Dynamics and Supramolecular Organization of the 1D Spin Transition Polymeric Chain Compound [Fe(NH₂trz)₃](NO₃)₂. Muon Spin Relaxation

Abstract

The thermal spin transition that occurs in the polymeric chain compound [Fe(NH(2)trz)3](NO3)2 above room temperature has been investigated by zero-field muon spin relaxation (microSR) over the temperature range approximately 8-402 K. The depolarization curves are best described by a Lorentzian and a Gaussian line that represent fast and slow components, respectively. The spin transition is associated with a hysteresis loop of width DeltaT = 34 K (T1/2 upward arrow = 346 K and T1/2 downward arrow = 312 K) that has been delineated by the temperature variation of the initial asymmetry parameter, in good agreement with previously published magnetic measurements. Zero-field and applied field (20-2000 Oe) microSR measurements show the presence of diamagnetic muon species and paramagnetic muonium radical species (A = 753 +/- 77 MHz) over the entire temperature range. Fast dynamics have been revealed in the high-spin state of [Fe(NH(2)trz)3](NO3)2 with the presence of a Gaussian relaxation mode that is mostly due to the dipolar interaction with static nuclear moments. This situation, where the muonium radicals are totally decoupled and not able to sense paramagnetic fluctuations, implies that the high-spin dynamics fall outside the muon time scale. Insights to the origin of the cooperative effects associated with the spin transition of [Fe(NH(2)trz)3](NO3)2 through muon implantation are presented.

Rapid Cooling Experiments and Use of an Anionic Nuclear Probe to Sense the Spin Transition of the 1D Coordination Polymers [Fe(NH2trz)3]SnF6⋅n H2O (NH2trz=4‐amino‐1,2,4‐triazole)

“…Ce comportement inhabituel au chauffage pour les Øchantillons piØgØs a ØtØ attribuØ à lactivation thermique du mouvement molØculaire des anions; dune forme gelØe distordue vers une forme rØgulire à des tempØra-tures bien au-delà de % 210 K. Les applications potentielles de cette nouvelle famille de matØriaux sont discutØes. [ 44] www.chemeurj.org 3 ]SnF 6 ·0.5 H 2 O (2) and its degree of hydration was confirmed by TGA measurements (Figure 2). The reproducibility of this preparation method under the very same conditions was checked twice.…”

Spin state switching in iron coordination compounds

“…The possibility of investigating spin fluctuation rates was established with the classical iron(II) complex [Fe(phen) 2 (NCS) 2 ], polymorph I [135–136]. In another case, fast dynamics have been revealed in the HS regime of the ST coordination polymer [Fe(NH 2 trz) 3 ](NO 3 ) 2 (NH 2 trz = 4-amino-1,2,4-triazole) [138–139]. …”

“…25), solvent and ligand substitution in the crystal lattice [159,268,288]. In a few cases, the hysteresis width could be increased up to ~35–50 K, when noncoordinated anions were connected to 1D chains by hydrogen bonds [139,180,289–293]. Consequently, abrupt spin transitions with broad thermal hysteresis loops along with a color change from pink/purple (LS) to white (HS) have been observed (Fig.…”

Influence of Hydrogen Bonding on the Hysteresis Width in Iron(II) Spin‐Crossover Complexes

“…[11] Such observations are not limited to monomeric complexes. For the 1D chain material [Fe(NH 2 trz) 3 ](NO 3 ) 2 , the 33 K wide thermal hysteresis loop is associated with a network of hydrogen bonds, [22,33] and for the very similar [Fe(Htrz) 2 (trz)](BF 4 ), an extended network of hydrogen bonds had been singled out to be the origin of the 40 K large hysteresis above room temperature. [4,34] A detail X-ray structure analysis on the 2D network of [Fe(btr) 2 (NCS) 2 ]·H 2 O reveals that the HSǞLS transition reduces the O-H···N contacts between the water molecules and the free N atoms of the triazole ligand.…”