Rubidium chloride

Rubidium chloride

Names
Other names rubidium(I) chloride
Identifiers
CAS Number	7791-11-9
ChEBI	CHEBI:78672
ChemSpider	56434
Jmol interactive 3D	Image
PubChem	62683
RTECS number	VL8575000
InChI InChI=1S/ClH.Rb/h1H;/q;+1/p-1 Key: FGDZQCVHDSGLHJ-UHFFFAOYSA-M InChI=1/ClH.Rb/h1H;/q;+1/p-1
SMILES [Rb+].[Cl-]
Properties
Chemical formula	RbCl
Molar mass	120.921 g/mol
Appearance	white crystals hygroscopic
Density	2.80 g/cm^3 (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)
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
Thermochemistry
Specific heat capacity (C)	52.4 J K^−1 mol^−1
Std molar entropy (S^o298)	95.9 J K^−1 mol^−1
Std enthalpy of formation (ΔfH^o298)	−435.14 kJ/mol
Hazards
Safety data sheet	Fisher Scientific
NFPA 704	0 1 0
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (Median dose)	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 otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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.

Structure

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]

Synthesis

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.

Reactions

Rubidium chloride reacts with sulfuric acid to rubidium hydrogen sulfate.

Uses

• Rubidium chloride has been shown to modify coupling between circadian oscillators via reduced photaic input to the suprachiasmatic nuclei. The outcome is a more equalized circadian rhythm, even for stressed organisms.^[7]
• RbCl is an excellent non-invasive biomarker. The compound dissolves well in water and readily be taken up by organisms. Once broken in the body, Rb⁺ replaces K⁺ in tissues because they are from the same chemical group.^[8] An example of this is the use of a radioactive isotope to evaluate perfusion of heart muscle.
• RbCl transformation for competent cells is arguably the compound's most abundant use. Cells treated with a hypotonic solution containing RbCl expand. As a result, the expulsion of membrane proteins allows negatively charged DNA to bind.^[9]
• RbCl has been used as an antidepressant in Europe under the trade name Rubinorm in doses ranging from 180 to 720 mg.^[10][11][12] Every 18 mg of RbCl is approximately equivalent to 1 Banana equivalent dose due to the large fraction (27.8%) of naturally occurring isotope Rubidium-87. It increases dopamine and norepinephrine levels and has stimulating effects, hence it is useful for anergic and apathetic depressives.^[10]

References

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. 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. doi:10.1088/0953-8984/18/2/023.
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. doi:10.3109/07420529409055892. PMID 8033243.
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. doi:10.1046/j.1570-7458.2003.00073.x.
9. "RbCl Transformation Protocol". New England Biolabs. 2006.
10. Baumel, S. (2000). Dealing with depression naturally: complementary and alternative therapies for restoring emotional health. Los Angeles: Keats Pub. p. 101. ISBN 0-658-00291-0.
11. Budavari, S. (1996). The Merck index: an encyclopedia of chemicals, drugs, and biologicals. Rahway, NJ, U.S.A.: Merck. ISBN 0-911910-12-3.
12. Lake, J. A. (2006). Textbook of Integrative Mental Health Care. New York: Thieme Medical Publishers. p. 165. ISBN 1-58890-299-4.