Insights into the extraction mechanism from the coordination chemistry of copper(II) with a synergistic mixture which mimics Versatic10 and 2-ethylhexyl 4-pyridinecarboxylate ester

In the present work, a copper(II) synergist complex with methyl isonicotinate (L^I, a short chain analog of 2-ethylhexyl 4-pyridinecarboxylate ester) and isobutyric acid (HB^I, a short chain analog of Versatic10) was synthesized and studied by X-ray single-crystal diffraction. The results indicated that the copper(II) synergist complex obtained with isobutyric acid and methyl isonicotinate crystallizes in the monoclinic C2/c space group and confirmed the composition Cu(B^I)₂(L^I)]₂. The crystal structure consisted of centrosymmetric dimeric units, in which the two Cu ions are bridged in pairs by four carboxylate groups of the deprotonated isobutyric acid. In order to bridge the gap between the solid-state structure of the copper(II) synergist complex obtained with isobutyric acid and methyl isonicotinate and the solution structure of the extracted copper(II) complex in the non-polar organic phase, the two copper(II) complexes were further investigated by Fourier transform infrared spectroscopy (FT-IR) and electrospray ionization mass spectrometry (ESI-MS). The results indicated that the extracted copper(II) complex in the non-polar organic phase has a similar coordination structure as the copper(II) synergist complex obtained with isobutyric acid and methyl isonicotinate.