Characteristics of Coordination Complexes

• The transition metal atom can often exist in more than one oxidation state.
• Many coordination complexes are colored.
• Many coordination complexes are paramagnetic.
  • paramagnetic substance: a substance that contains unpaired electrons; paramagnetic substances tend to move into a magnetic field
  • diamagnetic substance: a substance that contains no unpaired electrons; diamagnetic substances tend to move out of a magnetic field

The Crystal Field Model

The crystal field model concentrates on the splitting of the d orbitals of the transition metal atom into groups as a result of electrostatic interactions between the ligands and the electrons in the unhybridized orbitals of the transition metal atom. The model can be used to understand, interpret and predict the magnetic behavior, colors and some structures of coordination complexes.

Note that the crystal field model does not explain the bonding in coordination complexes; it describes only behavior that can be attributed to electrons on the transition metal atom in the coordination complex.

 

 

Color

When atoms or compounds absorb light of the proper frequency, their electrons are excited to higher energy levels. Colored compounds absorb visible (colored) light and this absorption is responsible for their color.

Our eyes perceive a mixture of all of the colors, as in the proportions in sunlight, as white light. The following figure shows how the mixture of colors that the eye perceives as white light is separated as the light passes through a prism.

As shown in the next figure, an object is seen as black if it absorbs all colors of white light. A white object reflects all colors of white light equally.

If an object absorbs all colors but one, we see the color it does not absorb. The yellow strip in the following figure absorbs red, orange, green, blue, indigo and violet light. It reflects yellow light and we see it as yellow.

The eye also uses complementary colors in color vision. When a color is removed from white light we see the complementary color. The following table shows the colors seen when a complementary color is removed (for example, by a color filter).

Wavelength (Angstroms) Removed	Color Removed	Color Seen (Complementary color)
6800 6100 5800 5600 5300 5000 4800 4300 4100	Red Orange Yellow Lemon Yellow Green Blue-green Blue Indigo Violet	Blue-green Blue Indigo Violet Purple Red Orange Yellow Lemon Yellow

The yellow strip in the following figure looks yellow because it absorbs indigo light from white light. Indigo is the complementary color of yellow.

A solution containing the complex ion, [Cu(NH₃)₄]²⁺, is blue because the complex absorbs red and orange light, the complementary colors of blue and blue-green.

Computer monitors produce colors by producing mixtures of light

 

 

do rate me if helpfull n pass u r comments 2