In situ diffuse reflectance UV/visible/near-IR and EPR spectroscopies, and also XAFS, were used to study the changes in the coordination sphere of copper complexes during the different steps of preparation by cation exchange of supported Cu/SiO₂ catalysts. Three different Cu^II precursors were used: [Cu(NH₃)₄(H₂O)₂]²⁺, [Cu(en)₁(H₂O)₄]²⁺ and [Cu(en)₂(H₂O)₂]²⁺. Before drying, the coordination sphere of the different Cu^II complexes remains the same as in solution, and the complexes are in electrostatic interaction with the silica support. Depending on the strength of the ligands, the Cu^II complexes are grafted onto the silica support as (SiO)₂Cu(NH₃)₂(H₂O)₄ or (SiO)₂Cu(en)₁(H₂O)₂, or remain in electrostatic interaction with the latter as [Cu(en)₂(H₂O)₂]²⁺ when the samples are dried at 25°C. Extended drying at 100°C and re-exposure to air induces weak loss of NH₃ and en ligands, and some water ligands are reversibly eliminated. When the samples are calcined, the NH₃ and en ligands are completely eliminated, and the same three Cu^II species are identified on the three samples: (SiO)₂Cu^II(H₂O)_4−x, (SiO)₃Cu^II and pairs of octahedral Cu^II species. On exposure to air, the three species transform into a single species: (SiO)₂Cu^II(H₂O)₄.