Max Jean-Joseph, Gessinger Véronique, van Driessche Caroline, Larouche Pascal, Chapados Camille
Département de Chimie-Biologie, Université du Québec à Trois-Rivières, Trois-Rivières, Quebec G9A 5H7, Canada.
J Chem Phys. 2007 May 14;126(18):184507. doi: 10.1063/1.2717184.
The analysis by infrared spectroscopy of aqueous solutions of the binary inorganic salts NaI and NaCl and the ternary salts CaCl2 and BaCl2 at concentrations from 1000 to 2 mM was carried out to complement a previous study done at higher concentrations on nine binary salts (alkali halides) and one ternary salt (MgCl2) [J.-J. Max and C. Chapados, J. Chem. Phys. 115, 2664 (2001)]. These salts are completely ionized in aqueous solutions, forming monoatomic species that do not absorb IR but that perturb the surrounding water, modifying its spectrum. The factor analysis of the spectra revealed that all these salt solutions were composed of two water types: pure water and salt solvated water. The authors obtained pure salt solvated water spectra for all the salts using an extrapolation technique. The water types obtained are constant for the binary and ternary salts down to 2 mM. For the binary salts, we determine that 5.0 and 4.0 water molecules are solvated to the Na+-Cl- and Na+-I- ion pairs, respectively. These numbers are the same as that obtained at higher concentrations. For the new ternary salts, we find that 6.0 and 8.0 water molecules are solvated to Ca++-(Cl-)2 and Ba++-(Cl-)2 ion pairs, respectively. These numbers are higher than the four water molecules solvated to Mg++-(Cl-)2 ion pairs determined previously, but show a progression that follows their atomic numbers. These results constitute new experimental results on "simple" systems whose molecular organization is still a matter of debate. The IR method that probes the system at the molecular level is a method different than the macroscopic ones that give the activity coefficients. The IR gives direct observation at the molecular level of the strong ion-water interactions that are often neglected and its water structure not considered in macroscopic methods. The present results and their analysis together with those obtained by other methods will facilitate the determination of the organization of these aqueous systems.
对浓度范围为1000至2 mM的二元无机盐NaI和NaCl以及三元盐CaCl2和BaCl2的水溶液进行了红外光谱分析,以补充先前在较高浓度下对九种二元盐(碱金属卤化物)和一种三元盐(MgCl2)所做的研究[J.-J. 马克斯和C. 查帕多斯,《化学物理杂志》115, 2664 (2001)]。这些盐在水溶液中完全电离,形成不吸收红外光但会扰动周围水分子、改变其光谱的单原子物种。光谱的因子分析表明,所有这些盐溶液都由两种水类型组成:纯水和盐溶剂化水。作者使用外推技术获得了所有盐的纯盐溶剂化水光谱。所得到的水类型对于二元盐和三元盐而言,在低至2 mM时都是恒定的。对于二元盐,我们确定分别有5.0个和4.0个水分子溶剂化到Na+-Cl-和Na+-I-离子对。这些数字与在较高浓度下获得的数字相同。对于新的三元盐,我们发现分别有6.0个和8.0个水分子溶剂化到Ca++-(Cl-)2和Ba++-(Cl-)2离子对。这些数字高于先前确定的溶剂化到Mg++-(Cl-)2离子对的四个水分子,但呈现出随原子序数变化的规律。这些结果构成了关于“简单”系统的新实验结果,其分子组织仍然是一个有争议的问题。在分子水平上探测该系统的红外方法与给出活度系数的宏观方法不同。红外方法能在分子水平上直接观察到常常被忽视的强离子 - 水相互作用及其水结构,而宏观方法并未考虑这些。目前的结果及其分析与通过其他方法获得的结果一起,将有助于确定这些水体系的组织情况。