The interaction of Eu(III) with organoborates – a further approach to understand the complexation in the An/Ln(III)–borate system

The formation equilibria of salicylatoborate, lactatoborate and 3-hydroxybutyratoborate were studied by means of 11B NMR spectroscopy. The smaller the pKa of the respective organic acid, the higher is the formation constant of the organoborate. The complexation of Eu(III) with salicylatoborate and lactatoborate was investigated by means of TRLFS (time-resolved laser-induced fluorescence spectroscopy) and 11B NMR spectroscopy, yielding complexation constants lg β0(11) = 2.6–3.2. A Eu(III)–3-hydroxybutyrate complex was characterized by TRLFS and 1H NMR spectroscopy (lg β0(11) = 2.89). DFT calculations of the investigated Eu(III)–organoborates and inorganic Eu(III)–(poly)borates provided information about the Eu(III) coordination (most likely chelate). They support the hypothesis that the complexation of Eu(III) with organic as well as inorganic borate structures containing the binding site “B(OR)4−” (R = H, threefold coordinated boron center(s), organic moiety) is comparable.