ABINITIO STUDY OF BONDING TRENDS .4. THE 22-ELECTRON A=B=C SERIES - POSSIBLE NEW ANIONS DOWN TO NCB4- AND POSSIBLE NEW CATIONS UP TO FNF3+

The 22-electron double-bonded A=B=Cn systems with net charges -4 ≤ n ≤ 4 are screened for possible new species near known "stability islands". Initial HF/6-31G* results are screened further with a 6-311G* basis and MPn or CISD methods for the possible gas-phase species. The bond lengths of C22- and NCN2- in a simple crystal field model differ by only a few picometers from the free-ion values, indicating that the anion calculations are meaningful. The calculated bond lengths and vibrational frequencies reproduce the experimental trends down to NBN3-. The possible new species include NCB4- or NBC4- near the known CCC4-, NCC3- or OBC3- near the known NBN3-, and OBN2- near the known NCN2-. The calculated geometry for NNC2- is close to that observed for the nitrile imine R-NNC-R′. The cations OOO2+ and FNF3+ of ref 2 are still predicted to be locally stable. © 1990 American Chemical Society.