All-metal σ-antiaromaticity in dimeric cluster anion {[CuGeMes]}

In this work, we report a dimeric cluster anion, {[CuGe 9 Mes] 2 } 4− , which was isolated as the [K(2,2,2-crypt)] + salt and characterized by using single-crystal X-ray diffraction and ESI mass spectroscopy. The title cluster represents the first locally σ-antiaromatic compound in the solid state, as well as the first heteroatomic antiaromatic compound. In this work, we firstly synthesized a solid-state compound {[CuGe 9 Mes] 2 } 4− with a planar Cu 2 Ge 2 fragment. By performing the thorough theoretical analysis, we showed that Cu 2 Ge 2 diamond fragment possesses σ-antiaromatic properties.