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(SEt(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 reaction with formation of the species Pd(hfac-C)(hfac-O,O)(SEt(2)) and [(hfac)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-coordinate structure of this molecule with two different hfac bonding modes. Crystal data: empirical formula C14H12PdF12O4S: crystal system monoclinic; 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)'' tetramers connected by bridging SEt(2) groups to forman infinite polymer. This structure is remarkable for the presence of unusual unsupported mu-SEt(2) and mu(4)-hfac ligand binding modes. Crystal data: empirical formula C24H14Ag4F24O8S; crystal system monoclinic; space group C2/c; unit cell dimensions a = 24.776(2), b = 9.5179(8), c = 19.940(3) Angstrom; beta = 126.724(8)degrees; Z = 4. The observation of this unusual coordination mode for mu-SEt(2) prompted us to structurally characterize (hfac)Ag(SEt(2)) in the solid state by single-crystal X-ray diffraction. Crystal data: empirical formula C9H11AgF6O2S; crystal system hexagonal; 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 exchange reaction between (hfac)Ag(SEt(2)) and Pd(hfac)(2) in a 1:1 mole ratio with formation of the species Pd(hfac-C)(hfac-O,O)(SEt(2)) and [(hfac)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 equation, 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 unreacted Pd(hfac)(2) was observed, consistent with the presence of an equilibrium between all the species involved, In order to prevent this ligand exchange reaction in solutions containing both Ag(I) and Pd(II) compounds 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 suitable source for the deposition of Ag1-xPdx alloys by AACVD.