Structure search for B₇Mn₂ clusters: Inverse sandwich geometry with a high-spin state

Abstract

Herein, we present a density functional theory (DFT) investigation of the B7Mn2 cluster, a boron based system doped with two manganese atoms. The most stable structure adopts an inverse sandwich configuration, in which the B7 ring is symmetrically coordinated by two Mn atoms and exhibits a spin multiplicity of eight. Higher-energy isomers retain the B7 wheel-like motif, with Mn atoms positioned either above the ring or at peripheral sites. The Mn2–B7 complex exhibits moderate interaction energy, arising from a balance between favorable electrostatic and orbital contributions and significant Pauli repulsion. Strong π-type interactions between the Mn d-orbitals and the delocalized B7 ring lead to substantial charge transfer (∼1.3 e−), rendering the Mn centers electron-deficient. This behavior is consistent with their Lewis acidic character and a weak Mn–Mn bonding interaction. Nucleus-independent chemical shift (NICS) isosurface analysis reveals a pronounced antiaromatic character, with extended deshielding under a magnetic field applied along the z-axis. In contrast, fields oriented along the x- and y-directions produce more localized effects, highlighting the planar delocalization of the antiaromatic B7 framework