Group 8 Metal-Metal Bonds

Cognization of metal-metal bonding arose from the structural elucidation of metal clusters, where two or more metals were in close proximity. This chapter presents the vast collection of coordination complexes, attesting to the fact that Group 8 metals are highly versatile at forming metal-metal bonds. Of the Group 8 triad, Ru2 complexes remain the most studied. In the past decade, the coordination chemistry of Os2 has stagnated, but that for Fe2 have flourished. The chapter first discusses the homobimetallics with Group 8-metal bonds, and then describes heterobimetallics with Group 8-metal bonds. It characterizes the metal-metal interactions by their formal shortness ratio (FSR), which is defined as the ratio of the metal-metal bond distance to the sum of the single bond radii. The chapter focuses on covalent d-d bonds of Group 8 metals.