Observation of Extremely Weakly Interacting OH (∼3600 cm–1) in the Vicinity of High Charge Density Metal Ions (Mz+; z = 1, 2, 3): A Structural Heterogeneity in the Extended Hydration Shell,The Journal of Physical Chemistry C

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Observation of Extremely Weakly Interacting OH (∼3600 cm–1) in the Vicinity of High Charge Density Metal Ions (Mz+; z = 1, 2, 3): A Structural Heterogeneity in the Extended Hydration Shell
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-01-23 , DOI: 10.1021/acs.jpcc.9b09692
Animesh Patra ₁ , Subhadip Roy ₂ , Subhamoy Saha ₂ , Dipak K. Palit ₁ , Jahur A. Mondal ₂

Affiliation

Hydration of metal ions is critical to their adsorption, complexation, and discharge but remained elusive due to counterion interference. We introduce Raman difference spectroscopy with simultaneous curve fitting (RD-SCF) analysis to quantitatively retrieve the counterion-free OH stretch spectra of water in the hydration shell of various metal ions such as Li⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, La³⁺, Gd³⁺ Dy³⁺, and Lu³⁺ as well as that of a proton (H⁺). The RD-SCF-extracted spectra show that “extremely weakly” (OH stretch ∼ 3600 cm^–1) and “strongly” (∼3300 cm^–1) interacting OHs coexist in the hydration shell of the high charge density metal ions and proton. The weakly interacting OH originates from the second hydration shell water–OH (W_2hs–OH) that donates the hydrogen-bond to the electron-deficient oxygen at the first hydration shell (W_1hs−O) and is largely localized at the boundary between the first and second hydration shells. For high charge density ions, such as Mg²⁺ and La³⁺, at least 4 and 8 water molecules are affected in their respective second hydration shell, which is ∼70% and 90% of their first hydration shell. The coexistence of different water–OHs discloses a heterogeneous water structure in the extended hydration shell of metal ions.

中文翻译：

在高电荷密度金属离子（M ^z⁺；z = 1，2，3 ）附近观察到极弱相互作用的OH（〜3600 cm ^–1）：扩展水化壳中的结构异质性

金属离子的水合对其吸附，络合和放电至关重要，但由于抗衡离子的干扰而难以捉摸。我们引入具有同时曲线拟合（RD-SCF）分析的拉曼差光谱法，定量检索各种金属离子（如Li ⁺，Mg 2 ⁺，Ca ²⁺，Sr ^2）的水合壳中水的无反离子OH拉伸谱⁺，Ba 2 ⁺，La ³⁺，Gd ³⁺ Dy ³⁺和Lu ³⁺以及质子（H ⁺）的^离子。RD-SCF提取的光谱表明，“极弱”（OH拉伸〜3600 cm ^–1）和“强”（〜3300 cm）^–1）相互作用的OHs共存于高电荷密度金属离子和质子的水合壳中。弱相互作用的OH源自第二个水合壳水-OH（W _2hs -OH），它在第一个水合壳（W _1hs -O）_上将氢键提供给缺电子的氧，并且主要位于第一和第二水化壳。对于高电荷密度的离子，例如Mg ²⁺和La ³⁺，它们各自的第二水合壳中至少有4和8个水分子受到影响，这分别是其第一水合壳的70％和90％。不同水-OH的共存揭示了金属离子扩展水化壳中的异质水结构。

更新日期：2020-01-24

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