| Several types of organic radicals have been studied for utilization in magnetic materials, as well as for their interesting chemical and bonding properties. Nitronyl nitroxide radicals have been introduced into the room temperature high-spin copper(II) carboxylate dimers, but show either very minimal interaction with the copper system when placed in the equatorial bridging positions, or strong antiferromagnetic interactions when placed in the capping axial positions. The radical anion of tetracyanoethylene (TCNE) has previously been investigated for its role in polymeric M[TCNE]2 magnetic materials. However, there are many reported examples in which the radical anion dimerizes to form either σ- or π-[TCNE]22− dimers. The σ-[TCNE]22− contains long σ-bonds (1.60 Å) between two of the ethylene carbons. The π-[TCNE]2 2− dimers, however, interact through the π* orbitals which contain the unpaired electron, resulting in the longest carbon-carbon bonds reported to date, averaging 2.9 Å. These π*-π* bonds form between all four of the central ethylenic carbons, resulting in an unprecedented 2-electron/4-center C-C bond. The radical anions of two tricyanoarene molecules—1,3,5-tricyanobenzene (TCB) and 2,4,6-tricyano-1,3,5-triazine (TCT)—also dimerize to form σ-bonded dimer dianions. Interestingly decomposition of the dimer of the TCT radical anion results in a new and potentially useful redox-active ligand-4,4 ′,6,6′-tetracyano-2,2′-bitriazine (TCBT). |
