Studies on singlet oxygen in aqueous solution. Part 2. Water-soluble square-planar nickel complexes as quenchers

Abstract

Three water-soluble square-planar nickel complexes have been investigated as quenchers of ¹O₂ in aqueous solution, using anthracene-9,10-bis(ethanesulphonate) as a trap. Disodium [NN′-ethylenebis(5-sulphosalicylideneiminato)] nickelate(II) and its propylene analogue are efficient quenchers, with k_Q= 1.6 × 10⁹ and 1.3 × 10⁹ dm³ mol^–1 s^–1 respectively. The value of k_Q, for disodium [NN′-o-phenylenebis(5-sulphosalicylideneiminato)] nickelate(II) is much less, and seems to be concentration-dependent. This is attributed to aggregation, in agreement with the electronic and ¹H n.m.r. spectra.