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

Abstract

The formation equilibria of salicylatoborate, lactatoborate and 3-hydroxybutyratoborate were studied by means of ¹¹B NMR spectroscopy. The smaller the pK_a 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 β⁰₁₁ = 2.6–3.2. A Eu(III)–3-hydroxybutyrate complex was characterized by TRLFS and ¹H NMR spectroscopy (lg β⁰₁₁ = 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.