Thanks to E.Salamin for the tip; I then found a few papers A.I. Boldyrev & J.Simons: Theoretical Search for Small Linear Doubly Charged Anions, J. Chem. Phys. 98 (1993) 4745-??. M.K. Scheller, R.N. Compton, L.S. Cederbaum: Gas Phase Multiply Charged Anions, Science 270 (1995) 1160-1166. ALEXANDER I. BOLDYREV, MACIEJ GUTOWSKI, AND JACK SIMONS Small Multiply Charged Anions as Building Blocks in Chemistry, Acc. Chem. Res. 29 (1996) 497-502 http://simons.hec.utah.edu/papers/paperso/201.pdf the conclusion seems to be (based on both experiments and computation) that apparently no N-atom doubly-negatively-charged ions exist in isolation for N=1,2,3, despite fact many such ions exist inside crystals and sometimes in solutions too. The 4-atom (LiF3) 2- is electronically and locally geometrically stable, but not chemically thermodynamically stable. Both 2 and 3 charged negative ion species are known to exist but usually with a lot bigger formulas than you'd think from chemistry textbook negative ion formulas (most of which cannot exist in isolation).