Synthesis, characterization and reactivity of crown ether adducts of barium carboxylates:: Ba(O2CCH3)2(18-crown-6)•4H2O and Ba(O2C(CH2)4CO2)(18-crown-6)•8H2O

The compounds Ba(O2CCH3)(2)(18-crown-6). nH(2)O and Ba(O2C(CH2)(4)CO2)(18-crown-6). nH(2)O were prepared by the reaction between barium carbonate and the appropriate organic acid in the presence of 18-crown-6. These compounds were characterized by a variety of spectroscopic and analytical methods which showed that various hydrates could be formed. The species Ba(O2CCH3)(2)(18-crown-6). 4H(2)O (1) and Ba(O2C(CH2)(4)CO2)(18-crown-6). 8H(2)O (2) were structurally characterized by single-crystal X-ray diffraction. In the solid state compound I was comprised of a Ba atom in the center of the 18-crown-6 ring with chelating acetate ligands being in the axial positions of the equitorial coordination plane. Water molecules were hydrogen bonded to the oxygen atoms of the acetate ligands. Compound 2 is an infinite polymer in the solid stale with the Pa atom also in the center of the 18-crown-6 ring with each carboxylate group chelating to one Ba and each adipate bridging through the second carboxylate group of the dicarboxylate to another Pa atom. Compound 1 crystallizes in the monoclinic space group P2(1)/c with cell dimensions of a = 9.512(1) Angstrom, b = 7.811(1) Angstrom, c = 16.906(1) Angstrom, beta = 99.049(8)degrees, V = 1240.5(3) Angstrom(3) and Z = 2. Compound 2 crystallizes in the triclinic space group <P(1)over bar> with cell dimensions of a = 8.525(1) Angstrom, b = 9.769(1) Angstrom, c = 10.200(1) Angstrom, alpha = 106.59(1)degrees, beta = 90.37(1)degrees, gamma = 110.34(1)degrees, V = 757.4(1) Angstrom(3) and Z = 1. Compounds 1 and 2 thermally decompose to evolve the 18-crown-6 ligand intact at approximately 200 degrees C, prior to the thermal decomposition of the carboxylate ligand to form BaCO3. Compounds 1 or 2 were mixed with Ti(O-i-Pr)(4) in ethanol, spin coated onto Pt substrates and heated to 400 degrees C followed by annealing at 700 degrees C for 1 h in air. Coumpound 1 resulted in formation of a mixture of BaTiO3, BaCO3 and TiO2, while 2 produced only BaCO3 films. The difference in reactivity of 1 and 2 may be connected to the availability of a thermal window for ester elimination as indicated by the TGA results. (C) 1998 Elsevier Science Ltd. All rights reserved.