title: Photomagnetic properties of iron(II) spin crossover complexes of 2,6-dipyrazolylpyridine and 2,6-dipyrazolylpyrazine ligands.
abstract: The photomagnetic properties of the following iron(II) complexes have been investigated: [Fe(L1)2][BF4]2, [Fe(L2)2][BF4]2, [Fe(L2)2][ClO4]2, [Fe(L3)2][BF4]2, [Fe(L3)2][ClO4]2 and [Fe(L4)2][ClO4]2 (L1 = 2,6-di{pyrazol-1-yl}pyridine; L2 = 2,6-di{pyrazol-1-yl}pyrazine; L3 = 2,6-di{pyrazol-1-yl}-4-{hydroxymethyl}pyridine; and L4 = 2,6-di{4-methylpyrazol-1-yl}pyridine). Compounds display a complete thermal spin transition centred between 200-300 K, and undergo the light-induced excited spin state trapping (LIESST) effect at low temperatures. The T(LIESST) relaxation temperature of the photoinduced high-spin state for each compound has been determined. The presence of sigmoidal kinetics in the HS --> LS relaxation process, and the observation of LITH hysteresis loops under constant irradiation, demonstrate the cooperative nature of the spin transitions undergone by these materials. All the compounds in this study follow a previously proposed linear relation between T(LIESST) and their thermal spin-transition temperatures T(1/2): T(LIESST) = T(0)- 0.3T(1/2). T(0) for these compounds is identical to that found previously for another family of iron(II) complexes of a related tridentate ligand, the first time such a comparison has been made. Crystallographic characterisation of the high- and low-spin forms, the light-induced high-spin state, and the low-spin complex [Fe(L4)2][BF4]2, are described.
authors.affiliation: Institut de Chimie de la Matière Condensée de Bordeaux, UPR CNRS 9048-Université de Bordeaux 1, Groupe des Sciences Moléculaires, 87 Av. Doc. A. Schweitzer, F-33608, Pessac, France.
authors.forename: Chiara
authors.initials: C
authors.lastname: Carbonera
authors.forename: José
authors.initials: J
authors.lastname: Sánchez Costa
authors.forename: Victoria A
authors.initials: VA
authors.lastname: Money
authors.forename: Jérôme
authors.initials: J
authors.lastname: Elhaïk
authors.forename: Judith A K
authors.initials: JA
authors.lastname: Howard
authors.forename: Malcolm A
authors.initials: MA
authors.lastname: Halcrow
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Létard