Effects of Intramolecular Hydrogen Bonding on the Rates of Complex Formation of Co2+ and Zn2+ with Substituted Salicylic Acids

Article abstract of DOI:10.1021/j100342a006

The kinetics of the complex formation of Co²⁺ and Zn²⁺ with two substituted salycilates have been investigated and compared to those of Ni²⁺ (reported previously).The rate constants for the unprotonated salicylates are consistent with a rate-determining first substitution step at the respective aquometal ion.Because of strong intramolecular hydrogen bonding, the monoprotonated ligands are much less reactive (80-4000-fold).The metal ion dependence of the rate constants for these species leads to the conclusion that in the rections involving Ni²⁺ and Co²⁺ ring closure is rate determining, whereas in case of the very labile Zn(II) the opening of the internal H bond in the initial complex becames rate determining.