从头算量子化学计算方法对高氯酸镁溶液中存在的离子缔合物种及缔合过程的研究

Ab-initio Investigation on the Ion-associated Species and Process in Mg(ClO_4)_2 Solution

使用了量子化学计算方法在HF/6-31+G*水平下对高氯酸镁溶液中的高氯酸根水合,可能存在的离子缔合物种以及离子缔合过程进行了研究.高氯酸根的第一水合层至少需要6个水分子才能填满,在水合数6以下时,每增加一个水分子可以造成v1-ClO-4频率1.7cm-1的蓝移.高氯酸根与第一个无水镁离子结合可以造成较大的红移,与第二个和第三个镁离子结合后,可使v1-ClO-4频率连续的反向蓝移,这种变化与镁离子的极化作用相关.高氯酸根与水合镁离子可形成水合的缔合物种,包括溶剂共享离子对、接触离子对、溶剂共享型三离子团簇和接触型三离子团簇,其中溶剂共享型离子对和含有两个高氯酸根和一个镁离子的三离子团簇,可对v1-ClO-4频率造成较小的蓝移,与实验的拉曼光谱符合较好.高氯酸镁在溶液浓度升高时发生的离子缔合过程被推测为:自由水合离子→溶剂共享型离子对→含有两个高氯酸根的溶剂共享型三离子团簇→六水合高氯酸镁晶体,这一过程与硫酸镁有较大不同而与硝酸镁接近.

In the present article,the hydration of ClO4^-,ion-associated species and process in the Mg（ClO4）2 solution were investigated at the HF/6-31＋G^＊ level.The first aqueous sphere can be filled by 6 water molecules at least.When the hydrated number is less than 6,the blue-shift of the v1-ClO4^- frequency of 1.7 cm^-1 can be resulted by each added water molecule.The direact contact of the first Mg2＋ can lead the v1-ClO4^- frequency a large red-shift,and the second and the third Mg2＋ will make the reversed shift.The shifts will be contributed to the polarization of the Mg2＋.Some associated species will form between ClO4^- and aqueous Mg2＋,such as solvent-shared ion pairings,contact ion pairings and triple ion clusters.In these species,the solvent-shared ion pairing and triple ion cluster with one aqueous Mg2＋ and two ClO4^- ions can lead the v1-ClO4^- frequencies to small blue-shifts which are corresponding with the Raman spectra in experiment.The ion associated process which is not analogous with the MgSO4 but Mg（NO3）2 system,is predicted to be：free ions→solvent-shared ion pairing→solvent-shared triple ion cluster with one aqueous Mg2＋ and two ClO4^- ions→Mg（ClO4）2？6H2O（crystal）.