Aerosol-Assisted Chemical Vapor Deposition of ZnS from Thioureide Single Source Precursors

Article abstract of DOI:10.1021/acs.inorgchem.8b03363

A family of 12 zinc(II) thoureide complexes, of the general form [{L}ZnMe], [{L}Zn{N(SiMe₃)₂}], and [{L}₂Zn], have been synthesized by direct reaction of the thiourea pro-ligands ⁱPrN(H)CS(NMe₂) H[L¹], CyN(H)CS(NMe₂) H[L³], ^tBuN(H)CS(NMe₂) H[L²], and MesN(H)CS(NMe₂) H[L⁴] with either ZnMe₂ (1:1) or Zn{N(SiMe₃)₂}₂ (1:1 and 2:1) and characterized by elemental analysis, NMR spectroscopy, and thermogravimetric analysis (TGA). The molecular structures of complexes [{L¹}ZnMe]₂ (1), [{L²}ZnMe]₂] (2), [{L³}ZnMe]_a? (3), [{L⁴}ZnMe]₂] (4), [{L¹}Zn{N(SiMe₃)₂}]₂ (5), [{L²}Zn{N(SiMe₃)₂}]₂ (6), [{L³}Zn{N(SiMe₃)₂}]₂] (7), [{L⁴}Zn{N(SiMe₃)₂}]₂] (8), [{L¹}₂Zn]₂ (9), and [{L⁴}₂Zn]₂ (12) have been unambiguously determined using single crystal X-ray diffraction studies. Thermogravimetric analysis has been used to assess the viability of complexes 1-12 as single source precursors for the formation of ZnS. On the basis of TGA data compound 9 was investigated for its utility as a single source precursor to deposit ZnS films on silica-coated glass and crystalline silicon substrates at 150, 200, 250, and 300 °C using an aerosol assisted chemical vapor deposition (AACVD) method. The resultant films were confirmed to be hexagonal-ZnS by Raman spectroscopy and PXRD, and the surface morphologies were examined by SEM and AFM analysis. Thin films deposited from (9) at 250 and 300 °C were found to be comprised of more densely packed and more highly crystalline ZnS than films deposited at lower temperatures. The electronic properties of the ZnS thin films were deduced by UV-Vis spectroscopy to be very similar and displayed absorption behavior and band gap (E_g = 3.711-3.772 eV) values between those expected for bulk cubic-ZnS (E_g = 3.54 eV) and hexagonal-ZnS (E_g = 3.91 eV).

Full text of DOI:10.1021/acs.inorgchem.8b03363

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Aerosol-Assisted Chemical Vapor Deposition of ZnS from Thioureide
Single Source Precursors
†
†
†
‡
†
̈
Hannah S. I. Sullivan, James D. Parish, Prem Thongchai, Gabriele Kociok-Kohn, Michael S. Hill,
and Andrew L. Johnson*,†
†Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
‡Materials and Chemical Characterisation Facility (MC2), Department of Chemistry, University of Bath. Claverton Down, Bath,
BA2 7AY, U.K.
S
* Supporting Information
ABSTRACT: A family of 12 zinc(II) thoureide complexes, of the general form [{L}ZnMe], [{L}Zn{N(SiMe3)2}], and
[{L}2Zn], have been synthesized by direct reaction of the thiourea pro-ligands iPrN(H)CS(NMe2) H[L1], CyN(H)CS(NMe2)
t
H[L3], BuN(H)CS(NMe2) H[L2], and MesN(H)CS(NMe2) H[L4] with either ZnMe2 (1:1) or Zn{N(SiMe3)2}2 (1:1 and
2:1) and characterized by elemental analysis, NMR spectroscopy, and thermogravimetric analysis (TGA). The molecular
structures of complexes [{L1}ZnMe]2 (1), [{L2}ZnMe]2] (2), [{L3}ZnMe]∞ (3), [{L4}ZnMe]2] (4), [{L1}Zn{N(SiMe3)2}]2
(5), [{L2}Zn{N(SiMe3)2}]2 (6), [{L3}Zn{N(SiMe3)2}]2] (7), [{L4}Zn{N(SiMe3)2}]2] (8), [{L1}2Zn]2 (9), and [{L4}2Zn]2
(12) have been unambiguously determined using single crystal X-ray diffraction studies. Thermogravimetric analysis has been
used to assess the viability of complexes 1−12 as single source precursors for the formation of ZnS. On the basis of TGA data
compound 9 was investigated for its utility as a single source precursor to deposit ZnS films on silica-coated glass and crystalline
silicon substrates at 150, 200, 250, and 300 °C using an aerosol assisted chemical vapor deposition (AACVD) method. The
resultant films were confirmed to be hexagonal-ZnS by Raman spectroscopy and PXRD, and the surface morphologies were
examined by SEM and AFM analysis. Thin films deposited from (9) at 250 and 300 °C were found to be comprised of more
densely packed and more highly crystalline ZnS than films deposited at lower temperatures. The electronic properties of the
ZnS thin films were deduced by UV−Vis spectroscopy to be very similar and displayed absorption behavior and band gap (Eg =
3.711−3.772 eV) values between those expected for bulk cubic-ZnS (Eg = 3.54 eV) and hexagonal-ZnS (Eg = 3.91 eV).
ZnS),3 with each phase possessing unique physical properties.4
In both cubic and hexagonal structures, Zn and S atoms exist
in tetrahedral environments, where the only difference is in the
INTRODUCTION
■
As one of the first semiconducting materials to be discovered,
zinc sulfide (ZnS) is the prototype II−VI semiconductor and
stacking sequence of atomic layers. A consequence of this
has habitually displayed remarkable fundamental properties
difference in the physical arrangement of the atoms within the
and versatility of application, finding utility in a wide range of
lattice is the difference in band gap energy observed for ZB-
areas such as electronics and optoelectronics, photovoltaic
cells, optical sensors, lasers, infrared windows, electro-
ZnS (Eg = 3.54 eV) and W-ZnS (Eg = 3.91 eV).2
Zinc sulfide is generally considered one of the best materials
available as a buffer layer for the fabrication of CIGS solar cells.
ZnS provides a nontoxic and environmentally safe alternative
to cadmium sulfide and displays improved lattice matching to
luminescent and photoluminescent devices, antireflection
coatings, reflectors, interference filters, and displays.1
Understanding the relationship between structural and
electronic properties of semiconducting materials is crucial to
CIGS absorbers in addition to being capable of transmitting
the design of novel nanostructures with tunable properties.
Zinc sulfide exists in three polymorphic forms:2 cubic zinc
blende (ZB-ZnS, also called β-ZnS or “sphalerite”), hexagonal
Received: December 5, 2018
Wurtzite (W-ZnS), or the rarely observed cubic rock salt (RS-
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b03363
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
higher energy photons and increasing light absorption in the
absorber layer (cf. CdS).5
Scheme 1
A wide range of thin film deposition techniques6 have been
applied to the fabrication of ZnS thin films. From a commercial
and technological viewpoint, many of these techniques entail
high operating cost and often require complicated operational
steps and instrumentation, without the guarantee of high
reproducibility. As such, studies have focused on routes by
which high quality ZnS thin films can be produced at low cost
in a consistent and reproducible manner.
To this end, a variety of metalorganic complexes of zinc
(including dialkyldithiocarbamates,1d,7 alkyl xanthates,8 thio-
semicarbazones,9 dialkylthiocarbamates and monothiocarbox-
ylates,10 dithiophosphinate,11 N-thiophosphorylated-thiour-
eas,12 and thio- and dithio-biuret13) have been designed and
developed for application in the chemical vapor deposition
(CVD) of ZnS thin films.14 Reviews by Gleizes15 and
O’Brien14b,16 provide detailed accounts of the use of other
single source precursors for the deposition of chalcogenide
materials by MOCVD. Of these precursors, [Zn(S2CNEt2)2]
was the first precursor compound employed, yielding only
poor quality ZnS via a low-pressure CVD (LP-CVD) process.
Reports suggest that the implementation of [Zn(S2CNEt2)2] in
other thin film deposition methods can produce good quality
hexagonal and cubic ZnS films on Si(111) substrates,17 and in
related studies, nanocrystalline W-ZnS thin films have been
deposited on crystalline silicon and silicon dioxide substrates
as colorless microcrystalline powders in high yields (81−86%).
In all cases, the products were characterized by solution state
NMR (1H and 13C) spectroscopy and elemental analysis.
The 1H NMR spectra of the pro-ligands all display a
resonance ca. δ 4.42−5.64 ppm associated with the {NMe2}
functionality, a feature which is absent from the starting
thioisocyanates, while the 13C{1H} NMR spectra demonstrate
a characteristic shift in the resonance associated with the
thioisocyanates’ {SCN} carbon resonance from δ 129−
134 ppm to δ 182−183 ppm for the {CS} double bonds.
The zinc thioureide derivatives, compounds 1−4 and 5−8,
were readily synthesized through the reaction in hexane of 1
equivalent of either [ZnMe2] or [Zn{N(SiMe3)2}2] with the
pro-ligands HL1, HL2, HL3, and HL4 and were isolated as
colorless solids (Scheme 2).
The reaction of both [ZnMe2] and [Zn{N(SiMe3)2}2] with
the pro-ligands HL1-HL4 in a stoichiometric 1:1 reaction
results in the formation, and isolation after recrystallization, of
the monothioureide complexes 1−4 and 5−8, respectively.
8a,c
i
by CVD from [Zn(S2COR2)2] (R = Et or Pr).
Many of these systems, however, suffer from inconveniently
low precursor volatility unless used at very low pressur-
es.14b,15,18 An alternative variant on the CVD technique, which
circumvents this limitation and avoids the use of highly
reactive metal alkyls or H2S, is aerosol-assisted CVD
(AACVD),19 where the only restriction on precursor identity
in this respect is its solubility in appropriate solvents, with the
subsequent solutions nebulized and transported as micron-
scale droplets to a heated substrate.18,20 Despite its obvious
advantages, however, only the monothiocarboxylate complexes
[Zn(SOCMe)2(tmeda)] and [Zn(SOCtBu)2(tmeda)] (tmeda
= N,N,N,N-tetramethylethylenediamine) and the tetramethyl-
dithiobiurete complex [Zn{(SC(NMe2))2N}2] have been
utilized in AACVD studies to date. The former of these two
complexes produced thin films in which mixtures of ZB-ZnS
and W-ZnS were observed at temperatures as low as 125 °C,10a
while the latter deposited ZB-ZnS below 350 °C and W-ZnS at
deposition temperatures above 400 °C.13a,14b
Recently we described the design and synthesis of metal
precursors based around thioamidate21 and thioureide22 ligand
systems for the production of metal sulfide thin films by
AACVD processes. In the present work, we describe the
synthesis and characterization of a family of 12 homo- and
heteroleptic zinc-thioureide complexes, which have been
synthesized by direct reaction of the free thioureates with
either ZnMe2 (1:1) or Zn{N(SiMe3)2}2 (1:1 and 2:1). We also
report the potential of selected complexes to act as single
source precursors to thin films of ZnS.
1
The H NMR spectra clearly show the absence of the broad
singlet resonance associated with the {NH} group in the pro-
ligands, indicating loss of this acidic proton as either CH4 or
HN(SiMe3)2. In the case of complexes 1, 2 and 4, and 5−8,
the complexes are all soluble in C6D6 whereas in contrast,
complex 3 displayed limited solubility in C6D6, suggestive of
subtle differences between the solution state structures of
1
complexes 3 and 7. Despite this observation, the H NMR
spectra of the respective compounds clearly show the presence
of singlet resonances at δ = −0.01 ppm (1), 0.05 ppm (2), 0.01
ppm (3), and 0.41 ppm (4), representative of the {Zn-Me}
moiety in compounds 1−4, and at δ = 0.46 ppm (5), 0.46 ppm
(6), 0.44 ppm (7), and 0.31 ppm (8) in compounds 5−8,
representative of a {Zn−N(SiMe3)2} moiety. These resonances
appear in relative ratios of 3H:6H and 18H:6H respectively,
with the dimethylamine group, {NMe2}, of the ligands {L1}-
{L4}, indicative of the presence of the thioureide ligand and
{Me} or {N(SiMe3)2} groups in a 1:1 ratio as expected for the
formation of the heteroleptic methyl-zinc thiouride complexes
1−4 and the amide zinc thiouride complexes 5−8 (Scheme 2).
Elemental analyses of the products are consistent with the
formation of the heteroleptic complexes [{L}ZnMe], 1−4, and
[{L}Zn−N(SiMe3)2], 5−8, respectively.
Comparable reaction of the pro-ligands HL1-HL4 with
[Zn{N(SiMe3)2}2] in a 2:1 ratio results in the formation of the
bis-thioureide complexes, 9−12, in moderate to high isolated
1
yields (56−83%). In contrast to the H NMR spectra of 5−8,
1
the H NMR spectra of 9−12 clearly show the absence of
RESULTS AND DISCUSSION
resonances associated with the {N(SiMe3)2} units (ca. 0.31−
0.48 ppm) and are consistent with the formation of the bis-
thioureide complexes (Scheme 3). The appearance of only one
■
Synthesis. The thiourea pro-ligands, HL1-HL4, were
prepared by direct reaction of the appropriate commercially
available isothiocyanates with anhydrous HNMe2 in hexane
(Scheme 1), followed by isolation by filtration, washing with
fresh hexane, and drying in-vacuo to yield the pure pro-ligands
1
set of resonances in the H and 13C NMR spectra for the
thioureide ligands in all four sets of spectra is indicative of the
fact that the ligands occupy identical environments on the
B
DOI: 10.1021/acs.inorgchem.8b03363
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 2
chelating fashion to one zinc center, while participating in a S-
bridging interaction with an adjacent zinc center. While each
zinc atom in the series of complexes is four coordinate, the
coordination at the metal is not simply described in terms of
any regular polyhedron. In the case of complex 1, the geometry
about the zinc atoms is best described as distorted trigonal
pyramidal, with the base defined by the atoms C(3), N1(12)
and S(l)* [∑Zn = 354.54(6)°]. Coordination of the sulfur
atom from the chelating thioureide, Zn−Sint [2.5348(7) Å],
which is significantly longer than the dimer-forming exocyclic
Zn−S*exo interaction [2.4474(7) Å], completes the coordina-
tion environment and distorts the geometry away from ideal
due to the restricted S(1)−Zn(1)−N(11) bite angle [68.10°].
The Zn−Me bond [1.970(3) Å] is similar to those found in
related complexes.7b The C−S bond length [1.775(3) Å] is
close in value to that expected for typical C−S single bonds,
whereas the C−N bond [1.362(3) Å] is more consistent with
its assignment as a localized CN double bond. Despite the
approximate coplanarity of the {CNS} and {NMe2} moieties
(the angle between the two planes is ∼27.79°) within the
thioureide ligand, there is no evidence of multiple bonding
character between {CNS} and {NMe2} groups, as indicated by
the approximately single C−N bond [1.301(3)Å]. The same
general trends observed in complex 1 are repeated in
complexes 2 and 4. Table 1 shows selected bond lengths
and angles for complexes 1, 2, and 4, and their molecular
structures are shown in Figure 2.
Scheme 3
NMR time scale. Elemental analysis of 9−12 is consistent with
the formation of the bis-thioureide complexes.
Solid State Molecular Structures. X-ray quality single
crystals of compounds 1−4, 5−8, 9, and 12 were obtained
from a saturated toluene solution at −28 °C. Figure 1 shows
the molecular structure of compounds 1, 2, and 4, which
present as an essentially iso-reticular series consisting of
dimeric molecular units, [{L}ZnMe]2.
In stark contrast to the molecular structures of complexes 1,
2, and 4, the solid state structure of 3, containing the sterically
t
more demanding Bu group, adopts a rather unexpected
structure in the solid state, favoring the formation of a
polymeric system in which the coordination mode of the
thioureide moiety differs significantly from that observed in 1,
2, and 4. The molecular structure of complex 3 is shown in
Figure 3 and selected bond lengths and angles in Table 2.
Complex 3 crystallizes in the orthorhombic space group
P212121 with one complete molecule in the asymmetric unit
cell. The asymmetric units are connected in the form of one-
dimensional zigzag polymeric chains extended along the
crystallographic a-axis. As with complexes 1, 2, and 4 the
zinc metal center possesses a 4-coordinate geometry. Unlike 1,
2, and 4, however, the coordination environment is made up of
the two nitrogen atoms of the thioureide ligand, the carbon of
the terminal {Me} group and the {S} atom of an adjacent
[{L3}ZnMe] unit. This contrasting κ2-N,N′ coordination mode
of the thioureide ligand is comparable to that observed in the
related ureide-coordinated complex [Sn{κ2-N,O-OC(NMe2)-
NtBu}{κ2-N,N′-N(tBu)C(S)NMe2}].24 The coordination
Figure 1. Molecular structure of [{L1}ZnMe]2 (1). Thermal
ellipsoids are shown at 50% probability. Symmetry transformations
used to generate equivalent atoms: −X + 1, −Y, −Z + 1.
Complex 1, which crystallizes in the monoclinic space group
P21/n, forms a centrosymmetric dimer with anti-arrangement
of the thioureide ligands about the central {Zn2S2} metallo-
cycle, similar to the amidinate and dithiocarbamate systems
23
[{tBuC(Ni-Pr)2}ZnMe]2 and [{Et2NCS2}ZnMe]2.7b Each
thioureide ligand can be best described as being coordinated to
the zinc centers in a μ,κ2:κ1 coordination mode, i.e. η2-N,S-
C
DOI: 10.1021/acs.inorgchem.8b03363
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 1. Selected Bond Lengths (Å) and Bond Angles (deg) for Complexes 1, 2, and 4
1
2
4
Zn−Me
Zn−Sint
Zn−N
Zn−Sexo
C−NMe2
S−C
1.970(3) Å
2.5348(7) Å
2.036(2) Å
2.4474(7) Å
1.362(3) Å
1.775(3) Å
1.301(3) Å
68.10(5)°
1.963(2) Å & 1.968(2) Å
2.5295(6) Å & 2.5374(6) Å
2.0261(16) Å &2.0253(16) Å
2.4447(5) Å & 2.4493(5) Å
1.354(3) Å & 1.354(3) Å
1.7821(19) Å & 1.7834(19) Å
1.308(3) Å & 1.308(3) Å
68.20(5)° & 67.85(5)°
1.965(4) Å
2.5217(10) Å
2.046(3) Å
2.4748(10) Å
1.350(4) Å
1.788(3) Å
1.307(4) Å
68.20(8)°
N−C
S−Zn−N
Figure 2. Molecular structure of A: [{L2}ZnMe]2 (2) and B: [{L4}ZnMe]2 (4). Thermal ellipsoids are shown at 50% probability. Hydrogen atoms
have been omitted for clarity. Symmetry transformations used to generate equivalent atoms in B: −X + 1, −Y + 1, −Z.
Figure 3. A projection along the c axis showing both the molecular structure of [{L3}ZnMe]∞ (3) and the formation of the one-dimensional
polymeric chains. Thermal ellipsoids are shown at 50% probability. Hydrogen atoms have been omitted for clarity. Symmetry transformations used
to generate equivalent atoms in 3: * −X + 1, Y + 1/2, −Z + 3/2; ** −X + 1, Y − 1/2, −Z + 3/2.
mode of the thioureide ligand in 2 can be best described as
being N,N′-chelating (κ2) to the zinc atom along with the
terminal {CS} acting as a bridging atom to an adjacent zinc
center. The central planar carbon atom of the thioureide ligand
is appended by a sulfur atom, with a S−C bond length
indicative of significant double character (1.743 Å), in addition
to the {NtBu} and {NMe2} moieties. The carbon−nitrogen
bonds at 1.268(3) Å and 1.472(4) Å, respectively, are
approaching values observed for {CNtBu}25 and {C-
NMe2}25b bonds, indicative of some delocalization of charge
across the {S−C−NtBu} moiety.
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg)
for Complex 3
3
Zn−Me
1.968(3) Å
2.090(2) Å
2.203(2) Å
2.3540(8) Å
1.472(4) Å
1.743(2) Å
1.268(3) Å
62.57(9)°
Zn−NtBu
Zn←NMe2
Zn···S
C−NMe2
S−C
tBuN−C
tBuN−Zn−NMe2
Me−Zn···S
The bond angles around the zinc atom in 3 are in the range
expected for a more tetrahedral geometry cf. 1, 2, and 4. The
124.54(10)°
D
DOI: 10.1021/acs.inorgchem.8b03363
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Zn−C bond lengths observed in 3 (1.968(3) Å) are
comparable to those described above and are in the typical
range reported for Zn-Me groups.7b The Zn−NtBu (Zn−N =
2.090(2) Å)25b and Zn ← {NMe2} bond lengths (Zn−N =
2.203(3) Å)26 are also in the range expected for comparable
bonds in literature complexes. The intermolecular Zn···S bond
(2.3540(8) Å) is comparable to that found in zinc blende
(∼2.342 Å).1c
coordination mode and, as with the methyl-zinc complexes
described earlier, the molecular structures of 5−8 exist as
centrosymmetric dimers with an anti-arrangement of ligands
about the central {Zn2S2} metallocycle. The molecular
structure of complex 7 is described here as an exemplar with
similar features to those observed in complexes 5, 6, and 8.
The {Zn2S2} core of 7 is planar and forms an angle of 77.0°
to the equally planar {ZnNCS} metallocycle. As with complex
1, the geometry about zinc atoms in complexes 5−8 is best
described as distorted trigonal pyramidal, with the base defined
by the atoms N(2), N(11), and S(l)* [∑Zn = 354.11(6)°] (5:
In the case of the bis-trimethylsilyl derivatives 5−8, there is
no comparable change in the coordination mode of the
i
t
thioureide ligand as the series traverses from Pr to Cy, Bu,
and Mes ligand systems. In general, the solid state molecular
structures of 5−8 possess a comparable structural topology
with the κ2-N,S complexes 1, 2, and 4, with the {N(SiMe3)2}
group taking the terminal position adopted by the methyl
groups. Figure 4 shows the molecular structure of 7. Selected
∑
= 355.88(5)°, 6: ∑Zn = 355.55(11)°, 8: ∑Zn =
Zn
347.58(4)°). As in 1, 2, and 4, a strong interaction between
the two “‘monomeric’” [{L3}Zn{N(SiMe3)2}] units is
indicated by the shorter Zn−S distance [2.0831(19) Å]
compared with Zn−S [2.1879(18) Å].
Coordination of the sulfur atom from the chelating
thioureide, Zn−Sint [2.5171(6) Å], which is significantly
longer than the dimer forming exocyclic Zn−S*exo interaction
[2.3837(6) Å], completes the coordination environment and
distorts the geometry away from ideal due to the restricted
S(1)−Zn(1)−N(11) bite angle [68.55(5)°].
The remaining Zn−N bond of the chelating {L3} anion is
marginally longer [2.0746(18) Å] than the analogous bonds in
compounds 1, 2, and 4. The Zn−N amide distance
[1.9141(18) Å] is comparable to the structurally related
[{hpp}Zn{N(SiMe3)2}]2 ({hpp} = 1,3,4,6,7,8-hexahydro-2H-
pyrimido[1,2-a]pyrimide) in which the zinc geometry is
described as distorted tetrahedral.27
Single crystals of the bis-thioureide complexes 9 and 12 were
obtained independently from solutions of toluene upon storage
at −28 °C. Complexes 9 and 12 crystallize in the monoclinic
̅
space group I2/a and the triclinic space group P1, respectively.
For 9 the asymmetric unit cell contains one [{L1}2Zn]
molecule, alongside one molecule of toluene, with symmetry
operators generating the second half of the dimeric [{L1}2Zn]2
system (Figure 5). Similarly for 12 the asymmetric unit cell
contains one complete [{L4}2Zn] molecule, with symmetry
operators generating the second half of the dimeric [{L4}2Zn]2
system (Figure 5). Table 4 shows selected bond lengths and
angles for complexes 9 and 12.
The molecular structures of 9 and 12 are related to those of
complexes 1, 2 and 4, and 5−8, which have been previously
described, and are based on dimeric molecules with highly
distorted five-coordinate geometries about each zinc atom,
comprising the sulfur and nitrogen atoms of the two chelating
thioureide ligands. The fifth, and final, coordinating atom is
found to be a sulfur atom belonging to an adjacent chelating
thioureide ligand, bridging two zinc atoms and resulting in the
formation of three fused four membered rings, i.e. {ZnSCN}/
Figure 4. Molecular structure of [{L3}Zn{N(SiMe3)2}]2 (7). Thermal
ellipsoids are shown at 50% probability. Hydrogen atoms have been
omitted for clarity. Symmetry transformations used to generate
equivalent atoms: −X, −Y, −Z + 1.
bond lengths and angles for complexes 5−8 are shown in
Table 3. The molecular structures of 5, 6, and 8 are shown in
the Supporting Information.
̅
Compound 7 crystallizes in the triclinic space group P1 with
two independent halves of the dimeric compound [{L3}Zn-
{N(SiMe3)2}]2 in the asymmetric unit cell. Complexes 5, 6,
̅
and 8 also crystallize in the triclinic space group P1, with one-
half of the respective dimer unit present in the asymmetric unit
cells for complexes 5 and 8, and two independent halves of the
dimeric unit in 6. As with complexes 1, 2, and 4, the thioureide
ligands in 5−8 are coordinated to the zinc centers in a μ,η2:η1-
Table 3. Selected Bond Lengths (Å) and Bond Angles (deg) for Complexes 5−8
5
6
7
8
Zn−N(SiMe3)2
Zn−Sint
Zn−N
Zn−Sexo
C−NMe2
S−C
1.9145(16) Å
2.5363(6) Å
2.0379(17) Å
2.3871(6) Å
1.359(3) Å
1.785(2) Å
1.300(3) Å
68.15(5)°
1.913(3) Å
2.5428(12) Å
2.030(3) Å
2.3930(11) Å
1.341(5) Å
1.785(4) Å
1.314(5) Å
67.98(11)°
1.9141(8) Å
2.5171(16) Å
2.0746(18) Å
2.3837(6) Å
1.369(3) Å
1.801(2) Å
1.295(3) Å
68.55(5)°
1.9037(14) Å
2.4970(4) Å
2.0278(13) Å
2.4282(4) Å
1.340(2) Å
1.7853(16) Å
1.312(2) Å
68.68(4)°
N−C
S−Zn−N
E
DOI: 10.1021/acs.inorgchem.8b03363
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 5. Molecular structure of the bis-thioureide complexes [{L1}Zn]2 (9) and [{L4}Zn]2 (12). Thermal ellipsoids are shown at 50% probability.
Hydrogen atoms and solvent of crystallization (toluene) associated with 9 have been omitted for clarity. Symmetry transformations used to
generate equivalent atoms: 9; −X + 1/2, −Y + 1/2, −Z + 1/2, 12; −X + 1, −Y + 2, −Z + 1.
{ZnSZnS}/{ZnSCN}. The structures resemble the dimeric
zinc units found in bis(diethyldithiocarbamates), bis-
(diethyldiselenocarbamates), and in mixed alkydialkydithio/
selenocarbamate systems.28 The Zn−N bonds and Zn−S bond
distances and angles are similar to those reported here and in
related Zn-dithiocarbamate systems.28 The S atoms are
engaged in both chelating/bridging interactions, showing
significantly longer Zn−S contacts associated with the bridging
3-coordinate S atoms within the {Zn2S2} ring [9: 2.8149(7) Å;
12: 2.8061(5) Å] compared to the 2-coordinate S atoms that
participate in only a chelating interaction [9: 2.4973(7) Å; 12:
2.3764(6) Å].
While the zinc centers in each complex are 5 coordinate, the
geometry about the zinc atoms in 9 is best described as
trigonal bypyramidal (τ = 0.70), and distorted square based
pyramidal in the case of 12 (τ = 0.36). These distortions arise
as a result of (i) the restricted bite distance associated with the
chelating ligands [9: 62.75(6)° and 62.75(6)°; 12: 70.45(5)°
and 63.03(5)°], (ii) the close approach of the dimer forming S
atoms [9: 2.3645(7)°; 12: 2.3666(6)°], and (iii) the relative
orientation of the isopropyl and mesityl substituents within the
two molecules.
Within each [{L1}2Zr] unit of complex 9, the two {iPr}
groups on the chelating thioureide ligands are arranged in
F
DOI: 10.1021/acs.inorgchem.8b03363
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 4. Selected Bond Lengths (Å) and Bond Angles (deg) for Complexes 9 and 12
9
12
Zn(1)−S(1)
Zn(1)−S(2)
Zn(1)−S(1)*
Zn(1)−N(11)
Zn(1)−N(21)
2.8149(7) Å
2.4973(7) Å
2.3645(7) Å
2.0199(19) Å
2.0174(19) Å
Zn(1)−S(1)
Zn(1)−S(2)
Zn(1)−S(2)*
Zn(1)−N(11)
Zn(1)−N(21)
2.3764(6) Å
2.8061(5) Å
2.3666(6) Å
2.0839(15) Å
2.0198(17) Å
C(11)−N(1)
S(1)−C(11)
N(11)−C(11)
C(21)−N(2)
S(2)−C(21)
N(21)−C(21)
1.355(3) Å
1.773(2) Å
1.303(3) Å
1.376(3) Å
1.735(2) Å
1.315(3) Å
C(11)−N(1)
S(1)−C(11)
N(11)−C(11)
C(21)−N(2)
S(2)−C(21)
N(21)−C(21)
1.352(2) Å
1.7529(19) Å
1.324(3) Å
1.350(3) Å
1.756(2) Å
1.324(2) Å
S(1)−Zn(1)−N(11)
S(2)−Zn(1)−N(21)
S(1)−Zn(1)−S(1)*
Zn(1)−S(1)−Zn(1)*
62.75(6)°
69.03(6)°
84.85(2)°
95.15(2)°
S(1)−Zn(1)−N(11)
S(2)−Zn(1)−N(21)
S(2)−Zn(1)−S(2)*
Zn(1)−S(2)−Zn(1)*
70.45(5)°
63.03(5)°
89.389(18)°
90.611(18)°
transoidal fashion, with each [{L1}2Zr] unit within the dimer
then itself arranged cisoidaly, resulting in a trans−cis [{L1}2Zr]2
dimer (Figure 6). Contrastingly, in 12, the two {Mes} groups
thermogravimetric analysis (TGA) was employed to inves-
tigate the volatility and thermal stability of complexes 1−12.
Table 5 shows the onset of mass loss, % mass residues, and
the expected % mass residue for ZnS from each of the
Table 5. Melting Point, Onset Temperature, Percent
Residual Mass, and Expected Percent Weight for ZnS in
Complexes 1, 2, 4−9, and 12
Onset
% Residual mass
(Temp.)
Expected % wt for
ZnS
a
Compound
Temp.
1
2
4
5
6
7
8
9
160.2 °C
175.4 °C
225.8 °C
180.2 °C
140.0 °C
175.3 °C
225.6 °C
142.1 °C
190.5 °C
31.3% (440 °C)
33.0% (450 °C)
13.5% (450 °C)
25.9% (360 °C)
25.2% (330 °C)
21.2% (450 °C)
26.0% (475 °C)
21.3% (420 °C)
18.1% (430 °C)
43.5%
36.9%
32.3%
26.3%
25.3%
23.7%
21.8%
27.4%
19.2%
12
a
Defined as temperature at 1% mass loss.
synthesized complexes. Because of its polymeric nature, the
tBu-derivative (3) was not investigated further as a potential
ZnS precursor. Similarly, because of the low decomposition
temperature of the bis-thioureide complexes 10 and 11,
thermogravametric studies were not undertaken.
TG analysis of the methyl zinc thioureide complexes 1 and
2, shows multistep decomposition pathways yielding %
residues which are lower than the expected % residue for the
formation of ZnS, suggestive of a degree of volatility in the
complexes (Figure 7a). In contrast, the mesityl derivative (4)
shows a higher degree of thermal stability than that observed
for 1 (160.2 °C) and 2 (175.4 °C). In contrast to complexes 1
and 2, the mesityl derivative 4 displays a sharp single step mass
loss over a narrow temperature range of (∼250−330 °C),
resulting in a significantly lower % residual mass than that of
ZnS or Zn (13.5% cf. 32.2%, 21.7%, respectively) suggestive of
a significantly high degree of volatilization.
Figure 6. Diagram showing the relative orientation of the {iPr} and
{Mes} substituents in the dimers [{L1}2Zr]2 (9) and [{L4}2Zr]2 (12).
on the thioureide ligands within each [{L4}2Zr] unit are
arranged in a cisoidal fashion about each zinc atom. Each
[{L4}2Zr] unit within the dimer then arranges itself in a trans
arrangement resulting in a cis−trans [{L4}2Zr]2 dimer (Figure
6). It should be noted that in the case of 12, the relative
displacement of the mesityl groups on the cis-[{L4}2Zr] unit is
such that π−π stacking is possible with the closest contact
between the two approximately parallel {Mes} rings found to
be 3.69(8) Å.
Thermal Profiles. The synthesis of Zn(II) bis-thioureide
compounds has been driven by our interest in the discovery of
novel precursors for the MOCVD of ZnS thin films. As such,
For the zinc amide complexes 5−8, the thermal decom-
position processes were all found to be multistep, displaying
rapid mass loss in the initial phase, tapering off over a wide
G
DOI: 10.1021/acs.inorgchem.8b03363
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
mass spectrometry was undertaken. Unfortunately TGA-MS
experiments did not yield conclusive results with respect to
precursor decomposition pathways: Peaks at m/z = 45 amu
and m/z = 101.1 amu were observed in the mass spectra which
we attribute to formation of dimethylamine and isopropyl
isothiocyanate, respectively, suggestive of a deinsertion path-
way. We suggest that these results provide strong further
support for the generalized assumption that thioureide ligands
are potentially significant ligands for the development of stable
metal sulfide precursors.
Thin Film Deposition. The low onset temperature for the
decomposition of compound 9 (∼142 °C), in conjunction
with ease of synthesis, stability, and reasonable solubility in
THF, led us to assess its viability as a low temperature single
source precursor for the AACVD of ZnS thin films. As part of a
preliminary viability study, films were deposited under hot wall
conditions in a previously described CVD reactor19,21,22,24
onto silica-coated float glass substrates (Pilkington NSG Ltd.).
The deposition conditions are shown in Table 6. The films
Table 6. Deposition Conditions Used for the AACVD of
ZnS Thin Films with Compound 9
Film Conc (mol dm−3
)
Substrate Temp (°C) Deposition Time (min)
A
B
C
D
0.15
0.15
0.15
0.15
150
200
250
300
60
60
60
60
were deposited from 0.15 M solutions of 9 in THF
(optimized) onto (100) silicon wafers and glass substrates, at
temperatures of 150, 200, 250, and 300 °C for films A−D,
respectively.
The films (A−D) were primarily transparent in appearance
with more visually yellow material at the leading edge of the
substrate, which could indicate the presence of S rich ZnS. At
the lower deposition temperatures (150 and 200 °C), films A
and B appeared to be very thin and slightly opaque with a very
slight yellow appearance. Higher temperatures, however,
delivered significantly improved coverage of the substrate to
provide films that were transparent.
The films (A−D) were air and water stable, showing no
observable change (as determined by powder X-ray diffraction
(PXRD) and UV−vis transmission spectroscopy) over a period
of 2 months. The films were insoluble in common organic
solvents but were quickly decomposed in dilute nitric acid and
bleach, yielding H2S.
Figure 7. Thermogravimetric plots for complexes 1, 2, and 4 (a), 5−8
(b), and 9 and 12 (c). (5 °C min−1, 20 mL min−1 N2 flow).
Films C and D, deposited at 250 and 300 °C, respectively,
appeared transparent with slight yellowing at the leading edge
of the substrate. The mechanical integrity of the as-deposited
thin films was assessed using the “Scotch Tape test”.29 The
Scotch tape test resulted in no obvious removal of material
from the films C and D; however, some material was removed
from the surface of films A and B, suggesting less well adhered
films. PXRD analysis was performed on all the deposited films
to determine the crystallinity of the materials. Similar analysis
of the slightly yellow regions of the films yielded analogous
results. Representative PXRD patterns for the films C and D
are shown in Figure 8.
temperature range (Figure 7b) to reach mass residues which
are all close to the expected values for the formation of ZnS,
with the exception of the tBu derivative (7) which is
fractionally lower.
For the bis-thioureides 9 and 12, the TGA plots (Figure 7c)
clearly display two complexes which, while both displaying a
single mass loss event, display very different thermal stabilities.
For the isopropyl derivative 9, mass loss begins at ∼142 °C,
whereas, for the mesityl derivative 12, mass loss only occurs at
∼190 °C (cf. 225.8 °C for [{L4}ZnMe]2 (4) and 225.6 °C for
[{L4}Zn(N(SiMe3)2)]2 (8)). In both instances, the resulting %
residual masses (21.3 and 18.1 wt %, respectively) are lower
than that expected for the formation of ZnS (27.4 and 19.4 wt
%, respectively). In an attempt to ascertain possible
decomposition pathways for precursors 9, TGA-coupled
Films A and B, deposited at 150 and 200 °C respectively,
were found to be amorphous within the limits of the
instrument. Films C and D, deposited at 250 and 300 °C
respectively, provided clear indication of crystallinity with one
H
DOI: 10.1021/acs.inorgchem.8b03363
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Deposition temperature, as well as choice of precursor,
clearly has an effect on the morphology, crystallite size, and
film thickness of the as deposited thin films. The role of the
carrier solvents has also previously been seen to influence the
morphology of the films (e.g., tungsten oxide32 and tin
oxide33), and is generally attributed to concentration effects,
chemical effects, and modulation of the rates of deposition and
droplet evaporation. The latter of these effects is more likely
the dominant here for solvents such as toluene and THF,
which do not form reactive radical species at the temperatures
used in our experiments. Attempts to increase the concen-
tration of precursor and change the carrier solvent from THF
to toluene were met with varying degrees of success. Initial
investigations of precursor concentrations >0.15 M (in THF)
resulted in inconsistent thin film deposition at 300 °C. The
reduced solubility of complex 9 in toluene also resulted in
uneven film growth from 0.1 M solutions of 9 in toluene.
Atomic force microscopy (AFM) (ESI) was performed to
determine the root-mean-square (rms) surface roughness of
the ZnS thin films (Table 7). In all cases, films A−D were
Table 7. Structural Characteristics of ZnS Thin Films
Roughness
Film
Average
Crystallite size
(D) (nm)
Values
Thickness
Lattice parameter
a
b
Film
(nm)
(d) (nm)
(Å) (c)
A
B
C
D
2.63
6.54
7.02
53.83
61.52
339.88
443.96
9.38
24.97
6.39 (2Θ = 27.9°)
6.19 (2Θ = 28.8°)
Figure 8. (a) PXRD patterns of films C−D resulting from AACVD
with compound 9, (b) Raman spectra of films C−D.
14.59
a
b
As determined from AFM over three positions. As determined by
SEM.
high intensity maximum, which could be readily indexed to the
(002) reflection of W-ZnS (JCPDS 36-1450), indicative of
ZnS films of polycrystalline nature with a hexagonal close-
packed structure. The reflection corresponding to the (002)
planes increased in intensity for films deposited at higher
temperature. For film D, broader peaks also present in the
PXRD pattern could be indexed to the (100), (101), (102),
(110), (103), and (112) reflections of W-ZnS. For the ZnS
films C and D, PXRD suggests that crystallites are
preferentially oriented with (002) planes parallel to the
substrate surface, with the c-axis of the hexagonal cell normal
to the substrate. In order to obtain more structural
information, the mean crystallite size (D) of the films was
calculated using the Debye−Scherrer formula. For films C and
D the minimum domains in the (00L) dimension, calculated
from X-ray line broadening using the (002) peak, were found
to be 9.4 and 25.0 nm, respectively, such that the films
deposited at higher temperatures were characterized by greater
crystallite size. Experimentally, the 2θ positions corresponding
to the (002) direction changed from 27.9° to 28.8° as the
deposition temperature was increased from 250 °C, C, to 300
°C, D. A simple calculation confirmed that the lattice constants
of the c-axes for both films were close to and within
experimental error of the reported lattice parameter for W-
ZnS (6.402(8) Å).30
relatively smooth and were consistent with our observation
that with increasing deposition temperature there was an
attendant increase in crystallite size, such that films A and B
were significantly less crystalline, with RMS values of 2.6 and
6.5 nm respectively, compared to the more crystalline thin
films C and D (RMS values of 7.0 and 14.6 nm).
Figure 9 displays images obtained from field emission
scanning electron microscopy (FESEM), which was carried out
to determine the morphology of the films. The plan view of
films C and D (Figure 9a and 9c) and the cross-sectional image
(Figure 9b and 9d) both illustrate that the thin films comprise
a collection of densely packed crystallites that are globular in
appearance. For film D these crystallites (Figure 9c) are
significantly larger (30−70 nm) than those observed in film C
(40−50 nm). This trend is also observed in films A and B,
where crystallite size decreases in line with deposition
temperature and is consistent with the PXRD and AFM
data. For films A and B FE-SEM images are shown in the
Supporting Information.
Energy dispersive X-ray (EDX) measurements revealed the
presence of Zn and S in all thin films deposited. Films
deposited at 150 °C (A) displayed a relative ratio of Zn:S of
1:1.05, close to the ideal 1:1 ratio, while films deposited at
higher temperatures, i.e. 200 °C (B), 250 °C (C), and 300 °C
(D) all appear to be sulfur rich with Zn/S ratios of 1.47, 1.41,
and 1.39, respectively, consistent with Zn/S ratios of p-type (S-
rich) ZnS.34 While it is possible that these films could be more
accurately described as cocrystalline ZnS with additional S,
there is no evidence of the presence of crystalline or
amorphous sulfur from PXRD or Raman spectroscopy analysis.
The Raman spectra of the crystalline films C and D (Figure
8) displayed absorptions at 275 (TO), 335 (SO), 402 (TA +
TO), 614 (2TO), and 684 (2LO) cm−1. These vibrations
correspond with those reported for W-ZnS in the literature.31
In both the PXRD and Raman spectra, no peaks from any
impurities such as ZnO or other compounds are detected.
I
DOI: 10.1021/acs.inorgchem.8b03363
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 9. FE-SEM images of AACVD ZnS films from compound 9: (a) plan view of film C (250 °C); (b) cross-sectional view of film C (250 °C);
(c) plan view of film D (300 °C); (d) cross-sectional view of film D (300 °C).
Figure 10. (a) UV−vis transmission plots of films A−D (150 °C, 200 °C, 250 °C, and 300 °C, respectively) resulting from AACVD with
compound 9, (b) Tauc plots of films A−D.
The room temperature UV−vis absorption spectra of the
ZnS samples in the wavelength range 400−850 nm were
recorded. All films displayed good visible light transmission,
with optical transmission (λ = 400−700 nm) ≥ 75% in all
cases. Band gap energies were estimated to lie in the range 3.71
to 3.79 eV from representative Tauc plots (Figure 10). These
observations are commensurate with the films behaving as the
bulk semiconductor, with direct band gaps similar to those
reported elsewhere in the literature for ZnS.35
rich films at higher temperatures. Optical analysis of the thin
films shows high optical transmission and band gap estimations
of between 3.17 and 3.79 eV. This study builds on our work,
described elsewhere,22 on the efficacy of thioureide systems as
a novel class of precursor for the deposition of metal sulfide
thin films. In contrast to our previous study22 into Sn(II)
thioureide systems in which the control of the deposition
temperature has a direct effect on the phase of SnS deposited
(α or π), no such control is observed here, and no obvious
correlation between precursor structure and phase of ZnS
deposited can be discerned. Further work on the structure−
reactivity relationships of metal thioureide complexes for the
deposition of a range of metal sulfide thin films is ongoing.
CONCLUSIONS
■
A family of zinc thioureide systems have been described and
their potential for the deposition of thin films of ZnS by
AACVD has been explored. The homoleptic precursor,
[{L1}2Zn]2 (9) bearing the isopropyl-thiouride ligand was
used to deposit ZnS films in the temperature range 150−300
°C, with hexagonal (Wurtzite) W-ZnS deposited at temper-
atures of 250 °C and above, as identified by PXRD and Raman
spectroscopy. EDX analysis confirmed the deposition of ZnS
over the entire temperature range with the manifestation of S-
EXPERIMENTAL SECTION
■
General Procedures. All reactions were carried out under an
inert atmosphere using standard Schlenk techniques. Solvents were
dried over activated alumina columns using an Innovative Technology
solvent purification system (SPS) and degassed under an argon
atmosphere. Zn(N(SiMe3)2)2 was produced according to literature
J
DOI: 10.1021/acs.inorgchem.8b03363
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
procedures,36 and all other reagents were purchased from commercial
sources.
6H, -NMe2), 3.25−3.19 (br m, 1H, -NCH(Cy)); 13C{1H} NMR
(125.7 MHz, C6D6): δC −11.8 (Zn-Me), 25.6 (Cy-CH2), 25.8 (Cy-
CH2), 36.0 (Cy-CH2), 43.0 (-NMe2), 58.5 (-NCHCy), 173.0 (S-C-
NMe2); Elemental analysis for C20H40N4S2Zn2 (expected): C 45.18%
(45.20%), H 7.58% (7.59%), N 10.54% (10.54%).
Elemental analyses were performed externally by London
Metropolitan University Elemental Analysis Service, UK. 1H, 13C,
and 119Sn NMR spectra were recorded on Bruker Advance 300 or 500
MHz FT-NMR spectrometers, as appropriate, in C6D6 at room
temperature. Chemical shifts are given in ppm with respect to Me4Si
(1H, 13C). UV−vis spectra were recorded using a PerkinElmer
LAMBDA 750/650 UV/vis/near-IR spectrophotometer. Measure-
ments were recorded at 1400 to 400 nm and zero referenced using 5
mm high-grade Pilkington-NSG float-glass substrates. The measure-
ments were recorded at 1 nm increments.
1
3: Yield: 0.22 g (93%). H NMR (500 MHz, C6D6): δH 0.01 (s,
3H, Zn-Me), 1.22 (s, 9H, -NCMe3), 2.47 (s, 6H, -NMe2); 13C{1H}
NMR (125.7 MHz, C6D6) δC −11.5 (Zn-Me), 31.0 (-NCMe3), 44.4
(-NMe2), 55.4 (-NCMe3), 181.9 (S-C-NMe2); Elemental analysis for
C16H36N4S2Zn2 (expected): C 39.98% (40.09%), H 7.60% (7.57%),
N 11.68%, (11.69%).
4: Yield: 0.31 g, (99%). 1H NMR (500 MHz, C6D6): δH 0.41 (br s,
3H, Zn-Me), 2.06 (s, 6H, ortho-Me), 2.15 (s, 3H, para-Me), 2.42 (s,
6H, -NMe2), 6.61 (s, 2H, Ar-CH); 13C{1H} NMR (125.7 MHz,
Synthesis of the Pro-ligand [iPrN(H)CSNMe2] (HL1). In a dry
round-bottom flask under nitrogen, dimethylamine was bubbled
through a colorless solution of isopropyl isothiocyanate (4.23g, 30
mmol) in hexane (100 mL) at 0 °C yielding a white precipitate. The
product was extracted from solution by filtration and washed with
δ
C6D6): C −10.4 (Zn-Me), 19.0 (ortho-Me), 20.9 (para-Me), 42.0
(-NMe2), 131.8 (ortho-CMe), 132.4 (para-CMe), 144.2 (-N-C), 178.0
(S-C-NMe2); Elemental analysis for C26H40N4S2Zn2 (expected): C
51.69%, (51.74%), H 6.65% (6.68%), N 9.28% (9.28%).
1
hexane. Yield 3.69 g (84%), (mp 75−77 °C). H NMR (500 MHz,
Synthesis of [{iPrNC(S)NMe2}Zn{N(SiMe3)2}]2([{L1}Zn{N-
(SiMe3)2}]2) (5). A cooled solution of Zn{N(SiMe3)2}2 (0.39g, 1
mmol) dissolved in toluene, was combined with a solution of the pro
ligand HL1 (0.146g, 1 mmol) in toluene (20 mL), and allowed to stir
for 8h. In vacuo removal of solvent resulted in the formation of a
cloudy suspension, which was resolved with gentle heating, and
allowed to crystallize at −28 °C affording white crystals. Yield: 0.25 g
(67%). 1H NMR (500 MHz, C6D6) δH 0.46 (s, 18H, Zn−N(SiMe3)2)
1.20−1.13 (m, 6H, -NCHMe2), 2.63 (s, 6H, -NMe2), 3.62−3.53 (m,
1H, -NCHMe2); 13C{1H} NMR (125.7 MHz, C6D6): δC 6.4 (Zn−
N(SiMe3)2), 24.9 (-NCHMe2), 43.6 (-NMe2), 50.9 (-NCHMe2),
186.1 (S-C-NMe2); Elemental analysis for C24H62N6S2Si4Zn2
(expected): C 38.37% (38.85%), H 8.38%, (8.42%), N 11.35%
(11.33%).
C6H6) δH: 0.99 (m, 6H (CHMe2), 2.52 (s, 6H, NMe2), 4.42 (br s, 1H,
N(H)), 4.87 (m, 1H, CHMe2); 13C{1H} NMR (125.7 MHz, C6D6)
δC; 22.9 (CH(CH3)2), 39.4 (NMe2), 47.3 (CH(CH3)2), 182.1 (C
S); Elemental analysis (expected): C 49.31% (49.28%); H 9.62%,
(9.65%); N 19.18% (19.15%)
Synthesis of the Pro-ligands [CyN(H)CSNMe2] (HL2), [tBuN-
(H)CSNMe2] (HL3) and [MesN(H)CSNMe2] (HL4). The pro-ligands
HL2-HL4 were made in an analogous manner to HL1 using of 5.59g
(30 mmol) cyclohexyl isothiocyanate, 4.81g (30 mmol) of tertiary-
butyl isothiocyanate and 5.32g (30 mmol) of 2,4,6-trimethylphenyl
isothiocyanate, respectively.
1
HL2: Yield: 4.81g (86%) (mp 91−93 °C). H NMR (500 MHz,
C6D6): δH 0.85−1.06 (m, 3H, CH2), 1.20−1.32 (m, 2H, CH2), 1.42−
1.48 (m, 1H, CH2), 1.49−1.57 (m, 2H, 6H, CH2), 2.08−2.15 (m, 2H,
CH2), 2.63(br s, 6H, NMe2), 4.64 (br m, 1H, NC(H)) 4.73 (br S, 1H,
N(H)); 13C{1H} NMR (125.7 MHz, C6D6); δC 25.4 (CH2), 26.1
(CH2), 33.5 (CH2), 39.5 (CH3), 54.3 (CH), 181.9 (C=S); Elemental
analysis (expected): C 58.02% (58.02%), H 9.78% (9.74%), N
15.08% (15.04%).
Synthesis of [{CyNC(S)NMe2}Zn{N(SiMe3)2}]2([{L2}ZnN{N-
(SiMe3)2}]2) (6), [{tBuNC(S)NMe2}ZnN{N(SiMe3)2}]2([{L3}ZnN{N-
(SiMe3)2}]2) (7) and [{MesNC(S)NMe2}ZnN{N(SiMe3)2}]2([{L4}-
ZnN{N(SiMe3)2}]2) (8). The complexes 6−8 were made in an
analogous manner to 5 using of 0.186g, (1 mmol) of HL2, 0.139g (1
mmol) of HL3 and 0.22g (1 mmol) of HL4 respectively.
1
HL3: Yield: 3.89g (81%) (mp 57−58 °C). H NMR (500 MHz,
6: Yield: 0.29 g (70%). 1H NMR (500 MHz, C6D6) δH 0.48 (s, 3H,
Zn−N(Si(Me3)2), 1.13−1.03 (m, 2H, Cy-CH2), 1.51−1.45 (m, 2H,
Cy -CH2, 1.70−1.60 (m, 2H, Cy-CH2), 1.91−1.815 (m, 2H, Cy-
CH2), 2.67 (s, 6H, -NMe2), 3.33−3.22 (m, 1H, -NCHCy); 13C{1H}
NMR (125.7 MHz, C6D6) δC 6.7 (Zn−N(SiMe3), 25.6 (Cy-CH2),
25.7 (Cy-CH2), 35.9 (Cy-CH2), 43.6 (-NMe2), 59.0 (-NCHCy),
179.2 (S-C-NMe2); Elemental analysis for C30H70N6S2Si4Zn2
(expected): C 43.86%, (43.83%), H 8.53% (8.58%), N 10.32%
(10.22%).
C6D6) δH 1.51 (s, 9H, CMe3), 2.60, (s, 6H, NMe2), 4.72 (bs s, 1H,
N(H)); 13C{1H} NMR (125.7 MHz, C6D6) δC 29.3 (CMe3), 39.6
(NMe2), 53.7 (CMe3), 181.7 (CS); Elemental analysis (expected):
C 52.59% (52.46%), H 10.09% (10.06%), N 17.51% (17.48%).
1
HL4: Yield: 5.47g (82%); (177−180 °C) H NMR (500 MHz,
C6D6) δH 2.17 (s, 3H, para-CMe3), 2.20 (s, 6H, ortho-CMe3), 2.64 (s,
6H NMe2), 5.64 (br s, 1H, N(H)), 6.82 (s, 2H, Ar−CH); 13C{1H}
NMR (125.7 MHz, C6D6) δC; 18.6 (ortho-MeH3) 21.1 (para-Me),
40.2 (NMe2), 129.2 (Ar-CH), 135.7 (Ar-C), 136.5 (Ar-C), 136.7 (Ar-
C), 183.0 (C=S); Elemental analysis (expected): C 64.82% (64.83%),
H 8.16% (8.16%), N 12.60% (12.58%).
1
7: Yield: 0.16 g (42%); H NMR (500 MHz, C6D6): δH 0.44 (s,
18H, Zn−N(SiMe3)2), 1.31 (s, 9H, -NCMe3), 2.52 (s, 6H,
-N(CH3)2); 13C{1H} NMR (125.7 MHz, C6D6): δC 6.6 (Zn−
N(SiMe3), 31.1 (-NCMe3), 44.7 (-NMe2), 57.9 (-NCMe3), 179.1 (S-
C-NMe2); Elemental analysis for C26H66N6S2Si4Zn2 (expected): C
39.96%, (40.55%), H 8.69% (8.64%), N 10.98% (10.91%).
Synthesis of [{iPrNC(S)NMe2}ZnMe]2([{L1}ZnMe]2) (1). To a
cooled solution of HL1 (0.197g, 1.35 mmol) in 20 mL of toluene was
added 0.675 mL (1.35 mmol) of a 2.0 M dimethyl zinc solution in
toluene and the resulting reaction mixture was left to stir overnight.
Visible gas was seen to be produced in the colorless solution. The
solution was reduced in vacuo and recrystallized at −28 °C affording
1
8: Yield: 0.23 g (52%); H NMR (500 MHz, C6D6) δH 0.31 (s,
18H, -N(SiMe3)2), 2.09 (s, 3H, para-Me), 2.35 (s, 6H, ortho-Me), 2.58
(s, 6H, -NMe2), 6.73 (s, 2H, meta-CH); 13C{1H} NMR (125.7 MHz,
C6D6) δC 6.0 (-N(SiMe3)2), 19.4 (ortho-Me), 20.9 (para-Me), 42.9
(-NMe2), 128.9 (meta-CH), 134.2 (para-C-Me), 143.5 (ortho-C-Me),
144.3 (-N-C), 168.4 (S-C-NMe2); Elemental analysis for
C36H70N6S2Si4Zn2 (expected): C 48.87%, (48.83%), H 7.86%
(7.89%), N 9.57% (9.40%).
1
white crystals. Yield: 0.13 g (43%). H NMR (500 MHz, C6D6): δH
−0.01 (s, 3H, Zn−CH3), 1.03 (d, J = 6.20 Hz, 6H, -NCHMe2), 2.58
(s, 6H, -NMe2, 3.50 (sept, J = 6.20 Hz, 1H, -NCHMe2); 13C{1H}
NMR (125.7 MHz, C6D6): δc −11.9 (Zn-Me), 25.0 (NCHMe2), 42.9
(−CNMe2), 49.8 (NCHMe2), 173.0 (S-C-NMe2); Elemental analysis
for C14H32N4S2Zn2 (expected): C 37.19% (37.26%), H 7.17%
(7.15%), N 12.39% (12.41%).
Synthesis of Bis-[{iPrNC(S)NMe2}2Zn]2([{L1}2Zn]2) (9). Zn{N-
(SiMe3)2}2 (0.39g, 1 mmol) was dissolved in toluene (20 mL) and
added to a cooled solution of the pro-ligand HL1 (0.292g, 2 mmol) in
20 mL of toluene, and stirred for 8 h. The volume of solvent was
reduced by half, in vacuo, yielding a cloudy suspension which was
redissolved with gentle heating, and allowed to crystallize at −28 °C,
Synthesis of [{CyNC(S)NMe2}ZnMe]2([{L2}ZnMe]2) (2),
[{tBuNC(S)NMe2}ZnMe]∞([{L3}ZnMe]∞) (3) and [{MesNC(S)-
NMe2}ZnMe]2([{L4}ZnMe]2) (4). The complexes 2−4 were made
in an analogous manner to 1 using of 0.186g, (1 mmol) of HL2,
0.139g (1 mmol) of HL3 and 0.22g (1 mmol) of HL4 respectively.
2: Yield: 0.08 g (29%). 1H NMR (500 MHz, C6D6): δH0.05 (s, 3H,
Zn-Me), 1.08−0.91 (m, 2H, Cy-CH2), 1.46−1.35 (m, 2H, Cy-CH2),
1.60−1.49 (m, 2H, Cy-CH2), 1.87−1.75 (m, 2H, Cy-CH2), 2.63 (s,
1
affording white crystals. Yield; 0.21g (60%). H NMR (300 MHz,
C6D6) δH1.21 (m, 6H, -NCHMe2), 2.64 (s, 6H, -NMe2), 3.63 (m, 1H,
-NCHMe2); 13C{1H} NMR (75.5 MHz, C6D6) δC25. Eight
K
DOI: 10.1021/acs.inorgchem.8b03363
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(-NCHMe2), 43.98 (-NMe2), 50.9 (-NCH(CH3)2), 181.0 (S-C-
NMe2); Elemental analysis for C24H52N8S4Zn2:C7H8 (expected): C
46.33%, (46.32%), H 7.50% (7.52%), N 14.13% (13.94%).
started. Gas flow is monitored via bubbler and gas pressure fixed 10
bar until it reaches the atomizer, as described previously.19,21,22,24
Thermogravimetric Analysis (TGA). TGA was collected using a
TGA 4000 PerkinElmer system. Samples were prepared air sensitively
using a crimped aluminum sample pan. TGA was performed under a
flow of N2 at 20 mL min−1 and heated from 30 to 600 °C at a ramp
rate of 5 °C min−1. TGA-MS was performed under argon (20 mL/
min) at a ramp rate of 5 °C/min between 30 and 600 °C on a
Setaram Setsys Evolution TGA 16/18 with the evolved gases passing
through a Pfeiffer Vacuum Omnistar GSD 320 quadrapole mass
spectrometer. Samples were contained in alumina crucibles. Experi-
ments were performed by MC2, University of Bath, UK, and results
were analyzed using Excel.
Powder X-ray Diffractometry (PXRD). PXRD data was
collected on a BRUKER D8-Advance. The X-ray diffraction spectra
were collected for the thin films using the flat plate mode from 5 to 70
2θ at 2° per minute. X-rays were generated from a Cu source at
wavelengths of 1.54 Å.
Scanning Electron Microscopy (SEM). SEM was performed to
visualize the morphology of the films as both cross sections (using a
Field Emission Scanning Electron Microscope 6301F) and top down
(JEOL 6480 Low Vacuum large stage SEM platform) images. The
films were prepared by mounting onto steel SEM mounts with
conductive carbon tape attached to the bottom and top surface of the
films, to maximize conductivity of electrons and prevent charge
accumulation. Samples were desiccated at 35 °C for 24 h prior to
analysis.
Synthesis of Bis-[{CyNC(S)NMe2}2Zn]([{L2}2Zn]) (10), Bis-
[{tBuNC(S)NMe2}2Zn]2([{L3}2Zn]2) (11) and Bis-[{MesNC(S)-
NMe2}2Zn]2([{L4}2Zn]2) (12). The complexes 10−12 were made in
an analogous manner to 9 using of 0.186 g, (1 mmol) of HL2, 0.139 g
(1 mmol) of HL3 and 0.22 g (1 mmol) of HL4 respectively.
10: Yield 0.25 g (56%); 1H NMR (500 MHz, C6D6) δH 1.17−1.03
(m, 3H, Cy-CH2) 1.51−1.41 (m, 1H, Cy-CH2), 1.71−1.57 (m, 2H,
Cy -CH2), 2.16−1.02 (m, 2H, Cy-CH2), 2.65 (s, 6H, -NMe2), 3.35−
3.23 (m, 1H, −N-CH(Cy)); 13C{1H} NMR (125.7 MHz, C6D6)
δC25.8 (Cy-CH2), 36.1 (Cy-CH2), 43.4 (-NMe2), 58.3 (-NC), 181.5
(S-C-NMe2); Elemental analysis for C36H68N8S4Zn2 (expected): C
49.49% (49.59%), H 8.01% (7.86%), N 12.79% (12.85%).
11: Yield 0.32g (83%); 1H NMR (500 MHz, C6D6) δH 1.22 (s, 9H,
-NCMe3), 2.47 (s, 6H, -NMe2); 13C{1H} NMR (125.7 MHz, C6D6)
δC 31.0 (-NCMe3), 44.4, (-NMe2), 65.3 (-NCMe3), 182.0 (S-C-
NMe2); Elemental analysis for C28H60N8S4Zn2(expected): C 43.48%
(43.80%), H 7.86% (7.88%), N 14.57% (14.59%).
12: 0.41g, (80%) 1H NMR (500 MHz, C6D6) δH2.06 (s, 6H, ortho-
Me), 2.16 (s, 3H, (para-Me), 2.42 (s, 6H, -NMe2), 6.65 (s, 2H, Ar-
CH); 13C{1H} NMR (125.7 MHz, C6D6) δC 19.0 (ortho-Me), 20.9
(para-Me), 42.0 (-NMe2), 110.4 (ortho-CMe), 128.5 (Ar-CH), 132.1
(para-C-Me), 144.2 (-NC(Ar)), 177.6 (S-C-NMe2); Elemental
analysis for C48H68N8S4Zn2 (expected): C 56.71% (56.74%), H
6.86%, (6.75%), N 10.87% (11.03%).
Atomic Force Microscopy (AFM). AFM analysis was performed
using a Digital Instruments Nanoscope IIIa, with BRUKER SNL-10
Silicon on Nitride Lever contact tips (tip radius <10 nm, f0: 50−80
kHz, k: 0.350 N/m and T: 600 nm), in contact mode. Images were
processed using the open access Gwyddion SPM data analyzer.
Energy Dispersive X-ray Spectroscopy (EDS). EDS was
performed using an Oxford Instruments Scanning Electron Micro-
scope 6480 LV and processed on INCA Wave software. All spectra
were standardized and calibrated against a standard silicon wafer
sample. The magnification, working distance, and beam energy (10
keV) were kept consistent between spectral analyses.
Single Crystal X-ray Diffraction Studies. Experimental details
relating to the single-crystal X-ray crystallographic studies for
compounds 1−9 and 12 are summarized in Table S1 (ESI). Single
crystal X-ray crystallography data were collected at 150 K on
RIGAKU SuperNova Dual wavelength diffractometer equipped with
an Oxford Cryostream, featuring a micro source with MoKα radiation
(λ = 0.71073 Å) and Cu Kα radiation (λ = 1.5418 Å). Crystals were
isolated from an argon filled Schlenk flask and immersed under oil
before being mounted onto the diffractometer. Structures were solved
by direct methods throughout and refined on F2 data using the
SHELXL-2014 suite of programs. All hydrogen atoms were included
in idealized positions and refined using the riding model. Refinements
were straightforward with no additional points that merit note. CCDC
1881545−1881554 contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ,
UK; fax: + 44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
AACVD Experiments. Thin films were deposited using a
horizontal hot wall reactor. The aerosol was generated with a TSI
3076 Constant Output Atomiser using N2 at 20 psi to generate the
aerosol and act as the carrier gas. Films were grown on either 2.5 cm
× 15 cm SiO2-coated glass (Pilkington NSG Ltd.), which were
cleaned with isopropanol, water, and acetone and then dried under a
flow of nitrogen gas, or commercial crystalline silicon. For each
deposition a 0.15 M THF solution of 9 was made up in a glovebox,
and transferred into a bubbler under an inert atmosphere. Depositions
were carried out at 200, 250, 300, and 350 °C for 1 h using N2 as a
carrier gas.
The precursor solution was prepared within a glovebox under an
atmosphere of argon and all solvents were dried and degassed prior to
use. The precursor bubbler was kept under an atmosphere of argon,
sealed, and attached onto to the AACVD apparatus. Once all
substrates were prepared and mounted into the deposition chamber,
nitrogen gas was allowed to flow through the system, bypassing the
precursor holder, for 20 min in order to purge the system with
nitrogen. Then with continuing gas flow the hot-wall furnace is
switched on and allowed to reach the target deposition temperature
and equilibrate for 20 min. Once this is achieved the gas flow is
diverted to flow via the precursor solution which draws the solution
into the TSI 3076 Constant Output Atomiser and out into the
deposition chamber where the deposition commences and the timer is
Raman Spectroscopy. Raman spectra were collected using a
Renishaw inVia Raman Microscope fitted with a 532 nm laser at a
10% spot size, 3 s exposure time, and 1% energy intensity. The data
was processed using a Renishaw WiRE software package.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b03363.
■
S
Figures showing the molecular structures of complexes
5, 6, and 8. Experimental details relating to the single-
crystal X-ray crystallographic studies and crystallo-
graphic data for complexes 1−9 and 12. Additional
FE-SEM and AFM images of thin films (PDF)
Accession Codes
CCDC 1881545−1881554 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
*E-mail: a.l.johnson@bath.ac.uk.
■
ORCID
Michael S. Hill: 0000-0001-9784-9649
L
DOI: 10.1021/acs.inorgchem.8b03363
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Films Deposited by RF Sputtering. Mater. Sci. Semicond. Process. 2017,
71, 7−11.
Andrew L. Johnson: 0000-0001-5241-0878
Notes
(7) (a) Frigo, D. M.; Khan, O. F. Z.; O’Brien, P. Growth of Epitaxial
and Highly Oriented Thin Films of Cadmium and Cadmium Zinc
Sulfide by Low-Pressure Metalorganic Chemical Vapour Deposition
Using Diethyldithiocarbamates. J. Cryst. Growth 1989, 96, 989−992.
(b) Hursthouse, M. B.; Malik, M. A.; Motevalli, M.; O’Brien, P. Mixed
Alkyl Dialkylthiocarbamates of Zinc and Cadmium: Potential
Precursors for II/VI Materials. X-ray Crystal Structure of
[MeZnS2CNEt2]2. Organometallics 1991, 10, 730−732. (c) Seo, K.
W.; Yoon, S. H.; Lee, S. S.; Shim, I. W. Preparation of ZnS Thin Film
Using Zn(dithiocarbamate)2 Precursors by MOCVD Method. Bull.
Korean Chem. Soc. 2005, 26, 1582−1584. (d) Nyamen, L. D.; Nejo, A.
A.; Pullabhotla, V. S. R.; Ndifon, P. T.; Malik, M. A.; Akhtar, J.;
O’Brien, P.; Revaprasadu, N. The Syntheses and Structures of Zn(II)
Heterocyclic Piperidine and Tetrahydroquinoline Dithiocarbamates
and Their use as Single Source Precursors for ZnS Nanoparticles.
Polyhedron 2014, 67, 129−135.
(8) (a) Barreca, D.; Tondello, E.; Lydon, D.; Spalding, T. R.;
Fabrizio, M. Single-Source Chemical Vapor Deposition of Zinc
Sulfide-Based Thin Films from Zinc bis(O-ethylxanthate). Chem. Vap.
Deposition 2003, 9, 93−98. (b) Barreca, D.; Gasparotto, A.; Maragno,
C.; Tondello, E.; Sada, C. CVD of Nanophasic (Zn, Cd)S Thin Films:
From Multi-Layers to Solid Solutions. Chem. Vap. Deposition 2004,
10, 229−236. (c) Barreca, D.; Gasparotto, A.; Maragno, C.; Seraglia,
R.; Tondello, E.; Venzo, A.; Krishnan, V.; Bertagnolli, H. Synthesis
and Characterization of Zinc Bis(O-isopropylxanthate) as a Single-
Source Chemical Vapor Deposition Precursor for ZnS. Appl.
Organomet. Chem. 2005, 19, 1002−1009.
(9) Pawar, A. S.; Mlowe, S.; Garje, S. S.; Akerman, M. P.;
Revaprasadu, N. Zinc Thiosemicarbazone Complexes: Single Source
Precursors for Alkylamine Capped ZnS Nanoparticles. Inorg. Chim.
Acta 2017, 463, 7−13.
(10) (a) Nyman, M.; Hampden-Smith, M. J.; Duesler, E. N. Low
Temperature, Aerosol-Assisted Chemical Vapor Deposition
(AACVD) of CdS, ZnS, and Cd1‑xZnxS Using Monomeric Single-
Source Precursors: M(SOCCH3)2TMEDA. Chem. Vap. Deposition
1996, 2, 171−174. (b) Vittal, J. J.; Ng, M. T. Chemistry of Metal
Thio- and Selenocarboxylates: Precursors for Metal Sulfide/Selenide
Materials, Thin Films, and Nanocrystals. Acc. Chem. Res. 2006, 39,
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors thank the EPSRC for funding (EP/L016354/1),
the EPSRC Centre for Doctoral Training in Sustainable
Chemical Technologies for a PhD studentship (H.S.I.S.), the
University of Bath for financial support (PhD studentship to
J.D.P.), and the Royal Thai Government for a postgraduate
scholarship (P.T.).
REFERENCES
■
(1) (a) Yanagiya, S.-i.; Iseki, Y.; Kaito, T.; Mori, A.; Kaito, C.;
Sekiguchi, T.; Inoue, T. Growth of ZnS Nano-Crystallites in Gel and
their Characterization. Mater. Chem. Phys. 2007, 105, 250−252.
(b) Fang, X.; Bando, Y.; Gautam, U. K.; Zhai, T.; Zeng, H.; Xu, X.;
Liao, M.; Golberg, D. ZnO and ZnS Nanostructures: Ultraviolet-Light
Emitters, Lasers, and Sensors. Crit. Rev. Solid State Mater. Sci. 2009,
34, 190−223. (c) Fang, X.; Zhai, T.; Gautam, U. K.; Li, L.; Wu, L.;
Bando, Y.; Golberg, D. ZnS Nanostructures: From Synthesis to
Applications. Prog. Mater. Sci. 2011, 56, 175−287. (d) Ehsan, M. A.;
Peiris, T. A. N.; Wijayantha, K. G. U.; Khaledi, H.; Ming, H. N.;
Misran, M.; Arifin, Z.; Mazhar, M. Surface Morphological and
Photoelectrochemical Studies of ZnS Thin Films Developed from
Single Source Precursors by Aerosol Assisted Chemical Vapour
Deposition. Thin Solid Films 2013, 540, 1−9.
(2) Yeh, C.-Y.; Lu, Z. W.; Froyen, S.; Zunger, A. Zinc-Blende−
Wurtzite Polytypism in Semiconductors. Phys. Rev. B: Condens. Matter
Mater. Phys. 1992, 46, 10086−10097.
́
(3) La Porta, F. A.; Gracia, L.; Andres, J.; Sambrano, J. R.; Varela, J.
A.; Longo, E.; Zhou, Y. A DFT Study of Structural and Electronic
Properties of ZnS Polymorphs and its Pressure-Induced Phase
Transitions. J. Am. Ceram. Soc. 2014, 97, 4011−4018.
(4) (a) Brafman, O.; Mitra, S. S. Raman Effect in Wurtzite- and
Zinc-Blende-Type ZnS Single Crystals. Phys. Rev. 1968, 171, 931−
934. (b) Wagner, H. P.; Kuhnelt, M.; Langbein, W.; Hvam, J. M.
̈
Dispersion of the Second-Order Nonlinear Susceptibility in ZnTe,
ZnSe, and ZnS. Phys. Rev. B: Condens. Matter Mater. Phys. 1998, 58,
10494−10501. (c) Ding, Y.; Wang, X. D.; Wang, Z. L. Phase
Controlled Synthesis of ZnS Nanobelts: Zinc Blende vs Wurtzite.
Chem. Phys. Lett. 2004, 398, 32−36.
́
869−877. (c) Vallejo-Sanchez, D.; Beobide, G.; Castillo, O.; Lanchas,
M. Zinc Thiocarboxylate Complexes as Precursors for Zinc Sulfide
Nanoparticles under Aerobic Conditions. Eur. J. Inorg. Chem. 2013,
32, 5592−5602.
(5) (a) Shao, L. X.; Chang, K. H.; Hwang, H. L. Zinc Sulfide Thin
Films Deposited by RF Reactive Sputtering for Photovoltaic
Applications. Appl. Surf. Sci. 2003, 212, 305−310. (b) Subbaiah, Y.
P. V.; Prathap, P.; Reddy, K. T. R. Structural, Electrical and Optical
Properties of ZnS Films Deposited by Close-Spaced Evaporation.
Appl. Surf. Sci. 2006, 253, 2409−2415. (c) Goudarzi, A.; Aval, G. M.;
Sahraei, R.; Ahmadpoor, H. Ammonia-Free Chemical Bath Deposi-
tion of Nanocrystalline ZnS Thin Film Buffer Layer for Solar Cells.
Thin Solid Films 2008, 516, 4953−4957.
(6) (a) Mandal, S. K.; Chaudhuri, S.; Pal, A. K. Optical Properties of
Nanocrystalline ZnS Films Prepared by High Pressure Magnetron
Sputtering. Thin Solid Films 1999, 350, 209−213. (b) Wei, M.; Choy,
K. L. Deposition of Highly Oriented ZnS Thin Films on Si(100)
Substrate Using Electrostatic Spray Assisted Vapor Deposition. Chem.
(11) Byrom, C.; Malik, M. A.; O’Brien, P.; White, A. J. P.; Williams,
D. J. Synthesis and X-ray Single Crystal Structures of Bis-
(diisobutyldithiophosphinato)Cadmium(II) or Zinc(II): Potential
Single-Source Precursors for II/VI Materials. Polyhedron 2000, 19,
211−215.
(12) Rojas-Montoya, I. D.; Santana-Silva, A.; García-Montalvo, V.;
́
́
Munoz-Hernandez, M.-A.; Rivera, M. N-(Chalcogen)phosphorylated
̃
(Chalcogen)ureas of Zinc and Cadmium(ii): SSPs for Group 12−16
Thin Films. New J. Chem. 2014, 38, 4702−4710.
(13) (a) Ramasamy, K.; Malik, M. A.; O’Brien, P.; Raftery, J. Metal
Complexes of Thiobiurets and Dithiobiurets: Novel Single Source
Precursors for Metal Sulfide Thin Film Nanostructures. Dalton Trans.
2010, 39, 1460−1463. (b) Ramasamy, K.; Malik, M. A.; Helliwell, M.;
Raftery, J.; O’Brien, P. Thio- and Dithio-Biuret Precursors for Zinc
Sulfide, Cadmium Sulfide, and Zinc Cadmium Sulfide Thin Films.
Chem. Mater. 2011, 23, 1471−1481. (c) Abdelhady, A. L.; Malik, M.
A.; O’Brien, P. Colloidal Synthesis of ZnS, CdS and Zn x Cd1−x S
Nanoparticles from Zinc and Cadmium Thiobiuret Complexes. J.
Inorg. Organomet. Polym. Mater. 2014, 24, 226−240.
́
Vap. Deposition 2002, 8, 15−17. (c) Hernandez-Fenollosa, M. A.;
́
́
Lopez, M. C.; Donderis, V.; Gonzalez, M.; Marí, B.; Ramos-Barrado,
J. R. Role of Precursors on Morphology and Optical Properties of ZnS
Thin Films Prepared by Chemical Spray Pyrolysis. Thin Solid Films
2008, 516, 1622−1625. (d) Chelvanathan, P.; Yusoff, Y.; Haque, F.;
Akhtaruzzaman, M.; Alam, M. M.; Alothman, Z. A.; Rashid, M. J.;
Sopian, K.; Amin, N. Growth and Characterization of RF-Sputtered
ZnS Thin Film Deposited at Various Substrate Temperatures for
Photovoltaic Application. Appl. Surf. Sci. 2015, 334, 138−144. (e) Le
Donne, A.; Cavalcoli, D.; Mereu, R. A.; Perani, M.; Pagani, L.;
Acciarri, M.; Binetti, S. Study of the Physical Properties of ZnS Thin
(14) (a) Maury, F. Trends in Precursor Selection for MOCVD.
Chem. Vap. Deposition 1996, 2, 113−116. (b) Afzaal, M.; Malik, M.
A.; O’Brien, P. Chemical Routes to Chalcogenide Materials as Thin
Films or Particles with Critical Dimensions with the Order of
Nanometres. J. Mater. Chem. 2010, 20, 4031−4040.
M
DOI: 10.1021/acs.inorgchem.8b03363
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(15) Gleizes, A. N. MOCVD of Chalcogenides, Pnictides, and
Heterometallic Compounds from Single-Source Molecule Precursors.
Chem. Vap. Deposition 2000, 6, 155−173.
(16) Marchand, P.; Hassan, I. A.; Parkin, I. P.; Carmalt, C. J.
Aerosol-Assisted Delivery of Precursors for Chemical Vapour
Deposition: Expanding the Scope of CVD for Materials Fabrication.
Dalton Trans. 2013, 42, 9406−9422.
(17) (a) Pike, R. D.; Cui, H.; Kershaw, R.; Dwight, K.; Wold, A.;
Blanton, T. N.; Wernberg, A. A.; Gysling, H. J. Preparation of Zinc
Sulfide Thin Films by Ultrasonic Spray Pyrolysis from Bis-
(diethyldithiocarbamato) Zinc(II). Thin Solid Films 1993, 224,
221−226. (b) Nomura, R.; Murai, T.; Toyosaki, T.; Matsuda, H.
Single-Source MOVPE Growth of Zinc Sulfide Thin Films using Zinc
Dithiocarbamate Complexes. Thin Solid Films 1995, 271, 4−7.
(18) Knapp, C. E.; Carmalt, C. J. Solution Based CVD of Main
Group Materials. Chem. Soc. Rev. 2016, 45, 1036−1064.
(19) Buckingham, M. A.; Catherall, A. L.; Hill, M. S.; Johnson, A. L.;
Parish, J. D. Aerosol-Assisted Chemical Vapor Deposition of CdS
from Xanthate Single Source Precursors. Cryst. Growth Des. 2017, 17,
907−912.
(20) Powell, M. J.; Carmalt, C. J. Aerosols: A Sustainable Route to
Functional Materials. Chem. - Eur. J. 2017, 23, 15543−15552.
(21) Catherall, A. L.; Harris, S.; Hill, M. S.; Johnson, A. L.; Mahon,
M. F. Deposition of SnS Thin Films from Sn(II) Thioamidate
Precursors. Cryst. Growth Des. 2017, 17, 5544−5551.
(22) Ahmet, I. Y.; Hill, M. S.; Johnson, A. L.; Peter, L. M.
Polymorph-Selective Deposition of High Purity SnS Thin Films from
a Single Source Precursor. Chem. Mater. 2015, 27, 7680−7688.
(23) Schmidt, S.; Schulz, S.; Bolte, M. [tBuC(NiPr)2]2Zn as Starting
Reagent for Monoamidinate Zinc Complexes {[tBuC(NiPr)2]ZnX}2.
Z. Anorg. Allg. Chem. 2009, 635, 2210−2213.
(24) Wildsmith, T.; Hill, M. S.; Johnson, A. L.; Kingsley, A. J.;
Molloy, K. C. Exclusive Formation of SnO by Low Temperature
Single-Source AACVD. Chem. Commun., 2013, 49, 8773
and Consolidation Characteristics of Historic Stone Surfaces. Mater.
Struct. 2012, 45, 505−520.
(30) Kole, A. K.; Kumbhakar, P. Cubic-to-Hexagonal Phase
Transition and Optical Properties of Chemically Synthesized ZnS
Nanocrystals. Results Phys. 2012, 2, 150−155.
(31) (a) Xiong, Q. H.; Wang, J. G.; Reese, O.; Voon, L.; Eklund, P.
C. Raman Scattering from Surface Phonons in Rectangular Cross-
Sectional W-ZnS Nanowires. Nano Lett. 2004, 4, 1991−1996.
(b) Nilsen, W. G. Raman Spectrum of Cubic ZnS. Phys. Rev. 1969,
182, 838−850. (c) Kim, J. H.; Rho, H.; Kim, J.; Choi, Y. J.; Park, J. G.
Raman Spectroscopy of ZnS Nanostructures. J. Raman Spectrosc.
2012, 43, 906−910. (d) Cheng, Y. C.; Jin, C. Q.; Gao, F.; Wu, X. L.;
Zhong, W.; Li, S. H.; Chu, P. K. Raman Scattering Study of Zinc
Blende and Wurtzite ZnS. J. Appl. Phys. 2009, 106, 123505-1−
123505-5.
(32) Vallejos, S.; Umek, P.; Blackman, C. Aerosol Assisted Chemical
Vapour Deposition Control Parameters for Selective Deposition of
Tungsten Oxide Nanostructures. J. Nanosci. Nanotechnol. 2011, 11,
8214−8220.
̀
(33) Vallejos, S.; Selina, S.; Annanouch, F. E.; Gracia, I.; Llobet, E.;
Blackman, C. Aerosol Assisted Chemical Vapour Deposition of Gas
sensitive SnO2 and Au-Functionalised SnO2 Nanorods via a Non-
Catalysed Vapour Solid (VS) Mechanism. Sci. Rep. 2016, 6, 1−12.
(34) (a) Madugu, M. L.; Olusola, O. I.-O.; Echendu, O. K.; Kadem,
B.; Dharmadasa, I. M. Intrinsic Doping in Electrodeposited ZnS Thin
Films for Application in Large-Area Optoelectronic Devices. J.
Electron. Mater. 2016, 45, 2710−2717. (b) Yoo, D.; Choi, M. S.;
Heo, S. C.; Chung, C.; Kim, D.; Choi, C. Structural, Optical and
Chemical Analysis of Zinc Sulfide Thin Film Deposited by RF-
Mganetron Sputtering and Post Deposition Annealing. Met. Mater.
Int. 2013, 19, 1309−1316.
(35) (a) Yoon, Y. G.; Choi, I. H. Preparation of ZnS Thin Films by
Using Photoassisted MOCVD. J. Korean Phys. Soc. 2013, 63, 1609−
1614. (b) Xu, H.; Li, Y.; Rosa, A. L.; Frauenheim, T.; Zhang, R. Q.
First-Principles Study of the Structural Stability and Electronic
Properties of ZnS Nanowires. J. Phys. Chem. C 2008, 112, 20291−
20294. (c) Wei, A. X.; Liu, J.; Zhuang, M. X.; Zhao, Y. Preparation
and Characterization of ZnS Thin Films Prepared by Chemical Bath
Deposition. Mater. Sci. Semicond. Process. 2013, 16, 1478−1484.
(d) Schrier, J.; Demchenko, D. O.; Wang, L. W. Optical properties of
ZnO/ZnS and ZnO/ZnTe Heterostructures for Photovoltaic
Applications. Nano Lett. 2007, 7, 2377−2382. (e) Li, Z. Q.; Shi, J.
H.; Liu, Q. Q.; Wang, Z. A.; Sun, Z.; Huang, S. M. Effect of Zn/S
Ratios on the Properties of Chemical Bath Deposited Zinc Sulfide
Thin Films. Appl. Surf. Sci. 2010, 257, 122−126. (f) Fang, X. S.; Zhai,
T. Y.; Gautam, U. K.; Li, L.; Wu, L. M.; Yoshio, B.; Golberg, D. ZnS
Nanostructures: From Synthesis to Applications. Prog. Mater. Sci.
2011, 56, 175−287.
(25) (a) Kanters, J. A.; Spek, A. L.; Postma, R.; van Stein, G. C.; van
Koten, G. Structure of Bis[N-(2-pyrrolylmethylene)-tert-butylamine]-
Zinc(II), Zn(C9H13N2)2. Acta Crystallogr., Sect. C: Cryst. Struct.
́
́
Commun. 1983, 39, 999−1001. (b) Fernandez-Galan, R.; Antin
̃
olo,
A.; Carrillo-Hermosilla, F.; Lopez-Solera, I.; Otero, A.; Serrano-
Laguna, A.; Villasenor, E. Migratory Insertion Reactions in Asym-
́
̃
metrical Guanidinate-Supported Zirconium Complexes. Organo-
metallics 2012, 31, 8360−8369.
(26) Johnson, A. L.; Hollingsworth, N.; Kociok-Kohn, G.; Molloy,
̈
K. C. Organozinc Aminoalcoholates: Synthesis, Structure, and
Materials Chemistry. Inorg. Chem. 2008, 47, 12040−12048.
(27) Coles, M. P.; Hitchcock, P. B. Zinc Guanidinate Complexes
and Their Application in Ring-Opening Polymerisation Catalysis. Eur.
J. Inorg. Chem. 2004, 13, 2662−2672.
́
́
(36) Rivillo, D.; Gulyas, H.; Benet-Buchholz, J.; Escudero-Adan, E.
C.; Freixa, Z.; van Leeuwen, P.W. N. M. Catalysis by Design: Wide-
Bite-Angle Diphosphines by Assembly of Ditopic Ligands for
Selective Rhodium-Catalyzed Hydroformylation. Angew. Chem., Int.
Ed. 2007, 46, 7247−7250.
(28) (a) Benson, R. E.; Ellis, C. A.; Lewis, C. E.; Tiekink, E. R. T.
3D-, 2D- and 1D-Supramolecular Structures of {Zn[S2CN-
(CH2CH2OH)R]2}2 and their {Zn[S2CN(CH2CH2OH)R]2}2(4,4′-
bipyridine) Adducts for R = CH2CH2OH, Me or Et: Polymorphism
and Pseudo-Polymorphism. CrystEngComm 2007, 9, 930−940.
(b) Malik, M. A.; O'Brien, P. Mixed Methyl-Zinc and Ethylzinc
Complexes with Diethylselenocarbamate - Novel Precursors for ZnSe.
Chem. Mater. 1991, 3, 999−1000. (c) Memon, A. A.; Afzaal, M.;
Malik, M. A.; Nguyen, C. Q.; O’Brien, P.; Raftery, J. The N-
alkyldithiocarbamato Complexes [M(S2CNHR)2] (M = Cd(II)
Zn(II); R = C2H5C4H9C6H13C12H25); Their synthesis, thermal
Decomposition and use to Prepare of Nanoparticles and Nanorods
of CdS. Dalton Trans. 2006, No. 37, 4499−4505. (d) O’Brien, P.;
Walsh, J. R.; Watson, I. M.; Motevalli, M.; Henriksen, L. Novel
Dithio- and Diseleno-Carbamates of Zinc and Cadmium as Single-
Molecule Precursors for Low-Pressure Metal-Organic Chemical
Vapour Deposition. J. Chem. Soc., Dalton Trans. 1996, 12, 2491−
2496.
́
́
́
̌
́
(29) Drdacky, M.; Lesak, J.; Rescic, S.; Slízkova, Z.; Tiano, P.;
Valach, J. Standardization of Peeling Tests for Assessing the Cohesion
N
DOI: 10.1021/acs.inorgchem.8b03363
Inorg. Chem. XXXX, XXX, XXX−XXX