SPECTROPHOTOMETRIC STUDY OF THIOCYANATO COMPLEXATION OF COBALT(II) AND NICKEL(II) IONS IN MICELLAR SOLUTIONS OF A NONIONIC SURFACTANT TRITON X-100

Complexation of cobalt(II) and nickel(II) with thiocyanate ions has be en studied by precise spectrophotometry in aqueous and micellar soluti ons of a nonionic surfactant Triton X-100 of varying concentrations (2 0-100 mmol-dm(-3)). With regard to cobalt(II), the formation of [Co(NC S)](+), [Co(NCS)(2)], and [Co(NCS)(4)](2-) was established. The format ion constant of [Co(NCS)(4)](2-) is increased with increasing concentr ation of the surfactant, suggesting that the [Co(NCS)(4)](2-) complex is formed in micelles. In contrast, the formation constants of [Co(NCS )](+) and [Co(NCS)(2)] are remained practically unchanged. On the othe r hand, with nickel(II), the formation of sole [Ni(NCS)](+) and [Ni(NC S)(2)] was established in both aqueous and micellar solutions examined , their formation constants being also remained unchanged. interesting ly no higher complex was confirmed in the nickel(ll) system, unlike co balt(II). The unusual affinity of the [Co(NCS)(4)](2-) complex with mi celles will be discussed from thermodynamic and structural points of v iew.