Water-Exchange Mechanism of Tetraaquapalladium(II). A Variable-Pressure and Variable-Temperature Oxygen-17 NMR Study |
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Authors: | Lothar Helm Lars I Elding Andr E Merbach |
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Institution: | Lothar Helm,Lars I. Elding,André E. Merbach |
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Abstract: | Water exchange of square-planar Pd(H2O)24+ has been studied as a function of temperature (240 to 345 K) and pressure (0.1 to 260 MPa, at 324 K) by measuring the 17/O-FT-NMR line-widths of the resonance from coordinated water at 27.11 and 48.78 MHz. The following exchange parameters were obtained: k298ex = (560 ± 40) s?1, ΔH* = (49.5 ± 1.9) kJ mol?1, ΔS* = – (26 ± 6) J K?1 mol?1 and ΔV* = – (2.2 ± 0.2) cm3 mol?1. The values refere to an aqueous perchlorate medium with an ionic strength between 2.0 and 2.6 m and a perchloric-acid concentration between 0.8 and 1.7 m, and are interpreted in terms of an associative (a) activation for the exchange. The exchange rate for Pd(H2O)24+ is 1.4 × 106 times faster than for Pt(H2O)24+ at 298 K. A comparison with reactions between other nucleophiles and Pd(H2O)24+ is also made. |
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