Two-Step Spin Crossover in a Mononuclear Compound [Fe(DPEA)(bim)](ClO4)2·0.5 H2O[DPEA = (2-Aminoethyl)bis(2-pyridylmethyl)amine, bim = 2,2-Bisimidazole] − Crystal Structure, Magnetic Properties, Mössbauer Spectroscopy, and Photomagnetic Effects

Abstract

Keywords: Iron / N ligands / Spin crossover / Mössbauer spectroscopy / PhotomagnetismThe synthesis and characterization of the new spin crossover mononuclear complex [Fe II (DPEA)(bim)](ClO 4 ) 2 ·0.5 H 2 O, where DPEA = (2-aminoethyl)bis(2-pyridylmethyl)amine and bim = 2,2-bisimidazole, are reported. Variable-temperature magnetic susceptibility measurements (77−295 K) reveal the occurrence of a two-step spin transition. Two steps on the magnetic curve are separated by an inflection point at 200 K, corresponding to about 50% of the complexes that have undergone a thermal spin transition. The first step is centered at 171 K and the second one at 218 K. Mössbauer spectroscopy and X-ray analysis show that the profile of the magnetic curve is a consequence of the presence of two inequivalent iron(II) molecules in the crystal lattice. The crystal structure was resolved at 293 K (high-spin form) and at 123 K (low-spin form). Both spin-state isomers belong to the mono-

Anomalous Spin Transition Observed in Bis(2,6‐bis(pyrazol‐3‐yl)pyridine)iron(II) Thiocyanate Dihydrate

“…[17,18] A two-step transition may also arise in mononuclear compounds when there are two distinct lattice sites for the spin-transition centers. [19,20] However, to the best of our knowledge, there is no mononuclear compound that exhibits a two-step spin transition associated with two broad hysteresis loops, as observed in the present compound. The chemical analysis and room temperature crystal structure revealed the existence of two solvate water molecules in the fresh sample.…”

Multimetastability, phototrapping, and thermal trapping of a metastable commensurate superstructure in a FeIIspin-crossover compound

“…72 Two-step relaxation following LIESST is very uncommon in SCO materials. It has been reported for just a few systems, 16,17,36,38,39,43 but it has never been characterized and successfully interpreted on the basis of the underlying evolution of the crystal structure. The most trivial situation is that of several crystallographic Fe I I sites in the metastable HS state, in which case the several steps of the relaxation are associated with the successive, and not concomitant, relaxation of the different sites owing to different lifetime of the metastable HS molecular species.…”

“…10 Although the vast majority of thermal spin transitions proceed in a single step, there has been an increasing number of two-step transitions reported for polymeric, [11][12][13][14][15][16][17] polynuclear, [18][19][20][21][22][23][24] or mononuclear SCO systems. [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] Such transitions result most frequently from the existence of two crystallographically (symmetrically) independent SCO Fe I I sites with slightly different coordination environments, leading to dissimilar transition temperatures delimiting a plateau (or shoulder), which usually occurs with an approximately equal populations of HS and LS species. Alternatively, the subtle interplay between short-range correlations and long-range interactions may be such that intermediate phases with remarkable structural topologies, characterized by well-ordered patterns of HS and LS Fe I I molecular species, may be stabilized in a more or less wide temperature range, providing a two-step character.…”

“…10,31,37,42 The corresponding isothermal relaxation curves, defined as the evolution of γ H S as a function of time in isothermal condition, exhibit single-exponential behaviors, with sometimes stretched elongated tails resulting from shortrange correlations. 10,42 In rare cases, a stepped LIESST relaxation 16,36,38,39,43 or stepped isothermal relaxation curves 17 have been reported and attributed to the successive relaxation of different Fe I I sites, although no crystallographic evidence has been provided. On the contrary, the possible stabilization of a long-range-ordered intermediate superstructure, resulting from a symmetry breaking scenario in the photoexcitation or relaxation regime, has never been reported.…”

Calorimetric Investigation of Phase Transitions Occurring in Molecule-Based Magnets

“…Matouzenko et al 339 N(1,4,7,10) ) the Schiff base condensation of 5-nitrosalicylaldehyde with 1,4,7,10-tetraazadecane in a 2:1 ratio, changes its space group depending on the spin state. Petrouleas and Tuchagues 363 reported a well-separated two-step spin-state conversion in this complex on the basis of Mössbauer spectroscopy and magnetic susceptibility measurement.…”