Selenium & tellurium chemistry at the beginning of the 3rd millennium: a celebration of ICCST

Up until a few decades ago, the chemistry of selenium was marginal as compared to that of sulfur, and the chemistry of tellurium was practically inexistent. Starting from the nineties, interest in the chemistry of Se and Te has grown significantly and rapidly. This can be seen through an electronic search on Scopus using as entries “sulfur/selenium/tellurium compounds”. The percentage of papers on Se/Te rises from 16.2% (of a total of 3281) in the period 1960–1970, to 32.9% (of a total of 111 065) in the period 2010–2019. One of the factors that initially has marked and determined this growth has been the development of synthetic methodologies that make use of more friendly reagents and avoid toxic compounds such as CSe₂ and H₂Se, as well as the development of instrumental techniques of investigation such as X-ray crystallography and more importantly multinuclear NMR spectroscopy. However, most importantly, the driving force of the increased interest in the chemistry of Se and Te has stemmed from the many applications discovered for their compounds in many research fields spanning from fundamental chemistry to applied chemistry in materials science, biology, pharmaceuticals, medicine and environmental science.^1,2

Selenium, which is an essential micronutrient for humans and animals with toxic effects at marginally higher concentrations, can be made less toxic as part of organo-selenium compounds, and ebselen (the first synthetic compound with glutathione peroxidase-mimicking activity) is being considered in clinical trials together with its derivatives as an antioxidant drug for heart disease and other pathologies linked to oxidative stress. On the other hand, selenocysteine and related polypeptides as well as organoselenium compounds are considered in cancer therapy, radiotherapy and cancer prevention. Interestingly, redox properties can be conveniently used to obtain specific biological activities such as antibacterial, anti-HIV, and anti-cancer activities and the ability to control and modulate the redox behavior of the selenium atom is becoming an even more attractive field of research with multidisciplinary interest.³

Se/Te rich molecules and in general metal poly-chalcogenides and chalcogenolate complexes, beside the remarkable diversity shown in their structures with interesting theoretical implications, show peculiar magnetic, conductive and optical properties which have found a large number of technological applications such as in semiconductors, magnets and NLO materials.^1,2,4,5 Starting from 1,2-dichalcogenolenes and charge-transfer salts of S/Se/Te rich molecules, materials science has developed up to well-defined (in terms of size, shape and composition) clusters with size-dependent properties, nanoparticles, quantum dots, polymers and glasses.^6,7

Further examples of this increasing interest in the chemistry of Se and Te come from the recent advances in organochalcogen chemistry for the preparation of new single source precursors for metal-chalcogenide vapor deposition of thin films with good compositional control, but also from the discovery that selenium- and tellurium-based organo-catalysts can be used conveniently in a series of functional group transformations following a “green” sustainable approach which is useful for the synthesis of new molecules with bio-pharmaceutical interest. Very recent applications have been reported using new enabling technology and non-conventional conditions.^8,9

Finally, “chalcogen-bonding” is emerging among secondary bonding interactions in materials science and crystal engineering for the production, via self-assembly of self-complementary arrays, of stable supramolecular architectures in the solid state with peculiar chemical–physical properties. More recently, intermolecular chalcogen bonding has also been exploited in solution in anion recognition and transport as well as in organocatalysis and functional group transformation.^10–13

Following the bicentenary in 2017 of the discovery of selenium by the Swedish scientist J. J. Berzelius, and with 2019 as the International Year of the Periodic Table of Chemical Elements as proclaimed by the United Nations General Assembly, we pursued a themed issue in New Journal of Chemistry encompassing all aspects of the chemistry of selenium and tellurium at the beginning of the third millennium. We also wanted in this way not only to underline the interest in the chemistry of these two elements by the Royal Society of Chemistry who have published several monographs on this topic over the past decades, but also to celebrate the “International Conference on the Chemistry of Selenium and Tellurium” (ICCST) in 2019 at its 14th edition in Italy (http://convegni.unica.it/iccst-14/). ICCST whose first edition was held in New York City in 1971, is a well-established conference dealing with all aspects of chemistry involving selenium and tellurium from small molecules to biomolecules and materials, and it is recognized as an international platform of discussion of the research on these two elements in multidisciplinary science.

The peculiarity of this collection is that it consists of papers published in the Royal Society of Chemistry journal portfolio by chemists who in the years starting from 2000 have actively participated in ICCST.

References

1. Handbook of Chalcogen Chemistry: New Perspectives in Sulfur, Selenium and Tellurium, ed. F. A. Devillanova and W.-W. du Mont, RSC Publishing, Cambridge, 2nd edn, 2013, ISBN: 978-1-84973-624-4.
2. PATAI's Chemistry of Functional Groups: The Chemistry of Organic Selenium and Tellurium Compounds, ed. Z. Rappoport, Wiley, 2013, ISBN: 978-1-118-33693-9.
3. Organoselenium Compounds in Biology and Medicine: Synthesis, Biological and Therapeutic Treatments, ed. V. K. Jain and K. I. Priyadarsini, RSC Publishing, Cambridge, 2017, ISBN: 978-1-78801-029-0.
4. Applications of Chalcogenides: S, Se, and Te, ed. G. K. Ahluwalia, Springer, 2017, ISBN: 978-3-319-41190-3.
5. M. Chhowalla, Z. Liu and H. Zhang, Chem. Soc. Rev., 2015, 44, 2584–2586 , Editorial for the themed collection: Two-dimensional transition metal dichalcogenide (TMD) nanosheets.
6. M. Green, Semiconductor Quantum Dots: Organometallic and Inorganic Synthesis, RSC Publishing, Cambridge, 2014, ISBN: 978-1-84973-985-6.
7. Chalcogenide Glasses: Preparation, properties and applications, ed. J.-L. Adam and X. Zhang, WP Woodhead Publishing, Cambridge, 2014, ISBN-13: 978-0857093455.
8. E. J. Lenardão, C. Santi and L. Sancineto, New Frontiers in Organoselenium Compounds, Springer, 2018, ISBN: 978-3-319-92405-2.
9. Selenium and Tellurium Reagents in Chemistry and Material Science, ed. R. S. Laitinen and R. Oilunkaniemi, De Gruyter, 2019, ISBN: 978-3-11-052794-0.
10. L. Vogel, P. Wonner and S. M. Huber, Angew. Chem., Int. Ed., 2018, 58, 1880–1891.
11. N. Biot and D. Bonifazi, Chem. – Eur. J., 2017, 24, 5439–5443.
12. K. T. Mahmudov, M. N. Kopylovich, M. F. C. Guedes da Silva and A. J. L. Pombeiro, Dalton Trans., 2017, 46, 10121–10138.
13. P. Scilabra, G. Terraneo and G. Resnati, Acc. Chem. Res., 2019, 52, 1313–1324.

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