Manipulating Slow Magnetic Relaxation by Light in a Charge Transfer {Fe₂Co} Complex

Abstract

Some cyanide‐bridged complexes are known for exhibiting slow magnetic relaxation behavior in a light‐induced metastable state. Herein, an unexpected reverse effect is observed for the first time in the S=1/2 {FeIILS‐CoIIILS‐FeIIILS} (HS=high spin, LS=low spin) ground state of a novel V‐shaped trinuclear cyanide‐bridged {Fe2Co} complex. In this complex, light‐switchable iron‐cobalt charge transfer with repeatable off/on switching of slow magnetic relaxation is discovered upon alternating laser irradiation at 785 and 560 nm. An important characteristic of the present compound is that the S=1/2 ground state exhibits slow magnetic relaxation before irradiation, whereas this is accelerated after irradiation. This is different from the typical behavior, where the light‐induced metastable state exhibits slow magnetic relaxation.

Two-Step Thermoinduced Metal-to-Metal Electron Transfer and ON/OFF Photoswitching in a Molecular [Fe2Co2] Square Complex

“…It has been started with the revolutionary example of metal-to-metal electron transfer (MMET) occurring between iron and cobalt centers via a cyanide bridge in a [FeCo] PBA, K 0.2 Co 1.4 [Fe­(CN) 6 ]·6.9H 2 O, where the low-temperature {Fe II LS ( S =0)–CN–Co III LS ( S =0)} diamagnetic ground state changes into the metastable {Fe III LS ( S = 1 / 2 )–CN–Co II HS ( S = 3 / 2 )} paramagnetic state via light irradiation at 5 K . In 2004, Dunbar et al synthesized the first-ever thermally induced MMET in a discrete cyanide-bridged [Co 3 Fe 2 ] complex, and later in 2011, the (photo)­magnetic effect of this complex was studied by Clérac and Dunbar et al After that, various molecular model complexes of [FeCo] PBAs; e.g., molecular cubes, , squares, − and dinuclear units , have been reported by different research groups, including us, which exhibit thermo- and/or photoinduced MMET. , Additionally, a few [FeCo] systems have also been investigated where the photoinduced metastable state exhibits a slow relaxation of magnetization, i.e., single molecule magnets, , while some 1D [FeCo] chains exhibit interesting single chain magnet properties in the photoinduced state. − All of these stimuli-responsive materials open a new horizon in the field of electronic device technology with their huge potential . The most challenging task down the lane is to synthesize a multiresponsive material that will exhibit bistability at ambient conditions.…”

Light actuated single-chain magnet with magnetic coercivity

“…32,46 47 Among all these reported examples, the {FeCo}-systems were mostly investigated, and seven {FeCo}-based examples showed photo-induced MMET with magnetic relaxation properties. [47][48][49][50][51][52] However, only one of them exhibited the magnetic hysteresis loop with a small coercive field of 50 Oe. 53 It is still challenging to construct photo-induced single-chain magnets with observable magnetic hysteresis.…”

Anion-Dependent Electron Transfer in the Cyanide-Bridged [Fe2Co2] Capsules

“…is an important topic associated with the emerging technologies like switches, sensors, and storage devices. − Among the well-studied systems are those mixed-valence Fe-Co cyanometallate complexes, which may exhibit thermo- and/or photo- induced electron-transfer-coupled spin transition (ETCST) between the diamagnetic {Fe II LS (μ-CN)­Co III LS } and paramagnetic {Fe III LS (μ-CN)­Co II HS } motifs (LS = low spin; HS = high spin), and the photo-responsive behavior was first reported in 1996 by Hashimoto and co-workers in a bulk Fe/Co Prussian Blue analogues (PBAs), K 0.2 Co 1.4 [Fe­(CN) 6 ]·6.9H 2 O . Since then, great efforts have been focused on the miniaturization of the three-dimensional PBAs, in order to better understand the key factors correlated with this particular behavior and ultimately satisfy the technological demand for molecule-based electronic devices like solubility, stability, and manipulability. − …”