Structures of simple anions from ab initio molecular orbital calculations

Abstract

Ab initio molecular orbital theory with the minimal STO-3G and split-valence 4-31G basis sets is used to obtain geometries of 18 anions:OH-, NH₂^-, HF₂^-, BH₄^-, BF₄^-, C₂^2-, CN^-, NCN^2-, N₃^-, NO₂^-, NO₃^-, 0CCO^2-, CO₃^2-, HCOO^-, CH₃COO^-, C₂O₄^2-, C₄O₄^2- and C(CN)₃^-. The theoretical results are compared with experimental results from the literature. The STO-3G basis set performs somewhat worse for anions than for neutral molecules. On the other hand, the 4-31G basis set gives good results and predicts bond lengths to within 0.02Å for all the molecules considered. Limited information on bond angle predictions suggests that these are of comparable quality to those for neutral molecules. The tricyanomethanide ion is predicted to be planar.