title: Coordination number of Li+ in nonaqueous electrolyte solutions determined by molecular rotational measurements.
abstract: 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.
authors.affiliation: State key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences , 457 Zhongshan Road, Dalian 116023, China.
authors.forename: Kaijun
authors.initials: K
authors.lastname: Yuan
authors.forename: Hongtao
authors.initials: H
authors.lastname: Bian
authors.forename: Yuneng
authors.initials: Y
authors.lastname: Shen
authors.forename: Bo
authors.initials: B
authors.lastname: Jiang
authors.forename: Jiebo
authors.initials: J
authors.lastname: Li
authors.forename: Yufan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Hailong
authors.initials: H
authors.lastname: Chen
authors.forename: Junrong
authors.initials: J
authors.lastname: Zheng