The nature of biomimetically relevant rate enhancement of hydrolysis in a coordination sphere of square-planar metal complexes suggested by an X-ray structural study of a,b-h,g-[Pt{o-C6H4C(Me)=NOC(=O)Me}(μ-Cl)]2

X-Ray structural data for a,b-h,g-[Pt{o-C₆H₄C(Me)=NOC(=O)Me}(μ-Cl)]₂ and ab initio quantum chemical calculations were used to show that the biomimetic hydrolysis of esters and amides within the coordination sphere of a square-planar complex, in general, and the deacylation of cyclometallated aryl oxime esters, in particular, is due to the stereochemical control which arises from the close proximity of the coordinated OH or H₂O ligand and the carbonyl carbon (O···C separation 3.47 Å) in the reactive complex [Pt{o-C₆H₄C(Me)=NOC(=O)Me}py(OH)] generated in aqueous solution.