Lanthanide aqua ions structures

Dynamic and Structural Parameters for some Lanthanide Aqua Ions at 298 K 67)... 

The early fluorides feature the tysonite (LaFs Figure 7) structure in which the lanthanide has nine nearest-neighbor fluorides in a tricapped trigonal prismatic array (like the aqua ions), with two rather more distant neighbors capping the trigonal faces. From SmFs onwards the stable form is the... 

In addition to the nitrate system, AUen et al. (1997) reported a structural study of U02, Np02, Np ", and Pu " species in HCl solution by the EXAFS method. They also conducted (Allen et al. 2000) EXAFS experiments on the trivalent lanthanide and actinide ions in HCl solutions. In the dilute HCl solution, on average, the Am and Cm aqua ions are coordinated by 10.3 oxygens at 2.48 A and by 10.2 oxygens at 2.45 A, respectively, while 9.2 water molecules are coordinated to the Pu . The average distance between the Pu " ion and the oxygens of water molecules is 2.51 A. They observed Cl coordination to the Cm above the 10.5 M LiCl concentration. However, Pu does not form inner sphere chloride complexation. 

Hay (1991) has studied the high-coordinate metal complexes containing lanthanide (III) ions using molecular mechanics calculations. He has applied the molecular mechanics technique to 58 known structures of eight- to twelve-coordinate aqua- and nitratolanthanide (III) complexes. He has also presented various required parameters for the computation of these species. He has studied complexes such as M(OH2)gX3,... 

The most successful synthetic approach to structurally well defined lanthanide hydroxide complexes is the ligand-controlled hydrolysis approach [69-71]. The essence of this methodology is schematically shown in Figure 6.25. It makes use of the high propensity of lanthanide ions toward hydrolysis, but controlled and limited by certain supporting ligands. The scheme starts with a lanthanide complex whose coordination sphere constitutes both organic and aqua... 

B. P. Hay, Inorg. Chem., 30, 2876 (1990). Extension of Molecular Mechanics to High-Coordinate Metal Complexes. Calculation of the Structures of Aqua and Nitrato Complexes of Lanthanide(III) Metal Ions. 

The Y + ion is comparable in size with heavier lanthanides, and its coordination chemistry therefore resembles them. Aqua complexes and simple hydrates have been discussed in Solvento Complexes of the Lanthanide Ions. Fewer solution studies of solvated species with other donors have been made for these metals, but an examination of the Y + ion in Odonor solvents using X-ray absorption fine structure (XAFS) and laige angle X-ray scattering shows that the metal is eight coordinate in dimethylformamide and dimethylsut-foxide, but seven coordinate in N, iV -dimethylpropyleneurea (dmpu), as are other lanthanides. It should be noted that in the solid state, six-coordinate [Ln(dmpu)6]l3 (Ln = La, Pr, Nd, Gd, Tb, Er, Yb, Lu) are isolated. ... 

Regarding the choice of the lanthanide salt, the nature of the counteranion (trifiate, nitrate, perchorate, etc.) is not innocent, depending on the solvent in which the complex will be studied. Indeed, the solvation process is total in water, and the aqua anion will not interact, whereas, in an organic solvent, there are possibilities of coordination of the counteranion. As an example, trifiate is more coordinating than a nitrate ion, and the choice of the counterions—with relatively weak or strong coordination abilities—may allow predicting the final structure of the lanthanide complexes. 

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