The hydration of all trivalent lanthanoid (Ln) ions is studied theoretically from two aspects: energy and wave function. With the help of the incremental scheme, for the first time the lanthanoid(III) aqua complexes are computed at the CCSD(T) level using large basis sets. These computations prove that SCS-MP2 is nearly as accurate as CCSD, thus enabling us to give the most accurate first principle hydration Gibbs free energies and reliable preferred coordination numbers (CNs) of lanthanoid(III) aqua complexes: 9, 8, and both, for light, heavy, and intermediate lanthanoids, respectively. Then a series of wave function analyses were performed to explore the deeper reasons for the preference of specific CNs. An unexpected observation is that as Ln goes from samarium to lutetium, the capping Ln-O bonds in nona-aqua lanthanoid complexes become weaker while they get shorter. Therefore, as the capping Ln-O bonds are getting easier to disrupt, heavier lanthanoids will prefer a low CN, i.e., 8. On the basis of this and previous work of other groups, a model for the water exchange kinetics of lanthanoid(III) ions is proposed. This model suggests that the capping Ln-O bonds of moderate strength, which occur for intermediate lanthanoids, are advantageous for the formation of a bicapped trigonal prism intermediate during water exchange. This explains some NMR experiments and, more importantly, an observation which puzzled investigators for a long time, i.e., that the exchange rate reaches a maximum for the middle region but is low at the beginning and end of the lanthanoid series. This nontrivial behavior of capping Ln-O bonds is interpreted and is believed to determine the hydration behavior of lanthanoid(III) ions.

The Gibbs energies of hydration of actinoid(III) ions are evaluated for density functional optimized geometries of [An(H2O)h](3+) complexes (h = 8, 9) at the coupled cluster singles, doubles, and perturbative triples level by means of the incremental scheme. Scalar-relativistic 5f-in-core pseudopotentials for actinoids and basis sets of polarized triple-ζ quality were applied. The calculated Gibbs energies for the octa- and nona-aquo complexes agree within 1% with the experimental values which are available only for uranium and plutonium. Compared to the hydrate complexes of the lanthanoid(III) ions those of the actinoid(III) series are slightly less stable.

Density functional calculations have been performed to study selected hydrated lanthanide(iii) motexafins (Ln-Motex, Ln = La, Gd, Lu) by using energy-consistent 4f-in-core lanthanide pseudopotentials to include the major relativistic effects due to the heavy metals. The maximum number (n) of water molecules bound strongly to [Ln-Motex] (Ln = La, Gd, Lu) was determined to be 6 by calculating the change of the Gibbs energies for the reactions [Ln-Motex(HO)] + HO → [Ln-Motex(HO)]. The number of water molecules coordinated directly to Ln was found to be 3 for La, and 2 for Gd and Lu. The explicit treatment of the tightly bound water molecules in [Ln-Motex(HO)] in combination with the COSMO solvation model yielded calculated reduction potentials and UV-vis absorption spectra in good agreement with available experimental data.

Reactions involved in the autoxidation of ascorbate have been investigated with quantum chemical first-principles and ab initio methods. Reaction energies and Gibbs energies of the reactions were calculated at the density functional theory level applying the gradient-corrected BP86 and the hybrid B3LYP functionals together with def2-TZVP basis sets. Results of single-point CC2, CCSD, and CCSD(T) calculations were used for calibration of the density functional theory data and show excellent agreement with the B3LYP values. Based on the Gibbs energy ascorbic acid AscH2 is found to be the energetically lowest species in aqueous solution, whereas the monoanion ascorbate AscH - is the most abundant one near pH = 7. Asc 2- was found to be the preferred reducing agent for autoxidation and oxidation processes. The results also support a metal-catalyzed synthesis of the reactive oxygen species H2 O2 according to a redox cycling mechanism proposed in literature. © 2016 Wiley Periodicals, Inc.

A detailed theoretical study of the mechanism and energetics of an organocatalysis based on C=N activation by halogen-bonding is presented for the hydrocyanation of N-benzylidenemethylamine. The calculations at the level of scalar-relativistic gradient-corrected density functional theory give an insight in this catalytic concept and provide information on the characteristics of four different monodentate catalyst candidates acting as halogen-bond donors during the reaction.