Chemical Properties Of Chelating Agents

A complex ion composed of a positive ion (called a central ion) and several neutral molecules or ions (called a ligand) is called a complex ion (also called a complex ion), and a compound containing a complex ion is called a coordination compound . This coordination compound has a cyclic structure. Its stability is higher than non-chelated compounds with similar composition and structure.
In the complex, the central ion and the ligand are combined through coordination bonds. Coordination bond is a special type of covalent bond. A common covalent bond is formed by two bonding atoms each providing an electron to form a common electron pair. In a coordination bond, one atom provides an electron pair and the other Atoms provide empty orbitals. In order to distinguish, the covalent bond is represented by "one", such as H·+·H=H:H (H-H), the coordination bond is represented by "←", and the arrow points to the atom providing an empty orbital, such as Cu+NH3= CuNH3 (Cu←NH3).
If there is only one coordination atom in the ligand, only one coordination bond can be formed between the central ion and the ligand. When some ligand molecules contain more than two coordinated atoms and there are two to three other non-coordinated atoms between the two atoms, the ligand can form two ligands with the central ion (or atom) at the same time. The above coordination keys. The number of atoms that directly coordinate with the central ion is called the coordination number. Usually the coordination number is 4 or 6, but there are also 2 and 8. The coordination number depends on the electronic structure and steric factors of the central particle.
The most common coordinating atoms are oxygen, sulfur, and nitrogen. Phosphorus, arsenic, and selenium can also form chelates. In the chelating agent molecule, the coordination atoms are connected through other atoms (mainly carbon atoms) into a suitable structure. According to the number of coordination atoms contained in the chelating agent molecule that can participate in coordination, it is divided into two-, three-, four- and six-terminal chelating agents.
Chelating agents include inorganic and organic types. Most are organic compounds. Commonly used chelating agents include polyphosphates, aminocarboxylic acids, 1,3-diketones, hydroxycarboxylic acids, polyamines, etc.
Chelating agents have various structural formulas, including straight-chain and branched-chain structures. There are also cyclic chelating agents such as porphyrin derivatives and crown ether derivatives.