Circular dichroism spectrophotometric determination of metal ions using optically active tris(thiolato) type rhodium(III) complexes

Sparingly soluble neutral fac(S)-[Rh(aet)₃] was newly optically resolved in order to apply the optically active isomer as a CD-inducing reagent to the circular dichroism (CD) spectrophotometric determination of the transition metal ions. Simple determinations of cobalt(II) and nickel(II) and a simultaneous determination for the binary solution were successful by using an excess of powdery Λ-fac(S)-[Rh(aet)₃] with the dissolution equilibrium. A more sensitive determination of the transition metal ions, such as iron(III), iron(II), cobalt(III), cobalt(II), and nickel(II), was possible by using a homogeneous solution of Λ(LLL)-fac(S)-[Rh(L-cys-N,S)₃]^3- without the dissolution equilibrium. The latter CD spectrophotometric determination is quite effective for a simultaneous determination of the transition metal ions in binary and ternary solutions of metal ions, such as iron(III)-cobalt(III), cobalt(III)-cobalt(II), and cobalt(II)-nickel(II)-zinc(II).