Solvation effects on the valence tautomeric transition of a cobalt complex in the solid state

Abstract

A detailed investigation of a valence tautomeric (VT) transition for the new complex [Co(III)(3,5-DBCat)(3,5-DBSQ)(py)₂]/[Co(II)(3,5-DBSQ)₂(py)₂] (1) is reported, where 3,5-DBCatH₂ is 3,5-di-tert-butyl-catechol, 3,5-DBSQH is 3,5-di-tert-butyl-semiquinone and py is pyridine. Complex 1 exists as a mixture of the two valence tautomers, with the relative proportion of each depending on the external conditions. Three differently solvated forms of the complex have been synthesized and variable temperature structural and magnetic investigations of one of these, 1·0.5py, reveals that this compound undergoes a thermally-induced VT transition from the [Co(III)(3,5-DBCat)(3,5-DBSQ)(py)₂] tautomer at temperatures below 150 K to a 1 : 1 mixture of the two tautomers at temperatures above 300 K. The VT transition may also be photo-induced at 9 K, affording a similar mixture of the two tautomers. In both cases the incomplete transition is attributed to the presence of π-π stacking interactions between the pyridine molecules of solvation and one of the two crystallographically independent complex molecules, which inhibits the expansion of this molecule that would accompany a VT transition. Studies on alternatively solvated forms 1·2MeCN and 1·1.67hexane also suggest a significant dependence of the VT transition on solvation-induced packing effects and/or intermolecular interactions.

Modulation of Magnetic Properties at Room Temperature: Coordination‐Induced Valence Tautomerism in a Cobalt Dioxolene Complex

“…Since the structural features of bis( o ‐dioxolene)cobalt complexes are diagnostic of the electron distribution in the system,3 the oxidation states of o‐ dioxolene ligands and the metal center can be assigned on the basis of bond‐length analysis. The CoN (1.89(1) Å) and CoO (1.886(2) Å) bond lengths in 1 determined at 120 K resemble those in analogous ls‐[Co III (SQ)(Cat)L 2 ] complexes reported in the range 1.932–1.964 Å and 1.888–1.898 Å, respectively (L 2 : two monodentate pyridyl‐derived ligands or a bidentate ligand, see Table S6 in the Supporting Information) 15. 20, 21 In contrast, the CoN and CoO bond lengths in hs‐[Co II (SQ) 2 L 2 ] isomers are significantly longer, in the ranges of 2.118–2.161 and 2.010–2.057 Å, respectively 15.…”

“…This geometric diversity causes different orientations of ligand‐based magnetic orbitals in cis ‐[Co(dioxolene) 2 ($\widehat{NN}$ )] and trans ‐[Co(dioxolene) 2 L 2 ] species that may yield distinct electronic properties. In contrast to cis ‐[Co(dioxolene) 2 ($\widehat{NN}$ )] species, which are well investigated both in the solid state and in solution, thorough studies of VT interconversion in trans ‐[Co(dioxolene) 2 L 2 ] complexes are almost exclusively restricted to the solid state 12–15…”

Redox-promoted associative assembly of metal–organic materials

“…The structures of 12 , 13 and 14 were confirmed by comparing the PXRD patterns of the milled products to simulated patterns generated from the known crystal structures (CCDC codes: PUTFAM for isostructural 12 and 13 , and PITSIU for 14 ). 79,80 In addition to their complementary nuclearity, these complexes result from distinct 2- or 3-electron oxidations of Cu, Co and Mn, respectively. A similar 2-electron oxidation of metallic Cu is also possible by LAG with the ditopic ligand 4,4′-dipyridyl ( BIPY ), which provides the known linear coordination polymer 15 , possessing a Cu II – SQ 2 repeat unit (CCDC code DUDZOR).…”

Photoswitchable stable charge-distributed states in a new cobalt complex exhibiting photo-induced valence tautomerism

“…However, during this process, the sample lost its valence tautomeric property and, accordingly, its photo-and thermally-switchable phase transition (Fig. SI1), underlying the fact that valence tautomeric complexes are quite sensitive to their environment 36,39,40 .…”

“…Therefore, it is of crucial importance to create a large surface to volume ratio and accordingly thin samples. Solving the Co VT molecules and drying out on a thin nonmagnetic substrate may not work as these kinds of complexes can deteriorate in solution 29,39 . Quantitative light power dependent investigations can be carried out on a pellet sample owing to its well-defined shape.…”