A new Cu (II) complex with bidentate o-phenanthroline (phen) ligand, ([Cu(phen)](2)(H2PO4)(2)HPO4)(2)(H3PO4)(4), has been synthesized and characterized by single crystal X-ray diffraction, IR spectroscopy and magnetic data. The crystal structural analysis shows that the title compound contains two phosphate-bridged dimeric units ([Cu(phen)](2)(H2PO4)HPO4), which are crystallographically independent. In these units, each copper atom is five coordinated and the geometry around the Cu(II) can be described as slightly distorted square-based pyramidal, with tau parameter varying between 0.001 and 0.04. The crystal structure is stabilized by O-HaEuro broken vertical bar O and C-HaEuro broken vertical bar O hydrogen bonds between the dimeric units and the phosphoric acid molecules. In addition, the organic ligands are associated by pi-pi stacking interactions between neighboring non-nitrogen aromatic rings. The infrared spectrum recorded at room temperature was interpreted on the basis of data published in the literature. The magnetic susceptibilities data show a weak intra-dimer ferromagnetic interaction with J = 31.8 K.