Chromium(III) acetylacetonate

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Chromium(III) acetylacetonate [1]
Lambda-tris(acetylacetonato)manganese(III)-3D-balls.png
Chromium(III) acetylacetonate Solid.jpg
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 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 244-526-0
PubChem CID
  • InChI=1S/3C5H7O2.Cr/c3*1-4(6)3-5(2)7;/h3*3H,1-2H3;/q3*-1;+3 Yes check.svgY
    Key: GMJCSPGGZSWVKI-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/3C5H7O2.Cr/c3*1-4(6)3-5(2)7;/h3*3H,1-2H3;/q3*-1;+3
    Key: GMJCSPGGZSWVKI-UHFFFAOYAF
  • [Cr+3].O=C([CH-]C(=O)C)C.O=C([CH-]C(=O)C)C.O=C([CH-]C(=O)C)C
Properties
Cr(C5H7O2)3
Molar mass 349.32
Appearancedeep maroon
Density 1.34 g/cm3
Melting point 210 °C (410 °F; 483 K)
Boiling point 340 °C (644 °F; 613 K) (sublimes near 110°C) [2]
Solubility in non-polar organic solventssoluble
Hazards
GHS labelling:
GHS-pictogram-exclam.svg
Warning
H315, H319, H335
P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

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.

Contents

Synthesis, structure, bonding

The compound is prepared by the reaction of chromium(III) oxide with acetylacetone (Hacac): [3]

Cr2O3 + 6 Hacac → 2 Cr(acac)3 + 3 H2O

The complex has idealized D3 symmetry. The Cr-O distances are 1.93 Å. [4] The complex has been resolved into individual enantiomers by separation of its adduct with dibenzoyltartrate. [5]

Like many other Cr(III) compounds, it has a quartet ground state, meaning that it has three unpaired electrons. This situation is consistent with the electronic configuration (t2g)3(eg)0. The color of the complex arises from d-d electronic transitions.

The complex is relatively inert toward substitution (hence it is susceptible to optical resolution). It reacts with a variety of electrophiles at the 3-positions of the chelate rings, giving the corresponding bromo-, nitro-, and formyl-substituted derivatives. [6]

Use in NMR

Cr(acac)3 is paramagnetic, a property which is often detrimental for NMR spectroscopy as the spin-lattice relaxation times are very short, leading to excessively broad peaks. However, this can be put to advantage in the right circumstances, particularly quantitative 13C NMR.

The spin-lattice relaxation times for diamagnetic nuclei can be variable. In particular, 13C quaternary carbons suffer from low signal intensity due to long relaxation times and lack of enhancement from the Nuclear Overhauser effect. To circumvent the first issue, the addition of a small quantity (on the order of 0.1 mM) of Cr(acac)3 to an NMR sample reduces the relaxation time by providing an alternative relaxation pathway - namely through the unpaired electron. [7] By reducing the relaxation time, more scans can be acquired in a given amount of time, resulting in higher signal intensity. This is particularly advantageous for quantitative 13C NMR, [8] which requires that all signals have fully relaxed between pulses. By reducing the relaxation time, the delay between pulses can be reduced without affecting the relative integrations of peaks.

See also

Related Research Articles

<span class="mw-page-title-main">Inorganic chemistry</span> Field of chemistry

Inorganic chemistry deals with synthesis and behavior of inorganic and organometallic compounds. This field covers chemical compounds that are not carbon-based, which are the subjects of organic chemistry. The distinction between the two disciplines is far from absolute, as there is much overlap in the subdiscipline of organometallic chemistry. It has applications in every aspect of the chemical industry, including catalysis, materials science, pigments, surfactants, coatings, medications, fuels, and agriculture.

<span class="mw-page-title-main">Chromium(III) chloride</span> Chemical compound

Chromium(III) chloride (also called chromic chloride) is an inorganic chemical compound with the chemical formula CrCl3. It forms several hydrates with the formula CrCl3·nH2O, among which are hydrates where n can be 5 (chromium(III) chloride pentahydrate CrCl3·5H2O) or 6 (chromium(III) chloride hexahydrate CrCl3·6H2O). The anhydrous compound with the formula CrCl3 are violet crystals, while the most common form of the chromium(III) chloride are the dark green crystals of hexahydrate, CrCl3·6H2O. Chromium chlorides find use as catalysts and as precursors to dyes for wool.

<span class="mw-page-title-main">Acetylacetone</span> Chemical compound

Acetylacetone is an organic compound with the chemical formula CH3COCH2COCH3. It is a colorless liquid, classified as a 1,3-diketone. It exists in equilibrium with a tautomer CH3C(O)CH=C(OH)CH3. These tautomers interconvert so rapidly under most conditions that they are treated as a single compound in most applications. It is a colorless liquid that is a precursor to acetylacetonate anion, a bidentate ligand. It is also a building block for the synthesis of heterocyclic compounds.

<span class="mw-page-title-main">Nuclear magnetic resonance spectroscopy</span> Laboratory technique

Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique to observe local magnetic fields around atomic nuclei. This spectroscopy is based on the measurement of absorption of electromagnetic radiations in the radio frequency region from roughly 4 to 900 MHz. Absorption of radio waves in the presence of magnetic field is accompanied by a special type of nuclear transition, and for this reason, such type of spectroscopy is known as Nuclear Magnetic Resonance Spectroscopy. The sample is placed in a magnetic field and the NMR signal is produced by excitation of the nuclei sample with radio waves into nuclear magnetic resonance, which is detected with sensitive radio receivers. The intramolecular magnetic field around an atom in a molecule changes the resonance frequency, thus giving access to details of the electronic structure of a molecule and its individual functional groups. As the fields are unique or highly characteristic to individual compounds, in modern organic chemistry practice, NMR spectroscopy is the definitive method to identify monomolecular organic compounds.

<span class="mw-page-title-main">Chromium hexacarbonyl</span> Chemical compound

Chromium hexacarbonyl (IUPAC name: hexacarbonylchromium) is a chromium(0) organometallic compound with the formula Cr(CO)6. It is homoleptic complex, which means that all the ligands are identical. It is a white, air-stable solid with a high vapor pressure.

<span class="mw-page-title-main">Metal carbonyl</span> Coordination complexes of transition metals with carbon monoxide ligands

Metal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. Metal carbonyls are useful in organic synthesis and as catalysts or catalyst precursors in homogeneous catalysis, such as hydroformylation and Reppe chemistry. In the Mond process, nickel tetracarbonyl is used to produce pure nickel. In organometallic chemistry, metal carbonyls serve as precursors for the preparation of other organometallic complexes.

Carbon-13 (C13) nuclear magnetic resonance is the application of nuclear magnetic resonance (NMR) spectroscopy to carbon. It is analogous to proton NMR and allows the identification of carbon atoms in an organic molecule just as proton NMR identifies hydrogen atoms. 13C NMR detects only the 13
C
isotope. The main carbon isotope, 12
C
is not detected. Although much less sensitive than 1H NMR spectroscopy, 13C NMR spectroscopy is widely used for characterizing organic and organometallic compounds.

<span class="mw-page-title-main">EuFOD</span> Chemical compound

EuFOD is the chemical compound with the formula Eu(OCC(CH3)3CHCOC3F7)3, also called Eu(fod)3. This coordination compound is used primarily as a shift reagent in NMR spectroscopy. It is the premier member of the lanthanide shift reagents and was popular in the 1970s and 1980s.

<span class="mw-page-title-main">Nickel(II) bis(acetylacetonate)</span> Coordination complex

Nickel(II) bis(acetylacetonate) is a coordination complex with the formula [Ni(acac)2]3, where acac is the anion C5H7O2 derived from deprotonation of acetylacetone. It is a dark green paramagnetic solid that is soluble in organic solvents such as toluene. It reacts with water to give the blue-green diaquo complex Ni(acac)2(H2O)2.

<span class="mw-page-title-main">Ruthenium(III) acetylacetonate</span> Chemical compound

Ruthenium(III) acetylacetonate is a coordination complex with the formula Ru(O2C5H7)3. O2C5H7 is the ligand called acetylacetonate. This compound exists as a dark violet solid that is soluble in most organic solvents. It is used as a precursor to other compounds of ruthenium.

<span class="mw-page-title-main">Tris(acetylacetonato)iron(III)</span> Chemical compound

Tris(acetylacetonato) iron(III), often abbreviated Fe(acac)3, is a ferric coordination complex featuring acetylacetonate (acac) ligands, making it one of a family of metal acetylacetonates. It is a red air-stable solid that dissolves in nonpolar organic solvents.

Metal acetylacetonates are coordination complexes derived from the acetylacetonate anion (CH
3
COCHCOCH
3
) and metal ions, usually transition metals. The bidentate ligand acetylacetonate is often abbreviated acac. Typically both oxygen atoms bind to the metal to form a six-membered chelate ring. The simplest complexes have the formula M(acac)3 and M(acac)2. Mixed-ligand complexes, e.g. VO(acac)2, are also numerous. Variations of acetylacetonate have also been developed with myriad substituents in place of methyl (RCOCHCOR). Many such complexes are soluble in organic solvents, in contrast to the related metal halides. Because of these properties, acac complexes are sometimes used as catalyst precursors and reagents. Applications include their use as NMR "shift reagents" and as catalysts for organic synthesis, and precursors to industrial hydroformylation catalysts. C
5
H
7
O
2
in some cases also binds to metals through the central carbon atom; this bonding mode is more common for the third-row transition metals such as platinum(II) and iridium(III).

<span class="mw-page-title-main">Vanadyl acetylacetonate</span> Chemical compound

Vanadyl acetylacetonate is the chemical compound with the formula VO(acac)2, where acac is the conjugate base of acetylacetone. It is a blue-green solid that dissolves in polar organic solvents. The coordination complex consists of the vanadyl group, VO2+, bound to two acac ligands via the two oxygen atoms on each. Like other charge-neutral acetylacetonate complexes, it is not soluble in water.

Chromium pentafluoride is the inorganic compound with the chemical formula CrF5. It is a red volatile solid that melts at 34 °C. It is the highest known chromium fluoride, since the hypothetical chromium hexafluoride has not yet been synthesized.

<span class="mw-page-title-main">Chromium(I) hydride</span> Chemical compound

Chromium(I) hydride, systematically named chromium hydride, is an inorganic compound with the chemical formula (CrH)
n
. It occurs naturally in some kinds of stars where it has been detected by its spectrum. However, molecular chromium(I) hydride with the formula CrH has been isolated in solid gas matrices. The molecular hydride is very reactive. As such the compound is not well characterised, although many of its properties have been calculated via computational chemistry.

<span class="mw-page-title-main">Dysprosium acetylacetonate</span> Chemical compound

Dysprosium acetylacetonate is a chemical compound of dysprosium with formula Dy(C5H7O2)3(H2O)n.

<span class="mw-page-title-main">Chromium(III) iodide</span> Chemical compound

Chromium(III) iodide, also known as chromium triiodide, is an inorganic compound with the formula CrI3. It is a black solid that is used to prepare other chromium iodides.

<span class="mw-page-title-main">Zirconium acetylacetonate</span> Chemical compound

Zirconium acetylacetonate is the coordination complex with the formula Zr(C5H7O2)4. It is a common acetylacetonate of zirconium. It is a white solid that exhibits high solubility in nonpolar organic solvents, but not simple hydrocarbons.

<span class="mw-page-title-main">Tris(acetylacetonato)cobalt(III)</span> Chemical compound

Tris(acetylacetonato)cobalt(III) is the coordination complex with the formula Co(C5H7O2)3. Often abbreviated Co(acac)3, it is a green, diamagnetic solid that is soluble in organic solvents, but not in water. Owing to its solubility in organic solvents, tris(acetylacetonato)cobalt(III) is used to produce homogeneous catalysts by reduction.

<span class="mw-page-title-main">Holmium acetylacetonate</span> Chemical compound

Holmium acetylacetonate is a coordination complex, with the chemical formula of Ho(C5H7O2)3 or Ho(acac)3. It can be obtained via the reaction between metallic holmium or holmium(III) hydride with acetylacetone, or via the reaction between holmium(III) chloride and ammonium acetylacetonate. Its anhydrous form is stable in a dry atmosphere but forms a hydrate in humid air.

References

  1. Chromium acetylacetonate Archived 2015-04-16 at the Wayback Machine at American Elements
  2. Semyannikov, P.P.; Igumenov, I.K.; Trubin, S.V.; Chusova, T.P.; Semenova, Z.I. (February 2005). "Thermodynamics of chromium acetylacetonate sublimation". Thermochimica Acta. 432 (1): 91–98. doi:10.1016/j.tca.2005.02.034.
  3. Fernelius, W. Conard; Blanch, Julian E. (2007). "Chromium(III) Acetylacetonate". Inorganic Syntheses. Vol. 5. pp. 130–131. doi:10.1002/9780470132364.ch35. ISBN   9780470132364.
  4. Morosin, B. (1965). "The crystal structure of trisacetylacetonatochromium(III)". Acta Crystallographica. 19: 131–137. doi:10.1107/S0365110X65002876.
  5. 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.
  6. Schirado, T.; Gennari, E.; Merello, R.; Decinti, A.; Bunel, S. (1971). "Reactivity of Chromium(III) and Cobalt(III) Acetylacetonato Complexes". Journal of Inorganic and Nuclear Chemistry. 33 (10): 3417–3426. doi:10.1016/0022-1902(71)80664-4.
  7. Berger, Stefan; Braun, Siegmar (2004). 200 And More NMR Experiments: A Practical Course. Weinheim: Wiley-VCH. ISBN   3-527-31067-3.
  8. 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.