A Bis(μ-phenoxo)-Bridged Dizinc Complex with Hydrolytic Activity

The dinuclear complex [Zn2(papy)2]·2CH3OH [H2papy = N-
(2-hydroxybenzyl)-N-(2-picolyl)glycine] was synthesized and characterized.
The crystal structure of the complex reveals that both ZnII ions
are pentacoordinate with distorted pentagonal bipyramidal coordination
arrangements. The phenoxyl groups of each ligand bridge the two
metal atoms, whereas each carboxylate of the ligand is terminally
bound to one ZnII ion. Potentiometric studies of the ZnII:H2papy system
in a methanol/water mixture show the existence of a mononuclear species at lower pH; but at a pH above 5, a dimeric species starts to
dominate and transforms further into a bis(μ-phenoxo) bridged dizinc
complex by deprotonation of phenolic hydrogen. A kinetic study of
the hydrolysis of bis(2,4-dinitrophenyl)phosphate at different pH, catalyzed
by complex 1, indicates a maximum rate at pH 9, where the
bis(μ-phenoxo)-bridged dizinc species corresponding to 1 dominates
in solution.