Cr(TMHD)3: Properties, Uses & Handling FAQ

Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)chromium(III) (Cr(TMHD)3) is a thermally stable, volatile chromium(III) β-diketonate complex widely used as a precursor in metal–organic chemical vapor deposition (MOCVD), atomic layer deposition (ALD), and related thin-film fabrication processes.

Chemical Name

Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)chromium(III)

Common Abbreviation

Cr(TMHD)3

Strem Catalog Number

24-1500

Aladdin SKU

T282397

Metal Center

Chromium(III), octahedral coordination with three bidentate TMHD ligands

Key Application

MOCVD and ALD precursor for chromium-containing thin films

Notable Property

High volatility and thermal stability relative to many chromium salts, enabling vapor-phase delivery

What Is Cr(TMHD)3 and What Are Its Key Chemical Properties?

Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)chromium(III), abbreviated Cr(TMHD)3, is a coordination compound in which a chromium(III) center is chelated by three TMHD (dipivaloylmethanate) ligands, each acting as a bidentate O,O-donor. The resulting complex adopts an octahedral geometry and carries no net charge, making it a neutral, monomeric molecule.

The bulky tert-butyl groups flanking each β-diketonate carbonyl significantly reduce intermolecular interactions, lowering the melting point and increasing volatility relative to simpler chromium carboxylates or halides. This volatility is the central property exploited in vapor-deposition applications. The compound is typically obtained as a dark green crystalline solid.

As a chromium(III) compound the metal center is paramagnetic (three unpaired d-electrons, S = 3/2), which has been exploited in NMR shift-reagent applications where the paramagnetic complex induces large pseudo-contact shifts in nearby nuclei, aiding spectral dispersion.

What Are the Primary Applications of Cr(TMHD)3 in Research and Industry?

Thin-film deposition precursor: The dominant application of Cr(TMHD)3 is as a single-source or co-precursor in MOCVD and ALD for depositing chromium oxide (Cr₂O₃), chromium metal, or mixed-oxide films. Chromium oxide films are valued for their hardness, corrosion resistance, and catalytic activity. The compound's sufficient vapor pressure at moderate temperatures allows controlled delivery to the reaction zone without premature decomposition.

NMR shift reagent: Paramagnetic lanthanide and transition-metal β-diketonates have historically been used to resolve overlapping NMR resonances. Cr(TMHD)3 functions as a broadening and shift reagent, particularly useful for ¹H NMR spectral simplification of complex organic mixtures.

Catalyst and dopant precursor: Chromium-containing coatings and bulk materials prepared from Cr(TMHD)3 have been explored in heterogeneous catalysis and as dopants in ceramic and glass matrices.

Reference standard and research reagent: High-purity Cr(TMHD)3 serves as an analytical reference standard and a model compound for studying metal–ligand bonding, coordination chemistry, and precursor decomposition mechanisms.

How Should Cr(TMHD)3 Be Stored and Handled Safely?

Storage: Cr(TMHD)3 should be stored in a tightly sealed container under an inert atmosphere (nitrogen or argon) in a cool, dry location away from light. Although the complex is considerably more air-stable than many organometallic reagents, prolonged exposure to moisture or oxygen can lead to hydrolysis or oxidation of the ligand system, degrading purity over time. Refrigerated storage (2–8 °C) is generally recommended to maximise shelf life.

Personal protective equipment: Chromium(III) compounds are generally regarded as less acutely toxic than Cr(VI) species; however, appropriate PPE—nitrile gloves, safety goggles, and a laboratory coat—should always be worn. Work in a well-ventilated fume hood, especially when handling fine powders or heating the compound, to avoid inhalation of dust or vapor.

Regulatory considerations: Users should consult the current Safety Data Sheet (SDS) for Cr(TMHD)3 before use. Chromium compounds may be subject to local environmental regulations regarding disposal; waste must be collected and disposed of through an approved hazardous-waste contractor.

Incompatibilities: Avoid contact with strong oxidising agents, strong acids, and strong bases, which can decompose the β-diketonate ligands or alter the oxidation state of the chromium center.

How Do I Order Cr(TMHD)3 from Aladdin Scientific and What Should I Specify?

Cr(TMHD)3 is available from Aladdin Scientific under SKU T282397. When placing an order, customers should confirm the required quantity and packaging format. For vapor-deposition applications where precursor purity directly affects film quality, it is advisable to request the certificate of analysis (CoA) and verify purity by the stated analytical method (typically ICP-MS for metal content and GC or HPLC for organic purity).

For bulk or custom packaging inquiries, laboratory managers and procurement staff are encouraged to contact Aladdin Scientific's sales team directly. Strem Catalog Number 24-1500 can be quoted as a cross-reference when communicating with suppliers familiar with that catalogue.

Orders can be placed through the Aladdin Scientific website or via your institutional procurement system using the SKU above. Standard shipping conditions apply; ensure that receiving staff are aware of the inert-atmosphere storage requirement so that integrity is maintained upon receipt.

Troubleshooting Common Issues with Cr(TMHD)3 in MOCVD/ALD Processes

Insufficient precursor delivery: If film growth rates are lower than expected, verify that the precursor bubbler or solid source temperature is set correctly and that carrier-gas flow rates are within the recommended range. Partial clogging of delivery lines with sublimed solid is a common cause; periodic line baking under inert gas can help.

Carbon or oxygen contamination in films: Incomplete ligand decomposition at the substrate surface is a frequent source of carbon incorporation. Optimising substrate temperature, oxidant partial pressure (for oxide films), and pulse/purge timing in ALD sequences can reduce this. Ensure precursor is of adequate purity, as ligand degradation products from aged material can introduce additional contaminants.

Precursor degradation: Dark discolouration beyond the normal deep green, unusual odour, or reduced volatility may indicate partial decomposition or hydrolysis. If in doubt, request a fresh CoA from Aladdin Scientific or replace the batch. Storing the precursor under strict inert conditions and limiting the number of open-close cycles on the container will prolong usable life.

Reproducibility issues: Batch-to-batch variation in film properties often traces to precursor purity or delivery consistency. Specifying a minimum purity threshold when ordering and maintaining consistent bubbler fill levels are practical mitigation strategies.

Frequently asked questions

What is the difference between Cr(TMHD)3 and Cr(acac)3, and which should I choose for thin-film deposition?

Both are chromium(III) β-diketonates, but Cr(TMHD)3 uses the bulkier dipivaloylmethanate (TMHD) ligand while Cr(acac)3 uses the smaller acetylacetonate ligand. The larger tert-butyl substituents in TMHD reduce intermolecular packing forces, giving Cr(TMHD)3 higher volatility and a lower sublimation temperature, which makes it generally preferred for MOCVD and ALD where controlled vapor-phase delivery at moderate temperatures is critical. Cr(acac)3 may be adequate for applications requiring lower cost and where higher source temperatures are acceptable.

Is Cr(TMHD)3 air-stable, and how long can I store it once opened?

Cr(TMHD)3 is moderately air-stable compared to many organometallic reagents, but prolonged exposure to atmospheric moisture or oxygen will gradually hydrolyse or oxidise the TMHD ligands, reducing purity and performance. Once opened, the container should be immediately back-filled with dry nitrogen or argon, sealed, and stored at 2–8 °C. Under these conditions, shelf life can typically extend to 12–24 months, but users should verify quality against the CoA before critical depositions. Always request a fresh CoA if the appearance or volatility of the compound has changed.

Can Cr(TMHD)3 be used as an NMR shift reagent, and how does it work?

Yes, Cr(TMHD)3 can be used as a paramagnetic NMR reagent. The unpaired electrons on the chromium(III) center generate strong local magnetic fields that perturb the resonances of nuclei in nearby molecules, inducing pseudo-contact shifts and significant line broadening. This allows overlapping peaks in complex organic mixtures to be dispersed across a wider chemical-shift range, aiding assignment. However, Cr(TMHD)3 causes more line broadening than lanthanide shift reagents such as Eu(TMHD)3, so lanthanide reagents are preferred when sharp, well-resolved peaks are needed; Cr(TMHD)3 is more often used where broadening itself is informative.

What purity grade should I specify when ordering Cr(TMHD)3 for ALD applications?

For ALD precursor applications, electronic-grade or high-purity material with metal-basis purity typically ≥99% and stringent limits on metallic impurities (ideally <10 ppm individual metals by ICP-MS) is strongly recommended, as trace metal contaminants can be incorporated into the film and degrade device performance. Request the full CoA including ICP-MS trace metal data, thermogravimetric analysis (TGA) to confirm complete and clean volatilisation, and water content (Karl Fischer) before committing to a batch for critical process use.

How do I safely dispose of Cr(TMHD)3 waste and unused material?

Cr(TMHD)3 waste must not be poured down the drain or disposed of in regular solid waste. Collect all waste material, including contaminated packaging and used containers, in labelled, compatible waste containers and arrange disposal through a licensed hazardous-waste management contractor in compliance with local environmental regulations. Consult the current SDS for specific disposal guidance and applicable waste classification codes. Institutions should also check whether chromium-containing waste is subject to specific reporting thresholds under local legislation.

References

1. Strem Chemicals product listing for Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)chromium(III), Catalog No. 24-1500.
2. Aladdin Scientific product page for Cr(TMHD)3, SKU T282397.
3. General reference on metal β-diketonate MOCVD precursors: textbook-level knowledge on volatility and thermal stability of chromium β-diketonates.
4. General reference on paramagnetic NMR shift reagents including transition-metal β-diketonates: textbook-level knowledge.

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