A study of the EPR frozen solution spectra of copper(II) citrate heterodinuclear species containing Mg(II), Zn(II) or Pd(II) has been carried out. The comparison of the spin Hamiltonian parameters suggests that copper(II) is in a coordination environment considerably different from that found in the case of the copper(II) mono-citrate complex. These results have been interpreted considering that two possible sites with different arrangements of oxygen donors are accessible to copper: a square-planar geometry for copper(II) heterodinuclear species containing Mg(Il) or Zn(II) or a tetragonally distorted octahedral geometry when the heterodinuclear species contains Pd(II).