The Role of Orbital Symmetries in Enforcing Ferromagnetic Ground State in Mixed Radical Dimers

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.

Triply Bonded Pancake π-Dimers Stabilized by Tetravalent Actinides

“…When the energy differences are described by an isotropic Heisenberg–Dirac–van Vleck Hamiltonian, i.e., Ĥ HDvV = − JŜ A · Ŝ B with Ŝ A and Ŝ B denoting effective spin operators on the [HAN] 3– radicals, the exchange coupling constants is J = −2803 cm –1 , indicating a strong antiferromagnetic interaction that is practically a covalent bond. For comparison, the J -value in the dimer of 2,5,8-tri tert -butylphenalenyl is in the region of −1300 to −3000 cm –1 , − with computational values closer to the lower estimate. ,, Thus, it is reasonable to classify the interaction between the [HAN] 3– anions as a covalent bond.…”

“…For comparison, the J-value in the dimer of 2,5,8-tritert-butylphenalenyl is in the region of −1300 to −3000 cm −1 , 53−55 with computational values closer to the lower estimate. 20,22,56 Thus, it is reasonable to classify the interaction between the [HAN] 3− anions as a covalent bond.…”