Dinuclear platinum(II) complexes, [{Pt(en)Cl}2(-qx)]Cl2·2H2O (1), [{Pt(en)Cl}2(-qz)](ClO4)2 (2), and [{Pt(en)Cl}2(-phtz)]Cl2·4H2O (3), were synthesized and characterized by different spectroscopic techniques. The crystal structure of 1 was determined by single-crystal X-ray diffraction analysis, while the DFT M06-2X method was applied in order to optimize the structures of 1–3. The chlorido Pt(II) complexes 1–3 were converted into the corresponding aqua species 1a–3a, and their reactions with an equimolar amount of Ac–L–Met–Gly and Ac–L–His–Gly dipeptides were studied by 1H NMR spectroscopy in the pH range 2.0