Double-Proton-Transfer Processes in Dithiooxamide: UV-Induced Dithione → Dithi...

• Author(s): Lapinski, Leszek ; Rostkowska, Hanna ; Khvorostov, Artem ; Yaman, Müjgan ; Fausto, Rui ; Nowak, Maciej J.
• Date: 2004
• Persistent ID: http://hdl.handle.net/10316/17880
• Origin: Estudo Geral - Universidade de Coimbra
• Document Type: Article
• Language: English

Description

Dithiooxamide [rubeanic acid, NH2C(S)C(S)NH2)] monomers were studied by FTIR spectroscopy combined with the low-temperature matrix-isolation technique. The most stable dithione−diamino tautomer of the compound was exclusively observed in argon matrixes immediately after deposition. Upon UV (λ > 345 nm) irradiation the dithione−diamino form transformed, by a double-proton transfer, into the dithiol−diimino tautomer. Theoretically supported analysis of the infrared spectrum emerging upon UV irradiation allowed identification of one of the conformers of the dithiol−diimino tautomer as the dominating photoproduct. Smaller quantities of other conformers of the dithiol−diimino tautomer were also found to be photogenerated. For the UV-irradiated matrix kept subsequently at 10 K and in darkness, a dithiol−diimino → dithione−diamino tautomerization leading to partial recovery of the initial form of the compound was observed. The only possible mechanism of this ground-state transformation at cryogenic temperature is synchronous double-proton tunneling. The experimentally obtained time constant of this process was 18 h.