Study of binary and ternary metal complexes containing the sulfato ligand: molecular models for selected non-catalytic sites in sulfurylase

Abstract

[Cd^II(μ₂-O²,O′,O″-SO₄)(terpy)]₂·2H₂O, 1·2H₂O (terpy, 2,2′:6′,2″-terpyridine) was obtained from the reaction of 3CdSO₄·8H₂O with terpy and consists of centrosymmetric dimeric units in which the two Cd(terpy)²⁺ moieties are held together by two tridentate sulfato anions that act as chelators towards the two metal centres, one oxygen being tri-coordinate. This coordination mode for the sulfato ligand has never been reported before in the solid state. [Zn^II(μ₂-O,O′-SO₄)(terpy)]₂·2H₂O, 2·2H₂O, was obtained by using ZnSO₄·7H₂O through a procedure similar to that followed for 1·2H₂O. Semi-empirical quantum mechanics and density functional structure optimisations were performed at the AM1 and Becke3LYP/(6-31G**, S) levels. The computations reproduced well the main features of the Zn(μ₂-O,O′-SO₄)₂Zn unit as found in 2. A [Zn(imidazole)₂(O-OOCCH₃)₂(O-SO₄)]²⁻ model was also optimised as a model for ATP-sulfurylase from Saccharomices cerevisae.