Coordinative saturation of cationic niobium– and rhodium–argon complexes

Abstract

Mass spectra of Nb + and Rh + complexes with argon ligands exhibit `magic' peaks Nb +Ar 4 and Rh +Ar 6, similar to observations for V +Ar 4 and Co +Ar 6, indicating coordinative saturation. A consistent explanation is obtained by assuming that the rare gas ligands seek out electron density minima in the valence shell of the ion, which permit a closer approach to the metal core and a stronger charge-induced dipole bond. Ab initio density functional calculations, which predict stable square planar complexes for the d 4 ions and octahedral for the d 8 species, support this interpretation and show that rare gas complexes of d 4 metal ions fit perfectly well into the coordination chemical framework based on the Jahn–Teller effect.