Transition-Metal Ion Colors

Synonyms

d-block elements

Definition

Transition metals are d-block elements with partially filled 3d, 4d, and 5d orbitals.

Color Production

The transition metals are (somewhat imprecisely) described as being colored because when cations of these elements are incorporated into colorless solids or liquids, the material frequently takes on a characteristic hue (Fig. 1, Table 1). The color arises from electronic transitions between the ionic ground state and energy levels lying between 1.77 and 3.10 eV above it, giving absorption maxima in the visible wavelength range (400–700 nm). The low-lying energy levels that give rise to color arise from interactions of the d orbitals on the cation with neighboring atoms in a material and are a function of the symmetry of the surroundings [1–3]. (These ions in the gaseous state are not colored). The energy levels that occur with the 4d and 5d transition metals are higher in energy than those of the 3d series and are of lesser importance in color...