Ultraviolet photochemistry of Co{sup III}L(H{sub 2}O)SO{sub 3}{sup +} [L = Me{sub 6}[14]dieneN{sub 4}, [14]aneN{sub 4}] complexes. Quandaries about the linkage isomerization to O-bonded sulfite and the photogeneration of cobalt(I) in sequential biphotonic photolysis

The catalyzed and uncatalyzed oxidation of sulfite have been a matter of continued interest. Attention to these processes has a basic science motive as well as the need to resolve a number of long-recognized technical problems, i.e., gas desulfurization, pollution, and health problems. Two new macrocyclic complexes with S-bonded sulfite, Co(Me{sub 6}[14]diene N{sub 4})(H{sub 2}O)SO{sub 3}{sup +} and Co([14]ane N{sub 4})(H{sub 2}O)SO{sub 3}{sup +}, were prepared. The type of the So{sub 3}{sup 2{minus}} linkage in [Co(Me{sub 6}[14]diene N{sub 4})(H{sub 2}O)SO{sub 3}]ClO{sub 4} was established by means of the X-ray structure (crystal system, orthorhombic). In a study of the photochemical properties, transient spectra revealed the photoredox formation of Co(II) macrocycles and the photoisomerization to O-bonded sulfite. Precursors of these products were also observed and tentatively identified as an ion pair and an adduct of the SO{sub 3}{sup {sm_bullet}{minus}} radical and the unsaturated macrocycle Me{sub 6}[14]diene N{sub 4}. The photogeneration of SO{sub 3}{sup {sm_bullet}{minus}} was verified by means of the radical`s ESR spectrum. High power laser irradiations resulted in the secondary photolysis of the intermediates and the formation of Co(I) products. The mechanism of the primary and secondary photolysis is discussed.