Alcoholysis of 2,2'-pyridil, (2-C5H4N)C(O)C(O)(2-C5H4N), in the presence of copper(II): A family of planar pentanuclear copper(II) complexes stabilized by [(2-C5H4N)C(O)(OR)C(O)(OR)(2-C5H4N)](2-) and carboxylate ligands