Hydrogen-1 nuclear magnetic resonance studies of the ion association of some unsymmetrically substituted tetra-alkylammonium tribromo(triphenylphosphine)cobaltate(II) complexes in various solvents
Hydrogen-1 nuclear magnetic resonance studies of the ion association of some unsymmetrically substituted tetra-alkylammonium tribromo(triphenylphosphine)cobaltate(II) complexes in various solvents
复制标题
一些不对称取代的四烷基铵三溴（三苯基膦）钴（II）络合物在各种溶剂中的离子缔合的氢1核磁共振研究
DOI：
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发表时间：
1976
期刊：
影响因子：
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通讯作者：
Y. Lim
中科院分区：
文献类型：
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作者：
T. Tan;K. Chua;Y. Lim
用核磁共振方法测定了34℃时[NME(n-C8H17)3][CoBr3(PPh3)]在硝基苯中的浓度缔合常数。光谱分析。将这一结果与[NRBun3][CoBr3(PPh3)](R=Me和Bun)的结果进行了比较，得出结论：阳离子的对称性对决定这类离子对络合物的离子缔合程度起着非常重要的作用。观察到的N-甲基和N-亚甲基质子各向同性位移的差异与Iµ⩽10溶剂的介电常数(Iµ)之间存在线性关系，但在较高的Iµ值时则不是线性相关。这可以从N-甲基对阴离子的择优取向、离子间距离随I_u减小而减小、在低介电常数的溶剂中形成胶束以及在高介电常数的溶剂中形成1：1离子对来解释。讨论了分析低介电常数溶剂中观测到的各向同性位移随浓度变化的问题。
The concentration association constant of [NMe(n-C8H17)3][CoBr3(PPh3)] in nitrobenzene at 34 °C has been determined by n.m.r. spectrometry. On comparing this result with those obtained earlier for [NRBun3][CoBr3(PPh3)](R = Me and Bun), it is concluded that the symmetry of the cation plays a very important role in determining the extent of ion association for this type of ion-pair complex. There is a linear correlation between the observed difference in isotropic shift of the N-methyl and N-methylene protons and the dielectric constant (Iµ) of the solvents for Iµ⩽ 10, but not at higher values of Iµ. This is interpreted in terms of the preferred orientation of the N-methyl group towards the anion, the decrease in interionic distance with decreasing Iµ, the formation of micelles in solvents of low dielectric constant, and the 1:1 ion-pair formation in solvents of higher dielectric constant. The problem of analyzing the concentration dependence of observed isotropic shifts in solvents of low dielectric constant is discussed.