Fe(II) complexes with ligands of an intermediate field strength often show switching between the high-spin (HS) and low-spin (LS) electronic configurations, known as spin crossover (SCO). This spin-state conversion is achieved by changes in temperature, pressure, or photoexcitation, which make SCO complexes promising materials for various applications that rely on bistable systems. Multifunctional materials that exhibit both spin-state switching and conductivity can be created by combining Fe(II) SCO complexes with organic TCNQ-type acceptors. In such complexes, TCNQ●– radical anions are arranged in stacks that provide conducting pathways (Fig.1). The stacking distance can be affected by structural changes induced by the change in the electronic configuration at the Fe(II) center, resulting in the synergy between SCO and conductivity. The synthesis of such materials can be approached in two ways: (1) by coordinating TCNQ●– ligands directly to the Fe(II) center, which is partially protected by blocking ligands that limit the growth of extended structures or (2) by co-crystallizing completely blocked Fe(II) centers with free TCNQ●– radicals. We will discuss several examples of the second approach, in which homoleptic Fe(II) cationic SCO complexes with tridentate bis-pyrazolyl-pyridine type ligands have been co-crystallized with fractionally-charged TCNQ●– radical anions. The temperature- and light-dependent magnetic behavior and transport properties of these materials will be discussed.

Conducting Fe(II) spin crossover complexes with organic TCNQ radicals

2019 Spring National Meeting

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