Rubidium chloride

Rubidium chloride
Other names	rubidium(I) chloride
Identifiers
CAS number	7791-11-9 Y
PubChem	62683
RTECS number	VL8575000
InChI	1/ClH.Rb/h1H;/q;+1/p-1
Properties
Molecular formula	RbCl
Molar mass	120.921 g/mol
Appearance	white crystals hygroscopic
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
Thermochemistry
Std enthalpy of formation ΔfHo298	−435.14 kJ/mol
Standard molar entropy So298	95.9 J K−1 mol−1
Specific heat capacity, C	52.4 J K−1 mol−1
Hazards
MSDS	External MSDS
EU Index	Not listed
NFPA 704	0 1 0
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
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Rubidium chloride is the alkali metal halide RbCl. This alkali halide finds diverse uses, 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 body-centered cubic arrangement with chloride anions occupying the vertices of a cube surrounding a central Rb⁺. This is RbCl’s densest packing motif.^[6] 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^[7].

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.^[8]

Synthesis

The most common preparation of pure rubidium chloride involves the reaction of its hydroxide with hydrochloric acid, followed recrystallization:^[9]

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.

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^[10].
• Infusing tumor cells with rubidium chloride increases their pH. Some researchers believe that this increase prohibits the activation of enzymes such as oncogenic phosphatases and that would usually increase the cells’ malignant potential. This is thought to occur through rubidium chloride’s inactivation of essential ionic hydrogen.
• 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⁺ replace K⁺ in tissues because they are from the same chemical group^[11]. 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 are treated with a hypotonic solution containing RbCl expand. As a result, the expulsion of membrane proteins allows negatively charged DNA to bind^[12].

References

This article's citation style may be unclear. The references used may be made clearer with a different or consistent style of citation, footnoting, or external linking. (September 2007)

1. ^ Lide, D.R.; Cahill, P.; Gold, JL.P. (1963). "Cohesion and polymorphism in solid rubidium chloride". Journal of Chemical Physics 40: 156–159. doi:10.1088/0953-8984/18/2/023. http://www.iop.org/EJ/abstract/0953-8984/18/2/023. 
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. http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=APPLAB000087000023231914000001&idtype=cvips&gifs=yes. 
4. ^ Pyper, N.C.; Kirkland, A. I.; Harding, J. H. (2006). "Cohesion and polymorphism in solid rubidium chloride". Journal of Physics: Condensed Matter 18: 683–702. doi:10.1088/0953-8984/18/2/023. http://www.iop.org/EJ/abstract/0953-8984/18/2/023. 
5. ^ Shriver, D.F.; Atkins, P.W.; Cooper, H.L. (1990) Inorganic Chemistry, (Freeman), ch. 2 .
6. ^ Winter, Mark, Ph.D. (2006) Compounds of Rubidium. WebElements.
7. ^ Akutagawa, T.; Ohta, T.; Hasegawa, T.; Nakamura, T.; Christensen, C.A.; Becher, J. (April 2002). "Formation of oriented molecular nanowires on mica surface". Proc. Natl. Acad. Sci. U.S.A. 99 (8): 5028–33. doi:10.1073/pnas.082644299. PMID 11959953. PMC 122716. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=11959953. 
8. ^ Hallonquist, J.; Lindegger, M.; Mrosovsky, N. (April 1994). "Rubidium chloride fuses split circadian activity rhythms in hamsters housed in bright constant light". Chronobiol. Int. 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: 107. doi:10.1046/j.1570-7458.2003.00073.x. http://www.blackwell-synergy.com/links/doi/10.1046/j.1570-7458.2003.00073.x/abs/. 
10. ^ New England Biolabs, Inc. (2006) RbCl Transformation Protocol

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