1 Synthesis, characterization, X-ray structural determination and theoretical study of the complexes [RuCp(8MTT-kS)LL’] (8MTT = 8-methylthio- theophyllinate; L,L’ = PTA, mPTA; L = mPTA, L’ = PPh3; PTA = 1,3,5-triaza- 7-phosphaadamantane, mPTA = N-methyl-1,3,5-triaza-7- phosphaadamantane). Lazhar Hajii, Vicente Jara-Pérez, Cristobal Saraiba-Bello, Gaspar Segovia- Torrente, Manuel Serrano-Ruiz, Antonio Romerosa * a Área de Química-Física y Química Inorgánica, Facultad de Ciencias Experimentales, Universidad de Almería, 04071 Almería – Spain Graphical Abstract Two new thiopurine-kS-complexes, [RuCp(8MTT-kS)(mPTA)(PPh3)] + (1) and [RuCp(8MTT-kS)(mPTA)2] 2+ (2) were synthesized and characterized by single crystal X-ray diffraction. The thiopurine coordination was evaluated by DFT theoretical methods by study of the isomer complexes in gas phase and water.