Gas phase hydrolysis and oxo-exchange of actinide dioxide cations. Elucidating intrinsic chemistry from protactinium to einsteinium

Gas-phase bimolecular reactions of metal cations with water provide insights into intrinsic characteristics of hydrolysis. For the actinide dioxide cations, actinyl(V) AnO${}_2$${}^{+}$, melding of experiment and computation provides insights into trends for hydrolysis, as well as for oxo-exchange between actinyls and water that proceeds by a hydrolysis pathway. Here this line of inquiry is further extended into the actinide series with CCSD(T) computations of potential energy surfaces, for the reaction pathway for oxo-exchange through hydrolysis of nine actinyl(V) ions, from PaO${}_2$${}^{+}$ to EsO${}_2$${}^{+}$. The computed surfaces are in accord with previous experimental results for oxo-exchange, and furthermore predict spontaneous exchange for CmO${}_2$${}^{+}$, BkO${}_2$${}^{+}$, CfO${}_2$${}^{+}$ and EsO${}_2$${}^{+}$, but not for AmO${}_2$${}^{+}$. Natural Bond Order analysis of the species involved in both hydrolysis and oxo-exchange reveals an inverse correlation between the barrier to hydrolysis and the charge on the actinide centre, q(An). Based on this correlation, it can be concluded that hydrolysis, and related phenomena such as oxo-exchange, become less favourable as the charge on the metal centre decreases. The new results provide a straightforward rationalization of trends across a wide swathe of the actinide series. (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)