Stoichiometric diversity of Ni(II) metallacrowns with β-alaninehydroxamic acid in aqueous solution

The system consisting of Ni(II) and β-AlaHA (β-alanyl-hydroxamic acid was investigated in order to verify the possible formation of metallacrowns, in aqueous solution. The system Ni(II)/AHA (acetohydroxamic acid) was also studied, for the sake of comparison, The techniques used for this purpose were the following: potentiometry, which gives the speciation model consisting in the formation constants and stoichiometries of formed complexes; electro-spray ionization mass spectrometry (ESI-MS) , in order to confirm the stoichiometry of the species; solution calorimetry, giving the complex-formation thermodynamic quantities ΔH° and ΔS°, useful to hypothesize complex structure in combination with UV-Vis spectra at different pH values.