Transition Metals - Complex Ion Shape (A-Level Chemistry)

Complex Ion Shape

Shapes of Complexes

Like all covalent molecules, transition metal complexes have shapes due to their co-ordinate covalent bonding with ligands.

Co-ordination Number: 6

If the transition metal complex has a coordination number of 6, with small ligands like water or ammonia, the shape of the complex is octahedral with a bond angle of 90°.

Complex Ion Shape
Complex Ion Shape

Likewise, bidentate and multidentate ligands with a co-ordination number of 6, will also have an octahedral shape.

Complex Ion Shape
Complex Ion Shape
Complex Ion Shape
Complex Ion Shape

Co-ordination Number: 4

If the transition metal complex has larger ligands, like chloride ions, it has a co-ordination number of 4. Fewer larger ligands can fit around the central transition metal. The shape is either tetrahedral or square planar.

Complex Ion Shape
Complex Ion Shape

The tetrahedral shape [Cu(Cl)₄]²- has a bond angle of 109.5°.

The square planar shape [Pt(NH₃)₂(Cl)₂] has a bond angle of 90°.

Co-ordination Number: 2

If the transition metal complex has a co-ordination number of two, the shape is linear. The bond angle is 180°.

Complex Ion Shape
Complex Ion Shape

This linear complex silver diammine (I) [Ag(NH₃)₂]⁺ is used in Tollen’s reagent, which is used to test for the presence of aldehydes.

If aldehydes are present, a silver mirror forms around the tube, as the Ag⁺ ions are reduced to Ag metal.

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