Volatility by design. Synthesis and characterization of polyether adducts of bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)barium and their implementation as metal-organic chemical vapor deposition precursors

The synthesis and characterization of a series of polyethers and volatile, low-melting polyether complexes of bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedio)barium having the general formula Ba(hfa)(2) . RO(CH2CH2O)(n)R' where R = R' = CH3, n = 3; R = CH3, R' = C2H5, n = 3; R = R' = H, n = 5, 6; R = R' = CH3, n = 4; R = CH3, R' = C2H5, n = 5; R = CH3, R' = n-C4H9, n = 5, 6; R = CH3, R = C5H11O, n = 3; R = CH3, R' = n-C6H13, n = 4, 5; R = C2H5, R' = n-C4H9, n = 5; R = n-C4H9, RI = n-C4H9, n = 4, 6; R = n-C4H9, R' = n-C6H13, n = 5 are reported. The complexes are conveniently synthesized by reaction of n-propylammonium(+)-hfa(-) in DMF with an aqueous solution of Ba(NO3)(2) and the polyether or, alternatively, by reaction of the polyether with Ba(hfa)(2) in toluene. These new complexes were characterized by elemental analysis, FT-IR, H-1, C-13, and F-19 NMR, MS, X-ray diffraction (Ba(hfa)(2) . CH3O(CH2CH2O)(3)CH3 . H2O, Ba(hfa)(2) . CH3O(CH2CH2O)(5)C2H5), and thermogravimetric analysis. The melting points of the complexes are strongly dependent on the architecture of the polyether chain and dimensions of the terminal polyether substituent, with the lowest melting points corresponding to the longest polyethers having the largest terminal groups. The volatility of the Ba(hfa)(2) . polyether compounds is dependent on molecular weight and molecular structure; however, there is little direct correlation between melting point depression and enhanced volatility. The applicability of these complexes in metal-organic chemical vapor deposition is demonstrated by the successful growth of phase-pure BaTiO3 thin films using Ba(hfa)(2) . CH3O(CH2CH2O)(5)C2H5 as the Ba source. Phase composition and epitaxy in these films is analyzed by energy-dispersive X-ray spectroscopy and X-ray diffraction Theta-2 Theta, omega, and phi scans.