Structure and heats of formation of iodine fluorides and the respective closed-shell ions from CCSD(T) electronic structure calculations and reliable prediction of the steric activity of the free-valence electron pair in CIF6-, BrF6-, and IF6-

Atomization energies at 0 K and heats of formation at 0 and 298 K are predicted for IF, IF2-, IF2+, IF3, IF4-, IF4+, IF5, IF6-, IF6+, IF7, IF8-, BrF6-, and CIF6- from coupled cluster theory [CCSD(T)] calculations with effective-core potential correlation-consistent basis sets for I. In order to achieve near chemical accuracy (+/-1 kcal/mol), three corrections were added to the complete basis set binding energies based on frozen-core coupled-cluster theory energies: a correction for core-valence effects, a correction for scalar relativistic effects, and a correction for first-order atomic spin-orbit effects. Vibrational zero-point energies were computed at the coupled-cluster level of theory except for IF6-, IF7, and IF8-. The calculated heats of formation for the neutral and ionic IFn fluorides were used to predict fluoride affinities. It is shown that high-level calculations are required to predict correctly the steric activity of the free-valence electron pair on the central atoms in IF6- (C-3v), BrF6- (O-h), and CIF6- (O-h). The vibrational spectrum of IF8- was reanalyzed, and complete mode descriptions for square-anti prismatic XF8 species of D-4d symmetry are given.