Comparative Chelate Stabilities By Potentiometric Titrations

Abstract

A chelate is a particular type of a complex or coordination compound. When a metal ion occupies two or more places on an electron donor to form a ring, it is said to form a chelation compound, the electron donor being considered the chelating agent. The word "chelate", applied to such a structure, comes from the Greek "chele", meaning claw, and thus ligands (or chelating agents) are saide to be bidentate, tridentate, quadridentate (two teeth, three teeth, four teeth, etc.) depending on the number of atoms open on the ligand for chelation. Complexes and chelates are formed by nearly all of the metals of the periodic system. Although the number of know chelating and complexing agents is very large, the donor atoms which undergo combination with the metal are restricted to the strongly non-metalic elements of Groups V and VI. Of these, N, O, and S are the only common examples. The number of applications which man has found for this class of compounds is remarkable. However, man cannot take credit for the two most important uses of chelate compounds; the use of the magnesium chelate, chlorophyll, as a catalyst for the incorporation of the hydrodgen of water into plant systems; and the use of the iron chelate, heme, as an oxygen carrier in human respiration. Chelates have found use as textile dyes, bacteriacides, water softeners, enzyme deactivators, or artificial "oxygen-carriers". They are used for approximate colorimetric estimation of ions in analytical chemistry, and they have proven valuable in separating metal ions by solvent extraction. A chelate is a particular type of a complex or coordination compound. When a metal ion occupies two or more places on an electron donor to form a ring, it is said to form a chelation compound, the electron donor being considered the chelating agent. The word "chelate", applied to such a structure, comes from the Greek "chele", meaning claw, and thus ligands (or chelating agents) are saide to be bidentate, tridentate, quadridentate (two teeth, three teeth, four teeth, etc.) depending on the number of atoms open on the ligand for chelation. Complexes and chelates are formed by nearly all of the metals of the periodic system. Although the number of know chelating and complexing agents is very large, the donor atoms which undergo combination with the metal are restricted to the strongly non-metalic elements of Groups V and VI. Of these, N, O, and S are the only common examples. The number of applications which man has found for this class of compounds is remarkable. However, man cannot take credit for the two most important uses of chelate compounds; the use of the magnesium chelate, chlorophyll, as a catalyst for the incorporation of the hydrodgen of water into plant systems; and the use of the iron chelate, heme, as an oxygen carrier in human respiration. Chelates have found use as textile dyes, bacteriacides, water softeners, enzyme deactivators, or artificial "oxygen-carriers". They are used for approximate colorimetric estimation of ions in analytical chemistry, and they have proven valuable in separating metal ions by solvent extraction.