SYNTHESIS AND STRUCTURE DETERMINATION OF (HFAC)AG(SET(2)), PD(HFAC-C)(HFAC-O,O)(SET(2)), AND [(HFAC)AG](4)(SET(2)) - LIGAND-EXCHANGE REACTIONS RELEVANT TO AEROSOL-ASSISTED CHEMICAL-VAPOR-DEPOSITION (AACVD) OF AG1-XPDX FILMS

This paper describes the solution chemistry of the species (hfac)Ag(SE t(2)) and Pd(hfac)(2) which have been used as metal-organic precursors for the aerosol-assisted (AA) chemical vapor deposition (CVD) of Ag1- xPdx alloy films. The reaction between (hfac)Ag(SEt(2)) and Pd(hfac)(2 ) was investigated in toluene solution and found to result in a reacti on with formation of the species Pd(hfac-C)(hfac-O,O)(SEt(2)) and [(hf ac)Ag](4)(SEt(2)). These two species were characterized in solution by NMR spectroscopy and in the solid state by FTIR, elemental analysis, and single-crystal X-ray diffraction. The solid state structure of Pd( hfac-C)(hfac-O,O)(SEt(2)) confirmed the monomeric square planar four-c oordinate structure of this molecule with two different hfac bonding m odes. Crystal data: empirical formula C14H12PdF12O4S: crystal system m onoclinic; space group P2(1)/n; unit cell dimensions a = 9.0273(9) (2) , b = 26.248(3), c = 9.763(8) Angstrom; beta = 103.042(2)degrees; Z = 4. The species [(hfac)Ag](4)(SEt(2)), comprised ''(hfacAg)(4)'' tetram ers connected by bridging SEt(2) groups to forman infinite polymer. Th is structure is remarkable for the presence of unusual unsupported mu- SEt(2) and mu(4)-hfac ligand binding modes. Crystal data: empirical fo rmula C24H14Ag4F24O8S; crystal system monoclinic; space group C2/c; un it cell dimensions a = 24.776(2), b = 9.5179(8), c = 19.940(3) Angstro m; beta = 126.724(8)degrees; Z = 4. The observation of this unusual co ordination mode for mu-SEt(2) prompted us to structurally characterize (hfac)Ag(SEt(2)) in the solid state by single-crystal X-ray diffracti on. Crystal data: empirical formula C9H11AgF6O2S; crystal system hexag onal; space group P6(1)22; unit cell dimensions a = 10.853(4), c = 18. 850(1) Angstrom; Z = 6. This compound is monomeric in the solid state with a unidentate SEt(2) ligand. The observation of this ligand exchan ge reaction between (hfac)Ag(SEt(2)) and Pd(hfac)(2) in a 1:1 mole rat io with formation of the species Pd(hfac-C)(hfac-O,O)(SEt(2)) and [(hf ac)Ag](4)(SEt(2)) leads to the following balanced equation: 4(hfac)Ag( SEt(2)) + 3Pd(hfac)(2) reversible arrow 3Pd(hfac-C)(hfac-O,O)(SEt(2)) + [(hfac)Ag](4)(SEt(2)). When this reaction was repeated by mixing the reagents in the correct mole ratios as defined in the preceding equat ion, the product Pd(hfac-C)(hfac-O,O)(SEt(2)) was obtained in only 45- 50% yield in solution as determined by H-1 NMR integration and unreact ed Pd(hfac)(2) was observed, consistent with the presence of an equili brium between all the species involved, In order to prevent this ligan d exchange reaction in solutions containing both Ag(I) and Pd(II) comp ounds required for AACVD of Ag1-xPx alloys, it is reasonable to use Pd (hfac-C)(hfac-O,O)(SEt(2)) as a Pd source. It is shown that Pd(hfac-C) (hfac-O,O)(SEt(2)) and (hfac)Ag(SEt(2)) do not undergo ligand exchange (or any other reaction) in toluene solution, and so represent a suita ble source for the deposition of Ag1-xPdx alloys by AACVD.