Bühl Michael, Diss Romain, Wipff Georges
Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany.
Inorg Chem. 2007 Jun 25;46(13):5196-206. doi: 10.1021/ic0622555. Epub 2007 May 25.
According to Car-Parrinello molecular dynamics simulations for UO(2)(NO(3))(3), UO(2)(NO(3))(4), and UO(2)(OH(2))(4-)(NO(3)) complexes in the gas phase and in aqueous solution, the nitrate coordination mode to uranyl depends on the interplay between ligand-metal attractions, interligand repulsions, and solvation. In the trinitrate, the eta(2)-coordination is clearly favored in water and in the gas phase, leading to a coordination number (CN) of 6. According to pointwise thermodynamic integration involving constrained molecular dynamics simulations, a change in free energy of +6 kcal/mol is predicted for eta(2)- to eta(1)-transition of one of the three nitrate ligands in the gas phase. In the gas phase, the mononitrate-hydrate complex also prefers a eta(2)-binding mode but with a CN of 5, one H(2)O molecule being in the second shell. This contrasts with the aqueous solution where the nitrate binds in a eta(1)-fashion and uranyl coordinates to four H2O ligands. A driving force of ca. -3 kcal/mol is predicted for the eta(2)- to eta(1)- transition in water. This structural preference is interpreted in terms of steric arguments and differential solvation of terminal vs uranyl-coordinated O atoms of the nitrate ligands. The UO(2)(NO(3))(4) complex with two eta(2)- and two eta(1)- coordinated nitrates, observed in the solid state, is stable for 1-2 ps in the gas phase and in solution. In the studied series, the modulation of uranyl-ligand distances upon immersion of the complex in water is found to depend on the nature of the ligand and the composition of the complex.
根据对气相和水溶液中[UO(2)(NO(3))(3)]⁻、[UO(2)(NO(3))(4)]²⁻和[UO(2)(OH₂)(4⁻)(NO(3))]⁺配合物进行的Car-Parrinello分子动力学模拟，硝酸根与铀酰的配位模式取决于配体-金属吸引力、配体间排斥力和溶剂化之间的相互作用。在三硝酸根配合物中，η²配位在水相和气相中明显更受青睐，导致配位数（CN）为6。根据涉及受限分子动力学模拟的逐点热力学积分，预测气相中三个硝酸根配体之一从η²到η¹转变的自由能变化为+6千卡/摩尔。在气相中，单硝酸根-水合物配合物也倾向于η²结合模式，但配位数为5，一个H₂O分子在第二配位层。这与水溶液形成对比，在水溶液中硝酸根以η¹方式结合，铀酰与四个H₂O配体配位。预测在水中从η²到η¹转变的驱动力约为 -3千卡/摩尔。这种结构偏好是根据空间位阻论据以及硝酸根配体末端与铀酰配位的O原子的不同溶剂化来解释的。在固态中观察到的具有两个η²和两个η¹配位硝酸根的[UO(2)(NO(3))(4)]²⁻配合物，在气相和溶液中稳定1 - 2皮秒。在所研究的系列中，发现配合物浸入水中时铀酰-配体距离的调制取决于配体的性质和配合物的组成。
