Exchange of N,N-dimethylacetamide on dioxopentakis(N,N-dimethylacetamide)uranium(VI) ion. Proton magnetic resonance study

The species UO/sub 2/(DMA)/sup 2 +//sub 5/ is shown from /sup 1/H NMR studies to be the greatly predominant dioxouranium(VI) species existing in a series of dilute N,N-dimethylacetamide (DMA) solutions in CD/sub 2/Cl/sub 2/ diluent. Complete line shape analyses of exchange-modified /sup 1/H NMR DMA line shapes show the rate law for DMA exchange to be 5k/sub ex/(UO/sub 2/(DMA)/sup 2 +//sub 5/) over a 24.05-fold variation of (DMA). The mechanism of the DMA exchange is considered to be of the D type. A typical set of rate parameters are k/sub ex/(260 K) = 81 +- 2 s/sup -1/, ..delta..H/sup 2 +/ = 10.2 +- 0.2 kcal mol/sup -1/ and ..delta..S/sup 2 +/ = -10.4 +- 0.7 cal deg/sup -1/ mol/sup -1/ for a solution in which (UO/sub 2/(DMA)/sup 2 +//sub 5/), (DMA), and (CD/sub 2/Cl/sub 2/) are respectively 0.1518, 0.7108, and 14.15 M.