Abstract
In this study, crystals of the hybrid layered structure, combined with Fe(III) Spin-Crossover (SCO) complexes with metal-dithiolate anionic radicals, and the precursors with nitrate and iodine counterions, are obtained and characterized. [Fe(III)(3-OMe-Sal2trien)][Ni(dmit)2] (1), [Fe(III)(3-OMe-Sal2trien)]NO3·H2O (2), [Fe(III)(3-OMe-Sal2trien)]I (3) (3-OMe-Sal2trien = hexadentate N4O2 Schiff base is the product of the condensation of triethylenetetramine with 3-methoxysalicylaldehyde; H2dmit = 2-thioxo-1,3-dithiole-4,5-dithiol). Bulk SCO transition was not achieved in the range 2.0–350 K for all three compounds. Alternatively, the hybrid system (1) exhibited irreversible segregation into the spatial fractions of Low-Spin (LS) and High-Spin (HS) phases of the ferric moiety, induced by thermal cycling. Fractioning was studied using both SQUID and EPR methods. Magnetic properties of the LS and HS phases were analyzed in the framework of cooperative interactions with anionic sublattice: Anion radical layers Ni(dmit)2 (1), and H-bonded chains with NO3 and I (2,3). LS phase of (1) exhibited unusual quasi-two-dimensional conductivity related to the Arrhenius mechanism in the anion radical layers, ρ||c = 2 × 105 Ohm·cm and ρ⊥c = 7 × 102 Ohm·cm at 293 K. Ground spin state of the insulating HS phase was distinctive by ferromagnetically coupled spin pairs of HS Fe3+, S = 5/2, and metal-dithiolate radicals, S = 1/2.
Highlights
The construction of multifunctional molecular materials, in particular switchable electronic conductors, remains one of the challenges for molecular science, and raises fundamental problems for condensed matter physics [1,2,3,4]
Integration of spin-crossover complexes with metal-bisdithiolene complexes, as redox-active building blocks, gave rise to numerous magnetoactive crystalline materials [5,6,7]
The coexistence of conductivity and SCO properties in a combined hybrid structure opens promising prospective of their mutual synergy
Summary
The construction of multifunctional molecular materials, in particular switchable electronic conductors, remains one of the challenges for molecular science, and raises fundamental problems for condensed matter physics [1,2,3,4]. The structures with [M(dmit)2 ]n− complexes in a fractional oxidation state (where (dmit) is 2-thioxo-1,3-dithiole-4,5-dithiolato, M-3d metal ion) are known as Molecules 2020, 25, 4922; doi:10.3390/molecules25214922 www.mdpi.com/journal/molecules. The cationic complexes of the [Fe(sal trien)]+ family are well known for the bi-stable configuration of the ligand shell, resulting in the low-spin (LS) or high-spin (HS) states of the Fe(III) ion (S = 1/2 and 5/2 respectively) [2,3]. Exchange interactions between delocalized spin moments of the conduction electrons and local magnetic moments of HS Fe(III) ions would facilitate ferromagnetic (FM) or antiferromagnetic (AFM) coupling in the SCO sublattice [10,11], which, in turn, may lead to a switchable spin-dependent transport in M(dmit) sublattice.
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