Boron Atoms as Spin Carriers in Two- and Three-Dimensional Systems



To “B” or not to “B”: The unusual bonding of boron in organoboranes or oligoboron clusters is not only apparent in diamagnetic molecules but also in paramagnetic systems, including mixed-valent species and oligoborane/carborane cluster radicals. The picture shows the singly occupied molecular orbital of the radical ion [C4B8R4H8].−, determined by DFT calculations.

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Paramagnetic compounds with at least partially boron-centered electron spin can be constructed using either the prototypically electron-accepting boron atoms bridged by planar π-conjugated organic systems, or by taking advantage of the three-dimensional delocalized bonding in oligonuclear borane, haloborane, or carborane clusters. The concept of mixed valency can thus be transferred from organic and transition-metal chemistry to main-group-element molecules, and density functional theory is capable of reproducing the variable spin distribution.