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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 βSTACKABOVE0/ABOVEBELOW11/BELOW/STACK = 2.6–3.2. A Eu(iii)–3-hydroxybutyrate complex was characterized by TRLFS and 1H NMR spectroscopy (lg βSTACKABOVE0/ABOVEBELOW11/BELOW/STACK = 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. [ABSTRACT FROM AUTHOR]

In the presence of polyborates (detected by 11B-NMR) the formation of a weak Eu(III) borate complex (lg ß11 ˜ 2, estimated) was observed by time-resolved laser-induced fluorescence spectroscopy (TRLFS). This complex is a precursor for the formation of a solid Eu(III) borate species. The formation of this solid in solution was investigated by TRLFS as a function of the total boron concentration: the lower the total boron concentration, the slower is the solid formation. The solid Eu(III) borate was characterized by IR spectroscopy, powder XRD and solid-state TRLFS. The determination of the europium to boron ratio portends the existence of pentaborate units in the amorphous solid. [ABSTRACT FROM AUTHOR]