Molecular structure and vibrational spectra of spin-crossover complexes in solution and colloidal media: Resonance Raman and time-resolved resonance Raman studies
Molecular structure and vibrational spectra of spin-crossover complexes in solution and colloidal media: Resonance Raman and time-resolved resonance Raman studies
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DOI：
10.1021/ic049809t
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发表时间：
2004-07-12
影响因子：
4.6
通讯作者：
Wolny, JA
中科院分区：
文献类型：
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作者：
Brady, C;Callaghan, PL;Wolny, JA
自旋交叉体系[Fe（btpa）]（PF 6）（2）（btpa = N，N，N '，N'-四（2-吡啶基甲基）-6，6 '-双（氨基甲基）-2，2 '联吡啶）和主要低自旋物质[Fe（B（bdpa））]（PF 6）（2）（（B（bdpa）= N，N'-双（苄基）-N，N '-双（2-吡啶甲基）-6，6 '-双（氨甲基）-2，2'-联吡啶）的结构用X射线衍射法进行了表征。[Fe（btpa）]（PF 6）（2）的晶胞包含两个晶体学上独立的分子，具有八面体低自旋和准七配位高自旋结构。[Fe（B（bdpa））]（PF 6）2的晶胞中含有两个晶体学上独立的分子，其中一个分子对应于低自旋结构，而另一个分子则显示出无序结构。在磁化率和穆斯堡尔谱测量的基础上，有人提出这种无序涉及低自旋和高自旋六配位分子。并测定了[Zn（btpa）]（PF_6）（2）和[Ru（btpa）]（PF_6）（2）的结构。脉冲激光光微扰，这里耦合时间分辨共振拉曼光谱（TR 3），已被用来调查，首次通过这种技术，在纳秒和皮秒时间尺度上的低自旋，LS（（1）A）-高自旋，HS（T-5）电子自旋态交叉在这些Fe（II）配合物的溶液中的弛豫动力学。对于纳秒实验，使用的探针波长在321 nm，落在π-π * 过渡的多吡啶骨架的配体，使调查的LS和HS异构体的振动模式，通过耦合到自旋状态依赖的角度变化的骨干。补充调查的自旋交叉（SCO）平衡在均匀的解决方案和胶体介质中协助分配的突出特点，在拉曼光谱的LS和HS异构体。纳秒研究的弛豫数据证实并扩展了早期的分光光度研究结果（Schenker，S.; Stein，P. C.; Wolny，J. A.;布雷迪，C.; McGarvey，J. J.; Toftlund，H.;豪瑟，A. Inorg.Chem.2001，40，134），指出在[Fe（btpa）]（PF 6）（2）的情况下是双相的自旋态弛豫，但在[Fe（B（bdpa））]（PF 6）2的情况下是双相的。皮秒结果表明在20 ps或更短时间内完成的早期过程，这对两种复合物是共同的，并且可能包括初始形成的T-5（2）态中的振动弛豫。
The spin-crossover system [Fe(btpa)](PF6)(2) (btpa = N,N,N',N'-tetrakis(2-pyridylmethyl)-6,6'-bis(aminomethyl)-2,2'bipyridine) and the predominantly low-spin species [Fe(b(bdpa))](PF6)(2) ((b(bdpa) = N,N'-bis(benzyl)-N,N'-bis(2-pyridylmethyl)-6,6'-bis(aminomethyl)-2,2'-bipyridine) have been characterized by means of X-ray diffraction. The unit cell of [Fe(btpa)](PF6)(2) contains two crystallographically independent molecules revealing octahedral low-spin and quasi-seven-coordinated high-spin structures. The unit cell of [Fe(b(bdpa))](PF6)2 contains two crystallographically independent molecules one of which corresponds to a low-spin structure, while the other reveals a disordering. On the basis of magnetic susceptibility and Mossbauer measurements, it has been proposed that this disorder involves low-spin and high-spin six-coordinated molecules. The structures of [Zn(btpa)](PF6)(2) and [Ru(btpa)](PF6)(2) have been determined also. Pulsed laser photoperturbation, coupled here with time-resolved resonance Raman spectroscopy (TR3), has been used to investigate, for the first time by this technique, the relaxation dynamics in solution on nanosecond and picosecond time scales of low-spin, LS ((1)A) - high-spin, HS (T-5) electronic spin-state crossover in these Fe(II) complexes. For the nanosecond experiments, use of a probe wavelength at 321 nm, falling within the pi-pi* transition of the polypyridyl backbone of the ligands, enabled the investigation of vibrational modes of both LS and HS isomers, through coupling to spin-state-dependent angle changes of the backbone. Supplementary investigations of the spin-crossover (SCO) equilibrium in homogeneous solution and in colloidal media assisted the assignment of prominent features in the Raman spectra of the LS and HS isomers. The relaxation data from the nanosecond studies confirm and extend earlier spectrophotometric findings, (Schenker, S.; Stein, P. C.; Wolny, J. A.; Brady, C.; McGarvey, J. J.; Toftlund, H.; Hauser, A. Inorg. Chem. 2001, 40, 134), pointing to biphasic spin-state relaxation in the case of [Fe(btpa)](PF6)(2) but monophasic in the case of [Fe(b(bdpa))](PF6)2, The picosecond results suggest an early process complete in 20 ps or less, which is common to both complexes and possibly includes vibrational relaxation in the initially formed T-5(2) state.