinating anions


The thermodynamic stability of the [HCB11Cl11] salts of the cationic one-electron oxidizers [NO]+ and [O2]+ was estimated by Born–Haber–Fajans cycles based on quantum-chemical calculations and lattice enthalpy estimations. [NO][HCB11Cl11] is predicted to be a stable compound, whereas [O2][HCB11Cl11] should decompose into O2 and the HCB11Cl11· radical. Consequently, [NO][HCB11Cl11] can be prepared by metathesis reaction from Na[HCB11Cl11] and [NO][BF4] in liquid sulfur dioxide, while attempts to synthesize [O2][HCB11Cl11] failed. [NO][HCB11Cl11] has been fully characterized by NMR and vibrational spectroscopy. Single crystals of [NO][HCB11Cl11]·SO2 were obtained from liquid sulfur dioxide solution. The crystal structure determination revealed several intermolecular cation–anion contacts, which are significantly shorter than the sum of the van der Waals radii of the respective atoms. [NO][HCB11Cl11] reacts with white phosphorus in CH2Cl2 solution to give yellow-orange [P4NO][HCB11Cl11] containing the [P4NO]+ cation. An in-situ NMR spectroscopic study indicates the presence of the homopolyatomic phosphorus cation [P9]+ in the reaction mixture.