Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Inorg Chem. 2013 Apr 1;52(7):3547-55. doi: 10.1021/ic3020139. Epub 2013 Mar 13.
Hexavalent neptunium can be solubilized in 0.5-3.5 M aqueous MOH (M = Li(+), Na(+), NMe4(+) = TMA(+)) solutions. Single crystals were obtained from cooling of a dilute solution of Co(NH3)6Cl3 and NpO2(2+) in 3.5 M [N(Me)4]OH to 5 °C. A single-crystal X-ray diffraction study revealed the molecular formula of [Co(NH3)6]2[NpO2(OH)4]3·H2O, isostructural with the uranium analogue. The asymmetric unit contains three distinct NpO2(OH)4(2-) ions, each with pseudooctahedral coordination geometry with trans-oxo ligands. The average Np═O and Np-OH distances were determined to be 1.80(1) and 2.24(1) Å, respectively. EXAFS data and fits at the Np L(III)-edge on solid [Co(NH3)6]2[NpO2(OH)4]3·H2O and aqueous solutions of NpO2(2+) in 2.5 and 3.5 M (TMA)OH revealed bond lengths nearly identical with those determined by X-ray diffraction but with an increase in the number of equatorial ligands with increasing (TMA)OH concentration. Raman spectra of single crystals of [Co(NH3)6]2[NpO2(OH)4]3·H2O reveal a ν1(O═Np═O) symmetric stretch at 741 cm(-1). Raman spectra of NpO2(2+) recorded in a 0.6-2.2 M LiOH solution reveal a single ν1 frequency of 769 cm(-1). Facile exchange of the neptunyl oxo ligands with the water solvent was also observed with Raman spectroscopy performed with (16)O- and (18)O-enriched water solvent. The combination of EXAFS and Raman data suggests that NpO2(OH)4(2-) is the dominant solution species under the conditions of study and that a small amount of a second species, NpO2(OH)5(3-), may also be present at higher alkalinity. Crystal data for [Co(NH3)6]2[NpO2(OH)4]3·H2O: monoclinic, space group C2/c, a = 17.344(4) Å, b = 12.177(3) Å, c = 15.273 Å, β = 120.17(2)°, Z = 4, R1 = 0.0359, wR2 = 0.0729.
六价锝能溶解在 0.5-3.5 M 的水合 MOH（M = Li(+)、Na(+)、NMe4(+) = TMA(+)）溶液中。从 3.5 M [N(Me)4]OH 中冷却含有 Co(NH3)6Cl3 和 NpO2(2+)的稀溶液中获得了单晶。单晶 X 射线衍射研究表明，[Co(NH3)6]2[NpO2(OH)4]3·H2O 的分子式与铀类似物相同。不对称单元包含三个不同的 NpO2(OH)4(2-)离子，每个离子都具有反式氧配体的拟八面体配位几何形状。平均 Np═O 和 Np-OH 距离分别为 1.80(1) 和 2.24(1)Å。在固态 [Co(NH3)6]2[NpO2(OH)4]3·H2O 和 2.5 和 3.5 M (TMA)OH 中的 NpO2(2+)的 Np L(III)-边的 EXAFS 数据和拟合表明，键长几乎与 X 射线衍射确定的键长相同，但随着 (TMA)OH 浓度的增加，赤道配体的数量增加。[Co(NH3)6]2[NpO2(OH)4]3·H2O 单晶的拉曼光谱显示 ν1(O═Np═O)对称伸缩在 741 cm(-1)处。在 0.6-2.2 M LiOH 溶液中记录的 NpO2(2+)的拉曼光谱显示 ν1 频率为 769 cm(-1)。用 (16)O 和 (18)O 富集水溶剂进行的拉曼光谱也观察到了水溶剂中锝氧配体的易交换。EXAFS 和拉曼数据的结合表明，在研究条件下，NpO2(OH)4(2-)是主要的溶液物种，而少量的第二种物种 NpO2(OH)5(3-)也可能在较高碱度下存在。[Co(NH3)6]2[NpO2(OH)4]3·H2O 的晶体数据：单斜晶系，空间群 C2/c，a = 17.344(4)Å，b = 12.177(3)Å，c = 15.273 Å，β = 120.17(2)°，Z = 4，R1 = 0.0359，wR2 = 0.0729。
