Lanthanide
Lutetium is a d-block element (thus also a transition metal),[6][7] and on this basis its inclusion has been questioned; however, like its congeners scandium and yttrium in group 3, it behaves similarly to the other 14.
[8] All lanthanide elements form trivalent cations, Ln3+, whose chemistry is largely determined by the ionic radius, which decreases steadily from lanthanum (La) to lutetium (Lu).
Primordial From decay Synthetic Border shows natural occurrence of the element The term "lanthanide" was introduced by Victor Goldschmidt in 1925.
[9][10] Despite their abundance, the technical term "lanthanides" is interpreted to reflect a sense of elusiveness on the part of these elements, as it comes from the Greek λανθανειν (lanthanein), "to lie hidden".
Together with the stable elements of group 3, scandium, yttrium, and lutetium, the trivial name "rare earths" is sometimes used to describe the set of lanthanides.
[14] Very small differences in solubility are used in solvent and ion-exchange purification methods for these elements, which require repeated application to obtain a purified metal.
The diverse applications of refined metals and their compounds can be attributed to the subtle and pronounced variations in their electronic, electrical, optical, and magnetic properties.
[13] By way of example of the term meaning "hidden" rather than "scarce", cerium is almost as abundant as copper;[13] on the other hand promethium, with no stable or long-lived isotopes, is truly rare.
[15] * Between initial Xe and final 6s2 electronic shells ** Sm has a close packed structure like most of the lanthanides but has an unusual 9 layer repeat Gschneider and Daane (1988) attribute the trend in melting point which increases across the series, (lanthanum (920 °C) – lutetium (1622 °C)) to the extent of hybridization of the 6s, 5d, and 4f orbitals.
[18] As there are seven 4f orbitals, the number of unpaired electrons can be as high as 7, which gives rise to the large magnetic moments observed for lanthanide compounds.
The similarity in ionic radius between adjacent lanthanide elements makes it difficult to separate them from each other in naturally occurring ores and other mixtures.
[1][25] When in the form of coordination complexes, lanthanides exist overwhelmingly in their +3 oxidation state, although particularly stable 4f configurations can also give +4 (Ce, Pr, Tb) or +2 (Sm, Eu, Yb) ions.
4f electrons have a high probability of being found close to the nucleus and are thus strongly affected as the nuclear charge increases across the series; this results in a corresponding decrease in ionic radii referred to as the lanthanide contraction.
Hard Lewis acids are able to polarise bonds upon coordination and thus alter the electrophilicity of compounds, with a classic example being the Luche reduction.
The large size of the ions coupled with their labile ionic bonding allows even bulky coordinating species to bind and dissociate rapidly, resulting in very high turnover rates; thus excellent yields can often be achieved with loadings of only a few mol%.
This allows for easy tuning of the steric environments and examples exist where this has been used to improve the catalytic activity of the complex[31][32][33] and change the nuclearity of metal clusters.
[34][35] Despite this, the use of lanthanide coordination complexes as homogeneous catalysts is largely restricted to the laboratory and there are currently few examples them being used on an industrial scale.
The normal range of oxidation states can be expanded via the use of sterically bulky cyclopentadienyl ligands, in this way many lanthanides can be isolated as Ln(II) compounds.
[49] The CuTi2 structure of the lanthanum, cerium and praseodymium diiodides along with HP-NdI2 contain 44 nets of metal and iodine atoms with short metal-metal bonds (393-386 La-Pr).
CeO2 is basic and dissolves with difficulty in acid to form Ce4+ solutions, from which CeIV salts can be isolated, for example the hydrated nitrate Ce(NO3)4.5H2O.
As an example, gadolinium oxysulfide, Gd2O2S doped with Tb3+ produces visible photons when irradiated with high energy X-rays and is used as a scintillator in flat panel detectors.
[63] When mischmetal, an alloy of lanthanide metals, is added to molten steel to remove oxygen and sulfur, stable oxysulfides are produced that form an immiscible solid.
[48] The other pnictides phosphorus, arsenic, antimony and bismuth also react with the lanthanide metals to form monopnictides, LnQ, where Q = P, As, Sb or Bi.
Because of their large size, lanthanides tend to form more stable organometallic derivatives with bulky ligands to give compounds such as Ln[CH(SiMe3)3].
Monazite is a phosphate of numerous group 3 + lanthanide + actinide metals and mined especially for the thorium content and specific rare earths, especially lanthanum, yttrium and cerium.
[86] Other lanthanide-bearing minerals include bastnäsite, florencite, chernovite, perovskite, xenotime, cerite, gadolinite, lanthanite, fergusonite, polycrase, blomstrandine, håleniusite, miserite, loparite, lepersonnite, euxenite, all of which have a range of relative element concentration and may be denoted by a predominating one, as in monazite-(Ce).
Three of the lanthanide elements have radioactive isotopes with long half-lives (138La, 147Sm and 176Lu) that can be used to date minerals and rocks from Earth, the Moon and meteorites.
Lanthanide oxides are mixed with tungsten to improve their high temperature properties for TIG welding, replacing thorium, which was mildly hazardous to work with.
The SPY-1 radar used in some Aegis equipped warships, and the hybrid propulsion system of Arleigh Burke-class destroyers all use rare earth magnets in critical capacities.
[95][96] These are well-suited for this application due to their large Stokes shifts and extremely long emission lifetimes (from microseconds to milliseconds) compared to more traditional fluorophores (e.g., fluorescein, allophycocyanin, phycoerythrin, and rhodamine).
