Giesecke Marianne, Mériguet Guillaume, Hallberg Fredrik, Fang Yuan, Stilbs Peter, Furó István
Division of Applied Physical Chemistry, Department of Chemistry, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden.
Phys Chem Chem Phys. 2015 Feb 7;17(5):3402-8. doi: 10.1039/c4cp04446k. Epub 2014 Dec 22.
The results of diffusion and electrophoretic NMR (eNMR) measurements are reported for a series of tetramethylammonium (TMA) electrolytes (with sulphate, fluoride, acetate, chloride, bromide, nitrate, iodide and perchlorate as anions) in deuterated solvents such as water, dimethylsulphoxide (DMSO), acetonitrile, methanol and ethanol. In addition, similar data are presented for aqueous solutions of tetraalkylammonium salts with increasing alkyl chain length. The combination of diffusion NMR and eNMR yields the effective charge for the TMA cation. Relative to the nominal charge of znom = 1 of TMA, the effective charge in the different solvents is found to be progressively smaller in the order water > DMSO > methanol > acetonitrile > ethanol. A part of this observed trend is ascribed to regular ion-ion interactions incorporated in the Onsager limiting law. Indeed, in solvents with high dielectric constants such as water, DMSO and methanol, the Onsager limiting law describes well the observations for all tetraalkylammonium ions. For ethanol and acetonitrile, there is a significant difference between the experimental data and the expected limiting-law behavior that is attributed to ion association (ion pairing) not taken into consideration by the Onsager limiting law.
报道了一系列四甲基铵（TMA）电解质（阴离子分别为硫酸根、氟离子、醋酸根、氯离子、溴离子、硝酸根、碘离子和高氯酸根）在氘代溶剂（如水、二甲亚砜（DMSO）、乙腈、甲醇和乙醇）中的扩散和电泳核磁共振（eNMR）测量结果。此外，还给出了烷基链长度增加的四烷基铵盐水溶液的类似数据。扩散核磁共振和eNMR相结合得出了TMA阳离子的有效电荷。相对于TMA的标称电荷znom = 1，发现不同溶剂中的有效电荷按水>DMSO>甲醇>乙腈>乙醇的顺序逐渐减小。观察到的这种趋势的一部分归因于Onsager极限定律中包含的常规离子-离子相互作用。实际上，在水、DMSO和甲醇等高介电常数的溶剂中，Onsager极限定律很好地描述了所有四烷基铵离子的观测结果。对于乙醇和乙腈，实验数据与预期的极限定律行为之间存在显著差异，这归因于Onsager极限定律未考虑的离子缔合（离子对）。
