Insights into coextraction of water and ammonia with nickel(II) through structural investigation

The coordination structures of the nickel(II) complexes of 4-ethyl-a-pheneyl-1,3-octadione (denotes A) formed upon solvent extraction from ammoniacal media have been investigated. The combination analysis of their X-ray absorption spectroscopy with IR, UV-Vis and NMR spectroscopies provides a molecular-level understanding on the coextraction behavior of both water and ammonia molecules during nickel extraction. XANES spectra not only verify that the nickel extracts with octahedral configuration are independent on aqueous pH of ammoniacal solutions; and also demonstrates the structures are independent of the nickel complexes being solid or in solution. The structural investigation and elemental analysis of solid nickel extract indicate that both water and ammonia molecules can simultaneously coordinate with nickel extract to form a hexa-coordination complex of NiA2·H2O·NH3. The structural parameters of nickel extracts were extracted by EXAFS fitting. The mean Ni-Oeq bond length of nickel chelate rings is 2.00 Å, and the mean Ni-O/Nax bond length of axially coordinated water and ammonia is 2.09 Å.