Synthesis, magnetic properties and dynamic behavior of cobalt complexes with an anthracene-containing dioxolene ligand

Abstract

The anthracene-functionalized cobalt complexes [Co(L)(TPA)]PF6 (1) and [Co(L)(Me(n)TPA)]PF6 (2, n = 1; 3, n = 2; 4, n = 3) were synthesized by the combination of 9-(3,4-dihydroxyphenyl)anthracene (H2L) and tris(2-pyridylmethyl)amine (TPA) or its derivatives (Me(n)TPA, n = 1, 2, 3). Characterization of complexes 1-4 was performed by UV-vis absorption, IR, (1)H NMR, and magnetic susceptibility measurements. In the solid state, the variable-temperature magnetic susceptibility data showed that complex 1 is low-spin cobalt(III) catecholate (Co(III)(LS)-Cat), while complex 4 is high-spin cobalt(II) semiquinonate (Co(II)(HS)-SQ) in the range 4.5-400 K. The susceptibility data of complexes 2 and 3 suggested valence tautomerism between the Co(III)(LS)-Cat and Co(II)(HS)-SQ forms. Light-induced valence tautomerism was observed in complexes 2 and 3 at 5 K by photo-irradiation. In solution, the temperature dependence of (1)H NMR spectra of 1 and 2 showed an equilibrium between their geometrical isomers.

Spectroscopic, Structural, and Kinetic Investigation of the Ultrafast Spin Crossover in an Unusual Cobalt(II) Semiquinonate Radical Complex

“…It is further estimated that any possible contribution of the hs complex to absorption in this spectral region is by at least one order of magnitude smaller. It is also worthwhile to note that, to the best of our knowledge, none of the reported hs Co II semiquinonate complexes display such an intense CT band in this energy range, which is consistent with our observation . This relatively intense CT band can therefore be identified as a marker band characteristic for the presence of an ls Co II semiquinonate complex.…”

“…It is furthere stimated that any possible contribution of the hs complex to absorption in this spectralr egion is by at least one order of magnitude smaller.I ti sa lso worthwhile to note that, to the best of our knowledge,n one of the reported hs Co II semiquinonate complexes display such an intense CT band in this energy range, which is consistent with our observation. [31][32][33][34][35][36][37][38][39][40][41][42] This relatively intense CT band can therefore be identified as am arker band characteristicf or the presence of an ls Co II semiquinonate complex. In addition, the temperature-dependentV is/NIR spectra demonstrate that ag round sample of 1 in aK Br matrix already starts to undergo SCO between 173 and 223 K, slightly below those temperatures of the crystalline substance (i.e.,withoutgrinding).…”

“…The latter complex is unique in two aspects. First, in general, octahedral mononuclear Co II semiquinonate complexes are only known to contain hs Co II ions . In contrast, the Co II semiquinonate complex [Co II ( l ‐N 4 t Bu 2 )(dbsq)][B( p ‐C 6 H 4 Cl) 4 ] ( 1 , complex cation depicted in Figure ; dbsq 1− =3,5‐di‐ tert ‐butylsemiquinonate, l ‐N 4 t Bu 2 = N , N′ ‐di‐ tert ‐butyl‐2,11‐diaza[3.3](2,6)pyridinophane) is the first reported ground‐state octahedral ls Co II semiquinonate complex.…”

“…First, in general, octahedral mononuclear Co II semiquinonate complexes are only known to contain hs Co II ions. [31][32][33][34][35][36][37][38][39][40][41][42] In contrast, the Co II semiquinonate complex [Co II (l-N 4 tBu 2 )(dbsq)][B(p-C 6 H 4 Cl) 4 ]( 1, complexc ation depicted in Figure 1; dbsq 1À = 3,5-di-tert-butylsemiquinonate, l-N 4 tBu 2 = N,N'-di-tert-butyl-2,11-diaza [3.3](2,6)pyridinophane) is the first reported ground-stateo ctahedral ls Co II semiquinonate complex. Secondly, in any of the reported octahedral hs Co II semiquinonate complexes that are also capable of changing their electronic states upon lowering the temperature, the underlying process has only been linked to VT.I ns olid 1,o nt he other hand, at emperature-induced SCO transition from an ls to ah sC o II semiquinonate complex has been observed (Scheme 1).…”

Magnetic Properties of Acenes and Their o-Quinone Derivatives: Computer Simulation

“…However, instability of this compound and its homologs-hexacene and heptacene-toward light and air makes difficult their practical application [8]. To solve this problem, it was suggested to use derivatives with paramagnetic substituents showing high stability on exposure to light due to ultrafast singlet-triplet conversion of acene moiety in photoexcited states [9,10].The aim of this work is to study acenes 2 modified with two o-benzoquinone groups and their complexes with sodium cations 3 containing free-radical semiquinone (SQ) states of redox-active moieties (Fig. 2).…”