Hydrogen-1 nuclear magnetic resonance studies of the ion association of some unsymmetrically substituted tetra-alkylammonium tribromo(triphenylphosphine)cobaltate(II) complexes in various solvents

Tong Chiew Tan, Kee Lam Chua, Yau Yan Lim

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Abstract

The concentration association constant of [NMe(n-C8H17)3][CoBr3(PPh 3)] 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 (ε) of the solvents for ε ≤ 10, but not at higher values of ε. This is interpreted in terms of the preferred orientation of the N-methyl group towards the anion, the decrease in interionic distance with decreasing ε, 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.

Original languageEnglish
Pages (from-to)863-866
Number of pages4
JournalJournal of the Chemical Society, Dalton Transactions
Issue number10
DOIs
Publication statusPublished - 1976
Externally publishedYes

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