Tris(bipyridine)ruthenium(II) chloride

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Tris(bipyridine)ruthenium(II) chloride
Other names Ru-bipy
Ruthenium-tris(2,2’-bipyridyl) dichloride
Identifiers
CAS number
RTECS number VM2730000
Properties
Molar mass 748.62 g/mol
Appearance red-orange solid
Density solid
Melting point

>300 °C
Solubility in water Soluble
Structure
Molecular shape Octahedral
Dipole moment 0 D
Hazards
Main hazards mildly toxic
R-phrases none
S-phrases 22-24/25
Related compounds
Related compounds Ruthenium trichloride
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Tris(bipyridine)ruthenium(II) dichloride is the chemical compound with the formula [Ru(bipy)3]Cl2. This salt is obtained as the hexahydrate, although all of the properties of interest are in the cation [Ru(bipy)3]2+, which has received much attention because of its distinctive optical properties. The chlorides can be replaced with other anions, such as PF6−.

Contents

[edit] Synthesis and structure

Structure of [Ru(bipy)3]2+
Structure of [Ru(bipy)3]2+

This orange crystalline salt is prepared by treating aqueous solution of ruthenium trichloride with 2,2'-bipyridine. In this conversion, Ru(III) is reduced to Ru(II), and hypophosphorous acid is typically added as a reducing agent.[1]. [Ru(bipy)3]2+ is an octahedral coordination complex. The complex is chiral, with D3 symmetry. It has been resolved into its enantiomers, which are kinetically stable.

[edit] Photochemistry of [Ru(bipy)3]2+

Distinctively, [Ru(bipy)3]2+ absorbs UV light and visible light to give an excited state with a comparatively long lifetime of 600 nanoseconds. The excited state relaxes to the ground state by emission of a photon at the wavelength of 600 nm. The long lifetime of the excited state is attributed to the fact that it is triplet, whereas the ground state is a singlet state and in part due to the fact that the structure of the molecule allows for charge separation. Singlet-triplet transitions are often slow.

The triplet excited state has both oxidizing and reducing properties. This unusual situation arises because the excited state can be described as an Ru3+ complex containing a bipy- ligand. Thus, the photochemical properties of [Ru(bipy)3]2+ are reminiscent of the photosynthetic assembly, which also involves separation of an electron and a hole.[2]

[Ru(bipy)3]2+ has been examined as a photosensitiser for both the oxidation and reduction of water. Upon absorbing a photon, [Ru(bipy)3]2+ converts to the aforementioned triplet state, denoted [Ru(bipy)3]2+*. This species transfers an electron, located on one bipy ligand, to a sacrificial oxidant such as persulfate (S2O82-). The resulting [Ru(bipy)3]3+ is a powerful oxidant and oxidizes water into O2 and protons via a metal oxide catalyst.[3] Alternatively, the reducing power of [Ru(bipy)3]2+* can harnessed to reduce methylviologen, a recyclable carrier of electrons, which in turn reduces protons at a platinum catalyst. For this process to be catalytic, a sacrificial reductant, such as EDTA4- or triethanolamine is provided to return the Ru(III) back to Ru(II).

[edit] Derivatives

The family of derivatives of [Ru(bipy)3]2+ is enormous. These complexes are widely used in biodiagnostics, photovoltaics and organic light-emitting diode.

[edit] Safety

Metal bipyridine as well as related phenanthroline complexes are generally bioactive.

[edit] References

  1. ^ Broomhead, J. A.; Young, C. G. “Tris(2,2’-bipyridine)Ruthenium(II) Dichloride Hexahydrate” Inorganic Syntheses, 1990, volume 28, ISBN 0-471-52619-3
  2. ^ A. J. Bard and M. A. Fox (1995). "Artificial Photosynthesis: Solar Splitting of Water to Hydrogen and Oxygen". Acc. Chem. Res. 28 (3): 141–145. doi:10.1021/ar00051a007. 
  3. ^ M. Hara, C. C. Waraksa, J. T. Lean, B. A. Lewis and T. E. Mallouk (2000). "Photocatalytic Water Oxidation in a Buffered Tris(2,2'-bipyridyl)ruthenium Complex-Colloidal IrO2 System". J. Phys. Chem. A 104 (22): 5275–5280. doi:10.1021/jp000321x.