Mechanistic information from oxygen-17 NMR measurements. Evidence for the existence of oxygen-bonded (sulfito)pentaamminecobalt(III) in weakly acidic aqueous solution

Abstract

It has been suggested in the literature that Co(NH3)5OH2+ reacts with S02 in aqueous solution to produce an O-bonded sulfilo complex Co(NH3)5OS02+, which on acidification releases S02 and forms the corresponding aquo complex. The kinetics of both processes suggested that no Co-0 bond breakage is involved. l70-exchange experiments have now been performed with nO NMR and indicate that the earlier suggestions are correct.

Thermal and photochemical reactions of bis(diamine)(sulfito)cobalt(III) complexes: effect of chelate-ring size

“…This is understandable as the reaction involves addition of SO 2 to the Co III ᎐OH bond. 1 The SO 2 (OH) Ϫ ion is reported to have a long S᎐OH bond. 35 Thus the lack of a significant dependence of k 1 on the steric and electronic effects of the ligands bound to cobalt() might indicate that the bond between Co III ᎐OH and SO 2 [Co III ᎐(H)O ؒ ؒ ؒ SO 2 ] is long enough in the transition state to be influenced by the non-labile ligands bound to the cobalt() centre.…”

“…. 4 Accordingly the observed rate constant is given by equation (1) where k 1 , k Ϫ1 denote the rate constants…”

“…Using pK 3 = 6.0 and the known values of pK 1 , pK 2 (see footnote reversible. The values of k 1 , K 3 Ϫ1 and Q being known from the formation study (see footnote b of Table 2), k Ϫ1 was calculated from the k obs data using equation (1). Values of k Ϫ1 are also collected in Table 2.…”

“…The O-and S-bonded sulfito complexes of cobalt() differ remarkably in their reactivities. [1][2][3][4][5][6][7][8][9][10][11] While the O-bonded species, Co III ᎐OSO 2 ϩ , is formed by the addition of SO 2 to the Co III ᎐OH bond, 1-4 the corresponding S-bonded isomers result either by isomerisation of the former 4-6 and/or direct replacement of co-ordinated H 2 O (OH Ϫ ) in Co III ᎐OH 2 (OH) species by (-S-)-SO 3…”

Chemistry of Multiphase Atmospheric Systems

“…The catalytic process is presumably only of minor importance in cloud or rain droplets compared to H202 or 03 chemistry (Martin [47]; Penkett [52]). It is however possible that metal ion complexes contribute significantly to the generation of H202 in the presence of U.V.…”