21.5 Color and Paramagnetism of Complex Ions and Coordination Compounds
Color of Coordination Compounds
Coordination compounds are often brightly colored as they often absorb visible light. This is the result of the fact that the crystal field splitting energy (CFSE) often corresponds to the energy of visible light. Light is absorbed resulting in the promotion of an electron in the lower energy d orbital to a higher energy d orbital. For this reason, most complexes having partially filled ‘d’ orbitals are colored (compounds that are d0 or d10 are not expected to be colored). The color of the light absorbed corresponds to the CFSE, while the color of a complex’s appearance is the corresponding complimentary color.
Paramagnetic vs Diamagnetic
Paramagnetic - Elements and compounds, including transition metals and their complexes, that have unpaired electrons have magnetic properties and are said to be paramagnetic as they experience an attraction when moving through a magnetic field. The more unpaired electrons, the higher the degree of paramagnetism.
Diamagnetic - Elements and compounds not having unpaired electrons are diamagnetic and experience and very slight repulsion when moving through a magnetic field.
Decide whether complexes with the following ions
1) would be expected to be colored and
2) if they are paramagnetic or diamagnetic.
Fe2+ (octehedral, low spin)
Fe2+ (octahedral, high spin)
FeF63- (F- is a weak field ligand)
Cr3+ (octahedral, low spin)
Ni2+ (Square Planar)
Which of the following complexes is most likely to absorb blue light?