X-Ray structural and gas phase studies of silver(I) perfluorinated carboxylate complexes with 2,2′-bipyridyl as potential precursors for chemical vapour deposition (CVD)

Article abstract of DOI:10.1039/b911741e

[Ag(CF₃COO)(bpy)] (1), [Ag₂(C₂F ₅COO)₂(bpy)] (2) and [Ag₂(C₃F ₇COO)₂(bpy)] (3) were prepared and characterized by MS-EI, ¹H, ¹³C NMR, variable-temperature IR (VT-IR) spectroscopy (solid sample and evolved volatile species) and thermal analysis. Single-crystal X-ray diffraction data revealed the polymeric structure for [Ag₂(C₂F₅COO)₂(bpy)] and [Ag ₆(C₃F₇COO)₆(bpy)₄], with bridging bpy ligand, whereas for [Ag(CF₃COO)(bpy)] the dimeric system with monodentately linked carboxylate was noted. Mass spectra analysis of (1-3) over 30-300 °C indicates the presence of binuclear ions [(RCOO)Ag ₂]⁺ as a main volatile particles, which can be transported in CVD process. VT-IR studies of gases evolved during the thermal decomposition process, demonstrate the presence of fluorocarbon species and CO₂ as the most abundant molecules. Thermal analysis of (1-3) revealed a multi-stage decomposition mechanism resulting in Ag⁰ formation below 290 °C. Compounds were tested for silver metal spray pyrolysis and obtained layers were characterized by scanning electron microscopy (SEM-EDX) and XRD. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b911741e

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www.rsc.org/dalton | Dalton Transactions
X-Ray structural and gas phase studies of silver(I) perfluorinated carboxylate
complexes with 2,2¢-bipyridyl as potential precursors for chemical vapour
deposition (CVD)†
Edward Szłyk,* Robert Szcze˛sny and Andrzej Wojtczak
Received 19th June 2009, Accepted 10th December 2009
First published as an Advance Article on the web 15th January 2010
DOI: 10.1039/b911741e
[Ag(CF3COO)(bpy)] (1), [Ag2(C2F5COO)2(bpy)] (2) and [Ag2(C3F7COO)2(bpy)] (3) were prepared and
characterized by MS-EI, 1H, 13C NMR, variable-temperature IR (VT-IR) spectroscopy (solid sample
and evolved volatile species) and thermal analysis. Single-crystal X-ray diffraction data revealed the
polymeric structure for [Ag2(C2F5COO)2(bpy)] and [Ag6(C3F7COO)6(bpy)4], with bridging bpy ligand,
whereas for [Ag(CF3COO)(bpy)] the dimeric system with monodentately linked carboxylate was noted.
Mass spectra analysis of (1–3) over 30–300 ◦C indicates the presence of binuclear ions [(RCOO)Ag2]+ as
a main volatile particles, which can be transported in CVD process. VT-IR studies of gases evolved
during the thermal decomposition process, demonstrate the presence of fluorocarbon species and CO2
as the most abundant molecules. Thermal analysis of (1–3) revealed a multi-stage decomposition
mechanism resulting in Ag0 formation below 290 ◦C. Compounds were tested for silver metal spray
pyrolysis and obtained layers were characterized by scanning electron microscopy (SEM-EDX) and
XRD.
Therefore we have focused our effort on the preparation of new
Introduction
silver(I) carboxylates complexes with bpy for further CVD studies.
Thermal properties and volatility of silver complexes are impor-
In order to characterise complexes as precursors the thermal
tant features which determine their usage in fabrication of metallic
decomposition and IR spectra of gases evolved in this process have
thin films by the chemical vapour deposition (CVD) technique.1
been examined by variable-temperature MS and IR. Moreover,
These nanolayers can be applied to produce ultra-fast optical
X-ray crystal structures of studied compounds have been solved
switches, or used as components of high-temperature supercon-
and discussed.
ducting materials and infrared sensors.2 Organometallics or Ag(I)
complexes with b-diketonates and tertiary phosphines (PMe3,
PEt3),3 silylated alkenes,4 alkynes5 and recently carboxylates6 are
currently the most often studied CVD precursors.
Experimental
The low thermal stability of Ag(I) complexes with hard oxygen
donors, such as perfluorinated carboxylates, can be enhanced
by a ligand which stabilizes the coordination sphere of silver(I).
Secondary soft donor atoms such as P or S were widely used for this
purpose, however contamination of the layers by these elements
was often observed. Another way of carboxylate complexes
stabilization is to use the chelating ligand, therefore 2,2-bipyridyl
was chosen in the studies reported here.
Several reports on silver(I) salts with 2,2-bipyridyl (bpy) were
published.7 These complexes are air-stable, exhibit good sol-
ubility in organic solvents and for the majority of them the
crystal structures were solved. Among reported compounds only
[Ag(hfac)(bpy)] (hfac = hexafluoroacetylacetonate) was studied as
a CVD precursor but, to the best of our knowledge, there are no
reports on other Ag(I) compounds with bpy tested for this method.
General
CF3COOH (99%), C2F5COOH (97%) and C3F7COOH (98%) were
purchased from Aldrich, whereas 2,2¢-bipyridyl (bpy), AgNO3,
NaHCO3 and C2H5OH from POCh (Poland) and were used as
received.
Thermal studies (TG, DTG and DTA) were performed on a
SDT 2960 TA instrument. Mass spectra were registered by a
Finnigan MAT 95 spectrometer using the EI technique (heating
range 30–300 ◦C). 1H and 13C NMR spectra in CDCl3 were
collected with a Varian Gemini 200 MHz and Bruker 300 MHz
spectrometer against TMS. IR spectra were registered using a
Perkin–Elmer 2000 FT IR spectrometer in the range 4000–
400 cm-1, in KBr discs. Variable-temperature IR (VT-IR) studies in
the solid phase were carried out with a SPECAC (Perkin–Elmer)
temperature variable cell (30–250 ◦C). IR spectra of vapours
formed during the thermolysis of complexes and transported
with the carrier gas (Ar), were measured using the equipment
as reported.8 The electron micrograph studies were carried out
with a LEO 1430 VP (Cambridge Ltd) equipped with an
EDX Spectrometer Quantax 200 (with XFlash 4010 detector)
from Bruker AXS. X-Ray diffraction of the residues from the
thermal decomposition and layers was performed by an Expert
Nicolaus Copernicus University, Faculty of Chemistry, 87 100, Torun´,
Poland. E-mail: eszlyk@chem.uni.torun.pl; Fax: +48 (056) 654 24 77;
Tel: +48 (056) 611 43 04
† Electronic supplementary information (ESI) available: Additional data.
CCDC reference numbers 734740 (1), 734738 (2) and 734739 (3). For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/b911741e
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Table 1 Thermal analysis results
Philips diffractometer. Silver was determined argentometrically
(after complex mineralization), and C, H and N by elemental
microanalysis (Vario-Macro Analyser).
T/◦C
Mass loss [%]
Heat effect
on DTA
Compound
Tinit
Tmax
Tf
Calcd
Found
(1)
(2)
(3)
Endo
Exo
Exo
148
198
210
214
247
240
285
286
290
71.4
69.1
73.0
69.1
69.0
74.5
Synthesis
In a general procedure, complexes were obtained in the reaction
of RCOOAg,9 R = CF3, C2F5 and C3F7 with 2,2¢-bipyridyl (bpy)
ligand (M : L = 1 : 1). Silver(I) salts were suspended in a water–
ethanol solution (3 : 1) and then bpy was added. The solution was
stirred for 4 h at room temperature, filtered and the solvent was
evaporated leaving a white precipitate, which was recrystallized
from ethanol.
Tinit = initial temperature; Tmax = maximum temperature; Tf = final
temperature.
Table 2 Mass spectra analysis data
Compound/Temp./◦C/Int.[%]
(1)
(2)
(3)
[Ag(CF3COO)(bpy)] (1). Anal. calcd for C12H8Ag1F3N2O2: C
38.2, H 2.1, Ag 28.6. Found: C 38.0, H 2.4, Ag 28.5%. IR (nmax
(KBr)/cm-1): 1673 (nasymCOO), 1555, 1477, 1417 (nsymCOO), 1405,
1366, 1357, 1290. 1H NMR (CDCl3)/ppm: 7.51 (2 H, m), 7.99 (2 H,
m), 8.18 (2 H, m), 8.77 (2 H, m). 13C NMR (CDCl3)/ppm: 122.0,
125.5, 138.9, 151.2, 151.6, 162.6 (q, 2JCF = 32.7 Hz, dCOO).
Fragmentation ion
m/z 150
300
177
300
221
[COO]+
[CF2]+
44
50
69
78
97
—
3
—
9
18
13
69
13
19
N/A
22
N/A
—
100
N/A
10
1
11
99
12
—
N/A
2
—
4
—
11
—
—
—
—
17
12
43
14
7
26
18
64
8
9
38
9
[CF3]+
[C5H4N]+
[CF3CO]+
[C2F4]+
—
—
38
24
13
—
54
19
14
2
—
N/A
—
—
N/A
N/A
100
100 N/A
107
119 N/A
147
Ag+
—
[C2F5]+
[Ag2(C2F5COO)2(bpy)] (2). Anal. calcd for C16H8Ag2F10N2O4:
C 27.5, H 1.2, Ag 30.9. Found: C 27.4, H 1.4, Ag 30.8%. IR (nmax
(KBr)/cm-1): 1674 (nasymCOO), 1550, 1472, 1411 (nsymCOO), 1399,
1359, 1286, 960. 1H NMR (CDCl3)/ppm: 7.51 (2 H, m), 7.99 (2 H,
m), 8.18 (2 H, m), 8.77 (2 H, m). 13C NMR (CDCl3)/ppm: 121.9,
125.7, 138.9, 151.3, 151.5, 162.6 (t, 2JCF = 24.7 Hz, dCOO).
[Ag(COO)]+
[C10H8N2]+
[C3F7]+
—
—
20
156 100
169 N/A
100
N/A
—
—
—
N/A
—
—
—
N/A
N/A
100
N/A
12
1
—
N/A
5
0,5
73
N/A
N/A
+
Ag2
216
263
284
329
335
370
—
—
—
—
—
—
[C10H8N2Ag]+
[Ag2CF3]+
[Ag2(CF3COO)]+
[Ag2(C2F5)]+
[C10H8N2Ag2]+
[Ag2(C2F5COO)]+
[Ag2(C3F7COO)2(bpy)] (3). Anal. calcd for C18H8Ag2F14N2O4:
C 27.1, H 1.0, Ag 27.0. Found: C 27.1, H 1.2, Ag 27.2%. IR (nmax
(KBr)/cm-1): 1681 (nasymCOO), 1549, 1458, 1405, 1397 (nsymCOO),
1364, 1045, 764 cm-1. 1H NMR (CDCl3)/ppm: 7.51 (2 H, m), 7.99
(2 H, m), 8.18 (2 H, m), 8.77 (2 H, m). 13C NMR (CDCl3)/ppm:
122.1, 125.6, 138.9, 151.5, 163.0 (t, 2JCF = 25.4 Hz, dCOO).
379 N/A
[Ag2(CF3COO)(CF3)]+ 398
—
[Ag2(C3F7COO)]+
429 N/A
N/A
N/A = unable to observe; — = was not detected.
Results and discussion
Crystal structure determination
IR and NMR spectra
Colourless crystals of (1–3) were obtained by recrystallization
from ethanol solutions. The X-ray data were collected with an
Oxford Sapphire CCD diffractometer using Mo Ka radiation l =
Carboxylate ions can coordinate in many modes such as: mon-
odentate, chelating or bridging bidentate.13 The way of binding
can be proposed by calculation of the parameter DnCOO
=
˚
0.71073 A, byw - 2q method. The numerical absorption correction
n
asymCOO - nsymCOO for the studied compounds and comparison
was applied (RED171 package of programs, Oxford Diffraction,
2000).10 The space groups have been determined based on the
systematic absences. The structures were solved by Patterson
methods and refined with the full-matrix least-squares method
on F2 with the use of SHELX-97 program package.11 For (1) the
rotational disorder of the trifluoromethyl moiety was detected with
two defined populations of 0.686/0.314 occupancy. The structure
of (1) is similar to that reported previously by other authors.12 In
(2), the rotational disorder of the terminal trifluoromethyl group
was detected with two populations of occupancy 0.526 and 0.474.
In the structure of (3) the trifluoromethyl of one C3F7 moiety
revealed the rotational disorder (two populations of 50%) and the
whole C3F7 moiety of another ligand revealed the conformational
disorder with 0.55/0.45 populations. The data collection and
refinement processes of (1–3) are summarized in Table 3. Selected
bond lengths and angles are presented in Table 4.
with the value found for analogous sodium salts.14 In the case of
[Ag(CF3COO)(bpy)] (1) DnCOO = 256 cm-1 is bigger, than that for
CF3COONa (DnCOO = 223 cm-1), what suggests the unidentate
coordination of CF3COO-. For compounds (2) and (3) the DnCOO
values ((2): 263 cm-1, (3): 289 cm-1) are comparable to Dn for
C2F5COONa = 268 cm-1 and C3F7COONa = 272 cm-1, hence
one can propose the bidendate coordination of carboxylates.
=
=
Stretching vibrations of C N and C C bonds in the free bpy
ligand (1579 cm-1 and 1553 cm-1)15 are shifted upon complexation
towards higher wavenumbers ca. 10 cm-1.
13C NMR spectra of (1–3) revealed the COO carbon line at
162.6–163.0 ppm, with the coordination shift (D = dCOO(complex)
-
dCOO(acid); 0.5, 3.4 and 3.9 ppm for (1), (2) and (3)) downfield
in comparison to free acids. The observed D can be related to
change of the charge on the carbonyl carbon caused by Ag–O bond
formation. However the similar or even larger shifts of the COO
1824 | Dalton Trans., 2010, 39, 1823–1830
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Table 3 Crystal data and structure refinement
1
2
3
Empirical formula
Formula weight
Crystal system
Space group
C12H8AgF3N2O2
377.07
Monoclinic
P21/n
7.2330(10)
14.942(3)
12.034(2)
90
103.78(3)
90
1263.1(4)
4
1.983
1.635
0.37 ¥ 0.24 ¥ 0.12
293(2)
C8H4AgF5NO2
348.99
Monoclinic
C2/c
13.5630(10)
16.1960(10)
10.4560(10)
90
113.53(1)
90
2105.9(3)
8
2.202
1.974
0.60 ¥ 0.50 ¥ 0.20
293(2)
C64H32Ag6F40.5N8O12
2521.70
Monoclinic
P21/n
16.476(3)
29.367(6)
17.436(3)
90
103.15(3)
90
8215(3)
4
2.039
1.556
0.17 ¥ 0.16 ¥ 0.07
292(2)
37 533
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
Dc/Mg m-3
m/mm-1
Crystal size/mm
T/K
Reflections collected
Independent reflections/Rint
Max. and min. transmission
GOF on F2
R1 [I > 2s(I)]
wR2 [I > 2s(I)]
12 312
10 150
3833/0.0432
0.8243/0.5853
1.117
0.0428
0.1031
3182/0.0517
0.6935/0.3838
1.115
0.0633
0.1927
8815/0.1202
0.8962/0.7757
1.155
0.1079
0.2206
-3
˚
Largest diffraction peak and hole/e A
1.180/-1.019
1.799/-1.581
1.000/-0.777
◦
˚
Table 4 Selected bond lengths (A) and angles ( ) for the crystal structures
C12H8AgF3N2O2 (1)
Ag(1)–O(1)
Ag(1)–N(1¢)
Ag(1)–N(1)
O(1)–Ag(1)–N(1¢)
O(1)–Ag(1)–N(1)
N(1¢)–Ag(1)–N(1)
O(1)–Ag(1)–Ag(1)#1
N(1¢)–Ag(1)–Ag(1)#1
N(1)–Ag(1)–Ag(1)#1
C(7)–O(1)–Ag(1)
O(2)–C(7)–O(1)
C8H4AgF5NO2 (2)
Ag(1)–O(2)#1
C64H32Ag6F40.5N8O12 (3)
Ag(1)–N(1)
Ag(1)–N(3)
Ag(1)–O(2A)
Ag(2)–N(4)
Ag(2)–O(1B)
Ag(2)–N(2)
Ag(3)–O(1C)
Ag(3)–O(2B)
Ag(3)–O(1E)
Ag(4)–N(5)
Ag(4)–O(2C)
Ag(4)–N(7)
Ag(5)–N(8)
Ag(5)–O(1D)
Ag(5)–N(6)
2.178(2)
2.298(3)
2.323(3)
149.08(9)
138.35(9)
71.93(9)
116.03(7)
71.07(7)
75.76(7)
109.83(19)
129.6(3)
2.270(12)
2.318(12)
2.349(14)
2.286(12)
2.342(12)
2.330(12)
2.311(13)
2.354(12)
2.335(13)
2.232(13)
2.342(12)
2.342(13)
2.282(15)
2.324(12)
2.336(11)
2.461(19)
2.222(15)
2.274(17)
2.55(3)
O(1B)–Ag(2)–N(2)
Ag(1)–Ag(2)–Ag(3)
O(1C)–Ag(3)–O(2B)
O(1C)–Ag(3)–O(1E)
O(2B)–Ag(3)–O(1E)
Ag(4)–Ag(3)–Ag(2)
N(5)–Ag(4)–O(2C)
N(5)–Ag(4)–N(7)
O(2C)–Ag(4)–N(7)
93.7(5)
137.89(6)
107.1(5)
142.5(5)
108.1(5)
109.47(5)
125.1(5)
138.2(5)
92.9(5)
Ag(5)–Ag(4)–Ag(3)
Ag(4)–Ag(5)–Ag(6)
135.90(6)
142.36(6)
138.73(7)
158.80(9)
155.44(7)
158.04(7)
146.77(9)
-132.35(10)
-47(2)
Ag(5)–Ag(6)–Ag(1)#2
Ag(6)#1–Ag(1)–Ag(2)–Ag(3)
Ag(1)–Ag(2)–Ag(3)–Ag(4)
Ag(2)–Ag(3)–Ag(4)–Ag(5)
Ag(3)–Ag(4)–Ag(5)–Ag(6)
Ag(4)–Ag(5)Ag(6)–Ag(1)#2
N(1)–C(5)–C(6)–N(2)
N(3)–C(15)–C(16)–N(4)
N(5)–C(25)–C(26)–N(6)
N(7)–C(35)–C(36)–N(8)
2.217(4)
2.242(4)
2.491(4)
2.542(4)
2.8277(7)
1.483(8)
152.71(19)
99.29(17)
102.41(16)
105.1(2)
95.94(15)
76.67(14)
103.33(14)
Ag(1)–N(1)
Ag(1)–O(1)
Ag(1)–O(1)#2
Ag(1)–Ag(1)#3
Ag(5)–O(2F)
Ag(6)–O(2D)
Ag(6)–O(1A)#2
Ag(6)–O(1F)
N(1)–Ag(1)–N(3)
N(1)–Ag(1)–O(2A)
N(3)–Ag(1)–O(2A)
Ag(2)–Ag(1)–Ag(6)#1
N(4)–Ag(2)–O(1B)
N(4)–Ag(2)–N(2)
C(2)–C(2)#3
O(2)#1–Ag(1)–N(1)
O(2)#1–Ag(1)–O(1)
N(1)–Ag(1)–O(1)
O(2)#1–Ag(1)–O(1)#2
N(1)–Ag(1)–O(1)#2
O(1)–Ag(1)–O(1)#2
Ag(1)–O(1)–Ag(1)#2
-51.7(18)
-45(2)
-43(2)
131.0(5)
129.4(5)
92.0(5)
142.04(6)
124.7(5)
138.1(4)
Symmetry codes used: C12H8AgF3N2O2 #1 [-x + 1, -y, -z]; C8H4AgF5NO2 #1 [-x + 1, -y, -z] #2 [-x + 1, -y + 1, -z] #3 [-x + 1, y, -z - 1/2];
C64H32Ag6F40.5N8O12 #1 [x - 1, y, z] #2 [x + 1, y, z].
carbon signals have been reported for silver(I) aliphatic carboxy-
lates (bidentately bonded) complexes with tertiary phosphines:
[Ag(Me3SiCH2COO)(PPh3)] (D = 0.2 ppm),16 [Ag(RCOO)(PMe3)]
(D = 1–2.7 ppm),17 [Ag(RCOO)(PMe3)2] (D = 0.9–1.3 ppm),18
[Ag(RCOO)(PEt3)] (D = 0.6–2.7 ppm)19 and [Ag(RCOO)(PPh3)]
(DdCOO = 2.0–6.5 ppm).20 Even more interesting, the chemical shifts
of COO group for the non-fluorinated Ag(I) carboxylates and
their complexes with tertiary phosphines were noted at lower fields
(~170–180 ppm), than fluorinated.6,21 The latter cannot be related
to the inductive effect which decreases with distance, because
b-substituent effect is connected rather with stereoelectronic
factors. There are reports on application of 13C NMR resonances
for elucidation of the RCOO- group binding modes.22 However
usage of this parameter for silver(I) perfluorinated carboxylates
complexes as presented above is disputable. Moreover, observed
differences can also be caused by changes in the perfluorinated
chain length. Considering studied compounds (1–3) it is evident
that deshielding of COO in trifluoroacetate (1) complex is smaller
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than for (2) and (3). Nevertheless, the observed values probably can
be related to the RCOO- coordination mode. The slight variations
of dCOO suggest that effect of two binding oxygen atoms have
a smaller impact on tertiary carbon deshielding, than induction
effects of the electronegative fluorine atoms in the nearest distance
from the carbonyl group.
Decomposition studies
Thermal properties of compounds, especially the temperature
of the decomposition process onset and temperature of silver
formation, are significant factors for the assessment of their future
usage as precursors in CVD. Results of the thermal analysis are
listed in Table 1. Complex (1) decomposes in one endothermic
Scheme 1 MS fragmentation scheme of the analyzed complexes.
derived from 2,2¢-bipyridyl ligand upon heating, whereas above
200 ◦C these bands disappeared. Simultaneously, the number and
frequencies of the COO bands were unchanged (up to 150 ◦C).
Besides that, spectra of vapours evolved from (1), registered in the
process (DTA curve: Mp. = 134 ◦C and decomposition Tmax
=
214 ◦C). Experimental mass loss on TG curve for (1) (exp.
69.1%) does not correspond to the detachment of carboxylate and
bipyridyl ligands (calcd 71.4%). This discrepancy can be related to
partial formation of AgF at 500 ◦C. SEM-EDX analysis indicates
small amount of fluorine (probably AgF), whereas at 1000 ◦C only
Ag0 was detected as the final product (see ESI).† Upon prolonged
heating (to 1000 ◦C) the detected mass loss was 71.6%. Complexes
(2) and (3) decompose in the one stage process (Table 1).
Additional endothermic peaks which were registered on DTA
curves at 183 ◦C for (2) and 120 ◦C for (3) correspond to melting
points. The final product of the decomposition reactions is metallic
silver, as proven by the X-ray diffractograms analysis (0.2352;
0.2026; 0.1179; 0.1444; 0.1233 nm).23 The observed Tf for studied
compounds are considerably lower than those observed for the
silver(I) carboxylates (Tf = CF3COOAg > 300 ◦C, C2F5COOAg >
400 ◦C, C3F7COOAg > 450 ◦C) and for [Ag(hfac)(bpy)] (Tf >
600 ◦C). This facts allow to assume, that compounds (1–3) can be
promising CVD precursors below 300 ◦C, however their volatility
at different pressure should be tested.
◦
range 160 and 200 C, exhibit bands from CF3H25 (1151, 1376,
2328 and 3034 cm-1) and CO2 (2320 cm-1 and 669 cm-1). The
latter suggest the dissociation of carboxylate residue, followed
by decarboxylation and rearrangement of the carbon chain to
trifluoromethane. Simultaneously, the bands from the N-donor
ligand were detected, in the spectra registered at 250 ◦C. That can
be caused by the lower volatility of bpy and slower transport from
TGA instrument via the heated connector to the gas cell. Therefore
the bpy bands were not observed at lower temperatures, shortly
after the thermal dissociation, but were noted in the VT-IR spectra
registered for the solid compound.
In the case of (2) the asymmetric COO vibrations frequencies
were shifted from 1667 to 1679 cm-1 over 20–250 ◦C (Fig. 1). More-
-1
=
over, the C O stretching band (1744 cm ) from the uncoordinated
or monodentately bonded with silver(I) carboxylate group was
noted above 140 ◦C. The absorption of this band increased, while
nas(COO) = 1667 cm-1 reveals the opposite effect. Furthermore
-1
=
intensities for the bpy ligand absorptions: n(C N) = 1591 cm ,
d(CH) = 1007 cm-1 and g(CH) = 754 cm-1 have decreased, while
at 250 ◦C they have not been detected. These effects can be related
to the detachment of bpy ligand below 250 ◦C and simultaneous
rearrangement of carboxylates in the coordination sphere. For
complex (2) the gaseous products of thermolysis were observed
over 170–270 ◦C. When the temperature reached Tmax.= 230 ◦C, the
intense absorption bands from C–F stretching vibrations (1100–
1300 cm-1) (probably C4F10 is formed)26 and bpy (1585, 1561 and
1456 cm-1) were found (Fig. 2). Besides the mentioned bands, the
The variable-temperature EI-MS spectra of (1), (2) and (3) were
recorded in the range 30–300 ◦C and results are listed in Table 2. In
all cases the signal from [Ag2(RCOO)]+ was the most intensive and
revealed the line pattern characteristic for disilver species [(3 lines,
R.I. = 1 : 1.860 : 0.865, natural isotopic abundance of 107Ag (51.4%)
and 109Ag (48.6%)]. Analogous dimeric silver species were observed
in MS spectra of perfluorinated and aliphatic silver carboxylates.24
It is noteworthy, that monomeric species of the type [(RCOO)Ag]+
were not detected, except [Ag(bpy)]+ ions, which exhibited low
R.I.< 2%. The latter suggests that monomeric species are less
stable and volatile than dimeric, due to relatively large charge of
the ion and smaller number of perfluorinated residues.
In the case of (1) and (2) the fragmentation proceeds in two
stages. Below 200 ◦C, spectra indicate detachment of N-donor
ligand and its fragmentation, whereas in the second stage (above
◦
290 C) the fragmentation of carboxylates was also detected. In
contrast the significant difference was found for (3), because both
effects occur simultaneously in the range 200–250 ◦C, as presented
at Scheme 1. This fact can be related to the lower stability of Ag–
O bond, coming out from the stronger Lewis base character of
C3F7COO-.
Application of precursors in the CVD technique requires
the determination of the thermal stability and composition of
vapours, formed during thermolysis. IR spectra of (1), deposited
on KBr plates, demonstrate the reduction of intensity of bands
Fig. 1 Variable temperature IR spectra of (2), registered over 40–250 ◦
(solid).
C
1826 | Dalton Trans., 2010, 39, 1823–1830
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X-Ray structure analysis
The structure of (1) was already reported by Bowmaker et al.12
However, that structure was determined at slightly higher temper-
ature 300 K. The comparison reveals that difference in the unit
cell parameters is less than 0.1%. The asymmetric part of the
structure (1) is formed by a Ag ion, the bipyridyl ligand and the
trifluoro-acetic ion (Fig. 4), and constitutes the half of a dimer.
The crystal structure is built with the centrosymmetric dimers of
a formula [Ag(CF3COO)(bpy)]2. Bidentate coordination of the
bipyridyl ligand is found, the Ag1–N1 and Ag1–N1¢ distances
˚
being 2.323(3) and 2.298(3) A, respectively, and the N1–Ag1–N1¢
angle is 71.93(9)◦, the trifluoro-acetic ligand participates in a single
˚
Ag1–O1 coordination bond of 2.178(2) A (Fig. 4), while the second
oxygen atom does not form any bond to Ag. Such molecular
architecture is almost identical to that reported previously.12 The
only interaction bridging two halves of the dimer is that of Ag1–
Fig. 2 VT-IR spectra of vapours formed during the thermal decomposi-
tion of (2) (T = 230 ◦C).
additional absorption at 2309 cm-1 from C N or/and C C bonds
stretching vibrations of unidentified compounds were detected.
Species with bidentate coordinated carboxylate ions were not
observed as well.
˚
Ag1 [-x + 1, -y, -z] being 3.0521(9) A. The angles between Ag1–
≡
≡
Ag1 [-x + 1, -y, -z] and three coordination bonds vary between
71.07(7) and 116.03(7)◦ (Table 4). The AgN2O coordination sphere
˚
is planar, with the rms deviation of fitted atoms being 0.0385 A.
Spectra of (3) registered below 110 ◦C, suggest the lack
of structural changes, while above this temperature the bpy
detachment can be noted. Simultaneously, the nas(COO) band
(1668 cm-1) is shifted towards higher wavenumbers (Fig. 3).27 In
the gas phase, between 160–170 ◦C, bands from fluorocarbon
species (n(C–F): 1140, 1183, 1232, 1268 cm-1) and CO2 (668,
2350 cm-1) were observed. The COO stretching bands revealed
similar changes as for (2), hence the presence of the mon-
odentately bonded carboxylates in monomeric species cannot be
excluded.
The dihedral angle between that plane and the best plane of the
C7–C8–O1–O2 carboxylate moiety is 12.1(2)◦.
Fig. 4 Dimeric unit in the crystal structure [Ag(CF3COO)(bpy)] (1).
Analysis reveals the lack of packing interactions involving the
CF3 moieties. Short intermolecular contacts are detected between
the chelate rings and the pyridyl rings of the adjacent molecules,
the distances between the respective centers of their gravity being
˚
3.963, 4.157 and 3.434 A between Ag1–N1–C2–C2¢–N1¢ and its
equivalents related by [-x, -y, -z] and [1 - x, -y, -z] and the
N1–C6 [1 - x, -y, -z] pyridyl, respectively. The distance between
centers of gravity of pyridyl rings N1–C6 and N1¢–C6¢[-x, -y, -z]
˚
is 4.277 A. The carboxylic O2 atom, not involved in coordination
Fig. 3 Frequency of nas(COO) vibrations vs. temperature (3).
of Ag1, forms an intermolecular contacts to H3A–C3[-x, -y, -z]
and H5¢A–C5¢[1/2 + x, -1/2 - y, 1/2 + z], with the O2 ◊ ◊ ◊ H3A
and O2 ◊ ◊ ◊ H5¢A distances of 2.67 and 2.45 A, respectively.
˚
Considering our earlier studies, the comprehensive analysis,
including TGA, VT-IR and EI-MS, can be used for evaluation
of the suitability of compounds as precursor for (MO)CVD.28 MS
data reveal the presence of the metal binding species which can be
formed in the gas phase and transported in the CVD equipment.
When these metallated species exhibit sufficient stability, then they
can be detected in the VT-IR spectra of vapours. According to the
MS results, the silver binding species ([Ag2(RCOO)]+) were present
in the gas phase. However, their thermal stability can be too low
to enable their transport in the gas phase in CVD processes, hence
(1–3) are probably not suitable for (MO)CVD.
The CF3 moiety reveals significant rotational disorder with two
rotamers defined, and that feature seems to be characteristic for
the structure reported here. That seems to result from only weak
CF3 interactions in the space available for that moiety in the
crystal structure. This dynamical effect found in the crystal is
consistent with the usability of the investigated compound in the
CVD technique.
The asymmetric part of the structure (2) consists of the Ag ion,
half of the bipyridyl ligand and the pentafluoropropionic anion.
The rotational disorder of the terminal CF3 group is detected
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(occupancies 0.526/0.474), reflecting the lack of significant inter-
actions involving that group in the crystal lattice.
The architecture of the reported structure might be described
as a hybrid between the polymeric chain similar to that found in
[Ag(C2F5COO)(PMe3)] and the pairs of bridging pentafluoropro-
pionates found in [Ag(C2F5COO)(PPh3)], as reported by Ro¨mbke
et al.29 The structure is built with the polymeric chains parallel
to the Z axis. The chain is formed by the Ag ions bridged by
the bipyridyl ligands, with the N atoms coordinated to Ag, the
-
˚
Ag1–N1 distance being 2.242(4) A. Two C2F5COO ligands also
bridge the adjacent Ag centers, with the O1 atoms forming two
coordination bonds, while O2 participates in only one such bond
(Fig. 5). The respective bond distances are Ag1–O1 2.491(4), Ag1–
O1[-x + 1, -y + 1, -z] 2.542(4) and Ag1–O2 [x, -y + 1, z -
˚
1/2] 2.217(4) A. Such architecture results in a coordination sphere
Fig. 6 Fragment of the polymeric chain of [Ag6(C3F7COO)6(bpy)4], with
that could be described as strongly deformed tetrahedron. Angles
within the coordination sphere vary between N1–Ag1–O1 [-x +
1, -y + 1, -z] of 95.9(2) and O2[x, -y + 1, z - 1/2]–Ag1–O1[-x +
1, -y + 1, -z] of 105.1(2)◦. Only two of them, O1–Ag1–O1[-x +
1, -y + 1, -z] being 76.7(1) and O2[x, -y + 1, z - 1/2]–Ag1–
N1 of 152.7(2) significantly deviate from the tetrahedral values.
the numbering scheme. Fluorine and hydrogen atoms skipped for clarity.
ligands and six heptafluorobutyrate ions (Labelled with A-F
letters) coordinated to the metal centers. However, the architecture
of the chain is rather complicated and different for each metal
center. The pairs of the neighbouring Ag centers are linked by
pairs of bipyridyl bridges (Ag1–Ag2, Ag4–Ag5 or by the single
carboxylate bridge (Ag2–Ag3, Ag3–Ag4, Ag6–Ag1 [x + 1, y, z]).
All the bipyridyl ligands form the bridges linking the adjacent
Ag atoms in the chain. The heptafluorobutyrate ions A-D form
the bridges between the Ag atoms via both oxygen atoms, while
carboxylates E–F are only monodentate ligands.
˚
The structure reveals the short distance of 2.8276(7) A between
adjacent Ag1 and Ag1 [-x + 1, y, -z - 1/2] atoms. Two adjacent
Ag centers and two O1 atoms related by the center of symmetry
form a four-membered ring Ag1–O1–Ag1[-x + 1, -y + 1, -z]–O1
[-x + 1, -y + 1, -z]. The Ag1–O1–Ag1 and O1–Ag1–O1 angles
are 103.3(1) and 76.7(1)◦, respectively.
The coordination sphere of Ag1–Ag4 ions is formed with three
Ag–O or Ag–N bonds. In particular, Ag1, Ag2 and Ag4 participate
in two Ag–N and single Ag–O interactions, while Ag3 forms three
bonds to the O atoms. Ag5 forms two Ag–N and two Ag–O
bonds, while Ag6 interacts only with a pair of O atoms. The Ag–N
˚
˚
distances vary from 2.232(13) A for Ag4–N5 to 2.342(13) A for
Ag4–N7, while Ag–O distances range from 2.222(15) for Ag6–
O2D to 2.55(3) for Ag6–O1F.
The angles in the coordinations sphere correspond to the
strongly deformed triangular geometry for Ag1–Ag4, the angles
within the coordination sphere of each Ag atom ranging from
approximately 93 to 143◦ (Table 4). Ag5 has a strongly deformed
tetrahedral coordination sphere, whereas Ag6 has a strongly
deformed triangular geometry when two coordination bonds and
˚
a short contact Ag6 ◊ ◊ ◊ O1F[-1 + x, y, z] 2.5486 A are considered.
The puckering analysis30 of the chelate rings formed in the
structure indicated that the rings have a following conformation:
envelope on Ag6 for Ag1–Ag6–O1A–C1A–O2A, an envelope on
Ag6 for Ag5–Ag6–O1F–C1F–O2F, Ag5–Ag6–O2D–C1D–O1D is
twisted on Ag5–Ag6, twist-boat conformation for Ag1–Ag2–N2–
C6–C5–N1, twist-boat for Ag1–Ag2–N4–C16–C15–N3, screw-
boat for Ag4–N5–C25–C26–N6–Ag5 and Ag4–N7–C35–C36–
N8–Ag5, Ag2–Ag3–O2B–C1B–O1B is an envelope on Ag2, Ag3–
Ag4–O2C–C1C–O1C is an envelope twisted on Ag3–Ag4.
Fig. 5 Fragment of the polymeric chain of (2), with the numbering
scheme. Fluorine and hydrogen atoms are omitted for clarity. Ag1¢ and
O1¢ are generated from the basic coordinates with the [-x + 1, -y + 1, -z]
transformation.
The bridging bipyridyl ligand is significantly twisted around the
C2–C2 [-x + 1, y, -z - 1/2] bond, with the dihedral angle between
the ring best planes being 41.8(2)◦. The dihedral angle between two
carboxylic groups bridging the adjacent Ag centers is 79.3(6)◦.
Despite the significant disorder of the pentafluoropropionic
moieties in the structure, the analysis revealed that they are found
in the extended conformation, with the O1–C11–C12–C13 torsion
angle being 175.0(1)◦.
The structure obtained by the recrystallization of complex (3)
from the ethanol solution is composed of the infinite chains based
on the asymmetric part of [Ag6(C3F7COO)6(bpy)4] (Fig. 6). The
asymmetric unit contains a fragment Ag1–Ag6 with four bipyridyl
Analysis revealed the metal–metal interactions along the poly-
˚
meric chain with the Ag–Ag distances varying between 2.932(2) A
˚
for Ag1–Ag2 and 3.229(2) A for Ag2–Ag3. The Ag–Ag–Ag angles
in that chain are similar to each other and range from 135.90(6)◦
to 142.36(6)◦, for Ag5–Ag4–Ag3 and Ag4–Ag5–Ag6, respectively.
Only one angle Ag4–Ag3–Ag2 of 109.487(5)◦ differs significantly
from those mentioned above, probably due to the presence of
only monodentate heptafluorobutyrate E ligand on Ag3 inserted
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Table 5 Summary of deposition conditions for (2)
Parameter
Concentration of solution/mg cm-3
Flow rate/dm3 min-1
Carrier gas
4–10
1–5
Ar
400
0.2–2.5
Substrate T/◦C
Film thickness/mm
between the carboxylate and bipyridne bridges with its carboxylic
group almost perpendicular to the Ag1–Ag6 chain axis. The
Ag–Ag–Ag–Ag torsion angles reflecting the rotations around
Ag1–Ag2, Ag2–Ag3 and Ag3–Ag4 are almost identical and are
158.80(9), 155.44(7) and 158.04(7)◦, respectively. The significant
difference is found for Ag3–Ag4–Ag5–Ag6 and Ag4–Ag5–Ag6–
Ag1 [x + 1, y, z] being 146.77(9)◦ and -132.35(10)◦, respectively.
The bidentate coordination of bipyridyl ligands bridging the
adjacent Ag centers results in their twisted conformation with the
N–C–C–N torsion angles ranging from -43(2)◦ to -51.7(18)◦ for
N7–C35–C36–N8 and N3–C15–C16–N4, respectively.
Fig. 7 SEM micrographs silver layers after thermal decomposition of
[Ag2(C2F5COO)2(bpy)] (2) on Si(111).
The heptafluoropropyl moieties of the carboxylic ligands show
significant conformational disorder, what strongly affects the
atomic displacement parameters. However, only for the C3F7
moiety of ligand B and for the CF3 group of ligand F the alternative
positions of the disordered groups could be defined. In all these
cases the relative occupancy of the disordered groups is close to
50%.
Analysis of the packing interactions revealed numerous contacts
between fluorine atoms of heptafluorobutyrate ligands of the
adjacent chains. Also, an interaction was found between N3–C11–
C12–C13–C14–C15 and N6–C26–C27–C28–C29–C30 [-1/2 + x,
1/2 - y, 1/2 + z] rings, the distance between their centers of gravity
˚
being 4.007 A.
Results of depositions experiments
Fig. 8 SEM micrographs silver layers after thermal decomposition of
[Ag2(C2F5COO)2(bpy)] (2) on Si(111) (uniform phase).
The results presented above suggest, that despite low temperature
of silver formation, the studied compounds presumably are
less suitable (MO)CVD precursor, than other Ag(I) complexes
with phosphines or alkenes. Nevertheless, preliminary deposition
experiments were carried out using horizontal hot-wall CVD
reactor.6c Tests performed at moderate conditions (substrate:
Si(111), pevap. = 300 Pa, deposition temperature: 250–300 ◦C)
confirmed, that the volatility of the complexes (1–3) was not
sufficient for this technique.
also the coalescence of these grains into the continuous sponge
structures. The SEM image of the latter layer revealed spatial
structures of silver nanoparticles. The results of the SEM-EDX
and XRD analyses clearly indicate the presence of Ag clusters (see
ESI).† Moreover, EDX spectra indicated the contamination of
layers with carbon and oxygen for thinner films and the presence
of fluorine in the layers of the highest thickness.
Series of spray pyrolysis experiments with [Ag2(C2F5COO)2-
(bpy)] (2) as a precursor were performed and the obtained layers
were studied with SEM and EDX methods. The complex was
dissolved in CHCl3 and nebulized on a silicon (111) plate, and
subsequently heated at 400 ◦C, in the air. The procedure was
repeated four times, using different concentrations of (2) and gas
pressure in nebulizer (Table 5). The obtained coatings were non-
uniform with bigger silver aggregations (Fig. 7) at the center of
the plate, probably due to the solution concentration in this area.
Among them silver clusters with diameter approximately 200–
250 nm were formed (Fig. 8).
In comparison to complexes (1–3), the perfluorinated carboxy-
lates and their complexes with tertiary phosphines earlier exam-
ined seem to be more convenient for (MO)CVD.31 For example
C2F5COOAg sublimes in the range 220–270 ◦C with simultaneous
decomposition. The IR spectra of vapour indicate the bands
at 1606 cm-1 derived from bridging or chelating coordinated
carboxylate groups while the EI-MS measurement exhibit signals
from [Ag(C2F5COO)]. In the case of [Ag(C2F5COO)PMe3], the
presence of silver carboxylate was also evident in the gas phase.
Above compounds have been used as precursors and analysis
demonstrated a surface with the size of metal grains in the range
0.1–1.5 mm. Similarly for [Ag(CH3CH2C(CH3)2COO)(PEt3)] the
volatile and stable silver–phosphine intermediates were noted
during the thermal decomposition processes (MS, IR).28b The
In the case when higher solutions concentration (10 mg cm-3)
and smaller argon flow rate were applied, clusters have aggregated
into bigger grains (ca. 300–500 nm, Fig. 9). Micrographs show
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5 (a) K.-M. Chi and Y.-H. Lu, Chem. Vap. Deposition, 2001, 7, 117; (b) A.
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Chim. Acta, 2002, 328, 134; (b) E. Szłyk, P. Piszczek, A. Grodzicki, M.
Chaberski, A. Golinski, J. Szatkowski and T. Błaszczyk, Chem. Vap.
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7 (a) C. Di Nicola, Effendy, F. Marchetti, C. Pettinari, B. W. Skelton and
A. H. White, Inorg. Chim. Acta, 2007, 360, 1433; (b) C. Pettinari, J.
Ngoune, B. W. Skelton and A. H. White, Inorg. Chem. Commun., 2007,
10, 329; (c) Effendy, F. Marchetti, C. Pettinari, B. W. Skelton and A. H.
White, Inorg. Chim. Acta, 2007, 360, 1424.
8 P. Piszczek, A. Grodzicki, M. Richert and A. Radtke, Materials
Science-Poland, 2005, 23, 663.
9 E. Szlyk, I. Lakomska and A. Grodzicki, Thermochim. Acta, 1993, 223,
207.
10 CrysAlis CCD171 and RED171 package of programs, Oxford Diffrac-
tion, 2000.
11 G. M. Sheldrick, SHELXL-97, Program for refinement of crystal
structures, University of Go¨ttingen, Germany, 1997; G. M. Sheldrick,
SHELXS-97, Program for solution of crystal structures, University of
Go¨ttingen, Germany, 1997.
Fig. 9 SEM micrographs silver layers after thermal decomposition of
[Ag2(C2F5COO)2(bpy)] (2) on Si(111) (largest thickness).
12 G. A. Bowmaker, Effendy, S. Marfuah, B. W. Skeleton and A. H. White,
Inorg. Chim. Acta, 2005, 358, 4371.
13 K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordina-
tion Compounds, Wiley & Sons, 1978, p. 230.
CVD experiments with [Ag(CH3CH2C(CH3)2COO)(PEt3)] re-
vealed deposition of nanometric silver films (thicknesses below
50 nm) at temperature 220–250 ◦C.
14 (a) G. B. Deacon and R. J. Phillips, Coord. Chem. Rev., 1980, 33,
227; (b) G. Wilkinson, R. D. Gillard, J. A. McClaverty, Comprehensive
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Studied compounds reveal good solubility in organic sol-
vents (ethanol, benzene, acetonitrile and chloroform) and do
not hydrolyze in water. These facts suggest the future usage
of [Ag2(C2F5COO)2(bpy)] as precursor in aerosol-assisted CVD
(AACVD).32
Conclusions
17 E. Szłyk, I. Łakomska and A. Grodzicki, Thermochim. Acta, 1997, 303,
Analysis of the temperature variable MS, IR and TG data revealed,
41.
◦
18 E. Szłyk and I. Łakomska, Polish J. Chem., 2002, 76, 1399.
19 E. Szłyk, I. Łakomska and A. Grodzicki, Thermochim. Acta, 1998, 315,
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that studied complexes (1–3) decompose below 290 C with the
formation of the metallic silver. Low pressure CVD with (1–3)
as precursors does not provide silver layers, hence complexes
were tested as precursors in aerosol assisted CVD. Single-
crystal X- ray diffraction data of Ag(I) complexes with 2,2¢-
bipyridyl exhibit the polymeric structure of [Ag2(C2F5COO)2bpy]
and [Ag6(C3F7COO)6(bpy)4], with bridging bpy. Crystal data for
[Ag2(CF3COO)2bpy] prove that it crystallizes in the dimeric archi-
tecture, with monodentately linked carboxylate. Solved structures
with bridging bpy are interesting for the silver chemistry, also
considering the design and synthesis of supramolecular molecules.
21 (a) S. W. Ng and A. H. Othman, Acta Crystallogr., Sect. C: Cryst.
Struct. Commun., 1997, 53, 1393; (b) D. E. Edwards, M. F. Mahon,
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Inorg. Chem., 2002, 41, 6426; (d) S.-J. Lin, T.-N. Hong, J.-Y. Tung and
J.-H. Chen, Inorg. Chem., 1997, 36, 3886.
23 Powder Diffraction File, Sets 4-783, International Centre for Diffraction
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25 The National Institute of Standards and Technology NIST Standard
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26 R. N. Haszeldine and K. Leedham, J. Chem. Soc., 1953, 1548.
27 N. W. Alcock and V. M. Tracy, J. Chem. Soc., Dalton Trans., 1976,
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28 (a) I. B. Szyman´ska, P. Piszczek and E. Szłyk, Polyhedron, 2009, 28, 721;
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2007, 26, 2440.
29 P. Ro¨mbke, A. Schier, H. Schmidbaur, S. Cronje and H. Raubenheimer,
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30 D. Cremer and J. A. Pople, J. Am. Chem. Soc., 1975, 97, 1354.
31 A. Grodzicki, I. Łakomska, P. Piszczek, I. Szyman´ska and E. Szłyk,
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32 (a) M. N. McCain, S. Schneider, M. R. Salata and T. J. Marks, Inorg.
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Acknowledgements
Authors wish to thank the Polish Ministry of Science and Higher
Education for financial support grant: N204 049 31/1376.
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