Colour in Transition Metal complexes
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What is the colour of transition metal complexes due to?
the presence of incompletely filled d-orbitals in the TM ion.
Explain how TM compounds appear coloured?
Because absorption occurs in the visible region of the EM spectrum
What does absorption of EM radiation of the correct frequency/ wavelength cause?
an electron to be promoted to a higher energy orbital
In transition metal compounds, what are the electrons in the d-orbitals involved in?
electronic transitions
What are all 3d-orbitals in an isolated TM ion?
degenerate
In the presence of ligands, what happens to the degeneracy of the 3d-orbitals?
it is lifted
What are the 5 d-orbitals split into? What does this allow?
2 groups, allowing electronic transitions to occur
What are the 2 groups?
lower = dxy dxz dyx higher= dz2 dx2-y2
What does absorption of visible radiation promote?
an electron in the lower energy orbitals into one of higher energy. This is called a d-d transition
What is the energy gap determined by?
the ligands surrounding the TM ion.
Some ligands cause greater d-d splitting than others, hence what will this effect?
the colour (wavelengths of light absorbed)
What can complexes of the same TM ion have?
different colours
Explain complementary colours.
if a particular colour is absorbed from white light, what your eye detects by mixing up all other wavelengths of light is its complementary colour. Copper (II) sulfate solution is pale blue (cyan) because it absorbs light in the red region of the spectrum. Cyan is the complementary colour of red.
Why is permanganate purple?
it absorbs green light, and transmits blue and red.
What does the presence of unpaired electrons or unfilled d orbitals allow transition metals to act as? Why?
catalysts. It is believed that the empty d-orbitals allows intermediate complexes to form, thus providing an alternative route to the products (with a lower activation energy).