Yuan Kaijun, Bian Hongtao, Shen Yuneng, Jiang Bo, Li Jiebo, Zhang Yufan, Chen Hailong, Zheng Junrong
State key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences , 457 Zhongshan Road, Dalian 116023, China.
J Phys Chem B. 2014 Apr 3;118(13):3689-95. doi: 10.1021/jp500877u. Epub 2014 Mar 24.
The coordination number of Li(+) in acetonitrile solutions was determined by directly measuring the rotational times of solvent molecules bound and unbound to it. The CN stretch of the Li(+) bound and unbound acetonitrile molecules in the same solution has distinct vibrational frequencies (2276 cm(-1) vs 2254 cm(-1)). The frequency difference allows the rotation of each type of acetonitrile molecule to be determined by monitoring the anisotropy decay of each CN stretch vibrational excitation signal. Regardless of the nature of anions and concentrations, the Li(+) coordination number was found to be 4-6 in the LiBF4 (0.2-2 M) and LiPF6 (1-2 M) acetonitrile solutions. However, the dissociation constants of the salt are dependent on the nature of anions. In 1 M LiBF4 solution, 53% of the salt was found to dissociate into Li(+), which is bound by 4-6 solvent molecules. In 1 M LiPF6 solution, 72% of the salt dissociates. 2D IR experiments show that the binding between Li(+) and acetonitrile is very strong. The lifetime of the complex is much longer than 19 ps.
通过直接测量与Li(+)结合和未结合的溶剂分子的旋转时间，确定了Li(+)在乙腈溶液中的配位数。同一溶液中与Li(+)结合和未结合的乙腈分子的CN伸缩振动具有不同的振动频率（2276 cm(-1) 对 2254 cm(-1)）。频率差异使得通过监测每个CN伸缩振动激发信号的各向异性衰减来确定每种乙腈分子的旋转成为可能。无论阴离子的性质和浓度如何，在LiBF4（0.2 - 2 M）和LiPF6（1 - 2 M）乙腈溶液中，Li(+)的配位数均为4 - 6。然而，盐的解离常数取决于阴离子的性质。在1 M LiBF4溶液中，发现53%的盐解离成Li(+)，其与4 - 6个溶剂分子结合。在1 M LiPF6溶液中，72%的盐解离。二维红外实验表明Li(+)与乙腈之间的结合非常强。复合物的寿命远长于19 ps。
