The di-2-pyridylketone ligand (dpk) exhibits several coordination modes and is a good candidate for preparation of a variety of metal complexes. In this work we present a potentiometric study (in water and in ethanol : water mixtures) of Ln-dpk and Cu(II)-dpk complexes. The thermodynamic stability of the species with La, Sm and Yb is compared to that of Cu(II). In addition, [Ln(NCS)3{(py)2C(OEt)(OH)}3] (Ln = Pr, Sm, Gd) and [Cu(SCN)2{(py)2C(OEt)(OH)}]2 · 2EtOH have been prepared and characterized by X-ray diffraction. ∥Dedicated to Professor Alfredo Mederos on the occasion of his retirement as Professor of Inorganic Chemistry of Universidad de La Laguna, Tenerife, Spain.