Periodic Table, The: Past, Present, And Future

it seems to be on the borderline of some ion-packing arrangements. For the lanthanoid(III) fluorides, from lanthanum to promethium, the crystal structure is based upon the nine-coordinate lanthanum(III) fluoride tricapped trigonal prism arrangement. Then from samarium to lutetium, the crystal structure is, by contrast, based upon the eight-coordinate yttrium(III) fluoride bicapped trigonal prism. Similarly, for the lanthanoid(III) iodides, from lanthanum to promethium, the crystal structure is based upon the eight-coordinate plutonium(III) bromide bicapped trigonal prism. Then from samarium to lutetium, the crystal structure is based upon the six-coordinate iron(III) chloride octahedral structure.

External Lanthanoid Relationships

Surprisingly, all the lanthanoid(III) (and yttrium(III)) ions have been shown to be essential cofactors in certain enzymes in methylotrophic bacteria. They bind 10⁸ times more strongly to the ligand sites than calcium, which is the usual metal ion in such enzymes [41]. Nevertheless, it is with the two “unusual” oxidation states of lanthanoids for which there are interesting similarities with other elements.

Similarities of Europium(II) with Strontium (and Calcium)

The europium(II) ion behaves very similarly to an alkaline earth ion; for example, its carbonate, sulfate, and chromate are insoluble, as are those of the heavier alkaline earth metals. The ionic radius of europium(II) is actually very similar to that of strontium, and, as might be expected, several europium(II) and strontium compounds are isostructural.

In the study of lanthanoid-containing minerals, the proportion of europium can be significantly different from that of the other lanthanoids [42]. In anaerobic geothermal conditions, europium(III) can be reduced to europium(II). Then, though significantly larger than the calcium ion, europium(II) can replace calcium in minerals. This ion exchange process is known as the europium anomaly and it is said to be “positive” if europium is enriched with respect to the other lanthanoids and “negative” if it is depleted.

Similarities of Cerium(IV) with Zirconium(IV) and Hafnium(IV)

Whereas europium has a lower than normal oxidation state, cerium has a higher than normal oxidation state of +4. Cerium(IV) behaves like zirconium(IV) and hafnium(IV) of Group 4. For example, all three of these ions form insoluble fluorides and phosphates. The similarity can be seen from a comparison of acid–base behavior under strongly oxidizing conditions (Table 12.2).

The ready oxidation of cerium(III) to cerium(IV) has significant geochemical implications. For example, the similar ion sizes of cerium(IV) and zirconium(IV) resulted in incorporation of Ce⁴⁺ ions into zircons, key minerals in the context of the earliest Earth’s rocks [43].

Table 12.2 Schematic of predominant species with pH under oxidizing conditions

Commentary

It is time for the lanthanoids to have their “day in the Sun” and not be relegated to a passing mention — if anything at all — in chemistry courses. Apart from the fact that they do have interesting chemistry, their many applications in the real world require students to be aware of them.

References

1.S. Cotton, Lanthanide and Actinide Chemistry: Inorganic Chemistry (A Textbook Series), Wiley, Chichester, England (2006).

2.H. Liu et al., “One-Pot Solvothermal Synthesis of Singly Doped Eu³⁺ and Codoped Er³⁺,Yb³⁺ Heavy Rare Earth Oxysulfide Y₂O₂S Nano-Aggregates and their Luminescence Study,” RSC Adv. 4(100), 57048–57053 (2014).

3.S. P. Petrosyants, “Coordination Polymers of Indium, Scandium, and Yttrium” Russ. J. Inorg. Chem. 58(13), 1605–1624 (2013).

4.Z. Ahmad, “The Properties and Application of Scandium-Reinforced Aluminum,” JOM 55(2), 35–39 (2003).

5.J. W. van Spronsen, The Periodic System of the Chemical Elements: A History of the First Hundred Years, Elsevier, Amsterdam, 260–284 (1969).

6.G. C. Pimentel and R. D. Sprately, Understanding Chemistry, Holden-Day, San Francisco, CA, 862 (1971).

7.T. Moeller, The Chemistry of the Lanthanides: Pergamon Texts in Inorganic Chemistry (Volume 26), Pergamon Press, New York, NY (1973).

8.C. J. Jones, d- and f-block Chemistry: Tutorial Chemistry Texts, Royal Society of Chemistry, London, England (2001).

9.H. C. Aspinall, Chemistry of the f-Block Elements: Advanced Chemistry Texts, Gordon & Breech, Amsterdam (2001).

10.C.-H. Huang (Ed.), Rare Earth Coordination Chemistry: Fundamentals and Applications, John Wiley, Singapore (2010).

11.B. D. Cullity and C. D. Graham, Introduction to Magnetic Materials, 2nd ed., Wiley, New York, NY (2009).

12.G. A. Molander, “Application of Lanthanide Reagents in Organic Synthesis,” Chem. Revs. 92, 29–68 (1992).

13.W. J. Evans, “Perspectives in Reductive Lanthanide Chemistry,” Coord. Chem. Revs. 206–207, 263–283 (2000).

14.J.-C. G. Bünzli et al., “New Opportunities for Lanthanide Luminescence,” J. Rare Earths 25(3), 257–274 (2007).

15.K. Binnemans, “Lanthanide-Based Luminescent Hybrid Materials,” Chem. Rev. 109, 4283–4374 (2009).

16.J.-C. G. Bünzli and S. V. Eliseeva, “Intriguing Aspects of Lanthanide Luminescence,” Chem. Sci. 4, 1939–1949 (2013).

17.A. Pol et al., “Rare Earth Metals Are Essential for Methanotrophic Life in Volcanic Mudpots,” Environ. Microbiol. 16(1), 255–264 (2014).

18.N. E. Holden and T. Coplen, “The Periodic Table of Elements,” Chem. Int. 26(1), 1 (2004).

19.E. D. Cater, “High Temperature Chemistry of Rare Earth Compounds: Dramatic Examples of Periodicity,” J. Chem. Educ. 55(11), 697–701 (1978).

20.D. A. Johnson, “Principles of Lanthanide Chemistry,” J. Chem. Educ. 57(7), 475–477 (1980).

21.M. Laing, “A Revised Periodic Table with the Lanthanides Repositioned,” Found. Chem. 7, 203–233 (2005).

22.P. F. Lang, “Is a Metal ‘Ions in a Sea of Delocalized Electrons’?” J. Chem. Educ. 95, 1787–1793 (2018).

23.D. A. Johnson and P. G. Nelson, “Valencies of the Lanthanides,” Found. Chem. 20, 15–27 (2018).

24.M. Seitz et al., “The Lanthanide Contraction Revisited,” J. Am. Chem. Soc. 129, 11153–11160 (2007).

25.B. E. Douglas, “The Lanthanide Contraction,” J. Chem. Educ. 31(11), 598–599 (1954).

26.D. W. Pearce and P. W. Selwood, “Anomalous Valencies of the Rare Earths,” J. Chem. Educ. 13(5), 224–230 (1936).

27.D. R. Lloyd, “On the Lanthanide and ‘Scandinide’ Contractions,” J. Chem. Educ. 63(6), 502–503 (1986).

28.Q. Zhang et al., “Pentavalent Lanthanide Compounds: Formation and Characterization of Praseodymium(V) Oxides,” Angew. Chem. Int. Ed. Engl. 55(24), 6896–6900 (2016).

29.S. Fabre et al., “Paleoceanographic Significance of Cerium Anomalies during the OAE 2 on the NW African Margin,” J. Sediment. Res. 88(11), 1284–1299 (2018).

30.M. N. Bochkarev, “Molecular Compounds of ‘New’ Divalent Lanthanides,” Coord. Chem. Rev. 248(9–10), 835–851 (2004).

31.C. T. Palumbo et al., “Molecular Complex of Tb in the +4 Oxidation State,” J. Am. Chem. Soc. 141(25), 9827–9831 (2019).

32.P. F. Lang and B. C. Smith, “Ionization Energies of the Lanthanides,” J. Chem. Educ. 87(8), 875–881 (2010).

33.R. Schmid, “The Noble Gas Configuration — Not the Driving Force but the Rule of the Game in Chemistry,” J.