Origin of the Magnetic Bistability in Molecule-Based Magnets: A First-Principles Bottom-Up Study of the TTTA Crystal

Abstract

The magnetic bistability present in some molecule-based magnets is investigated theoretically at the microscopic level using the purely organic system TTTA (1,3,5-trithia-2,4,6-triazapentalenyl). The TTTA crystal is selected for being one of the best-studied molecule-based systems presenting magnetic bistability. The magnetic properties of the high- and low-temperature structures (HT and LT phases, respectively) are accurately characterized by performing a First-Principles Bottom-Up study of each phase. The changes that the magnetic exchange coupling constants (J AB) undergo when the temperature is raised (LT → HT) or lowered (HT → LT) are also fully explored in order to unravel the reasons behind the presence of these two different pathways. The triclinic LT phase is diamagnetic due to the fact that the nearly eclipsed π dimer is effectively magnetically silent and not to formation of a covalent bond between two TTTA molecules. It is also shown that bistability in TTTA results from the coexistence of the monoclinic HT and triclinic LT phases in the temperature range studied.

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.…”

The magnetic fingerprint of dithiazolyl-based molecule magnets

“…[15][16][17] First, one selects all possible magnetically relevant pairs of radicals in the crystal by analysis of the crystal packing from the X-ray resolved experimental structure. As for the DTA-based crystals, although the spin density of a DTA radical is delocalized over the atoms of the entire DTA-ring (see the ESI † Section 1), the pairs of radicals have been chosen based on the N*Á Á ÁN* distance, where N* refers to the nitrogen atom that formally holds the unpaired electron (Fig.…”

“…16 Let us now briefly describe the main features of the compounds under study. TTTA exhibits bistability at room temperature (namely, T Ck = 220 K to T Cm = 315 K).…”

Reversible Spin Pairing in Crystalline Organic Radicals

“…Computational studies by Novoa indicate that the diamagnetism associated with the LT phase can be attributed to an open-shell singlet rather than closed-shell singlet configuration. 43 The magnetism of the paramagnetic HT phase can be modelled as a one-dimensional chain (J/k = -320 K) consistent with strong antiferromagnetic interactions along the stacking direction with weaker inter-chain interactions.…”