A Proton and Oxygen‐17 Nuclear Magnetic Resonance Study of the Aquo Beryllium(II) Nitrate System

Abstract

Kinetic measurements of proton and oxygen exchange of the aquo beryllium(II) ion in concentrated solutions of beryllium(II) nitrate are reported. These measurements have been performed by means of 1H spin‐echo NMR and by 17O FT‐NMR using natural abundance 17G and europium(III) nitrate as a shift reagent for the 17O bulk water line. The combination of both methods allows one to separate the contributions from protolysis and water exchange. The data obtained for water exchange are k298ex = 1.8 · 103 sec−1 (rate constant for one water molecule), ΔH+ex = 41.5 kJ mol−1, and ΔS+ex = ‐44 JK−1 mol−1. Protolytic dissociation of the aquo beryllium(II) ion is found to be approximately one order of magnitude faster than water exchange: k298d = 8 · 104 sec−1 (rate constant for the tetra aquo beryllium(II) ion). ΔH+d = 31.2 kJ mol−1, and ΔS+d = −45 JK−1 mol−1 for beryllium concentrations up to 0.2 molal.

Water exchange rates and mechanisms in tetrahedral [Be(H2O)4]2+ and [Li(H2O)4]+ complexes using DFT methods and cluster‐continuum models

“…The BLYP, B3LYP, CAM‐B3LYP, PBE, PBE0, TPSS, and TPSSh functionals provide relatively similar activation parameters (Table ), with activation enthalpies Δ H ‡ in the range 54.4–62.8 kJ mol −1 and activation entropies of Δ S ‡ = −47.5 to −62.5 J mol −1 K −1 . The negative activation entropy is expected for an associatively activated water exchange mechanism, and is in line with the experimental value reported by Füldner (−44 J mol −1 K −1 ) . A slightly positive Δ S ‡ value was determined by Merbach et al, although the water exchange rates determined by these two groups are in reasonably good mutual agreement.…”

“…These functionals were developed by Truhlar using a wide range of databases that included thermochemical data. The calculated activation free energies at 298.15 K (Δ = 53.6 and 52.7 kJ mol −1 using M06 and M062X, respectively) are in excellent agreement with the experiment, while the Δ H ‡ and Δ S ‡ values are close to those reported by Füldner . Furthermore, the calculated Δ V ‡ values present also an excellent agreement with that determined by Merbach using variable pressure NMR measurements.…”

Ligand Substitution Reactions at Inorganic Centers

“…81 The water ligand residence time at 25 °C was estimated to be around 2-10 ms thus well within the range of monitoring by normal linebroadening NMR methods. At the time of the early measurements the [Be-(H 2 O) 4 ] 2+ exchange process attracted much interest as the first example of a measured proton exchange (k H ) 8.0 × 10 4 s -1 , determined using 1 H NMR 82 ), which was faster than water exchange (determined using 17 O NMR 83,84 ). The variable pressure 17 O NMR water exchange study by Merbach et al 84 is probably the most reliable.…”

Theoretical studies of borylphosphine, its conjugate base, and the lithium salt of its conjugate base. The use of orbital kinetic energies to determine the origin of the driving force for changes in molecular geometry

“…(-367.717 93) (-367.95969) (-367.98513) " Results with the DZ + 2P + diff basis set are listed in parentheses;…”