colour of molecules Flashcards
describe the process that allows transition metal complexes to be coloured
- when ligands are attached to the central metal ion the orbitals are split into two sets of non degenerate orbitals, forming a difference in energy between the two.
- when light shines on this transition metal complexe, an electron will absorb this exact amount of energy, exciting it from HOMO to LUMO.
- the frequencies of light that are not absorbed are combined to form the complementary colour
which factors can have an impact on the colour of the transition metal complex
the type of ligand
the coordination number
the oxidation state
how does the type of ligand have an impact on the colour of transition metal complexes
different ligands will split the d orbital by a different amount of energy, which depends on the repulsion that the d orbital experiences from the ligands. this energy then changes which wavelengths are emitted as colour.
as the splitting energy increases, the wavelength absorbed will be shorter
how does the coordination number have an impact on the colour of transition metal complexes
changing the coordination number usually involves changing the ligand as well, so the combination of these factors can alter the strength of interactions
how does oxidation state have an impact on the colour of transition metal complexes
as the oxidation state of the metal increases, so also does the amount of splitting of the d orbitals.
how does oxidation state an an impact on the splitting of d orbitals
a higher oxidation state means the transition metal is more electropositive, so it draws more electron density toward itself, meaning there are more repulsions in the d orbitals, so the field splitting energy will increase.
why does oxidation state change colour
different oxidation state correlates to different numbers of electrons in the outer shell. the more electrons there are, the more energy is required to move them up an energy level, meaning the emitted wavelength of light will differ
