Two original dinuclear (LnYb, 3 and LnEr, 4) and one trinuclear Cu^II-Ln^III-Cu^II (LnGd, 5) complexes derived from a polydentate non symmetrical Schiff base ligand H₂L have been prepared. The ligand possesses two functions (phenol and oxime) able to coordinate the Ln ions, but structural studies (X-ray diffraction and powder X-ray diffraction) show that the Cu^II and Ln^III ions are only bridged by the oximato (N-O) pair. The missing phenoxo bridge is replaced by a surprising pseudo-bridge involving one oxygen atom of the nitrato anion linked to the Cu and Ln ions according to a η²: η¹: μ mode. Although this latter contact has no role from the magnetic point of view, it introduces a large deformation of the unique bridging network. The Cu-Yb complex 3 and the trinuclear Cu-Gd-Cu complex 5 present antiferromagnetic interactions, with a J_CuGd interaction equal to −1.25cm⁻¹ in 5. The genuine single bridge can be considered as responsible for the antiferromagnetic character of the interaction.