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首页> 外文期刊>Chemistry: A European journal >Ligand Strain and the Nature of Spin Crossover in Binuclear Complexes:Two-Step Spin Crossover in a 4,4'-Bipyridine-Bridged Iron(II) Complex [{Fe(dpia)(NCS)_2}_2(4,4'-bpy)] (dpia = di(2-picolyl)amine; 4,4'-bpy = 4,4'-bipyridine)
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Ligand Strain and the Nature of Spin Crossover in Binuclear Complexes:Two-Step Spin Crossover in a 4,4'-Bipyridine-Bridged Iron(II) Complex [{Fe(dpia)(NCS)_2}_2(4,4'-bpy)] (dpia = di(2-picolyl)amine; 4,4'-bpy = 4,4'-bipyridine)

机译：配体应变和双核络合物中自旋交叉的性质：在4,4'-联吡啶-桥联铁（II）络合物[{Fe（dpia）（NCS）_2} _2（4,4'- bpy）]（dpia =二（2-吡啶甲基）胺; 4,4'-bpy = 4,4'-联吡啶）

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The synthesis and detailedcharacterization of the new spin cross-over (SCO) binuclear complex [{Fe-(dpia)(NCS)212,(4,4'-bpy)] (1; dpia=di(2-picolyl)amine, 4,4'-bpy = 4,4'-bipyr-idine) are reported. Variable-tempera-ture magnetic susceptibility measure-ments show a relatively cooperativetwo-step spin transition suggesting theoccurrence of three spin-state isomers:[HS—HS], [HS—LS], and [LS—LS] (HS:high spin, LS: low spin). A short pla-teau at 204 K separates the two stepsand conforms with about 50 % of thecomplexes having undergone a thermalspin conversion. Routine Mossbauerspectroscopy without applying a mag-netic field clearly separates fouriron(II) one-center spin states in three [HS—HS], [HS—LS], and [LS—LS] pairsand unambiguously confirms that thespin transition at the plateau tempera-ture goes through the intermediate[HS—LS] state. The single-crystal X-raystructure was solved for three spin iso-mers at 293, 208, and 120 K. The struc-tural study at the plateau temperaturewas unable to resolve the HS and LSsites in the [HS—LS] pair and only anaverage Fe—N bond length was ob-tained, which suggests that there is anintermediate [HS—LS] phase. The struc-tural analysis at three temperatures re-vealed a dense three-dimensional net-work of both intra- and intermolecularinteractions. The relative energies ofthe three spin-state isomers were eval-uated by quantum-chemical DFT cal-culations. Comparison of compound 1with previously known analogues, aswell as the overall analysis of structuraldata for numerous binuclear com-plexes, allowed a conclusion to bereached on the crucial role of ligandstrain effects in the SCO behavior ofbinuclear complexes. The suggested in-tramolecular mechanism explains thedifferent types of SCO observed in bi-nuclear complexes: one-step, two-step,and partial (50 %) transitions.
机译：新的自旋交联（SCO）双核络合物[{Fe-（dpia）（NCS）212，（4,4'-bpy）]（1; dpia = di（2-picolyl）amine，据报道有4,4'-bpy = 4,4'-联吡啶。可变温度磁化率测量值显示相对合作的两步自旋跃迁，表明出现了三种自旋态异构体：[HS-HS]，[HS-LS]和[LS-LS]（HS：高自旋，LS：低自旋）。在204 K处的一个简短的平台将两个步骤分开，并与大约50％经历了热纺转化的复合物相符。不施加磁场的常规Mossbauerspecs光谱术清楚地将四铁（II）一中心自旋态分为三个[HS-HS]，[HS-LS]和[LS-LS]对，并明确确认了高原温度上的自旋转变-ture经历中间[HS-LS]状态。在293、208和120 K上解析了三种自旋异构体的单晶X射线结构。在高原温度下的结构研究无法解析[HS-LS]对中的HS和LS位点，仅获得平均的Fe-N键长，这表明存在中间的[HS-LS]相。在三个温度下的结构分析重新揭示了分子内和分子间相互作用的密集三维网络。通过量子化学DFT计算计算了三种自旋异构体的相对能。将化合物1与先前已知的类似物进行比较，以及对许多双核络合物的结构数据进行整体分析，得出了关于配体应变效应在双核络合物SCO行为中的关键作用的结论。建议的分子内机制解释了在双核复合物中观察到的SCO的不同类型：一步，两步和部分（50％）转变。

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