Aspects of Anion Coordination from Historical Perspectives

Abstract

Supramolecular chemistry, the chemistry beyond themolecule, gained its entrywith the pioneering work of Pedersen, Lehn, and Cram in the decade 1960–1970 [1–5]. The concepts and language of this chemical discipline, which were in part borrowed from biology and coordination chemistry, can be to a large extent attributed to the scientific creativity of Lehn [6–8]. Recognition, translocation, catalysis, and self-organization are considered as the four cornerstones of supramolecular chemistry. Recognition includes not only thewell-known transitionmetals (classical coordination chemistry) but also spherical metal ions, organic cations, and neutral and anionic species. Anions have a great relevance from a biological point of view since over 70% of all cofactors and substrates involved in biology are of anionic nature. Anion coordination chemistry also arose as a scientific topic with the conceptual development of supramolecular chemistry [8]. An initial reference book on this topic published in 1997 [9] has been followed by two more recent volumes [10, 11] and a number of review articles, many of them appearing in special journal issues dedicated to anion coordination. Some of these review articles are included in Refs [12–52]. Very recently, an entire issue of the journal Chemical Society Reviews was devoted to the supramolecular chemistry of anionic species [53]. Since our earlier book [9] the field has catapulted way beyond the early hosts and donor groups. Because covering the historical aspects of this highly evolved field would be impossible in the limited space here, a slightly different approach will be taken in this chapter. Rather than detail the entry of the newer structural strategies toward enhancing anion binding and the many classes of hydrogen bond donor groups that have come into the field, only the earlier development will be described. This will be linked with aspects of naturally occurring hosts, to provide a slightly different perspective on this exciting field. Interestingly enough, the birth of the first-recognized synthetic halide receptors occurred practically at the same time as the discovery by Charles Pedersen of the alkali and alkaline-earth complexing agents, crown ethers. While Pedersen