Tin(II) ketoacidoximates: Synthesis, X-ray structures and processing to tin(II) oxide

Article abstract of DOI:10.1039/c5dt03103f

Tin(ii) ketoacidoximates of the type [HONCRCOO]₂Sn (R = Me 1, CH₂Ph 2) and (MeONCMeCOO)₃Sn]^- NH₄⁺·2H₂O 3 were synthesized by reacting pyruvate- and hydroxyl- or methoxylamine RONH₂ (R = H, Me) with tin(ii) chloride dihydrate SnCl₂·2H₂O. The single crystal X-ray structure reveals that the geometry at the Sn atom is trigonal bipyramidal in 1, 2 and trigonal pyramidal in 3. Inter- or intramolecular hydrogen bonding is observed in 1-3. Thermogravimetric (TG) analysis shows that the decomposition of 1-3 to SnO occurs at ca. 160 °C. The evolved gas analysis during TG indicates complete loss of the oximato ligand in one step for 1 whereas a small organic residue is additionally removed at temperatures >400 °C for 2. Above 140 °C, [HONC(Me)COO]₂Sn (1) decomposes in air to spherical SnO particles of size 10-500 nm. Spin coating of 1 on Si or a glass substrate followed by heating at 200 °C results in a uniform film of SnO. The band gap of the produced SnO film and nanomaterial was determined by diffuse reflectance spectroscopy to be in the range of 3.0-3.3 eV. X-ray photoelectron spectroscopy indicates surface oxidation of the SnO film to SnO₂ in ambient atmosphere.

Full text of DOI:10.1039/c5dt03103f

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Tin(II) ketoacidoximates: synthesis, X-ray structures
and processing to tin(II) oxide†‡
Cite this: Dalton Trans., 2015, 44,
19820
Jayaprakash Khanderi, Bambar Davaasuren, Buthainah Ameen Alshankiti and
Alexander Rothenberger*
Tin(II) ketoacidoximates of the type [HONvCRCOO]
MeONvCMeCOO) ·2H O 3 were synthesized by reacting pyruvate- and hydroxyl- or
Sn]− NH +
methoxylamine RONH (R = H, Me) with tin(II) chloride dihydrate SnCl ·2H O. The single crystal X-ray
structure reveals that the geometry at the Sn atom is trigonal bipyramidal in 1, 2 and trigonal pyramidal in
. Inter- or intramolecular hydrogen bonding is observed in 1–3. Thermogravimetric (TG) analysis shows
2
Sn (R
=
2
Me 1, CH Ph 2) and
(
3
4
2
2
2
2
3
that the decomposition of 1–3 to SnO occurs at ca. 160 °C. The evolved gas analysis during TG indicates
complete loss of the oximato ligand in one step for 1 whereas a small organic residue is additionally
2
removed at temperatures >400 °C for 2. Above 140 °C, [HONvC(Me)COO] Sn (1) decomposes in air to
Received 11th August 2015,
Accepted 21st October 2015
spherical SnO particles of size 10–500 nm. Spin coating of 1 on Si or a glass substrate followed by heating
at 200 °C results in a uniform film of SnO. The band gap of the produced SnO film and nanomaterial was
determined by diffuse reflectance spectroscopy to be in the range of 3.0–3.3 eV. X-ray photoelectron
DOI: 10.1039/c5dt03103f
www.rsc.org/dalton
2
spectroscopy indicates surface oxidation of the SnO film to SnO in ambient atmosphere.
1
9,23–27
been investigated.
The recent literature reports a variety
Introduction
of physical methods such as e-beam evaporation, reactive/
Semiconducting stannic oxide (SnO ) and stannous oxide radio-frequency/magnetron sputtering and pulsed laser depo-
2
2
8–30
(
SnO) have attracted considerable research interest in the area sition to deposit p-type SnO thin films.
Chemical methods
of electronics and optoelectronics. SnO
in transparent conducting electrodes as indium tin oxide such as Sn O (OSiMe ) , [{Sn(OSiMe ) } ], Sn(II)bis(ureide)
2
has found application involve vapor phase deposition using molecular precursors
3
1
6
4
3 4
3 2 2
1
,2
3,4
5,6
t
32
(ITO),
thin film transistors,
sensors,
heat reflecting (ureide
=
BuNCONMe2),
bis(1-dimethylamino-2-methyl-
(ONep = OCH
7
7
33
34
filters and solar cells. Research on SnO is focused on the syn- 2propoxy)tin, [Sn(μ-ONep)
2
]
∞
2
CMe
3
)
and
8
–12
35
thesis of nanostructures
Li ion batteries.
to metallic tin, Sn
as anode materials in rechargeable solution based methods using SnCl ·2H O and NH3(aq.). The
Tin(II) oxide is also a versatile intermediate formation of elemental tin in SnO films
2
2
1
3,14
31,34
and sub-stoichio-
1
5
16,17
18
34
3
O
4
and SnO
2
−1
.
SnO thin films have metric tin oxide at higher deposition temperatures (>300 °C)
shown a hole mobility of 2.4 cm V s−1, the largest among is the drawback of reported routes.
2
31,34,35
The challenge in
the p-type oxide semiconductors. Antimony doped SnO the preparation of SnO films is to find a low-temperature
1
9
2
0
shows n-type conduction, opening the possibility of ambi- route to crystalline SnO, avoiding disproportionation or
polar oxide TFTs. Homo-junction p–n diodes with p-type oxidation to SnO2 and the scale-up of optimized SnO film
SnO and n-type SnO2 thin film transistors and inverters have deposition.
Metal complexes with oxime/oximate ligands have been
2
1
2
2
19,22,32,36,37
3
8,39
extensively studied and reviewed.
One important aspect of
Physical Sciences and Engineering Division, 4700 King Abdullah University of Science oximate ligands, derived from the reaction of pyruvic or
&
Technology (KAUST), Thuwal, 23955-6900, Kingdom of Saudi Arabia.
glyoxylic acid with hydroxylamines, is the complete decompo-
sition to H O, CO , CH CN and functionalized nitriles below
E-mail: alexander.rothenberger@kaust.edu.sa; Fax: +966 12 8021258;
2
0,41
2
3
Tel: +966 12 808 0745
4
200 °C.
Thus, it is of interest to examine oximate com-
†
‡
In memory of Professor Ken Wade.
Electronic supplementary information (ESI) available: IR, gas phase IR, mass of plexes of tin(II) that could address the challenges associated
decomposition products, and UV-Vis spectrum of SnO thin films. Details of with SnO formation at lower temperatures.
atomic coordinates, anisotropic atomic displacement parameters, bond lengths
Cyanoximate and ketoacidoximate complexes of Sn(IV) have
and angles for the reported complexes, XRD and SEM of decomposition product
of 2, XPS, and I–V characteristics of the film. CCDC 1048727–1048729. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c5dt03103f
42,43
been reported.
The Sn(IV) in cyanoximate complexes,
which also show cytotoxicity, are mononuclear and tetra-
4
2
nuclear with a trigonal pyramidal geometry, whereas Sn(IV)
19820 | Dalton Trans., 2015, 44, 19820–19828
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ketoacidoximates are reported to be monomeric with Sn(IV) in
4
3
octahedral and trigonal bipyramidal geometries. The other
reported complexes contain ketoacidoximate ligands with Pd,
4
4,45
46
47
48
49,50
44,51,52
53
50
Ru, Rh, Ir,
Mn, Ti, Ni, Cu,
Co,
Zn, Cd,
5
4
55
alkali, and alkaline earth metal ions. The interest in these
complexes was due to the fact that: (1) they act as an inter-
4
5
mediate in the metal activated synthesis of α-amino acids,
2) the oximate ligands are structurally analogous to 2-amino
acids and the complexes have shown medical and biological
(
4
6,52,56
functions
and (3) they are used in the synthesis of
5
7
57–61
53,61
metal and metal oxide
nanoparticles and thin films.
Here, we report the synthesis and crystal structures of tin(II)
ketoacidoximate complexes 1–3, experimental conditions for
the synthesis and detailed characterization of SnO nano-
particles and thin films obtained by the decomposition of
1
and 2.
Results and discussion
Tin(II) ketoacidoximate complexes 1–3 were synthesized by the
condensation reaction of α-ketocarboxylate and hydroxyl- or
methoxyl amine with tin(II) chloride dihydrate in water
(Scheme 1). 1 and 2 are isolated as crystalline solids in good
yield (67–78%) whereas 3 was isolated in poor yield (∼10%).
All the complexes are soluble in N,N-dimethyl formamide and
dimethyl sulfoxide and sparingly soluble in methanol and
ethanol. The IR spectra of 1–3 show characteristic absorptions
−
1
between 1650 and 550 cm (ESI Fig. S1‡). The absorption
−
1
−1
bands at 1620 cm (CvN), 1590 cm (asymmetric vibrations
−
51
−1
−1
of COO ), 1350 cm (–CvO symmetric or CH ), 1050 cm
3
1
43
(
N–O), and 850 cm− (–OCO– in plane) could be assigned
unambiguously. The appearance of ν(sym) and ν(asym) COO
bands indicates possible π-delocalization of the C–O bond.
−
1
The absorption bands at 3280–3290 cm
for 3 could be
assigned to NH stretching vibrations of the ammonium ion.
The NMR chemical shifts observed for 1, 2 and 3 are in
agreement with the previously reported transition metal
51,53
complexes.
Description of the molecular structures of 1–3
The crystal structures of 1, 2 and 3 were determined from
Fig. 1 Solid state structure of (a) 1, (b) 2 and (c) anionic part of 3; H atoms
single crystal X-ray diffraction data. Fig. 1a–c show the mole- on C, and the solvate molecules of 3 were omitted for clarity; thermal ellip-
cular geometry, bonding and atom labelling of 1, 2 and 3. The soids are drawn at the 50% probability level. Selected bond lengths [Å] and
angles [°]: 1 Sn(1)–O(1) 2.1776(18), Sn(1)–O(4) 2.2038(18), Sn(1)–N(1)
details of data collection and refinement are summarized
in Table 1.
2.508(2), Sn(1)–N(2) 2.526(2), O(1)–Sn(1)–O(4) 85.90(7), O(1)–Sn(1)–N(1)
6
7.29(7), O(4)–Sn(1)–N(1) 83.38(8), O(1)–Sn(1)–N(2) 83.17(7), O(4)–
Sn(1)–N(2) 66.86(8), N(1)–Sn(1)–N(2) 139.50(8), 2 Sn(1)–O(1) 2.167(5),
Sn(1)–O(4) 2.175(6), Sn(1)–N(1) 2.487(8), Sn(1)–N(2) 2.391(8), O(4)–
Sn(01)–N(1) 67.7(2), O(1)–Sn(1)–O(4) 86.2(3), N(2)–Sn(01)–N(1) 132.9(3),
O(1)–Sn(1)–N(2) 70.0(3), O(4)–Sn(1)–N(2) 74.8(2), O(1)–Sn(1)–N(1)
79.9(3),
3 Sn(1)–O(5) 2.1782(12), Sn(1)–O(1) 2.1792(12), Sn(1)–O(4)
2.1988(12), O(5)–Sn(1)–O(1) 82.45(4), O(5)–Sn(1)–O(4) 77.36(4), O(1)–
Sn(1)–O(4) 81.55(4), C(1)–O(1)–Sn(1) 133.15(9), C(6)–O(4)–Sn(1)113.13(8),
C(8)–O(5)–Sn(1) 112.68(10).
2
Scheme 1 Synthesis of Sn(II) ketoacidoximates, where R = Me 1, CH Ph 2.
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Table 1 Details of the X-ray data collection and refinement for 1, 2
and 3
The first structural difference between 1, 2 and the pre-
viously reported Ni(II), Co(III), Zn(II), Cu(II) and Cd(II) complexes
is the long Sn–N bond distance. This bond length ranges
between 2.391(2) and 2.526(8) Å for 1 and 2 while it is 2.111(1),
Compound
12 16 4 2 16 2 6 12 26 4
C H N O12Sn (1) C18H N O Sn (2) C H N O11Sn (3)
Formula weight 645.68
475.05
Orthorhombic
521.06
Monoclinic
C2/c
1.875(1), 2.334(2), 2.049(2), and 2.461(15) Å for Ni–N, Co–N,
Crystal system
Space group
Triclinic
Pˉ1
48,51,53
Zn–N, Cu–N, and Cd–N respectively.
The long metal–N
P2
1 1 1
2 2
Formula unit, Z
Radiation, λ/Å
Monochromator Graphite
Temperature/K 150(2)
2
4
8
bond distance is also observed in the sodium oximate
Mo Kα, 0.71073
54
complex. The other interatomic distances in both 1 and 2 are
4
5,67,68
in the same range as that found in the literature.
The
a/Å
b/Å
c/Å
α/°
β/°
γ/°
9.3126(6)
11.0220(6)
11.5938(6)
113.644(4)
108.010(4)
93.80
1011.7(4)
2.120
2.538
12.039(5)
12.259(5)
12.506(5)
90
90
90
1845.7(13)
1.709
1.422
944
58.54
17.653(4)
14.077(3)
18.854(4)
90
117.11(3)
90
4170.6(18)
1.660
1.285
2112
58.44
10 110
−24 < h < 22
−16 < k < 19
−25 < l < 23
5478, 349
second difference is the O–Sn–N bite angle of the ligand to the
metal ion. The bite angles in 1 are 67.29°(7) and 66.86°(8) and
4
9
are 70.0°(8) and 67.7°(2) in 2. In the similar Cu(II) complex it
53
is 80.69(6)° and it decreases in Zn(II) to 77.69(1)° and in
3
50
V/Å
Cd(II) to 67.88(5)° and 65.77(5)°. The smaller bite angle of
−
3
ρcalc./g cm
−1
the ligand in 1 and 2 as well as in the Cd(II) complex is related
to the larger ionic radii of Sn(II) and Cd(II) ions.
The Sn atom, in the crystal structure of 3, is coordinated
by three monodentate 2-methoxyiminopropionato-ligands
μ/mm
F(000)
θ max./°
624
59.32
2
No. ref., I > 2σ(I) 9854
hkl range
17 869
−12 < h < 12
−16 < h < 16
−14 < k < 16
−17 < l < 17
4985, 241
−
15 < k < 15
15 < l < 13
forming a perfect trigonal bipyramidal geometry with the τ-
−
63,69
value of unity.
The three-fold coordination of the Sn(II) ion
Unique ref.,
parameters
5018, 281
−
by COO groups results in the accumulation of negative charge
on the Sn atom, which is balanced by NH
R
R
int
a
0.018
0.020
0.054
1.089
0.129
0.054
0.075
1.072
0.064
0.047
0.118
0.999
+
4
counter ions. The
1
b
wR
2
H O molecules form H-bonds with oxygen atoms of the car-
2
c
GooF
boxyl groups (ESI Fig. S2‡). The Sn–O distances d(2.178(2)–
Max./min.
0.67/−0.52
0.70/−0.75
0.69/−0.71
Δρ/e Å−
3
2.199(1)Å) are in good agreement with the distances reported
6
9
in the literature. Similar to 1 and 2, short C–O distances,
d(C3–O5) = 1.237(6)Å and d(C3–O4) = 1.287(6)Å, are found in
the carboxylic group of the 2-methoxyiminopropionato-
ligands. However, the Sn1⋯N3 distance is 2.862(1)Å, longest
among reported oximato-complexes. The atomic coordinates,
a
b
2
2 2
4
1/2
R
1
= ∑||F
o
2
| − |F
)
c
||/∑|F
o
|. wR
2
= {∑[w(|F
o
|
− |F
c
| ) ]/∑[w(|F
o
| )]} and w
2
2
2
2
c
=
1/[σ (F
hklw(|F
o
+
(nP)
+
mP] where
|) /(ndata − nvar)]
P
=
(F
o
c
+ 2F )/3. GooF =
2
1/2
[
∑
o
| − |F
c
.
The crystal structure of 1 and 2 contains two bidentate interatomic distances and angles are listed in Tables S9–S12
-oxyiminopropionato anions, which are bonded to the Sn (ESI‡). The interatomic distances in this structure are close to
2
core through the oxime nitrogen atom and one of the car- the distances found in similar tin coordination complexes and
4
5,67,68
boxylic oxygen atoms forming a trans complex with a butterfly tin oxides.
configuration (Fig. 1a and b). The Sn(II) atom lies on an inver-
Thermal decomposition of 1, 2 and 3
sion centre. A distorted trigonal bipyramidal geometry around
the Sn atom is enforced by the stereochemically active lone Thermal behaviours of 1–3 were studied under nitrogen and
6
2
pair on the tin(II) atom in 1 and 2, as observed previously
air atmospheres by thermogravimetry, TG coupled IR and
and confirmed by a τ-test. The Sn–O distances of 2.178(2)– mass spectrometry. Fig. 2a is the TG curve for 1 under N . The
6
3
2
2
2
.204(2) Å in 1, 2.167(5)–2.175(6) Å in 2 and Sn–N distances decomposition is not affected by the reaction atmosphere (air
.508(2)–2.526(2) Å in 1, 2.487(8)–2.391(8) Å in 2 are similar or nitrogen) and takes place between 155 and 160 °C. The
3
1
t
32
to those observed in Sn (O) (OSiMe ) , [ BuNCONMe ] Sn
2
residual mass observed in N (36.9%) and air (43.4%) agrees
6
4
3 4
2 2
as well as Sn(II) complexes containing poly-functional well with the theoretical value for the formation of SnO
6
4–66
ligands.
bonding exists between –NOH and COO groups in both the This is supported by the Gram–Schmid curve showing one
molecules.
maximum for the IR signal, indicating simultaneous removal
Extensive donor type intermolecular hydrogen (41.5%) for 1, implying complete decomposition of the ligand.
Short C–O bonding distances of d(C1–O1) = 1.272(3) Å and of all gaseous fragments (ESI Fig. S3‡). The IR spectra and
d(C1–O2) = 1.240(3) Å (1) and d(C1–O4) = 1.2774(4) Å and d mass spectrometry of the gases evolved during the decompo-
(
C1–O6) = 1.2379(5) Å (2) in carboxylic groups suggest π-de- sition of 1 could be assigned to water, CO, CO , and aceto-
2
localization, which is probably caused by H-bonding and nitrile (ESI Fig. S4 and S5‡). The fragments observed in the
intermolecular Sn←O dative interactions. A similar π-de- TG-MS of 2 are H O, CO, CH CN, CO benzene, toluene and
2
3
2
localization of the C–O bond is also observed in Co(III), Ni(II) benzyl cyanide (Fig. 2b: only the fragments with higher m/z are
4
8,51,53
and Zn(II) 2-oxyiminopropionate complexes.
The atomic shown). Decomposition of similar Zn and alkali metal com-
coordinates, anisotropic atomic displacement parameters, plexes indicates a second order Beckmann rearrangement with
bond lengths and angles are listed in Tables S1–S8 (ESI‡) elimination of CH CN, H O and CO . The metal complex with
3
2
2
respectively.
a monoalkylcarbonate ligand is suggested as the intermediate,
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Fig. 2 (a) The TG for decomposition of bis(2-(hydroxyimino)propionato) tin(II) 1 measured by heating at 10 °C min− in a nitrogen flow of 20 mL
1
min . (b) TG and TG-MS of bis[2-(hydroxyimino)3-phenyl-propionato] tin(II) 2 measured by heating at 5 °C min−1 in a helium flow of 20 mL min
−
1
−1
.
The ion current signals are smoothened and normalized. (c) XRD and (d) Raman spectra of SnO powder and films formed by the decomposition of
bis(2-(hydroxyimino)propionato) tin(II) 1 at 200 °C.
4
1,54
which finally forms the metal oxide.
A similar decompo- higher temperature, attributed to the removal of surface
sition pathway could be responsible for the formation of SnO organic carbon.
from 1 and 2 (Scheme 2).
Tin(II) oxide synthesis
The CHN analysis of the residue obtained after heating of 1
in air shows the average carbon of 1.65% for decomposition SnO was synthesized by decomposing 1 and 2, whereas 3 has
temperatures between 140 and 180 °C whereas a carbon value not been used for the decomposition study due to its low yield
of 0.86% for the temperature of 200 °C (ESI, Table 13‡). during synthesis.
Carbon contents of <1% have been reported for ZnO films
from similar Zn oximate complexes at 150 °C and these have from 140 to 200 °C for one hour in air. SnO formation is
SnO powder formation from 1 and 2. 1 and 2 are heated
7
0
been used for FET devices. The decomposition of 2 and 3 in observed at 140 °C itself for 1 (Fig. 2c). The crystallinity of the
nitrogen follows the same trend as that of complex 1 (ESI formed SnO is independent of the decomposition temperature
Fig. S6‡). In air, 2 and 3 undergo additional weight loss at (140–200 °C). Amorphous SnO was obtained from 2 even at
200 °C (ESI Fig. S7‡). The formation of amorphous SnO from 2
could be attributed to incomplete removal of the benzene frag-
ment during the decomposition at 163 °C. This is supported
by the appearance of signals for benzene (m/z 78) and toluene
(
2
m/z 92) fragments above 400 °C during the decomposition of
(Fig. 2b). Hence, 1 was chosen for making nanoparticles and
thin films of SnO. The average crystallite size of SnO from 1 is
in the range of 47–50 nm for temperatures between 140 and
2
00 °C, determined by using the Scherrer equation. Raman
Scheme 2 Proposed decomposition of 1 and 2 based on TG-IR and
TG-MS measurements.
−
1
spectra of SnO from 1 recorded from 100 to 500 cm show
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Fig. 3 (a) SEM and (b) TEM images of SnO from the decomposition of 1
at 200 °C. Spherical particles observed at 200 °C and composed of
smaller particles of 10 nm grouped together as well as forming hollow
spheres. Inset: atomic fringes of the 101 plane of SnO.
Fig. 4 SEM micrograph of SnO films (a) after one layer and (b) after
16 layers, formed by spin-coating and decomposition of 1 at 200 °C.
The 16 layer spin coated sample shows a film thickness of
68 nm. Thus, the average thickness per layer is estimated to
be 16–20 nm on the silicon substrate. Comparison of the mor-
2
−
1
two vibrational absorptions at 109 and 209 cm
corres-
3
2
ponding to characteristic B1g and A1g modes of SnO (Fig. 2d).
The similarity of the Raman spectra for both 140 °C and
phology of SnO thin films from reported metalorganic precur-
31,32,34
sors
showed platelets and cubes with several grain
2
00 °C shows a similar decomposition at these temperatures
boundaries, whereas with 1, smooth films could be obtained
over a larger area.
(ESI Fig. S8‡).
Scanning and transmission electron microscopy images of
UV-Vis spectra of the SnO film recorded in the diffuse
SnO particles formed at 200 °C are shown in Fig. 3a and b
respectively. At 200 °C SnO particles appear spherical in shape
and have rough surface morphology. The particle size is
between 50 and 250 nm. At 140 °C they are lumped together,
with fewer non-agglomerated particles. The particle size is
between 100 and 150 nm at 140 °C (ESI Fig. S9‡). Trans-
mission electron microscopy images (Fig. 3b) of the SnO par-
ticles at 200 °C indicate the presence of hollow and dense SnO
particles. The high resolution TEM image (inset: Fig. 3b)
shows lattice fringes of 0.30 nm spacing corresponding to the
reflection setup show a band gap in the range of 3.0–3.3 eV
72
(
ESI Fig. S11‡) and are comparable to the reported data.
X-ray photoelectron spectroscopy (XPS) spectra for the samples
spin coated with 10 layers of SnO are shown in Fig. S12a–c
(
ESI‡). The XPS survey spectrum of the SnO layer indicates
incorporation of carbon and a small amount of nitrogen (ESI,
Fig. S13 and S14‡). The occlusion of these elements could be
due to the residual solvent remaining or the incomplete
removal of the decomposition product of 1 during several
heating cycles. The binding energies of 487.0 and 495.4 eV can
(101) plane of SnO.
28
be assigned to Sn 3d5/2 and 3d3/2 electrons of tin (Fig. S12a,
Comparison of spherical SnO particles from 1 with those
ESI‡). The O1s spectral line shows binding energies of 530.8
eV and 532.4 eV. The binding energy of 530.8 eV can be corre-
lated to lattice oxygen in the tin oxide film and 532.4 eV for
6 4 4
prepared by the aqueous route using Sn O (OH) derived from
9
,11,71
tin halides and amides
bothermal reaction of SnO
or by vapour deposition and car-
reveals various hierarchical mor-
8
,12
73
adsorbed OH on the surface (Fig. S12b, ESI‡). The valence
phologies such as nanoribbons, nanobelts, dendrimers and
meshes. In addition, some level of control on the oxidation
state in the final tin oxide has been achieved through the use
of well-defined Sn(II) centred precursors. However, rapid pre-
cipitation in the aqueous route and formation of sub-stoichio-
metric tin oxide in vapour based methods are not suitable for
thin film preparation. The tin oximate thus provides process
flexibility for thin film preparation.
band spectral peaks at 9 eV and below 2 eV (ref. 32 and 74)
due to the formation of antibonding and bonding Sn(II) 5s–O
2p states were not observed, indicating that the surface of the
SnO film from 1 has oxidised to Sn(IV) (Fig. S12c, ESI‡). Thus it
can be concluded that the SnO film reacts with adsorbed/
atmospheric oxygen to convert to SnO as observed in the XPS
2
analysis. A similar surface oxidation was observed for the SnO
film deposited from Sn(II) bis(ureide) during its exposure to an
3
2
ambient atmosphere.
To understand the oxidation of the deposited SnO thin
SnO thin films from 1
Thin films of SnO are prepared by spin-coating a saturated film, a drop-cast film from 1 in DMF solution on the Si sub-
solution of 1 in methanol or an ethylene glycol/methanol strate is analysed by IR before heating and by Raman spec-
mixture (1 : 9 v/v). The SEM micrograph of the single and 16 troscopy after heating to 200 °C. IR spectra of the precursor
layers of SnO films on the Si substrate, from an ethylene film on Si and 1 as powder show the same absorption bands
glycol/methanol mixture, after heating the substrate to 200 °C (ESI, Fig. S15‡), indicating that 1 remains in the Sn(II) state on
is shown in Fig. 4a and b respectively. The energy-dispersive the substrate. Raman spectra of the SnO film formed after
X-ray spectroscopy (EDX) analysis confirmed the presence of heating to 200 °C show both the characteristic B1g and A1g
tin in the film for single layer SnO deposition (ESI Fig. S10‡). vibrational modes (Fig. 2d), in agreement with the SnO powder
19824 | Dalton Trans., 2015, 44, 19820–19828
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produced from 1 at 200 °C. This result clearly indicates that in situ generation of the α-ketoacid oxime ligand in water
the observed Sn(IV) state in the XPS analysis is due to the was carried out according to the procedure described by
4
0
surface oxidation.
Spenser et al.
Synthesis of bis[2-(hydroxyimino)propionato] tin(II) (1).
The SnO thin films formed from the reported metalorganic
precursor e.g. Sn O (OSiMe ) , [{Sn(OSiMe3)2}2], Sn(II)bis- Ammonium bicarbonate (9.49 g, 120 mmol) was added
6
4
3 4
t
(
ureide) (ureide = BuNCONMe
2
), and [Sn(μ-ONep)
2 ∞
] (ONep = portionwise to a stirred solution of hydroxylamine hydro-
3
1,32,34
2 3
OCH CMe )
indicate stringent control of the oxygen chloride (4.17 g, 60 mmol) and pyruvic acid (5.28 g, 60 mmol)
environment, higher deposition temperature (>300 °C) and for- in water (50 mL) at room temperature and the mixture was
mation of metallic Sn along with the desired tin(II) oxide stirred until all gas evolution had ceased. SnCl ·2H O (6.77 g,
2
2
phase. The air/moisture sensitivity of these precursors and the 30 mmol) was then added, and the mixture was stirred for 4 h,
disproportionation of SnO to Sn and SnO at higher tempera- after which a white powder of 1 was filtered off and washed
2
ture make the process complicated. The air/moisture stability, with ice cold water. The single crystals were obtained from
low decomposition temperature and solubility of 1 in common concentrated ethanol solution of the compound at −35 °C.
organic solvents make it suitable for large area processing Yield (6.5 g, 67%), mp 161 °C (TG) (decomp.), Found: C, 22.3;
such as spin coating and printing.
6 8 2 6
H, 2.5; N, 8.6, Calc. for C H N O Sn: C, 22.3; H, 2.5; N, 8.7%,
−
1
Thin films of SnO of thickness 30–50 nm and 300–400 nm IR (νmax/cm ) ATR, powder: 3170 (w), 3050 (w), 2797 (w),
were prepared on the interdigitated substrate at 200 °C. The 2725 (w), 1584 (s), 1487 (ms), 1366 (s), 1345 (s), 1195 (s), 1049 (s),
1
I–V characteristics of these films in the forward bias indicate the 851(s), 759 (ms), 732 (s), H NMR (400 MHz;(CD
3
)
2
SO, 25 °C),
SO,
1
3
semiconducting properties of the film (ESI Fig. S16 and S17‡) δ: 1.95 (s, 6H, CH
3
–CvN), C NMR (100 MHz; (CD
3
)
2
with a breakdown voltage of 8.9 V in the forward bias. Further 25 °C) δ: 11.5 (CH –CvN), 151.1 (CvN ), 167.2 (CvO).
3
studies to understand the thin film behaviour for transistor
applications are currently underway.
Synthesis of bis[2-(hydroxyimino)3-phenyl-propionato] tin(II)
(2). Ammonium bicarbonate (0.395 g, 5 mmol) was added
portionwise to a solution of hydroxylamine hydrochloride
(
0.347 g, 5 mmol) in 10 mL water and the mixture was stirred
Conclusions
until all gas evolution had ceased. To the above solution
sodium phenyl pyruvate (0.931 g, 5 mmol) in water (10 mL)
was added at room temperature. The reaction was allowed to
continue for 2 h. To the above mixture SnCl
2
4
washed with ice cold water. The single crystals were obtained
from concentrated methanol solution by the slow evaporation
method. Yield (1 g, 78%), mp 163 °C (TG) (decomp.), Found
Tin(II) ketoacidoximate complexes were successfully syn-
thesized and characterized. The Sn atom is four-fold co-
ordinated and is donor stabilised by the oxime nitrogen of the
ligand in all the complexes. The bis[2-(hydroxyimino)propio-
nato] tin(II) decomposes above 140 °C in both air and nitrogen
with complete elimination of the ligand to form SnO. The SnO
particles of average size 50 nm were synthesized below 200 °C
by heating 1. SnO thin films of 16–20 nm thickness were pre-
pared by spin-coating. The films slowly convert to Sn(IV) oxide
at the surface on exposure to air. The bulk of the films remain
in the Sn(II) state. The ambient atmosphere synthesis and pro-
cessing make Sn(II) oximate attractive for solution processable
applications.
2
·2H
.5 mmol) was then added, and the mixture was stirred for
h, after which a creamy yellow powder 2 was filtered off and
2
O (0.564 g,
C, 44.1; H, 3.4; N, 6.1, Calc. for C18
H
16
N
2
O
6
Sn: C, 45.5; H, 3.4;
N, 5.9%, IR (νmax/cm ), ATR, powder: 3175 (w), 3062 (w), 2846
w), 1600 (s), 1493 (m), 1453 (w), 1426 (w), 1373 (ms), 1337 (w),
−
1
(
1
298 (w), 1230 (ms), 1158 (ms), 1137 (ms), 1055 (s), 1026 (s),
31 (w), 862 (s), 774 (ms), 754 (m), 715 (s), 695 (s), 552 (w),
9
1
H NMR (400 MHz; (CD
.24 (s, 10H, Ph) 12.4 (s, 2H, –N–OH), C NMR (100 MHz;
CD ) SO, 25 °C) δ: 30.7(–CH ), 126.6 (Ph), 128.7 (Ph), 129.2
3 2 2
) SO, 25 °C), δ: 3.83 (s, 4H, –CH –Ph),
1
3
7
(
(
3
2
2
Experimental section
Reagents and general procedures
Ph), 137.1(Ph) 152.2 (CvN), 167.1 (CvO).
Synthesis of diaqua tris[2-(methoxyimino)propionato]
All the syntheses were performed under an ambient atmos- tin(II) ammonium salt (3). Ammonium bicarbonate (9.49 g,
phere and with deionized water. SnCl ·2H O (98%, Alfa Aesar), 120 mmol) was added portionwise to a stirred solution of
2
2
pyruvic acid (98%, Alfa Aesar), sodium phenyl pyruvate (98%, methoxylamine hydrochloride (5.01 g, 60 mmol) and pyruvic
Sigma-Aldrich), hydroxylamine hydrochloride (99%, Sigma- acid (5.28 g, 60 mmol) in water (30 mL) at room temperature,
Aldrich), methoxylamine hydrochloride (98%, Sigma-Aldrich), and the mixture was stirred until all gas evolution had ceased
ammonium bicarbonate (≥99%, Sigma-Aldrich), methanol, and was stirred further for 3 h. SnCl ·2H O (6.77 g, 30 mmol)
2 2
ethanol and N,N-dimethylformamide of HPLC grade were used was then added; at the start, the reaction is slow. As time pro-
as-received. The melting point/decomposition of 1–3 were gresses a white precipitate is seen. The precipitate is dissolved
determined from the DTA (ESI Fig. S18‡).
in ethanol, reduced in volume and kept at −35 °C for recrystal-
lization. Yield (0.8 g, 10%), mp 151 °C (TG) (decomp.), Found
Precursor synthesis
26 4
C: 27.9, H: 4.2, N: 10.3, Calc. for C12H N O11Sn: Calc. C: 27.7,
−1
Syntheses of Sn ketoacidoximato complexes were performed by H: 5.0, N: 10.8%. IR (νmax/cm ), ATR, powder: 3284 (w),
5
3,57,60
an adaptation of a method described previously.
The 3144 (w), 3052 (w), 2988 (w), 2943 (w), 2827 (w) 1649 (ms),
This journal is © The Royal Society of Chemistry 2015
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1
1
7
633 (s), 1593(s), 1536 (m), 1442 (m), 1418 (ms), 1371 (w), of the lattice parameters as well as for data reduction
349 (s), 1204(s), 1172 (s), 1043, (s) 927 (ms), 855 (s), 768 (m), including LP correction, the STOE X-Area software package
7
5
1
23 (s), 579(m), H NMR (400 MHz; (CD
), 3.93 (s, 9H, N–OCH
100 MHz; (CD ) SO, 25 °C) δ: 12.3(NvC–CH ), 62.4(N–OCH ), The crystal structure was solved by direct methods and refined
3 2
) SO, 25 °C), was used. The intensity data were corrected for absorption
1
3
76
δ: 1.91 (s, 9H, NvC–CH
(
1
3
3
), C NMR numerically using the crystal habit and the program X-Shape.
3
2
3
3
7
7
52.7 (CvN), 168.0 (CvO).
using the program packages SHELXS97 and SHELXL97.
Synthesis of SnO
Heating 1. 150 mg of complex 1 is heated in a nickel
crucible to 140–200 °C in air for one hour in a general purpose
laboratory furnace. 52 mg (83 % yield based on Sn supplied in
Acknowledgements
This work was supported by the King Abdullah University of
Science & Technology (KAUST) baseline (BAS/1/1302-01-01)
and AEA funding. J. K. thanks Dr Rachid Sougrat and Ms Nini
Wei for TEM imaging and Dr Mohamed Nejib Hedhili for XPS
analysis.
1
50 mg of complex 1).
Thin film deposition – spin coating. A saturated solution of
in methanol or ethylene glycol mixture (9 : 1) is used to spin-
1
coat a thin layer of precursor on the Si substrate. A filtered,
0 μL of the solution is dropped on the substrate with the
5
coating programme of 1000 rpm/30 seconds/5000 rpm/20
seconds. The relative humidity during spin coating was
between 57 and 60%.
Thin film deposition – drop casting. 100 μL of a saturated
solution of 1 in DMF is drop-cast on the Si substrate. The
solvent is allowed to evaporate in a well-ventilated chemical
hood.
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