The Creutz–Taube ion is the

metal complex A coordination complex consists 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 complexing agents. Many ...

with the formula ⁵⁺. This cationic species has been heavily studied in an effort to understand the intimate details of

inner sphere electron transfer Inner sphere electron transfer (IS ET) or bonded electron transfer is a redox chemical reaction that proceeds via a covalent linkage—a strong electronic interaction—between the oxidant and the reductant reactants. In inner sphere electron trans ...

, that is, how

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...

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 ) , image = Nobel Prize.png , alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then "M ...

for this and related discoveries on electron transfer.

Properties

The complex consists of two pentammine

ruthenium Ruthenium is a chemical element with the Symbol (chemistry), 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 inert to ...

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. Characteristic of a

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 in ...

, this ion strongly absorbs light in the near-infrared part of the

electromagnetic spectrum The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies. The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from ...

. 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 Tos) is a univalent functional group with the chemical formula –. It consists of a tolyl group, –, joined to a sulfonyl group, ––, with the open valence on s ...

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