Synthesis and Characterization of Volatile, Thermally Stable, Reactive Transition Metal Amidinates

Article abstract of DOI:10.1021/ic0345424

A series of homoleptic metal amidinates of the general type [M(R-R′AMD)_n]_x (R = ⁱPr, ^tBu, R′ = Me, ^tBu) has been prepared and structurally characterized for the transition metals Ti, V, Mn, Fe, Co, Ni, Cu, Ag, and La. In oxidation state 3, monomeric structures were found for the metals Ti(III), V(III), and La(III). Bridging structures were observed for the metals in oxidation state 1. Cu(I) and Ag(I) are held in bridged dimers, and Ag(I) also formed a trimer that cocrystallized with the dimer. Metals in oxidation state 2 occurred in either monomeric or dimeric form. Metals with smaller ionic radii (Co, Ni) were monomeric. Larger metals (Fe, Mn) gave monomeric structures only with the bulkier tert-butyl-substituted amidinates, while the less bulky isopropyl-substituted amidinates formed dimers. The new compounds were found to have properties well-suited for use as precursors for atomic layer deposition (ALD) of thin films. They have high volatility, high thermal stability, and high and properly self-limited reactivity with molecular hydrogen, depositing pure metals, or water vapor, depositing metal oxides.

Full text of DOI:10.1021/ic0345424

Inorg. Chem. 2003, 42, 7951−7958
Synthesis and Characterization of Volatile, Thermally Stable, Reactive
Transition Metal Amidinates
Booyong S. Lim, Antti Rahtu, Jin-Seong Park, and Roy G. Gordon*
Department of Chemistry and Chemical Biology, HarVard UniVersity,
Cambridge, Massachusetts 02138
Received May 19, 2003
A series of homoleptic metal amidinates of the general type [M(R-R′AMD)n]x (R ) iPr, tBu, R′ ) Me, tBu) has been
prepared and structurally characterized for the transition metals Ti, V, Mn, Fe, Co, Ni, Cu, Ag, and La. In oxidation
state 3, monomeric structures were found for the metals Ti(III), V(III), and La(III). Bridging structures were observed
for the metals in oxidation state 1. Cu(I) and Ag(I) are held in bridged dimers, and Ag(I) also formed a trimer that
cocrystallized with the dimer. Metals in oxidation state 2 occurred in either monomeric or dimeric form. Metals with
smaller ionic radii (Co, Ni) were monomeric. Larger metals (Fe, Mn) gave monomeric structures only with the
bulkier tert-butyl-substituted amidinates, while the less bulky isopropyl-substituted amidinates formed dimers. The
new compounds were found to have properties well-suited for use as precursors for atomic layer deposition (ALD)
of thin films. They have high volatility, high thermal stability, and high and properly self-limited reactivity with molecular
hydrogen, depositing pure metals, or water vapor, depositing metal oxides.
Introduction
have been discovered for many metal oxides, nitrides,
fluorides, and sulfides and a few pure metals.4 Applications
of ALD to the production of thin films have recently grown
rapidly.5 Magnetic disk drives now incorporate an ALD
layer,6 and ALD insulating layers are used in microelectronic
memory chips.7 Wider use of ALD is, however, hindered
by the scarcity of suitable precursors. In particular, no fully
satisfactory precursors are known for ALD of the later first-
row transition metals (Mn, Fe, Co, Ni, Cu), or for the
lanthanide metals.
For deposition of films by ALD, precursors need to be
designed in such a way that the compounds are highly
reactive toward the surfaces of substrates and also to the
surface prepared by a complementary precursor such as H2O,
NH3, or H2. Such precursors also must be volatile and must
be thermally stable at growth temperatures, and preferably
the reaction byproducts should be nonreactive and non-
corrosive. ALD precursor chemistry has been dominated by
halides, alkoxides, â-diketonates, alkyls, cyclopentadienyl
derivatives, and heteroleptic compounds involving mixtures
Highly conformal thin films of transition metals and metal
oxides are needed in a variety of technological applications
including microelectronics, magnetic information storage, and
catalysis. For example, transition metal thin films can be used
as adhesion/seed layers in copper interconnects1 and as
magnetoresistive multilayers in advanced designs of magnetic
random access memory devices.2 There is also considerable
interest in lanthanide oxides such as La2O3 due to their
potential application as an insulator for memory and logic
devices.3
Atomic layer deposition (ALD) is a modified chemical
vapor deposition (CVD) process that can provide very
uniform and conformal films needed for these applications.
In ALD, films are grown by alternating exposures of a heated
substrate to vapors of two complementary chemical precur-
sors. The main difference between ALD and CVD is that,
in ALD, the surface reactions are self-limited. ALD processes
* Author to whom correspondence should be addressed. E-mail:
Gordon@chemistry.harvard.edu.
(1) International Technology Roadmap for Semiconductors 2002 Update;
Semiconductor Industry Association, 2002. Published on the Internet
at http://public.itrs.net/ Files/2002Update/Home.pdf, Interconnect Chap-
ter.
(2) Durlam, M., Chen, E. Y.; Tehrani, S. N.; Slaughter, J. M.; Kerszykow-
ski, G.; Kyler, K. W. US Patent 6,211,090 2001.
(3) Copel, M.; Cartier, E.; Ross, F. M. Appl. Phys. Lett. 2001, 78, 1607-
1609.
(4) Ritala, M.; Leskela¨, M. In Handbook of Thin Film Materials; Nalwa,
H. S., Ed.; Academic Press: New York, 2001; Vol. 1, pp 103-159.
(5) Suntola, T., Simpson, M., Eds. Atomic Layer Epitaxy; Blackie and
Sons Ltd.: Glasgow, 1990.
(6) Xiong, W.; Gong, H.; Park, C.-M.; Zhang, J.; Lam, A.; Huai, Y. MMM
Conf. 2001, Session HP-03.
(7) Seidel, T.; Londergan, A.; Winkler, J.; Liu, X.; Ramanathan, S. Solid
State Technol. 2003, 46, 67-68.
10.1021/ic0345424 CCC: $25.00 © 2003 American Chemical Society
Published on Web 10/25/2003
Inorganic Chemistry, Vol. 42, No. 24, 2003 7951

Lim et al.
have been studied for only three magnesium amidinates,
[Mg(R-MeAMD)2]x (x ) 1, R ) tBu; x ) 2, R ) iPr, Et).24
We demonstrate here that bidentate amidinate ligands
provide volatile, thermally stable, homoleptic compounds
with a wide range of transition metals and lanthanum with
oxidation states of 1 (Cu, Ag), 2 (Mn, Fe, Co, Ni), and 3
(Ti, V, La). The compounds [M(R-R′AMD)3] (M ) Ti, V,
La), [M(R-MeAMD)2]x (M ) Mn, Fe, Co, Ni, x ) 1, 2),
Figure 1. Bidentate chelating N,N′-dialkyl-2-alkyl-amidinate ligand.
of these ligands.8 Recently, dialkylamido compounds [Zr-
(NR2)4], [Hf(NR2)4], and mixed dialkylamido/alkylimido
compounds [W(NR2)2(NtBu)2] have been successfully uti-
lized for the ALD of thin films of zirconium and hafnium
oxides9 and tungsten nitride.10 Because these amide-type
precursors do not have M-C bonds, carbon incorporation
in the resulting films was found to be minimal, and the low
M-N bond strengths as compared to the M-Cl and M-O
bonds allowed deposition at relatively low temperatures.
These amide derivatives produce no corrosive byproducts,
unlike metal halides.
i
and [M(R-MeAMD)]x (M ) Cu, Ag, x ) 2, 3) (R ) Pr,
t
tBu, R′ ) Me, Bu) were characterized by X-ray crystal-
lography, elemental analysis, NMR, physical characteristics
(color, melting point, vapor pressure), thermal stability, and
chemical reactivity. All of these metal amidinates are volatile.
Among them, manganese, iron, cobalt, nickel, copper, and
lanthanum compounds were tested for thin film deposition,
and were found thermally stable and reactive enough to be
used as vapor sources for the ALD of pure transition metal
films of Fe, Co, Ni, and Cu and of metal oxides La2O3, FeO,
MnO, and CoO.25
The most extensively studied homoleptic amido metal
compounds are those with bis(trimethylsilyl)amide (TMS)
ligand. This bulky TMS group has been used to stabilize
especially low coordination numbers (2, 3) and oxidation
states (1, 2, 3) throughout the periodic table.11-14 Although
this class of metal compounds generally provided high
chemical reactivity, silicon contamination in films and low
thermal stability have often limited their use in ALD.15
Volatile homoleptic amido metal compounds containing
moieties other than the TMS group are rare, with most
examples from the group 4-6 metals. It is notable that most
volatile homoleptic dialkylamido metal compounds are those
with high oxidation states of 4 or more. Dialkylamides of
transition metals with low oxidation states of 1-3 are not
volatile. For example, tetrameric [Cu(NR2)]4 (R ) Me, Et,
nBu, Cy) decomposed before sublimation, which prevents
their use as precursors for vapor deposition.16
N,N′-Dialkyl-2-alkyl-amidinates (R-R′AMD) are alterna-
tives to alkylamides (Figure 1). The amidinate ligand can
be tuned by substitution of the R and R′ groups to be bulky
enough to limit oligomerization and hence increase the
volatility of amidinate compounds of metals in low oxidation
states. The bidentate chelating effect should increase the
thermal stability of resulting metal compounds. While
numerous metal compounds with amidinate ligands can be
found in the literature,17-23 volatility and thermal stability
Experimental Section
Preparation of Compounds. All reactions and manipulations
were conducted under a pure nitrogen atmosphere using either an
inert atmosphere box or standard Schlenk techniques. Tetrahydro-
furan (THF), ether, and hexanes were dried using an Innovative
Technology solvent purification system and stored over 4 Å
molecular sieves. Methyllithium, tert-butyllithium, 1,3-diisopro-
pylcarbodiimide, 1,3-di-tert-butylcarbodiimide, TiCl3, VCl3, MnCl2,
FeCl2, CoCl2, NiCl2, CuBr, and AgCl (Aldrich) were used as
received. LaCl3(THF)2 was prepared as described in the literature.26
Copper (N,N′-Diisopropylacetamidinate) ([Cu(iPr-MeAMD)]2)
(7). A solution of methyllithium (1.6 M in Et2O, 34 mL, 0.054
mol) in Et2O was added dropwise to a solution of 1,3-diisopropyl-
carbodiimide (6.9 g, 0.055 mol) in 100 mL of Et2O at -30 °C.
The mixture was warmed to room temperature and stirred for 4 h.
This colorless resultant solution was then added to a solution of
copper bromide (7.8 g, 0.054 mol) in 50 mL of Et2O. The reaction
mixture was stirred for 12 h under the exclusion of light. All
volatiles were then removed under reduced pressure, and the
resulting solid was extracted with hexanes (100 mL). The hexane
extract was filtered through a pad of Celite on a glass frit to afford
a pale yellow solution. Concentration of the filtrate and its cooling
to -30 °C afforded colorless crystals. Subsequent sublimation
afforded pure white products (70%). Sublimation: 70 °C at 50
mTorr. Mp: 147 °C. 1H NMR (C6D6, 25 °C): 1.16 (d, 12H), 1.65
(s, 3H), 3.40 (m, 2H). Anal. Calcd for C16H34N4Cu2: C, 46.92; H,
8.37; N, 13.68. Found: C, 46.95; H, 8.20; N, 13.78.
(8) Leskela¨, M.; Ritala, M. Thin Solid Films 2002, 409, 138-146.
(9) Hausmann, D. M.; Kim, E.; Becker, J.; Gordon, R. G. Chem. Mater.
2002, 14, 4350-4358.
(18) Cotton, F. A.; Daniels, L. M.; Murillo, C. A. Inorg. Chem. 1993, 32,
2881-2885 and references therein.
(10) Becker, J. S.; Gordon, R. G. Appl. Phys. Lett. 2003, 82, 2239-2241.
(11) Bradley, D. C.; Ghotra, J. S.; Hart, F. A. J. Chem. Soc., Dalton Trans.
1973, 1021.
(19) Cotton, F. A.; Daniels, L. M.; Matonic, J. H.; Murillo, C. A. Inorg.
Chim. Acta 1997, 256, 277-282.
(20) Cotton, F. A.; Daniels, L. M.; Feng, X.; Maloney, D.; Matonic, J. H.;
Murillo, C. A. Inorg. Chim. Acta 1997, 256, 291-301.
(21) Cotton, F. A.; Feng, X.; Matusz, M.; Poli, R. J. Am. Chem. Soc. 1988,
110, 7077-7083.
(22) Luo, Y.; Yao, Y.; Shen, Q.; Sun, J.; Weng, L. J. Organomet. Chem.
2002, 662, 144-149.
(23) Vendemiati, B.; Prini, G.; Meetsma, A.; Hessen, B.; Teuben, J. H.;
Traverso, O. Eur. J. Inorg. Chem. 2002, 707-711.
(24) Sadique, A. R.; Heeg, M. J.; Winter, C. H. Inorg. Chem. 2001, 40,
6349-6355.
(25) Lim, B. S.; Rahtu A.; Gordon, R. G. Nature Materials, in press.
(26) Deacon, G. B.; Feng, T.; Nickel, S.; Skelton, B. W.; White, A. H. J.
Chem. Soc., Chem. Commun. 1993, 1328.
(12) Olmstead, M. M.; Power, P. P. Shoner, S. C. Inorg. Chem. 1991, 30,
2547 and references therein.
(13) Hitchcock, P. B.; Lappert, M. F.; Pierssens, L. J.-M. Chem. Commun.
1996, 1189.
(14) Lappert, M. F., Ed. Metals and Metalloid Amides; John Wiley &
Sons: New York, 1980; p 465.
(15) Kim, D.-H.; Gordon, R. G. Unpublished results.
(16) (a) Tsuda, T.; Watanabe, K.; Miyata, K.; Yamamoto, H.; Saegusa, T.
Inorg. Chem. 1981, 20, 2728-2730. (b) Hope, H.; Power, P. P. Inorg.
Chem. 1984, 23, 936-937.
(17) Edelmann, F. T.; Freckmann, D. M. M.; Schumann, H. Chem. ReV.
2002, 102, 1851-1896.
7952 Inorganic Chemistry, Vol. 42, No. 24, 2003

Volatile, Thermally Stable, ReactiWe Transition Metal Amidinates
Silver (N,N′-Diisopropylacetamidinate) ([Ag(iPr-MeAMD)]x
(x ) 2, 8a; x ) 3, 8b)). These compounds were prepared in the
same manner as described for [Cu(iPr-MeAMD)], and obtained as
a 1:1 mixture of dimer and trimer. The product was isolated as
colorless crystals (90%). Sublimation: 80 °C at 40 mTorr. Mp:
3.26 (br, 6H), 96.3 (br, 2H). Anal. Calcd. for C24H51N6V: C, 60.73;
H, 10.83; N, 17.71. Found: C, 61.45; H, 11.17; N, 17.78.
Lanthanum tris(N,N′-diisopropylacetamidinate) ([La(iPr-
MeAMD)3]) (9a): following a similar procedure as described above
for [Co(iPr-MeAMD)2], but using LaCl3(THF)2,26 off-white solids
were obtained as a product by sublimation of the crude solid
materials (77%). Sublimation: 80 °C at 40 mTorr. 1H NMR (C6D6,
25 °C): 1.20 (d, 12H), 1.67 (s, 3H), 3.46 (m, 2H). Anal. Calcd for
C24H51N6La: C, 51.24; H, 9.14; N, 14.94. Found: C, 51.23; H,
8.22; N, 14.57.
1
95 °C. H NMR (C6D6, 25 °C): 1.10 (d, dimer), 1.21 (d, trimer),
1.74 (s, trimer), 1.76 (s, dimer), 3.52 (m, peaks for dimer and trimer
are not well resolved.) Anal. Calcd for [C8H17N2Ag]x: C, 38.57;
H, 6.88; N, 11.25. Found: C, 38.62; H, 6.76; N, 11.34.
Cobalt Bis(N,N′-Diisopropylacetamidinate) ([Co(iPr-Me-
AMD)2]) (5a). This compound was obtained in a similar manner
as described for [Cu(iPr-MeAMD)], but with Et2O/THF (1:1, v/v)
as solvents. Recrystallization in hexanes at -30 °C gave dark green
Lanthanum tris(N,N′-diisopropyl-2-tert-butylamidinate) ([La-
(tPr-tBuAMD)3]‚1/2C6H12) (9b): colorless crystals (80%). Sublima-
1
tion: 120 °C at 50 mTorr. Mp: 140 °C. H NMR (C6D6, 25 °C):
1
crystals as product (77%). H NMR (C6D6, 25 °C): -70.56 (br,
1.33 (br, 21H), 4.26 (m, 2H); the methyl resonance of isopropyl
groups and tert-butyl group of the ligand was not resolved. Anal.
Calcd for C33H75N6La: C, 57.04; H, 10.88; N, 12.09. Found: C,
58.50; H, 10.19; N, 11.89.
12H), 310.53 (br, 3H), 326.34 (br, 2H). Sublimation: 40 °C at 50
mTorr. Mp: 84 °C. Anal. Calcd for C16H34N4Co: C, 56.29; H,
10.04; N, 16.41. Found: C, 54.31; H, 9.69; N, 15.95.
All the following compounds have been synthesized in the same
way as [Co(iPr-AMD)2] unless described otherwise.
Cobalt bis(N,N′-di-tert-butylacetamidinate) ([Co(tBu-Me-
AMD)2]) (5b): dark blue crystals (84%). 1H NMR (C6D6, 25 °C):
-28.86 (br, 18H), 312.21 (br, 3H). Sublimation: 45 °C at 50 mTorr.
Mp: 90 °C. Anal. Calcd for C20H42N4Co: C, 60.43; H, 10.65; N,
14.09. Found: C, 58.86; H, 10.33; N, 14.28.
X-ray Structure Determinations. Compounds [V(iPr-MeAMD)3]
(2), [Fe2(µ-iPr-MeAMD)2(η2-iPr-MeAMD)2] (4a), [Fe(tBu-MeAMD)2]
(4b), [Co(iPr-MeAMD)2] (5a), [Cu(iPr-MeAMD)]2 (7), [Ag(iPr-
MeAMD)]x (8a, 8b), and [La(iPr-tBuAMD)3] (9b) were structurally
characterized by X-ray crystallography. Crystals were grown by
standing saturated hexane solutions at -30 °C overnight. Diffraction
data were obtained with a Siemens (Bruker) SMART CCD area
detector system using ω scans of 0.3°/frames, and 30-s frames such
that 1271 frames were collected for a hemisphere of data. The first
50 frames were re-collected at the end of the data collection to
monitor for crystal decay; no significant decay was observed. Cell
parameters were determined using SMART software. Data reduc-
tions were performed with SAINT software, which corrects for
Lorenz polarization and decay. Absorption corrections were applied
using SADABS. Space groups were assigned by analysis of
symmetry and observed systematic absences determined by the
program XPREP and by successful refinement of the structure. All
structures were solved by direct methods with SHELXS and
subsequently refined against all data by the standard technique of
full-matrix least squares on F2 (SHELXL-97).
Iron bis(N,N′-diisopropylacetamidinate) ([Fe2(µ-iPr-MeAMD)2-
(η2-iPr-MeAMD)2]) (4a): yellow-green crystals (75%). 1H NMR
(C6D6, 25 °C): 5.12 (br, 12H), 130.66 (br, 3H), 177.44 (br, 2H);
unassignable broad peaks (5-10% intensity of that at 5.12 peak)
at -10.30, -6.75, -2.31, 22.10, 110.27, 139.39, 199.64, and 217.03
were also observed. Sublimation: 70 °C at 50 mTorr. Mp: 110
°C. Anal. Calcd for C32H68N8Fe2: C, 56.80; H, 10.13; N, 16.56.
Found: C, 55.24; H, 10.05; N, 16.17. Complexity in solution (p-
xylene): 2.0(2).
Iron bis(N,N′-di-tert-butylacetamidinate) ([Fe(tBu-MeAMD)2])
1
(4b): white crystals (77%). H NMR (C6D6, 25 °C): 15.78 (br,
18H), 154.46 (br, 3H). Sublimation: 55 °C at 60 mTorr. Mp: 107
°C. Anal. Calcd for C20H42N4Fe: C, 60.90; H, 10.73; N, 14.20.
Found: C, 59.55; H, 10.77; N, 13.86.
Nickel bis(N,N′-diisopropylacetamidinate) ([Ni(iPr-MeAMD)2])
(6). This compound was prepared in the manner of 7 but with
refluxing the reaction mixtures at 60 °C overnight. Brown crystals
The asymmetric units contain one-half (4a, 4b, 5a, 8a), one (8b,
9b), two of one-half (7), or one-third (2) formula weights. The
structure of 2 was highly disordered over four different positions
and refined accordingly, and also refined with a chiral twin
treatment with BASF ) 0.59. Isopropyl groups in 5a and 9b were
disordered over two positions and were refined accordingly. All
non-hydrogen atoms except for the solvated hexane molecule found
in 9b were described anisotropically. In the final stages of
refinement, hydrogen atoms were added at idealized positions and
refined as riding atoms with a uniform value of Uiso. Crystal data
and final agreement factors are listed in Table 1.
1
(49%). Sublimation: 35 °C at 70 mTorr. Mp: 69 °C. H NMR
(C6D6, 25 °C): -5.39 (br, 12H), 30.9 (br, 3H), 81.16 (br, 2H). Anal.
Calcd. for C16H34N4Ni: C, 56.34; H, 10.05; N, 16.42. Found: C,
55.22; H, 10.19; N, 16.12. Complexity in solution (p-xylene):
1.0(2).
Manganese bis(N,N′-diisopropylacetamidinate) ([Mn2(µ-iPr-
MeAMD)2(η2-iPr-MeAMD)2]) (3a): pale yellow crystals (79%).
Sublimation: 65 °C at 50 mTorr. Mp: 148 °C. Anal. Calcd for
C32H68N8Mn2: C, 56.96; H, 10.16; N, 16.61. Found: C, 57.33; H,
9.58; N, 16.19.
Other Physical Measurements. Elemental analysis was per-
1
formed by Desert Analytics Laboratory, Tucson, AZ. H NMR
Manganese bis(N,N′-di-tert-butylacetamidinate) ([Mn(tBu-
MeAMD)2]) (3b): pale yellow crystals (87%). Sublimation: 55
°C at 60 mTorr. Mp: 100 °C. Anal. Calcd for C20H42N4Mn: C,
61.04; H, 10.76; N, 14.24. Found: C, 60.53; H, 11.31; N, 14.03.
Titanium tris(N,N′-diisopropylacetamidinate) ([Ti(iPr-Me-
AMD)3]) (1): brown crystals (70%). Sublimation: 70 °C at 50
spectra were recorded with a Bruker AM-500 spectrometer. Melting
points were obtained in sealed capillaries. Molecular weight
determinations of compounds in solution were performed using
3.0-3.5 g of recrystallized p-xylene and 0.20-0.30 g of compound.
The temperature was recorded electronically from a thermocouple
every 10 s for at least 2 min, and the measurements were repeated
at least three times to ensure reproducibility. Thermal gravimetric
analysis (TGA) and differential scanning calorimetry (DSC) were
done in a Netzsch STA 449C operated inside a drybox. Samples
(10-20 mg) were loaded into open aluminum crucibles. Measure-
ments were carried out at atmospheric pressure in a carrier gas of
purified N2, at a temperature ramp rate of 10 K/min.
1
mTorr. H NMR (C6D6, 25 °C): -12.3 (br, 3H), 0.77 (br, 6H),
1.46 (br, 6H), 40.7 (br, 2H). Anal. Calcd. for C24H51N6Ti: C, 61.13;
H, 10.90; N, 17.82. Found: C, 60.22; H, 10.35; N, 17.14.
Vanadium tris(N,N′-diisopropylacetamidinate) ([V(iPr-Me-
AMD)3]) (2): red-brown powder (80%). Sublimation: 70 °C at 45
1
mTorr. H NMR (C6D6, 25 °C): -39.1 (br, 3H), 0.41 (br, 6H),
Inorganic Chemistry, Vol. 42, No. 24, 2003 7953

Lim et al.
Table 1. Crystallographic Dataa for Compounds 2, 4a, 4b, 5a, 7, 8a, 8b, and 9b
2
4a
4b
5a
7
8
9b‚1/2C6H12
formula
fw
C24H51N6V
474.65
hexagonal
R3m
3
16.205(3)
16.205(3)
9.355(2)
C32H68Fe2N8
676.64
monoclinic
C2/c
4
C20H42FeN4
394.43
tetragonal
Aba2
4
14.687(2)
13.942(2)
11.756(1)
C16H34CoN4
341.41
monoclinic
C2/c
4
C16H34Cu2N4
409.56
monoclinic
C2/c
8
C32H68Ag4N8
996.44
monoclinic
C2(1)/c
4
C36H75LaN6
730.94
monoclinic
C2/c
8
cryst syst
space group
Z
a, Å
23.290(6)
9.629(2)
18.194(4)
110.804(4)
3814(2)
1.178
14.109(2)
9.455(2)
15.476(2)
100.875(3)
2027.3(5)
1.119
28.85(6)
11.09(3)
18.88(4)
133.20(2)
3946(2)
1.379
24.942(3)
9.924(1)
17.122(2)
104.739(2)
4098.7(9)
1.615
38.22(2)
11.840(6)
21.01(1)
118.604(6)
8347(8)
1.163
b, Å
c, Å
â, deg
V, Å3
2127.6(7)
1.111
0.370
2407.3(5)
1.088
0.635
d
calc, g/cm3
µ, mm-1
0.791
0.847
2.158
1.913
1.052
θ range, deg
2.51-28.23
1.87-22.50
2.77-28.31
2.80-28.27
2.13-22.49
0.84-28.28
1.82-28.41
GOF (F2)
1.050
1.089
1.057
1.047
1.040
1.058
1.053
R1b (wR2 ), %
4.24(11.30)
2.88(8.65)
2.94(8.26)
3.83(10.84)
4.29(10.54)
3.76(9.85)
3.19(0.13)
c
2
2
2
a Obtained with graphite monochromated Mo KR (λ ) 0.71073 Å) radiation. b R1 ) ∑||Fo| - |Fc||/∑|Fo|. c wR2 ) {∑[w(Fo - Fc )2]}/{∑[w(Fo )2]}1/2
.
Table 2. Physical Properties of Amidinato Metal Compounds 1-9
are collected in Table 3. Its structure was highly disordered
over four positions, and only one position is shown in Figure
2 for the purpose of clarity. The molecule has a distorted
geometry from octahedral toward trigonal prismatic with a
N-V-N transoid angle of 163.9(7)° and a dihedral angle
of θ ) 85.9-95.8° between VN2 planes; its structure is
similar to that observed in the analogous compound [V(p-
tolyl)-HAMD)3].18 The mean V-N bond distance is 2.02(2)
Å, and the bite angle of the chelating η2-amidinate ligand is
63.5(6)°.
vapor pressure
mp
compound
(°C/Torr)
(°C)
color
brown
red-brown
pale yellow
pale yellow
yellow-green
white
dark green
dark blue
brown
white
white
[Ti(iPr-MeAMD)3], 1
[V(iPr-MeAMD)3], 2
70/0.05
70/0.05
65/0.05
55/0.06
70/0.05
55/0.06
40/0.05
45/0.05
35/0.07
70/0.05
80/0.04
80/0.04
120/0.05
[Mn(iPr-MeAMD)2]2, 3a
[Mn(tBu-MeAMD)2], 3b
[Fe(iPr-MeAMD)2]2, 4a
[Fe(tBu-MeAMD)2], 4b
[Co(iPr-MeAMD)2], 5a
[Co(tBu-MeAMD)2], 5b
[Ni(iPr-MeAMD)2], 6
[Cu(iPr-MeAMD)]2, 7
[Ag(iPr-MeAMD)]x, 8a,b
[La(iPr-MeAMD)3], 9a
[La(iPr-tBuAMD)3], 9b
148
100
110
107
84
90
69
147
95
Unlike early transition metals, the tendency of lanthanide
elements to acquire a coordination number higher than 3 is
well-known, which often results in “ate” complexes pos-
sessing alkali-metal-bearing solvent molecules or one or two
bridging halide anions.27 For example, attempted synthesis
of neutral homoleptic lanthanum compounds with diisopro-
pylamide or 2,2,5,5-tetramethylpyrrolidinate (TMPR) ligands
generated [La(NiPr2)2](µ-NiPr2)2[Li(THF)] and [La(TMPR)3]2-
(µ-X)(M(THF)4) (X ) Cl, I, M ) Li, Na), respectively.28
With the more bulky 2,2,6,6-tetramethylpiperidinate (TMPD)
ligand, we were able to synthesize successfully the neutral
lanthanum compound [La(TMPD)3].29 This three-coordinate
lanthanum compound was, however, thermally unstable, and
decomposed at 138 °C. The strategy to increase the thermal
stability of resultant compounds using the chelating bidentate
white
white
140
Results and Discussion
Synthesis and Structures of Compounds. All neutral
metal amidinate compounds listed in Table 2 were synthe-
sized by the metathesis reactions of a metal halide with
corresponding equivalents of lithium amidinates (N,N′-
diisopropylacetamidinate (iPr-MeAMD), N,N′-di-tert-butyl-
acetamidinate (tBu-MeAMD), and, N,N′-diisopropyl-2-tert-
butylamidinate (iPr-tBuAMD)) in Et2O or Et2O/THF as
described in reaction 1.
MXn + nLi(RNC(R′)NR) f
i
i
ligands, Pr-MeAMD and Pr-tBuAMD, finally led us to
obtain thermally stable, neutral lanthanum compounds 9a
and 9b, respectively, in good yields. A comparison of vapor
(1/x)[M(RNC(R′)NR)n]x + nLiX (1)
Lithium amidinates were prepared in situ from the cor-
responding carbodiimide and alkyllithium and not isolated;
the metal complexes are depicted in Scheme 1. The reactions
went to completion after stirring at room temperature
overnight, except for the reaction for Ni(II) compound 6,
which was refluxed in THF/Et2O (1:1, v/v) overnight.
Compounds 1-9 are all solids at room temperature, and their
physical properties are summarized in Table 2.
(27) Just, O.; Rees, W. S., Jr. Inorg. Chem. 2001, 40, 1751-1755 and
references therein.
(28) (a) The compound [La(NiPr2)2](µ-NiPr2)2[Li(THF)] was prepared by
the reaction of LaCl3(THF)2 with lithium diisopropylamide in THF.
The compound crystallizes in monoclinic space group P2(1) with a
) 15.26(1) Å, b ) 21.43(2) Å, c ) 21.47(2) Å, â ) 95.251(8)o, Z )
2, and V ) 6988(9) Å3. Flame test further confirmed the incorporation
of lithium with this compound. Because this compound is not of direct
interest in this work, it was not further characterized. (b) Compounds
[La(TMPR)3]2(µ-X)[M(THF)4] (X ) Cl, I.; M ) Li, Na) were prepared
by the reaction of LaX3(THF)n (X ) Cl, n ) 2, X ) I, n ) 4) with
sodium or lithium salt of 2,2,5,5-tetramethylpyrrolidine (Lunt, E.
Tetrahedron Suppl. 1963, 291) in THF. One of these compounds, [La-
(TMPR)3]2(µ-I)[Na(THF)4], crystallizes in monoclinic space group P2-
(1)/c with a ) 11.04(1) Å, b ) 27.81(2) Å, c ) 24.25(2) Å, â )
94.32(2)°, Z ) 4, and V ) 7428(1) Å3. Silver nitrate experiments and
flame test further confirmed the incorporation of halide and sodium
or lithium, in these compounds, respectively. Because these compounds
are not of direct interest in this work, they were not further
characterized.
i
(a) Trivalent Metals. The acetamidinate ligand Pr-
MeAMD was utilized in the synthesis of Ti(III) and V(III)
compounds. Dark brown titanium (1) and red-brown vana-
dium (2) compounds were obtained with 70% and 80%
1
yields, respectively (Scheme 1). The H NMR data and
sublimation data supported the monomeric formulation for
compounds 1 and 2 (Table 2). The structure of vanadium
compound 2 is shown in Figure 2, and selected metric data
7954 Inorganic Chemistry, Vol. 42, No. 24, 2003

Volatile, Thermally Stable, ReactiWe Transition Metal Amidinates
Scheme 1. Synthesis of Metal Amidinates
Table 3. Bond Distances (Å) and Angles (deg) for Trivalent Metal
Amidinates 2 and 9b
Table 4. Vapor Pressures of Lanthanum(III) and Copper(I) Compounds
with Various Amide-Type Ligands
2
9b
2.53(2)
1.332(3)
111.8(1)
149(2)
compound
[La(TMS)3]
vapor pressure (°C/Torr)
refs
M-Na
2.06(4)
1.30(2)
102/0.0001
105/0.0001
120/0.05
80/0.04
>90, dec
160/0.1
11
N-Ca,b
[La(TMPD)3]
this work
this work
this work
16
N-C-Nb
N-M-Nc
N-M-Nchelating
θd
114(2)
[La(iPr-tBuAMD)3]
[La(iPr-MeAMD)3]
[Cu(NEt2)]4
163.9(7)
63.5(6)
85.9, 93.3, 95.8
a
51.8(2)
96.2, 98.7, 98.9
[Cu(TMS)]4
32
a Mean values. b Amidinate backbone. c Transoid angle, involving N
atoms in different chelate rings. d Dihedral angle between MN2 planes.
[Cu(TMPR)]3
100/0.04
70/0.05
this work
this work
[Cu(iPr-MeAMD)]2
time, as small as vanadium(III), generating six-coordinate
compounds. The structure of 9b is distorted trigonal prismatic
with dihedral angles of θ ) 96.2-98.9° and a mean
N-La-N transoid angle of 149(2)° (Figure 2). The mean
La-N bond length is 2.53(2) Å. The chelating η2-amidinate
ligand in 9b has a very small bite angle (N-M-N) of 51.8-
(2)°, as compared to that of the vanadium compound 2 (63.5-
(6)°). The geometry of the three La-N-C-N four-
membered rings is essentially planar with a mean deviation
from planarity of 0.0173-0.0473 Å.
(b) Divalent Metals. In the acetamidinate compounds of
the divalent, first-row transition metals, the nitrogen atom
substituents have a steric influence on the structures of the
resulting metal compounds. Reactions of anhydrous MCl2
Figure 2. Structures of trivalent metal amidinate compounds 2 (left) and
9b (right) showing 30% probability ellipsoids and partial atom-labeling
schemes. Atoms labeled A and B are related to other atoms by C3 symmetry.
(29) This compound was prepared by the reaction of LaCl3(THF)2 with
lithium 2,2,6,6-tetramethylpiperidinate in THF. 1H NMR (C6D6): 1.277
(m, 4H), 1.384 (s, 12H), 1.686 (m, 2H). It crystallizes in monoclinic
space group P2(1)/n with a ) 7.824(8) Å, b ) 18.71(2) Å, c ) 20.38-
(2) Å, â ) 94.34(1)°, Z ) 4, and V ) 2975(5) Å3. With use of 7044
unique data, the structure was refined to R1/wR2 ) 2.82/6.44%.
Selected parameters: La-N, 2.363(1) Å; N-La-N, 120.0(4)°.
pressures among homoleptic lanthanum compounds with
amide-type ligands is summarized in Table 4. Lanthanum
acetamidinate 9a shows the highest volatility among them.
Bidentate iPr-MeAMD seems to have proper steric bulk for
stabilizing ions both as big as lanthanum(III) and, at the same
Inorganic Chemistry, Vol. 42, No. 24, 2003 7955

Lim et al.
(M ) Mn, Fe, Co, Ni) with 2 equivalents of iPr-MeAMD or
tBu-MeAMD afforded dimeric [Mn2(µ-iPr-MeAMD)2(η2-iPr-
MeAMD)2] (3a) and [Fe2(µ-iPr-MeAMD)2(η2-iPr-MeAMD)2]
(4a) and monomeric compounds [Mn(tBu-MeAMD)2] (3b),
[Fe(tBu-MeAMD)2] (4b), [Co(iPr-MeAMD)2] (5a), [Co(tBu-
MeAMD)2] (5b), and [Ni(iPr-MeAMD)2] (6). The assignment
of solid structures for the compounds 3-6 was made on the
basis of X-ray crystal structure determinations and/or mo-
1
lecular weight determination, H NMR, sublimation, and
elemental analysis data. It is notable that no lantern-type
dinuclear compounds were formed in the case of acetamidi-
nate ligands (iPr-MeAMD or tBu-MeAMD) unlike the earlier
observation found in various metal compounds with aryl-
susbstituted formamidinate ligands.18-20
For the metals Mn(II) and Fe(II) with greater ionic size
than that of Co(II) and Ni(II), the isopropyl substituents were
not sufficient to provide monomeric structures, and generated
dinuclear compounds containing two nonbridging and two
bridging acetamidinate liagands. This behavior is similar to
i
that reported for Mg(II) dimers bridged by Pr-MeAMD
ligands.24 The iron compound 4a is dimeric in both solution
and solid states, as confirmed by the molecular weight
(complexity ) 2.0(2)) and X-ray structure determinations.
Although X-ray structure determination was not done for
manganese compound 3a, its similar sublimation temperature
to that of the corresponding iron compound 4a suggests that
3a is also a dimer (Table 2). The structure of 4a is shown in
Figure 3, and selected bond distances and angles are
contained in Table 5. The iron atoms are coordinated by both
one η2-amidinate ligand 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-N-
C-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]219 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.19
Figure 3. Structures of divalent metal amidinate compounds 4a (top), 4b
(middle), and 5a (bottom) showing 30% probability ellipsoids and partial
atom-labeling schemes. Atoms labeled A are related to other atoms by C2
symmetry (4a), mirror plane (4b), and C2 symmetry (5a).
Table 5. Bond Distances (Å) and Angles (deg) for Divalent Metal
Amidinates 4a, 4b, and 5a
4a
4b
5a
M-Na
2.074(5)
2.112(1)
1.328(1)
113.1(2)
116.5(2)
133.58(6)
113.86(6)
105.09(6)
106.40(6)
113.23(7)
63.32(7)
2.033(1)
2.012(8)
a
M-Nbridging
N-Ca,b
1.337(1)
111.18(9)
1.320(2)
111.2(2)
N-C-N
N-C-Nbridging
N-M-N
139.72(7)
127.78(4)
146.54(7)
127.78(4)
132.31(9)
137.02(6)
133.68(8)
137.02(7)
In the case of Co(II) and Ni(II), the isopropyl groups are
bulky enough to afford monomeric species. The nickel
compound 6 is believed to be monomeric on the basis of
N-M-Nchelating
65.52(4)
65.57(6)
a Mean values. b Amidinate backbone.
1
the similarity of its H NMR data and sublimation temper-
ature to those of the related Co(II) compound 5a, whose
identity was confirmed by X-ray structure determination
(Table 2, Figure 3). Molecular weight determination in
p-xylene further showed that compound 6 is monomeric in
solution; the determined complexity was 1.0(2). Introducing
the larger tert-butyl groups in place of isopropyl groups in
3b, 4b, and 5b prevents dimerization, affording monomeric
species even for the larger Mn(II) and Fe(II) ions. This is
again similar to the geometries reported for amidinate
compounds of Mg.24
given in Table 5. These compounds adopt a distorted
tetrahedral environment around the metal center with two
η2-amidinate ligands, which is similar to other reported
compounds.19,23,24 The geometries of the M-N-C-N four-
membered rings in both 4b and 5a are planar with an
imposed mirror plane and C2 symmetry, respectively. The
mean M-N distances are 2.033(1) Å (4b) and 2.012(8) Å
(5a), and the bite angles of amidinate ligand (N-M-N) are
65.52(4)° (4b) and 65.57(6)° (5a). Interestingly, the bite angle
of 65.52(4)° in 4b is very close to the value of the known
[Fe(Cy-tBuAMD)2] (65.38(8)°).23 Although comparison is
imprecise because of differences in ligand system and
The structures of monomeric compounds 4b and 5a are
shown in Figure 3. Selected bond distances and angles are
7956 Inorganic Chemistry, Vol. 42, No. 24, 2003

Volatile, Thermally Stable, ReactiWe Transition Metal Amidinates
accuracy in X-ray structure determination, this observation
indicates that the alkyl substituent on the carbon atom of
the amidinate ligand from methyl group to tert-butyl group
does not have a significant effect on the bite angles of the
ligands in the resulting Fe(II) compounds.
Although tetrahydrofuran (THF) was used in the synthesis
of 3-6, THF adducts were not isolated, suggesting that the
coordination of THF in these compounds is very weak or
easily lost upon isolation. All the compounds 3-6 are
1
paramagnetic as demonstrated by broad peaks in their H
NMR spectra.
(c) Monovalent Metals. Reaction of CuBr with 1 equiv
of iPr-MeAMD produced pale yellow solutions from which
colorless copper compound 7 was isolated in 83% yield.
i
When CuCl2 was treated with 2 equiv of Pr-MeAMD, a
redox reaction occurred instead of the expected metathesis
reaction, generating the Cu(I) compound 7 in a quantitative
yield. Similar redox chemistry caused by amide ligands has
been previously shown.30 The compound 7 turned out dimeric
by the X-ray structure determination (Figure 4). The dimeric
unit in 7 is the smallest unit among known homoleptic Cu-
(I) amide-type compounds. Known examples of [Cu(NR2)]4
and [Cu(TMS)]4 are tetrameric, and the compound with
TMPR ligand is trimer [Cu(TMPR)]3, whose identity was
confirmed by X-ray structure determination.31 Because of
its small molecular weight, dimeric 7 showed the highest
volatility among the Cu(I) amide compounds, as summarized
in Table 4.
In a similar way, but with AgCl, silver compound 8 was
also prepared in 90% yield. While the copper compound 7
is dimeric in both solution and solid states, the corresponding
silver compound 8 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, as accessed by 1H
NMR spectroscopy and by X-ray structure determination
(Figure 4). 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. This observa-
tion suggests 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 silver
compounds (8a, 8b).
Figure 4. Structures of monovalent metal amidinate compounds 7 (top),
8a (middle), and 8b (bottom) showing 30% probability ellipsoids and partial
atom-labeling schemes. Atoms labeled A are related to other atoms by an
inversion center.
Table 6. Bond Distances (Å) and Angles (deg) for Monovalent Metal
Amidinates 7, 8a, and 8b
7
8a
8b
M-Na
1.869(1)
1.329(2)
2.414(1)
120.0(7)
176.4(1)
2.111(3)
1.331(5)
2.645(1)
121.4(3)
170.8(1)
2.12(2)
1.328(4)
2.99(2)
119.0(7)
164(3)
N-Ca,b
M-Ma
N-C-Nb
N-M-Na
Structures of the copper (7) and silver compounds (8a,
8b) are shown in Figure 4, and selected bond lengths and
angles are collected in Table 6. The compound 7 is a dimer
in the solid state in which acetamidinate ligands bridge
copper atoms in a µ,η1: η1-fashion. The average Cu-N
distance is 1.869(1) Å, and this distance is quite similar to
a Mean values. b Amidinate backbone.
that observed in the analogous compound [Cu(p-tolyl-
HAMD)]2 (1.87(1) Å).20 The geometry of the silver com-
pound 8a is very close to that of the corresponding copper
compound 7. Again, the Ag-N distance of 2.111(3) Å is
similar to that observed in [Ag(p-tolyl-HAMD)]2 (1.87(1)
Å).20 The distances between metal atoms in these dimers
are 2.414(1) Å in 7 and 2.645 Å in 8a, indicating the presence
of some metal-metal interaction. The geometries of the
M-N-C-N-M in 7 and 8a are planar with imposed
centrosymmetry, and N-M-N are essentially linear with
176.4(1)° and 170.8(1)°, respectively. In the trimeric silver
(30) Tayebani, M.; Kasani, A.; Feghali, K.; Gambarotta, S.; Bensimon, C.
Chem. Commun. 1997, 2001-2002 and references therein.
(31) This compound was prepared by the reaction of CuCl with lithium
1
2,2,5,5-tetramethylpyrrolidinate in Et2O. H NMR (C6D6): 1.548 (s,
12H), 1.671 (s, 4H). It crystallizes in hexagonal space group P6(3)/m
with a ) 10.219 (6) Å, b ) 10.219 (6) Å, c ) 14.48(1) Å, Z ) 6, and
V ) 1309(2) Å3. With use of 1039 unique data, the structure was
refined to R1/wR2 ) 3.73/9.83%. Selected parameters: Cu-N, 1.93-
(1) Å; Cu-Cu, 2.471(2) Å; Cu-N-Cu, 79.6(1)°; N-Cu-N, 160.4-
(1)°.
(32) Baxter, D.; Chisholm, M. H. Chem. Vap. Deposition 1995, 1, 49.
Inorganic Chemistry, Vol. 42, No. 24, 2003 7957

Lim et al.
of the samples). Thermal stability for short times (e1 s) at
higher temperatures was determined by flowing the vapors
(entrained in N2) through a tube furnace, and noting the
lowest temperature at which material is deposited on a heated
substrate in the tube. The resulting decomposition temper-
atures are the following: 3b (Mn) 300 °C, 4b (Fe) 300 °C;
5a (Co) 350 °C; 6 (Ni) 300 °C; 7 (Cu) 300 °C; 9a (La) 350
°C. In order to preserve self-limited reactivity in ALD
processes using these precursors, the substrate temperatures
must be kept below these values.
We recently showed that 4b, 5a, 6, and 7 could be used
for ALD of pure Fe, Co, Ni, and Cu thin films, respectively,
using hydrogen as the second precursor.25 When water vapor
was used in place of hydrogen as the complementary reactant,
metal oxide films such as FeO, CoO, and La2O3 were
deposited. Because of their high reactivity with oxygen and
water vapor, these compounds must be carefully protected
from contact with ambient atmosphere. The nitrogen carrier
gas must also be purified to remove traces of oxygen and
moisture, which interfere with the ALD processes.
Figure 5. TG curves for mass changes of acetamidinate compounds of
iron (4b), cobalt (5a), copper (7), and lanthanum (9a) measured in a nitrogen
flow at atmospheric pressure.
compound 8b, the amidinate ligands are bridging three silver
atoms in a µ,η1: η1-fashion as depicted in Figure 4. The mean
Ag-N distance of 2.12(2) Å in this trimer is essentially the
same as that observed in the dimer 8a.
Compounds 1-9 are successful as ALD precursors; they
are sufficiently volatile, thermally stable, and highly reactive.
The high volatility is achieved because the outer regions of
the molecules are largely hydrocarbon, leading to weak
interactions between the molecules. The volatility is also
enhanced by the low nuclearity of the structures (mostly
monomeric) enforced by the bulky ligands. This lack of
oligomerization also allows them to vaporize rapidly even
from the solid state. They are highly soluble in hydrocarbon
solvents, so direct liquid injection of their solutions is also
a convenient method for vaporizing them. The chelating
effect of the amidinate ligands contributes to the high thermal
stability of the compounds. Despite this high thermal
stability, the compounds are highly reactive, in part because
the order of the metal-nitrogen bonds is only one-half. Their
high reactivity under ALD conditions is shown by the nearly
complete removal of the ligands, which results in low
impurity levels of the deposited films, as demonstrated in
ALD of pure Fe, Co, Ni, Cu, FeO, CoO, and La2O3 thin
films.25 Another attractive feature of the metal amidinates
is that they do not contain halides, which can contaminate
films or corrode apparatus. Furthermore, amidinates are very
versatile ligands, forming a series of compounds with metals
having a wide range of sizes from V(III) to La(III) and
oxidation states 1, 2, and 3.
Utility as Precursors for ALD. Finding effective ALD
precursors is difficult because they must meet several very
stringent requirements: (1) sufficient volatility (>about 0.1
Torr); (2) sufficient thermal stability (>months at vaporiza-
tion temperature, >seconds at deposition temperature); (3)
high but self-limited reactivity with surfaces prepared by a
complementary reactant and also with suitably prepared
substrates; (4) saturation thickness independent of the flux
of molecules to the surfaces; (5) saturated surface suitable
for reaction with a complementary precursor.
As our initial goal of preparing these metal amidinate
compounds is to use them as precursors for ALD, we
examined the volatility and thermal stability of compounds
1-9. No decomposition was observed during sublimation,
showing that the compounds are stable at the sublimation
temperatures listed in Table 2. These precursors are all
volatile enough for use in ALD with the precursor vapor
sources held at temperatures below 120 °C. TGA/DSC
measurements of the manganese (3b), iron (4b), cobalt (5a),
nickel (6), copper (7), and lanthanum (9a) acetamidinates at
atmospheric pressure were also performed. Representative
TGA curves are given in Figure 5. Vaporization occurs
cleanly in one step with low residual mass (3b left 4%, 4b
left 12%, 5a left 9%, 7 left 1%, 9a left 12%), except for the
nickel compound 6, which had a step suggesting decomposi-
tion at about 180 °C and a higher residual mass (27%). This
suggests that the compounds are thermally stable during
vaporization even at a pressure as high as 1 atm. The only
features in most of the DSC curves (not shown) were
endothermic peaks due to the melting and evaporation of
the compounds, which further demonstrates their thermal
stabilities. Only 6 (Ni) showed an exothermic peak in its
DSC, indicating decomposition at 180 °C. The TGA/DSC
studies demonstrate the stability of the compounds for
minutes at temperatures above 200-250 °C (the maximum
measurement temperature being limited by the vaporization
Acknowledgment. We thank Ms. Ying Wang for as-
sistance in the preparation of 2,2,5,5-tetramethylpyrrolidine
and [La(TMPD)3]. We appreciate the TGA/DSC analyses
provided by Dr. Xinjian Lei of Schumacher, a unit of Air
Products. This work was supported in part by the National
Science Foundation (Grant No. ECS 9975504).
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determinations of the eight
compounds in Table 1. This material is available free of charge
via the Internet at http://pubs.acs.org.
IC0345424
7958 Inorganic Chemistry, Vol. 42, No. 24, 2003