Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
Inorg Chem. 2015 May 4;54(9):4192-9. doi: 10.1021/ic5024345. Epub 2015 Apr 22.
A-type tri-lacunary heteropolyoxotungstate anions (e.g., PW9O34, AsW9O34, SiW9O34, and GeW9O34) are multidentate oxygen donor ligands that readily form sandwich complexes with actinyl cations ({UO2}(2+), {NpO2}(+), {NpO2}(2+), and {PuO2}(2+)) in near-neutral/slightly alkaline aqueous solutions. Two or three actinyl cations are sandwiched between two tri-lacunary anions, with additional cations (Na(+), K(+), or NH4(+)) also often held within the cluster. Studies thus far have indicated that it is these additional +1 cations, rather than the specific actinyl cation, that direct the structural variation in the complexes formed. We now report the structural characterization of the neptunyl(VI) cluster complex (NH4)13[Na(NpO2)2(A-α-PW9O34)2]·12H2O. The anion in this complex, Na(NpO2)2(PW9O34)2, contains one Na(+) cation and two {NpO2}(2+) cations held between two PW9O34 anions, with an additional partial occupancy NH4(+) or {NpO2}(2+) cation also present. In the analogous uranium(VI) system, under similar reaction conditions that include an excess of NH4Cl in the parent solution, it was previously shown that (NH4)2(U(VI)O2)2(A-PW9O34)2 is the dominant species in both solution and the crystallized salt. Spectroscopic studies provide further proof of differences in the observed chemistry for the {NpO2}(2+)/PW9O34 and {UO2}(2+)/PW9O34 systems, both in solution and in solid state complexes crystallized from comparable salt solutions. This work reveals that varying the actinide element (Np vs U) can indeed measurably impact structure and complex stability in the cluster chemistry of actinyl(VI) cations with A-type tri-lacunary heteropolyoxotungstate anions.
A 型三缺位杂多氧阴离子（例如，PW9O34, AsW9O34, SiW9O34, 和 GeW9O34) 是多齿氧供体配体，在近中性/微碱性水溶液中，很容易与锕系阳离子（{UO2}(2+), {NpO2}(+), {NpO2}(2+), 和 {PuO2}(2+)) 形成夹心配合物。两个或三个锕系阳离子夹在两个三缺位阴离子之间，此外还有额外的阳离子（Na(+), K(+), 或 NH4(+)) 也通常存在于簇中。到目前为止的研究表明，正是这些额外的 +1 阳离子，而不是特定的锕系阳离子，决定了形成的配合物的结构变化。我们现在报告六价锕系元素簇配合物（NH4)13[Na(NpO2)2(A-α-PW9O34)2]·12H2O 的结构特征。该配合物中的阴离子Na(NpO2)2(PW9O34)2 包含一个 Na(+) 阳离子和两个 {NpO2}(2+) 阳离子夹在两个 PW9O34 阴离子之间，此外还有一个部分占据的 NH4(+) 或 {NpO2}(2+) 阳离子。在类似的铀（VI）体系中，在包括母体溶液中过量 NH4Cl 的类似反应条件下，以前表明(NH4)2(U(VI)O2)2(A-PW9O34)2 是溶液中和从类似盐溶液中结晶的盐中占主导地位的物种。光谱研究进一步证明了观察到的 {NpO2}(2+)/PW9O34 和 {UO2}(2+)/PW9O34 体系的化学性质的差异，无论是在溶液中还是在固态配合物中。这项工作表明，改变锕系元素（Np 与 U）确实可以在 A 型三缺位杂多氧阴离子与锕系（VI）阳离子的簇化学中显著影响结构和配合物稳定性。
