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.
|Number of pages||4|
|Journal||Journal of the Chemical Society, Dalton Transactions|
|Publication status||Published - 1976|