Silver alkylamidinates have been synthesized and applied by group of R. Gordon as precursors for ALD deposition of silver containing films.[613]
Silver(I) (N,N’-diisopropylacetamidinate) ([Ag(iPr-MeAMD)]x (x=2,3) was prepared from lithium amidinate and silver chloride in diethylether solution and obtained as a 1:1 mixture of dimer and trimer. The product was isolated as colorless crystals (90%) and purified by sublimation at 80 °C at 40 mTorr. No decomposition was observed during sublimation, showing that the compounds are stable at the sublimation temperatures This precursor is volatile enough for use in ALD with the precursor vapor sources held at temperatures below 120 °C.
According to 1H NMR spectroscopy and X-ray crystallography (X-ray quality crystals were grown by standing saturated hexane solutions at -30 °C overnight), silver (N,N’-diisopropylacetamidinate) exists as a mixture of dimer and trimer in a 1:1 (mol/mol) ratio in solution at room temperature and in a 1:2 (mol/mol) ratio in the solid state. Attempts to separate the dimeric form from the mixture by sublimation at 80 °C under 40 mTorr gave a 1:1 mixture of dimer and trimer after sublimation, suggesting that the sublimed dimer quickly equilibrated to a dimer/trimer mixture on the coldfinger or in benzene solution during the NMR measurement. A relatively low melting point of 95 °C was observed for the mixture of dimer and trimer.
The geometry of the dimer is very close to that of the corresponding copper compound. The Ag-N distance of 2.111(3) Å is similar to that observed in [Ag(p-tolyl-HAMD)]2 (1.87(1) Å). The distance between metal atoms is 2.645 Å, indicating the presence of some metal-metal interaction. The geometries of the M-N-C-N-M are planar with imposed centrosymmetry, and N-M-N are essentially linear with 176.4(1)° and 170.8(1)°, respectively. In the trimer, the amidinate ligands are bridging three silver atoms in a μ,η1:η1-fashion, forming a 12-atom metallacycle. The mean Ag-N distance of 2.12(2) Å in this trimer is essentially the same as that observed in the dimer.