Complexation of late transition metal(II) ions (M = Co, Ni, Cu, and Zn) by a macrocyclic thiacrown ether studied by means of electrospray ionization mass spectrometry.

Electrospray ionization mass spectrometry (ESI-MS) is used to probe the metal-binding selectivity of a macrocyclic thiacrown ether (C(44)H(32)S(20)) towards Co(II), Ni(II), Cu(II), and Zn(II). In homogeneous 1:1 v/v methanol/dichloromethane solutions, it is found that the thia ligand very selectively binds traces of copper even in the presence of an excess of the other metal ions. The large selectivity is ascribed to the redox-active nature of copper which enables a reduction from Cu(II) to Cu(I), occurring upon ESI-MS, whereas Co(II), Ni(II) and Zn(II) cannot undergo similar redox reactions.