Competing phases involving spin-state and ligand structural orderings in a multistable two-dimensional spin crossover coordination polymer
Résumé
Competition between spin-crossover (SCO) and structural ligand ordering is identified as responsible for multi-stability and generation of six different phases in a rigid two-dimensional (2D) coordination polymer formulated {FeII[HgII(SCN)3][μ-(4,4’-bipy)]2} (1) (4,4’-bipy = 4,4’-bipyridine). The structure of 1 consists of infinite linear [Fe(μ-4,4’-bipy)]n2n+ chains linked by in-situ formed {[HgII(SCN)3]2(μ-4,4’-bipy)}2n- anionic dimers. The thermal dependance of the high-spin fraction, γHS, features four magnetic phases defined by steps following the sequence γHS = 1 (phase 1) ↔ γHS = 1/2 (phase 2) ↔ γHS ≈ 1/3 (phase 3) ↔ γHS = 0 (phase 4). These four magnetic states are consistent with structural ordering stemming from the different commensurate or incommensurate high- and low-spin populations [HS] ↔ [HS:LS] ↔ ≈[HS:2LS] ↔ [LS1] inferred from single crystal analysis. Furthermore, two additional phases are generated at low temperature. One, LS2 (γHS = 0, phase 5), is due to spontaneous symmetry breaking of the LS1 state below 85 K. The other, results from irradiating the low-temperature LS2 phase at 15 K with red light to photo-generate a HS phase of low symmetry (HS*) (γHS = 1, phase 6). Detailed structural studies of the six phases unravel the pivotal role played by the internal dihedral angle of the 4,4’-bipy ligands in the microscopic mechanism responsible for multi-stability and multi-step behavior in 1.
Origine : Fichiers produits par l'(les) auteur(s)
Loading...