Octacyanidorhenate(V) Ion as an Efficient Linker for Hysteretic Two‐Step Iron(II) Spin Crossover Switchable by Temperature, Light, and Pressure

Abstract

A two‐step hysteretic FeII spin crossover (SCO) effect was achieved in programmed layered Cs{[Fe(3‐CNpy)2][Re(CN)8]}⋅H2O (1) (3‐CNpy=3‐cyanopyridine) assembly consisting of cyanido‐bridged FeII‐ReV square grid sheets bonded by Cs+ ions. The presence of two non‐equivalent FeII sites and the conjunction of 2D bimetallic coordination network with non‐covalent interlayer interactions involving Cs+, [ReV(CN)8]3− ions, and 3‐CNpy ligands, leads to the occurrence of two steps of thermal SCO with strong cooperativity giving a double thermal hysteresis loop. The resulting spin‐transition phenomenon could be tuned by an external pressure giving the room‐temperature range of SCO, as well as by visible‐light irradiation, inducing an efficient recovery of the high‐spin FeII state at low temperatures. We prove that octacyanidorhenate(V) ion is an outstanding metalloligand for induction of a cooperative multistep, multiswitchable FeII SCO effect.

Reverse Hofmann-Type Spin-Crossover Compound Showing a Multichannel Controllable Color Change in an Ambient Environment

“…59 Moreover, variation of the chemical pressure in response to adsorption− desorption of the solvent guests should also contribute to the spin transition of crystals. 11,12,60,61 Hence, the compound manifests the unusual two-step solvatochromism.…”

Guest-Induced Pore Breathing Controls Spin State in a Cyanido-Bridged Framework

“…On the one side, 1•4H2O shows a 48 K wide hysteresis loop, unprecedented among octacyanidometallate-based SCO frameworks. [25][26][27][28][29][30][31][32][33][34]54 This points to very high cooperativity of the system, but is accompanied by a relatively gradual χT change in the 60-140 K range in both the cooling and heating process. Interestingly, increasing the temperature sweep rate does not lead to a significant change in the width of the hysteresis loop (Figure S10), yet it decreases the total amount of iron(II) centers that undergo the SCO phenomenon.…”

“…The observed Fe-N bond lengths at 200 K are 2.080(2) Å for Fe-NC and 2.243(2) or 2.258(2) Å for Fe-Npyridine, in line with expectations for iron(II) in a high-spin (HS) state. [25][26][27][28][29][30][31][32][33][34] Octacyanidotungstate(IV) forms four cyanide bridges with iron(II), leaving four terminal cyanides engaged in hydrogen bonding with water molecules with a CN … O distance of 2.867(5) Å (Table S2). Crystallization water molecules do not leave empty spaces in the framework (no void spaces were detected for 1.3 Å probe radius, 35 while the kinetic diameter of water is estimated to be 2.65 Å).…”

“…The sudden decrease of the bond length in the 140-80 K temperature range is in line with the transition temperature determined from magnetic and Mössbauer measurements, and the variation of the bond length is consistent with observations for other SCO frameworks featuring [Fe II (py)4(μ-NC)2] moieties. [25][26][27][28][29][30][31][32][33] As the observed contraction of bond lengths falls in the typical range for similar assemblies, this raises the question about the source of unusually small ΔHHL. This could be explained by stabilization of the HS state or destabilization of the LS state.…”

Isomorphism between the electro-elastic modeling of the spin transition and Ising-like model with competing interactions: Elastic generation of self-organized spin states

“…Under the effect of external perturbations, such as a variation of temperature [25][26][27][28][29][30] , pressure [31][32][33][34][35][36] , light irradiation [36][37][38][39][40][41][42][43] , electric or magnetic field [44][45][46][47][48][49][50] , or chemical composition 36,[51][52][53] etc, the SCO solids may switch reversibly between HS and LS configurations leading to first-order or continuous (gradual)…”