Decamethylbimetallocenes have been synthesized for Fe, Co, and Rh, and the crystal structures of the 36-electron iron and rhodium complexes show a fully transoid conformation; electron-transfer studies indicate the 35-electron mixed-valence PF6- diiron salt is localized and suggest the neutral dicobalt and dirhodium bis-sandwich species have respectively 38 and 36 valence electrons. © 1992, American Chemical Society. All rights reserved.