Vibrational spectroscopy of Co⁺(CH₄)n and Ni⁺(CH₄)n (n = 1-4).
Vibrational spectroscopy of Co⁺(CH₄)n and Ni⁺(CH₄)n (n = 1-4).
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Co+(CH4)n 和 Ni+(CH4)n (n = 1-4) 的振动光谱。
DOI：
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发表时间：
2014
影响因子：
2.9
通讯作者：
R. Metz
中科院分区：
文献类型：
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作者：
Abdulkadir Kocak;Zachary Sallese;M. Johnston;R. Metz
在C-H伸缩区(2500-3100 cm(-1))测量了M(+)(CH4)m(Ar)(3-m)和M(+)(CH4)n(M=Co，Ni；m=1，2；n=3，4)的振动光谱，监测了Ar或甲烷的损失。与金属的相互作用导致近氢的C-H伸缩发生较大的红移。这种变化的程度对配位(η(2)对η(3))和金属-甲烷距离很敏感。通过在B3LYP/6-311++G(3df，3pd)水平上将测量光谱与候选结构的计算结果进行比较，确定了配合物的结构。结合能也是用CAM-B3LYP泛函计算的。在所有情况下，甲烷都显示η(2)与金属配位。相对于自由CH4的对称伸展，m=1络合物在最低的C-H伸缩中表现出很大的红移，分别为370 cm(-1)(M=Co)和320 cm(-1)(M=Ni)。它们采用C2v结构，重原子和近邻氢原子共面。M=2的络合物红移略有减少，呈T型结构。对于n=3的络合物，既观察到T形结构，又观察到等边(或准等边)结构。测得的低频率C-H伸展的光解离起始和强度显著降低，表明Ni(+)(CH4)2-CH4的结合能为2650±50 cm(-1)。Co(+)(CH4)4络合物具有准四面体和扭曲四面体两种低位结构，具有丰富的光谱。相反，对称的方形平面的Ni(+)(CH4)4络合物具有非常简单的振动光谱。
Vibrational spectra of M(+)(CH4)m(Ar)(3-m) and M(+)(CH4)n (M = Co, Ni; m = 1, 2; n = 3, 4) in the C-H stretching region (2500-3100 cm(-1)) are measured using photofragment spectroscopy, monitoring the loss of argon or methane. Interaction with the metal leads to large red shifts in the C-H stretches for proximate hydrogens. The extent of this shift is sensitive to the coordination (η(2) vs η(3)) and to the metal-methane distance. The structures of the complexes are determined by comparing measured spectra with those calculated for candidate structures at the B3LYP/6-311++G(3df,3pd) level. Binding energies are also computed using the CAM-B3LYP functional. In all cases, CH4 shows η(2) coordination to the metal. The m = 1 complexes show very large red shifts of 370 cm(-1) (for M = Co) and 320 cm(-1) (for M = Ni) in the lowest C-H stretch, relative to the symmetric stretch of free CH4. They adopt a C2v structure with the heavy atoms and proximate hydrogen atoms coplanar. The m = 2 complexes have slightly reduced red shifts, and Tee-shaped structures. Both Tee-shaped and equilateral (or quasi-equilateral) structures are observed for the n = 3 complexes. The measured photodissociation onset and significantly reduced intensity for low-frequency C-H stretches imply a value of 2650 ± 50 cm(-1) for the binding energy of Ni(+)(CH4)2-CH4. The Co(+)(CH4)4 complexes have two low-lying structures, quasi-tetrahedral and distorted square-planar, which contribute to the rich spectrum. In contrast, the symmetrical, square-planar Ni(+)(CH4)4 complex is characterized by a very simple vibrational spectrum.