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NMR and Electron Paramagnetic Resonance Studies of [Gd(CH3CN)9]3+ and [Eu(CH3CN)9]2+: Solvation and Solvent Exchange Dynamics in Anhydrous Acetonitrile

Homoleptic acetonitrile complexes [Gd(CH3CN)9][Al(OC(CF3)3)4]3 and [Eu(CH3CN)9][Al(OC(CF3)3)4]2 have been studied in anhydrous acetonitrile by 14N- and 1H NMR relaxation as well as by X- and Q-band EPR. For each compound a combined analysis of all experimental data allowed to get microscopic information on the dynamics in solution. The second order rotational correlation times for [Gd(CH3CN)9]3+ and [Eu(CH3CN)9]2+ are 14.5 ± 1.8 ps and 11.8 ± 1.1 ps, respectively. Solvent exchange rate constants determined are (55 ± 15) × 106 s–1 for the trivalent Gd3+ and (1530 ± 200) × 106 s–1 for the divalent Eu2+. Surprisingly, for both solvate complexes CH3CN exchange is much slower for the less strongly N-binding acetonitrile than for the more strongly coordinated O-binding H2O. It is concluded that this exceptional behavior is due to the extremely fast water exchange, whereas the exchange behavior of CH3CN is more regular. Electron spin relaxation on the isoelectronic ions is much slower than on the O-binding water...

Authors:   Gabriella Bodizs; Lothar Helm
Journal:   Inorganic Chemistry
Year:   2012
DOI:   10.1021/ic300478c
Publication date:   03-05-2012

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