Spatially inhomogeneous, stepwise phase transitions in a thiazyl diradical: a structural mismatch induced by lattice transformation

Abstract

A heterocyclic thiazyl diradical, bis(1,2,3,5-dithiadiazolyl)-4,4 0 -biphenylene (1), was synthesized, and its structural and thermodynamic properties were characterized. This compound exhibits unique spatially inhomogeneous, first-order phase transitions at 306 and 359 K, in a stepwise fashion. The unit cell in the high-temperature phase above 359 K consists of four regular p-stacking columns with the same stacking manners having a uniform interplanar distance d. These four columns are connected by intermolecular SÁ Á ÁS and SÁ Á ÁN contacts between the thiazyl radical moieties, but the molecular planes are shifted by a distance of d/4 due to a steric hindrance between the bulky biphenylene moieties. Below 359 K, three of the four stacking columns exhibit structural transitions toward zigzag chain structures, formed by an alternating dimerization between the radical moieties, while one column maintains the uniform p stacking.In the low-temperature phase below 306 K, the last column finally exhibits the radical dimerization toward a zigzag chain structure. These unique phase transitions in 1 can be understood in terms of the stepwise transitions from a ''dimer liquid'' to a ''dimer solid'' through a ''dimer soliton phase''.Scheme 1 The dimerization patterns: (a) monoradical, (b) diradical with a central bulky group and two terminal radical moieties.

Structural, Magnetic, and Optical Studies of the Polymorphic 9′-Anthracenyl Dithiadiazolyl Radical

“…56,63 Such reversible phase transitions between different polymorphs in DTDA chemistry are extremely rare. 57,59,60,64 The observation of two single-crystal-to-single-crystal transitions between paramagnetic phases associated with 3β ↔3γ ↔ 3δ is almost unprecedented in DTDA chemistry. The successive breakdown in pancake bonding interactions in Preuss' Ln(hfac)3(boaDTDA)2 complex, perhaps provides the closest comparison (also two transitions) but a much more pronounced change in magnetic response since the latter is based around cleavage of the enthalpically favorable π * −π * pancake bond, switching from an S = 0 state to two S = ½ spins.…”

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

“…However,i nh ysteretic spin-switch systems, the LT !HT transition takes place at ad ifferent temperature than that of the HT!LT transition. [23,24] Among the group of bistable DTAr adicals, the case of 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA) is especially remarkable, since its bistability region spans 70 degrees and encompassesr oom temperature (T c› = 310 K, T cfl = 230 K) [7,[25][26][27][28][29][30][31][32][33][34][35] (Figure 1a). Bistable materials based on transition-metal complexes have been associated with spin transitions for many years [3][4][5] ,b ut recent work has demonstrated that purely-organic radicals can also be versatile building blocks to achievebistability.…”

“…Among the purely organic radicals exhibiting spin‐switch behavior, the family of dithiazolyl (DTA) neutral radicals is particularly interesting, as it has furnished numerous switchable materials, some of them presenting hysteretic phase transitions, and some of them presenting non‐hysteretic phase transitions . It is worth mentioning that the closely related family of dithiadiazolyl radicals has most recently furnished two examples of non‐hysteretic spin transition compounds . Among the group of bistable DTA radicals, the case of 1,3,5‐trithia‐2,4,6‐triazapentalenyl (TTTA) is especially remarkable, since its bistability region spans 70 degrees and encompasses room temperature ( T c↑ =310 K, T c↓ =230 K) (Figure a).…”

A simple graphical method to pinpoint local pseudosymmetries inZ′ > 1 cases

“…In fact, this plausibility criterion applies to all the suspected ill-refined structures analyzed in this work and deposited as files SM3a to SM3h in the supporting information, viz. (3a) CSD refcode ADUVEA (Usuda et al, 2002), (3b) BEYVEH01 (Akkurt et al, 2007), (3c) CUNBET (Popsavin et al, 2009), (3d) LOPLEJ (Long et al, 2014), (3e) CUQCAU02 (Suizu et al, 2015), (3f) SAGDUA (Yamada et al, 2004), (3g) AHEDAU (Naik et al, 2015) and (3h) MEWMUY (Praveen et al, 2013).…”