BARIUM β-KETOIMINATES

 T. Marks introduced new ligands: β-ketoiminate, containing appended polyether “lariats” to prepare the barium complexes, one of which was volatile enough for MOCVD experiments. [[i]]

Ba(dpmCAP-4)2

 Ba(dpmCAP-4)2 is a monomeric β-ketoiminate based on thd (two tBu groups connected to the backbone of the ligand), and containing a polyether ligand bonded to the N atom by a carbon chain providing intramolecular neutral Lewis base saturating Ba atom coordination sphere. Ba(dpmCAP-4)2 is one of rare fluorine-free volatile Ba CVD/ALD  precursors. It has been applied to prepare epitaxial films of BaTiO3. [4]

[i] Schulz, D. L.; Hinds, B. J.; Stern, C. L.; Marks, T. J. Inorg.Chem. 1993, 32, 249.

Ba(hfaethyldiki)2 and Ba(hfaethyltriki)2

Fig. Crystal structure of Ba(hfaethyltriki)2 (R=(CH2CH2O)3Et )

     A series of volatile, fluorinated Ba(ketoiminate)2 complexes Ba[CF3COCHC(NR)CF3]2 where equipped with appended alkoxy “lariat” groups R = (CH2CH2O)2Me, (CH2CH2O)2Et, and (CH2CH2O)3Et was synthesized (by reaction of BaH2 with corresponding ligand), purified (by sublimation at 160 °C/0.05 Torr).  The volatility of the synthesized complexes (f.e Ba(hfaethyldiki)2 (R=(CH2CH2O)2Et)) appeared to be higher than of conventional Ba precursor Ba(thd)2. as well). The synthesized barium complexes were characterized by elemental analysis, 1H, 19F, and 13C NMR spectroscopy, mass spectroscopy, and thermogravimetric analysis. The crystal structure Ba[CF3COCHC(NR)CF3]2 was determined by single crystal XRD: complex Ba(hfaethyldiki) (R = (CH2CH2O)2CH2CH3 ) is eight- coordinate [C22H28N2F12O6Ba; space group = monoclinic, P21; a = 12.1175(2) Å, b = 14.9238(2) Å, c = 16.9767(3) Å, α = γ = 90°, β = 90.0840(10)°, Z = 4] , whereas complex with R = (CH2CH2O)3CH2CH3 is ten-coordinate [C26H36N2F12O8Ba; space group = triclinic, P1̄ (#2); a = 10.971(2) Å, b = 12.134(2) Å, c = 15.280(4) Å, α = 89.94(2)°, β = 110.00(2)°, γ = 116.75(2)°, Z = 2]. Both complexes have monomeric structures with the β-ketoiminate ligands coordinated to the Ba2+ center through all available oxygen and nitrogen atoms. Ba[CF3COCHC(NR)CF3]2 are much more volatile than Ba(thd)2, but less volatile than the most volatile Ba(hfac)2·polyether complexes.

    Due to their volatility, these complexes were proposed as potential Ba precursors for the growth of Ba-containing layers by MOCVD.[i]

[i] D.A. Neumayer, J.A. Belot, R.L. Feezel, Ch. Reedy, Ch.L. Stern, T.J. Marks, L.M. Liable-Sands, A.L. Rheingold, Inorg. Chem., 1998, 37 (21), pp 5625–5633, “Approaches to Alkaline Earth Metal−Organic Chemical Vapor Deposition Precursors. Synthesis and Characterization of Barium Fluoro-β-ketoiminate Complexes Having Appended Polyether “Lariats”, DOI: 10.1021/ic980208+

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