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 11 B 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 11 B NMR spectroscopy, yielding complexation constants lg β 0 11 = 2.6-3.2. A Eu(iii)-3-hydroxybutyrate complex was characterized by TRLFS and 1 H 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.