Ligands color effects

Bithiazole, 4,4 -btz = (97), is not a diimine its iron(II) complex [Fe(4,4 -btz)3] is only weakly colored but its magnetic properties and Fe—N bond distances 1.970-1.973A suggest that the ligand field effect of 4,4 -btz is not enormously less than that of bipy. ... 

Color Effects due to Ligand Exchange in Nickel Complexes... 

Color effects clue to ligand exchange reactions... 

Absorption in the visible is perceived as color. A number of mechanisms exist for the creation of color in glasses. The most important commercial colored glasses contain either 3d transition metal ions or 4f rare earth (lanthanide) ions, where the coloration arises from the so-called ligand field effect. Other sources of color include the formation of metal or semi-conductor colloidal particles, optical defects induced by solarization or radiation, and charge transfer bands in the visible region of the spectrum. 

Since the coloration of glasses by transition metal and rare earth ions results from ligand field effects, several general trends can be predicted. First, a change in oxidation state results in a change in the number of 3d or 4f electrons, resulting in a different number of possible electronic transitions for otherwise identical conditions. Since each possible electronic transition represents an absorption with a different energy, a difference in oxidation state will result in a different absorption spectrum. 

Details of the coloration of glasses due to ligand field effects are further complicated by the possibility of redox interactions between two or more different transition metal ions. Other elements such as arsenic and antimony, which do not directly affect color, may alter the oxidation state of a coloring ion and alter the color of the glass. Changes in furnace atmosphere can also inadvertently alter the oxidation state of coloring ions due to changes in the concentrations of O2, CO, CO2, and H2O vapor. 

Use the spectrochemical series to predict the effect of a ligand on the color, electron configuration, and magnetic properties of a d-metal complex (Examples 16.4 and 16.5). 

Cu(II) Complexes with Diethylethylenediamine. The complexes [Cu(dieten)2]X2, where X is an anion and dieten is the bivalent ligand N, V-diethylethylendiamine, well illustrate the effect of the medium on the extent of cooperativity of the transformation. These systems present interesting properties, and they have been investigated extensively [498-503]. When X is BF4, CIO4, or NO3 the complexes have thermochromic behavior and the color changes from red, at low temperature, to blue in the high-temperature form [499, 504]. 

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