Anion control of isomerism, crystal packing and binding properties in a mononuclear zinc complex

The coordination chemistry of the tetradentate pyridyl N-donor ligand cis-3,5-bis-[2-pyridinyleneamin]-trans-hydroxycyclohexane (DDOP) has been investigated with zinc(II) nitrate and triflate. The resulting complexes, [Zn(DDOP)(H2O)(NO3)](NO3) (1), and [Zn(DDOP)(H2O)(OTf)](OTf) (2) differ not only in their counterions, but also the arrangement of the axial ligands and their solid state hydrogen bonded networks. Isothermal titration calorimetry was used to assess the difference in binding properties exhibited by the two zinc complexes at physiological pH in an aqueous environment. A series of coordinating amino acids were found to preferentially bind to the mononuclear zinc triflate (1) complex over the corresponding nitrate (2) assembly, with histidine exhibiting a two centre binding mode.

Mononuclear zinc(II) complexes of the tetradentate pyridyl N-donor ligand cis-3,5-bis-[2-pyridinyleneamin]-trans-hydroxycyclohexane (DDOP) have been synthesised with nitrate and triflate counterions. The nature of the anion is seen to exert a significant influence on the arrangement of the axial ligands, construction of the solid state hydrogen bonded networks, and the ability to bind amino acid substrates.Figure optionsDownload as PowerPoint slide