Approaches to Alkaline Earth Metal-Organic Chemical Vapor Deposition Precursors. Synthesis and Characterization of Barium Fluoro-beta-ketoiminate Complexes Having Appended Polyether "Lariats"

The synthesis and characterization of a family of beta-ketoimines derived from 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (hfa) and the corresponding volatile barium beta-ketoiminate-polyether complexes having the general formula Ba[CF(3)COCHC(NR)CF(3)](2) where R = (CH(2)CH(2)O)(2)CH(3), (CH(2)CH(2)O)(2)CH(2)CH(3), and (CH(2)CH(2)O)(3)CH(2)CH(3) is reported. These complexes can be transported in the vapor phase at 160 degrees C/0.05 Torr without decomposition. The beta-ketoiminate ligands are synthesized by condensation of the appropriate amine-terminated poly(ethylene oxide)s with the trimethylsilyl enol ether derivative of hfa and converted to barium beta-ketoiminate-polyether complexes by reaction with BaH(2). The poly(ethylene oxide) amines are in turn synthesized by triphenylphosphine-mediated reduction of the corresponding poly(ethylene oxide) azides (synthesized via the tosylates) to afford the amines in good yields and analytical purity. The amines, beta-ketoimines, and barium complexes were characterized by elemental analysis, (1)H, (19)F, and (13)C NMR spectroscopy, mass spectroscopy, and thermogravimetric analysis. The eight- and ten-coordinate Ba(2+) complexes having the formula Ba[CF(3)COCHC(NR)CF(3)](2) where R = (CH(2)CH(2)O)(2)CH(2)CH(3) [C(22)H(28)N(2)F(12)O(6)Ba; space group = monoclinic, P2(1); a = 12.1175(2) Å, b = 14.9238(2) Å, c = 16.9767(3) Å, alpha = gamma = 90 degrees, beta = 90.0840(10) degrees, Z = 4] and R = (CH(2)CH(2)O)(3)CH(2)CH(3) [C(26)H(36)N(2)F(12)O(8)Ba; space group = triclinic, P&onemacr; (#2); a = 10.971(2) Å, b = 12.134(2) Å, c = 15.280(4) Å, alpha = 89.94(2) degrees, beta = 110.00(2) degrees, gamma = 116.75(2) degrees, Z = 2] were characterized by single-crystal X-ray diffraction. Both analyses reveal monomeric structures with the beta-ketoiminate ligands coordinated to the Ba(2+) center through all available oxygen and nitrogen atoms. These complexes are substantially more volatile than Ba(2,2,6,6,-tetramethyl-3,5-heptanedionate)(2) but less so than the most volatile Ba(1,1,1,5,5,5-hexafluoro-2,4-pentanedionate)(2).polyether complexes.

Mononuclear, five-coordinate lanthanide amido and aryloxide complexes bearing tetradentate (N2O2) Schiff bases.

Two monomeric, five-coordinate lanthanide complexes, [bis-5,5'-(1,3-propanediyldiimino)-2,2-dimethyl-4-hexene-3-onato]samarium[2,6-bis(tert-butyl)-4-methylphenoxide] and [bis-5,5'-(1,3-propanediyldiimino)-2,2-dimethyl-4-hexene-3-onato]erbium[2,6-bis(tert-butyl)-4-methylphenoxide], were isolated from the reactions of 2,6-bis(tert-butyl)-4-methylphenol with [bis-5,5'-(1,3-propanediyldiimino)-2,2-dimethyl-4-hexene-3-onato]lanthanide[bis(trimethylsilyl)amido] (lanthanide = Er(3+) and Sm(3+)). The purified phenoxides were recovered in excellent yields and analytical purity, and the reactions proceeded cleanly without Schiff-base degradation or cluster formation. Analogously, [bis-3,3'-(1,3-propanediyldiimino)-1-phenyl-2-butene-1-onato]erbium[bis(trimethylsilyl)amido] was also directly converted to [bis-3,3'-(1,3-propanediyldiimino)-1-phenyl-2-butene-1-onato]erbium[2,6-bis(tert-butyl)-4-methylphenoxide]; however, a less sterically demanding alcohol (i.e., ethanol) yielded a neutral trinuclear oxo alkoxide species with each dianionic Schiff base asymmetrically bridging through micro-oxo interactions. In this polynuclear cluster, each symmetry-related, seven-coordinate erbium(III) ion exhibits monocapped trigonal prismatic geometry, which assembles by sharing triangular capped faces. Single-crystal X-ray diffraction revealed square-pyramidal metal coordination in each five-coordinate lanthanide ion with varied S(4) ruffling of the "square base" donor atoms and the six-membered propylene diamine chelate ring adopting the boat conformation. To contrast the effect of subtle ligand changes, we also report the synthesis and characterization of [bis-5,5'-(2,2-dimethyl-1,3-propanediyldiimino)-2,2-dimethyl-4-hexene-3-onato]samarium[bis(trimethylsilyl)amido], having gem-dimethyl substituents appended to the propylene bridge central carbon. The six-membered diamine chelate ring in this compound adopts the chair conformation without metal-hydrocarbon interaction. Also presented are qualitative activity observations and polymerization data for the polymerization of rac-lactide and epsilon-caprolactone using the five-coordinate lanthanide amidos and phenoxides.

Synthesis and characterization of volatile, fluorine-free beta-ketoiminate lanthanide MOCVD precursors and their implementation in low-temperature growth of epitaxial CeO(2) buffer layers for superconducting electronics.

A new class of volatile, low-melting, fluorine-free lanthanide metal-organic chemical vapor deposition (MOCVD) precursors has been developed. The neutral, monomeric Ce, Nd, Gd, and Er complexes are coordinatively saturated by a versatile, multidentate ether-functionalized beta-ketoiminato ligand series, the melting point and volatility characteristics of which can be tuned by altering the alkyl substituents on the keto, imino, and ether sites of the ligand. Direct comparison with conventional lanthanide beta-diketonate complexes reveals that the present precursor class is a superior choice for lanthanide oxide MOCVD. Epitaxial CeO(2) buffer layer films can be grown on (001) YSZ substrates by MOCVD at significantly lower temperatures (450-650 degrees C) than previously possible by using one of the newly developed cerium beta-ketoiminate precursors. Films deposited at 540 degrees C have good out-of-plane (Deltaomega = 0.85 degrees ) and in-plane (Deltaphi = 1.65 degrees ) alignment and smooth surfaces (rms roughness approximately 4.3 A). The film growth rate decreases and the films tend to be smoother as the deposition temperature is increased. High-quality yttrium barium copper oxide (YBCO) films grown on these CeO(2) buffer layers by pulsed organometallic molecular beam epitaxy exhibit very good electrical transport properties (T(c) = 86.5 K, J(c) = 1.08 x 10(6) A/cm(2) at 77.4 K).