Iron (II) bis(N,N’-diisopropylacetamidinate) was synthesized by reaction of synthesized in situ Li(N,N’-diisopropylacetamidinate) with anhydrous FeCl2 with in Et2O/THF mixture (1:1), and evaporation of solvent from hexanes extract of the reaction products. [Fe(iPr-MeAMD)2]2 is yellow-green solid with melting point 110°C and subliming at 70° C/ 50 mTorr.
[Fe(iPr-MeAMD)2]2 is dimeric both in solution (1H NMR, molecular weight determination) and solid state (single-crystal X-Ray analysis, the more precise formula is [Fe2(µ-iPr-MeAMD)2(η2-iPr-MeAMD)2]. Isopropyl substituents are insufficient to provide monomeric structures; the formed dinuclear compound contains two non-bridging η2-amidinate and two bridging μ,η1: η1- amidinate ligands.The Fe-N distance of 2.112(1) Å in the bridging ligand is slightly longer than that observed in the terminal chelating ligand (2.074(5) Å). While the η2-amidinate ligand bound to Fe has a planar geometry with mean deviation of 0.0055 Å, the geometry of Fe-N-C-N-Fe containing the bridging amidinate ligands is not planar with an Fe-NC-N dihedral angle of 62.5°. The relatively long Fe-Fe distance of 2.979(1) Å in 4a as compared to 2.462 Å found in the lantern-type dimer [Fe(Ph-HAMD)2]2 indicates that there is no iron-iron bond formation in this dimer; a similar observation was also made in the analogous compound [Fe2(µ-Ph-PhAMD)2(η2-Ph-PhAMD)2)]∙2THF.
Iron (II) bis(N,N’-diisopropylacetamidinate)
[Fe(iPr-MeAMD)2]2 was proposed as potential precursor for the ALD growth of metallic Fe and iron oxide FeO thin films.[i]
[i] R.G. Gordon, B.S. Lim, US Patent US7737290B2, «Atomic layer deposition using metal amidinates » , https://patents.google.com/patent/US7737290B2/en , https://patentimages.storage.googleapis.com/99/5e/7f/e20606f8f5f3ad/US7737290.pdf
Iron (II) bis(N,N’-di-tert-butylacetamidinate) [Fe(η2-tBu-MeAMD)2] is monomeric (in contrast to isopropyl analogue), due to higher steric bulk of tBu groups. According to TGA/DSC data at atmospheric pressure, its vaporization occurs cleanly in one step with low residual mass (12%). This suggests that the compound is thermally stable during vaporization even at 1 atm pressure.Thermal stability for short times (≤1 s) at higher temperatures was determined by flowing the vapors (carried by N2) through a tube furnace, the lowest temperature at which material was deposited on a heated substrate in the tube was considered as decomposition temperature (300 °C). In order to preserve self-limited reactivity in ALD processes using this precursor, the substrate temperature must be kept below these value.
Iron (II) bis(N,N’-di-tert-butylacetamidinate) has been used for ALD of pure Fe thin films using H2 as the reducing agent. When water vapor was used in place of hydrogen as the complementary
reactant, metal oxide films FeO was deposited. Due to high reactivity with oxygen and water vapor, the compounds must be carefully protected from contact with ambient atmosphere. [i]
[i]V. Krisyuk, A.N. Gleizes, L. Aloui, A. Turgambaeva, B. Sarapata, N. Prud’Homme, F. Senocq, D. Samélor, A. Zielinska-Lipiec, D. de Caro, C. Vahlas, J. Electrochem. Soc. 2010 vol. 157, iss. 8, D454-D461, doi: 10.1149/1.3430105 , “Chemical Vapor Deposition of Iron, Iron Carbides, and Iron Nitride Films from Amidinate Precursors”, http://jes.ecsdl.org/content/157/8/D454.abstract
[Fe(tBu-MeAMD)2]2 was applied as precursor for the growth of metallic Fe films by ALD on Si/SiO2/WNx substrates
(by using hydrogen H2 as reducing agent). [Fe(tBu-MeAMD)2]2 was evaporated at 75°C, substarte temperature was 280°C. In each ALD cycle, the dose of Fe precursor was 4x10 moles/cm (the exposure of the substrates to Fe precursor was 8x104 Langmuirs/cycle(, whereas the dose of H was 4x10 moles/cm (and exposure to H was 4x107 Langmuirs/cycle). Films of pure iron metal Fe, 5x1016 atoms/cm thick (8x10 moles/cm thick) were obtained, according to RBS measurements.[i]
[i] R.G. Gordon, B.S. Lim, US Patent US7737290B2, «Atomic layer deposition using metal amidinates » , https://patents.google.com/patent/US7737290B2/en , https://patentimages.storage.googleapis.com/99/5e/7f/e20606f8f5f3ad/US7737290.pdf