one of the classes of complex compounds. A classical example of a chelate compound is copper glycinate:
The donor (a glycine radical of structure NH2CH2COO-) is simultaneously linked to the central atom (Cu) by two functional groups. The Cu—O bond is ionic, and the Cu—N bond is covalent. The central atom is, as it were, drawn toward the inside of the donor; hence the name of compounds of this type. Chelate compounds are characterized by low solubility in water and by anomalous colors that differ greatly for different metal ions (which has led to their extensive application in analytical chemistry as very sensitive and selective re-agents). A well-known special volumetric method of analytical chemistry, complexometry, is based on the formation of chelate compounds of various metals with polybasic amino acids, especially Trilon B (a disodium salt of ethylenediaminetetraacetic acid). The most important natural pigments, chlorophyll and hemoglobin, are chelate compounds.
REFERENCESGrinberg, A. A. Vvedenie v khimiiu kompleksnykh soedinenii, 3rd ed. Moscow-Leningrad, 1966.
Shvartsenbakh, G. “Kompleksometricheskoe titrovanie.” In Kompleksometriia. Moscow, 1958.
Basolo, F., and R. Johnson. Khimiia koordinatsionnykh soedinenii. Moscow, 1966. (Translated from English.)