• bonding analysis;
  • carbodiphosphoranes;
  • cations;
  • density functional calculations;
  • donor–acceptor systems


Quantum chemical calculations at the BP86/TZVPP//BP86/SVP level of theory have been performed for the isoelectronic series of compounds [(PPh3)2C[RIGHTWARDS ARROW]EH2]q (Eq=Be, B+, C2+, N3+, O4+). The equilibrium geometries and bond dissociation energies were calculated and the nature of the C[RIGHTWARDS ARROW]E bond was investigated with charge and energy decomposition methods. The dication [(PPh3)2C[RIGHTWARDS ARROW]CH2]2+ could become isolated as a salt compound with two counter ions [AlBr4]. The X-ray structure analysis of [(PPh3)2C[RIGHTWARDS ARROW]CH2]2+ gave bond lengths and angles that are in good agreement with the calculated data. The geometry optimization of [(PPh3)2C[RIGHTWARDS ARROW]OH2]4+ gave [(PPh3)2C[RIGHTWARDS ARROW]OH]3+ as the equilibrium structure. Bonding analysis of [(PPh3)2C[RIGHTWARDS ARROW]EH2]q shows that [(PPh3)2C[RIGHTWARDS ARROW]BeH2] and [(PPh3)2C[RIGHTWARDS ARROW]BH2]+ possess donor–acceptor bonds in which the σ and π lone-pair electrons of (PPh3)2C donate into the vacant orbitals of the acceptor fragment. The multiply charged compounds are better described as substituted olefins [(PPh3)2C[DOUBLE BOND]CH2]2+, [(PPh3)2C[DOUBLE BOND]NH2]3+, and [(PPh3)2C[DOUBLE BOND]OH]3+, which possess electron-sharing σ and π bonds that arise from the interaction between the triplet states of [(PPh3)2C]2+ and the respective fragment CH2, (NH2)+, and (OH)+. The multiply charged cations [(PPh3)2C[DOUBLE BOND]CH2]2+, [(PPh3)2C[DOUBLE BOND]NH2]3+, and [(PPh3)2C[DOUBLE BOND]OH]3+ are calculated to be stable toward dissociation.