Formulae of ligands

Type Electron Charge Ligand Name Formula of Ligand What They re Called... 

In empirical formulas of inorganic compounds, electropositive elements are listed first [3]. The stoichiometry of the element symbols is indicated at the lower right-hand side by index numbers. If necessary, the charges of ions are placed at the top right-hand side next to the element symbol (e.g., S "). In ions of complexes, the central atom is specified before the ligands are listed in alphabetical order, the complex ion is set in square brackets (e.g., Na2[Sn(OH)+]). 

Besides structure and substructure searches, Gmclin provides a special search strategy for coordiuation compouuds which is found in no other database the ligand search system, This superior search method gives access to coordination compounds from a completely different point of view it is possible to retrieve all coordination compounds with the same ligand environment, independently of the central atom or the empirical formula of the compound. 

You know die charge of die complex and those of the ligands. To find the formulas of the coordination compounds, apply the principle of electrical neutrality. 

The physical and chemical properties of complex ions and of the coordination compounds they form depend on the spatial orientation of ligands around the central metal atom. Here we consider the geometries associated with the coordination numbers 2,4, and 6. With that background, we then examine the phenomenon of geometric isomerism, in which two or more complex ions have the same chemical formula but different properties because of their different geometries. 

Two or more species with different physical and chemical properties but the same formula are said to be isomers of one another. Complex ions can show many different kinds of isomerism, only one of which we will consider. Geometric isomers are ones that differ only in the spatial orientation of ligands around the central metal atom. Geometric isomerism is found in square planar and octahedral complexes. It cannot occur in tetrahedral complexes where all four positions are equivalent... 

The names of coordination compounds can become awesomely long because the identity and number of each type of ligand must be included. In most cases, chemists avoid the problem by using the chemical formula rather than the name itself. For instance, it is much easier to refer to [FeCl(H20)5]+ than to pen-taaquachloroiron(II) ion, its formal name. However, names are sometimes needed, and they can be constructed and interpreted, in simple cases at least, by using the rules set out in Toolbox 16.1. Table 16.4 gives the names of common ligands and their abbreviations, which are used in the formulas of complexes. 

The chemical symbols of anionic ligands precede those of neutral ligands in the chemical formula of the complex (but not necessarily in its name). Thus, Cl precedes H20 and NH3. 

The following letters are used in formulas and equations to denote different types of ligands ... 

Where the second axial ligand or counter-anion is not known (e.g., in solution), this is indicated by . Dinuclear complexes are indicated by the addition of two Co atoms to the formula of the ligand, e.g., Co—CH=CH—Co. 

The stoichiometiy of a metal complex is described by its chemical formula. For example, each cation of the silver-ammonia complex contains one Ag cation bound to two neutral NH3 ligands and carries a net charge of -i-l, as shown in Figure 18-11. The formula of a complex ion is enclosed in square brackets, as in [ Ag (NH3)2. The... 

Complex ions, also called coordination complexes, have well-defined stoichiometries and structural arrangements. Usually, the formula of a coordination complex is enclosed in brackets to show that the metal and all its ligands form a single structural entity. When an ionic coordination complex is isolated from aqueous solution, the product is composed of the complex ion and enough counter-ions to give a neutral salt. In the chemical formula, the counter-ions are shown outside the brackets. Examples include the sulfate salt of [Ni (NH3)g, ... 

For more electropositive elements, which have an inferior number of valence electrons in the first place, and which in addition have to supply electrons to a more electronegative partner, the number of available electrons is rather small. They can gain electrons in two ways first, as far as possible, by complexation, i.e. by the acquisition of ligands and second, by combining their own atoms with each other. This can result in the formation of clusters. A cluster is an accumulation of three or more atoms of the same element or of similar elements that are directly linked with each other. If the accumulation of atoms yields a sufficient number of electrons to allow for one electron pair for every connecting line between two adjacent atoms, then each of these lines can be taken to be a 2c2e bond just as in a common valence bond (Lewis) formula. Clusters of this kind have been called electron precise. 

Usually the value of the /asym//sym ratio is used for estimating the angle between geminal ligands in the M(XY)2 " complexes, based on the approximate formula of Cotton [21] ... 

When the ligand is placed or found inside the receptor pocket, then the free energy of binding of the molecular complex is estimated computationally. Therefore the 3D-coordinates of the atoms in the protein receptor, a structural formula of the ligand, with bond lengths and angles and in addition knowledge of the position of the active site are required. 

If an octahedral complex has the formula MX3Y3, there are two possible isomers. In an octahedron, the positions are assigned numbers so the locations of ligands in the structure can be identified. The usual numbering system for ligands in an octahedral complex is... 

A striking feature of the formulas (4.68a)-(4.68c) is that the coordination number (CN) of ligands bonded to Co is six (CN = 6) in each case. Werner conjectured that such six-fold coordination corresponds to idealized octahedral geometry about the central Co ion, which leads to unique structures for [Co(NH3)6]3+ and [Co(NH3)5C1]2+ but distinct cis and trans isomers for [Co(NH3)4Cl2]+, as observed. X-ray studies subsequently confirmed the accuracy of Werner s brilliant structural inferences. 

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