Fundamental gas-phase clustering reactions for F-(Sol)(n-1) + Sol = F-(Sol)(n) for Sol = O-2, N-2, and CO were studied by using a pulsed electron beam mass spectrometer. While the interaction of F- with Oz ligands is mainly electrostatic, those with N-2 and CO have some contribution from charge transfer (i.e,, the formation of incipient covalent bonds in the complexes F- --> N-2 and F- --> CO). The cluster ion F-(CO)(6) was found to have an octahedral structure with equivalent F-... CO bonds. F-(O-2)(n) was found to involve the smallest binding energy among F- cluster ions ever reported.