Ruthenium(III) chloride

Ruthenium(III) chloride is the chemical compound with the formula RuCl3. "Ruthenium(III) chloride" more commonly refers to the hydrate RuCl3·xH2O. Both the anhydrous and hydrated species are dark brown or black solids. The hydrate, with a varying proportion of water of crystallization, often approximating to a trihydrate, is a commonly used starting material in ruthenium chemistry.

Ruthenium(III) chloride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.139
RTECS number
  • VM2650000
UNII
  • InChI=1S/3ClH.Ru/h3*1H;/q;;;+3/p-3 checkY
    Key: YBCAZPLXEGKKFM-UHFFFAOYSA-K checkY
  • InChI=1/3ClH.Ru/h3*1H;/q;;;+3/p-3
    Key: YBCAZPLXEGKKFM-DFZHHIFOAX
  • Cl[Ru](Cl)Cl
  • [Cl-].[Cl-].[Cl-].[Ru+3]
Properties
RuCl3·xH2O
Molar mass 207.43 g/mol
Melting point >500°C (decomposes)
Soluble, Anhydrous is insoluble
+1998.0·10−6 cm3/mol
Structure
trigonal (RuCl3), hP8
P3c1, No. 158
octahedral
Hazards
Flash point Nonflammable
Related compounds
Other anions
 Ruthenium(III) bromide
Other cations
 Rhodium(III) chloride
Iron(III) chloride
Related compounds
 Ruthenium tetroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Preparation and properties

Anhydrous ruthenium(III) chloride is usually prepared by heating powdered ruthenium metal with chlorine. In the original synthesis, the chlorination was conducted in the presence of carbon monoxide, the product being carried by the gas stream and crystallising upon cooling.[1][2] Two polymorphs of RuCl3 are known. The black α-form adopts the CrCl3-type structure with long Ru-Ru contacts of 346 pm. This polymorph has honeycomb layers of Ru3+ which are surrounded with an octahedral cage of Cl− anions. The ruthenium cations are magnetic residing in a low-spin J~1/2 ground state with net angular momentum L=1.[3][4] Layers of α-RuCl3 are stacked on top of each other with weak Van der Waals forces. These can be cleaved to form mono-layers using scotch tape.[5]

The dark brown metastable β-form crystallizes in a hexagonal cell; this form consists of infinite chains of face-sharing octahedra with Ru-Ru contacts of 283 pm, similar to the structure of zirconium trichloride. The β-form is irreversibly converted to the α-form at 450–600 °C. The β-form is diamagnetic, whereas α-RuCl3 is paramagnetic at room temperature.[6]

RuCl3 vapour decomposes into the elements at high temperatures ; the enthalpy change at 750 °C (1020 K), ΔdissH1020 has been estimated as +240 kJ/mol.

Solid state physics

α-RuCl3 was proposed as a candidate for a Kitaev quantum spin liquid state[7] when neutron scattering revealed an unusual magnetic spectrum,[8][9][10] and thermal transport revealed chiral Majorana Fermions when subject to a magnetic field.[11]

Coordination chemistry of hydrated ruthenium trichloride

As the most commonly available ruthenium compound, RuCl3·xH2O is the precursor to many hundreds of chemical compounds. The noteworthy property of ruthenium complexes, chlorides and otherwise, is the existence of more than one oxidation state, several of which are kinetically inert. All second and third-row transition metals form exclusively low spin complexes, whereas ruthenium is special in the stability of adjacent oxidation states, especially Ru(II), Ru(III) (as in the parent RuCl3·xH2O) and Ru(IV).

Illustrative complexes derived from "ruthenium trichloride"
  • RuCl2(PPh3)3, a chocolate-colored, benzene-soluble species, which in turn is also a versatile starting material. It arises approximately as follows:[12]
2 RuCl3·xH2O + 7 PPh3 → 2 RuCl2(PPh3)3 + OPPh3 + 5 H2O + 2 HCl
2 RuCl3·xH2O + 2 C6H8 → [RuCl2(C6H6)]2 + 6 H2O + 2 HCl + H2
  • Ru(bipy)3Cl2, an intensely luminescent salt with a long-lived excited state, arising as follows:[15]
2 RuCl3·xH2O + 6 bipy + CH3CH2OH → 2 [Ru(bipy)3]Cl2 + 6 H2O + CH3CHO + 2 HCl

This reaction proceeds via the intermediate cis-Ru(bipy)2Cl2.[15]

2 RuCl3·xH2O + 2 C5Me5H → [RuCl2(C5Me5)]2 + 6 H2O + 2 HCl

[RuCl2(C5Me5)]2 can be further reduced to [RuCl(C5Me5)]4.

RuCl3·xH2O + 3 C5H8O2 → Ru(C5H7O2)3 + 3 H2O + 3 HCl
  • RuO4, is produced by oxidation.

Some of these compounds were utilized in the research related to two Nobel Prizes. Ryōji Noyori was awarded the Nobel Prize in Chemistry in 2001 for the development of practical asymmetric hydrogenation catalysts based on ruthenium. Robert H. Grubbs was awarded the Nobel Prize in Chemistry in 2005 for the development of practical alkene metathesis catalysts based on ruthenium alkylidene derivatives.

Carbon monoxide derivatives

RuCl3(H2O)x reacts with carbon monoxide under mild conditions.[18] In contrast, iron chlorides do not react with CO. CO reduces the red-brown trichloride to yellowish Ru(II) species. Specifically, exposure of an ethanol solution of RuCl3(H2O)x to 1 atm of CO gives, depending on the specific conditions, [Ru2Cl4(CO)4], [Ru2Cl4(CO)4]2−, and [RuCl3(CO)3]−. Addition of ligands (L) to such solutions gives Ru-Cl-CO-L compounds (L = PR3). Reduction of these carbonylated solutions with Zn affords the orange triangular cluster Ru3(CO)12.

3 RuCl3·xH2O + 4.5 Zn + 12 CO (high pressure) → Ru3(CO)12 + 3x H2O + 4.5 ZnCl2

Sources
  • Becker, Ramona; Hartwig, Helga; Köppe, Herbert; Vanecek, Hans; Velić, Paul; Warncke, Rudolf; Zelle, Anna (1978). Warncke, Rudolf (ed.). Gmelin Handbuch der Anorganischen Chemie. doi:10.1007/978-3-662-06224-1. ISBN 978-3-662-06226-5.

References
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  2. Bublitz, D. E; McEwen, W. E.; Kleinberg, J. (1961). "Ruthenocene". Organic Syntheses. 41: 96. doi:10.15227/orgsyn.041.0096.
  3. Fletcher, J. M.; Gardner, W. E.; Hooper, E. W.; Hyde, K. R.; Moore, F. H.; Woodhead, J. L. (September 1963). "Anhydrous Ruthenium Chlorides". Nature. 199 (4898): 1089–1090. Bibcode:1963Natur.199.1089F. doi:10.1038/1991089a0. ISSN 0028-0836. S2CID 4179795.
  4. Plumb, K. W.; Clancy, J. P.; Sandilands, L. J.; Shankar, V. Vijay; Hu, Y. F.; Burch, K. S.; Kee, Hae-Young; Kim, Young-June (2014-07-29). "α−RuCl3: A Spin-Orbit Assisted Mott Insulator on a Honeycomb Lattice". Physical Review B. 90 (4): 041112. arXiv:1403.0883. Bibcode:2014PhRvB..90d1112P. doi:10.1103/physrevb.90.041112. ISSN 1098-0121. S2CID 29688091.
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  7. Banerjee, A.; Bridges, C. A.; Yan, J.-Q.; Aczel, A. A.; Li, L.; Stone, M. B.; Granroth, G. E.; Lumsden, M. D.; Yiu, Y. (2016-04-04). "Proximate Kitaev quantum spin liquid behaviour in a honeycomb magnet". Nature Materials. 15 (7): 733–740. arXiv:1504.08037. Bibcode:2016NatMa..15..733B. doi:10.1038/nmat4604. ISSN 1476-1122. PMID 27043779. S2CID 3406627.
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  9. Do, Seung-Hwan; Park, Sang-Youn; Yoshitake, Junki; Nasu, Joji; Motome, Yukitoshi; Kwon, Yong Seung; Adroja, D. T.; Voneshen, D. J.; Kim, Kyoo (2017-09-18). "Majorana fermions in the Kitaev quantum spin system α-RuCl3". Nature Physics. 13 (11): 1079–1084. Bibcode:2017NatPh..13.1079D. doi:10.1038/nphys4264. ISSN 1745-2473. S2CID 126423385.
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Further reading
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