Thermodynamic Properties of Rare Earth Complexes. XVII. The Partial Molar Heat Capacities of Rare Earth Perchlorates and Oxydiacetate Complexes.

Chemistry and thermodynamics of europium and some of its simpler inorganic compounds and aqueous species

“…Heat capacities of RE3+ in perchlorate solutions also exhibit no maximum with ionic radius as would be expected for such an equilibrium. 174 Hinchey and Cobble175® found that the standard-state ionic entropies plotted vs. the inverse of the ionic radius squared were nearly linear. This was later shown to result from inaccurate and, in some cases, estimated input data; these entropies do in fact show an S-shape when more accurate input data are used.168 Marcus30 has reviewed hydration trends in detail and cites ref- erences for other studies that indicate a constant hydration number, especially the work of Geier and Karlen.175b Some of these authors consider the twoseries trends to be due to structural changes rather than a hydration number change.…”

Longitudinal relaxation rates of lanthanum-139 in aqueous salt solutions

“…A large volume of data on the thermodynamic and transport properties of aqueous solutions of rare earth salts, recently augmented by X-ray and Raman spectral studies, has been interpreted by Spedding and his coworkers in terms of the structure and microdynamic behavior of the aquo complexes.1,2 The interpretation of the partial molal heat capacities has been subjected to some criticism by Grenthe et al 3 A more direct way to look into this problem is by nuclear magnetic resonance in general and nuclear relaxation rates in particular.4 Work in this laboratory has focused in the past on the proton and oxygen-17 NMR of the solvent and anion nuclei.5,6 Advantage was taken of the fact that most of the trivalent lanthanides are paramagnetic and exert their influence on nuclei in their vicinity through the electron-nuclear hyperfine interaction. Among the trivalent rare earth ions only lanthanum and lutetium are diamagnetic and it appears that lanthanum-139, a nucleus of spin 7/2 with a natural abundance of 99.91% and NMR sensivitity (relative to that of protons) of 5.92%, is suitable for NMR experiments.…”

The lanthanide ions as structural probes in biological and model systems

“…This was accepted as evidence for a change in the primary hydration number between Nd and Tb, presumably from 9 to 8 (74). Recently, Grenthe et al (75) have objected to this interpretation on the basis of evidence from partial molar heat capacity measurements of rare earth perchlorates. They conclude, in accordwith earlier 170 chemical shift data (76), that equilibrium (1) (2) and (3).…”

“…Equilibrium (6) is also believed to be important for the Ln (diglycolate)~ species (81,97). We will briefly return to the EDTA system in a later section.…”

“…It is based on the assumption that 30 or more fluxional isomers interconvert rapidly on the NMR time scale. The stereochemical lability and abundance of geometric isomers for polyhedra of high co-ordination number (> 7) is well established (75,720). Even though the full form of Eq.…”