Spin-crossover cobalt(III) complexes: steric and electronic control of spin state
Spin-crossover cobalt(III) complexes: steric and electronic control of spin state
复制标题
自旋交叉钴(III)配合物：自旋态的空间和电子控制
DOI：
10.1021/ic00271a004
复制
发表时间：
1987
影响因子：
4.6
通讯作者：
P. Guetlich
中科院分区：
文献类型：
--
作者：
W. Klaeui;W. Eberspach;P. Guetlich
描述了一系列八面体钴(III)自旋交叉配合物[CoL2]+的制备，其中配体L"=[(C5H5) Co| P (0) R2| 3]"，其中R= OCH3、OC2H5、OCH(CH3)2、OCH2CH2CH2CH3、OCH2C(CH3)3、C2H5、CH2C6H5，充当氧 三脚配体。根据取代基 R 的空间和电子效应，可以在给定温度下实现磁行为的系统微调，从基本高自旋超过自旋平衡到完全抗磁性。顺磁性配合物呈深绿色；抗磁性络合物是黄色的。固态自旋交叉配合物的磁化率在4.2-320 K的温度范围和300 K的溶液中进行了测量。溶液中的自旋转变在NMR时间尺度上很快，并且平衡可以通过高自旋和低自旋状态之间的玻尔兹曼分布来描述。低自旋到高自旋跃迁的热力学参数 AG、AH 和 AS 已由变温 (170-330 K) 31P NMR 谱确定。过渡金属配合物 ML2、M= Co (II)、Ni (II)、Cu (II) 的配体场光谱将 L" 表征为非常硬的配体，其在光谱化学系列中的位置接近氟化物。配体 L" 中取代基 R 的变化导致配体场强的微小变化，顺序为 R= C2H5> OCH3» OC2H5» OCH2CH2CH2CH3> OCH (CH3) 2。这与在 300 K 下观察到的 hs/ls 比率一致，按照相反的顺序 R= OCH (CH3) 2» OCH2CH2CH2CH3> OC2H5> OCH3» C2H5，根据 31P NMR 谱确定。观察到取代基R=烷氧基对自旋平衡位置的影响的原因很可能是随着取代基变得更大而增加配体间排斥力。
The preparation of the series of octahedral cobalt (III) spin-crossover complexes [CoL2]+ is described where the ligands L"=[(C5H5) Co| P (0) R2| 3]", with R= OCH3, OC2H5, OCH (CH3) 2, OCH2CH2CH2CH3, OCH2C (CH3) 3, C2H5, CH2C6H5, act as oxygen tripod ligands. Depending on the steric and electronic effects of the substituents R, a systematic fine tuning of the magnetic behavior, at a given temperature, from essentially high spin over spin equilibrium to completely diamagnetic can be achieved. The paramagnetic complexes are dark green; the diamagnetic complexes are yellow. The magnetic susceptibilities of the spin-crossover complexes in the solid state have been measured in the temperature range 4.2-320 K and in solution at 300 K. The spin transition in solution is fast on the NMR time scale, and the equilibrium can be described by a Boltzmann distribution between the high-spin and the low-spin state. The thermodynamic parameters AG, AH, and AS of the low-spin to high-spintransition have been determined from variable-temperature (170-330 K) 31P NMR spectra. The ligandfield spectra of the transition-metal complexes ML2, M= Co (II), Ni (II), Cu (II), characterize L" as very hard ligands whose position in the spectrochemical series is near that of fluoride. The variation of the substituents R in the ligands L" causes a small variation in ligand field strength in the order R= C2H5> OCH3» OC2H5» OCH2CH2CH2CH3> OCH (CH3) 2. This is in accord with the observed hs/ls ratio at 300 K in the opposite order R= OCH (CH3) 2» OCH2CH2CH2CH3> OC2H5> OCH3» C2H5 as determined from the 31P NMR spectra. The cause of the observed influence of the substituents R= alkoxy on the spin equilibrium position is very probably increasing interligand repulsion as the substituents become more bulky.