Variable-temperature and -pressure nitrogen-14 magnetic resonance studies on solvent exchange of nickel(II), iron(II), and manganese(II) ions in neat 1,3-propanediamine and n-propylamine

The solvent exchanges of nickel(II), iron(II), and manganese(II) ions in 1,3-propanediamine (tn) and n-propylamine (pal have been studied by the (NNMR)-N-14 line-broadening method. The rate constants of the amine exchanges for the first-row transition metal ions are in the order of ethylenediamine (en) < tn < pa, which is largely affected by the difference in the activation enthalpies. The differences in the rate constants and the activation enthalpies among the three amine solvents become greater along the series from manganese(II) ion to nickel(II) ion. These kinetic results have clarified that the differences in the kinetic chelate strain effect in the transition state and the chelate strain effect in the ground state can be attributed to the difference in the chelate ring sizes and the ion radii.