Investigation of metal–ion complexes of triazino crown ethers with podand arms by electrospray ionization

Abstract

Double-armed triazino diaza crown ethers form stable complexes with alkali cations. In electrospray ionization [C2M]+ ions from 2:1 complexes appear additionally to the [CM]+ ions (C = crown ether ligand, M = metal). The portion of 2:1 complexes depends on the podand type. On collision-induced dissociation the [C1C2M]+ ions of asymmetrical 2:1 complexes form [CM]+ fragments with different intensities in correspondence to the complex stability. Triazino crown ethers with donor-active hydroxyalkyl podands give more stable 1:1 complexes with K+. However, this was only found in the larger of the two ring sizes compared. The electrospray ionization of solutions composed of Mg(II),Mn(II), Ni(II), Cu(II), Zn(II) or Mg(II) nitrates and triazino crown ethers generates four different types of metal complexes. However, the sum of all complex ions is only small compared to the total ion sum. Crown ethers without acidic hydrogen form [CM(II)NO3]+ ions. Hydroxyalkyl substituted triazino crown ethers produce [(C – H)M(II)]+ ions. With copper containing solutions of some crown ether types additionally [CCu(I)]+ are obtained at higher cone voltages. Only with Cd2+ doubly-charged complex ions like [CM(II)]2+ are found with significant intensities. In all cases the conventionally protonated molecule appears as the base peak in the ESI spectra.