Johnson Aaron T, Parker T Gannon, Dickens Sara M, Pfeiffer Jana K, Oliver Allen G, Wall Donald, Wall Nathalie A, Finck Martha R, Carney Kevin P
Global Security & International Safeguards, Idaho National Laboratory , Idaho Falls, Idaho 83401, United States.
Department of Chemistry, Washington State University , Pullman, Washington 99164, United States.
Inorg Chem. 2017 Nov 6;56(21):13553-13561. doi: 10.1021/acs.inorgchem.7b02290.
Production of certified reference materials in support of domestic nuclear forensics programs require volatile precursors for introduction into electromagnetic isotopic separation instruments. β-Diketone chelates of tetravalent actinides are known for their high volatility, but previously developed synthetic approaches require starting material (NpCl) that is prohibitively difficult and hazardous to prepare. An alternative strategy was developed here that uses controlled potential electrolysis to reduce neptunium to the tetravalent state in submolar concentrations of hydrochloric acid. Four different β-diketone ligands of varying degrees of fluorination were reacted with an aqueous solution of Np. Products of this reaction were characterized via X-ray diffraction and infrared spectroscopy, and were found to be neutral 8-coordinate complexes that adopt square antiprismatic crystal geometry. Synthesis of Np β-diketonates by this approach circumvents the necessity of using NpCl in tetravalent Np coordination compound synthesis. The volatility of the complexes was assessed using thermogravimetric analysis, where the temperature of sublimation was determined to be in the range of 180° to 205 °C. The extent of fluorination did not appreciably alter the sublimation temperature of the complex. Thermal decomposition of these compounds was not observed during sublimation. High volatility and thermal stability of Np β-diketonates make them ideal candidates for gaseous introduction into isotopic separation instruments.
生产支持国内核法医项目的标准参考材料需要挥发性前体，以便引入电磁同位素分离仪器。四价锕系元素的β-二酮螯合物因其高挥发性而闻名，但先前开发的合成方法需要起始材料（NpCl），其制备难度极大且具有危险性。此处开发了一种替代策略，该策略使用控制电位电解在亚摩尔浓度的盐酸中将镎还原为四价态。将四种不同程度氟化的β-二酮配体与镎的水溶液反应。通过X射线衍射和红外光谱对该反应的产物进行了表征，发现它们是采用方形反棱柱晶体几何结构的中性8配位配合物。通过这种方法合成镎β-二酮螯合物避免了在四价镎配位化合物合成中使用NpCl的必要性。使用热重分析评估了配合物的挥发性，其中升华温度确定在180℃至205℃范围内。氟化程度并未明显改变配合物的升华温度。在升华过程中未观察到这些化合物的热分解。镎β-二酮螯合物的高挥发性和热稳定性使其成为气态引入同位素分离仪器的理想候选物。
