Cobalt (II) bis(β-diketonates)

Cobalt β-diketonates [Co(acac)2]4, Co(thd)2 and their adducts with N,N,N’,N’-tetramethylethylendiamine: Co(acac)2 (TMEDA) and Co(thd)2 (TMEDA), were applied for  the deposition of epitaxial Co3O4 films on monocrystalline LaAlO3 and Si substrates. Although all complexes produced Co3O4 layers of similar quality, the adducts were more advantageous over their parent unadducted diketonates in terms of volatility, stability to oxidation in air and growth rate of oxide films. [[i], [ii]] Higher volatility of Co(acac)2 (TMEDA) over unadducted cobalt acetylacetonate was explained by its lower molecular mass over tetrameric [Co(acac)2]4[[iii]] (Fig. , )

[i] S. Pasko, L.G. Hubert-Pfalzgraf, A.Abrutis, J. Vaissermann, Polyhedron, 2004, 23, 735

[ii] S.Pasko, A.Abrutis, L.G. Hubert-Pfalzgraf, V.Kubilius, J.Cryst.Growth, 262 (2004) 653–657

[iii] F. A. Cotton, R. C. Elder, J. Amer. Chem. Soc., 1964, 86, 2294.

Cobalt acetylacetonate tetramer [Co(acac)2]4

Cobalt (II) acetylacetonate is paramagnetic solid (having electronic configuration d7). It is synthesized by methathesis reaction of cobalt (II) salts and ionic acetyl-acetonates (like alkaline metal acetylacetonates): Co2+ + 2 acac- → Co(acac)2. Cobalt acetylacetonate has tetrameric molecular structure [Co(acac)2]4, as was determined by single crystal XRD. (see Fig.)[[i],[ii]]

[i] P. A. Premkumar, A. Turchanin and N. Bahlawane, Chem. Mater., 2007, 19, 6206–6211.

[ii] P.A. Premkumar, N. Bahlawane, K.Kohse-Höinghaus, Chem.Vap.Dep., 2007, vol.13, 5 , p.227

[Co(acac)2]4 for metallic Co for MOCVD

 [Co(acac)2]4 has been applied as precursor for the deposition of metallic cobalt films in the hot-wall MOCVD reactor at the growth temperature 270 – 430 °C. Metallic Co films deposited in the presence of H2 had  < 0.5="" %="" c="" and="">< 0.2="" %="" o="">2 was essential for getting pure Co films), gthe overall reaction was  :

Co(acac)2 + H2 → Co + 2 acacH + solids

Solid by-products most probably formed by catalytic reactions of the acac ligand on the Co surface.

[Co(acac)2]4 for CoO by plasma-enhanced MOCVD

Cobalt (II) acetylacetonate (Co(acac)2 was applied as precursor for the growth of thin films of CoO (having  NaCl-type structure) by plasma-enhanced MOCVD on soda-lime glass, Si(111), stainless steel and fused SiO2 substrates. X-ray diffraction patterns indicated that (100) preferred-orientation CoO films were obtained at substrate temperatures of 150°C or above, independent of the kind of substrate. Each film had a smooth surface and a columnar structure with growth perpendicular to the film surface, according to SEM images. [[i]]

[i]Eiji Fujii, Atsushi Tomozawa, Satoru Fujii, Hideo Torii, Masumi Hattori ,Ryoichi Takayama, Jpn. J. Appl. Phys. 32 (1993) pp. L1448-L1450, “ NaCl-Type Oxide Films Prepared by Plasma-Enhanced Metalorganic Chemical Vapor Deposition”

Cobalt bis(acetylacetonate) TMEDA adduct Co(acac)2(TMEDA) , Cobalt bis(2,2,6,6-tetramethyl-3,5-heptanedionate) TMEDA adduct Co(thd)2(TMEDA)

Cobalt (II) bis(acetylacetonate) TMEDA adduct Co(acac)2(TMEDA)  and cobalt (II) bis(2,2,6,6-tetramethyl-3,5-heptanedionate) TMEDA adduct Co(thd)2(TMEDA) were synthesized by the reaction of corresponding unadducted β-diketonates [Co(acac)2]4  and Co(thd)2 and TMEDA and characterized by elemental analyses, FT-IR, 1H NMR, mass spectrometry and TGA. The monomeric molecular structure of Co(acac)2 (TMEDA)  was determined by single crystal X-Ray diffraction the flms were chsracterized.

            The most volatile and stable new adducts Co(acac)2(TMEDA)  and Co(thd)2(TMEDA) were applied as precursors for the growth of cobalt oxide thin fims. by liquid injection MOCVD in dimethoxyethane solvent on monocrystalline LaAlO3 and Si substrates. Films were characterized by XRD and XPS, they were identified as having Co3O4 films. .[ [i]]

[i] S. Pasko, L.G. Hubert-Pfalzgraf, A.Abrutis, J. Vaissermann, Polyhedron, 2004, 23, 735

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