Four copper complexes with hydroxylated bipyridyl-like ligands, namely [Cu₂(ophen)₂] (1), [Cu₄(ophen)₄(tp)] (2), [Cu₄(obpy)₄(tp)] (3), and [Cu₄(obpy)₄(dpdc)] · 2H₂O (4), (Hophen = 2-hydroxy-1,10-phenanthroline, Hobpy = 6-hydroxy-2,2′-bipyridine, tp = terephthalate, dpdc = diphenyl-4,4′-dicarboxylate) have been synthesized hydrothermally. X-ray single-crystal structural analyses of these complexes reveal that 1,10-phenanthroline (phen) or 2,2′-bipyridine (bpy) ligands are hydroxylated into ophen or obpy during the reaction, which provides structural evidence for the long-time argued Gillard mechanism. The dinuclear copper(I) complex 1 has three supramolecular isomers in the solid state, in which short copper - copper distances (2.66 - 2.68 Å) indicate weak metal-metal bonding interactions. Each of the mixed-valence copper(I,II) complexes 2-4 consists of a pair of [Cu₂(ophen)₂]⁺ or [Cu₂(obpy)₂]⁺ fragments bridged by a dicarboxylate ligand into a neutral tetranuclear dumbbell structure. Dinuclear 1 is an intermediate in the formation of 2 and can be converted into 2 in the presence of additional copper(II) salt and tp ligands under hydrothermal conditions. In addition to the ophen-centered π→π* excited-state emission, 1 shows strong emissions at ambient temperature, which may be tentatively assigned as an admixture of copper-centered d →s,p and MLCT excited states.