Zinc(II) complexes of tripodal ligands providing phenolate and pyridine donors: formation, structure and hydrolytic activity

Abstract

A group of zinc(II) complexes derived from tri- and tetra-dentate proligands bearing pyridyl and phenolic arms have been prepared and characterised. Potentiometric titrations suggested that a stepwise complexation initially to the pendant OH, and then to pendant O^– occurred. The crystal structures of [Zn₂L³₂][ClO₄]₂(L³= 2-{bis[2-(2-pyridyl)ethyl]aminomethyl}phenolate) and [Zn₂L⁶₂][Zn(NCS)₄]·0.5H₂O (L⁶= 2-{bis[2-(2-pyridyl)ethyl]aminomethyl}-4-nitrophenolate) reveal that both complexes are dimers in the solid state; the co-ordination geometries around zinc(II) can be best described as distorted square pyramidal with one pyridyl nitrogen atom, one tertiary nitrogen atom and two phenolic oxygen atoms forming the basal plane and a pyridyl nitrogen atom in the axial position. The interzinc separations are 3.284 Å and 3.274 Å respectively. The crystal structure of [Zn L⁷₂](L⁷= 4-nitro-2-{[2-(2-pyridyl)ethyl]aminomethyl}phenolate) reveals an octahedral complex with the zinc atom on a symmetry centre. The complexes [Zn₂L³₂][ClO₄]₂ and [Zn₂L⁶₂][BPh₄]₂, promote the hydrolysis of tris(4-nitrophenyl) phosphate; the former also has a small activity in the hydrolysis of bis(4-nitrophenyl) phosphate.