Rupp Fabian, Chevalier Katharina, Graf Michèle, Schmitz Markus, Kelm Harald, Grün Anneken, Zimmer Manuel, Gerhards Markus, van Wüllen Christoph, Krüger Hans-Jörg, Diller Rolf
Department of Physics, University of Kaiserslautern, Erwin Schrödinger Str. 46, 67663, Kaiserslautern, Germany.
Department of Chemistry, University of Kaiserslautern, Erwin Schrödinger Str. 52, 67663, Kaiserslautern, Germany.
Chemistry. 2017 Feb 10;23(9):2119-2132. doi: 10.1002/chem.201604546. Epub 2017 Jan 16.
A comprehensive spectroscopic and structural investigation of [Co (l-N tBu )(dbsq)][B(p-C H Cl) ] (1, l-N tBu =N,N'-di-tert-butyl-2,11-diaza3.3pyridinophane, dbsq =3,5-di-tert-butylsemiquinonate), the first known octahedral complex with a low-spin (ls) Co semiquinonate ground state, is reported. Above 200 K, solids as well as solutions of 1 exhibit thermally induced spin-crossover (SCO) from the ls to the high-spin (hs) Co semiquinonate state instead of the frequently observed valence tautomerism from ls Co catecholate to hs Co semiquinonate. DFT calculations demonstrate that the (closed shell) Co catecholate suffers from a triplet instability leading to the ls Co semiquinonate ground state. The thorough temperature-dependent spectroscopic study of the SCO enables a photophysical investigation. Thus, by selective photoexcitation of the ls fraction of 1 in solution at room temperature, ultrafast conversion to the hs state is observed using femtosecond electronic and IR-vibrational (infrared) transient absorption spectroscopy. The kinetics of the photocycle is described by a stretched exponential with τ=3.3-3.6 ps and β=0.52-0.54, representing an upper limit for the hs-ls relaxation time. This is, to our knowledge, the fastest interconversion ever determined for a SCO complex, and is attributed to the special situation that in 1 a Co complex is coordinated to a π-radical ligand allowing very efficient coupling between the ls and hs spin states.
报道了对[Co(l-N tBu)(dbsq)][B(p-C 6H 4Cl) 4]（1，l-N tBu = N,N'-二叔丁基-2,11-二氮杂3.3吡啶并环）的全面光谱和结构研究，它是首个已知的具有低自旋(ls)钴半醌基态的八面体配合物。在200 K以上，1的固体以及溶液表现出热诱导自旋交叉(SCO)，从ls钴半醌态转变为高自旋(hs)钴半醌态，而不是常见的从ls钴儿茶酚盐到hs钴半醌的价互变异构。密度泛函理论(DFT)计算表明，(闭壳层)钴儿茶酚盐存在三重态不稳定性，导致基态为ls钴半醌。对SCO进行的全面的温度依赖光谱研究使得光物理研究成为可能。因此，通过在室温下对溶液中1的ls部分进行选择性光激发，使用飞秒电子和红外振动瞬态吸收光谱观察到超快转变为hs态。光循环动力学由拉伸指数描述，τ = 3.3 - 3.6 ps且β = 0.52 - 0.54，代表hs - ls弛豫时间的上限。据我们所知，这是SCO配合物中确定的最快的相互转换，这归因于1中钴配合物与π - 自由基配体配位的特殊情况，使得ls和hs自旋态之间能够非常有效地耦合。
