Coordination number of lanthanides

Although some of the lanthanides form compounds with oxidation states other than + 3, the vast majority of stable species involve the trivalent state. Due to the nature of the weak bonding f electrons, complexes in solution are normally quite labile, and as described below, the preparation and the isolation of pure enantiomers containing a central lanthanide ion and achiral ligands are extremely rare. The coordination number of lanthanide(III) ions is somewhat variable and depends on the size and charge of the coordinated ligands, and the size of the lanthanide ion that varies slightly... 

In Table 4.11 the coordination numbers of lanthanides in the solid state and in solution are compared. 

The question of coordination in aqueous solutions is not as clear as in solid state. Sped-ding s work [53] on the partial molar volumes of aquo ions of lanthanides and the irregular trends of these quantities in the lanthanides has been taken as evidence for change in coordination number in the lanthanide series [54]. The change in coordination from 9 to 8 in the lanthanide series has been confirmed by X-ray and neutron diffraction studies of LnCb solutions [55], The coordination numbers of lanthanides determined in aqueous solutions by various techniques along with the coordination numbers obtained are given below ... 

Nephelauxetic effects (1 — f ), mean lanthanide-ligand distances (R (Ln-O) and effective coordination numbers of lanthanides (CNeff) in Pr(III) and Nd(III) ODA complexes determined from baricentres (a) of spectral bands ODA = oxydiacetate, OOCCH2OCH2COO- [184],... 

Large coordination numbers. For example, the coordination number of 3d transition metals is generally four or six. However, the most common coordination number of lanthanide complexes is eight or nine. This number is close to the sum of the 6s, 6p, and 5d orbitals. Another fact responsible for the large coordination number of lanthanide complexes... 

To saturate the demand of the high coordination number of lanthanide metal ions, the cyclopentadienyl group adopts a ti -coordination mode, and occupies three sites in the coordination sphere of the metal center. A typical structure for LnCp3 is shown in Figure 8.1. 

The hard-Lewis acidities, high ligand exchange rates and large coordination numbers of lanthanide complexes have enabled their application to both the Meerwin-Ponndorf-... 

The coordination. Transition element ions are in general tetrahedrally or octahedrally coordinated. The ligand field is about twice lower for the fourfold coordination than for the sixfold one (5ee Ligand Field Theory Spectra). The coordination number of lanthanide ions varies from 6 to 12. The nephelauxetic effect and crystal field decrease with increasing coordination number. 

Several determinations of the average coordination number of lanthanide ions in non-aqueous and mixed solutions have been made, using both grating infra-red spectroscopy (Lugina and Davidenko 1980, Batyaev et al. 1985) and FT-IR difference spectra (Biinzli et al. 1982b, Bunzli and Mabillard 1986a, Biinzli and Kasparek 1991, Milicic-Tang and Bunzli 1992). With the latter technique, a spectroscopic accuracy of 0.01 unit of absorbance can be reached and coordination numbers may be determined to 0.3 unit. 

Scheme 8.2 Evaluation of the Water Coordination Number of Lanthanide Triflate-Based Catalysts Using Dynamic Luminescence Decay Measurements. With permission from Ref [57],...

Scandium trichloride possesses the rhombohedral FeClj-type structure. The trichlorides of lanthanum through gadolinium possess the hexagonal UClj-type structure (Coordination Number of lanthanide CN = 9). Terbium chloride and a-DyCljpossess the orthorhombic PuBtj-type structure (CN = 8), while the trichlorides of yttrium and those of dysprosium ( 5-form) to lutetium possess the monoclinic AlClj-type structure (CN = 6). 

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