3-Formylsalicylic acid oxime (H₃L) formed the following dinuclear Cu^II and Ni^II complexes: [Cu₂(HL)₂]·0.5H₂O (1), Na[Cu₂(HL)(L)]·3H₂O (2) and [Ni₂(HL)₂]·2.5H₂O (3). The structures of Na[Cu₂(HL)(L)(H₂O)] (2′) and [Ni₂(HL)₂(H₂O)₄]·8H₂O (3′) have been determined by X-ray crystallography. Complex 2 has a cis arrangement of the two ligands providing dissimilar {CuN₂O₂} and {CuO₄} chromophores sharing the two phenolic oxygen atoms. The N₂O₂ cavity has a hydrogen-bonded N–O⋯H⋯O–N linkage as the lateral chain, and the Cu in this site has a square-pyramidal geometry with a water molecule at the axial site. The Cu in the O₄ cavity has a planar geometry. Complex 3 has a trans configuration with respect to its two ligands and each Ni has a six-coordinate geometry with two water molecules at the axial sites. Complex 1 has a trans configuration based on its having a chemical formula and IR spectrum similar to 3. The following interconversion among dinuclear Cu complexes has been established by pH adjustment: trans-[Cu₂(HL)₂] (1) ⇌  cis-[Cu₂(HL)(L)]⁻ (2) ⇌  trans-[Cu₂(L)₂]²⁻ (water molecules are omitted). On the other hand, 3 showed the following interconversion: trans-[Ni₂(HL)₂] (3) ⇌  trans-[Ni₂(L)₂]²⁻. The cis Cu2 complex 2 was reacted with Mn^II to afford [Mn{Cu₂(HL)(L)}₂(H₂O)₄]·H₂O·2DMF (4) that has a linear pentanuclear Cu^IICu^IIMn^IICu^IICu^II structure formed by the coordination of two molecules of 2 to a Mn^II through a carboxylate group.