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Flash Photolysis Studies of Roussin's Black Salt Anion: Fe(4)S(3)(NO)(7)(-)
James Bourassa1, Brian Lee, Stefan Bernard
1Department of Chemistry, University of California, Santa Barbara Santa Barbara, California 93106-9510, and Integrated Spectroscopy Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545.
Abstract:
A time-resolved optical (UV-vis) spectroscopic study of Roussin's black salt anion, Fe(4)S(3)(NO)(7)(-), revealed two separate intermediates, X and Y, following laser flash photolysis. Both intermediates react with nitric oxide with second-order kinetics to re-form the parent complex (k(NO)(X)() = 1.3 x 10(7) M(-)(1) s(-)(1); k(NO)(Y)() = 7.0 x 10(5) M(-)(1) s(-)(1) in aqueous solutions). The shorter-lived intermediate X was observed in time resolved infrared spectroscopic studies. Isotopic labeling experiments involving the exchange of black salt nitrosyls with (15)NO(2)(-) or (15)N(18)O were used to probe the correlation between nu(NO) bands and the anion structures. The identities of the intermediates are interpreted in terms of photolytic loss of chemically distinct nitrosyls found on the Fe(4)S(3)(NO)(7)(-) anion.