Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon34141, Republic of Korea.
Disposal Performance Demonstration Research Division, Korea Atomic Energy Research Institute (KAERI), Daejeon34057, Republic of Korea.
Inorg Chem. 2023 Jan 16;62(2):756-768. doi: 10.1021/acs.inorgchem.2c03003. Epub 2022 Dec 29.
A spontaneous crystallization of an uranium(VI)-organic coordination compound with sodium and 2-methoxybenzoate (2-mba) was observed in acidic solutions, and the solubility product, molecular vibrations, crystal structure, thermal stability, and emission properties of the atypically low-soluble U(VI) complex (Na[UO(2-mba)]·12HO(s)) were fully investigated for the first time. A long-term solubility experiment and speciation modeling gave a solubility product of log = -12.18 ± 0.02 ( = 25 °C and = 0.1 M NaClO), and vibrational analyses confirmed the overall molecular structure of complex and the frequencies of characteristic stretching motions of uranyl moiety as well. The crystal quality of Na[UO(2-mba)]·12HO(s) was improved by a digestion method, and X-ray diffraction analysis of the single crystalline specimen verified that the newly studied uranyl-organic compound contains one-dimensional channels with a diameter of 20 Å along the [001] direction; the sodium and water molecules are arranged in the channel structures. In the coordination environment around uranyl, three aromatic carboxylates are symmetrically bound in the equatorial plane of uranyl coplanarily, and the unit [UO(2-mba)] complexes are further extended along the plane to form the layered-morphologies. The three-dimensional packing of [UO(2-mba)] anions is driven by the parallel-displaced π-stacking of aromatic rings with a centroid-centroid distance of 3.7 Å. Additional thermogravimetric analysis confirmed that the Na[UO(2-mba)]·12HO(s) is stable up to 250 °C, and dehydration and release of the organic ligand were subsequently observed beyond that temperature. Photoluminescence spectrum of the Na[UO(2-mba)]·12HO(s) clearly displayed the characteristic U(VI) emission, and a band spacing between the ground electronic states of U(VI) uranyl was evaluated to be 831 ± 14 cm. Such detailed characterization of the unique Na[UO(2-mba)]·12HO(s) is advancing upon a systematic understanding of the structural effects of the aromatic model ligands on U(VI) complexation, with relevance to the environmental chemistry of U(VI) and crystal engineering for development of diverse uranyl-organic frameworks.
在酸性溶液中观察到铀(VI)-有机配位化合物与钠离子和 2-甲氧基苯甲酸（2-mba）的自发结晶，首次全面研究了这种异常低溶解度的 U(VI)配合物（Na[UO(2-mba)]·12HO(s)）的溶度积、分子振动、晶体结构、热稳定性和发射特性。通过长期溶解度实验和形态建模，得到了溶度积 log = -12.18 ± 0.02（ = 25 °C 和 = 0.1 M NaClO），振动分析也证实了配合物的整体分子结构以及铀酰部分的特征伸缩运动的频率。通过消化法提高了 Na[UO(2-mba)]·12HO(s)的晶体质量，单晶 X 射线衍射分析证实，新研究的铀有机化合物含有沿[001]方向直径为 20 Å 的一维通道；钠离子和水分子排列在通道结构中。在铀酰的配位环境中，三个芳基羧酸以对称的方式结合在铀酰的赤道平面内，单位[UO(2-mba)]配合物进一步沿平面延伸，形成层状形态。[UO(2-mba)]阴离子的三维堆积是由芳香环的平行位移π-堆积驱动的，芳香环的质心-质心距离为 3.7 Å。额外的热重分析证实，Na[UO(2-mba)]·12HO(s)在 250°C 以下稳定，超过该温度后观察到脱水和有机配体的释放。Na[UO(2-mba)]·12HO(s)的光致发光光谱清晰地显示出特征的 U(VI)发射，并且 U(VI)铀酰的基态之间的能带间隔被评估为 831 ± 14 cm。对独特的 Na[UO(2-mba)]·12HO(s)的这种详细表征，推进了对芳香模型配体对 U(VI)配位结构影响的系统理解，这与 U(VI)的环境化学和开发不同铀有机框架的晶体工程有关。
