On the Hydration of the Rare Earth Ions in Aqueous Solution

Abstract

The totally symmetric stretching mode 1 Ln-(OH 2 ) of the first hydration shells of all the rare earth (RE) ions across the series from lanthanum to lutetium has been measured on dilute aqueous perchlorate solutions at room temperature. An S-shaped relationship has been found between the 1 Ln-(OH 2 ) peak positions and the Ln-(OH 2 ) bond distances of the lanthanide(III) aqua ions. While the light rare earth ions form nona-hydrates, the heavy ones form octa-hydrates and the rare earth ions in the middle of the series show non integer hydration numbers between 9 and 8. A relationship between wavenumber positions 1 Ln-(OH 2 ) and the Ln-(OH 2 ) bond distances of the RE hydrates has been given. Recent quantum mechanical calculations support the given interpretation.

Complexation of trivalent metal cations (Al3+, Ga3+, In3+, La3+, Lu3+) to cucurbiturils: a DFT/SMD evaluation of the key factors governing the host–guest recognition

“…The number of the first shell water molecules for Al 3+ , Ga 3+ and In 3+ cations is six, [36][37][38] while the number of the first shell water molecules determined for La 3+ and Lu 3+ cations varies depending on the environment and experimental/theoretical approach used. 39 It is accepted that lighter lanthanoid ions (La-Eu) are predominantly ninefold-coordinated while the higher species (Gd-Lu) are mostly eightfold-coordinated. 40 The pH of the medium affects the protonation state of the metal-bound water molecules: the reactions for Al 3+ , Ga 3+ and In 3+ are modelled at acidic (pH D 2) and neutral (pH D 7) conditions with metal Table 1 Gibbs energies for the complex formation in the gas phase (superscript 1), and in a water environment (superscript 78), for the CB[n], n = 5-8, complex formation with bare Al 3+ and La 3+ cations, in kcal mol cations bound to water molecules and to a combination of water molecules/negatively charged OH À groups, respectively.…”

“…Since some experimental studies indicate that the light rareearth cations coordinate nine water molecules, while for the heavier ones are typical octahydrates, 39 we modelled structures in which the hydration shell of the La 3+ and Lu 3+ cations consists of eight explicit water molecules, while in the case of La 3+ we additionally modelled a complex with nine H Comparing the values of the Gibbs energies for the formation of CB [6]-M 3+ and CB [6]-hydrated metal complexes, one can conclude that the presence of a hydration shell leads to decrease of the complexation energy (in absolute value) due to the coordinated water molecules, which mediate the interaction between the metal cation and the carbonyl groups.…”

Electronic Structure of Ytterbium(III) Solvates – A Combined Spectro-scopic and Theoretical Study

“…Later EXAFS studies however provided results in contradiction with the early work, proposing that the aqua-ions are nona-coordinated throughout the series. 33 The more recent results based on EXAFS, 44 Raman spectroscopy, 45,46 optical spectroscopy 47 and theoretical studies 48,49 support that the light lanthanide(III) aqua ions are nine-coordinated, while the heaviest lanthanide(III) ions are octa-coordinated in aqueous solutions. In this study, we aim to use high-resolution optical spectroscopy and state-of-the-art computational chemistry to determine the coordination number and structure of four Yb 3+ solvates in order to -hopefully -close this discussion.…”

Preparation of Gellan Gum-Inorganic Composite Film and Its Metal Ion Accumulation Property

“…In the trivalent metal ions, the binding affinity partially coincided with the order of the hydrated ion radius size. The order of the hydrated ion radius size is In(III) < Sc(III) < Y(III) < La(III) < Al(III) [29,[31][32][33]. The Al(III) ion, which possesses the largest hydrated ion radius of these metal ions, showed the smallest accumulated amount of these trivalent ions.…”