Synthesis and characterization of diorganohydrazido(2-) tungsten complexes

Article abstract of DOI:10.1021/ic701151m

Diorganohydrazido(2-) complexes of tungsten (L)Cl₄W(NNR ₂) [R₂ = Me₂, Ph₂, -(CH ₂)₅-; L = CH₃CN, pyridine] were synthesized by reacting the corresponding 1,1-diorganohydrazine with WCl₆, followed by reaction with acetonitrile or pyridine. Crystallographic structure determination of (CH₃CN)Cl₄W(NNMe₂) and (CH₃CN)Cl₄W(NNPh₂) allows a comparison of the structural features of the diorganohydrazido(2-) functionality with varying substituents. Mass spectrometry, thermogravimetric analysis, and preliminary chemical vapor deposition experiments were performed to determine the viability of these complexes as single-source precursors for deposition of WN_x and WN_xC_y films.

Full text of DOI:10.1021/ic701151m

Inorg. Chem. 2008, 47, 4457-4462
Synthesis and Characterization of Diorganohydrazido(2–) Tungsten
Complexes
Jürgen Koller, Hiral M. Ajmera, Khalil A. Abboud, Timothy J. Anderson,* and Lisa McElwee-White*
Department of Chemistry, UniVersity of Florida, GainesVille, Florida 32611-7200, and Department
of Chemical Engineering, UniVersity of Florida, GainesVille, Florida 32611-6005
Received June 12, 2007
Diorganohydrazido(2–) complexes of tungsten (L)Cl4W(NNR2) [R2 ) Me2, Ph2, –(CH2)5–; L ) CH3CN, pyridine]
were synthesized by reacting the corresponding 1,1-diorganohydrazine with WCl6, followed by reaction with acetonitrile
or pyridine. Crystallographic structure determination of (CH3CN)Cl4W(NNMe2) and (CH3CN)Cl4W(NNPh2) allows a
comparison of the structural features of the diorganohydrazido(2–) functionality with varying substituents. Mass
spectrometry, thermogravimetric analysis, and preliminary chemical vapor deposition experiments were performed
to determine the viability of these complexes as single-source precursors for deposition of WNx and WNxCy films.
Introduction
tion as single-source precursors for chemical vapor deposition
(CVD) or atomic layer deposition (ALD) of tungsten nitride
(WNx) and tungsten carbonitride (WNxCy),18,19 materials of
interest to the semiconductor industry as diffusion barriers
in copper metallization schemes.20–27 Preparing the hydrazido
complexes provides an alternative to the addition of hydra-
zine derivatives into the carrier gas during deposition of metal
nitride films, a process that has been reported to lower the
deposition temperature of TiN films significantly because of
the high reducing power of hydrazines toward high-valent
transition metals.28–30 In particular, it has been demonstrated
Early transition-metal complexes of diorganohydrazido(2–)
ligands have appeared in the literature since the 1970s.1–14
The potential application of these compounds as single-
source precursors for the deposition of transition-metal
nitrides has generated renewed interest in synthesizing them
for use in materials chemistry.15–17 One motivation for
exploring the tungsten derivatives is their potential applica-
* To whom correspondence should be addressed. E-mail: lmwhite@
chem.ufl.edu (L.M.-W.), tim@ufl.edu (T.J.A.). Tel.: +1-3523928768
(L.M.-W.). Fax: +1-3528460296 (L.M.-W.).
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10.1021/ic701151m CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 11, 2008 4457
Published on Web 09/15/2007

Koller et al.
analyses were performed using a Thermo Trace DSQ (quadrupole
MS) mass spectrometer with a heated probe (Thermo Finnigan,
San Jose, CA).
that diorganohydrazido(2–) titanium complexes serve as
precursors for the deposition of titanium nitride films.31
Incorporation of the diorganohydrazido(2–) functionality into
the metal coordination sphere resulted in viable single-source
precursors for the deposition of TiN thin films while
maintaining the positive effects of hydrazine as a coreactant.32
Previously, we reported that the tungsten imido complexes
(RCN)Cl4W(NiPr), (RCN)Cl4W(NPh), and (RCN)Cl4W-
(NC3H5) (R ) Me, Ph) could be used as single-source
precursors for WNx and WNxCy deposition.33–36 Recently
reported uses of 1,1-dialkylhydrazido(2–) complexes in the
CVD of other materials suggested that the
(RCN)Cl4W(NNR2) derivatives of our imido complexes
could be effective precursors for the CVD/ALD of WNx and
WNxCy. Herein, we describe the synthesis and characteriza-
tion of a series of diorganohydrazido(2–) tungsten complexes
and briefly discuss their application in the CVD of WNxCy.
Crystallinity of films deposited by CVD was examined by X-ray
diffraction (XRD) using a Phillips APD 3720 system. Cu KR
radiation generated at 40 kV and 20 mA was used for the XRD
analysis. Film composition and atomic bonding were obtained from
X-ray photoelectron spectroscopy (XPS) measurements. The XPS
spectra were taken using monochromatic Mg KR radiation, with
the X-ray source operating at 300 W (15 kV and 20 mA). The film
thickness was measured by cross-sectional scanning electron
microscopy (SEM) on a JEOL JSM-6335F.
(CH3CN)Cl4W(NNMe2) (1). A Schlenk flask was charged with
WCl6 (2.10 g, 5.30 mmol) and 40 mL of methylene chloride. 1,1-
Dimethylhydrazine (0.39 mL, 5.2 mmol) was added via syringe
under vigorous stirring at -78 °C. After 10 min of stirring, the
solvent was removed in vacuo during warming to room temperature.
Acetonitrile (15 mL) was added via syringe, and the mixture was
stirred for an additional 30 min. The solvent was removed in vacuo
and the solid extracted with 2 × 15 mL of methylene chloride.
The combined extracts were filtered, and the volume was reduced
to 15 mL. The product was precipitated by adding the solution into
vigorously stirred pentane (200 mL) at 0 °C. The orange product
was filtered off as a microcrystalline powder and dried in vacuo.
Yield: 1.66 g (75%, 3.92 mmol). 1H NMR (benzene-d6, 25 °C): δ
5.35 (s, 6H, N(CH3)2), 0.15 (s, 3H, CH3CN). 13C NMR (benzene-
d6, 25 °C): δ 0.58 (CH3CN), 36.89 (N(CH3)2), 120.86 (CH3CN).
Anal. Calcd for C4H9Cl4N3W: C, 11.31; H, 2.14; N, 9.89. Found:
C, 10.89; H, 1.97; N, 9.52.
(CH3CN)Cl4W(Npip) (2). A Schlenk flask was charged with
WCl6 (2.00 g, 5.04 mmol) and 40 mL of methylene chloride.
1-Aminopiperidine (0.53 mL, 4.9 mmol) was added via syringe
under vigorous stirring at -78 °C. After 10 min of stirring, the
solvent was removed in vacuo during warming to room temperature.
Acetonitrile (15 mL) was added via syringe, and the mixture was
stirred for an additional 30 min. The solvent was removed in vacuo
and the solid extracted with 2 × 20 mL of methylene chloride.
The extract was filtered and the volume reduced to 15 mL. The
product was precipitated by adding the methylene chloride solution
into vigorously stirred pentane (200 mL) at 0 °C. The rust-colored
product was filtered off as a microcrystalline powder and dried in
vacuo. Yield: 1.75 g (76%, 3.76 mmol). 1H NMR (benzene-d6, 25
°C): δ 4.86 (t, 4H, NCH2), 1.34 (m, 4H, CH2), 1.01 (m, 2H, CH2),
0.17 (s, 3H, CH3CN). 13C NMR (benzene-d6, 25 °C): δ 0.75
(CH3CN), 22.73 (CH2), 30.70 (CH2), 51.00 (NCH2), 120.78
(CH3CN).
Experimental Procedures
General Procedures. Unless specified otherwise, all manipula-
tions were performed under an inert atmosphere (N2) using standard
Schlenk or glovebox techniques. All reaction solvents were purified
using an MBraun MB-SP solvent purification system prior to use.
NMR solvents were degassed by three freeze-pump-thaw cycles
and stored over 4 Å molecular sieves in an inert-atmosphere
glovebox. 1H and 13C NMR spectra were recorded on Gemini 300,
Mercury 300, or VXR 300 spectrometers using residual protons of
deuterated solvents for reference. Pentane, pyridine, acetonitrile,
and benzonitrile (all anhydrous) were used as received from Aldrich.
1,1-Dimethylhydrazine, 1,1-diphenylhydrazine, and 1-amino-
piperidine were degassed by three freeze-pump-thaw cycles and
stored over 4 Å molecular sieves. All other chemicals were used
as received without further purification. Thermogravimetric analysis
(TGA) was carried out using a Perkin-Elmer TGA7 thermogravi-
metric analyzer under nitrogen with a heating rate of 10 °C/min
1
(sample size ≈ 3 mg). H NMR spectra for kinetic studies were
recorded on a Varian Inova spectrometer at a frequency of 500
MHz, on a 5 mm indirect detection probe. The variable-temperature
spectra were recorded on automation. To achieve temperature
stability, for each temperature step of 2 °C, a preacquisition delay
of 1200 s was followed by shimming on the lock level. The spectra
were collected in 64 transients, with an acquisition time of 5 s. No
relaxation delay and no apodization were used. The simulation of
the spectra was done using the gNMR program.37 All mass spectral
(CH3CN)Cl4W(NNPh2) (3). A Schlenk flask was charged with
WCl6 (2.00 g, 5.04 mmol) and 40 mL of methylene chloride. 1,1-
Diphenylhydrazine (0.91 g, 4.9 mmol) was added via syringe under
vigorous stirring at -78 °C. After 10 min of stirring, the solvent
was removed in vacuo during warming to room temperature.
Acetonitrile (15 mL) was added via syringe, and the mixture was
stirred for an additional 30 min. The solvent was removed in vacuo
and the solid extracted with 2 × 20 mL of methylene chloride.
The combined extracts were filtered, and the volume was reduced
to 15 mL. The product was precipitated by adding the solution into
vigorously stirred pentane (200 mL) at 0 °C. The deep-purple
product was filtered off as a microcrystalline powder and dried in
vacuo. Yield: 2.07 g (76%, 3.77 mmol). 1H NMR (benzene-d6, 25
°C): δ 7.15 (br s, 8H, Ph), 6.53–6.47 (m, 2H, Ph), 0.11 (s, 3H,
CH3CN). 13C NMR (benzene-d6, 25 °C): δ 0.97 (CH3CN), 121.23
(CH3CN), 125.65 (Ph), 125.77 (Ph), 128.80 (Ph), 128.94 (Ph),
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Symp. Proc. 2000, 606, 91–96.
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C. G.; Brooks, B. C.; Powell, D. H.; McElwee-White, L. J. Cryst.
Growth 2003, 249, 262–274.
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(37) gNMR; Adept Scientific PLC: Herts, U.K., 1995.
4458 Inorganic Chemistry, Vol. 47, No. 11, 2008

Diorganohydrazido(2–) Tungsten Complexes
Scheme 1. Synthesis of Diorganohydrazido(2–) Complexes
130.53 (Ph), 130.65 (Ph), 131.39 (Ph), 131.61 (Ph), 133.38 (Cipso),
135.34 (Cipso).
bridged tungsten dimer was not isolated but was subsequently
treated with acetonitrile or pyridine to yield compounds 1–4
as orange, rust-colored, purple, and red solids, respectively.
1H and 13C NMR spectra are in good agreement with the
symmetry equivalence of the substituents on the hydrazido
functionality in compounds 1 and 2. Contrary to this finding,
NMR spectra reveal the inequivalence of the two phenyl
rings in compounds 3 and 4.
Single crystals suitable for XRD were obtained from com-
pounds 1 and 3, and their structures were determined. Crystal
data and structure refinement for these complexes can be found
in Table 1. Compound 1 adopts a pseudooctahedral geometry
as shown in the ORTEP representation of 1 (Figure 1). The
W-Cl bond distances are on the order of 2.34 Å,39 which is
within the expected range for WVI-Cl bonds. The short W-N1
bond distance [1.769(5) Å] and a short bond distance of 1.271(8)
Å between N1 and N2 suggest a high degree of delocalization
and significant multiple-bond character throughout the
W1-N1-N2 unit, which is consistent with other hydrazido
complexes of tungsten with multiple chloride ligands such as
[W(η5-C5Me5)Cl3(NNPh2)]40 [W-N 1.769(2) Å; N-N 1.296(3)
Å] and cis-[WCl3(NNH2)(PMe2Ph)2]41 [W-N 1.752(10) Å;
N-N 1.300(17) Å]. This observation can be explained based
upon two possible limiting electronic structures, A and B, with
representation A being the major contributor. Furthermore, the
(py)Cl4W(NNPh2) (4). A Schlenk flask was charged with WCl6
(2.00 g, 5.04 mmol) and 40 mL of methylene chloride. 1,1-
Diphenylhydrazine (0.91 g, 4.94 mmol) was added via syringe under
vigorous stirring at -78 °C. After 10 min of stirring, the solvent
was removed in vacuo during warming to room temperature.
Pyridine (15 mL) was added via syringe, and the mixture was stirred
for an additional 30 min. The solvent was removed in vacuo and
the solid extracted with 2 × 30 mL of benzene. The combined
extracts were filtered, and the solvent was removed in vacuo to
afford 4 in 27% yield as a dark-red microcrystalline solid (0.81 g,
1
1.38 mmol). H NMR (benzene-d6, 25 °C): δ 9.58–9.55 (m, 2H),
7.19–7.11 (m, 10H), 6.68–6.36 (m, 3H). 13C NMR (benzene-d6,
25 °C): δ 118.56, 121.51, 124.02, 124.73, 125.98, 128.86, 128.91,
129.89, 130.67, 133.46, 139.32, 143.95, 152.91. Anal. Calcd for
C17H15Cl4N3W: C, 34.79; H, 2.58; N, 7.16. Found: C, 34.60; H,
2.31; N, 6.96.
Crystallographic Structure Determination of 1 and 3. Data
were collected at 173 K on a Siemens SMART PLATFORM
equipped with a CCD area detector and a graphite monochromator
utilizing Mo KR radiation (λ ) 0.710 73 Å). Cell parameters were
refined using up to 8192 reflections. A full sphere of data (1850
frames) was collected using the ω-scan method (0.3° frame width).
The first 50 frames were remeasured at the end of data collection
to monitor instrument and crystal stability (the maximum correction
on I was <1%). Absorption corrections by integration were applied
based on measured indexed crystal faces.
The structure was solved by the direct methods in SHELXTL638
and refined using full-matrix least squares. The non-H atoms were
treated anisotropically, whereas the H atoms were calculated in ideal
positions and were riding on their respective C atoms. For
compound 1, the molecules are located on 2-fold rotation axes. A
total of 60 parameters were refined in the final cycle of refinement
using 1228 reflections with I > 2σ(I) to yield R1 and wR2 of 3.25%
and 7.93%, respectively. For compound 3, the highest electron
density peak in the final difference Fourier map is most likely the
result of a small disorder in one of the phenyl rings. The disorder
could not be resolved. A total of 399 parameters were refined in
the final cycle of refinement using 6166 reflections with I > 2σ(I)
to yield R1 and wR2 of 2.74% and 5.84%, respectively. Refinement
was done using F.2
W1-N3 bond distance of 2.224(7) Å is significantly shorter
than those reported for related tungsten imido compounds,36
suggesting a decreased trans influence of the diorganohy-
drazido(2–) ligand compared to the imido moiety. A list of
selected bond lengths and angles for 1 is given in Table 2.
Results and Discussion
The tungsten hydrazido complexes 1–4 were prepared by
reacting the corresponding diorganohydrazine with WCl6 in
methylene chloride at -78 °C (Scheme 1). The resulting Cl-
(39) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D. G.;
Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1–S83.
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Thi, N. T. J. Chem. Soc., Dalton Trans. 1982, 345–352.
(38) SHELXTL6; Bruker AXS: Madison, WI, 2000.
Inorganic Chemistry, Vol. 47, No. 11, 2008 4459

Koller et al.
Figure 1. Thermal ellipsoids diagram of the molecular structure of 1.
Thermal ellipsoids are drawn at 50% probability. H atoms are omitted for
clarity.
Figure 2. Thermal ellipsoids diagram of the molecular structure of 3.
Thermal ellipsoids are drawn at 50% probability. H atoms are omitted for
clarity.
Table 1. Crystal Data and Structure Refinement for Complexes 1 and 3
complex
empirical formula
fw
1
3
C4H9Cl4N3W
424.79
173(2)
C28H26Cl8N6W2
1097.85
173(2)
T (K)
wavelength (Å)
cryst syst
space group
unit cell dimens
a (Å)
0.710 73
monoclinic
C2/c
0.710 73
monoclinic
P21/n
8.7700(7)
13.8203(11)
9.7343(8)
90
100.575(2)
90
1159.80(16)
4
2.433
10.8288(8)
17.8753(13)
18.2409(13)
90
101.006(1)
90
3465.9(4)
4
2.104
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
Z
density (Mg/m3)
Figure 3. TGA curve of compounds 1 and 2 recorded at a heating rate of
10 °C/min under nitrogen.
abs coeff (mm-1
F(000)
)
10.837
784
7.280
2080
cryst size (mm3)
θ range for data
0.19 × 0.15 × 0.08
0.12 × 0.11 × 0.04
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Compound 1
2.78–27.49
1.61–27.50
collection (deg)
index ranges
W1-N1
W1-N3
1.769(5)
2.224(7)
N1-W1-N3
N1-W1-Cl1
180.000(1) N2-N1-W1 180.0(0)
-8 e h e 11
-17 e k e 15
-12 e l e 11
3683
1333 (0.1092)
99.4
-14 e h e 13
-22 e k e 23
-21 e l e 23
23 178
7931 (0.0559)
99.7
96.85(4)
83.15(4)
95.02(3)
84.98(3)
89.25(7)
N1-N2-C1
C1–N2-C1A 121.9(7)
119.1(4)
W1-Cl1 2.3374(16) N3–W1-Cl1
W1-Cl2 2.3562(16) N1-W1-Cl2
N1-N2
N2-C1
1.271(8)
1.438(7)
N3–W1-Cl2
Cl1–W1-Cl2
reflns colld
indep reflns (Rint
)
completeness to
distance of 1.312(5) Å suggest less conjugation throughout
the hydrazido moiety as compared to compound 1. One
hydrazido phenyl ring is coplanar with the N2-N1-W1 unit,
maximizing the conjugation between the two subunits, as
has been observed for other 1,1-diphenylhydrazido com-
plexes of tungsten.42 This additional mode of conjugation
decreases the electron density between N1 and N2, resulting
in a noteworthy elongation of the N-N bond. In addition,
the slightly shorter W-N bond suggests higher π-bonding
character such that compound 3 may be better described by
representation B. The large bond angles of N1-W1-Cl2
and N1-W1-Cl3 of 99.2° and 98.0°, respectively, reflect
θ ) 24.60 (%)
abs corrn
integration
0.5020 and 0.1814
1333/0/60
1.027
0.0325
0.0793
+4.084 and -1.814
integration
0.7594 and 0.4754
7931/0/399
0.961
0.0274
0.0584
max and min transmn
data/restraints/param
GOF on F2
R1a
wR2b
largest diff peak and
1.264 and -0.947
hole/e·Å3
a R1 ) ∑(|Fo| – |Fc|)/∑|Fo|. b wR2 ) [∑[w(Fo – Fc )2]/∑[w(Fo )2]]1/2
.
2
2
2
2
2
2
S ) [∑[w(Fo – Fc )2](n – p)]1/2, w ) 1/[σ2(Fo ) + (mp)2 + np], p )
2
2
[max(Fo ,0) + 2Fc ]/3.
The structure of compound 3 shows similarities to that of
compound 1. Complex 3 also exhibits a pseudooctahedral
geometry at the tungsten center (Figure 2). However, the
W1-N1 bond distance of 1.742(4) Å and the N1-N2
(42) Niemoth-Anderson, J. D.; Debord, J. R. D.; George, T. A.; Ross, C. R.,
II; Stezowski, J. J. Polyhedron 1996, 15, 4031–4040.
4460 Inorganic Chemistry, Vol. 47, No. 11, 2008

Diorganohydrazido(2–) Tungsten Complexes
Figure 4. XRD patterns for films deposited at 300 and 550 °C from 1 on a Si(100) substrate.
Figure 5. SEM images for films deposited at 300 and 550 °C from 1 on a Si(100) substrate.
amount of acetonitrile in toluene-d8. The 1H NMR spectrum
of this sample at 40 °C displayed the signals for 1 at 0.53
ppm and acetonitrile at 0.83 ppm, in a ratio of 1:2.09. The
exchange of 1 with acetonitrile was monitored by 1H NMR
in a temperature range from 40 to 84 °C. The exchange rate
k was determined by line-shape analysis in the temperature
interval 50–84 °C. A plot of ln(k/T) vs 1/T in the temperature
interval from 50 to 84 °C afforded an activation enthalpy of
23.0 kcal/mol and an activation entropy of 28.8 cal/mol · K,
consistent with dissociative exchange. The corresponding
Gibbs free energy of activation is 14.4 kcal/mol.
Because a correlation between the mass spectrometric
fragmentation patterns of precursors and likely decomposition
pathways during CVD has been postulated in the litera-
ture,36,43,44 mass spectra were obtained from compounds 1–3.
Table 4 summarizes the major fragment ions observed in
the positive-ion chemical ionization (CI) spectra of com-
pounds 1–3. No molecular ion peak was observed in the CI
spectrum of 1, 2, or 3, consistent with facile loss of the
acetonitrile ligand. Instead, the highest values were in mass
envelopes at m/z 384, 354, and 508, corresponding to
Table 3. Selected Bond Distances (Å) and Angles (deg) for
Compound 3
N1-N1
N1-N3
1.742(4)
2.216(4)
N1-N2
N2-C1
1.312(5)
1.447(5)
1.429(6)
N1-N1-Cl4 91.80(11)
N3–N1-N1
N1-N1-N2
174.91(14)
169.8(3)
115.0(4)
120.7(3)
123.6(4)
N1-Cl1 2.3191(11) N2-C7
N1-Cl2 2.3445(11) N1-N1-Cl1 96.58(11) N1-N2-C1
N1-Cl3 2.3519(11) N1-N1-Cl2 99.15(11) N1-N2-C7
N1-Cl4 2.3537(11) N1-N1-Cl3 98.02(11) C1–N2-C7
the increased steric demand of the coplanar phenyl ring. A
list of selected bond lengths and angles for 3 is given in
Table 3.
The thermal behavior of compounds 1 and 2 was inves-
tigated as preliminary screening for use of complexes 1–4
as precursors for the metal-organic CVD of WNx. TGA
experiments were run at a heating rate of 10 °C/min from
50 to 900 °C. The TGA curves of 1 and 2 show residual
masses of 58 and 50%, respectively, which are constant
above 550 °C (Figure 3). In both cases, an initial drop in
mass of about 10% is observed corresponding to the loss of
the acetonitrile ligand. Because this dissociation is observed
in the low-temperature range, it can be assumed that the
acetonitrile is bound weakly to the tungsten metal center.
To corroborate this observation, the kinetics of acetonitrile
exchange were determined via NMR spectroscopy. The
sample for the exchange study was prepared in the glovebox
by dissolving complex 1 and an approximately equivalent
(43) Lewkebandara, T. S.; Sheridan, P. H.; Heeg, M. J.; Rheingold, A. L.;
Winter, C. H. Inorg. Chem. 1994, 33, 5879–5889.
(44) Amato, C. C.; Hudson, J. B.; Interrante, L. V. Mater. Res. Soc. Symp.
Proc. 1990, 168, 119–124.
Inorganic Chemistry, Vol. 47, No. 11, 2008 4461

Koller et al.
Table 4. Summary of Relative Abundances for Positive-Ion CI Mass
Spectra of Compounds 1–3
within 2θ ) 0.95°, accurate phase identification was not
possible from XRD measurement. Thus, XPS measurements
were taken to obtain the bonding state of different atoms in
the film. XPS spectra (not shown) revealed that both N and
C atoms are bonded to W. From XRD and XPS measure-
ments, it can be concluded that the film deposited from 1
consists of either a mixture of ꢀ-W2N and ꢀ-W2C phases or
single-phase ꢀ-WNxCy. Film composition measurement by
XPS showed that the film contained W, N, C, and O atoms.
No Cl atom impurity was present within the detection limits
of XPS (ca. 1 atom %). Figure 5 shows cross-sectional
images obtained from SEM for films deposited at 300 and
550 °C. The film growth rate for deposition at 300 and 550
°C was 1.3 and 10.4 Å/min, respectively. A detailed report
on the characterization and diffusion barrier performance of
films from 1–3 is forthcoming.
compound
CI fragment
m/z
abundancea
1
[Cl4W(NNMe2)]+
[Cl3W(NNMe2)]+
[Cl3W]+
384
349
289
354
289
114
86
8
100
4
30
12
18
70
100
5
21
4
19
100
2
3
[Cl2W(HN-pip)]+
[Cl3W]+
[Me2pip]+
[H2pip]+
[pip]+
84
[Cl4W(NNPh2)]+
[Cl3W(NNPh2)H]+
[Cl3WNH2]+
[Ph2NMe2]+
[Ph2NH2]+
508
473
307
198
170
a Relative abundances were adjusted by summing the observed intensities
for the predicted peaks of each mass envelope and normalizing the largest
sum to 100%.
[Cl4W(NNMe2)]+, [Cl2W(HN-pip)]+, and [Cl4W(NNPh2)]+,
respectively. The base peak in the CI spectrum of 1 was
observed at m/z 349, corresponding to the [Cl3W(NNMe2)]+
fragment. Interestingly, the base peaks in the CI spectra of
2 and 3 at m/z 84 and 170, corresponding to the [pip]+ and
[Ph2NH2]+ fragments, respectively, are indicative of the
hydrazido N-N bond being broken under ionization condi-
tions, which is additionally supported by the presence of the
[Cl3WNH2]+ fragment in the CI spectrum of 3 at m/z 307.
Cleavage of the N-N bond would also be on the pathway
for decomposition of 2 and 3 to WNx films under CVD
conditions.
Preliminary CVD experiments were performed in the
temperature range of 300–700 °C in 50 °C increments. A
custom cold-wall CVD reactor was used in these screening
experiments and has been discussed elsewhere.34 The lowest
temperature for film deposition from 1 was 300 °C. The color
of the deposited film varied from golden brown at low
deposition temperature to grayish at higher deposition
temperature. Figure 4 shows the XRD spectra for films
deposited from 1 at 300 and 550 °C. The XRD measurement
for deposition at 300 °C shows peaks assignable to only the
silicon substrate, indicating that the film is X-ray amorphous.
Crystallinity first appears for the film deposited at 550 °C,
as indicated by the two peaks at 2θ ) 37.65 and 43.50° in
the XRD pattern for this sample. The peak position indicates
the presence of ꢀ-W2N, ꢀ-W2C, or their solid solution
ꢀ-WNxCy phase. Because the XRD peak position for both
the (111) and (200) reflections of ꢀ-W2N and ꢀ-W2C is
Conclusions
In conclusion, we have prepared the diorganohydrazido-
(2–) tungsten complexes (L)Cl4W(NNR2) [1–4; R2 ) Me2,
Ph2, –(CH2)5–; L ) CH3CN, pyridine] by reacting the
corresponding 1,1-diorganohydrazines with tungsten hexachlo-
ride followed by treatment with acetonitrile or pyridine. The
crystallographic structure determination of (CH3CN)Cl4W-
(NNMe2) and (CH3CN)Cl4W(NNPh2) allows a comparison
of the structural features of the diorganohydrazido function-
ality as the hydrazido substituents R are varied. Preliminary
experiments suggest that compound 1 is a viable single-
source precursor for the deposition of WNxCy films. Further
CVD experiments and subsequent film characterization are
underway.
Acknowledgment. We thank the National Science Foun-
dation for support under NSF-CRC Grant CHE-0304810.
K.A.A. acknowledges the National Science Foundation and
the University of Florida for funding of the purchase of the
X-ray equipment. Giovanni Rojas provided assistance with
the TGA measurements.
1
Supporting Information Available: H NMR spectra of com-
plexes 1–3 and tables of bond distances, bond angles, positional
parameters, and anisotropic displacement parameters for 1 and 3.
This material is available free of charge via the Internet at
http://pubs.acs.org.
IC701151M
4462 Inorganic Chemistry, Vol. 47, No. 11, 2008