Polymorphism in a π-Stacked 1,3,2-Dithiazolyl Radical: Pyridyl-1,3,2-Dithiazolyl

Alberola, Antonio; Clements, Owen P.; Collis, Rebecca J.; Cubbitt, Louisa; Grant, Craig M.; Less, Robert J.; Oakley, Richard T.; Rawson, Jeremy M.; Reed, Robert W.; Robertson, Craig M.

doi:10.1021/cg7010056

Cited by 40 publications

(20 citation statements)

References 24 publications

(32 reference statements)

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“…the quinoxaline-1,3,2-dithiazolyl radical [38] and the a polymorph of the pyridyl-1,3,2-dithiazolyl radical [39] ). PED) suggests that the PED processi sac ommon feature in the DTAf amily of radicals.…”

Section: Resultsmentioning

confidence: 99%

Bistability in Organic Magnetic Materials: A Comparative Study of the Key Differences between Hysteretic and Non‐hysteretic Spin Transitions in Dithiazolyl Radicals

Vela

Reardon

Jakobsche

et al. 2017

Chemistry A European J

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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 1,3,5-trithia-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 (⋅⋅⋅A-A⋅⋅⋅A-A⋅⋅⋅) and regular (⋅⋅⋅A⋅⋅⋅A⋅⋅⋅A⋅⋅⋅A⋅⋅⋅) π-stacks of radicals, respectively. We show that the regular π-stacks are not potential energy minima but average structures arising from a dynamic inter-conversion between two degenerate dimerized configurations: (⋅⋅⋅A-A⋅⋅⋅A-A⋅⋅⋅) ↔(-A⋅⋅⋅A-A⋅⋅⋅A-) . The emergence of this intra-stack 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 (⋅⋅⋅A-A⋅⋅⋅A-A⋅⋅⋅) ↔(-A⋅⋅⋅A-A⋅⋅⋅A-) 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 π-stacks via a first-order phase transition.

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Section: Resultsmentioning

confidence: 99%

Bistability in Organic Magnetic Materials: A Comparative Study of the Key Differences between Hysteretic and Non‐hysteretic Spin Transitions in Dithiazolyl Radicals

Vela

Reardon

Jakobsche

et al. 2017

Chemistry A European J

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“…[28][29][30][31][32][33][34][35][36] Several other DTA derivatives exhibit spin-Peierls like behaviour. 37,38 Amongst these spin-transition dithiazolyls, TTTA has been most comprehensively studied and is presented as a case study in the next section.…”

Section: Spin-transition Radical Dimersmentioning

confidence: 99%

“…Whilst neutral organic molecules tend to favour herringbone motifs, 46 the inclusion of electronegative atoms in the molecular backbone of DTAs appears to favour the layer-like motifs desirable for spin-transition properties. [31][32][33][34][35] …”

Section: Summary and Future Perspectivesmentioning

confidence: 99%

Reversible Spin Pairing in Crystalline Organic Radicals

Rawson

Hayward

2013

Spin‐Crossover Materials

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The concept of high spin and low spin configurations in d-block complexes is taught in every undergraduate introduction to the coordination chemistry of the transition metals. In this situation the interplay between interelectron repulsion or 'pairing energy' (P E ) and crystal (ligand) field splitting ( ) determines the electronic structure and provides an elegant example of how chemical tuning and modification of the ligand donor set can manipulate electronic structure. When is of a similar magnitude to P E then there is a fine balance between crystal field stabilisation energy (an enthalpic term which favours the low spin configuration) and maximising the number of microstates (an entropic term which favours the high spin configuration). In these cases spin-transitions typically occur between a low temperature enthalpically stabilised low spin configuration and a high temperature entropically favoured high spin configuration. The ability to drive spin-transitions thermally, through light-irradiation or pressure-induced transitions are the focus of the rest of this book. In this chapter we consider organic 'spin-transition' materials whose electronic structures can be manipulated in a conceptually similar but substantially different chemical fashion, that is by examining the fine interplay between inter-electron repulsion (P E ) and promotion energy to a low-lying vacant orbital ( ) within the context of organic chemistry.In order to understand the behaviour of such systems we shall begin with a discussion (Section 8.2) of stable free-radicals and their tendency to associate to form dimers, focusing on computational and experimental studies of the electronic structures of these dimers in the gas phase and in solution. In Section 8.3 we extend these discussions to the solid state and investigate examples in which we observe (i) thermal population of electronic excited states leading to a gradual thermal evolution of paramagnetism upon warming and (ii) firstorder solid state phase transitions in which bond cleavage can lead to abrupt diamagnetic-paramagnetic phase Spin-Crossover Materials: Properties and Applications, First Edition. Edited by Malcolm A. Halcrow.

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“…Two types of dimer structures have been found. The two structurally characterized monocyclic derivatives (63, R/R = CN 158 or CF 3 166 ) both adopt a cofacial arrangement (Figure 9.13a), as does pyridyl-fused radical 70 161 (Figure 9.13b) and the radical cation of 80. 167 There is substantial variation in the structural specifics of the dimers: the interplanar separation in the 4,5-dicyano derivative is 3.14Å but substantially longer in 80 + (which exists as two different polymorphs, with average S-S distances of 3.35 and 3.26Å).…”

Section: 32-dithiazolyl Radicalsmentioning

confidence: 99%

“…13 X-ray structures of 1,3,2-dithiazolyl radical dimers: (a) 4,5-bis(trifluoromethyl) derivative,166 (b) 70,161 and (c) 69 165. …”

mentioning

confidence: 99%

The Synthesis and Characterization of Stable Radicals Containing the Thiazyl (SN) Fragment and Their Use as Building Blocks for Advanced Functional Materials

Hicks

2010

Stable Radicals

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Polymorphism in a π-Stacked 1,3,2-Dithiazolyl Radical: Pyridyl-1,3,2-Dithiazolyl

Cited by 40 publications

References 24 publications

Bistability in Organic Magnetic Materials: A Comparative Study of the Key Differences between Hysteretic and Non‐hysteretic Spin Transitions in Dithiazolyl Radicals

Bistability in Organic Magnetic Materials: A Comparative Study of the Key Differences between Hysteretic and Non‐hysteretic Spin Transitions in Dithiazolyl Radicals

Reversible Spin Pairing in Crystalline Organic Radicals

The Synthesis and Characterization of Stable Radicals Containing the Thiazyl (SN) Fragment and Their Use as Building Blocks for Advanced Functional Materials

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