Abstract
In relevance to advanced nuclear fuel recycling, we investigated the structural chemistry of UO(2)(NO(3))(2) coordination polymers bearing trans-1,4-cyclohexanediamine-based cyclic/acyclic diamides/dicarbamide cross-linkers (L1-L6) to know how the ligand structure impacts precipitation behavior of UO(2) (2+) from HNO(3)(aq). In a similar manner to the γ-lactam analogue (L2) we reported previously, 1D coordination polymers of [UO(2)(NO(3))(2)(Lx)] (n) were obtained in the use of any Lx's having β-/δ-lactam (L1, L3), acetamide (L4), propionamide (L5), and N,N,N'-trimethylcarbamide (L6) terminals. These compounds exhibit the typical structural features of uranyl nitrates. Indeed, [UO(2)(NO(3))(2)(Lx)] (n) (x = 2-6) deposited in 71-90% yield from 3 M HNO(3)(aq). In contrast, no [UO(2)(NO(3))(2)(L1)] (n) precipitated under the same condition. The packing efficiency of [UO(2)(NO(3))(2)(Lx)] (n) and the electronic nature of Lx seem to control the solubility of [UO(2)(NO(3))(2)(Lx)] (n) . Reaction kinetics of precipitation of [UO(2)(NO(3))(2)(Lx)] (n) with the cyclic diamides (L2 and L3) was faster than that of the acyclic diamides (L4 and L5), being associated with the rotational isomerism around the amide C-N bonds occurring only in the latter series. Despite the availability of similar E-Z isomerism, the precipitation kinetics in the use of dicarbamide L6 was as rapid as the cyclic amides (L2, L3), being ascribed to the lower energy barrier in its C-N bond rotation compared with those in the acyclic diamides (L4, L5).