Synthesis, Magnetic Properties, and Phosphoesterase Activity of Dinuclear Cobalt(II) Complexes

A series of dinuclear cobalt­(II) complexes has been prepared and characterized to generate functional and spectroscopic models for cobalt­(II) substituted phosphoesterase enzymes such as the potential bioremediator GpdQ. Reaction of ligands based on 2,2′-(((2-hydroxy-5-methyl-1,3-phenylene)­bis­(methylene))­bis­((pyridin-2-ylmethyl)­azanediyl)))­diethanol (<b>L1</b>) and 2,6-bis­(((2-methoxyethyl)­(pyridin-2-ylmethyl)­amino)­methyl)-4-methylphenol (<b>L2</b>) with cobalt­(II) salts afforded [Co₂(CO₂EtH₂<b>L1</b>)­(CH₃COO)₂]­(PF₆), [Co₂(CO₂Et<b>L2</b>)­(CH₃COO)₂]­(PF₆), [Co₂(CH₃<b>L2</b>)­(CH₃COO)₂]­(PF₆), [Co₂(Br<b>L2</b>)­(CH₃COO)₂]­(PF₆), and [Co₂(NO₂<b>L2</b>)­(CH₃COO)₂]­(PF₆). Complexes of the <b>L2</b> ligands contain a coordinated methyl-ether, whereas the <b>L1</b> ligand contains a coordinated alcohol. The complexes were characterized using mass spectrometry, microanalysis, X-ray crystallography, UV–vis–NIR diffuse reflectance spectroscopy, IR absorption spectroscopy, solid state magnetic susceptibility measurements, and variable-temperature variable-field magnetic circular dichroism (VTVH MCD) spectroscopy. Susceptibility studies show that [Co₂(CO₂EtH₂<b>L1</b>)­(CH₃COO)₂]­(PF₆), [Co₂(CO₂Et<b>L2</b>)­(CH₃COO)₂]­(PF₆), and [Co₂(CH₃<b>L2</b>)­(CH₃COO)₂]­(PF₆) are weakly antiferromagnetically coupled, whereas [Co₂(Br<b>L2</b>)­(CH₃COO)₂]­(PF₆) and [Co₂(NO₂<b>L2</b>)­(CH₃COO)₂]­(PF₆) are weakly ferromagnetically coupled. The susceptibility results are confirmed by the VTVH MCD studies. Density functional theory calculations revealed that magnetic exchange coupling occurs mainly through the phenolic oxygen bridge. Implications of geometry and ligand design on the magnetic exchange coupling will be discussed. Functional studies of the complexes with the substrate bis­(2,4-dinitrophenyl) phosphate showed them to be active towards hydrolysis of phosphoester substrates