title: Temperature-dependent interactions and disorder in the spin-transition compound [Fe(II)(L)2][ClO4]2.C7H8 through structural, calorimetric, magnetic, photomagnetic, and diffuse reflectance investigations.
abstract: The title compound [Fe (II)(L) 2][ClO 4] 2.C 7H 8 (L = 2-[3-(2'-pyridyl)pyrazol-1-ylmethyl]pyridine) has been isolated while attempting to grow single crystals of the spin-transition (continuous-type) compound [Fe (II)(L) 2][ClO 4] 2, published earlier ( Dalton Trans. 2003, 3392-3397). Magnetic susceptibility measurements, as well as Mossbauer and calorimetric investigations on polycrystalline samples of [Fe(L) 2][ClO 4] 2.C 7H 8 revealed the occurrence of an abrupt HS ( (5) T 2) <--> LS ( (1) A 1) transition with steep and narrow (2 K) hysteresis at approximately 232 K. The photomagnetic properties exhibit features typical for a broad distribution of activation energies, with relaxation curves in the shape of stretched exponentials. We performed a crystal structure determination of the compound at 120, 240, and 270 K. A noteworthy temperature-dependent behavior of the structural parameters was observed, in terms of disorder of both the anions and solvent molecules, leading to a strong thermal dependence of the strength and dimensionality of the interaction network. Additional data were obtained by diffuse reflectance measurements. We model and discuss the antagonistic effects of interactions and disorder by using a two-level cooperative mean-field approach which includes a distribution of barrier energies at the microscopic scale.
authors.affiliation: GEMAC, CNRSUniversite de Versailles, 78035 Versailles cedex, France.
authors.forename: Vibha
authors.initials: V
authors.lastname: Mishra
authors.forename: Rabindranath
authors.initials: R
authors.lastname: Mukherjee
authors.forename: Jorge
authors.initials: J
authors.lastname: Linares
authors.forename: Chérif
authors.initials: C
authors.lastname: Balde
authors.forename: Cédric
authors.initials: C
authors.lastname: Desplanches
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Létard
authors.forename: Eric
authors.initials: E
authors.lastname: Collet
authors.forename: Loic
authors.initials: L
authors.lastname: Toupet
authors.forename: Miguel
authors.initials: M
authors.lastname: Castro
authors.forename: François
authors.initials: F
authors.lastname: Varret