AS/A-Level Chemistry - Ligand & Complex ions

Let's see how transition metals have special ion and properties in A-Level Chemistry!

An ion or molecule with a lone pair of electrons that forms a coordinate bond with a transition metal is called a ligand. When ligands surround the central metal ion, it forms a complex ion.

The ligands may be unidentate - they form one coordiante bond; bidentate or multdentate.

Unidentate ligands include H₂O, NH₃, Cl^-:

 Bidentate lignands include NH₂CH₂CH₂NH₂ and C₂O₄:

Multidentate ligands include EDTA^4- (etheylenediamminetetraacetate):

Naming complex ions

1. Number of each type of lignand
2. Name of ligand
3. Name of transition metal (ending in -ate if it is a negative ion)
4. Charge on transition metal

Shape of complex ions

The coordinate number tells us how many bonds the central metal ion forms with the ligand. It corresponds to how they are arranged.

When the ligand is small, the shape is usually octahedral. With larger lignands such as Cl^-, the complex ion ususally takes on a tetrahedral shape. In Tollen's reagent, the solution is a linear complex ion diammine silver(I) [Ag(NH₃)₂]⁺:

With nickel and platinum, sqaure planar complexes may form:

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Drafted by Eunice (Chemistry)

References 

https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=69339

https://www.breakingatom.com/learn-the-periodic-table/complex-ions