Abstract
One of the first steps in designing ferromagnetic (FM) molecular materials of p-block radicals is the suppression of covalent radical–radical interactions that stabilize a diamagnetic ground state. In this contribution, we demonstrate that FM coupling between p-block radicals can be achieved by constructing mixed dimers from different radicals with differing symmetries of their singly occupied molecular orbitals. The applicability of this approach is demonstrated by studying magnetic interactions in organic radical dimers built from different derivatives of the well-known phenalenyl radical. The calculated enthalpies of dimerization for different homo- and heterodimers show that the formation of a mixed dimer with FM coupling is favored compared to the formation of homodimers with antiferromagenetic (AFM) coupling. We argue that cocrystallization of radicals with specifically tuned morphologies of their singly occupied molecular orbitals is a feasible and promising approach in designing new organic magnetic materials.
Highlights
One of the first steps in designing ferromagnetic (FM) molecular materials of pblock radicals is the suppression of covalent radical−radical interactions that stabilize a diamagnetic ground state
In the context of transition-metal complexes, Kahn and coworkers enforced strong FM coupling by taking advantage of symmetry-imposed orthogonality of the singly occupied molecular orbitals (SOMOs) of two transition-metal ions within a common ligand framework.[17−19] In this Letter we demonstrate how Kahn’s strict orthogonality approach can be extended to p-block radical chemistry by using two different radicals with complementary SOMO morphologies, resulting in complete cancellation of SOMO− SOMO overlap and FM coupling
We will demonstrate the applicability of the approach by quantum chemical calculations on radical dimers constructed from derivatives of the real-life odd-alternate hydrocarbon phenalenyl (1).[27−31] Compound 1 was chosen as a testing ground for the proposed approach because of its structural tunability[32] and the wealth of available data
Summary
Letter properties of SOMOs has been noted,[16] and various systems composed of neutral organic radicals and diamagnetic spacers have been thoroughly investigated.[33−37]. We have shown both by theoretical rationalization and by practical calculations on dimers of different phenalenyl derivatives that constructing mixed dimers from radicals with SOMOs that transform differently under the symmetry operations of the dimer will lead to a triplet ground state and FM interaction. The results were demonstrated here for phenalenyl-based systems, but they can be generalized to any p-block radical framework where the radicals have sufficient symmetry or pseudosymmetry (namely, a mirror plane) that the SOMOs can be assigned to different representations of the overall point group. Correlation functionals, additional computational data, and optimized Cartesian coordinates of the studied systems (PDF)
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