The formation equilibria of salicylatoborate, lactatoborate and 3-hydroxybutyratoborate were studied by means of (11)B 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 (11)B NMR spectroscopy, yielding complexation constants lg β₁₁⁰ = 2.6-3.2. A Eu(III)-3-hydroxybutyrate complex was characterized by TRLFS and (1)H NMR spectroscopy (lg β₁₁⁰ = 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.