A tetrathiafulvalene salt of the nitrite (NO2?) anion: investigations of the spin-Peierls phase?

Journal of Materials Chemistry C Pub Date: 2023-01-24 DOI: 10.1039/D2TC05431K

Abstract

Electrocrystallization of ortho-dimethyltetrathiafulvalene (o-DMTTF) in the presence of a nitrite (NO2?) anion affords a 2?:?1 phase, namely (o-DMTTF)2NO2, the first example of an isolated cation radical salt with NO2?. The o-DMTTF molecule organizes into strongly dimerized stacks that adopt a rare chessboard organization, associated with a strongly 1D structure. As a consequence of dimerization, the salt exhibits a semiconducting behavior (σRT = 5 S cm?1, Eact = 0.1 eV). The bent NO2? anion is disordered on the inversion center but does not exhibit any anion-ordering transition. Combined SQUID magnetometry and electron paramagnetic resonance (EPR) experiments demonstrate the appearance of a spin-Peierls transition with TSP = 70 K. The temperature dependence of the spin gap and associated dimerization parameter δ across the spin-Peierls transition have been determined. The low-temperature narrow EPR line observed below TSP is attributable to intrinsic magnetic defects localized on the o-DMTTF molecules themselves. The broadening of the EPR line at higher magnetic fields is associated with the disordered NO2? anions surrounding these magnetic defects, contributing to the inhomogeneity of their g factor.

Graphical abstract: A tetrathiafulvalene salt of the nitrite (NO2?) anion: investigations of the spin-Peierls phase
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