Individual solvation number of first-row transition metal(II) ions in solvent mixtures of N,N-dimethylformamide and N,N-dimethylacetamide—Solvation steric effect
Individual solvation number of first-row transition metal(II) ions in solvent mixtures of N,N-dimethylformamide and N,N-dimethylacetamide—Solvation steric effect
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N,N-二甲基甲酰胺和N,N-二甲基乙酰胺溶剂混合物中第一列过渡金属(II)离子的单独溶剂化数——溶剂化空间效应
DOI：
10.1039/b107342g
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发表时间：
2001
影响因子：
3.3
通讯作者：
S. Ishiguro
中科院分区：
文献类型：
--
作者：
Y. Umebayashi;K. Matsumoto;Manabu Watanabe;S. Ishiguro
在298K下，用滴定拉曼光谱测定了N，N-二甲基甲酰胺、N，N-二甲基乙酰胺及其混合物中不同摩尔分数的高氯酸锰、镍、铜、锌溶液的拉曼光谱。DMF的660 cm−1处的面内OC-N弯曲振动和DMA的740 cm−1处的N-CH3伸缩振动表明，溶剂分子与金属离子配位后，其振动频率明显向高频移动。这些拉曼光谱被去卷积，并从自由溶剂带(不含ν)中提取与金属离子结合的溶剂带(ν)。通过分析自由溶剂带的强度随金属离子摩尔分数的增加而减小的情况，估算了与金属离子结合的溶剂分子数或混合溶剂中的单个溶剂化数n，即对DMF和DMA分别为nDMF和NDMA。结果表明，在混合物中，锰(II)离子在整个溶剂组成范围内是六配位的，即nDMF + ndma = 6，并且在混合物中符合nDMF/ndma = xDMF/xDMA关系，其中x表示溶剂的摩尔分数。对于锌(II)离子，随着混合物中xDMA的增加，总溶剂化数从6下降。在纯DMA中，提取了两个结合的溶剂带，表明锌(DMA)62+和锌(DMA)42+两种物种平衡共存。对于六配位的锌(II)溶剂化离子，nDMF/NDMA >； /xDMF/xDMA在混合物中保持关系。这表明DMA的溶剂化空间效应适用于六配位锌(II)溶剂化离子，而不是锰(II)溶剂化离子。铜(II)离子是六配位的，但由于Jahn-Teller效应，配位结构严重扭曲。事实上，提取了两个可归因于赤道位置和轴向位置的溶剂的谱带。在混合物中，nDMF/ndma >； xDMF/xDMA关系适用于赤道位置的溶剂，即溶剂分子间存在溶剂化空间效应，而nDMF/ndma ⩽ xDMF/xDMA关系适用于轴向位置的溶剂。这是预期的，因为对于轴向位置的溶剂来说，铜-氧(溶剂)键的长度更长，而对于DMA来说，电子对的给予能力略强一些。移位Δν的大小
(=νBound − νFree)强烈依赖于金属离子。事实上，在纯DMF和DMA中的Δν值根据关系Δν = (Ar)−n变化，该关系是金属离子离子半径r的函数，并估算了参数a和n。混合物中的位移Δν表明，M(DMF)6-−n(DMA)N_2+溶剂化离子的M-O(DMF)键长随着DMA配位数的增加而延长。
Raman spectra of solutions of manganese(II), nickel(II), copper(II) and zinc(II) perchlorate with varying molality were measured in N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA) and their mixtures by titration Raman spectroscopy at 298 K. The in-plane OC–N bending vibration at 660 cm−1 of DMF and the stretching N–CH3 vibration at 740 cm−1 of DMA show an appreciable shift to a higher frequency upon coordination of the solvent molecules to the metal ion. These Raman spectra were deconvoluted and the bound solvent bands (νbound) to the metal ion were extracted from the free solvent band (νfree). The number of solvent molecules bound to the metal ion or the individual solvation number n in a solvent mixture, i.e., nDMF and nDMA for DMF and DMA, respectively, were evaluated by analyzing the intensity decrease of the free solvent bands with increasing molality of the metal ion. It turned out that the manganese(II) ion is six-coordinated over the whole solvent composition range in the mixtures, i.e., nDMF + nDMA = 6, and the relationship nDMF/nDMA = xDMF/xDMA, where x denotes the mole fraction of the solvent, holds in the mixture. With regard to the zinc(II) ion, the total solvation number decreases from 6 with increasing xDMA in the mixtures. In neat DMA, two bound solvent bands are extracted, indicating that two species, Zn(DMA)62+ and Zn(DMA)42+, coexist in equilibrium. With the six-coordinate zinc(II) solvated ion, the relationship nDMF/nDMA > xDMF/xDMA holds in the mixture. This shows that the solvation steric effect of DMA operates for the six-coordinate zinc(II) solvated ion, unlike for the manganese(II) one. The copper(II) ion is six-coordinated, although the coordination structure is strongly distorted owing to the Jahn–Teller effect. Indeed, two bands ascribable to the solvents bound at the equatorial and axial positions were extracted. In the mixtures, the relationship nDMF/nDMA > xDMF/xDMA holds for solvents bound at the equatorial position, i.e., the solvation steric effect operates among solvent molecules, while the relationship nDMF/nDMA ⩽ xDMF/xDMA holds for solvents bound at the axial position. This is expected because the Cu–O(solvent) bond length is longer for the solvent at the axial position, and the electron-pair donating ability is slightly stronger for DMA. The magnitude of the shift Δν
(=νbound − νfree) depends strongly on the metal ion. Indeed, the Δν values in neat DMF and DMA vary according to the relationship Δν = (ar)−n, a function of the ionic radius r of the metal ion, and the parameters a and n were evaluated. The shift Δν in the mixtures implies that the M–O(DMF) bond length in the M(DMF)6−n(DMA)n2+ solvated ion is elongated with increasing coordination number nDMA of DMA.
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影响因子：
2.9
作者：
Inada, Y;Hayashi, H;Funahashi, S
通讯作者：
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