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 [C 4 B 8 R 4 H 8 ] .− , determined by DFT calculations. magnified image 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.