Lutetium coordination number

The Lu—C cr-bonding distances range from 2.425(15) to 2.501(17) A. These distances are approximately 0.2 A shorter than the corresponding distance for a pentahapto cyclopentadienide lutetium bond as predicted from ionic radii. Coordination about the lutetium atom is a slightly distorted tetrahedron. The formal coordination number of four is extremely low for the lanthanides. The only other lanthanide complex with such a low coordination number is the 3-coordinate compound [Lu N(SiMes)2 3] 131). In both cases, the low coordination number is stabilized by the use of bulky hgands. 

Hydrates of rare earth chlorides also have two different crystal systems a triclinic system for lanthanum, cerium, and praseodymium, as well as a monoclinic system for neodymium to lutetium and yttrium. CeCl3-7H20, as an example of the former system, is different from the above infinite polymer as two cerium atoms are connected by two [i2-bridges to form a dimer. The formula for this dimer is [(H20)7Ce([i2-Cl)2Ce(H20)7]Cl4 as shown in Figure 1.18. Therefore, the coordination number of cerium is nine and the polyhedron takes on a destroyed mono-capped square antiprism configuration. 

The REPO4 structure for the heavier rare earth elements (terbium to lutetium, yttrium, and scandium) belong to the tetragonal system. The coordination number of the central ions is... 

The lanthanide or rare earth elements (atomic numbers 57 through 71) typically add electrons to the 4f orbitals as the atomic number increases, but lanthanum (4f°) is usually considered a lanthanide. Scandium and yttrium are also chemically similar to lanthanides. Lanthanide chemistry is typically that of + 3 cations, and as the atomic number increases, there is a decrease in radius for each lanthanide, known as the lanthanide contraction. Because bonding within the lanthanide series is usually predominantly ionic, the lanthanide contraction often determines the differences in properties of lanthanide compounds and ions. Lanthanide compounds often have high coordination numbers between 6 and 12. see also Cerium Dysprosium Erbium Europium Gadolinium Holmium Lanthanum Lutetium Praseodymium Promethium Samarium Terbium Thulium Ytterbium. 

Similarly, for the change in cationic size with constant charge, as in the lanthanides (where the lanthanide contraction means that the elements with higher atomic numbers give the smallest 3+ ions) where only the metal ion changes, we generally find the stability of a series of coordination compounds to increase from lanthanum (atomic number 57) to lutetium (atomic number 71). 

The first sets of ionic radii for the trivalent rare earths were based on a cation coordination number (CN) of 6 and a fixed value of the anion radius or F. The lanthanide contraction, viz., the gradual decrease of ionic size from lanthanum to lutetium, is clearly apparent in the early values presented by Goldschmidt et al. (1926), who also noted that the radii varied with CN. 

The coordination number 6 was once thought to be characteristic for rare earth complexes (Moeller et al., 1965) but a recent survey of more than 500 crystal structures has revealed that this is the case only for scandium. Lanthanum has an average CN of 8.5 and the smallest lanthanide lutetium has a value of 7.1 (Leskel ti and Niinistb, 1980). 

The only example of this coordination number which is known at the present time occurs in the compound [Li(C4H80)4][Lu(CgH9)4] (Cotton et al., 1972). (The anion is the tetrakis(2,6-dimethylphenyl)lutetate(III) anion.) The structure of this compound is given in fig. 25.2 and shows that the lutetium-carbon bonds... 

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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