Metal–metal bonded compounds with uncommon low oxidation state

Abstract Over the past decade, the metal–metal bonded compounds with uncommon low oxidation state has tremendously facilitated the development of metal–metal bond chemistry. Herein, we review the syntheses, molecular and electronic structures, important properties and applications of more than one hundred metal–metal bonded compounds with uncommon low oxidation state. These compounds cover both homonuclear metal–metal bonded compounds and heteronuclear ones, as well various metal–metal bonds from localized bi-center to delocalized multi-center systems. Furthermore, theoretical calculations on some compounds systematically analyzed orbital bonding and electron occupancy, further elucidating the intrinsic relationship among the functions, stabilities and structures.