Bistability and Molecular Switching for Semiquinone and Catechol Complexes of Cobalt. Studies on Redox Isomerism for the Bis(pyridine) Ether Series Co(py₂X)(3,6-DBQ)₂, X = O, S, Se, and Te

Abstract

Intramolecular electron transfer between CoII(SQ) and CoIII(Cat) species has been investigated for the series of complexes Co(py2X)(3,6-DBQ)2, where 3,6-DBQ are semiquinonate and catecholate forms of 3,6-di-tert-butyl-1,2-benzoquinone and py2X is bis(pyridine) ether and its heteroatomic analogs with X = S, Se, and Te. Transition temperature for Co(III)/Co(II) redox isomerism decreases in steps of approximately 30 K in toluene solution and in steps of 80 K in the solid state for the complexes with X = S, Se, Te. This appears to be primarily associated with an entropy increase that results from low-energy shifts in vibrational modes with increasing heteroatomic mass. Complexes containing py2O have been isolated at room temperature in two charge distributions, CoII(py2O)(3,6-DBSQ)2 and CoIII(py2O)(3,6-DBSQ)(3,6-DBCat). Crystallographic characterization on both forms of the complex [CoII(py2O)(3,6-DBSQ)2, monoclinic, P21/c, a = 11.0280(2) Å, b = 30.2750(9) Å, c = 12.1120(2) Å, β = 113.490(2)°, V = 3708.7(1) Å3, Z = 4, R = 0.056; CoIII(py2O)(3,6-DBSQ)(3,6-DBCat), monoclinic, P21/n, a = 9.882(3) Å, b = 20.915(5) Å, c = 17.579(4) Å, β = 91.57(2)°, V = 3632(2) Å3, Z = 4, R = 0.054] has shown that the py2O ligand adopts a planar structure for the Co(II) isomer that shifts to a folded, nonplanar structure with the smaller Co(III) ion. This structural change is responsible for hysteresis in the Co(III) → Co(II) and Co(II) → Co(III) electron transfer steps in the solid state. Optically induced shifts in charge distribution have been investigated using a low-energy polychromatic light source.

A Valence Tautomeric Dinuclear Copper Tetrakisguanidine Complex

“…[2][3][4][5][6] The electronic structure is often influenced by a number of parameters, such as temperature, pressure, modifications of the coligands, the environment (solid state or solution), the solvent, and for charged complexes, even the counterions. [7][8][9][10] Most studied valence tautomeric transition-metal complexes are based on cobalt, [11] for which the change from the Co II high-spin to Co III low-spin state is associated with a relative high barrier. Initially, the studies concentrated on mononuclear complexes, but recently research on dinuclear cobalt complexes with bis(dioxolene) ligands was intensified due to their potential as materials with molecular-based switchable paramagnetic units (molecular spintronics).…”

First bistable monocobalt complex with six free nitrogen donors: 3,5-Di-tert-butylbenzoquinonatocobalt complex containing triethanolaminetriisonicotinate

“…properties such as the characteristic band near 4000 cm À1 for [Co III ] form [6], crystal bending effect [7], and huge hysteresis [8] have been observed. These phenomena are a consequence of charge localization within the molecule and the close energy separation between localized quinone and cobalt electronic levels.…”

“…The product is the first bistable monocobalt complex with six nitrogen donors. Synthetic procedure described in earlier studies has been used to prepare the complex of trans-[Co(3,5-dbq) 2 (tati) 2 ] [8]: the reaction between [Co 2 (CO) 8 ] and 3,5-dbq in the presence of tati coligand afforded the present complex in toluene at room temperature (Eq. (2)).…”

“…Electron transfer from the 3,5-dbcat to the Co III ion was accompanied by spin transition of the resulting Co II ion. The [Co III ]/[Co II ] transition gradually occurs in contrast to general similar compounds [8]. Thus, the donor effects of coligands may be used to tune transition temperature (T c ) with great sensitivity.…”

Bistable Molecular System via Intramolecular Electron Transfer: the First Cyclodimeric 1,2-Semiquinonato/Catecholatocobalt Complex Containing 1,4-Bis(dimethyl-3-pyridylsilyl)benzene

“…The cyclodimeric cobalt complex was smoothly synthesized using a potential horse-shoe type bidentate L instead of simple bidentate coligands according to the procedures described in earlier studies: 2,11,12 the reaction between [Co 2 (CO) 8 ] and 3,5-dbbq in the presence of L in diethyl ether at room temperature afforded single crystals suitable for X-ray crystallography. The product was soluble in common solvents such as toluene, benzene, tetrahydrofuran, acetone, dimethyl sulfoxide, and N,N-dimethylformamide, indicating that the product is discrete molecule rather than polymeric species.…”