maths_4_life
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Why does ligand exchange cause a change in colour of the solution when the oxidation state of the transition metal doesn't change?


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RMNDK
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(Original post by maths_4_life)
Why does ligand exchange cause a change in colour of the solution when the oxidation state of the transition metal doesn't change?


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Ah.. remember there are three factors that affect the colour of a transition metal complex:

1. The oxidation state of the metal, which you pointed out.

2. The nature of the ligand. Different ligands have different effects on the d-orbital splitting. A ligand might cause a greater degree of splitting of d-orbitals. This means the electron absorbs more light energy, and therefore a higher wavelength of light, to be excited into the higher orbital.

3. The coordination number. An octahedral formation has a greater orbital splitting than a tetrahedral formation.


So while the oxidation state of the metal stays the same and the d-orbitals available stay the same, the separation of these orbitals can change by these ligands.
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K3001N
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Basically, as a ligand is co-ordinately bonded onto a metal ion, it forms a complex. This complex will effect how the electrons in the d orbital split, they are at ground level to begin with (non excited state) but when a ligand is co-ordinately bonded onto the transition metal it forms a complex. As this complex forms the d orbital splits from the ground phase to an excited phase moving up the energy level, the energy the electron absorbs corresponds to the missing wavelength of light and therefore will display that colour, If I'm correct.

I HATE CHEMISTRY
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K3001N
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yeah you can have neutral ligands such as NH3 or H20; they just split the d sub orbital which causes all that above..
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Stiff Little Fingers
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Because it's not just the oxidation state that determines colour - the nature of the ligand will also affect the colour depending on how much of a split it causes in the energy levels of the d-orbitals.
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maths_4_life
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Thank you all soooo much! Great explanations!


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