Benzoic acid and phenol derivatives of nitronyl nitroxide biradical as building blocks of organic molecule-based ferrimagnets

Abstract

A crystal-engineering approach to organic ferrimagnets is reported. Coulombic energy between an anionic biradical with S = I and a cationic monoradical with S = 1/2 can be utilized as a driving force of cocrystallization of open-shell molecules with different spin quantum numbers, leading to organic salt ferrimagnets. In this study, 3,5-substituted phenol and benzoic acid derivatives of nitronyl nitroxide biradicals were synthesized as an ionizable S = 1 component of organic salt ferrimagnets. The molecular ground states of the biradicals in the neutral state were examined by continuous wave electron spin resonance (ESR) spectroscopy and static paramagnetic susceptibility measurements in the solid state. The molecular ground state of the phenol derivative was found to be triplet (S = 1) with the singlet-triplet energy gap of AE/k5 25 K, indicating that the biradical can be a building block of organic salt ferrimagnetics. The benzoic acid derivative was found to have a singlet (S = 0) ground state (4E/k5 ? -5 K), exemplifying that meta-(3,5)-linkage of unpaired electrons in it-aromatic rings does not necessarily give a triplet ground state for heteroatomic-substituted it conjugation. The molecular ground states of the biradicals determined in the ESR experiments were confirmed by the susceptibility in the solid state.

Clustering of molecular spins in the crystals of nitronylnitroxide and iminonitroxide triradicals based on benzene-1,3,5-triyl frameworks

“…The ferromagnetic interaction J p is in agreement with that of the parent phenol-substituted biradical. 12 The antiferromagnetic interactions J s1 /k B = J s2 /k B = 20.4 K in trisNN (3) observed for the film would contain a residue of intermolecular exchange interactions due to incomplete dispersion of the molecules in the film. 29 As discussed later, the amplitude of |J s |/k B = 0.4 K is the upper limit of the antiferromagnetic exchange interactions within the molecule.…”

“…The triradical trisNN (3) was synthesized by esterification of the phenol-based biradical 5 12 and the calboxylic acid monoradical 6 13,14 according to the literature procedure, 7,15 as shown in Scheme 2. A mixture of 5 (345 mg, 0.85 mmol), 6 (278 mg, 1.00 mmol) and 4-dimethylaminopyridine (92 mg, 0.76 mmol) was dissolved in dry dichloromethane (27 mL) at 0 uC under argon atmosphere.…”

Phenol-substituted nitronyl nitroxide biradicals with a triplet (S = 1) ground state

“…Chemical modifications are found to affect heterocyclic derivatives of carbene 11 and trimethylenemethane, 12 and a substituted m-phenylene bis(a-nitronyl nitroxide) biradical. 13 Molecular conformation has also been shown to affect the ground-state spin multiplicity. 14 For heteroatomic substituted m-phenylene derivatives, the preference for a triplet (S~1) ground state is not guaranteed.…”