Structurally colored substituted with metallic

Radialenes which are structurally related to 44, i.e. cyclopropanes bearing two quinoid and another acceptor-substituted methylene substituent, were obtained by condensation of bis(4-hydroxyphenyl)cyclopropenones with active methylene compounds, followed by oxidation (Scheme 6)19. Radialenes 45a-f are brilliantly colored solids that are blue or blue-violet in solution but appear metallic gold or red in reflected light. Instead... 

Alternatively, one can treat silicates as closest packed arrays of oxide ions with Si ions fitting into tetrahedral holes and other metal ions fitting into either tetrahedral holes as in phenacite or octahedral holes as in olivine. (See Fig. 7.3 for the alternative ways of describing olivine.) Transition metal ions in these structures behave as they do in complexes Olivine gets its name from the greenish color caused by partial substitution of Fe " for Mg ions in the octahedral holes. The hexa-aquairon(II) ion has a similar green color. The hue of garnets also comes from transition metal ions. 

The color of gold varies depending on the metals it is alloyed with. Gold is typically alloyed with silver and/or copper. All three elements crystallize with a lace-centered cuhk structure. The fact that all three elements have similar radii (Au and Ag are nearly the same size, Cu is roughly 11% smaller) and crystallize with the same type of structure make it possible to form substitutional alloys with nearly any composition. 

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