Department of Chemical Engineering, University of Patras and Institute of Chemical Engineering and High Temperature Chemical Processes (FORTH/ICE-HT), GR-26500 Patras, Greece.
J Phys Chem A. 2012 Sep 6;116(35):8861-72. doi: 10.1021/jp306701k. Epub 2012 Aug 24.
The structural and vibrational properties of molybdenum(VI) oxosulfato complexes formed in MoO(3)–K(2)S(2)O(7) and MoO(3)–K(2)S(2)O(7)–K(2)SO(4) molten mixtures under an O(2) atmosphere and static equilibrium conditions were studied by Raman spectroscopy at temperatures of 400–640 °C. The corresponding composition effects were explored in the X(MoO)(3)(0) = 0–0.5 range. MoO(3) undergoes a dissolution reaction in molten K(2)S(2)O(7), and the Raman spectra point to the formation of molybdenum(VI) oxosulfato complexes. The Mo═O stretching region of the Raman spectrum provides sound evidence for the occurrence of a dioxo Mo(═O)(2) configuration as a core. The stoichiometry of the dissolution reaction MoO(3) + nS(2)O(7)(2–) → C(2n–) was inferred by exploiting the Raman band intensities, and it was found that n = 1. Therefore, depending on the MoO(3 content, monomeric MoO(2)(SO(4))(2)(2–) and/or associated MoO(2)(SO(4))(2)(2m–) complexes are formed in the binary MoO(3)–K(2)S(2)O(7) molten system, and pertinent structural models are proposed in full consistency with the Raman data. A 6-fold coordination around Mo is inferred. Adjacent MoO(2)(2+) cores are linked by bidentate bridging sulfates. With increasing temperature at concentrated melts (i.e., high X(MoO)(3)(0)), the observed spectral changes can be explained by partial dissociation of MoO(2)(SO(4))(2)(2m–) by detachment of S(2)O(7)(2–) and formation of a Mo—O—Mo bridge. Addition of K(2)SO(4) in MoO(3)–K(2)S(2)O(7) results in a “follow-up” reaction and formation of MoO(2)(SO(4))(3)(4–) and/or associated MoO(2)(SO(4))(3)(4m–) complexes in the ternary MoO(3)–K(2)S(2)O(7)–K(2)SO(4) molten system. The 6-fold Mo coordination comprises two oxide ligands and four O atoms linking to coordinated sulfate groups in various environments of reduced symmetry. The most characteristic Raman bands for the molybdenum(VI) oxosulfato complexes pertain to the Mo(═O)(2) stretching modes: (1) at 957 (polarized) and 918 (depolarized) cm(–1) for the ν(s) and ν(as) Mo(═O)(2) modes of MoO(2)(SO(4))(2)(2–) and MoO(2)(SO(4))(2)(2m–) and (2) at 935 (polarized) and 895 (depolarized) cm(–1) for the respective modes of MoO(2)(SO(4))(3)(4–) and MoO(2)(SO(4))(3)(4m–). The results were tested and found to be in accordance with ab initio quantum chemical calculations carried out on MoO(2)(SO(4))(3) and {MoO(2)}(2)(SO(4))(4)(μ-SO(4))(2) ions, in assumed isolated gaseous free states, at the DFT/B3LYP (HF) level and with the 3-21G basis set. The calculations included determination of vibrational infrared and Raman spectra, by use of force constants in the Gaussian 03W program.
在氧气气氛和静态平衡条件下，通过拉曼光谱研究了 MoO(3)-K(2)S(2)O(7) 和 MoO(3)-K(2)S(2)O(7)-K(2)SO(4) 熔融混合物中形成的六价钼氧代硫酸盐配合物的结构和振动性质，温度范围为 400-640°C。在 X(MoO)(3)(0) = 0-0.5 的范围内探索了相应的组成效应。MoO(3)在熔融 K(2)S(2)O(7)中发生溶解反应，拉曼光谱表明形成了六价钼氧代硫酸盐配合物。拉曼光谱的 Mo ═ O 伸缩区为双核的二氧 Mo(═O)(2) 构型提供了有力证据。利用拉曼带强度推断溶解反应 MoO(3) + nS(2)O(7)(2–) → C(2n–) 的化学计量，发现 n = 1。因此，根据 MoO(3)含量，在二元 MoO(3)-K(2)S(2)O(7)熔融体系中形成单体 MoO(2)(SO(4))(2)(2–) 和/或缔合的 MoO(2)(SO(4))(2)(2m–) 配合物，并提出了与拉曼数据完全一致的相关结构模型。推断出 Mo 的六配位。相邻的 MoO(2)(2+)核通过双齿桥连硫酸盐连接。在浓熔（即高 X(MoO)(3)(0)）中，观察到的光谱变化可以通过 MoO(2)(SO(4))(2)(2m–) 的部分解离来解释，通过 S(2)O(7)(2–)的脱离和 Mo—O—Mo 桥的形成。在 MoO(3)-K(2)S(2)O(7)中加入 K(2)SO(4)会导致“后续”反应，并在三元 MoO(3)-K(2)S(2)O(7)-K(2)SO(4)熔融体系中形成 MoO(2)(SO(4))(3)(4–) 和/或缔合的 MoO(2)(SO(4))(3)(4m–) 配合物。Mo 的六配位包括两个氧化物配体和四个 O 原子，以各种对称性降低的环境连接到配位的硫酸盐基团。钼氧代硫酸盐配合物的最特征拉曼带涉及 Mo(═O)(2)伸缩模式：(1) 在 957（极化）和 918（去极化）cm(-1)处为 MoO(2)(SO(4))(2)(2–) 和 MoO(2)(SO(4))(2)(2m–)的 ν(s)和 ν(as)Mo(═O)(2) 模式，(2) 在 935（极化）和 895（去极化）cm(-1)处为 MoO(2)(SO(4))(3)(4–)和 MoO(2)(SO(4))(3)(4m–)的各自模式。结果与在假定的孤立气态自由状态下，在 DFT/B3LYP (HF) 水平和 3-21G 基组上对 MoO(2)(SO(4))(3)和{MoO(2)}(2)(SO(4))(4)(μ-SO(4))(2)离子进行的从头算量子化学计算相吻合，在 Gaussian 03W 程序中使用力常数计算了红外和拉曼光谱。
