Octahedral arrangement VSEPR

The VSEPR model for predicting structure does not work for complex ions. However, we can safely assume that a complex ion with a coordination number of 6 has an octahedral arrangement of ligands, and that complexes with two ligands are linear. On the other hand, complex ions with a coordination number of 4 can be either tetrahedral or square planar there is no reliable way to predict which will occur in a particular case. 

Ni(H20)g] (d ) and [Zn(H20)g]" (d ) to vary as the electronic configuration of the metal ion changes. However, each of these species has an octahedral arrangement of ligands (19.1). Thus, it is clear that VSEPR theory is not applicable to rZ-block metal complexes. 

A sulfur hexafluoride molecule, SF6, has six atoms attached to the central S atom and no lone pairs on that atom (8). According to the VSEPR model, the electron arrangement is octahedral, with four pairs at the corners of a square on the equator and the remaining two pairs above and below the plane of the square (see Fig. 3.2). An F atom is attached to each electron pair, and so the molecule is predicted to be octahedral. All its bond angles are either 90° or 180°, and all the F atoms are equivalent. 

When using VSEPR to predict the shape of a molecule, we often refer to a molecule with four repulsion axes as adopting a tetrahedral arrangement, even if the four repulsion axes are not identical. To belong to Td, however, the molecule or ion must have four identical bonds arranged tetrahedrally. Many metal complexes are tetrahedral or octahedral, and if you go on to study the chemistry of the transition elements, you will find these two groups play an important role. 

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