Trimethylphosphite stabilized disilver(I) methanedisulfonates as MOCVD precursors

Article abstract of DOI:10.1016/j.poly.2011.07.025

New disilver(I) methanedisulfonates complexes {CH₂(SO ₃)₂Ag₂·[P(OMe)_3n} (n = 2, 2a; n = 4, 2b; n = 6, 2c) were prepared by reacting [CH ₂(SO₃)₂Ag₂, which could be synthesized from methanedisulfonic acid and Ag₂CO₃ in water, with trimethylphosphite in dichloromethane. The molecular structure of 2a was determined using X-ray single crystal analysis. Complex 2a exhibits an infinite chain structure with eight-membered rings (AgOSOAgOSO) fully interconnected by the third sulfonic O atoms. Complex 2b was used to deposit silver films by metal organic chemical vapor deposition (MOCVD) for the first time. The silver film obtained was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersion X-ray analysis (EDX).

Full text of DOI:10.1016/j.poly.2011.07.025

Polyhedron 30 (2011) 2661–2666
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Trimethylphosphite stabilized disilver(I) methanedisulfonates as MOCVD precursors
⇑
Xian Tao, Ke-Cheng Shen, Meng Feng, Qing-Yun Tang, Jiang-Tao Fang, Yu-Long Wang, Ying-Zhong Shen
Applied Chemistry Department, School of Material Science & Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing 210016, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
New disilver(I) methanedisulfonates complexes {CH (SO ) Ag ꢀ[P(OMe) ] } (n = 2, 2a; n = 4, 2b; n = 6, 2c)
2
3
2
2
3 n
Received 5 June 2011
Accepted 13 July 2011
Available online 5 August 2011
2 3 2 2
were prepared by reacting [CH (SO ) Ag ], which could be synthesized from methanedisulfonic acid and
2 3
Ag CO in water, with trimethylphosphite in dichloromethane. The molecular structure of 2a was deter-
mined using X-ray single crystal analysis. Complex 2a exhibits an infinite chain structure with eight-
membered rings (AgOSOAgOSO) fully interconnected by the third sulfonic O atoms. Complex 2b was used
to deposit silver films by metal organic chemical vapor deposition (MOCVD) for the first time. The silver
film obtained was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and
energy-dispersion X-ray analysis (EDX).
Keywords:
Silver
Methanedisulfonates
Precursor
MOCVD
Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
Deposition
Trimethylphosphite
1
. Introduction
[(fod)Ag(PMe
3 2
)] with the carrier gas H , deposition temperature
n
5
03–573 K, system pressure 13.3 Pa [23]; [(CF COO)Ag(P Bu )]
3 3
In recent years, silver has received considerable attention in
with the carrier gas Ar, deposition temperature 480–590 K, system
pressure 101.3 Pa [24]. Thus, new classes of silver(I) precursors are
highly desirable. Known for their good chelating ability, the class of
cyclic b-diketones can impart desired chemical and physical prop-
erties as well as modulating the volatility. Silver methanedisulfo-
nate exhibits a novel structure with six-membered rings like
cyclic b-diketones and there are only a few reports about its metal
complexes [25]. In this paper, we reported the synthesis of trim-
ethylphosphite stabilized silver(I) methanedisulfonates which
were used as precursors for the deposition of silver by using MOC-
VD techniques for the first time. The single crystal structure of 2a
has been determined and is discussed as well.
many fields of materials science due to it having the lowest resis-
tivity and highest thermal conductivity of all metals [1,2]. For
example, silver films have been reported as contacts in microelec-
tronics [3], as a component of high-temperature superconducting
materials [4], magnetics [5] or bactericidal coatings [6]. Silver films
have been deposited by various methods, such as sputtering [7],
thermal evaporation [8], electron-beam evaporation [9] and chem-
ical vapor deposition (CVD) [10]. Among these techniques, metal
organic chemical vapor deposition (MOCVD) is a very effective
technique for the growth of silver with high quality because of
its high deposition rates with good step coverage [11] and the high
aspect ratio in the multilevel metallization structure [12].
One of the major problems in silver-MOCVD is the selection of
appropriate silver(I) precursors. The silver precursors most often
used are diverse inorganic and organometallic precursors, includ-
2. Experimental
ing AgF [8], [(C
4
7
F )Ag]
n
[13], (b-diketonato)Ag(PR
3
) [14,15], (hfa-
2.1. General procedures
c)Ag(CNMe) [16] various organophosphine stabilized silver
carboxylates [17], silver methanesulfonates [18,19] and silver suc-
cinimide [20]. The majority of the silver salts and complexes are
completely involatile [21], although this can be overcome when
tertiary phosphines are used as secondary ligands. Organometallic
silver compounds with tertiary phosphines are used in the CVD of
All operations were carried out under an atmosphere of purified
nitrogen with standard Schlenk techniques. The solvent dichloro-
2 2 2 5 2
methane (CH Cl ) was purified by distillation from P O under N
1
before use. H NMR were recorded on a Bruker Advance 300 spec-
trometer operating at 300.130 MHz in the Fourier transform mode;
1
3
1
silver layers, for example, [(hfac)Ag(PMe
)
3 n
] with no carrier gas,
C{ H} NMR spectra were recorded at 75.467 MHz. Chemical
deposition temperature 523–623 K, system pressure 6.7 Pa [22];
shifts are reported in d units (parts per million) downfield from tet-
ramethylsilane (d = 0.0 ppm) with the solvent as the reference sig-
nal ( H NMR, D O d = 4.79, CDCl d = 7.26; C{H} NMR, CDCl
2 3 3
1
13
⇑
Corresponding author. Tel.: +86 25 52112906x84765; fax: +86 25 52112626.
E-mail address: yz_shen@nuaa.edu.cn (Y.-Z. Shen).
d = 77.55). Infrared spectra were collected on a Bruker Vector 22
in KBr at room temperature. Elemental analyses were performed
0
277-5387/$ - see front matter Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.07.025

2
662
X. Tao et al. / Polyhedron 30 (2011) 2661–2666
on a Perkin–Elmer 240 C elemental analyzer. Thermogravimetric
studies (TG) and differential scanning calorimetric (DSC) studies
were carried out with a NETZSCH STA 409 PC/PG with a constant
(s), 1203 (s), 1073 (m), 1007 (vs), 788 (vs), 754 (vs), 634 (m), 579
(s), 521 (vs), 461 (m).
ꢁ1
3
ꢁ1
heating rate of 10 °C min
under N
2
(30 cm min ). Melting
2.2.4. Synthesis of {CH (SO ) Ag ꢀ[P(OMe) ] } (2c)
2
3 2
2
3 6
points were observed in sealed capillaries and are uncorrected.
The MOCVD experiments were carried out in a vertical quartz tube
hot-wall MOCVD reactor, 60 mm in diameter. Heating was
achieved by a resistively heated tube oven (AICHUANG Company).
The temperature was set by the temperature control FP 93 (SHI-
MADEN Company) and was calibrated with a thermocouple type
SR 3 (SHIMADEN Company) digital thermometer. The precursor
container was heated with a heating band for evaporation of the
precursor. The precursor vapor was transported to the reactor tube
Complex 2c was synthesized by following the same procedure,
only using [CH (SO ) Ag ] (0.3899, 1.00 mmol) with trim-
2
3 2
2
ethylphosphite (0.7446 g, 6.00 mmol). After appropriate work-up,
complex 2c was obtained as a colorless liquid. Yield: 1.04 g (92%,
based on [CH (SO ) Ag ]). Anal. Calc. for C19H56O24Ag P S : C,
2
3 2
2
2 6 2
1
20.12; H, 4.98. Found: C, 20.07; H, 4.89%. H NMR (CDCl ) d: 4.3
(s, 2H, CH –H), 3.7 (d, 54 H, J = 12.4 Hz, CH –H). C{ H} NMR
3
1
3
1
2
PH
3
(CDCl ) d: 68.4 (CH ), 50.9 (J = 3.6 Hz, CH ). IR (KBr) data
3
2
PC
3
ꢁ1
(cm ): 2997 (m), 2953 (m), 2845 (m), 1460 (s), 1250 (s), 1202
(vs), 1069 (m), 1005 (vs), 788 (vs), 633 (m), 580 (vs), 520 (s), 459
(m), 414 (m).
2
by N carrier gas. The carrier gas flow was regulated using a D07-
7
B (SEVENSTAR Company) mass flow controller which was con-
nected to the apparatus by a section of flexible stainless steel tub-
ing. The pressure control system consisted of a cooling trap and a
FT-110 (KYKY Company) molecular pump unit. The trap prevents
the reactor effluents from entering the vacuum pump. The film
thickness was measured with an Ambios Technology XP-1 Profi-
lometer. The powder X-ray diffraction pattern was recorded on a
D8 ADVANCE X-ray diffractometer. SEM images and EDX analysis
were carried out with an Hitachi Model S-4800 with scanning elec-
tron microscope and an energy dispersive X-ray detector.
2
.3. X-ray structure determination
Single crystals of 2a could be obtained by cooling a saturated
dichloromethane solution to 253 K. A suitable crystal for X-ray
determination was placed in glue under N due to its sensitivity
to oxygen and moisture. X-ray structure measurement was per-
formed on a BRUKER SMART Apex CCD detector equipped with
2
graphite monochromatic Mo K
a radiation (k = 0.71073 Å) at
1
53 K. Date collection and processing (cell refinement, data reduc-
2
.2. Synthesis
tion and empirical absorption correction) were performed using
the CRYSTALCLEAR program package [27]. The structure was solved
using direct methods and refined by full-matrix least-squares pro-
cedures on F (SHELX-97) [28]. All of the non-hydrogen atoms were
refined with anisotropic displacement parameters. Crystallo-
graphic data and details on refinement are presented in Table 1.
2 3 2 2
2.2.1. Synthesis of [CH (SO ) Ag ] (1)
Methanedisulfonic acid (4.58 g, 0.026 mol) dissolved in 30 mL
of H O was added dropwise into a stirred suspended solution of
Ag CO ] (7.72 g, 0.028 mol) in 20 mL of H O at 20 °C. A clear solu-
2
2
[
2
3
2
tion was obtained by filtration through a pad of Celite after stirring
the reaction mixture for 1 h at 20 °C. A white solid product was ob-
tained after removing water in a rotary evaporator and drying in a
vacuum oven at 50 °C. The product was stored under nitrogen and
2
.4. Metal organic chemical vapor deposition of 2b
The deposition of silver was conducted using a vertical quartz
2 3
kept in a dark place. Yield: 8.52 g (84%, based on Ag CO ). It could
tube hot-wall MOCVD reactor with 2b as the precursor. As sub-
be also synthesized by reacting methanedisulfonic acid with Ag
2
O
2
–
1
in water [26]. M.p.: 306 °C dec. H NMR (D
2
O) d: 4.4 (s, 2 H, CH
H). IR (KBr) data (cm ): 3029 (w), 2978 (w), 1271 (m), 1229 (vs),
080 (w), 1023 (s), 814 (m), 772 (w), 589 (m), 537 (w), 516 (m).
Table 1
ꢁ1
Crystallographic data and analysis parameters for {CH
2
(SO
3
)
2
Ag
2
ꢀ[P(OMe)
3 2
] }.
1
Formula
7 2 12 2 2
C H20Ag O P S
Formula weight
Space group
Crystal size (mm)
Crystal system
Z value
a (Å)
b (Å)
c (Å)
638.03
P2(1)/c
2
.2.2. Synthesis of {CH
Trimethylphosphite (0.3723 g, 3.00 mmol) dissolved in 20 mL of
Cl was added dropwise into stirred solution of
(SO Ag ] (0.5848 g, 1.50 mmol) suspended in 20 mL of
Cl at 0 °C. A clear solution was obtained by filtration through
2
(SO
3
)
2
Ag
2
ꢀ[P(OMe)
3 2
] } (2a)
0.2 ꢂ 0.2 ꢂ 0.2
monoclinic
4
9.305(2)
10.178(2)
20.719(4)
90
98.52(3)
90
2.184
CH
2
2
a
[
CH
2
)
3 2
2
CH
2
2
a pad of Celite after stirring the reaction mixture for 6 h at 0 °C. A
white solid was obtained after removing all the volatiles in oil-
a
(°)
b (°)
pump vacuo, Yield: 0.90 g (94%, based on [CH
9 °C dec. Anal. Calc. for C : C, 13.18; H, 3.16. Found:
) d: 4.5 (s, 2 H, CH –H), 3.7 (d, 18
–H). 13C{ H} NMR (CDCl
) d: 68.1 (CH ), 51.8
). IR (KBr) data (cm ): 3029 (m), 2975 (m),
2 3 2 2
(SO ) Ag ]. M.p.:
c
D
(°)
6
7 20 2 2 2
H O12Ag P S
calc (g/cm3)
1
C, 13.13; H, 3.05%. H NMR (CDCl
3
2
Index ranges
ꢁ11 6 h 6 9, ꢁ11 6 k 6 12,
1
H, JPH = 13.7 Hz, CH
PC = 5.2 Hz, CH
3
3
2
ꢁ24 6 l 6 20
prism/colorless
1256
ꢁ1
(J
3
Crystal shape/color
F (0 0 0)
2
1
839 (m), 1461 (m), 1381 (m), 1273 (s), 1223 (vs), 1077 (m),
022 (vs), 812 (s), 761 (s), 636 (m), 589 (s), 535 (m), 517 (s).
ꢁ
l
(Mo K
a
) (mm 1
)
2.45
0.71073
153(2)
k (Mo K
a) (Å)
Temperature (K)
2
.2.3. Synthesis of {CH
Complex 2b was synthesized by following the same procedure,
only using [CH (SO Ag (0.5848 g, 1.50 mmol) and trim-
2
(SO
3
)
2
Ag
2
ꢀ[P(OMe)
3
]
4
} (2b)
h range (°)
3.0–28.8
2653
Independent reflections
(I) > 2 (I)]
[I > 2
wR [I > 2
[
r
a
2
3
)
2
2
]
R
1
r
(h)]
0.036
0.082
1.01
0.86
ꢁ0.71
ethylphosphite (0.7446 g, 6.00 mmol). After appropriate work-up,
complex 2b was obtained as a colorless liquid. Yield: 1.21 g (91
%
1
(h)]b
2
r
2
c
Goodness-of-fit (GOF) on F
ꢁ
3
, based on [CH
7.62; H, 4.32. Found: C, 17.57; H, 4.24%. H NMR (CDCl
2
(SO
3
)
2
Ag
2
]). Anal. Calc. for C13
H
38
O
18Ag
2
P
4
S
2
: C,
D
D
q
max (e Å
)
qmin (e Åꢁ3)
1
3
) d: 4.4
–H). 13C{ H} NMR
1
(
(
(
s, 2 H, CH
CDCl ) d: 68.5 (CH
2
–H), 3.7 (d, 36 H, JPH = 12.9 Hz, CH
), 51.5 (JPC = 4.4 Hz, CH
cm ): 2999 (m), 2953 (s), 2845 (m), 1461 (s), 1386 (m), 1253
3
a
b
c
(w(F 2o ꢁ F ) )/
2
2
(wF )]1/2.
4
R
1
=
R
(||F
o
| ꢁ |F
c
||)/
R
|F
o
|; wR
2
= [
R
R
c
o
2
2
o
2
2
2
c
3
). IR (KBr) data
w = 1/[
r
(F
) + (0.0483P) ], P = (F
o
þ 2F
)/3.
3
1
2
2
2
2
1/2
ꢁ
S = [R
w(Fo ꢁ F ) ]/(n ꢁ p) , n = number of reflections, p = parameters used.
c

X. Tao et al. / Polyhedron 30 (2011) 2661–2666
2663
Table 2
Selected bond lengths (Å) and bond angles (°) for {CH
2
(SO
3
)
2
Ag
2
ꢀ[P(OMe)
3 2
] }.
Bond lengths (Å)
Ag1–O8A
Ag1–O4
Ag2–O5
Ag2–O9
C7–S1
O4–S1
O6–S1
O8–S2
2.317(3)
2.363(3)
2.306(3)
2.371(3)
1.783(4)
1.452(3)
1.446(3)
1.450(3)
Ag1–P1
2.329(1)
2.428(3)
2.308(1)
2.510(3)
1.790(4)
1.454(3)
1.447(3)
1.450(3)
Ag1–O6A
Ag2–P2
Ag2–O7B
C7–S2
O5–S1
O7–S2
O9–S2
Bond angles (°)
O8A–Ag1–P1
P1–Ag1–O4
P1–Ag1–O6A
O5–Ag2–P2
P2–Ag2–O9
P2–Ag2–O7B
S1–O4–Ag1
S1–C7–S2
132.5(9)
129.9(9)
120.6 (8)
140.8(9)
131.2(8)
112.9(9)
139.1(2)
116.6(2)
O8A–Ag1–O4
87.4(1)
84.1(1)
86.9(1)
80.3(1)
88.7(1)
86.0(1)
143.1(2)
O8A–Ag1–O6A
O4–Ag1–O6A
O5–Ag2–O9
O5–Ag2–O7B
O9–Ag2–O7B
S2–O7–Ag2B
Symmetry code for A: ꢁx, ꢁ1 + y, ꢁz; B: ꢁx + 1, ꢁy + 1, ꢁz.
Scheme 1. Synthesis of complexes 2a–2c.
strate pieces of silicon were applied, the typical deposition time
was limited to 60 min. The precursor vessel temperature was
maintained at 348 K by a heating band, with a nitrogen flow at
2 3 2 2
plexes were synthesized by the interaction of [CH (SO ) Ag ] (1)
with P(OMe)3 in stoichiometric ratios in CH Cl , as shown in
2
2
Scheme 1. The complexes were isolated in high yield (91–94%) as
a white solid (2a) or colorless liquids (2b, 2c), which were stable
under inert atmosphere for months at room temperature. On expo-
sure to air they all decomposed in days to form brown products.
Complexes 2a–2c were characterized by elemental analysis, FT-
2
0 sccm to pick up the precursor vapor and transport into the reac-
tion zone. The substrate susceptor was heated at 693 K by a resis-
tive heating element. The total pressure was maintained at 70 Pa
and the reaction by-products were exhausted by a pumping sys-
tem. The deposition of Ag films was carried out in a reaction cham-
ber (a hot-wall vertical cylindrical reactor). No reducing agent such
1
13
1
IR, H and C{ H} NMR spectroscopy (see Section 2).
As we know, the typical group vibration of sulfonates is in the
ꢁ1
as H
2
was used in the deposition processes. The average film thick-
range 1350–1050 cm [29,30]. In the IR spectra of 2a–2c, the
ꢁ1
ness was about 0.7
lm, giving a growth rate of 0.7
lm h
.
SO groups show their characteristic group frequencies. The prom-
3
ꢁ1
inent absorptions in the ranges 1250–1270 and 1202–1223 cm
can be attributed to the asymmetric and symmetric stretching
vibration of SO [31–35]. The absorptions around 1070 cm can
2
ꢁ1
3
. Results and discussion
be assigned as the stretching vibration of S–O, which is similar to
a previous report [36]. Compared with the free trimethylphosphite
3.1. Synthesis
ꢁ1
(
1012 cm ), the absorption bands of trimethylphosphite derived
Metal organic silver precursors of the type {CH
2
(SO
3
)
2
Ag
2
ꢀ[P(O-
from P–O–C linkage stretching vibrations are shifted to lower fre-
ꢁ1
Me)
this work. Compound [CH
reaction of methanedisulfonic acid with Ag
3
]
n
} (n = 2, 2a; n = 4, 2b; n = 6, 2c) were prepared and used for
(SO Ag ] (1) was synthesized by the
CO in water. The com-
quencies for 2b–2c by 5–7 cm , but are shifted to higher frequen-
ꢁ1
)
2
2
cies for complex 2a (1022 cm ) [37]. This may be caused by
2
3
structural changes, but the real reason is unclear.
2
3
Fig. 1. A centrosymmetric tetranuclear fragment in the crystal structure of 2a. The hydrogen atoms are omitted for clarity. Symmetry code for A: ꢁx, ꢁ1 + y, ꢁz; B: ꢁx + 1,
y + 1, ꢁz.
ꢁ

2
664
X. Tao et al. / Polyhedron 30 (2011) 2661–2666
Fig. 2. The polymeric chain of complex 2a: (a) view along the b axis; (b) view along the c axis with methoxy groups omitted for clarity.
Fig. 5. XRD pattern of the metallic silver thin film obtained from the MOCVD at
93 K using 2b as precursor on a Si wafer.
6
Fig. 3. TG curves of 2a–2c (heating rate 10 °C minꢁ1, nitrogen atmosphere).
1
13
1
The NMR spectra ( H and C{ H}) were recorded for all com-
1
plexes at room temperature. In the H NMR spectra, the integration
area ratios are consistent with the stoichiometries of the com-
plexes. The protons of complexes 2a–2c in the methyl proton
2 3 2 3
region appeared at 3.7 ppm. The proton of –CH – in –O SCH SO –
appeared in the range 4.3–4.5 ppm as a single signal, which agrees
1
3
1
well with a previous report [38]. In the C{ H} NMR spectra of
2
a
a–2c, the carbon resonances of –CH
lower field region (68.1–68.5 ppm) compared to that of
] (50.9–51.8 ppm).
2 3 2 3
– on –O SCH SO – show in
[P(OMe)
3
3.2. Single crystal structure of 2a
A single crystal of complex 2a could be grown by slowly cooling
a saturated dichloromethane solution containing 2a to 253 K. The
X-ray single crystal analysis results indicate that the molecular
formula of complex 2a is {CH
symmetric tetranuclear fragment in the crystal structure of 2a is
2
(SO
3
)
2
Ag
2
ꢀ[P(OMe)
3 2
] }. The centro-
depicted in Fig. 1. Selected bond distances (Å) and bond angles
(°) are given in Table 2.
Complex 2a crystallizes in the monoclinic space group P2(1)/c,
and is composed of centrosymmetric tetranuclear fragments
Fig. 1). A polymeric chain is formed (Fig. 2(a)), and it extends
along the axis and consists of {CH (SO Ag
ꢀ[P(OMe)
(
Fig. 4. DSC curves of 2a–2c (heating rate 10 °C minꢁ1, nitrogen atmosphere).
a
2
3
)
2
2
3 2
] }

X. Tao et al. / Polyhedron 30 (2011) 2661–2666
2665
Fig. 6. SEM image and EDX spectrum of the silver film obtained from the MOCVD at 693 K using 2b as precursor on a Si wafer.
fragments. Complex 2a represents a novel chain structure con-
tained eight-membered rings (AgOSOAgOSO), which are connected
by Ag atoms by the third sulfonic O atoms (Fig. 2(b)). The centro-
symmetric tetranuclear fragment (Fig. 1) possesses a crystallo-
graphically imposed inversion symmetry with the inversion
In general, a liquid precursor is better than a solid precursor
owing to its constant vapor pressure. The disilver complexes
decompose with the release of the auxiliary ligands first, and some
impurities or incomplete decomposition for the complexes 2a and
2c. In addition, the thermal measurement shows that complex 2b
should be suitable as a MOCVD precursor, and it has more a suit-
able thermal decomposition and thermal stability compared with
center in the centroid of the Ag
a pseudo-tetrahedral environment set up by one P atom from the
P(OMe) ligand and three O atoms from different methanedisulfo-
2 2
O core. The Ag(I) ion possesses
3
that of {[(MeO)
3
P]
2
ꢀAgO
3 3
SCH } [19]. This may be due to its novel
nate groups, with bond angles ranging from 80.2(2) to 140.8(2)°.
The S–C–S angle [116.6(2)°] is larger than those of the reported
structure with six-membered rings, like cyclic b-diketonates, giv-
ing good chelating ability to the disilver(I) methanedisulfonates
complexes. Considering the thermal properties obtained from the
TG and DSC studies, we chose 2b as a precursor for the CVD
experiment.
complex [CH
lated complex with no ring in it, [CH
The Ag1–O4 [2.363(3) Å] distance of the Ag
another connective bond, Ag2–O7B [2.510(3) Å], similar to the sit-
uation in complex {[CH (SO Ag (connective bonds
2
(SO
3
)
2
Ag
2
] [111.8(4)°] [26], but close to another re-
(SO Ag ] [116.4(7)°] [26].
core is shorter than
2
3
)
2
2
2 2
O
2
3
)
2
2 3 2 4
ꢀ[P(OEt) ] }
3.4. Silver film studies
Ag–O: 2.355(2), 2.593(2) and 2.526(2) Å) [39]. In addition, the
Ag–P distances in complex 2a [2.329(2) and 2.308(2) Å] are shorter
than the sum of the covalent radii of the P and Ag atoms (2.44 Å)
The surface morphology and composition of the silver films
from the MOCVD experiment using 2b were examined by X-ray
diffraction (XRD), scanning electron microscopy (SEM) and en-
ergy-dispersion X-ray analysis (EDX). The layer deposited is silver
colored. The structure of the films was established by XRD. Irre-
spective of the reaction atmosphere, the XRD investigation showed
the characteristic peaks of polycrystalline cubic metallic silver cor-
responding to the Ag(1 1 1), Ag(2 0 0), Ag(2 2 0), Ag(3 1 1) and
Ag(2 2 2) reflections, as reported by JCPDS data (Fig. 5), with no
preferential orientation of the growth.
[
[
40] and that of complex [(R
41].
3 2 8 4 2
P) AgPI] (PI = C H NO ) [2.494(7) Å]
3.3. Thermal analysis
Themogravimetry (TG) and differential scanning calorimetry
DSC) studies are required to optimize the temperature at which
(
the respective single silver precursor should be maintained during
the CVD experiments. The TG and DSC curves of complexes 2a–2c
are shown in Figs. 3 and 4. The decomposition of all the complexes
is completed at ca. 400 °C. It can be seen from the DSC curves that
complexes 2a and 2c possess at least two exothermic and/or endo-
thermic steps, but for complex 2b only one apparent endothermic
process exists, from 94 to 450 °C with peak temperatures at 219
and 325 °C. It can be seen that the metal–organic 2a starts to
decompose (ca. 120 °C) at a much higher temperature than both
SEM (Fig. 6) studies show that the film is composed of many
well isolated, granular particulates spreading all over the substrate
surface. The sizes of the silver grains are in the range 60–100 nm.
The EDX spectrum (Fig. 6) of the deposited film shows Ag as the
main component. Because of the discontinuous Ag particles expos-
ing the substrate and the relatively high penetration depth of the
electron beam during the EDX analysis, silicon as a substrate com-
ponent was detected. Other light elements, such as C, O and P,
which might be present as impurities or formed by surface oxida-
tion of silver, are below the detection limit.
2
b and 2c (ca. 90 °C), which most probably can be explained by
the higher aggregation of 2a.
3
For complex 2b, it may lose two P(OMe) groups from 94 to
1
85 °C with a corresponding weight loss of about 27.93%, which
is approximately equal to the theoretical loss (28.00%). Then, it
may lose other two P(OMe) groups from 185 to 234 °C with a cor-
4. Conclusions
3
A straightforward synthesis methodology for the preparation of
new disilver(I) methanedisulfonate complexes of the composition
responding weight loss of about 27.54% which is again close to the
theoretical loss (28.00%). It is very difficult to know the real ther-
mal decomposition mechanism of methanedisulfonates. The final
percentage of the residue is 24.40%, which is approximately equal
to the theoretical value of silver (24.34%). However, the final per-
centages of the residues for 2a and 2c are 37.89 and 29.57%,
respectively, which are little bit higher than the theoretical value
of silver (33.81% and 19.02%), indicating there may be some impu-
rities or the incomplete decomposition of the complexes.
{CH
2
(SO
3
)
2
Ag
2
ꢀ[P(OMe)
3 n
] } (n = 2, n = 4, n = 6) is described. The
molecular structure of 2a exhibits a novel structure with six-mem-
bered rings like cyclic b-diketonates. On the basis of the properties
of complexes 2a–2c, we chose 2b as a potential CVD precursor to
grow silver films for the first time. The silver film is composed of
many well isolated, granular particulates spreading all over the
substrate surface. It has been demonstrated that the complex is a
promising candidate as a precursor for the deposition of Ag.

2
666
X. Tao et al. / Polyhedron 30 (2011) 2661–2666
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Acknowledgments
1
This work was supported by the National Science and
Technology of Major Project (2009ZX020391-002). Funding of
Jiangsu Innovation Program for Graduate Education (CX10B_100Z),
and funding for Outstanding Doctoral Dissertation in NUAA
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Appendix A. Supplementary data
[
[
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for compound 2a. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
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