Tuning of Charge Transfer Assisted Phase Transition and Slow Magnetic Relaxation Functionalities in {Fe<sub>9–<i>x</i></sub>Co<sub><i>x</i></sub>[W(CN)<sub>8</sub>]<sub>6</sub>} (<i>x</i> = 0–9) Molecular Solid Solution

  • Szymon Chorazy
    Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland
  • Jan J. Stanek
    Institute of Physics, Jagiellonian University, Łojasiewicza 11, 30-348 Kraków, Poland
  • Wojciech Nogaś
    Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland
  • Anna M. Majcher
    Institute of Physics, Jagiellonian University, Łojasiewicza 11, 30-348 Kraków, Poland
  • Michał Rams
    Institute of Physics, Jagiellonian University, Łojasiewicza 11, 30-348 Kraków, Poland
  • Marcin Kozieł
    Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland
  • Ewa Juszyńska-Gałązka
    H. Niewodniczański Insitute of Nuclear Physics PAN, Radzikowskiego 152, 31-342 Kraków, Poland
  • Koji Nakabayashi
    Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
  • Shin-ichi Ohkoshi
    Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
  • Barbara Sieklucka
    Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland
  • Robert Podgajny
    Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland

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説明

Precisely controlled stoichiometric mixtures of Co(2+) and Fe(2+) metal ions were combined with the [W(V)(CN)8](3-) metalloligand in a methanolic solution to produce a series of trimetallic cyanido-bridged {Fe(9-x)Co(x)[W(CN)8]6(MeOH)24}·12MeOH (x = 0, 1, ..., 8, 9; compounds 0, 1, ..., 8, 9) clusters. All the compounds, 0-9, are isostructural, and consist of pentadecanuclear clusters of a six-capped body-centered cube topology, capped by methanol molecules which are coordinated to 3d metal centers. Thus, they can be considered as a unique type of a cluster-based molecular solid solution in which different Co/Fe metal ratios can be introduced while preserving the coordination skeleton and the overall molecular architecture. Depending on the Co/Fe ratio, 0-9 exhibit an unprecedented tuning of magnetic functionalities which relate to charge transfer assisted phase transition effects and slow magnetic relaxation effects. The iron rich 0-5 phases exhibit thermally induced reversible structural phase transitions in the 180-220 K range with the critical temperatures being linearly dependent on the value of x. The phase transition in 0 is accompanied by (HS)Fe(II) W(V) ↔ (HS)Fe(III) W(IV) charge transfer (CT) and the additional minor contribution of a Fe-based spin crossover (SCO) effect. The Co-containing 1-5 phases reveal two simultaneous electron transfer processes which explore (HS)Fe(II) W(V) ↔ (HS)Fe(III) W(IV) CT and the more complex (HS)Co(II) W(V) ↔ (LS)Co(III) W(IV) charge transfer induced spin transition (CTIST). Detailed structural, spectroscopic, and magnetic studies help explain the specific role of both types of CN(-)-bridged moieties: the Fe-NC-W linkages activate the molecular network toward a phase transition, while the subsequent Co-W CTIST enhances structural changes and enlarges thermal hysteresis of the magnetic susceptibility. On the second side of the 0-9 series, the vanishing phase transition in the cobalt rich 6-9 phases results in the high-spin ground state, and in the occurrence of a slow magnetic relaxation process at low temperatures. The energy barrier of the magnetic relaxation gradually increases with the increasing value of x, reaching up to ΔE/kB = 22.3(3) K for compound 9.

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