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ERIC Number: EJ1088169
Record Type: Journal
Publication Date: 2016-Jan
Pages: 7
Abstractor: As Provided
ISSN: ISSN-0021-9584
Origin of the Anomalous Color of Egyptian and Han Blue Historical Pigments: Going beyond the Complex Approximation in Ligand Field Theory
García-Fernandez, Pablo; Moreno, Miguel; Aramburu, José Antonio
Journal of Chemical Education, v93 n1 p111-117 Jan 2016
The complex approximation is widely used in the framework of the Ligand Field Theory for explaining the optical properties of crystalline coordination compounds. Here, we show that there are essential features of these systems that cannot be understood with the usual approximation that only considers an isolated complex at the correct equilibrium geometry. We also show that a quantitative understanding of such optical transitions cannot, in general, be reached unless the internal electric field, E[subscript R](r), created by the whole crystal on active electrons confined in the complex, is also taken into consideration. Seeking to prove the key role played by this internal field, usually ignored in crystalline transition metal compounds, we focus on the origin of the color displayed by the Egyptian Blue pigment (CaCuSi[subscript 4]O[subscript 10]), the first ever synthesized by humans. This pigment, together with Han Blue (BaCuSi[subscript 4]O[subscript 10]), are chosen as model systems because the anisotropic E[subscript R](r) field produces huge shifts, up to ~0.9 eV, in their d-d transitions, which are unusual compared to the majority of compounds containing the same square-planar CuO4[superscript 6-] chromophore. The relevance of the internal field for explaining phenomena such as the distinct color of ruby and emerald or the optical spectrum of CuF[subscript 6][superscript 4-] complexes in layered perovskites is also emphasized.
Division of Chemical Education, Inc and ACS Publications Division of the American Chemical Society. 1155 Sixteenth Street NW, Washington, DC 20036. Tel: 800-227-5558; Tel: 202-872-4600; e-mail:; Web site:
Publication Type: Journal Articles; Reports - Descriptive
Education Level: Higher Education; Postsecondary Education
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A
Grant or Contract Numbers: N/A