Thermally Activated Paramagnets from Diamagnetic Polymers of Biphenyl-3,5-diyl Bis(tert-butyl Nitroxides) Carrying Methyl and Fluoro Groups at the 2’- and 5’-Positions

Abstract

Three new biradicals-2',5'-dimethyl-, 2'-fluoro-5'-methyl-, and 5'-fluoro-2'-methylbiphenyl-3,5-diyl bis(tert-butyl nitroxides)-were synthesized. The magnetic susceptibility measurements revealed their diamagnetism below and around room temperature. The nitroxide groups are located close to each other in an intermolecular fashion to form a weakly covalent head-to-tail (NO) 2 ring. Biradical molecules are connected on both radical sites, constructing a diamagnetic chain. The dimethyl derivative underwent a structural phase transition at 83˝C, clarified via differential scanning calorimetry and powder X-ray diffraction, and a paramagnetic solid phase with S = 1 irreversibly appeared. The other analogues exhibited a similar irreversible upsurge of the magnetic susceptibility on heating, but the transition was characterized as the melting.

Ferromagnetic 2p-2p and 4f-2p Couplings in a Macrocycle from Two Biradicals and Two Gadolinium(III) Ions

“…The ground high-spin ( S = 1) state is consistent with the spin-polarization mechanism [ 19 , 20 , 21 , 22 , 23 , 24 ]. Furthermore, the notably wide singlet-triplet gap is demonstrated, and this finding is accepted among related compounds such as BPBN [ 48 ] and many other derivatives [ 32 , 33 , 34 , 48 , 49 , 50 , 51 ]. The negative θ value is attributed to intermolecular antiferromagnetic coupling.…”

“…The solution ESR spectroscopy (9.84 GHz, toluene at room temperature) clarified g = 2.0063 with a peak-to-peak linewidth Δ B pp = 2.2 mT ( Figure 1 a). Such a broad single line is regarded as a fingerprint of the m -phenylene bisnitroxide family [ 25 , 32 , 33 , 34 ], which can be explained in terms of intramolecular dipolar coupling. The solid-solution ESR spectrum of iPr 3 BPBN in a poly(vinyl chloride) film displayed a typical fine structure together with a |Δ m S | = 2 forbidden transition at 175 mT as a half-field ( Figure 1 b).…”

“…According to the method known for the preparation of a family of BPBN radicals decorated with substituents [ 32 , 33 , 34 ], the Suzuki coupling reaction was conducted from 3,5-bis( N - tert -butylhydroxylamino)bromobenzene (0.455 g; 1.38 mmol) and 2,4,6-triisopropylphenyl boronic acid (0.384 g; 1.55 mmol) in the presence of Pd(PPh 3 ) 4 (85 mg; 0.070 mmol) and Na 2 CO 3 (0.454 mg; 4.28 mmol) in dioxane (15 mL) under a nitrogen atmosphere. After the mixture was heated at 100 °C for 1 d, the reaction was quenched with an excess amount of water.…”

Molecular S = 2 High-Spin, S = 0 Low-Spin and S = 0 ⇄ 2 Spin-Transition/-Crossover Nickel(II)-Bis(nitroxide) Coordination Compounds

“…For pursuing ground triplet bridges, one of isomeric bpy-bis(NO) ligands, 3,4 -bipyridine-6,2 -diyl bis(tert-butyl nitroxide) (34bpybis(NO)), was synthesized [176]. The spin polarization mechanism [8,115,116,[177][178][179][180] seems to hold for azaaromatic-and oligopyridine-bis(NO) systems. ent conditions.…”

“…For pursuing ground triplet bridges, one of isomeric bpy-bis(NO) ligands, 3,4′-bipyridine-6,2′-diyl bis(tert-butyl nitroxide) (34bpy-bis(NO)), was synthesized [176]. The spin polarization mechanism [8,115,116,[177][178][179][180] seems to hold for azaaromatic-and oligopyridine-bis(NO) systems. Lahti et al have exploited benzimidazole-and benzothiazole-based isolable tert-butyl nitroxide compounds, bzimNO [181] and bzthNO [182], respectively, thanks to the stabilization from the electron delocalization.…”