Complete Direct and Reverse Optically Induced Valence Tautomeric Interconversion in a Cobalt–Dioxolene Complex

Abstract

A solvent tune: The crystallization solvent affects the temperature and light dependence of the valence tautomeric behaviour of a 1:1 Co–dioxolene compound, thus offering a new possibility of tuning its charge distribution (see figure). This approach paves the way for the development of molecular magnetic materials whose properties may be controlled by chemical means.

X‐ray Absorption Spectroscopy as a Probe of Photo‐ and Thermally Induced Valence Tautomeric Transition in a 1:1 Cobalt–Dioxolene Complex

“…It has recently been shown that the isotrop- Figure 1. Molecular structure of 1, derived by partial resolution of XRD data, [20] highlighting the octahedral coordination sphere of the Co ion. The presence of toluene in the lattice plays a determining role in the entropyand optically-driven intramolecular ET process.…”

“…[20] To get the appropriate mechanical stability, the microcrystalline powder sample was mixed with boron nitride in a 1:1 weight/ weight ratio and pelleted under a pressure of 1 ton.…”

“…[20] Magnetic characterization indicated that the entropydriven interconversion occurs in two steps (T c1 = 125 K, T c2 = 185 K). The toluene molecules in the lattice play a critical role because different solvates of 1 show VT interconversion at temperatures larger than 350 K. [25,31] Light-induced interconversion between the two redox isomers was obtained at cryogenic temperatures upon irradiation on the ligand-to-metal charge transfer (LMCT) band, located at 904 nm, with the highest photoinduced molar fraction for this class of molecular materials (90 %).…”

“…[8][9][10] Typical examples of such molecules are class-II mixed-valence complexes containing two different centers. [11] Among these systems, some interest has been raised by 3d metal-dioxolene complexes, which show valence tautomerism (VT, that is, redox isomerism) [12,13] as a result of an intramolecular electron-transfer (ET) process induced by external perturbations, such as changes in temperature, [14][15][16][17] pressure, [16,18] chemical environment, [14,19,20] and optical irradiation. [13,[20][21][22][23][24][25] In cobalt derivatives, this process is associated with a large variation of the magnetic properties, because the redox interconversion involves a change of the ground state of the complexes from diamagnetic low-spin (ls) cobaltA C H T U N G T R E N N U N G (III)-catecholato (ls-Co III Cat) moieties to paramagnetic high-spin (hs) cobalt(II)-semiquinonato (hs-Co II SQ) ones, thus making them particularly appealing to be investigated by using magnetic techniques.…”

Intermolecular control of thermoswitching and photoswitching phenomena in two spin-crossover polymorphs

“…7,8 It gives a nice opportunity to look into the interrelation between the physics of phase transition and that of nonlinear dynamics because these are the same cooperative interactions, that govern the stability of macroscopic states both at thermal equilibrium and out of equilibrium. The approach presented here, balancing the intra and intermolecular aspects involved during both thermal and photoconversions, can also be used in other bistable magnetic systems such as polycyanometallate derivatives, [9][10][11] valence tautomeric complexes, 12,13 ligand isomerization effects, 14 etc. The spin-state switching can occur in molecular solids 5 made of a metal ion located in a nearly octahedral ligand molecular field.…”