Lanthanides lutetium

The parent oxacalix[3]arenes show little ability to bind alkali metals, however, a range of quaternary ammonium cations are attracted to the symmetric cavity [4]. Deprotonation of the phenol moieties allows them to bind to transition metals (scandium, titanium, vanadium, rhodium, molybdenum, gold etc.) [5-7], lanthanides (lutetium, yttrium and lanthanum) [8,9] and actinides (uranium, as uranyl)... 

From the above structural analysis it becomes clear that metal triflates with charge-to-size ratios greater than "3" (i.e. greater than that of the smallest lanthanide lutetium) should be more effective nitration catalysts. We considered that the group IV metals hafnium (r4+ = 0.78 A, Z/r = 5.13) and zirconium (r4 = 0.79 A, Z/r = 5.06) might be suitable for such a purpose. In line with this reasoning we noted that hafnium(IV) triflate has been shown to be an effective catalyst for Friedel-Crafts acylations and alkylations where the corresponding lanthanide salts were less active.20... 

The results appear in the graphs on the opposite page. In the upper graph, the first element to traverse the column and reach the bottom is the heaviest of the lanthanides, lutetium. It is followed by ytterbium, thulium, erbium, and so forth. 

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). 

Reference has been made already to the existence of a set of inner transition elements, following lanthanum, in which the quantum level being filled is neither the outer quantum level nor the penultimate level, but the next inner. These elements, together with yttrium (a transition metal), were called the rare earths , since they occurred in uncommon mixtures of what were believed to be earths or oxides. With the recognition of their special structure, the elements from lanthanum to lutetium were re-named the lanthanons or lanthanides. They resemble one another very closely, so much so that their separation presented a major problem, since all their compounds are very much alike. They exhibit oxidation state -i-3 and show in this state predominantly ionic characteristics—the ions. 

Lanthanides is the name given collectively to the fifteen elements, also called the elements, ranging from lanthanum. La, atomic number 57, to lutetium, Lu, atomic number 71. The rare earths comprise lanthanides, yttrium, Y, atomic number 39, and scandium. Sc, atomic number 21. The most abundant member of the rare earths is cerium, Ce, atomic number 58 (see Ceriumand cerium compounds). 

To avoid this confusion, and because many of the elements are actually far from rare, the terms lanthanide , lanthanon and lanthanoid have been introduced. Even now, however, there is no general agreement about the position of La, i.e, whether the group is made up of the elements La to Lu or Ce to Lu. Throughout this chapter the term lanthanide and the general symbol, Ln, will be used to refer to the fourteen elements cerium to lutetium inclusive, the Group 3 elements, scandium, yttrium and lanthanum having already been dealt with in Chapter 20. 

The lanthanides comprise the largest naturally-occurring group in the periodic table. Their properties are so similar that from 1794, when J. Gadolin isolated yttria which he thought was the oxide of a single new element, until 1907, when lutetium was discovered, nearly a hundred claims were made for the discovery of elements... 

Di-rerr-butylsodium pyrrolate serves as a source of the complexes of lanthanides [93CB2657 95JOM(495)C12]. Thus, with cyclooctadienyl chlorides of samarium, thulium, and lutetium, it affords species 89 [96JOM(507)287]. The N-coordinated samarium(II) calix-pyrrole complex is known [99AG(E)1432]. 

The atomic radii of the second row of d-metals (Period 5) are typically greater than those in the first row (Period 4). The atomic radii in the third row (Period 6), however, are about the same as those in the second row and smaller than expected. This effect is due to the lanthanide contraction, the decrease in radius along the first row of the / block (Fig. 16.4). This decrease is due to the increasing nuclear charge along the period coupled with the poor shielding ability of /-electrons. When the d block resumes (at lutetium), the atomic radius has fallen from 217 pm for barium to 173 pm for lutetium. 

Metathetical routes using bulky lithium guanidinates as starting materials have also been employed to synthesize bis(guanidinato) lanthanide halides as well as reactive alkyls and hydrides. Scheme 63 shows as a typical example the formation of the lutetium chloro precursor, which was isolated in 76% yield. ... 

To date, the only organometallic lanthanide porphyrin complexes to be reported contain yttrium and lutetium, and they will be considered in the section on scandium. Representative structural types of porphyrin complexes containing groups 3 and 4 metals are shown in Fig. 3 and selected data for all the structurally characterized complexes are given in Table 11. 

Between barium (Group 2, element 56) and lutetium (Group 3, element 71), the 4f orbitals fill with electrons, giving rise to the lanthanides, a set of 14 metals named for lanthanum, the first member of the series. The lanthanides are also called the rare earths, although except for promethium they are not particularly rare. Between radium (Group 2, element 88) and lawrenclum (Group 3, element 103), are the 14 actinides, named for the first member of the set, actinium. The lanthanides and actinides are also known as the inner transition metals. 

The rare earth elements (R) are those from atomic numbers 57-71, emanating as a particular series from the parent element lanthanum (atomic no. 57). The set of 14 elements from cerium (58) through lutetium (71) inclusive are commonly known as the lanthanoid (or lanthanide Ln) series. The rare earths form a bridge at the... 

The last of the lanthanides, this metal is also the hardest and the densest of them. It is a component of cerium mischmetal. Lutetium has some applications in optoelectronics. Shows great similarities to ytterbium. Its discoverer, Georges Urbain, carried out 15 000 fractional crystallizations to isolate pure lutetium (record ). The element has special catalytic properties (oil industry). 176Lu is generated artificially and is a good beta emitter (research purposes). 177Lu has a half-life of six days and is used in nuclear medicine. 

Coordination compounds composed of tetrapyrrole macrocyclic ligands encompassing a large metal ion in a sandwich-like fashion have been known since 1936 when Linstead and co-workers (67) reported the first synthesis of Sn(IV) bis(phthalocyanine). Numerous homoleptic and heteroleptic sandwich-type or double-decker metal complexes with phthalocyanines (68-70) and porphyrins (71-75) have been studied and structurally characterized. The electrochromic properties of the lanthanide pc sandwich complexes (76) have been investigated and the stable radical bis(phthalocyaninato)lutetium has been found to be the first example of an intrinsic molecular semiconductor (77). In contrast to the wealth of literature describing porphyrin and pc sandwich complexes, re-... 

The leach liquor is first treated with a DEHPA solution to extract the heavy lanthanides, leaving the light elements in the raffinate. The loaded reagent is then stripped first with l.Smoldm nitric acid to remove the elements from neodymium to terbium, followed by 6moldm acid to separate yttrium and remaining heavy elements. Ytterbium and lutetium are only partially removed hence, a final strip with stronger acid, as mentioned earlier, or with 10% alkali is required before organic phase recycle. The main product from this flow sheet was yttrium, and the yttrium nitrate product was further extracted with a quaternary amine to produce a 99.999% product. 

The rate of extraction of the lanthanides by the 2-ethylhexyl ester of 2-ethylhexylphosphonic acid (e.g., PC88A, P507) is slower than for DEHPA but the higher distribution coefficients allow extraction from more dilute solutions. Also, as acidic stripping is easier than with DEHPA, the reagent has been used commercially to separate lutetium from terbium and ytterbium. 

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