Formation of mono- and binuclear complexes of Nd3+ with d-gluconate ions in hyperalkaline solutions – Composition, equilibria and structure

•Equilibria in strongly alkaline solutions of Nd3+ and d-gluconate were studied.•Formation of mono- and binuclear complexes was proven in solutions of pH > 12.•Nd2Gluc4H–53–, Nd2Gluc4H–64–, Nd2Gluc6H–44–, Nd2Gluc6H–55– and NdGluc2H–54– were identified.•The stability constants of these mono- and binuclear complexes were determined.•The model was validated with NMR, Raman, ESI-MS and freezing-point depression.