P. Roy and Diana T. Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104, United States.
Department of Chemistry and Graduate Program in Applied Physics, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
Inorg Chem. 2022 Jan 10;61(1):23-27. doi: 10.1021/acs.inorgchem.1c02976. Epub 2021 Dec 20.
The critical metals niobium (Nb) and tantalum (Ta) coexist in mineral sources, requiring a separation step to purify the elements from one another. The industrial separation process by solvent extraction uses stoichiometric hydrofluoric acid to manifest differences in the speciation of these otherwise chemically similar elements. The identification of alternative methods to separate Nb/Ta is desirable for fluoride waste reduction. In pursuit of this goal, the novel complexes [Na(CHCN)(EtO)][M(()-BINOLate)] [M = Nb (), Ta ()] were synthesized and characterized. In electrochemical studies, a reduction event at the potential -2.04 V versus ferrocene/ferrocenium was observed for , whereas exhibited no metal-based waves in the electrochemical window. In addition to the inherent 4d/5d orbital energy differences between Nb/Ta, density functional theory calculations suggest a larger degree of π donation from the ligands to the metal cation in compared to , destabilizing the lowest unoccupied molecular orbital. This phenomenon contributes to a calculated reduction potential difference of ca. 0.75 V, allowing for the selective reduction of and separation of the reduction product through leaching with diethyl ether for a separation factor of 6 ± 2.
关键金属铌 (Nb) 和钽 (Ta) 共存于矿物来源中，需要分离步骤才能将它们彼此从其他元素中纯化出来。工业分离溶剂萃取过程使用化学计量的氢氟酸来表现出这些化学性质相似的元素在形态上的差异。寻找替代方法来分离 Nb/Ta 以减少氟化物废物是可取的。为了实现这一目标，合成并表征了新型配合物 [Na(CHCN)(EtO)][M(()-BINOLate)] [M = Nb (), Ta ()]。在电化学研究中，观察到相对于 ferrocene/ferrocenium 的 -2.04 V 处发生了还原事件，而 在电化学窗口中没有显示出基于金属的波。除了 Nb/Ta 之间固有 4d/5d 轨道能量差异外，密度泛函理论计算表明，与 相比，配体向金属阳离子的 π 捐赠程度更大，从而使最低未占据分子轨道不稳定。这种现象导致计算出的还原电位差约为 0.75 V，允许选择性还原 并通过用二乙醚浸取来分离还原产物，分离因子为 6 ± 2。
