Multiple-decker and ring sandwich formation of manganese–benzene organometallic cluster anions: MnnBzn− (n = 1–5 and 18)

Abstract

Organometallic multiple-decker sandwich clusters are topics of great interest due to their unique electronic and magnetic properties originating from anisotropic structures. We report a joint anion photoelectron spectroscopic and computational study on a new family of manganese (Mn)–benzene (Bz) anionic clusters Mn_nBz_n⁻. In stark contrast to the most widely studied vanadium–Bz sandwich clusters, it is found that Mn_nBz_n⁻ (n = 1–5) clusters exhibit unprecedented multiple-decker structures with a tilted Mn–Bz stacking and a monotonically increasing behavior of their high spin multiplicities. Furthermore, a couple of closed ring forms of Mn₁₈Bz₁₈⁻ and its neutral state are computationally anticipated as an intriguing “cluster of Mn₁Bz₁ clusters” in which the neutral Mn₁₈Bz₁₈ has extremely high C_18h symmetry with an uncommon spin state of 2S + 1 = 55. The extensively delocalized electron environment of Mn₁₈Bz₁₈ allows the simple Hückel model to reveal the strong intra-atomic exchange interactions within the Mn 3d electrons.