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2017-03-01

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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/154513

Bistability in organic magnetic materials: a comparative study of the key differences between hysteretic and non-hysteretic spin transitions in dithiazolyl radicals

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https://doi.org/10.1002/chem.201700021

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Dithiazolyl (DTA)- based radicals have furnished many examples of organic spin- transition materials, some of them occurring with hysteresis and some others without. Herein, we present a combined computational and experimental study aimed at deciphering the factors controlling the existence or absence of hysteresis by comparing the phase transitions of 4- cyanobenzo- 1,3,2- dithiazolyl and 1,3,5trithia- 2,4,6- triazapentalenyl radicals, which are prototypical examples of non- bistable and bistable spin transitions, respectively. Both materials present low- temperature diamagnetic and high- temperature paramagnetic structures, characterized by dimerized (center dot center dot center dot A-A center dot center dot center dot A-A center dot center dot center dot) n and regular (center dot center dot center dot A center dot center dot center dot A center dot center dot center dot A center dot center dot center dot A center dot center dot center dot) n pi- stacks of radicals, respectively. We show that the regular pi-stacks are not potential energy minima but average structures arising from a dynamic inter-conversion between two degenerate dimerized configurations: (center dot center dot center dot A-A center dot center dot center dot A-A center dot center dot center dot)n <->(-A center dot center dot center dot A-A center dot center dot center dot A-)n. The emergence of this intrastack dynamics upon heating gives rise to a second-order phase transition that is responsible for the change in the dominant magnetic interactions of the system. This suggests that the promotion of a (center dot center dot center dot A-A center dot center dot center dot A-A center dot center dot center dot)n <->(-A center dot center dot center dot A-A center dot center dot center dot A-) n dynamics is a general mechanism for triggering spin transitions in DTA-based materials. Yet, this intra-stack dynamics does not suffice to generate bistability, which also requires a rearrangement of the intermolecular bonds between the pstacks via a first-order phase transition.

Matèries

Transformacions de fase (Física estadística), Radicals (Química)

Matèries (anglès)

Phase transformations (Statistical physics), Radicals (Chemistry)

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Articles publicats en revistes (Ciència dels Materials i Química Física)

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VELA LLAUSÍ, Sergi, et al. Bistability in organic magnetic materials: a comparative study of the key differences between hysteretic and non-hysteretic spin transitions in dithiazolyl radicals. Chemistry-A European Journal. 2017. Vol. 23, num. 14, pags. 3479-3489. ISSN 0947-6539. [consulted: 3 of August of 2026]. Available at: https://hdl.handle.net/2445/154513

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