Notes on Coordination Compounds

✍️Notes on Coordination Compounds

Ligands: an ion or molecule capable of donating a pair of electrons to the central atom via a donor atom.

➖Unidentate ligands: Ligands with only one donor atom, e.g. NH3, Cl-, F- etc.

➖Bidentate ligands: Ligands with two donor atoms, e.g. ethylenediamine, C2O42-(oxalate ion) etc. 

➖Tridentate ligands: Ligands which have three donor atoms per ligand, e.g. (dien) diethyl triamine.

➖Hexadentate ligands: Ligands which have six donor atoms per ligand, e.g. EDTA. 

Chelating Ligands: 

➖Multidentate ligand simultaneously coordinating to a metal ion through more than one site is called chelating ligand. Example: Ethylenediamine (NH2CH2CH2NH2)

➖These ligands produce a ring like structure called chelate.

➖Chelation increases the stability of complex. 

Werner’s Theory:

➖Metals possess two types of valencies i.e. primary (ionizable) valency and secondary (nonionizable) valency.

➖Secondary valency of a metal is equal to the number of ligands attached to it i.e. coordination number.

➖Primary valencies are satisfied by negative ions, while secondary valencies may be satisfied by neutral, negative or positive ions.

➖Secondary valencies have a fixed orientation around the metal in space.

  [Co(NH3)6]Cl3

  Primary Valencies = 3 Cl-

  Secondary Valencies = 6 NH3

  Coordination Sphere =  [Co(NH3)6]3-

Nomenclature of Complexes:

➖Positive ion is named first followed by negative ion.

➖Negative ligands are named by adding suffix - o.

➖Positive ligands are named by adding prefix – ium.

➖Neutral ligands are named as such without adding any suffix or prefix.

➖Ligands are named in alphabetical order.

➖Name of the ligands is written first followed by name of metal with its oxidation number mentioned in roman numbers in simple parenthesis.

➖Number of the polysyllabic ligands i.e. ligands which have numbers in their name, is indicated by prefixes bis, tris etc,

➖Number and name of solvent of crystallization if any, present in the complex is written in the end of the name of complex.

➖When both cation and anion are complex ions, the metal in negative complex is named by adding suffix-ate.

➖In case of bridging ligands:

[Name of the groups to the left of bridging ligand (Oxidation state)] –μ – [Name of the groups to the right of bridging ligand (Oxidation state)] – [Name of negative ion]