Chromium(III) acetylacetonate

Chromium(III) acetylacetonate is the coordination compound with the formula Cr(C5H7O2)3, sometimes designated as Cr(acac)3. This purplish coordination complex is used in NMR spectroscopy as a relaxation agent because of its solubility in nonpolar organic solvents and its paramagnetism.

Chromium(III) acetylacetonate[1]

Solid chromium(III) acetylacetonate
Names
IUPAC name
Tris(acetylacetonato)chromium(III)
Other names
Tris(2,4-pentanediono)chromium(III), Cr(acac)3, Cr(pd)3
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.040.463
EC Number
  • 244-526-0
Properties
Cr(C5H7O2)3
Molar mass 349.32
Appearance deep maroon
Density 1.34 g/cm3
Melting point 210 °C (410 °F; 483 K)
Boiling point 340 °C (644 °F; 613 K) (sublimes near 100 °C)
Solubility in non-polar organic solvents soluble
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

Synthesis and structure

The compound is prepared by the reaction of chromium(III) oxide with acetylacetone (Hacac):[2]

Cr2O3 + 6 Hacac → 2 Cr(acac)3 + 3 H2O

The complex has idealized D3 symmetry. The Cr-O distances are 1.93 Å.[3] The complex has been resolved into individual enantiomers by separation of its adduct with dibenzoyltartrate.[4]

Like many other Cr(III) compounds, it has a quartet ground state.

The complex is relatively inert toward substitution but undergoes bromination at the 3-positions of the chelate rings.

Use in NMR

The addition of small quantities of Cr(acac)3 to an NMR sample can allow for quantitative 13C NMR, i.e. accurate relative integrations of peaks. It achieves this by acting as a paramagnetic relaxation reagent which cancels out the Nuclear Overhauser effect, which can adversely effect the integration of 13C peaks.[5]

See also

References
  1. Chromium acetylacetonate at American Elements
  2. Fernelius, W. Conard; Blanch, Julian E. (2007). "Chromium(III) Acetylacetonate". Inorganic Syntheses. 5. pp. 130–131. doi:10.1002/9780470132364.ch35. ISBN 9780470132364.
  3. Morosin, B. (1965). "The crystal structure of trisacetylacetonatochromium(III)". Acta Crystallographica. 19: 131–137. doi:10.1107/S0365110X65002876.
  4. Drake, A. F.; Gould, J. M.; Mason, S. F.; Rosini, C.; Woodley, F. J. (1983). "The optical resolution of tris(pentane-2,4-dionato)metal(III) complexes". Polyhedron. 2 (6): 537–538. doi:10.1016/S0277-5387(00)87108-9.CS1 maint: uses authors parameter (link)
  5. Cookson, David J; Smith, Brian E (May 1984). "Optimal conditions for obtaining quantitative 13C NMR, data". Journal of Magnetic Resonance. 57 (3): 355–368. Bibcode:1984JMagR..57..355C. doi:10.1016/0022-2364(84)90253-1.
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