Valence Tautomeric Transitions of Three One-Dimensional Cobalt Complexes

Abstract

Three novel complexes, namely, [Co(III)(3,5-DBCat)(3,5-DBSq)(bpe)]·2CH3CN·2H2O (1·S), [Co(III)(3,5-DBCat)(3,5-DBSq)(azpy)]·2CH3CN·2H2O (2·S), and [Co(II)(3,5-DBSq)2(bpb)][Co(III)(3,5-DBCat)(3,5-DBSq)(bpb)]0.5·2CH3CN·2H2O (3·S), were synthesized and characterized by valence tautomeric (VT) X-ray diffraction and magnetic measurements [where 3,5-DBCatH2 = 3,5-di-tert-butyl-catechol, 3,5-DBSqH = 3,5-di-tert-butyl-semiquinone, bpe = trans-bis(4-pyridyl)ethylene, azpy = trans-4,4'-azopyridine, and bpb = 1,4-bis(4-pyridyl)benzene]. The three complexes have similar one-dimensional chain structure building from bidentate-bridging pyridine ligands and planar 3,5-DBCat/3,5-DBSq-fixed Co(II/III) entities. Complexes 1·S and 2·S could retain the crystallinity during desolvation, and the crystal structures of 1 and 2 were therefore able to be determined. Only when 1·S and 2·S desolvated above 310 K did the magnetic susceptibilities × temperatures values of the two complexes rise sharply, and then thermally induced complete, one-step VT transitions for 1 and 2 were available and repeatable. Complex 3·S showed an incomplete, one-step VT transition independent of solvent molecules. Among these complexes, only 1 was sensitive to photoexcitation at low temperature, its photoinduced metastable state relaxed with temperature-independent behavior at low temperature range (5-10 K) and with thermally assisted behavior at high temperature range (above 20 K), respectively.

Valence Tautomerism in One-Dimensional Coordination Polymers

“…43 [ with other ligands. 40 An acetonitrile solution (6.7 ml) of 3,5-dbcatH (15 mg, 0.067 mmol) and 1,2-bpe (12mg, 0.067mmol) was layered over an aqueous solution (1. Structure Description.…”

“…Selected single crystal X-ray data for the compounds are reported in Table 1, structural the cis-disposition of the N-donor linking ligands, 39 while the trans disposition has been observed in all other cases. 34,37,40 In addition to partially disordered solvent molecule, the asymmetric unit consists of two independent molecules, one for the each type of chain, each containing two dioxolene ligands and one 1,3-bpp ligand, coordinated to a cobalt center. The zig-zag cis chains pass alternately above and below each of the trans chains ( Figure 3).…”

Structural investigation of one- and two-dimensional coordination polymers based on cobalt–bis(dioxolene) units and 1-hydroxy-1,2,4,5-tetrakis(pyridin-4-yl)cyclohexane

“…Most valence tautomeric (VT) CPs are based on Co-dioxolene systems, where the electron transfer is accompanied by a spin transition at the cobalt centre, involving a transition from {ls-Co III (cat)} at low temperature to {hs-Co II (3,5-sq)} at high temperature (ls = low spin, hs = high spin, cat = catecholate and sq = semiquinonate). All but one of the previously structurally characterized Co VT CPs exhibit a one-dimensional (1D) chain topology (Drath et al, 2016(Drath et al, , 2017Imaz et al, 2008;Jung & Pierpont, 1994;Chen et al, 2014;Drath & Boskovic, 2018;Li et al, 2011). There is a single literature example of a twodimensional (2D) Co-dioxolene VT CP (Li et al, 2011), as well as a 2D VT CP based on Mn and nitronyl-nitroxide ligands (Lannes et al, 2016).…”

Liquid‐Filled Valence Tautomeric Microcapsules: A Solid Material with Solution‐Like Behavior

“…Although most of these factors are related to the composition and structure of the compound of choice (e.g., metal and ligand characteristics, steric hindrance, donor/acceptor abilities of the counter ligand, and/or the volume and Coulombic interactions of the counterion), the properties of valence tautomers also show a critical dependence on the surrounding medium, which is often hard to systematize . For instance, whereas most VT complexes undergo thermally induced interconversion in solution, the number of examples preserving this behavior in the solid state is rather limited .…”