The Highly Conducting Spin-Crossover Compound Combining Fe(III) Cation Complex with TCNQ in a Fractional Reduction State. Synthesis, Structure, Electric and Magnetic Properties

Yuri Shvachko,Aleksander Korolyov,Vladimir Zverev,Alexander Kotov,Denis Starichenko,Lev Buravov,Leokadiya Zorina,Eduard Yagubskii,Sergey Simonov

doi:10.3390/magnetochemistry3010009

Abstract

Three systems [Fe(III)(sal2-trien)](TCNQ)n·X (n = 1, 2, X = MeOH, CH3CN, H2O) showing spin-crossover transition, conductivity and ferromagnetic coupling were synthesized and studied by X-ray diffraction, Montgomery method for resistivity, SQUID magnetometry and X-band EPR. Spin-spin interactions between local magnetic moments of Fe(III) ions and electron spins of organic TCNQ network were discovered and discussed within the framework of intermolecular superexchange coupling.

Highlights

The synthesis and investigation of multifunctional molecule materials combining conductivity and magnetism in the same crystal lattice attract considerable attention, because the interplay of these properties may lead to novel behavior [1,2,3,4,5,6]
Conductivity is associated with mobile electrons in organic layers, whereas magnetism usually originates from localized spins of transition metal ions in insulating counterion layers
The trend is associated with the use of the octahedral cation complexes of Fe(II), Fe(III) and Co(II), showing reversible spin-crossover (SCO) between high-spin (HS) and low-spin (LS) states of the metal ion, in combination with the radical anion conducting subsystems [16,17]

Summary

Introduction

The synthesis and investigation of multifunctional molecule materials combining conductivity and magnetism in the same crystal lattice attract considerable attention, because the interplay of these properties may lead to novel behavior [1,2,3,4,5,6]. Research in this direction has been focused on the family of the quasi-two-dimensional (super)conductors based on the radical cation salts of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) and its derivatives with paramagnetic metal complex anions of different nature [2,3,4,5,6] In such materials, conductivity is associated with mobile electrons in organic layers, whereas magnetism usually originates from localized spins of transition metal ions in insulating counterion layers. The trend is associated with the use of the octahedral cation complexes of Fe(II), Fe(III) and Co(II), showing reversible spin-crossover (SCO) between high-spin (HS) and low-spin (LS) states of the metal ion, in combination with the radical anion conducting subsystems [16,17] The latter could be represented by the systems based on [M(dmit)2]δ− complexes (M = Ni, Pd, Pt; dmit = 4,5-dithiolato-1,3-dithiole-2-thione; 0 < δ < 1) [18] and/or 7,7,8,8,-tetracyanoquinodimethane ((TCNQ)δ−, 0 < δ < 1) [19,20,21,22,23]. Four spin-crossover compounds, combining Fe(II) and Co(II) cation complexes with TCNQδ− anions, have been obtained [32,33,40] and showed the conductivity in the range of 10−2–10−1 Ω−1·cm−1

Methods

Results

Conclusion