Lanthanide elements, coordination chemistry

The analytical chemistry of the transition elements see Transition Metals), that is, those with partly filled shells of d (see (f Configuration) or f electrons see f-Block Metals), should include that of the first transition period (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) and that of the second transition series (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, and Ag). The third transition series embraces Hf, Ta, W, Re, Os, Ir, Pt, and An, and although it formally begins with lanthanum, for historical reasons this element is usually included with the lanthanoids (rare-earth elements) see Scandium, Yttrium the Lanthanides Inorganic Coordination Chemistry Rare Earth Elements). The actinoid elements see Actinides Inorganic Coordination Chemistry) are all radioactive see Radioactive Decay) and those with atomic number see Atomic Number) greater than uranium (Z = 92) are artificial the analytical chemistry of these elements is too specialized to consider here. 

Higher coordination numbers of 8 -F 1 are adopted in the LT-YF3 type by the trifluorides of the larger ions TP+, bP+ and the smaller rare-earth ions Sm to Ln. The tysonite or LaF3 type with CN 9 + 3 is found for the trifluorides of the larger 4f and the 5f elements (see Scandium, Yttrium the Lanthanides Inorganic Coordination Chemistry). 

The structure and behavior of lanthanides and actinides in ILs has recently been summarized in detail by Binnemans and the reader is referred to this excellent review for more details [71]. Among others, it has been pointed out that solvation of the metal ions by the IL components is a major issue in f-element coordination chemistry [71, 79, 218, 219], Understanding the solvation is also a key to understanding f-element extraction processes. Among others, theoretical studies suggest that Ln3+ (Ln = La, Eu, Yb) are surrounded by six PF6 anions in Bmim-PF6 and by 11-13 imidazolium ions in the second ionic sphere. The same authors also suggest that free lanthanide cations, that is, cations without a solvation shell, are poorly soluble in Bmim-PF6 [149, 152, 220-223], They also report that, while [LnCls]3 complexes are unstable in the gas phase, they can be stabilized by solvation in ILs. 

Hudson, M.J., Drew, M.G.B., Foreman, M.R.StJ., Hill, C., Huet, N., Madic, C., Youngs, T.G.A. 2003. The coordination chemistry of 1,2,4-triazinyl bipyridines with lanthanides(EH) elements - implications for the partitioning of americium(III). Journal of the Chemical Society, Dalton Transactions 9 1675-1685. 

The historical sketch outlines the class of lanthanide amides this article is to deal with and which is further manifested in Scheme 1. Organometallic amides which can be classified as dialkyl (-aryl, -silyl) amides and amides derived from unsaturated heterocyclic ligands are seen with respect to N-unsubstituted (primary, inorganic) amides. The consideration of more classic coordination compounds like acid amides or sulfonamides, often ascribed as wet chemistry , is excluded. The historical data also demonstrate the relatively late start of lanthanide amide chemistry reflecting the late industrial establishment of the lanthanide elements (separation, purification, etc.) [9], However, lanthanide amides are still the youngest class in conjunction with the most important pillars of organometallic lanthanide chemistry, namely the alkyls/cyclopentadienyls (LnCp3, 1954, [10]) and the alkoxides (Ce(OR)4 1956 [11a] La(OR)3 , 1958 [lib]). Indeed most of the work has been conducted in the last ten years. 

Like 77 -CsHs, phospholyl ligands form stable complexes with a diverse array of alkaline, transition, and lanthanide metals, in addition to a variety of main group elements. Although the coordination chemistry of phospholyl ligands is potentially complicated as a consequence of a variety of coordination modes, it is now well established that the presence of sterically demanding groups in the position a to P on the ring favors 77 -coordination. 

Useful sources of information on these elements and their componnds inclnde the Gmelin Handbook / with extensive np-to-date coverage, and regular comprehensive reviews in the Handbook on the Physics and Chemistry of the Rare Earths / General acconnts of the elements, their inorganic chemistry, and coordination chemistry exist, the latter being the most np-to-date. There are also recent monographs, and compilations of in-depth and informed articles on different aspects of lanthanide chemistry and spectroscopy. ... 

Lanthanide elements have atomic numbers ranging from 57 to 71. With the inclusion of scandium (Sc) and yttrium (Y), a total of 17 elements are referred to as the rare earth elements. A mixture of rare earths was discovered in 1794 by J. Gadolin and ytterbium was separated from this mixture in 1878 by Mariganac, while the last rare earth element promethium (Pm) was separated by a nuclear reaction in 1974. Therefore, a period of more than 100 years separates the discovery of all the rare earth elements. In the latter part of the last century scientists started to focus on the applications of rare earth elements. Numerous interesting and important properties were found with respect to their magnetic, optical, and electronic behavior. This is the reason that many countries list all rare earth elements, except promethium (Pm), as strategic materials. Rare earth coordination chemistry, therefore, developed quickly as a result of this increased activity. 

Lanthanide elements (referred to as Ln) have atomic numbers that range from 57 to 71. They are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). With the inclusion of scandium (Sc) and yttrium (Y), which are in the same subgroup, this total of 17 elements are referred to as the rare earth elements (RE). They are similar in some aspects but very different in many others. Based on the electronic configuration of the rare earth elements, in this chapter we will discuss the lanthanide contraction phenomenon and the consequential effects on the chemical and physical properties of these elements. The coordination chemistry of lanthanide complexes containing small inorganic ligands is also briefly introduced here [1-5]. 

Tetrad Effect of Lanthanide Elements - Changing Gradation Rules in Lanthanide Coordination Chemistry... 

The Chemistry of the Heavier Transition Metals 587 Oxidation States and EMFs of Groups ]-12 588 The Lanthanide and Actinide Elements 599 Coordination Chemistry 608 The Transactinide Elements 613... 

Coordination Chemistry of the Lanthanide Elements — One Hundred Years of Development and Understanding... 

Although it might be assumed quite reasonably that the coordination chemistry of the some 15 elements known during Werner s lifetime would have developed significantly during that period, the literature contains only a few accounts of synthesis and characterization. Indeed, the 1920 edition of Werner s classic monograph (50) records essentially the same information as the 1908 edition, namely the compositions of a limited number of double nitrates, sulfates, and oxalates. Both Spencer ( 5) and Little in their comprehensive compilations of data at about the same time, describe only certain lanthanide double salts and adducts, but not within the framework of complex compounds or coordination chemistry. 

Subsequent developments prior to the 1940 were meager, and even as late as 1953 the significant aspects of this area were reviewed in terms of only 60 literature citations (55). Yet a 1965 review covering published information only through 1962 required in excess of 500 references (55), and the current literature contains literally a fiood of accounts of various aspects of the coordination chemistry of the lanthanide elements. 

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