Scheme 2. Zn²⁺ competition and transfer among PyAHs. (a) Zn²⁺ distribution in the mixture of 1 equiv. of ¹A¹B and ¹A³B (3.5 mM each) and 0.5 equiv. of Zn²⁺. (b) Zn²⁺ distribution in the mixture of 1 equiv. of ¹A¹B and ¹A²B (3.5 mM each) and 0.5 equiv. of Zn²⁺. (c) Zn²⁺ distribution in the mixture of 1 equiv. of N-methylated and N–H PyAHs (^pA¹B and ^bA^hB) with different substituents on the R group of the hydrazide side (3.5 mM each) and 0.5 equiv. of Zn²⁺. (c) Zn²⁺ distribution in the mixture of 1 equiv. of N-methylated and N–H PyAHs with different substituents on the R group of the hydrazide side (3.5 mM each); (d) 0.5 equiv. of Zn²⁺ and 1 equiv. of Et₃N. The CH₂OCH₃ group was merely used to improve the solubility of N–H PyAHs bearing a para NO₂ group. In all cases, thermal equilibration was achieved by heating at 60 °C for 6 h. The size of the blue dots qualitatively indicates the relative amount of zinc complex within the pair of complexes formed in a given reaction.