Rubidium chloride

Rubidium chloride is the chemical compound with the formula RbCl. This alkali metal halide is composed of rubidium and chlorine, and finds diverse uses ranging from electrochemistry to molecular biology.

Rubidium chloride
Other names
rubidium(I) chloride
3D model (JSmol)
ECHA InfoCard 100.029.310
RTECS number
  • VL8575000
Molar mass 120.921 g/mol
Appearance white crystals
Density 2.80 g/cm3 (25 °C)
2.088 g/mL (750 °C)
Melting point 718 °C (1,324 °F; 991 K)
Boiling point 1,390 °C (2,530 °F; 1,660 K)
77 g/100mL (0 °C)
91 g/100 mL (20 °C)
130 g/100 mL (100 °C)
Solubility in methanol 1.41 g/100 mL
46.0·10−6 cm3/mol
52.4 JK1mol1
95.9 JK1mol1
435.14 kJ/mol
Safety data sheet Fisher Scientific
NFPA 704 (fire diamond)
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
4440 mg/kg (rat)
Related compounds
Other anions
Rubidium fluoride
Rubidium bromide
Rubidium iodide
Rubidium astatide
Other cations
Lithium chloride
Sodium chloride
Potassium chloride
Caesium chloride
Francium chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references


In its gas phase, RbCl is diatomic with a bond length estimated at 2.7868 Å.[1] This distance increases to 3.285 Å for cubic RbCl, reflecting the higher coordination number of the ions in the solid phase.[2]

Depending on conditions, solid RbCl exists in one of three arrangements or polymorphs as determined with holographic imaging:[3]

Sodium chloride (octahedral 6:6)

The sodium chloride (NaCl) polymorph is most common. A cubic close-packed arrangement of chloride anions with rubidium cations filling the octahedral holes describes this polymorph.[4] Both ions are six-coordinate in this arrangement. This polymorph's lattice energy is only 3.2 kJ/mol less than the following structure's.[5]

Caesium chloride (cubic 8:8)

At high temperature and pressure, RbCl adopts the caesium chloride (CsCl) structure (NaCl and KCl undergo the same structural change at high pressures). Here, the chloride ions form a simple cubic arrangement with chloride anions occupying the vertices of a cube surrounding a central Rb+. This is RbCl's densest packing motif.[2] Because a cube has eight vertices, both ions' coordination numbers equal eight. This is RbCl's highest possible coordination number. Therefore, according to the radius ratio rule, cations in this polymorph will reach their largest apparent radius because the anion-cation distances are greatest.[4]

Sphalerite (tetrahedral 4:4)

The sphalerite polymorph of rubidium chloride is extremely rare, resulting in few structural studies. The lattice energy, however, for this formation is predicted to nearly 40.0 kJ/mol smaller than those of the preceding structures.[5]


The most common preparation of pure rubidium chloride involves the reaction of its hydroxide with hydrochloric acid, followed by recrystallization:[6]

RbOH(aq) + HCl(aq) → RbCl(aq) + H2O(l)

Because RbCl is hygroscopic, it must be protected from atmospheric moisture, e.g. using a desiccator. RbCl is primarily used in laboratories. Therefore, numerous suppliers (see below) produce it in smaller quantities as needed. It is offered in a variety of forms for chemical and biomedical research.


Rubidium chloride reacts with sulfuric acid to rubidium hydrogen sulfate.


Every 18 mg of rubidium chloride is equivalent to approximately one banana equivalent dose due to the large fraction (27.8%) of naturally-occurring radioactive isotope rubidium-87.



  1. Lide, D. R.; Cahill, P.; Gold, L. P. (1963). "Microwave Spectrum of Lithium Chloride". Journal of Chemical Physics. 40 (1): 156–159. doi:10.1063/1.1724853.
  2. Wells, A. F. (1984). Structural Inorganic Chemistry. Oxford University Press. pp. 410, 444.
  3. Kopecky, M.; Fábry, J.; Kub, J.; Busetto, E.; Lausi, A. (2005). "X-ray diffuse scattering holography of a centrosymmetric sample". Applied Physics Letters. 87 (23): 231914. Bibcode:2005ApPhL..87w1914K. doi:10.1063/1.2140084.
  4. Shriver, D. F.; Atkins, P. W.; Cooper, H. L. (1990). "Chapter 2". Inorganic Chemistry. Freeman.
  5. Pyper, N. C.; Kirkland, A. I.; Harding, J. H. (2006). "Cohesion and polymorphism in solid rubidium chloride". Journal of Physics: Condensed Matter. 18 (2): 683–702. Bibcode:2006JPCM...18..683P. doi:10.1088/0953-8984/18/2/023.
  6. Winter, M. (2006). "Compounds of Rubidium". WebElements.
  7. Budavari, S. (1996). The Merck index: an encyclopedia of chemicals, drugs, and biologicals. Rahway, NJ, U.S.A.: Merck. ISBN 0-911910-12-3.
  8. Hallonquist, J.; Lindegger, M.; Mrosovsky, N. (1994). "Rubidium chloride fuses split circadian activity rhythms in hamsters housed in bright constant light". Chronobiology International. 11 (2): 65–71. doi:10.3109/07420529409055892. PMID 8033243.
  9. Hougardy, E.; Pernet, P.; Warnau, M.; Delisle, J.; Grégoire, J.-C. (2003). "Marking bark beetle parasitoids within the host plant with rubidium for dispersal studies". Entomologia Experimentalis et Applicata. 108 (2): 107. doi:10.1046/j.1570-7458.2003.00073.x.
  10. "RbCl Transformation Protocol". New England Biolabs. 2006. Archived from the original on 2006-03-19.
  11. Gian F. Placidi; Liliana Dell'Osso; Giuseppe Nistico; Hagop S. Akiskal (6 December 2012). Recurrent Mood Disorders: New Perspectives in Therapy. Springer Science & Business Media. pp. 293–. ISBN 978-3-642-76646-6.
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