Functional tetranuclear square grids synthesized by in situ oxidation of ligand

A series of functionalized square [2 × 2] grids [M4(L-O)4] was prepared by the reactions of metal ions M with ligands 2,6-bis(pyrazine-2-carboxamido)pyridine (H2L) whose central pyridine were interestingly oxidized into pyridine-N-oxide in the formation of those grids to produce the new anionic ligands (L-O)2−. The selective oxidation of the central pyridine of H2L into pyridine-N-oxide through in situ reactions under an air condition as well as the properties of the resultant grids is of a certain practical significance.