Tin(ii) hexafluoroacetylacetonate as a precursor in atmospheric pressure chemical vapour deposition: Synthesis, structure and properties

Article abstract of DOI:10.1016/j.mencom.2012.09.003

A new method for the synthesis of volatile tin(ii) hexafluoroacetylacetonate [Sn(C5HO2F6)2] was suggested, the compound was characterized by elemental analysis, IR spectroscopy, and DTA/TGA; the crystal structure was established by X-ray diffraction; the morphology and composition of the coating deposited by atmospheric pressure chemical vapour deposition were studied by SEM-EDX and XRD.

Full text of DOI:10.1016/j.mencom.2012.09.003

Mendeleev
Communications
Mendeleev Commun., 2012, 22, 239–241
Tin(ii) hexafluoroacetylacetonate as a precursor in atmospheric pressure
chemical vapour deposition: synthesis, structure and properties
Vladimir G. Sevastyanov,* Elizaveta P. Simonenko, Petr A. Ignatov, Viktor S. Popov,
Andrei V. Churakov, Nikolai T. Kuznetsov and Vladimir S. Sergienko
N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 119991 Moscow,
Russian Federation. Fax: +7 495 954 4126; e-mail: v_sevastyanov@mail.ru
DOI: 10.1016/j.mencom.2012.09.003
A new method for the synthesis of volatile tin(ii) hexafluoroacetylacetonate [Sn(C5HO2F6)2] was suggested, the compound was charac-
terized by elemental analysis, IR spectroscopy, and DTA/TGA; the crystal structure was established by X-ray diffraction; the morphology
and composition of the coating deposited by atmospheric pressure chemical vapour deposition were studied by SEM-EDX and XRD.
Volatile tin compounds, passing into the gas phase at moderate
100.00
temperatures without thermal decomposition, are promising for
the synthesis of thin tin oxide films using gas-phase processes.1,2
99.96
The synthesis of layers and nanostructures with desired
properties (crystallite size, coating thickness, its structure and
morphology) depends on not only the chemical vapour deposi-
99.92
tion (CVD) process parameters, but also the properties of pre-
cursors, including their structure.3–5 Therefore, the development
99.88
ofmethodsforthesynthesisandstudyofcoordinationcompounds
99.84
– promising precursors for CVD of nanostructured thin films – is
practically important problem.6,7
4000
3000
2000
1000
Wavenumber/cm–1
Due to the most recognized and sought after sensitive material
for semiconductor gas sensors, CVD of the thin tin oxide films
has attracted much attention.8–11
Figure 1 IR spectrum of [Sn(C5HO2F6)2].
b-Diketonates are the most widely used precursors for the
preparation of thin films by metalorganic chemical vapour deposi-
tion.12 Kai-Ming et. al.13 attempted to synthesize and characterize
tin(ii) hexafluoroacetylacetonate by the interaction of tin dichloride
with sodium hexafluoroacetylacetonate in THF in an inert atmo-
sphere of nitrogen. They noted an obvious practical difficulty of
the experiment: the process should be carried out in an inert atmo-
sphere, careful preparation (dehydration) of the starting reagents
and solvents are needed.
From our point of view, since hexafluoroacetylacetone is a
sufficiently strong acid14 (pKa = 4.35), the simplest and most
effective preparation method is the direct interaction of tin powder
with b-diketone (hexafluoroacetylacetone) with further separa-
tion and identification of the volatile product, [Sn(C5HO2F6)2].†
A high intensity band nCO in the IR spectra of tin(ii) hexa-
fluoroacetylacetonate (Figure 1) is shifted from 1690 cm–1 in the
free ligand to 1652 cm–1, confirming the coordination of hexa-
fluoroacetylacetonato groups. The absence of absorption bands
due to the OH group stretch in the range of 3000–3400 cm–1
evidenced that the synthesized compound is anhydrous.
Comparison of the powder diffraction data for fresh-sublimated
product [Figure 2(a)] with those from the International Centre for
Diffraction Data and Cambridge Structural Database did not reveal
coincidences that confirm the formation of a new phase.
The beginning of the sublimation process was observed at
30 5°C (0.1 Torr). The melting temperature of [Sn(C5HO2F6)2]
determined by capillary method is 65 1°C. According to the
DTA data, decomposition of the compound did not occur up to
90 5°C.
†
Tin powder (99.9%, Khimreaktiv) was used without further purifi-
The molecular structure of [Sn(C5HO2F6)2] contains two crys-
tallographicallyindependentmoleculeswithveryclosegeometric
parameters (Figure 3).‡ The coordination polyhedron of tin(ii)
cation; 1,1,1,5,5,5-hexafluoropentane-2,4-dione (98%, P&M-Invest) was
distilled to remove impurities.
Elemental CH analysis was made on an EA1100 CHNS-0 elemental
analyzer from Carlo Erba Instruments.
The IR spectra were recorded on an Infralum FT-08 FTIR spectro-
photometer (Lumex, Russia) on Nujol mull in KBr pellets.
XRD data were collected on a DRON-2 diffractometer with germanium
monochromated CuKa radiation, Huber camera and an Imaging Plate
detector (LOMO, USSR).
DTA/TGA analysis was made on an SDT Q600 (TA Instruments, USA)
in aluminum crucibles; heating rate, 5 K min–1, argon carrier gas flow
rate, 20 ml min–1.
Deposited films were characterized by scanning electron microscopy
(SEM) using an NVision 40 instrument with EDX elemental analysis
(Carl Zeiss, Germany).
Tin powder (0.35 g, 2.94 mmol) was dissolved in an excess of freshly
distilled hexafluroacetylacetone (1 ml, 7.07 mmol). The synthesis was
carried out in a reflux system with ultrasonic activation and heating up
to 80°C. Powder tin dissolution and white crystals formation were observed
in the volume of the reactor after one-day expiration.
The atmospheric pressure chemical vapour deposition (APCVD) experi-
ments were carried out in a furnace-heating hot-wall reactor with a carrier
gas Ar (flow rate, 50 ml min–1). The temperatures in the evaporation and
deposition zones were 75 5 and 517 5°C, respectively.
The purification of the crude product by sublimation at 30–70°C under
reduced pressure (0.1 Torr) resulted in the formation of white crystalline
[Sn(C5HO2F6)2] (1.45 g, 93% yield) at the cold reactor zone. Found (%):
C, 21.84; H, 0.47. Calc. for C10H2O4F12Sn (%): C, 22.51; H, 0.38.
© 2012 Mendeleev Communications. All rights reserved.
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Mendeleev Commun., 2012, 22, 239–241
20
30
40
50
60
70
80
(a)
(b)
2q/°
Figure 4 XRD profiles of ( ) cassiterite tin dioxide film (ICDD 14-1445),
( ) silicon substrate and ( ) tin dioxide film deposited from [Sn(C5HO2F6)2].
approximetely 0.5 Å. In general, the geometry of [Sn(C5HO2F6)2]
is close to that previously found for the related complex Sn[Ph–
C(O)–CH–C(O)–Me]2.17
10
20
30
40
50
2q/°
Comparing simulated diffraction pattern of [Sn(C5HO2F6)2]
based on structure data [Figure 2(b)] calculated by means of the
program complex Mercury CSD 2.3 with experimentally obtained
by XRD for sublimated powder [Figure 2(a)] confirm that taken
crystal belongs to the base phase [Sn(C5HO2F6)2].
Figure 2 (a) Powder diffraction data and (b) simulated diffraction data
based on the structure of [Sn(C5HO2F6)2].
F(26)
F(21)
F(24A)
F(22A)
F(25A)
The volatile compound [Sn(C5HO2F6)2] was used as a pre-
cursor for the deposition of thin polycrystalline tin-containing
films on a polished silicon substrate by CVD. The parameters of
theAPCVD process were selected according to obtained thermo-
chemical properties of the compound: the temperatures in the
F(24)
F(25)
C(23)
C(22)
C(24)
F(23A)
C(21)
C(25)
F(23)
O(22)
F(26A)
O(21)
F(22)
Sn(1)
F(16)
F(14A)
F(15)
O(12)
F(21A)
F(15A)
C(15)
evaporation zone of 75 5°C and in the deposition zone of 517 5°C
.
C(14)
O(11)
F(13A)
X-ray analysis of the tin containing layer indicates the forma-
tion of tin dioxide in the cassiterite phase (Figure 4).
The microstructure of the coatings, obtained by SEM, is pre-
sented in Figure 5. The polycrystalline coating is a homogeneous
solid with no significant defects. Particle size distribution was made
using SEM data. The average grain size is 55 15 nm.
The results of the EDX analysis indicate involving of signi-
ficant fluorine impurities in coating (Sn:F = 2.89:1), that affect
the semiconductor properties of the films.18,19
In conclusion, the new, one-step, easy to implement method,
which does not require careful preparation of reagents and solvents,
was developed for the synthesis of tin(ii) hexafluoroacetylacetonate
[Sn(C5HO2F6)2]. The compound was identified by IR spectroscopy,
elemental analysis and XRD; the crystal structure was established
for the first time. According to experimentally derived thermochemi-
cal data (sublimation, melting and decomposition temperatures),
this highly volatile complex can be recommended as a precursor
of the nanostructured tin oxide films in gas-phase processes, that
was confirmed by the APCVD experiments.
F(14)
F(12)
C(13)
C(12)
C(11)
F(16A)
F(11)
F(12A)
F(11A)
F(13)
Figure 3 Molecular structure of [Sn(C5HO2F6)2]. Ellipsoids are shown at
50% probability level. For minor components of disorder, C–F bonds are
drawn as dashed lines. Selected bond lengths (Å) and angles (°): Sn–Oax
2.327(6)–2.348(6), Sn–Oeq 2.167(6)–2.196(6), C–Oax 1.210(14)–1.229(11),
C–Oeq 1.258(11)–1.280(11); Oax–Sn–Oax 141.4(3), 141.5(2), Oeq–Sn–Oeq
86.2(2), 86.4(2).
represents a distorted trigonal bypyramid. As usual, a stereo-
active lone electron pair occupies an equatorial position. Both
chelating ligands engage one equatorial and one axial sites. The
angles between axial oxygen atoms are approximately 150°,
while the angles between equatorial O atoms are close to 87°.
As expected, the Sn–O bonds formed by the central tin atom
with axial oxygen atoms are ~0.2 Å longer than those formed
by equatorial O atoms. Of interest, partially double C–Oax bonds
with endocyclic carbon atoms are approximately 0.05 Å shorter
than the same C–Oeq bonds. For both independent molecules,
hexafluoro ligands are planar within 0.135(2) Å. The displace-
ments of the tin atoms from least-squares planes of the ligands are
This work was supported by the Presidium of the Russian
Academy of Sciences (programme nos. 8P23 and 9P3) and the
Russian Foundation for Basic Research (grant no. 10-03-01036).
‡
Crystallographic data. Crystals (C10H2F12O4Sn, M = 532.81) are mono-
25
20
15
10
5
clinic, space group P21/c, a = 8.6097(16), b = 18.035(3) and c = 20.362(4)Å,
b = 101.238(2)°, V = 3101.2(10) Å3, Z = 4, dcalc = 2.282 g cm–3, F(000) =
= 2016, m(MoKa) = 1.799 mm–1. Total of 28836 reflections (6828 unique,
Rint = 0.0413) were measured on a Bruker SMART APEX II diffracto-
meter at 173 K using w scan mode. Absorption correction based on
measurements of equivalent reflections was applied.15 The structure was
solved by direct methods and refined by full matrix least-squares on F2
(SHELXTL) with anisotropic thermal parameters for all non-hydrogen
atoms except disordered trifluoromethyl groups.16 Six of eight CF3 substituents
were found to be rotationally disordered over two or three positions. For
these groups, fluorine atoms were refined isotropically with restrained
C–F distances. All hydrogen atoms were placed in calculated positions and
refined using a riding model. The studied crystal was a pseudomerohedral
twin (matrix –1 0 0 0 –1 0 1 0 1) with domain occupancies 0.94/0.06.
CCDC 881995 contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
For details, see ‘Notice to Authors’, Mendeleev Commun., Issue 1, 2012.
0
20
40
60
80
100
Particle size/nm
200 nm
Figure 5 Scanning electron micrographs and particle size distribution of
the tin dioxide film deposited from [Sn(C5HO2F6)2].
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Mendeleev Commun., 2012, 22, 239–241
10 G. Korotcenkov and B. K. Cho, Sens. Actuators, B, 2009, 142, 321.
References
11 M. Batzill, Sensors, 2006, 6, 1345.
12 V. G. Syrkin, CVD-metod. Khimicheskoe parofaznoe osazhdenie (CVD-
method. Chemical Vapour Deposition), Nauka, Moscow, 2000 (in Russian)
13 K.-M. Chi, C.-C. Lin,Y.-H. Lu and J.-H. Liao, J. Chin. Chem. Soc., 2000,
47, 425.
14 J. Gross and C. Keller, J. Inorg. Nucl. Chem., 1972, 34, 725.
15 G. M. Sheldrick, SADABS. Program for Scaling and Correction of Area
Detector Data, University of Göttingen, Germany, 1997.
16 G. M. Sheldrick, Acta Crystallogr., 2008, A64, 112.
17 P. F. R. Ewings, P. G. Harrison and T. J. King, J. Chem. Soc., Dalton
Trans., 1975, 14, 1455.
1 M. D. Allendorf and A. M. B. van Mol, Top. Organomet. Chem., 2005, 9, 1.
2 A. S. Antsyshkina, G. G. Sadikov, V. G. Sevastyanov, V. S. Popov,
P. A. Ignatov, A.V. Churakov, E. P. Simonenko, N. T. Kuznetsov and V. S.
Sergienko, Zh. Neorg. Khim., 2011, 56, 570 (Russ. J. Inorg. Chem., 2011,
56, 530).
.
3 G. Korotcenkov, Mater. Sci. Eng., R, 2008, 61, 1.
4 V. S. Popov, V. G. Sevastyanov and N. T. Kuznetsov, Compos. Nanostruct.,
2012, 1, 33.
5 T. T. Stoycheva, S. Vallejos, R. G. Pavelko, V. S. Popov, X. Correig and
V. G. Sevastyanov, Chem. Vap. Deposition, 2011, 17, 247.
6 K. R. Sharma, Nanostructuring Operations in Nanoscale Science and
Engineering, McGraw-Hill, New York, London, 2010.
7 N. T. Kuznetsov, V. G. Sevastyanov, E. P. Simonenko, P. A. Ignatov and
V. S. Popov, RF Patent 2397572, 2010.
18 E. Shanthi, A. Banerjee, V. Dutta and K. L. Chopra, J. Appl. Phys., 1982,
53 (3), 1615.
19 M. Batzill and U. Diebold, Prog. Surf. Sci., 2005, 79, 47.
8 N. Yamazoe, K. Suematsu and K. Shimanoe, Sens. Actuators, B, 2012,
163, 128.
9 N. Barsan, D. Koziej and U. Weimar, Sens. Actuators, B, 2007, 121, 18.
Received: 17th May 2012; Com. 12/3927
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