Chloropentamminecobalt chloride

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Chloropentamminecobalt(III) chloride
Identifiers
CAS number 13859-51-3
Jmol-3D images Image 1
Properties
Molecular formula [Co(NH3)5Cl]Cl2
Molar mass 250.4 g/mol
Appearance red-violet rhomb-shaped crystal
Density 1.783 g/mL
Boiling point 760 mm Hg
Solubility in water 0.4 g/100 mL
Vapor pressure 5990 mm Hg
Thermochemistry
Std enthalpy of
formation
ΔfHo298
−1.0376E+06 Jmol−1; Molar Gibbs energy of formation = −606480 J/mol
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Chloropentamminecobalt chloride is a cobalt coordination compound.

History[edit]

Cobalt's primary ores are cobaltite, CoAsS, and erythrite, Co3(AsO4)2. It was first isolated by Georg Brandt in 1739 and has been used in superalloys, magnetic alloys, steel, and ceramics. In the Middle Ages, it was used as a blue dye. During the mid-19th century, many scientists were interested in cobalt complexes because of the different colors it produced. One major contributor to cobalt coordination chemistry is Alfred Werner. Prior to Werner, the models of cobalt amine molecules had the nitrogen's being pentavalent and connected in a chain. This was known as the Jørgensen–Bloomstrand model. Werner was the one that introduced the idea of coordination around metal atoms that suggested octahedral and tetrahedral shapes, with the most common coordination numbers being six and four. Werner's model was able to account for why [Co(NH3)3Cl3] did not form a precipitate with Ag+, while Jørgensen–Bloomstrand's model was not. Simply, the coordination complex model accounted for the inner sphere ligands being less prone to dissociate, where a traditional molecule did not. However, despite this fact Werner's discoveries were highly controversial and were not accepted until his research group proved the chirality of certain coordination compounds. The optically active metal complexes, however, remained undiscovered until ten years later by a different lab group.[1]

Properties[edit]

Chloropentamminecobalt(III) chloride is a paramagnetic compound that can undergo adsorption with Ag.[2] It decomposes upon heating above 150 °C. Its solubility is 0.4 g per 100 mL at 25 °C. At high temperatures, chloropentamminecobalt(III) chloride will readily aquate forming an aquopentammine chloride. It can also react with hot aqueous ethylenediamine of dl-propylenediamine to create tris(ethylenediamine) cobalt (III) chloride, propylenediamine compound, both generating free ammonia. At room temperature, in the presence of concentrated sulfuric acid, chloropentamminecobalt(III) chloride can form a complex hydrogen sulfate of chloropentammine cobalt (III) ion. In a reaction with mercury (II) chloride, chloropentamminecobalt(III) chloride produced the characteristic double salt [Co(NH3)5Cl]Cl2 which is used in microchemical identification.[3]

Over the years x-ray diffraction, powder x-ray diffraction, and single crystal x-ray diffraction have been used to determine the structure of chloropentamminecobalt(III) chloride.[4] Sources vary on the actual structure to whether it is rhombic, as noted by Topsoee,[5] or tetragonal, as reported by Dana.[6]

When chloropentamminecobalt(III) chloride is in a molten state, the color is takes on a more purple color,[7] whereas I its solid state it ranges I color from violet to raspberry red.[8] At 190 °C, the compound changes color yet again to blue-black.[9] The solid state of chloropentamminecobalt(III) chloride is its most stable state,[10] and decomposes in boiling water.[11]

Method of synthesis[edit]

Often chloropentammine cobalt is used to synthesize choloropentaaminecobalt (III) chloride. A rapid and simple synthesis of chloropentammine cobalt is to use hydrogen peroxide with ammoniacal cobalt (II) chloride in the presence of ammonium chloride.[12]

First, dissolve 25 g NH4Cl into 150 mL 14.7 M aq. NH3 in a 1 L Erlenmeyer flask. Constant agitation while adding 50 g of finely powdered cobalt (II) chloride hexa-hydrate in small increments. The color at this point should be yellow to pink in color, indicating the presence of hexaamminecobalt (II) chloride.

In a hood, add 40 mL of 30% H2O2 in a constant stream while stirring. The solution will be releasing heat and gas. When the gas stops emitting, the solution should be a deep red, indicating the formation of aquopentaamine salt. Neutralize this by adding 150 mL of 12 M HCl slowly. More heat will be evolved and the product should form purple precipitate, leaving the solution blue-green in color. Heat the mixture for 15 minutes on a steam bath and then cool to room temperature before using a vacuum filtration apparatus. Wash the precipitate with 10 portions 10 mL of cold water and the cold 6 M HCl. This can be followed up with an alcohol and an acetone wash to complete the drying.

An alternative method is to use concentrated ammonium chloride and CoCl26H2O. In a fume hood, add 10 g of ammonium chloride to 60 mL concentrated aqueous ammonia to a 250-mL Erlenmeyer flask. This method is used to guarantees a large excess of the NH3 ligand. While stirring the ammonium chloride solution vigorously, add 20 g of finely divided CoCl2.6H20 in small portions. At this point, the solution should be brown. Then, add 16 mL 30% hydrogen peroxide dropwise. The quick addition will cause excessive gas release as this is an exothermic reaction. When gas stops evolving, add 60 mL of concentrated HCl while still stirring, adding in 1−2 mL portions. Then, heat the solution to 60oC using a Bunsen burner The heat should be kept constant for 15 minutes (enough time to displace all the aquo ligands). Then, add 50 mL of DI water and let the reaction sit until it reaches room temperature. A purple precipitate should form. Using vacuum filtration, isolate the precipitate, washing it with 15 mL of cold DI water and 15 mL of cold ethanol.[13]

Alternatively, using [Co(NH3)4CO3]NO3 can also yield the desired cobalt complex. First, dissolve 5.0 g of [Co(NH3)4CO3]NO3 in 50 mL of H2O. Then, while stirring, add 5−10 mL of concentrated HCl until there are no more CO2 gas bubbled evolving form the solution. Then, neutralize the solution with concentrated ammonium hydroxide until the vapor above the solution is basic. At that point, add 5 mL of the concentrated NH3. Then, heat the solution for 20 minutes without boiling. This will give the product [Co(NH3)5H2O]3+. Next, cool the solution and then add 75 mL concentrated HCl. Reheat this mixture for 20–25 minutes. After, cool to room temperature. A precipitate should form. Isolate the precipitate by vacuum filtration, washing with cold 95% ethanol. For further removal of the solvent, the compound can be heated at 100−120 °C.[14]

Synthesis reactions[edit]

Cl2Co + NH4Cl + NH3 →[Co(NH3)5Cl]Cl2

2NH4+CO32− + HCl + NH4Cl + NH3 + Co2+ CO32− → [Co(NH3)5Cl]Cl2

Thermal dissociation[edit]

The thermal dissociation of chloropentamminecobalt(III) chloride have also been studied. In general, the thermal stability of a compound is dependent on the ion. Chloropentamminecobalt(III) Chloride begins decomposing at 110 °C turning into trans [Co(NH3)4Cl2]Cl, in the process losing 1 mol of NH3 per mol of complex. This change can be indicated by a plateau on the TG curve at 8%mass loss. Visually, this change can also be noted by a transition into a green color. The [Co(NH3)4Cl2]Cl further decompoeses of CoCl2(NH4)2CoCl4, which is noted by the inflection point on a TG curve at 30% mass loss. This then further dissociated into CoCl2 and NH4Cl at an equal rate. CoCl2 is the stable intermediate that forms at 53% mass loss and then sublimes above 250oC. Visually this is marked by a black residue left over, indicating the presence of Co metal.

In mass spectrometry, two sharp peaks form between 100 and 200 °C. Above 200 °C the curve supports the constant rate of gas evolution. The first peak is formed by the presence of ammonia, the product of both [Co(NH3)5Cl]Cl2 and [Co(NH3)4Cl2]Cl. The mass spectrometry supports that almost all of the gas formed in these two phases is NH3. The second peak is the combination of NH3 and HCl—the product of trans [Co(NH3)4Cl2]Cl and(NH4)2CoCl4.[15]

Uses[edit]

Chloropentamminecobalt(III) chloride has been used in an experiment to the its effectiveness to inhibit Escherichia coli cells from populating. This was used as certain platinum (II) complexes had success as antitumor agents, thus the next step was to look at transition metals. The result of this experimentation was that chloropentamminecobalt(III) chloride actually causes cell elongation. At a concentration of 12.5 ppm the E. Coli was unaffected by the presence of chloropentamminecobalt(III) chloride. At 100 ppm, there were signs of inhibition of the metabolic processes. It was at two times this concentration that cell elongation arose. Unlike Platinum (II), Cobalt(III) underwent a substitution reaction via dissociative rather than associative pathways. This indicates that SN1 alkylating agents may provide a more viable model.[16]

Safety[edit]

Cobalt(II) cations are genotoxic under in vitro and in vivo conditions. They are known to have carcinogen, mutagen and reproduction toxicant properties.[17]

References[edit]

  1. ^ Schwab, E.; Chemical and Engineering News (2003), 81(36), 80.
  2. ^ Mikhalenko, I. I.; Zubarev, Yu. A.; Krasnyi-Admoni, L. V.; Yagodovskii, V. D. Journal of Applied Chemistry USSR (English Translation), 1990, vol. 63, pp. 1337–1341
  3. ^ S. Young Tyree Jr. (1967). "Chloropentaamminecobalt(III) Chloride". Inorganic Syntheses 9. McGraw-Hill Book Company, Inc. p. 160. doi:10.1002/9780470132401.ch43. 
  4. ^ West, C. D. Zeitschrift fuer Kristallographie, Kristallgeometrie, Kristallphysik, Kristallchemie, 1935, vol. 91, pp. 181–186
  5. ^ Topsoee, H. Joergensen, S. M. (J. pr. Ch. {2} 27 {1883} 441)
  6. ^ Dana, J. G. Gibbs, W., Genth, F. A. (Lieb. Ann. 104 {1857} 167)
  7. ^ Lyashenko, M. N. Trudy Inst. Kristallogr. (russ), 1952, vol. 7, pp. 67−72
  8. ^ Kerridge, David H.; Tariq, Shabbir A. Australian Journal of Chemistry, 1993, vol. 46, pp. 917−920
  9. ^ I. G. Farbenindustrie A.-G. Patent: FR822308, 1937
  10. ^ Lamb, A. B.; Marden, J. W. Journal of the American Chemical Society, 1911, vol. 33, pp. 1883−1883
  11. ^ Gibbs, W.; Genth, F. A. Am. J. Sci., 1857, vol. 23, pp. 263−263
  12. ^ Inorganic Syntheses, Volume IX McGraw-Hill Book company, Inc. http://onlinelibrary.wiley.com/doi/10.1002/9780470132401.ch43/pdf
  13. ^ "Shibboleth Authentication Request". Pubs.acs.org.proxy2.library.illinois.edu. Retrieved 2013-08-17. 
  14. ^ "Synthesis, Characterization of [Co(NH3)4CO3]NO3 and [Co(NH3)5Cl]Cl2". 12 December 2011. Retrieved 2014-06-11. 
  15. ^ Gibson, E; Colline, L. Thermochimica Acta, 8 (1974) 303−306.
  16. ^ Crawford, B.; Talburt, D.; Johnson, D. Bioinorganic Chemistry 3, 121−131 (1974)
  17. ^ EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) (19 July 2012). "Scientific Opinion on safety and efficacy of cobalt compounds (E3) as feed additives for all animal species". Retrieved 2014-06-11.