Rubidium chloride

Rubidium chloride

Rubidium chloride
Rubidium chloride's NaCl structure
Rubidium chloride's CsCl structure
CAS number  YesY
ChemSpider  YesY
RTECS number VL8575000
Jmol-3D images Image 1
Molecular formula RbCl
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
Boiling point 1390 °C
Solubility in water 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
Refractive index (nD) 1.5322
heat capacity
52.4 J K−1 mol−1
Std molar
95.9 J K−1 mol−1
Std enthalpy of
−435.14 kJ/mol
MSDS Fisher Scientific
EU Index Not listed
NFPA 704
Flash point Non-flammable
LD50 4440 mg/kg (rat)
Related compounds
Other anions Rubidium fluoride
Rubidium bromide
Rubidium iodide
Other cations Lithium chloride
Sodium chloride
Potassium chloride
Caesium chloride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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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.


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 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 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.



  1. ^ Lide, D. R.; Cahill, P.; Gold, L. P. (1963). "Microwave Spectrum of Lithium Chloride". Journal of Chemical Physics 40 (1): 156–159.  
  2. ^ a b 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.  
  4. ^ a b Shriver, D. F.; Atkins, P. W.; Cooper, H. L. (1990). "Chapter 2". Inorganic Chemistry. Freeman. 
  5. ^ a b 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.  
  6. ^ Winter, M. (2006). "Compounds of Rubidium". WebElements. 
  7. ^ 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.  
  8. ^ 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.  
  9. ^ "RbCl Transformation Protocol".  
  10. ^ a b Baumel, S. (2000). Dealing with depression naturally: complementary and alternative therapies for restoring emotional health. Los Angeles: Keats Pub. p. 101.  
  11. ^ Budavari, S. (1996). The Merck index: an encyclopedia of chemicals, drugs, and biologicals. Rahway, NJ, U.S.A.: Merck.  
  12. ^ Lake, J. A. (2006). Textbook of Integrative Mental Health Care. New York: Thieme Medical Publishers. p. 165.