A novel 24-membered macrocyclic compound having two hydroxyethyl pendants L, 3,6,9,17,20,23-hexazatricyclo[23.3.1.1.11,15]triconta-1(29),11(30),12,14,25,27-hexaene-6,20-bis(2-hydroxyethyl), has been synthesized as a dinucleating ligand. A new complex [Zn2H−2L]Br2(H2O)2 has been synthesized as a model to mimic the active center of alkaline phosphatase. The bridging coordination of the two alkoxides to two ZnII ions was confirmed by the crystal structure of [Zn2H−2L]Br2(H2O)2. The protonation constants of L as well as complexation constants of L with ZnII have been determined at 298.1 K by means of potentiometric titration. [Zn2H−2L]2+ and [Zn2H−2L(OH)]+ are the dominant species in aqueous solution at 7 < pH < 9. The kinetics of promoted hydrolysis of p-nitrophenyl acetate has also been studied; the second-order rate constant is 0.018 M−1 s−1 at pH = 9.0.
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