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Organophosphinephosphite-stabilized silver(I) complexes bearing N-hydroxysuccinimide ligand synthesis solid state structure and their potential use as MOCVD precursors.

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Full Paper
Received: 3 November 2011
Revised: 24 November 2011
Accepted: 1 December 2011
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.1868
Organophosphine/phosphite-stabilized silver
(I) complexes bearing N-hydroxysuccinimide
ligand: synthesis, solid state structure and their
potential use as MOCVD precursors
Xian Tao, Ke-Cheng Shen, Qing-Yun Tang, Meng Feng, Jiang-Tao Fang,
Yu-Long Wang and Ying-Zhong Shen*
Six organophosphine/phosphite-stabilized silver(I) N-hydroxysuccinimide complexes of type [C4H4NO3AgLn] (L = PPh3; n = 1,
2a; n = 2, 2b; L = P(OEt)3; n = 1, 2c; n = 2, 2 d; L = P(OMe)3; n = 1, 2e; n = 2, 2f) were prepared. These complexes were obtained
in high yields and characterized by elemental analysis, 1H NMR, 13 C{1H} NMR and IR spectroscopy, respectively. The molecular
structure of 2b has been determined by X-ray single-crystal analysis in which the silver atom is in a distorted tetrahedral
geometry. An interstitial methanol solvent molecule is hydrogen bonded to the oxygen atom of N-hydroxysuccinimide
molecule. Complex 2f was used to deposit silver films by metal-organic chemical vapor deposition (MOCVD) for the first time.
The silver film obtained at 480 C is dense and homogeneous, which is composed of many well-isolated, granular particulates
spreading all over the substrate surface. Copyright © 2012 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: silver; N-hydroxysuccinimide; precursor; MOCVD
Introduction
Appl. Organometal. Chem. 2012, 26, 67–73
Experimental
General Procedures
All operations were carried out under an atmosphere of purified
nitrogen with standard Schlenk techniques. The solvents methanol
(CH3OH) and ethanol (C2H5OH) were purified by distillation from
CaH2 under N2 before use. The synthesis of N-hydroxysuccinimide
was described previously[25] and purified by recrystallization from
acetidin. 1H NMR spectra were recorded on a Bruker Advance 300
* Correspondence to: Ying-Zhong Shen, Applied Chemistry Department, School
of Material Science and Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, People’s Republic of China.
E-mail: yz_shen@nuaa.edu.cn
Applied Chemistry Department, School of Material Science and Engineering,
Nanjing University of Aeronautics and Astronautics, Nanjing 210016, People’s
Republic of China
Copyright © 2012 John Wiley & Sons, Ltd.
67
In recent years, silver has received considerable attention in many
fields of materials science owing to its lower resistivity and superior
electromigration resistance.[1,2] Applications include contacts in
microelectronics,[3] components of high-temperature superconducting materials,[4] magnetics,[5] and bactericidal coatings.[6] Silver
films have been mostly grown by physical vapor deposition (PVD),
electrochemical deposition, and electroless methods. Among
various silver film deposition techniques, metal-organic chemical
vapor deposition (MOCVD) has the advantages of single-step
growth process, superior step coverage and high aspect ratio in
the multilevel metallization structure.[7–11] However, the major
limitation of this method is the requirement of highly volatile
metal-organic precursors.
As precursors for MOCVD, they should have (i) good volatility
during evaporation and transportation in the gas phase; (ii) high
purity and suitable thermal decomposition mechanism; (iii) suitable
thermal stability, which means that it should not decompose during
the transportation process but decompose easily in the MOCVD
reactor.[12,13] The silver precursors most often used in CVD are
diverse inorganic and organometallic complexes, including AgF,[14]
[(C4F7)Ag]n,[15] (b-diketonato)Ag(PR3),[16,17] (hfac)Ag(CNMe),[18] and
silver carboxylate derivatives.[1] Various organophosphine-stabilized
silver methanesulfonates[19–21] and silver succinimide[22–24] have
been used as CVD precursors in a number of studies by our previous
work. Thus new classes of fluorine-free silver(I) precursors are
highly desirable. N-Hydroxysuccinimide possesses a hydroxamic
acid group, which can give metal a five-membered ring for good
chelating ability. To the best of our knowledge, Lewis-base stabilized
silver(I) N-hydroxysuccinimide complexes have not been reported.
In order to search for the new kind of precursor in MOCVD
technique, herein we describe the synthesis and characterization
of a series of organophosphine/phosphite-stabilized silver(I) Nhydroxysuccinimide complexes of type [C4H4NO3AgLn] (L = PPh3;
n = 1, 2a; n = 2, 2b; L = P(OEt)3; n = 1, 2c; n = 2, 2 d; L = P(OMe)3;
n = 1, 2e; n = 2, 2f). Complex {C4H4NO3Ag[P(OMe)3]2} (2f) was tested
as a precursor for the deposition of silver by using MOCVD techniques for the first time. The single-crystal structure of 2b has also
been determined and discussed in this paper.
X. Tao et al.
spectrometer operating at 300.130 MHz in the Fourier transform
mode; 13 C{1H} NMR spectra were recorded at 75.467 MHz. Chemical shifts are reported in d units (parts per million) downfield from
tetramethylsilane (d = 0.0 ppm) with the solvent as the reference
signal (1H NMR, CDCl3 d = 7.26; 13 C{H} NMR, CDCl3 d = 77.55).
Infrared spectra were collected on a Bruker Vector 22 in KBr at room
temperature. Elemental analysis was performed on a PerkinElmer
240 C elemental analyzer. Thermogravimetric studies (TG) and
differential scanning calorimetric (DSC) studies were carried out
with the Netzsch STA 409 PC/PG with a constant heating rate of
10 C min1 under N2 (30 cm3 min1). Melting points were
observed in sealed capillaries and were uncorrected. The MOCVD
experiments were carried out in a vertical quartz tube hot-wall
MOCVD reactor of 60 mm diameter. Heating was achieved by a
resistively heated tube oven (Aichuang Co.). The temperature was
set by a temperature control FP 93 (Shimaden Co.) and calibrated
with a thermocouple type SR 3 (Shimaden Co.) 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 by N2 carrier gas. The carrier gas flow was
regulated using a D07-7B (Sevenstar Co.) mass flow controller,
which was connected to the apparatus by a section of flexible
stainless steel tubing. The pressure control system consisted of a
cooling trap and an FT-110 (KYKY Co.) molecular pump unit. The
trap prevented the reactor effluents from entering the vacuum
pump. Scanning electron microscopy (SEM) images and energydispersion X-ray (EDX) analysis were carried out using a Hitachi
Model S-4800 with scanning electron microscope and energydispersive X-ray detector. Atomic force microscopy (AFM)
images were taken using an MMAFM-2 (Digital Instruments) in
contact mode.
(cm1): 3050 (m), 2935 (m), 1752 (m), 1666 (s), 1644 (s), 1480 (m),
1434 (s), 1239 (s), 1095 (m), 1083 (m), 747 (m), 722 (m), 695 (s),
669 (m), 522 (m), 503 (m).
Synthesis of [C4H4NO3Ag(PPh3)2] (2b)
Complex 2b as a white solid was obtained by following
the above procedure, only using C4H4NO3Ag (1) (0.1109 g,
0.5 mmol) and triphenylphosphine (0.2622 g, 1.0 mmol)
instead. Yield: 0.36 g (95% based on C4H4NO3Ag); m.p.:
185 C dec.; anal. calcd for C40H34O3AgP2N: C, 64.36; H, 4.59; N,
1.88; found: C, 64.23; H, 4.47; N, 1.79%. 1H NMR (CDCl3): d 2.3
(s, 4 H, CH2=H), 7.3–7.5 (m, 15 H, Ph=H). 13 C{1H} NMR (CDCl3):
d 25.0 (CH2), d 176.5 (C), 133.9 (JPC = 16.8 Hz, C6H5), 132.6
(JPC = 24.7 Hz, C6H5), 130.0 (C6H5), 128.7 (JPC = 9.5 Hz, C6H5). IR
(KBr) data (cm1): 3041 (m), 3008 (m), 2982 (m), 2953 (m), 1748
(m), 1653 (s), 1629 (s), 1481 (m), 1435 (s), 1235 (s), 1097 (m),
1085 (m), 746 (s), 721 (m), 697 (s), 667 (m), 508 (s), 494 (m).
Synthesis of [C4H4NO3AgP(OEt)3] (2c)
Synthesis
Complex 2c could be synthesized using a similar procedure to that
for the synthesis of 2a. In this respect, [P(OEt)3] (0.0830 g, 0.5 mmol)
was reacted with C4H4NO3Ag (1) (0.1109 g, 0.5 mmol). After
appropriate work-up, complex 2c was isolated as a yellow liquid.
Yield: 0.1833 g (94% based on C4H4NO3Ag); anal. calcd for
C10H19O6AgPN: C, 30.95; H, 4.93; N, 3.61; found: C, 30.78; H, 4.81;
N, 3.55%. 1H NMR (CDCl3): d 1.4 (t, 9 H, CH3/CH3CH2=, JHH = 7.0 Hz),
d 2.7 (s, 4 H, CH2=H), 4.1 (qd, 6 H, CH2/CH3CH2=, JHH = 7.1 Hz, JPH = 2.8
Hz). 13 C{1H} NMR (CDCl3): d 25.0 (CH2), d 175.5 (C), 16.3 (d, JPC = 6.8
Hz, CH3/CH3CH2=), 61.3 (d, JPC = 5.7 Hz, CH2/CH3CH2=). IR (KBr) data
(cm1): 3437 (m), 2981 (s), 2937 (m), 2893 (m), 1750 (m), 1672
(s),1641 (s), 1389 (m), 1246 (s), 1164 (m), 1096 (s), 1053 (s), 1022 (s),
935 (s), 811 (m), 772 (s), 742 (m), 674 (m), 540 (m).
Synthesis of C4H4NO3Ag (1)
Synthesis of [C4H4NO3Ag[P(OEt)3]2] (2 d)
A solution of N-hydroxysuccinimide (3.50 g, 0.030 mol) in 30 ml
ethanol and Et3N (3.50 g, 0.035 mol) at 0 C was slowly added to
a solution of AgNO3 (5.16 g, 0.030 mol) in 30 ml ethanol and
5 ml acetonitrile. The reaction mixture was stirred for 2 h and a
large amount of white precipitate appeared. The reaction vessel
was wrapped with aluminum foil in order to exclude light as
much as possible. The suspension was filtered through a Büchner
funnel, which was also wrapped with aluminum foil, and was
washed with 20 ml ethanol twice. The C4H4NO3Ag was dried in
a vacuum oven at 50 C for 1 h. The product was stored under
nitrogen and kept in a dark place. Yield: 6.1 g (92%, based on
AgNO3); m.p.: 217 C dec.
Complex 2 d could be synthesized in the same manner as 2a,
instead utilizing [P(OEt)3] (0.1660 g, 1.0 mmol) and C4H4NO3Ag
(1) (0.1109 g, 0.5 mmol). After appropriate work-up, complex
2 d was obtained as a yellow liquid. Yield: 0.26 g, (95% based
on C4H4NO3Ag); anal. calcd for C16H34O9AgP2N: C, 34.67; H,
6.18; N 2.53; found: C, 34.49; H, 6.07; N, 2.47%. 1H NMR (CDCl3):
d 1.3 (t, 9 H, CH3/CH3CH2=, JHH = 7.1 Hz), d 2.6 (s, 4 H, CH2=H),
4.0 (qd, 6 H, CH2/CH3CH2=, JHH = 7.1 Hz, JPH = 2.5 Hz). 13 C{1H}
NMR (CDCl3): d 25.1 (CH2), d 175.9 (C), 16.4 (d, JPC = 6.4 Hz, CH3/
CH3CH2=), 60.7 (d, JPC = 6.4 Hz, CH2/CH3CH2=). IR (KBr) data
(cm1): 2980 (m), 2936 (m), 2898 (m), 1746 (m), 1673 (s), 1642
(s), 1390 (m), 1246 (s), 1164 (m), 1096 (m), 1023 (s), 938 (s), 813
(m), 773 (m), 744 (m), 674 (m), 543 (m).
Synthesis of [C4H4NO3AgPPh3] (2a)
68
Triphenylphosphine (0.1311 g, 0.5 mmol) dissolved in 20 ml methanol was added in one portion to a stirred solution of C4H4NO3Ag (1)
(0.1109 g, 0.5 mmol) suspended in 20 ml methanol at 0 C. The clear
solution was obtained by filtration through a pad of celite after
stirring the reaction mixture for 6 h at 0 C. A pink solid
product was obtained after removing all the volatiles under
vacuum using an oil-pump. Yield: 0.23 g (93% based on
C4H4NO3Ag); m.p.: 179 C dec.; anal. calcd for C22H19O3AgPN: C,
54.57; H, 3.95; N, 2.89; found: C, 54.36; H, 3.91; N, 2.82%. 1H NMR
(CDCl3): d 2.6 (s, 4 H, CH2=H), 7.3–7.6 (m, 15 H, Ph=H). 13 C{1H}
NMR (CDCl3): d 25.1 (CH2), d 175.7 (C), 133.9 (JPC = 16.5 Hz, C6H5),
130.9 (C6H5), 130.4 (C6H5), 129.1 (JPC = 10.7 Hz, C6H5). IR (KBr) data
wileyonlinelibrary.com/journal/aoc
Synthesis of [C4H4NO3AgP(OMe)3] (2e)
Complex 2e was prepared by a similar method to that for 2a, instead
utilizing [P(OMe)3] (0.0620 g, 0.5 mmol) and C4H4NO3Ag (1)
(0.1109 g, 0.5 mmol). After appropriate work-up, complex 2e was
isolated as a white solid. Yield: 0.17 g (96% based on C4H4NO3Ag);
m.p.: 73 C; anal. calcd for C7H13O6AgPN: C, 24.30; H, 3.79; N, 4.05;
found: C, 24.21; H, 3.68; N, 4.01%. 1H NMR (CDCl3): d 2.6 (s, 4 H,
CH2=H), 3.7 (d, 9 H, CH3=H, JPH = 13.4 Hz). 13 C{1H} NMR (CDCl3):
d 25.1 (CH2), d 175.3 (C), 51.4 (d, JPC = 5.5 Hz, CH3). IR (KBr) data
(cm1): 2951 (m), 2843 (m), 1779 (m), 1672 (s), 1650 (s), 1310 (m),
1239 (s), 1224 (s), 1182 (m), 1085 (m), 1010 (s), 790 (s), 752 (s), 726
(m), 666 (m), 559 (m), 523 (m).
Copyright © 2012 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2012, 26, 67–73
Silver(I) N-hydroxysuccinimide precursors
Synthesis of [C4H4NO3Ag[P(OMe)3]2] (2f)
Table 1. Crystallographic data and analysis parameters for 2b
Complex 2f was synthesized using a procedure similar to that
used for the synthesis of 2a. In this respect, [P(OMe)3] (0.1240 g,
1.0 mmol) is reacted with C4H4NO3Ag (1) (0.1109 g, 0.5 mmol).
After appropriate work-up, complex 2f was isolated as a yellow
liquid. Yield: 0.22 g (94% based on C4H4NO3Ag); anal. calcd for
C10H22O9AgP2N: C, 25.55; H, 4.72; N 2.98; found: C, 25.41; H,
4.58; N 2.93%. 1H NMR (CDCl3): d 2.6 (s, 4 H, CH2=H), 3.7 (d, 9 H,
CH3=H, JPH = 12.5 Hz). 13 C{1H} NMR (CDCl3): d 25.1 (CH2), d 175.8
(C), 51.2 (d, JPC = 5.5 Hz, CH3). IR (KBr) data (cm1): 3450 (m),
2949 (m), 2839 (m), 1777 (m), 1673 (s), 1642 (s), 1311 (m), 1246
(s), 1182 (m), 1094 (m), 1007 (s), 791 (m), 762 (m), 729 (m), 670
(m), 524 (m).
Compound
X-ray structure determination
A single crystal of 2b could be obtained by cooling a saturated
methanol solution containing 2b to 30 C. A suitable crystal for
X-ray determination was placed in glue under N2 because of to its
sensitivity to oxygen and moisture. X-ray structure measurement
was performed on a Bruker SMART Apex CCD detector equipped
with graphite monochromatic Mo Ka radiation (l = 0.71073 Å). Date
collection and processing (cell refinement, data reduction, and
empirical absorption correction) were performed using the
CrystalClear program package.[26] The structure was solved using
direct methods and refined by full-matrix least-squares procedures
on F2 (SHELX-97).[27] All of the non-hydrogen atoms were refined
with anisotropic displacement parameters. Crystallographic data
and details on refinement are presented in Table 1.
Metal organic chemical vapor deposition of 2f
MOCVD experiment using 2f as precursor was performed in a hotwall reactor using a continuous evaporation system. In a typical
MOCVD experiment silver was deposited onto a piece of Si
substrate at 480 C. The evaporation temperature was maintained
at 75 C with a nitrogen flow at 20 sccm (standard-state cubic
centimeters per minute). The run time was 1 h and the total
pressure was maintained at 7.0 104 bar with nitrogen as carrier
gas. No reducing reagent such as H2 was used in the deposition
processes. The average film thickness was about 0.55 mm, giving a
growth rate of 0.55 mm h1.
Results and Discussion
Synthesis and Characterization of Complexes 2a–2f
Appl. Organometal. Chem. 2012, 26, 67–73
Formula
Formula weight
Crystal dimensions (mm)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
b ( )
V [Å3]
Z value
Dcalc [g cm3]
Index ranges
C41H38AgNO4P2
778.53
0.2 0.2 0.2
Monoclinic
P21/c
9.883 (2)
23.355 (5)
15.711 (3)
96.52 (3)
3602.9(13)
4
1.435
12 ≤ h ≤ 12,
28 ≤ k ≤ 23,
16 ≤ l ≤ 19
1600
0.69
0.71073
153(2)
3.1–29.2
5867
0.046
0.089
1.07
0.58
0.68
F (000)
m (Mo Ka) (mm1)
l (Mo Ka) (Å)
Temperature (K)
θ range ( )
Independent reflections [(I) > 2s(I)]
R1 [I > 2s(θ)]
wR2 [I > 2s(θ)]
Goodness-of-fit on F2c
Δrmax (eÅ3)
Δrmin (eÅ3)
P
P
P
P
a
R1 = (||Fo| |Fc||)/ |Fo|; wR2 = ½ (w(F2o F2c )2) / (wFo4) 1/2.
b
w = 1 / [s2(F2o) + (0.0346P)2 + 2.8278P], P = (F2o + 2F2c ) / 3.
P 2
c
S= ½
w(Fo F2c )2 / (n p)1/2; n = number of reflections,
p = parameters used.
The complexes also could be prepared by treatment of AgNO3
with auxiliary donor ligands and C4H4NO3K in diethyl ether at 0 C
(equation (1)). The disadvantage of the synthesis procedures
described in equation (1) for 2a–2f is the low yield (yield: <10%
base on AgNO3) because of the low activity of C4H4NO3K. Another
adversarial aspect is the purification, because some products may
contain traces of chloride, which is detrimental to their use as
CVD precursors in microtechnology. Therefore, these preparative
studies show that an economical and straightforward synthesis
route is presented (Scheme 1; see above).
The IR spectroscopic data provide further support for the molecular constitution of the title complexes. A characteristic feature of
Scheme 1. Synthesis of complexes 2a–2 f.
Copyright © 2012 John Wiley & Sons, Ltd.
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69
The organophosphine/phosphite-stabilized silver(I) N-hydroxysuccinimide complexes of type [C4H4NO3AgLn] (L = PPh3; n = 1,
2a; n = 2, 2b; L = P(OMe)3; n = 1, 2c; n = 2, 2 d; L = P(OEt)3; n = 1,
2e; n = 2, 2f) were prepared by reaction of [C4H4NO3Ag] with
triphenylphosphine, trimethylphosphite or triethylphosphite in
stoichiometry using methanol as solvent at 0 C (Scheme 1).
The complexes were obtained in high yield as white solids
(2a–2b) or yellow liquids (2c–2f). They are very sensitive to
moisture and oxygen as well as light. The complexes are
insoluble in cold non-polar solvents such as petroleum, whereas
they are highly soluble in dichloromethane and tetrahydrofuran.
All the products obtained gave satisfactory elemental analysis
results and were characterized by FT-IR, 1H NMR and 13 C{1H}
NMR, respectively.
2b
X. Tao et al.
five-membered ring imides is the presence of bands at about
1785 cm1 (medium) and 1725 cm1 (strong) in the IR spectra of
N-hydroxydemethylcantharimide.[28] In the complexes prepared,
the absorption vibration frequencies of five-membered ring imides
are observed in the characteristic regions: two strong absorption
peaks at 1673–1653 cm1 for the non-bonded carbonyl and
1650–1629 cm1 for the ’chelated carbonyl’, and a medium absorption at 1779–1746 cm1 for the imine linkage. In the complexes,
the C = O stretching vibration are shifted to lower frequency
(about 33–77 cm1) compared to the free N-hydroxysuccinimide
ligand (1706 cm1). These changes, which are correlated with those
found for the uracil moiety,[29] could be ascribed to the delocalization of the anionic charge into the ring and carbonyl groups, thus
decreasing the C = O bond order (Scheme 2).
The disappearance of the stretching band (3431 cm1) for the OH
group in the free ligand suggests that deprotonation of the ligand
occurred. The P-O-C linkage stretching vibrations in the complexes
are shifted to lower frequency compared with the free triethylphosphite (1030 cm1) and trimethylphosphite (1012 cm1). It provides
good evidence that the occurrence of the organophosphine ligands
coordinated to silver ion.[30]
The NMR spectra (1H and 13 C{1H}) were recorded for all six complexes at room temperature. In 1H NMR spectra, the integration area
ratios are consistent with the stoichiometries of the complexes. The
chemical shift of -CH2- in C4H4NO3- appeared in the range of
2.3–2.7 ppm, which agrees well with a previous report.[22] The
aryl protons of complexes 2a–2b appeared in the range of
7.3–7.6 ppm. The complexes (2c–2f) are easily distinguished
because the resonances of the protons of organophosphite show
two groups (2c–2 d) and only one group (2e–2f), respectively. In
the 13 C{1H} NMR spectra, the chemical shifts of all carbonyls
appeared in the range of 175.3–176.5 ppm, which are similar to
those of other metal N-hydroxysuccinimide complexes.[31] The
triphenylphosphine carbon resonances of 2a–2b (128.7–133.9 ppm)
are easily distinguished from the resonance of -CH2- on C4H4NO3(25.0–25.1 ppm).
Figure 1. Molecular structure and atom numbering scheme for 2b.
forming a distorted tetrahedral geometry around silver.
The angles of P(2)–Ag(1)–O(1) (91.77 (6) ) and O(1)–Ag(1)–O(3)
(67.4 (8) ) are smaller than that of the ideal tetrahedron angle, while
the angles of P(1)–Ag(1)–P(2) (135.6 (3) ) and O(3)–Ag(1)–P(1)
(110.2 (6) ) are larger (Table 3).
Table 2. Selected bond lengths (Å) and bond angles ( ) for 2b
Single-crystal structure of 2b
Band lengths (Å)
A single crystal of [(Ph3P)2AgNC4H4O3CH3OH] (2b) could be
grown by slowly cooling a saturated methanol solution containing
2b to 20 C. The molecular structure of 2b is depicted in Fig. 1.
Selected bond distances (Å) and bond angles ( ) are given in
Table 2.
Complex 2b crystallizes in the monoclinic with space group
P21/c, which is composed of one molecule of [(Ph3P)2AgNC4H4O3]
and one molecule of methanol (Fig. 1). In the complex, a fourcoordinated silver(I) ion is presented with two PPh3 ligands
occupying two coordination sites (PP) and two oxygen atoms
of N-hydroxysuccinimide occupying the third and fourth sites,
Ag(1)–P(1)
Ag(1)–O(3)
O(1)–C(37)
O(2)–C(40)
N(1)–C(40)
C(39)–C(38)
P(1)–C(1)
P(1)–C(7)
P(2)–C(24)
Band angles ( )
O(3)–Ag(1)–P(1)
O(3)–Ag(1)–P(2)
P(1)–Ag(1)–P(2)
O(1)–Ag(1)–O(3)
P(1)–Ag(1)–O(1)
P(2)–Ag(1)–O(1)
C(1)–P(1)–Ag(1)
C(13)–P(1)–Ag(1)
C(7)–P(1)–Ag(1)
C(25)–P(2)–Ag(1)
C(24)–P(2)–Ag(1)
C(31)–P(2)–Ag(1)
70
Scheme 2. Delocalization of the anionic charge into the ring and carbonyl
groups.
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Copyright © 2012 John Wiley & Sons, Ltd.
2.410(9)
2.320(2)
1.231(4)
1.210(4)
1.383(4)
1.523(5)
1.814(4)
1.824(3)
1.828(3)
Ag(1)–P(2)
Ag(1)–O(1)
N(1)–O(3)
N(1)–C(37)
C(40)–C(39)
C(37)–C(38)
P(1)–C(13)
P(2)–C(25)
P(2)–C(31)
2.440(1)
2.686(3)
1.348(3)
1.364(4)
1.505(5)
1.507(5)
1.818(3)
1.822(3)
1.831(3)
110.2(6)
111.3(6)
135.6(3)
67.5(8)
118.5(6)
91.8(6)
112.1(1)
113.1(1)
117.8(1)
112.9(1)
112.9(1)
116.4(1)
N(1)–O(3)–Ag(1)
O(3)–N(1)–C(37)
O(3)–N(1)–C(40)
C(37)–N(1)–C(40)
O(2)–C(40)–N(1)
O(2)–C(40)–C(39)
N(1)–C(40)–C(39)
C(40)–C(39)–C(38)
C(37)–C(38)–C(39)
O(1)–C(37)–N(1)
O(1)–C(37)–C(38)
N(1)–C(37)–C(38)
109.3(2)
123.1(3)
122.9(3)
113.9(3)
124.3(3)
128.6(3)
107.1(3)
105.2(3)
104.2(3)
124.3(3)
127.2(3)
108.5(3)
Appl. Organometal. Chem. 2012, 26, 67–73
Silver(I) N-hydroxysuccinimide precursors
Table 3. Hydrogen bond geometry of metal-organic 2b (Å, )
Thermal analysis
D–HAa
D–H
HA
DA
D–HA
O(4)–H(4A)O(3)
C(6)–H(6)O(2)i
C(8)–H(8)O(4)i
C(14)–H(14)O(3)
C(20)–H(20)O(1)ii
C(28)–H(28)O(3)iii
0.82
0.93
0.93
0.93
0.93
0.93
1.97
2.59
2.56
2.48
2.53
2.48
2.791(4)
3.272(5)
3.185(4)
3.395(5)
3.415(4)
3.310(4)
178
130
125
167
159
149
Themogravimetry (TG) and differential scanning calorimetry
(DSC) studies are required to optimize the temperature at
which the respective silver precursor should be maintained
during the CVD experiments. For example, the TG and DSC curves
of complexes 2e and 2f are shown in Figs 2 and 3, respectively.
It can be seen from the DSC curve of 2e that there is one visible
endothermic process with a peak temperature at 73 C, which could
be attributed to the melting process of the complex. There is one apparent exothermic process from 116 C to 214 C, with the peak
temperature at 163 C. Seen from the TG curve of 2e, it is very
difficult to distinguish from one step to another and know the
sequence of decomposition of P(OMe)3 and N-acylhydroxylamine.
The final percentage of the residue is 35.01%, which is a little higher
than the theoretical value of silver (31.17%).
However, the decomposition of complex 2f takes place in one
consecutive endothermic process from 82 C to 473 C with the
peak temperatures at 158 C and 177 C. Firstly, it may illustrate
the dissociation of one P(OMe)3 ligand between 82 C and 177 C
with corresponding weight loss of about 26.52% which is close to
the theoretical loss (26.40%). Then, the weight loss between
177 C and 203 C is the result of the elimination of the second P
(OMe)3 ligand, with corresponding weight loss of about 26.85%. It
a
D = donor atom; A = acceptor atom.
Symmetry codes: (i) 1 + x, y, z; (ii) x, 1 y, 1 z; (iii) x, 1 y, z.
Appl. Organometal. Chem. 2012, 26, 67–73
Figure 2. TG and DSC curves of 2e (heating rate 10 C min1, N2).
Figure 3. TG and DSC curves of 2f (heating rate 10 C min1, N2).
Copyright © 2012 John Wiley & Sons, Ltd.
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71
The N-hydroxysuccinimide molecule [C(37)-C(38)-C(39)-C(40)N(1)-O(1)-O(2)-O(3)] is roughly planar, and the root-meansquares (RMS) deviation of the atoms from the best fit least
squares plane is 0.0488 Å. The O(2) atom is 0.0947 Å above the
N-hydroxysuccinimide plane, producing a slight distortion in
the ring. The dihedral angle between the N-hydroxysuccinimide
plane and the Ag(1)–O(1)–O(3) plane is 35.4 .
In complex 2b, the N-hydroxysuccinimide molecule can be functionalized as bidentate ligand, forming one short covalent and one
longer coordinative oxygen–silver bond. The Ag-O (N-hydroxyl
oxygen) distance for 2b is 2.320 (2) Å, while the Ag-O (carbonyl oxygen) distance is 2.686 (3) Å. It is different from the reported complex
(C6H5)4SbL (LH = N-hydroxy-demethyldehydrogencantharimide)[28]
and complex (nBu3P)AgX (X = N-hydroxyphthalimide anion),[31]
in which the carbonyl oxygen has no coordinating interactions
with silver.
The bonding in N-hydroxysuccinimide appears to be dominated
by resonance structure Ia, with structure IIa or IIIa accounting for
the partial double-bond character of the C-N bond and the planarity of the hydroxamic acid group (Scheme 2). The magnitude of the
difference between the two types of M-O bond lengths is considerably larger in complex 2b (Fig. 1) than in the chromic complex,[32]
which presents a pure octahedral symmetry to form the crystal field
effect. The difference between the two types of M-O bond lengths
shows that a greater portion of charge resides on the N-hydroxyl
oxygen atom than on the carbonyl oxygen atom. This large inequivalence in M-O bond lengths is explained by a higher charge density on the nitrogen oxygen, which requires a major contribution
from structure Ia.
An interstitial methanol solvent molecule is hydrogen bonded
to the oxygen atom of N-hydroxysuccinimide molecule and
weak C-HO interactions connect the molecules (Table 3).
Hydrogen bonds display an almost continuous distribution of
OO distance between 2.36 and 3.69 Å and have been subdivided into classes which are referred to us as ’very strong’
(<2.5 Å), ’strong’ (2.5–2.65 Å), ’medium’ (2.65–2.80 Å), or ’weak’
(>2.80 Å).[33] For complex 2b, the oxygen–oxygen distance is
2.791(4) Å and can be considered as ’medium’, which is also typical for Mn(III) compound {[Mn(C18H18N2O4)(CH3COO)]CH3OH}n
(do–o = 2.848 (2) Å).[34]
The Ag–P distances [2.410 (9), 2.440 (10) Å] are close to the
sum of covalent radio of P and Ag atoms (2.44 Å)[35] and shorter
than that of [(R3P)2AgPI] (PI = C8H4NO2) [2.4944(7) Å].[36] The
angles of P–Ag–P [135.6 (3) ] are much smaller than that of
[(Ph3P)2AgNC4H4O2] [145.4 (4) ],[24] but larger than that of
[(Ph3P)2AgPAZ] [130.88 (5) and 125.49 (8) ] (PAZ = C8H5N2O).[36]
X. Tao et al.
is very difficult to know the real thermal decomposition mechanism
of N-acylhydroxylamine from 203 C to 473 C. The final percentage
of the residue is 26.33%, which is a little higher than the theoretical
value of silver (22.94%).
On the basis of the thermal properties obtained from the TG
and DSC studies, we find that these complexes with a sharp
decomposition step may be promising precursors for the growth
of silver films. In addition, complex 2f, which is stabilized by two
P(OMe)3 ligands, is more stable towards air and moisture than
complex 2e. Thus we choose complex 2f as a potential MOCVD
precursor to grow silver films.
MOCVD depositions
Based on the TG studies (see above), complex 2f was applied as
MOCVD precursor for the deposition of silver on Si substrates. The
layer deposited is silver colored. The surface morphology and
composition of the silver film were characterized by SEM, AFM
and EDX analysis. SEM (Fig. 4) studies show that a dense and
homogeneous silver layer was formed. The film is composed of
many well-isolated, granular genuine pearls spreading all over the
substrate. The sizes of silver grains are in the range of 40–60 nm.
The surface roughness for blank Si substrate (Fig. 5a) and the
deposited film at 480 C (Fig. 5b) were measured using AFM. AFM
reveals that the substrate surface was covered with close-packed
silver clusters. It can be seen from Fig. 5(b) that the surface
roughness of the silver layer is about 34 nm. The EDX spectrum
(Fig. 4) of the deposited film shows that Ag is the main component.
Next to silver, silicon as substrate component was also detected,
which is due to the discontinuous Ag particles as well as the
relatively high penetration depth of the electron beam during
EDX analysis. Other light elements, such as C, O, P, which might
be present as impurities or due to a surface oxidation of silver,
are below the detection limit.
Figure 4. Scanning electron micrograph and EDX spectrum of silver film deposited from 2f (Ts = 480 C, Ptotal = 7.0 104 bar; carrier gas N2; flow
rate = 20 sccm).
72
Figure 5. Atomic force micrographs of (a) blank Si substrate and (b) silver film deposited at 480 C from 2f (Ts = 480 C, Ptotal = 7.0 104 bar; carrier gas
N2; flow rate = 20 sccm).
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Copyright © 2012 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2012, 26, 67–73
Silver(I) N-hydroxysuccinimide precursors
Conclusions
A straightforward synthesis methodology for preparation of
new silver(I) N-hydroxysuccinimide complexes of composition
[C4H4NO3AgLn] (L = PPh3, P(OEt)3, P(OMe)3; n = 1, 2) is described.
Complex 2b is a monomer with a four-coordinated silver atom. In
deposition experiments complex 2f was used as MOCVD precursor
to grow silver layers on Si substrates successfully. The result of
this deposition experiment shows that complex 2f is a promising
candidate for further MOCVD processing of silver nanoclusters or
silver films.
SUPPORTING INFORMATION
Supporting information can be found in the online version of this
article. CCDC-806044 (for complex 2b) 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.
Acknowledgments
This work was supported by the Natural Science Foundation of
Jiangsu Province (BK2007199), National Science and Technology
of Major Project (2009ZX02039-002); Funding of Jiangsu Innovation
Program for Graduate Education (CX10B_100Z), and Funding for
Outstanding Doctoral Dissertation in NUAA (BCXJ10-11) are also
acknowledged.
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