The Creutz–Taube ion is the
metal complex
A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or ...
with the formula
5+. This cationic species has been heavily studied in an effort to understand the intimate details of inner sphere electron transfer, that is, how electron
The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...
s move from one metal complex to another. The ion is named after Carol Creutz, who first prepared the complex, and her thesis advisor Henry Taube
Henry Taube (November 30, 1915 – November 16, 2005) was a Canadian-born American chemist who was awarded the 1983 Nobel Prize in Chemistry for "his work in the mechanisms of electron-transfer reactions, especially in metal complexes." He ...
, who received a Nobel Prize in Chemistry
The Nobel Prize in Chemistry () is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of chemistry. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895, awarded for outst ...
for this and related discoveries on electron transfer.
Properties
The complex consists of two pentammineruthenium
Ruthenium is a chemical element; it has symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is unreactive to most chem ...
units linked to the nitrogen atoms in a bridging pyrazine
Pyrazine is a heterocyclic aromatic organic compound with the chemical formula C4H4N2. It is a symmetrical molecule with point group D2h. Pyrazine is less basic than pyridine, pyridazine and pyrimidine. It is a ''"deliquescent crystal or wax-lik ...
ligand, which completes the octahedral coordination sphere
In coordination chemistry, the first coordination sphere refers to the array of molecules and ions (the ligands) directly attached to the central metal atom. The second coordination sphere consists of molecules and ions that attached in various ...
of each metal. The important feature of the compound is that the two metals have apparent fractional oxidation states of +2.5. Normally metal ions, like most ions, have integer oxidation states. For example, ruthenium ammine complexes are typically +2 or +3. The fact that the oxidation states are half-integer indicates that the two Ru(NH3)5 centers are equivalent in terms of their number of electrons. Crystallographic and theoretical studies are consistent with this description, that is, the two metal centers are equivalent.mixed-valence complex
Mixed valence complexes contain an element which is present in more than one oxidation state. Well-known mixed valence compounds include the Creutz–Taube complex, Prussian blue, and molybdenum blue. Many solids are mixed-valency including ...
, this ion strongly absorbs light in the near-infrared part of the electromagnetic spectrum
The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high ...
. In the case of the Creutz–Taube ion, the absorption maximum occurs at 1570 nm. This absorption is described as an intervalence charge-transfer band.
Synthesis
The ion was originally isolated as the hydrated tosylate
In organic chemistry, a toluenesulfonyl group (tosyl group, abbreviated Ts or TosIn this article, "Ts", unless otherwise stated, means tosyl, not tennessine.) is a univalent functional group with the chemical formula . It consists of a tolyl ...
salt u(NH3)5sub>2(C4H4N2)(O3SC6H4CH3)5·3H2O. It is prepared in two steps via the Ru(III)-Ru(III) pyrazine complex:.[
:2 u(NH3)5Clsup>2+ + C4H4N2 → 6+ + 2 Cl−
:2 6+ + Zn → 2 5+ + Zn2+
The Creutz–Taube ion illustrates the advantages of ruthenium complexes for examining redox reactions. Ru(II) and Ru(III) ions can be interconverted at mild redox potentials. Both of these oxidation states are kinetically inert. Many analogues of this ion have been prepared using different bridging ligands.
]
References
{{DEFAULTSORT:Creutz-Taube complex
Ruthenium complexes
Coordination complexes
Mixed valence compounds
Ammine complexes