ligand (lĭg`ənd), charged or uncharged molecule with one or more unshared pairs of electrons that can attach to a central metallic atom atom [Gr.,=uncuttable (indivisible)], basic unit of matter ; more properly, the smallest unit of a chemical element having the properties of that element.

Structure of the Atom

..... Click the link for more information. or ion ion, atom or group of atoms having a net electric charge .

Positive and Negative Electric Charges

A neutral atom or group of atoms becomes an ion by gaining or losing one or more electrons or protons.
..... Click the link for more information. to form an aggregate known as a complex ion (see chemical bond chemical bond, mechanism whereby atoms combine to form molecules . There is a chemical bond between two atoms or groups of atoms when the forces acting between them are strong enough to lead to the formation of an aggregate with sufficient stability to be regarded as
..... Click the link for more information. ). Some ligands that share electrons with metals form very stable complexes. Some common bases that act as ligands are water and ammonia molecules and halide, hydroxide, acetate, cyanide, thiocyanate, and nitrite anions anion (ăn`ī'ən), atom or group of atoms carrying a negative charge.
..... Click the link for more information. . These ligands are monofunctional, i.e., they are attached by one unshared pair of electrons during complexing. Polyfunctional ligands, which bind to the metal ion with two or more pairs of electrons, are called chelates (see chelating agents chelating agents (kē`lātĭng).
..... Click the link for more information. ). Ethylenediamine-tetraacetate, a commonly used chelating compound, has six pairs of electrons to bind to metal ions. Electron-donating functional groups containing nitrogen, oxygen, sulfur, phosphorous, or carbon may act as ligands in complex biological systems. For example, in enzymes that need complexed metal ions to function, mercapto (sulfur-containing) groups and amino (nitrogen-containing) groups act as chelating agents; these groups fix the metal ion in a specific position. Other biologically important molecules, such as chlorophyll, vitamin B₁₂, and heme, also have nitrogen-containing groups that donate electrons and have a chelating function.

ligand

Atom, group (see functional group), or molecule attached to a central atom, usually of a transition element, in a coordination or complex compound (see bonding). It is almost always the electron-pair donor (nucleophile) in a covalent bond. Common ligands include the neutral molecules water (H₂O), ammonia (NH₃), and carbon monoxide (CO) and the anions cyanide (CN⁻), chloride (Cl⁻), and hydroxide (OH⁻). Rarely, ligands are cations and electron-pair acceptors (electrophiles). Organic ligands include EDTA (see chelate) and nitrilotriacetic acid. Biological systems rely on ligands such as the porphyrin in hemoglobin and chlorophyll, and numerous cofactors are ligands. In chelates, the ligand attaches at more than one point, sharing more than one electron pair, and is called bidentate or polydentate—having two or many “teeth.” The ligands in a complex may be the same or different.

ligand (redirected from bidentate)

Structure of the Atom

Positive and Negative Electric Charges

ligand

ligand
(redirected from bidentate)