Synthesis and structural characterization of tricarbomethoxymethanate complexes of copper(II) and barium(II) and evaluation of their suitability for MOCVD applications

摘要

The reaction between Cu(OCH_3)_2 and HL [L = -C(CO_2CH_3)_3] in THF gives a mixture of two products, CUL(OCH3) and CuL2(THF)2 .CuL(OCH3) was characterized by elemental analysis, infrared spectroscopy and thermal decomposition studies, and its insolubility in THF, at room temperature, suggests that it may be polymeric. The solid state structure of CuL_2(THF)_2 was established via a single-crystal X-ray diffraction analysis. This complex has a tetragonally distorted trans-disubstituted octahedral structure with L binding like a conventional bidentate j3-diketonate ligand; the central CO_2CH_3 group of each Lis not coordinated. CuL2(THF)_2 readily loses the two THF molecules bound to the CU(II) center upon drying in a stream of dinitrogen to produce THF -free CuL_2. Alternatively, THF -free CUL_2 can be prepared by the reaction of CuL(OCH_3) with HL in refluxing toluene. X-ray crystallography shows that CUL_2 is a polymeric solid composed of a planar Cu(Tl_2-L)_2 repeat unit in which the central CO_2CH_3 group of each L binds weakly to the CU(II) center of a neighboring unit along a "stepped 00 (displaced) stack ofCuO_4 units. The reaction between elemental barium and HL in THF requires activation with NH_3(g) .The product is a white solid of empirical formula BaL2 .O.36THF. It was characterized by elemental analysis, IH NMR, 13C{lH} NMR, and infrared spectroscopies, and thermal decomposition studies. It is insoluble in common laboratory solvents but soluble in strong Lewis bases such as pyridine, dimethylsulfoxide, and hexamethylphosphoramide (HMP A). The product resulting from the depolymerization of BaL-2 .O.36THF with HMP A was characterized via a single-crystal X-ray diffraction analysis. It is a dimer of empirical formula Ba_2L_4(HMP A)_4 .It consists of two BaL_2(HMP A)_2 fragments linked together, in a centrosymmetric fashion, by two #mu#_2,T_(l3)_[-qCO_2CH_3)_3] ligands; this is made possible by the utilization of the donor power of the pendant C(O)OCH_3 group not used in CuL_2(THF)_2 .The remaining two -C(CO-2CH3)3ligands are also bidentate but are non-bridging, and the four HMPA molecules are bonded through oxygen, resulting in a coordination number of seven for each barium. CUL_2 is volatile and sublimes upon heating the amorphous material obtained from spontaneous desolvation of CuL_2(THF)_2 , or polymeric CuL_2, or CuL(OCH_3) under high vacuum. The barium complexes are not volatile. Metallic copper is obtained upon heating the CU(II) complexes to 1000 °C in a stream of argon, and formation of CuO results when these complexes are decomposed in the presence of oxygen. Thermal decomposition of BaL_2 .O.36THF and Ba_2L_4(HMPA)4 has been carried out under argon and 02-Ar atmospheres; residues containing varying amounts of BaO, BaO_2 and BaCO_3 were obtained depending on the experimental conditions.