9701 · 28.4
Stereoisomerism in transition element complexes — FAQ
Frequently asked questions for 9701 Stereoisomerism in transition element complexes. Direct answers first, then deeper explanation — then practise with marking.
Why don't tetrahedral complexes like `[ZnCl₄]²⁻` show cis-trans isomerism?
In a tetrahedral geometry, all four ligand positions are equivalent relative to each other. The angle between any two ligands is 109.5°. There are no 'opposite' positions (which would be 180° apart), so cis-trans isomerism is not possible.
What is the difference between a stereoisomer and a structural isomer?
Structural isomers have the same molecular formula but a different pattern of atomic connectivity (i.e., the atoms are bonded together in a different order). Stereoisomers have the same molecular formula and the same connectivity, but the atoms are arranged differently in three-dimensional space.
How can I tell if a complex has a plane of symmetry?
Visualise an imaginary plane cutting through the molecule. If this plane divides the molecule into two halves that are perfect mirror reflections of each other, it has a plane of symmetry and is achiral. For example, in trans-[Co(en)₂(Cl)₂]⁺, a plane can be drawn through the Co ion and the two Cl⁻ ions, which reflects one half of the molecule onto the other. This is not possible for the cis-[Co(en)₂(Cl)₂]⁺ isomer.