Strongly bound anions featuring bismuth fluoride building blocks

The stability of polynuclear superhalogen anions composed of BiF₅ building blocks was investigated using ab initio electronic structure methods and flexible basis sets. A comprehensive exploration of the ground state potential energy surfaces of (Bi₂F₁₁)⁻, (Bi₃F₁₆)⁻ and (Bi₄F₂₁)⁻ anions, which can be viewed as comprising BiF₅ fragments and an additional fluorine atom, led to the identification of their isomeric structures. It was found that the most stable isomers, predicted to dominate at room temperature, correspond to chain-like extended structures containing BiF₆ subunits, with fluorine ligands arranged octahedrally around Bi atoms, sharing F atoms to form Bi–F–Bi bridging linkages. The vertical electron detachment energies of the (Bi_nF_5n+1)⁻ anions (n = 1–4) were found to be very high (ranging from 10.91 to 13.36 eV) and increased with the number of bismuth atoms (n) and thus the BiF₅ building blocks involved in the structure. Thermodynamic stability of the (Bi_nF_5n+1)⁻ anions (i.e., their susceptibility to fragmentation) was also verified and discussed.