Modifying Lipophilicities of Zn(II) Coordination Species by Introduction of Ancillary Ligands: A Supramolecular Chemistry Approach

A homologous series of neutral Zn(II) coordination complexes including Zn(PNO)2 (1), Zn(PNO)2(3-Br-Py) (2), [Zn(PNO)2(1,10-phenanthroline)](H2O)5/3 (3), and Zn(PNO)2(2,2′-Bipy) (4), where PNO = deprotonated 2-hydroxypyridine N-oxide, have been synthesized and characterized. Complexes 2−4 were prepared by reacting ancillary ligands with complex 1. Ancillary ligands form coordinate bonds to transition metal center-Zn(II). Their solid-state crystal structures, solubilities, lipophilicities, and association−dissociation properties in aqueous phase have been investigated in the current work. Diffusion-ordered NMR data suggested that association−dissociation properties of mixed-ligand Zn(II) coordination complexes in the aqueous phase are greatly dependent upon the coordination mode of ancillary ligands to Zn(II). By introduction of ancillary ligands, we can rationally modify lipophilicities and solubilities of mixed-ligand Zn(II) coordination complexes on the basis of log P of the ancillary ligand. These in vi...