Unravelling of a [High Spin—Low Spin] ↔ [Low Spin—High Spin] Equilibrium in Spin‐Crossover Iron(II) Dinuclear Helicates Using Paramagnetic NMR Spectroscopy

Abstract

Spin‐crossover between high‐spin (HS) and low‐spin (LS) states of selected transition metal ions in polynuclear and polymeric compounds is behind their use as multistep switchable materials in breakthrough electronic and spintronic devices. We report the first successful attempt to observe the dynamics of a rarely found broken‐symmetry spin state in binuclear complexes, which mixes the states [HS‐LS] and [LS‐HS] on a millisecond timescale. The slow exchange between these two states, which was identified by paramagnetic NMR spectroscopy in solutions of two spin‐crossover iron(II) binuclear helicates that are amenable to molecular design, opens a path to double quantum dot cellular automata for information storage and processing.

Spin-State Regulation of Nickel Cobalt Spinel toward Enhancing the Electron Transfer Process of Oxygen Redox Reactions in Lithium–Oxygen Batteries

“…48 Nevertheless, the recent experimental and theoretical reports underline that the combination of LS and HS states is more reasonable. 57 Under this circumstance, the spin states of NiCo 2 S 4 and Vs-NiCo 2 S 4 were estimated to be 34.7% HS + 65.3% LS and 46.3% HS + 53.7% LS (Table S1 of the Supporting Information). These results further suggest that the fraction of HS Co 3+ increases in Vs-NiCo 2 S 4 compared to that in NiCo 2 S 4 .…”

“…For octahedral-coordinated Co 3+ , there has been controversy as to whether the higher spin state of Co 3+ at room temperature is an intermediate spin (IS) state or a mixture of LS and HS states . Nevertheless, the recent experimental and theoretical reports underline that the combination of LS and HS states is more reasonable . Under this circumstance, the spin states of NiCo 2 S 4 and Vs-NiCo 2 S 4 were estimated to be 34.7% HS + 65.3% LS and 46.3% HS + 53.7% LS (Table S1 of the Supporting Information).…”

Unique Spin Crossover Pathways Differentiated by Scan Rate in a New Dinuclear Fe(II) Triple Helicate: Mechanistic Deductions Enabled by Synchrotron Radiation Studies

“…Several distinct dinuclear triple helicates have been shown to exhibit spin switching, with different structures from those conjoining metal cations via ligand bridging. 14 Up to the present, the observation of two equivalent [HS-LS]/[LS-HS] species in equilibrium has been only reported for the solution state, 19 with no examples of [HS-LS] ↔ [LS-HS] equilibrium being reported for the solid state. Control of [HS-LS] ↔ [LS-HS] equilibria is desirable, as it may allow the generation of class II quantum cellular automata for signal and logic processes.…”

“…This may potentially stabilize, or destabilize the HS state, which can result in either abrupt SCO or gradual SCO for which there is little to no cooperativity, or in severe cases, trapping of the [HS-LS]/[LS-HS] at low temperature without the [LS-LS] state being formed. Such a structural rearrangement with SCO has been associated with crystallographic symmetry breaking in several studies, 7,[15][16][17][18][19] wherein structural rearrangement during SCO is severe enough to result in a change in the crystallographic phase of the material. The appearance of a phase change is, currently, fairly unpredictable.…”

Site Selectivity for the Spin States and Spin Crossover in Undecanuclear Heterometallic Cyanido-Bridged Clusters

“…One of the challenges in the field of molecular magnetism is the design of molecular spin-crossover (SCO) clusters with bistability controlled by external stimuli such as temperature, pressure, light irradiation, electric field, or guest inclusion and exchange. − Moreover, specific arrangement of high-spin (HS) and low-spin (LS) sites in one cluster may provide more than two stable phases, being beneficial for site-selective switching and multistability, the property that provides a potential toward applications in nanotechnological devices such as memory storage units, quantum cellular automata, and molecular binary logic devices. , Aiming at this goal, a number of SCO clusters of various nuclearities were prepared by combining the SCO-active ions with diverse bridging ligands that might cooperate in the fine-tuning of steric and electronic strain, e.g., multidentate organic ligands, − metalloligands, − cyanides, , and cyanidometallates. − Multistability and site-selective switching under thermal stimulation or photostimulation have been revealed in some dinuclear, square-like, − grid-like, − or metallocubane complexes as well as in the largest icosanuclear [Fe 20 ] SCO clusters …”