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In chemistry, coordination number, defined originally in 1893 by Alfred Werner, is the total number of neighbors of a central atom in a molecule or ion. [ 1 ] [ 3 ] The concept is most commonly applied to coordination complexes .
The number of coordination bonds (coordination number) can vary from two in K[Ag(CN) 2] as high as 20 in Th(η 5-C 5 H 5) 4. [ 2 ] One of the most common coordination geometries is octahedral , where six ligands are coordinated to the metal in a symmetrical distribution, leading to the formation of an octahedron if lines were drawn between the ...
As applied to coordination chemistry, this meaning has evolved. Some metal complexes are formed virtually irreversibly and many are bound together by bonds that are quite strong. [7] [8] The number of donor atoms attached to the central atom or ion is called the coordination number. The most common coordination numbers are 2, 4, and especially 6.
In coordination chemistry and crystallography, the geometry index or structural parameter (τ) is a number ranging from 0 to 1 that indicates what the geometry of the coordination center is. The first such parameter for 5-coordinate compounds was developed in 1984. [1] Later, parameters for 4-coordinate compounds were developed. [2]
The polyhedral symbol is sometimes used in coordination chemistry to indicate the approximate geometry of the coordinating atoms around the central atom. One or more italicised letters indicate the geometry, e.g. TP-3 which is followed by a number that gives the coordination number of the central atom. [1]
Also from this general form, the values for electron count, oxidation state, coordination number, number of d-electrons, [6] valence number and the ligand bond number [2] can be calculated. Electron Count = N + x + 2 l − Q {\displaystyle N+x+2l-Q}
While local cubic 8-coordination is common in ionic lattices (e.g., Ca 2+ in CaF 2), and some 8-coordinate actinide complexes are approximately cubic, there are no reported examples of rigorously cubic 8-coordinate molecular species. A number of other rare geometries for 8-coordination are also known. [2]
In coordination chemistry, hapticity is the coordination of a ligand to a metal center via an uninterrupted and contiguous series of atoms. [1] The hapticity of a ligand is described with the Greek letter η ('eta'). For example, η 2 describes a ligand that coordinates through 2 contiguous