Bismuth oxychloride

Bismuth oxychloride is an inorganic compound of bismuth with the formula BiOCl. It is a lustrous white solid used since antiquity, notably in ancient Egypt. Light wave interference from its plate-like structure gives a pearly iridescent light reflectivity similar to nacre. It is also known as pearl white.

Bismuth oxychloride
Names
Other names
bismuthyl chloride
bismuth oxochloride
bismuth oxide chloride
bismuth(III) oxide chloride
bismoclite
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.202
EC Number
  • 232-122-7
UNII
Properties
BiOCl
Density 7.36 (meas.), 7.78 g/cm3 (calc.)[1]
insoluble
Structure
Tetragonal, tP6[2]
P4/nmm, No. 129
a = 0.3887 nm, c = 0.7354 nm
Hazards
GHS pictograms
GHS Signal word Warning
H315, H319, H335
P261, P264, P271, P280, P302+352, P304+340, P305+351+338, P312, P321, P332+313, P337+313, P362, P403+233, P405, P501
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

Structure

The structure of bismuth oxychloride can be thought of as consisting of layers of Cl−, Bi3+ and O2− ions (in the image Bi = grey, O = red, Cl = green). These ions are ordered as Cl-Bi-O-Bi-Cl-Cl-Bi-O-Bi-Cl, i.e., with alternating anions (Cl−, O2−) and cations (Bi3+). The layered structure gives rise to the pearlescent properties of this material.

Focusing on the coordination environment of the individual ions, the bismuth centers adopt a distorted square antiprismatic coordination geometry. The Bi3+ ion is coordinated to four chloride, forming one of the square faces, each at a distance of 3.06 Å from Bi, and four oxygen atoms forming the other square face, each at a distance of 2.32 Å from Bi. The oxygen atoms are tetrahedrally coordinated by four bismuth atoms.[2]

Synthesis and reactions

BiOCl is formed during the reaction of bismuth chloride with water, i.e. the hydrolysis:

BiCl3 + H2O → BiOCl + 2 HCl

When heated above 600 °C, BiOCl converts to the Bi24O31Cl10, called the "Arppe compound" which has a complex layer structure.[3][4]

Use and occurrence

It has been used in cosmetics since the days of ancient Egypt. It is part of the "pearly pigment found in eye shadow, hair sprays, powders, nail polishes, and other cosmetic products".[5] Owing to the plate-like structure of the BiOCl, its suspensions exhibit optical properties like nacre. In cosmetic its name is C.I. 77163.[6]

BiOCl exists in nature as the rare mineral bismoclite, which is part of the matlockite mineral group.[7]

An analogous compound, bismuth oxynitrate, is used as a white pigment.

References
  1. Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (eds.). "Bismoclite". Handbook of Mineralogy (PDF). III (Halides, Hydroxides, Oxides). Chantilly, VA, US: Mineralogical Society of America. ISBN 0-9622097-2-4. Retrieved December 5, 2011.
  2. Keramidas, K. G.; Voutsas, G. P.; Rentzeperis, P. I. (1993). "The crystal structure of BiOCl". Zeitschrift für Kristallographie. 205 (Part-1): 35–40. doi:10.1524/zkri.1993.205.Part-1.35. ISSN 0044-2968.
  3. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 572. ISBN 978-0-08-037941-8.
  4. Eggenweiler, U.; Keller, E.; Krämer, V. (2000). "Redetermination of the crystal structures of the `Arppe compound' Bi24O31Cl10and the isomorphous Bi24O31Br10". Acta Crystallographica Section B. 56 (3): 431–437. doi:10.1107/S0108768100000550. ISSN 0108-7681.
  5. Völz, Hans G. et al. "Pigments, Inorganic" in Ullmann's Encyclopedia of Industrial Chemistry, 2006 Wiley-VCH, Weinheim. doi:10.1002/14356007.a20_243.pub2.
  6. Carrasco, F. 2009. Diccionario de Ingredientes Cosmeticos(Paperback)
  7. Bismoclite on Mindat.org
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