Q.Why tetrahedral complexes do not exhibit geometrical isomerism.

Step 1. Geometrical (cis/trans) isomerism requires being able to distinguish an 'adjacent' (cis) arrangement of two identical ligands from an 'opposite' (trans) arrangement of the same two ligands.

Step 2. In an octahedron or a square plane, some pairs of positions ARE genuinely opposite one another (180° apart, e.g. positions 1 and 6 in the octahedral numbering scheme of Figure 5.5), giving a real trans arrangement distinct from a cis one.

Step 3. In a TETRAHEDRON, however, all four vertex positions are mutually equivalent, each pair separated by the same bond angle of approximately 109.5° -- there is no pair of positions that sits 180° apart, so no position genuinely counts as 'opposite' another.

Step 4. Because every pair of positions in a tetrahedral complex is geometrically identical, swapping two ligands between any two positions gives back the exact same structure (just reoriented in space) -- there is no distinguishable cis or trans arrangement to be had. …

Compare the bond-angle geometry of a tetrahedron (all positions equivalent at ~109.5°) against a square plane or octahedron (which have genuinely opposite, 180°-separated …

• Assuming any heteroleptic complex automatically shows geometrical isomerism regardless of shape, without checking whether the geometry itself actually has distinguishable adjacent/opposite positions. …