Chemistry Everyday for Everyone
Some Linguistic Detail on Chelation Daniel T. Haworth Department of Chemistry, Marquette University, Milwaukee, WI 53201-1881 Abstract The term chelate was first applied by Morgan and Drew in 1920 to describe the heterocyclic rings formed from bidentate ligands bonding to a central atom. The history of the word chelate is traced from its original Greek meaning through the Latin language to its anglicized form, chela. This word has a very rich history and has been cited by both Greek (Aristotle) and Latin (Cicero, Vergil) philosophers and poets. Keywords History/Philosophy Coordination Chemistry Inorganic Chemistry Nomenclature/Units/Symbols Supplementary Materials No supplementary material available.
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JChemEd.chem.wisc.edu • Vol. 75 No. 1 January 1998 • Journal of Chemical Education
Abstract
Chemistry Everyday for Everyone
Some Linguistic Detail on Chelation Daniel T. Haworth Department of Chemistry, Marquette University, Milwaukee, WI 53201-1881
The term chelate was first applied in 1920 by G. T. Morgan and H. D. K. Drew (1), who stated: “The adjective chelate, derived from the great claw or chela (chely) of the lobster or other crustaceans, is suggested for the caliper like groups which function as two associating units and fasten to the central atom so as to produce heterocyclic rings.” Diehl later wrote that these chelated cyclic structures arise from the unions of metallic atoms with either organic or inorganic molecules such as ethylenediamine, the term chelate being derived from the Greek word chela (2). The early Russian investigator Chugaev first noted that chelating ligands are much less likely displaced from a complex than are monodentate ligands of the same type, hence the origin of the term chelate effect (3). With the discovery of metal complexes containing ligands with three or four bonds to a metal, Morgan devised the names tridentate (three-toothed) and quadridentate (four-toothed) (2). Examination of the Greek language (4) reveals that the word ch¯el¯e (χηλη′) has the basic meaning of a horse’s hoof, and by extension, anything resembling the hoof of a horse. It is also clear from various texts that it was used by Aristotle (ca. 325 BCE) to refer to a crab’s claw in his books Historia Animalium (History of Animals, 527 b5) and De Partibus Animalium (The Parts of Animals, 684a27). Other uses for this word in Greek include a breakwater and various cloven or hooked implements (forked probes as used in surgery). Although there are other native Latin words for claw, hoof, etc., the Greek word chele was taken over into Latin (5) bodily as chele to mean claw-shaped piece or mechanism—something like a manacle. Vitrius, a Roman of August’s time (first century CE) wrote on architecture and used the word ch¯el¯e in this sense. Chele was borrowed from the Greek and also applied by the writers Cicero, Vergil, Lucan, and Columella in an astronomical context to specifically re¯ ¯i) of the southfer to the claws (chalae—pronounced kal ern constellation Scorpio, which is partly in the Milky Way and adjoins the constellation Libra. Libra and Scor-
pio are also found in the zodiac as the seventh (balance) and eighth (scorpion) signs, respectively. These uses of the word chele come from the first century BCE and first century CE. More general words for claw in Latin are uniquis and ungula and even bracchium (to designate a cralis claw). A reference (5) to the use of chela in the meaning of crab’s claw is also found in medieval Latin (ca. 1200 CE). Thus the Greek word ch¯el¯e has been anglicized (6) to chela along with the English adjective, verb, and noun forms chelate and chelation. Most chemistry textbooks refer to the anglicized version as being Greek. The English use of this word by Morgan to represent the bidentate nature of a ligand such as ethylenediamine as forming a scorpion’s (crab’s) claw was used to represent the above situation. It would be most confusing to visualize a metal complex or to explain its cyclic structure using the original Greek chele as meaning a horse’s hoof. This is an interesting linguistic history of one word through twenty-four centuries. Acknowledgment The assistance of P. A. Marquardt and M. A. Haworth in the Greek and Latin translations is appreciated. Literature Cited 1. Morgan, G. T.; Drew, H. D. K. J. Chem. Soc. 1920, 117, 1456. 2. Diehl, H. Chem. Rev. 1937, 39, 21. 3. Crabtree, R. H. The Organometallic Chemistry of the Transition Metals; Wiley: New York, 1988; p 2. 4. The Greek–English Lexicon; Barber, E. A., Ed.; Clarendon: Oxford, 1968. 5. The Oxford Latin Dictionary; Glare, P. G. W., Ed.; Clarendon: Oxford, 1982. 6. Webster’s Third New International Dictionary; Babcock, P., Ed.; Merriam-Webster: Springfield, MA, 1993.
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