A Trigonal Bipyramidal Uranyl Amido Complex: Synthesis and Structural Characterization of [Na(THF)2][UO2(N(SiMe3)2)3]

The synthesis and structural characterization of a rare example of a uranyl complex possessing three equatorial
ligands, [M(THF)2][UO2(N(SiMe3)2)3] (3a, M = Na; 3b, M = K), are described. The sodium salt 3a is prepared
by protonolysis of [Na(THF)2]2[UO2(N(SiMe3)2)4], whereas the potassium salt 3b is obtained via a metathesis
reaction of uranyl chloride UO2Cl2(THF)2 (4) with 3 equiv of K[N(SiMe3)2]. A single-crystal X-ray diffraction
study of 3a revealed a trigonal-bipyramidal geometry about uranium, formed by two axial oxo and three equatorial
amido ligands, with average UO and U−N bond distances of 1.796(5) and 2.310(4) Å, respectively. One of the
oxo ligands is also coordinated to the sodium counterion. 1H NMR spectroscopic studies indicate that THF adds
reversibly as a ligand to 3 to expand the trigonal bipyramidal geometry. The degree to which the coordination
sphere in 3 is electronically satisfied with only three amido donors is suggested by (1) the reversible THF
coordination, (2) a modest elongation in the bond distances for a five-coordinate U(VI) complex, and (3) the
basicity of the oxo ligands as evidenced in the contact to Na. The vibrational spectra of the series of uranyl amido
complexes [UO2(N(SiMe3)2)n]2-n (n = 2−4) are compared, to evaluate the effects on the axial UO bonding as
a function of increased electron density donated from the equatorial region. Raman spectroscopic measurements
of the ν1 symmetric OUO stretch show progressive axial bond weakening as the number of amido donors is
increased. Crystal data for [Na(THF)2][UO2(N(SiMe3)2)3]:  orthorhombic space group Pna21, a = 22.945(1) Å,
b = 15.2830(7) Å, c = 12.6787(6) Å, z = 4, R1 = 0.0309, wR2 = 0.0524.

本文详细描述了一种罕见的三配位铀酰配合物[M(THF)2][UO2(N(SiMe3)2)3]（3a，M = Na；3b，M = K）的合成及其结构表征。钠盐3a通过[Na(THF)2]2[UO2(N(SiMe3)2)4]的质子解离法制备，而钾盐3b则通过铀酰氯化物UO2Cl2(THF)2（4）与3当量K[N(SiMe3)2]的置换反应获得。3a的单晶X射线衍射研究表明，铀原子周围形成了三角双锥构型，该构型由两个轴向氧配体和三个赤道氨基配体组成，平均U-O和U-N键长分别为1.796(5) Å和2.310(4) Å。其中一个氧配体还与钠反离子配位。1H NMR光谱研究表明，THF作为配体可逆地添加到3中，以扩展其三角双锥构型。3中仅由三个氨基供体组成的配位球电子满足度的程度，可从以下三个方面推断：（1）THF配位的可逆性，（2）五配位U(VI)配合物键长的适度伸长，以及（3）氧配体的碱性，这从与钠的接触中得以体现。该系列铀酰氨基配合物[UO2(N(SiMe3)2)n]2-n（n = 2−4）的振动光谱进行了比较，以评估随着赤道区域的电子密度增加，轴向U-O键的影响。拉曼光谱对ν1对称O-U-O伸缩振动的测量显示出，随着氨基供体数量的增加，轴向键逐渐减弱。对于[Na(THF)2][UO2(N(SiMe3)2)3]的晶体数据：正交晶系Pna21空间群，a = 22.945(1) Å，b = 15.2830(7) Å，c = 12.6787(6) Å，z = 4，R1 = 0.0309，wR2 = 0.0524。