Boron-based B3Zn6− alloy cluster as a hybrid between prismatic and sandwich-like structures: Stabilization of a linear B3 chain motif using electronic transmutation

Doping boron clusters with metallic elements can tune the structural, electronic, and bonding properties. We report on the computational design of a zinc-rich D3h (1A1') B3Zn6- alloy cluster, whose global-minimum structure is a hybrid between prismatic, sandwich-like, and core-shell tubular geometries. The binary cluster features a linear B3 chain along its C3 axis, as well as three lateral Zn-Zn dimers, in which a central B atom is sandwiched by two quasi-planar BZn3 units in an eclipsed form. Chemical bonding analyses show that the B3 chain motif has Lewis-type B-B σ single bonds and a pair of orthogonal three-center two-electron (3c-2e) π bonds, collectively leading to a B-B bond order of two. Stabilizing a boron single chain is scarce in the literature, as is observing a series of double B=B bonds in a monoatomic chain fashion. The triangular pyramid BZn3 units are each in a unique triplet σ2σ*1σ*1 configuration, thus rendering σ aromaticity to the cluster according to the reversed 4n Hückel rule. It is proposed that the alloy cluster can be rationalized using the concept of electronic transmutation, wherein a close chemical analogy to the carbon dioxide (CO2) molecule is established.