Many cases are not as simple as a \(d^9\) octahedral case because there are multiple possible electronic transitions, and also multiple absorption bands in the UV-vis spectrum. In these more complex cases, the actual energy of the transition are affected by differences in electron-electron repulsion energies in the ground state and the excited states. We will learn how to account for multiple possible excited states and electron-electron repulsions using Tanabe-Sugano diagrams later in this chapter.

Visiblelightwavelength

Angle Light remains best known for winning the April 21, 1973, Wood Memorial Stakes at Aqueduct Racetrack in Ozone Park, Queens, New York. [1] Stablemate, Secretariat, the reigning American Champion Two-Year-Old Colt and early favorite to win that May's Kentucky Derby, entered the race as a better than even-money favorite. However, unknown to most race fans, Secretariat had contracted a minor illness in the weeks before the Wood; an abscess was found under his lip hours before the race.[1] Angle Light, a true speed horse who never won a race without an early lead, ran wire-to-wire under Jacinto Vásquez, with Sham finishing second and Secretariat in third. [2] Angle Light finished tenth in the ensuing Kentucky Derby won by Secretariat.

Absorbance AU

Angle Light retired from racing with a record of 4-4-3 in 21 starts and earned $194,986. He is the only horse to defeat both Secretariat and Sham in the same race.

The absorption spectrum of a metal complex can be used to calculate the splitting energy, \(\Delta\), when the absorption corresponds to a \(d \rightarrow d \) transition. Let's use the \(d^9\) Cu(II) complex (discussed above) as an example. A \(d^9\) metal ion has only one visible-light \(d \rightarrow d\) transition. Let's assume that the coordination geometry is approximately octahedral (although it is actually a Jahn-Teller distorted octahedron, and more like a square plane). If we assume it's octahedral, then the \(d\)-orbital splitting diagram (see Figure \(\PageIndex{1}\)) leads us to expect one electronic transition: an electron is excited from the \(t_{2g}\) to \(e_g\). The energy absorbed is equal to the energy of the \(\Delta\).

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Lightabsorption

The absorption spectrum shown above in Figure \(\PageIndex{1}\) is a simple case in which only one absorption band is observed in the visible region of the spectrum. In a simple case like this, the color of a complex can be predicted as the complementary color of the light absorbed by the solution. When a solution or object absorbs a certain wavelength, we see the complementary color; or the color opposite to the absorbed wavelength on the color wheel in Figure \(\PageIndex{2}\). In the case of the Cu(II) complex spectrum shown in Figure \(\PageIndex{1}\), the color of the light absorbed at 530 nm is green, and the predicted color observed is pink.

Notes for reflection oflight

Angle Light (April 18, 1970 – unknown) was an American Thoroughbred racehorse who defeated the champion Secretariat in the 1973 Wood Memorial Stakes.

An example of such a measurement is shown below in Figure \(\PageIndex{1}\) for a Cu(II) complex. The sample appears a pink color to the eye, and when it is measured using a UV-visible spectrometer, it is shown to absorb visible light at approximately 530 nm. The absorption spectrum can indicate the oxidation state of Cu, the ligands bound to the Cu(II) ion, and the coordination geometry. The color of the solution in Figure \(\PageIndex{1}\) is a shade of pink.

After his retirement from racing, Angle Light stood as a stallion at Blue Ridge Farm in Virginia. He died at Flag's Up Farm.[2]

The table below lists the approximate colors of absorption corresponding to wavelengths of light absorbed, and gives similar information to that deduced from Figure \(\PageIndex{2}\).

The d-orbital splitting in coordination complexes results in a gap (\(\Delta\)) that happens to be just the right magnitude to absorb visible light. Because metal complexes can absorb visible light, they display an array of colors. Not only is the color attractive to the eye, it is an indication of the chemical and physical properties of the metal complex. The color (like the magnitude of \(\Delta\)) depends on the identity of the metal ion, the coordination geometry, and the ligand identity. Chemists don't just "look" at color, though - we measure it using electronic absorption spectroscopy. This is usually done in a lab using a UV-visible spectrophotometer.

Angle Light was bred by Howard B. Noonan and Runnymede Farm and was purchased and raced by Edwin Whittaker. He was sired by 1964 Belmont Stakes winner Quadrangle, out of the mare Pilot Light. He was trained by future U.S. Racing Hall of Fame inductee Lucien Laurin.

This page titled 11.1: Absorption of Light is shared under a not declared license and was authored, remixed, and/or curated by Kathryn Haas.