Structure of salts of lithium chloride and lithium hexafluorophosphate as solvates with pyridine and vinylpyridine and structural comparisons: (C_5H_5N)LiPF_6, [p-(CH_2CH)C_5H_4N]LiPF_6,[(C_5H_5N)LiCl]_n, and [p-(CH_2CH)C_5H_4N]_2-Li(μ-Cl)_2Li[p-(CH_2CH)C_5H_4N]_2

摘要

Due to the flammability of liquid electrolytes used in lithium ion batteries, solid lithium ion conductors are of interest to reduce danger and increase safety. The two dominating general classes of electrolytes under exploration as alternatives are ceramic and polymer electrolytes. Our group has been exploring the preparation of molecular solvates of lithium salts as alternatives. Dissolution of LiCl or LiPF_6 in pyridine (py) or vinylpyridine (VnPy) and slow vapor diffusion with diethyl ether gives solvates of the lithium salts coordinated by pyridine ligands. For LiPF_6, the solvates formed in pyridine and vinylpyridine, namely tetrakis(pyridine-κN)lithium(I) hexafluorophosphate, [Li(C_5H_5N)_4]PF_6 and tetrakis(4-ethenylpyridine-κN)lithium(I) hexafluorophosphate, [Li(C_7H_7N)_4] -PF_6, exhibit analogous structures involving tetracoordinated lithium ions with neighboring PF6 ~-anions in the I4 and Aea2 space groups, respectively. For LiCl solvates, two very different structures form. catena-Poly[[(pyridine-κN)lithium]-μ_3-chlorido], [LiCl(C_5H_5N)]_n, crystalizes in the P2_12_12_1 space group and contains channels of edge-fused LiCl rhombs templated by rows of π-stacked pyridine ligands, while the structure of the LiCl-VnPy solvate, namely di-μ-chlorido-bis[bis(4-ethenylpyridine-κN)lithium], [Li_2Cl_2(C_7H_7N)_4], is described in the P2_1/n space group as dinuclear (VnPy)_2Li(μ-Cl)_2Li(VnPy)_2 units packed with neighbors via a dense array of π-tπ interactions.