Chalcogenoether complexes of Nb(v) thio- and seleno-halides as single source precursors for low pressure chemical vapour deposition of NbS2 and NbSe2 thin films

Article abstract of DOI:10.1039/c7dt01911d

NbSCl₃ was obtained via reaction of NbCl₅ with S(SiMe₃)₂ in anhydrous CH₂Cl₂, whilst in MeCN solution the same reaction gives [NbSCl₃(MeCN)₂]. [NbSeCl₃(MeCN)₂] was obtained similarly from NbCl₅ with Se(SiMe₃)₂. The chalcogenoether complexes, [NbSCl₃(ER₂)] (E = S: R = Me, ⁿBu; E = Se: R = ⁿBu), were obtained from reaction of NbCl₅, ER₂ and S(SiMe₃)₂ in CH₂Cl₂. The structure of the [Nb₂S₂Cl₆(SMe₂)₂] reveals a Cl-bridged dimer with the SMe₂ ligands disposed syn. The Cl bridges are highly asymmetric, with the long Nb-Cl bond trans NbS. The complexes, [NbSCl₃(L-L)] (L-L = MeSCH₂CH₂SMe, MeS(CH₂)₃SMe, ⁱPrSCH₂CH₂SⁱPr, MeSe(CH₂)₃SeMe and ⁿBuS(CH₂)₃SⁿBu), were obtained from reaction of L-L with preformed [NbSCl₃(MeCN)₂]. The structures of the Me-substituted complexes reveal distorted octahedral monomers with the neutral ligands trans to S/Cl. Solution ¹H and ⁷⁷Se{¹H} NMR data showed that the neutral ligands are partially dissociated and undergoing fast exchange at ambient temperatures in CH₂Cl₂ solution, consistent with weak Lewis acidity for NbSCl₃. The complexes containing ⁿBu-substituted ligands have been used as single source precursors for low pressure chemical vapour deposition (CVD) of 3R-NbS₂ thin films. 2H-NbSe₂ thin films were also obtained via low pressure CVD using [NbSe₂Cl₃(SeⁿBu₂)]. The thin films were characterised by grazing incidence and in-plane XRD, pole figure analysis, scanning electron microscopy and energy dispersive X-ray analysis.

Full text of DOI:10.1039/c7dt01911d

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Chalcogenoether complexes of Nb(V) thio- and
seleno-halides as single source precursors for
low pressure chemical vapour deposition of
NbS and NbSe thin films†
Cite this: DOI: 10.1039/c7dt01911d
2
2
Yao-Pang Chang, Andrew L. Hector,
William Levason
and Gillian Reid
*
NbSCl
the same reaction gives [NbSCl
SiMe . The chalcogenoether complexes, [NbSCl
obtained from reaction of NbCl , ER and S(SiMe
reveals a Cl-bridged dimer with the SMe ligands disposed syn. The Cl bridges are highly asymmetric, with
the long Nb–Cl bond trans NbvS. The complexes, [NbSCl (L–L)] (L–L = MeSCH CH SMe, MeS
S Bu), were obtained from reaction of L–L
]. The structures of the Me-substituted complexes reveal distorted octa-
3
was obtained via reaction of NbCl
5
with S(SiMe
(MeCN)
(ER )] (E = S: R = Me, Bu; E = Se: R = Bu), were
in CH Cl . The structure of the [Nb Cl (SMe
3
)
2
in anhydrous CH
2
Cl
2
, whilst in MeCN solution
3
(MeCN) ]. [NbSeCl
2
3
2
] was obtained similarly from NbCl
5
with Se
n
n
(
3
)
2
3
2
5
2
3
)
2
2
2
2
S
2
6
2 2
) ]
2
3
2
2
i
i
n
n
(CH
2
)
3
SMe, PrSCH
2
CH
2
S Pr, MeSe(CH
2 3 2 3
) SeMe and BuS(CH )
with preformed [NbSCl
3
(MeCN)
2
1
77
1
hedral monomers with the neutral ligands trans to S/Cl. Solution H and Se{ H} NMR data showed that
the neutral ligands are partially dissociated and undergoing fast exchange at ambient temperatures in
n
CH Cl
2 2
solution, consistent with weak Lewis acidity for NbSCl
3
. The complexes containing Bu-substi-
Received 25th May 2017,
Accepted 26th June 2017
tuted ligands have been used as single source precursors for low pressure chemical vapour deposition
(
[
CVD) of 3R-NbS
2
thin films. 2H-NbSe
2
thin films were also obtained via low pressure CVD using
DOI: 10.1039/c7dt01911d
n
NbSe Cl
2 3
(Se Bu
2
)]. The thin films were characterised by grazing incidence and in-plane XRD, pole figure
rsc.li/dalton
analysis, scanning electron microscopy and energy dispersive X-ray analysis.
4–6
precursors.
control of deposit stoichiometry, cost-effective use of reagents,
(M = Nb, and in some cases the ability to selectively deposit the ME onto
Single source precursors potentially offer better
Introduction
Layered early transition metal dichalcogenides ME
2
2
Ta, V, W etc., E = S, Se or Te), inorganic analogues of graphite or nano-patterned substrates. Reagents for CVD of NbS or NbSe2
2
graphene, are highly stable, and their properties can be tuned are rare, but include niobium thiolate complexes for the
1
7
t
5 2
by varying the metal and the chalcogen. Applications of these former and a dual source approach using NbCl -Se Bu for the
6
materials in areas such as optoelectronics, spintronics, sensors, latter. We recently reported the deposition of thin films of
electrocatalysis and magnetic materials are being actively NbS and NbSe as the 3R-polytype (R3mh) using [NbCl (S Bu )]
n
2
2
5
2
1–3
n
developed.
5 2
Production of the materials as thin films maxi- and [NbCl (Se Bu )], respectively, as single source low pressure
8
mises the anisotropy of their magnetic or electronic properties chemical vapour deposition (LPCVD) precursors. The pro-
and thus methods to deposit 2D layers are of great current inter- perties of the potential precursors are key to successful
est. Chemical vapour deposition (CVD) is a low cost versatile applications in this area, requiring appropriate volatility and
method to deposit such films using either dual or single source clean deposition at accessible temperatures (a β-hydride
decomposition route for the neutral ligand is often helpful).
Our previous studies showed that Nb(III) dimers such as
n
n
[
Nb Cl (E Bu ) (μ-Cl) (μ-E Bu )] did not vaporise under
2
4
2 2
2
2
Chemistry, University of Southampton, Southampton SO17 1BJ, UK.
E-mail: G.Reid@soton.ac.uk
LPCVD conditions, probably due to their high molecular
9
n
†
Electronic supplementary information (ESI) available: Crystallographic para- weights, whilst the Nb(IV) complexes such [NbCl
4
(Se Bu
2
)
2
],
n
n
i
i
meters (Table S1), XRD data (Fig. S1) and SEM images (Fig. S2) for the NbS
2
film [NbCl { BuSe(CH ) Se Bu}] and [NbCl { PrSCH CH S Pr}], lost
4
2 3
4
2
2
n
n
obtained from [NbSCl
obtained by using less [NbSe
four crystallographically
542831–1542834. For ESI and crystallographic data in CIF or other electronic
3
{ BuS(CH
2
)
3
S Bu}] and XRD data from a NbSe
2
film
the chalogenoether on heating in vacuo, leaving a residue of
n
2
Cl
3
(Se Bu
2
)] precursor (∼50 mg). Cif files for the
precursor complexes. CCDC
10
4
the (strongly polymerised) NbCl .
characterised
Here we report on the synthesis and properties of chalco-
genoether complexes of niobium chalcogenide trichlorides
1
format see DOI: 10.1039/c7dt01911d
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3
NbECl (E = S or Se) and attempts to use them as LPCVD
reagents. Chalcogenohalides are known for many of the
1
1
transition elements, although their coordination chemistry
has been much less explored than those of the corresponding
1
2
halides or oxide halides.
Lewis bases include [NbSCl
Complexes of NbSX3 with
−
13
14
4
] ,
[NbSCl
3
(Ph
3
PS)],
and
and
1
5
15
[
[
NbSX
NbSX (MeCN) ],
3
(Ph
3
PO)
2
]
(X
=
Cl, Br),
[NbSCl
3
2
(SEt )],
1
5,16
However, in other systems rearrange-
3
2
ments occur to form compounds with dichalcogenide bridges,
including the structurally characterised [Nb Cl (Se (L) ] (L =
2
4
2
)
2
4
7,18
1
SMe or tetrahydrothiophene (tht)) and [Nb S X (tht) ].
2
2
3
4
4
Results and discussion
Complex synthesis and properties
Fig. 1 The structure of [Nb
scheme and with ellipsoids drawn at the 50% probability level. Hydrogen
2
S
2
Cl
6
(SMe
2
)
2
] showing the atom numbering
We obtained crude NbSCl as a dark green solid by reaction of
3
atoms are omitted for clarity. Selected bond lengths (Å): Nb1–S1 =
NbCl
5
with S(SiMe
3
)
2
in CH
2
Cl
2
in an ice-bath, and this solid 2.127(2), Nb1–S2 = 2.660(2), Nb1–Cl1 = 2.420(2), Nb1–Cl2 = 2.324(2),
Nb1–Cl3 = 2.305(2), Nb1–Cl4 = 2.921(2), Nb2–S3 = 2.123(2), Nb2–S4 =
was used to test the parent compound as an LPCVD reagent
(
1
9
2.655(2), Nb2–Cl1 = 2.939(2), Nb2–Cl4 = 2.405(2), Nb2–Cl5 = 2.326(2),
Nb2–Cl6 = 2.323(2).
see below). As pointed out by others, the colour of NbSCl is
3
variously described as golden-yellow to green or black in the
literature, and it was suggested that the darker coloured
samples contain Nb S Cl impurities. The ν(NbvS) vibration
2
3
4
at 550 cm− agrees with the literature value.
1
20
[NbECl
(S Bu
n
)] were similar, suggesting an analogous struc-
(SMe )] showed it to be a
] (Fig. 1). The bond lengths are
in an ice-bath, or by reaction unexceptional, with the exception that those associated with
] with the ligand in CH Cl
at ambient the bridging Cl ligands lying trans to Nb–S are highly asym-
temperatures. [NbSCl (MeCN) ] was made by the literature metric. Notably the two SMe ligands are syn-disposed, rather
in MeCN than the much more common anti arrangement found in
in MeCN, filter- many centrosymmetric d-block dimers.
ing to remove any insoluble material, and evaporating the
The MeCN ligands in [NbSCl (MeCN)
filtrate to dryness. The products of the two methods are substituted on reaction with an excess (three equivalents)
3
2
The thio- and seleno-ether complexes of NbSCl
obtained in good yield either by reaction of NbCl5 with the dimer, [Nb
ligand and S(SiMe in CH Cl
of [NbSCl (MeCN)
3
were ture. The X-ray structure of [NbSCl
3
2
S
Cl (μ-Cl) (SMe
)
2 2
2
2
4
2
3
)
2
2
2
3
2
2
2
3
2
2
method, involving reaction of NbCl
5
with S(SiMe
solution, or by dissolving the crude NbSCl
3 2
)
1
6
3
] were cleanly
2
3
i
i
spectroscopically identical, and the data agree well with the of MeSCH
2
CH
SeMe in CH
to give green [NbSCl
2
SMe, MeS(CH
Cl solution at ambient temperatures,
(L–L)] (L–L MeSCH CH SMe,
S Pr) or brown [NbSCl {MeSe
S Bu pro-
S Bu}] as a green oil. The X-ray
{MeSe(CH SeMe}] showed a dis-
2 3 2 2
) SMe, PrSCH CH S Pr or
1
5,16
literature.
NbSeCl
in MeCN as a brown solid. The IR spectroscopic properties, MeS(CH
ν(MeCN) = 2310, 2281, ν(NbvSe) = 397, ν(Nb–Cl) = 377, (CH SeMe}] powdered solids. Using BuS(CH )
2 3
MeSe(CH
2
)
3
2
2
[
3
(MeCN)
2
] was obtained from NbCl
5
and Se(SiMe
3
)
2
3
=
2
2
i
i
2
)
3
SMe, PrSCH
2
CH
2
3
n
n
)
3
2
3
44 cm− , are as expected, although our assignment of NbvSe duced [NbSCl
1
3 2 3
{ BuS(CH )
n
n
and Nb–Cl vibrations is tentative as they occur at similar fre- crystal structure of [NbSCl
3
2 3
)
9
3
quencies. The Nb NMR chemical shift, δ = 923, is at signifi- torted octahedral geometry, with the in plane terminal S/Cl
cantly higher frequency than in the thiochloride analogue, disordered. The disorder was successfully modelled using split
reflecting the effect of the selenium coordination.
sites for these two atoms and refined at 50 : 50 occupancies;
only one form is shown in Fig. 2. The key bond lengths are
The reaction of NbCl with SMe and S(SiMe ) in CH Cl
2
5
2
3 2
2
cooled to ∼0 °C produced a yellow–green solid of stoichiometry Nb1–Cl1 = 2.308(7), Nb1–S1 = 2.197(8) Å, whilst the axial
n
[
[
NbSCl
3
(SMe
2
)], whilst use of S Bu
2
gave
a
dark oil Nb1–Cl2 = 2.3686(6) Å, i.e. significantly longer.
The structures of two thioether
3 2 2
(MeSCH CH SMe)] and [NbSCl ( PrSCH CH S Pr)],
n
NbSCl (S Bu )]. The IR spectrum of [NbSCl (SMe )] shows a
strong vibration at 530 cm , assigned as a terminal ν(NbvS), [NbSCl
with ν(Nb–Cl) vibrations at 369, 356, 322 cm . In chloro- were also determined and are shown in Fig. 3 and 4. The X-ray
complexes,
3
2
3
2
−
1
i
i
3
2
2
−
1
carbon solution it shows a single δ(Me) resonance in the diffraction data were good quality and careful examination did
1
H NMR spectrum, shifted to high frequency from SMe
2
, and, not provide clear evidence for S/Cl disorder in these cases and
9
3
21
more interestingly, a Nb NMR resonance at δ = 651. the d(NbvS) = 2.10 Å and d(Nb–Cl) = 2.24 Å are nearly identi-
The resonances of niobium thiochloride complexes are found cal in the two structures. Notably, the d(Nb–S) distances trans
to high frequency of those of NbCl
2
2,23
.
(Note that the to the NbvS and trans to Nb–Cl are different, consistent with
5
chemical shifts in ref. 22 are reported using the old high a trans influence of NbvS > Nb–Cl. However, as pointed out by
1
4,17,18
frequency negative convention.) The spectroscopic data on others,
it is not possible to rule out some disorder in the
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i
i
Fig. 2 The structure of [NbSCl
3
{MeSe(CH
2
)
3
SeMe}] showing the atom
3 2 2
Fig. 4 The structure of [NbSCl ( PrSCH CH S Pr)] showing the atom
numbering scheme and with ellipsoids drawn at the 50% probability
level. Hydrogen atoms are omitted for clarity. Note that S1 and Cl1 are
disordered, and only one molecule is shown here. Selected bond
lengths (Å) and angles (°): Nb1–Cl1 = 2.308(7), Nb1–Cl2 = 2.3686(6),
Nb1–S1 = 2.197(8), Nb1–Se1 = 2.8799(4); Cl1–Nb1–Cl2 = 96.67(15),
numbering scheme and with ellipsoids drawn at the 50% probability
level. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
and angles (°): Nb1–Cl1 = 2.2475(7), Nb1–Cl2 = 2.3588(6), Nb1–Cl3 =
2.3623(6), Nb1–S1 = 2.7813(6), Nb1–S2 = 2.7464(6), Nb1–S3 = 2.2105(7);
Cl1–Nb1–Cl2
= 97.78(2), Cl1–Nb1–Cl3 = 97.49(3), Cl1–Nb1–S1 =
i
i
Cl1–Nb1–Cl2 = 95.98(15), Cl1–Nb1–S1 = 105.73(5), Cl1–Nb1–Se1
=
86.78(2), Cl1–Nb1–S3 = 103.84(3), Cl2–Nb1–S1 = 84.58(2), Cl2–Nb1–
S2 = 76.69(2), Cl2–Nb1–S3 = 98.20(2), Cl3–Nb1–S1 = 76.73(2), Cl3–
Nb1–S2 = 83.48(2), Cl3–Nb1–S3 = 97.13(3), S1–Nb1–S2 = 78.56(2), S2–
Nb1–S3 = 91.14(2).
1
i
8
9
5.29(6), S1–Nb1–Se = 89.90(8), S1–Nb1–Cl2 = 100.1(2), S1–Nb1–Cl2 =
i
4.0(2), Cl2–Nb1–Se1 = 79.07(2), Cl2–Nb1–Se1 = 83.86(2), Se1–Nb1–
i
Se1 = 79.274(13). Symmetry operation: i = −x, −y + 3/2, z.
energy vibration, indicating the same molecular geometry. As
0
expected, they are diamagnetic, confirming the presence of d
9
3
Nb(V). The Nb NMR spectra each exhibit a broad resonance
in the region δ = +500 to +550, significantly to high frequency
1
0,23
1
of NbOCl
spectrum of [NbSCl
shows two very broad resonances assignable to δ(MeS) and two
δ(CH ) resonances, which upon cooling the solution resolve
3
or NbCl
5
–thioether complexes.
The H NMR
3
(MeSCH CH SMe)] in CD
2
2
2
Cl at 295 K
2
2
2
4
into resonances due to free dithioether and coordinated
dithioether, and at 183 K some further splitting is evident,
probably due to slowing of pyramidal inversion at the sulfur
centres. The data are consistent with some dissociation of the
dithioether in solution, and fast exchange between co-
ordinated and ‘free’ dithioether at ambient temperature. This
is further evidence for the weaker Lewis acidity of NbSCl
3
com-
1
pared to NbOCl or NbCl . The H NMR spectra of the other
3
5
3 2 2
Fig. 3 The structure of [NbSCl (MeSCH CH SMe)] showing the atom
numbering scheme and with ellipsoids drawn at the 50% probability
level. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
four complexes also have broad resonances at ambient temp-
eratures, and show similar changes on cooling the samples.
and angles (°): Nb1–Cl1 = 2.354(1), Nb1–Cl2 = 2.242(1), Nb1–Cl3 = The complex [NbSCl (MeSeCH CH CH SeMe)] does not
3
2
2
2
7
7
1
2.362(1), Nb1–S1 = 2.739(1), Nb1–S2 = 2.717(1), Nb1–S3 = 2.210(1); Cl1–
exhibit a Se{ H} NMR resonance at 295 K, but on cooling to
23 K, resonances due to the ‘free’ diselenoether (δ = 68),
Nb1–Cl2 = 97.52(4), Cl1–Nb1–S1 = 77.05(4), Cl1–Nb1–S2 = 83.36(3),
Cl1–Nb1–S3 = 97.13(4), Cl2–Nb1–S1 = 90.37(4), Cl2–Nb1–S3 = 106.56(4),
Cl3–Nb1–S2 = 76.78(3), Cl3–Nb1–S3 = 97.00(4), S1–Nb1–S2 = 78.18(3),
S2–Nb1–S3 = 85.33(4).
25
2
and coordinated diselenoether (δ = 163, 70) appear. The
singlet at 70 ppm seems anomalous, but is reproducible and
1
may reflect the ‘free’ Se donor of a κ -coordinated dis-
elenoether, although it is possible this arises due to the Se
thiochloride systems due to the very similar scattering power donor atom trans to the terminal S.
of S and Cl atoms. We note in passing that all three structures
contain the dichalcogenoether in the DL form.
Attempts to prepare dithio- or diseleno-ether complexes
from [NbSeCl (MeCN) ], even using excess chalcogenoethers
3
2
The IR spectra of the five complexes exhibit ν(NbvS) ∼ or long reaction times, were unsuccessful. However, the reac-
1
n
5
3
25 cm− and two ν(Nb–Cl) stretches in the range tion of NbCl
5
with Se Bu
2 2 2
in CH Cl , followed by treatment
−
1
50–320 cm , sometimes with a shoulder on the higher with (Me Si) Se, gave a black solid which, on the basis of
3
2
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microanalysis and IR and H NMR spectroscopic analysis, was as a precursor for deposition of NbS
2
in the temperature
n
tentatively identified as [NbSe Cl (Se Bu )]. The structure of range 400–750 °C were unsuccessful. However, the
this material is unknown, but it may be dimeric like complexes, [NbSCl
2
3
2
n
n
n
3
(S Bu
2 3 2 3
)], [NbSCl { BuS(CH ) S Bu}] and
2
−
17
n
[Nb
2
Cl
4
(Se
2
)
2
(SMe
2
)
2
] and contain [Se–Se] groups.
[NbSe Cl (Se Bu )], were likely candidates for use as single
2 3 2
source CVD precursors for the low pressure CVD of NbS and
2
Application for LPCVD of NbE
2
thin films
NbSe thin films, owing to their volatility and the presence of
readily eliminated Bu groups. Thermogravimetric analyses
were undertaken for these complexes (ESI Fig. S4–S6†), and
while the mass loss observed does not correspond with the
2
n
Although the gas phase structure of [NbSCl ] has been
3
1
9
determined, indicating some volatility, attempts to use this
2 2
residue being simply NbS or NbSe , this is unsurprising given
the different experimental conditions used for TGA (progress-
ive heating under a flowing argon atmosphere) compared to
the vapour transport process involved in the low pressure CVD
experiments. However, the TGA experiments do indicate the
temperature at which mass loss begins, providing an indi-
cation of the low temperature threshold. Low pressure CVD
experiments were therefore performed at a pressure of ca.
0.05 mmHg using a range of temperatures around 600–750 °C.
No significant deposition was observed at lower temperatures.
n
Black reflective films were obtained from [NbSCl (S Bu )] at
3
2
700 °C, and grazing incidence XRD showed patterns consistent
with NbS in space group R3mh (3R-type NbS ) (Fig. 5). These
2
2
films appear to be air and moisture stable, and lattice para-
meters determined by Rietveld refinement of the grazing inci-
dence XRD pattern are: a = 3.317(6) and c = 17.79(4) Å (Rwp
=
6
.61%, Rp = 4.46%). These are close to literature values for
Fig. 5 In plane XRD (blue), grazing incidence (incidence angle = 1°)
2
6
2
bulk NbS (a = 3.3303(3), c = 17.918(2) Å). The grazing inci-
dent and in-plane XRD patterns shows considerable variations
in the intensities of reflections relative to the bulk pattern. The
XRD (black) from the NbS
2
thin film deposited by LPCVD using
n
26
[
NbSCl
3
(S Bu
2
)] at 700 °C; simulated XRD pattern from bulk NbS
substrate.
2
(red).
The broad feature at 2θ ∼22° is from the SiO
2
Fig. 6 Pole figures with cut line integral graphs for the 0 0 3 (2θ = 14.97°) (a) and 1 0 1 (2θ = 31.47°) (b) reflections of a film of NbS
2
deposited on a
SiO substrate.
2
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0
03 reflection is the strongest in the grazing incidence XRD
pattern, and 101, 012 and 110 reflections are highest in the in-
plane XRD pattern, suggesting <00l> preferred orientation.
Pole figure measurements were undertaken on a NbS
2
film
n
obtained from the [NbSCl (S Bu )] precursor to establish the
3
2
film texture. Using 2θ = 14.97°, corresponding to the 0 0 3
reflection, a single, sharp peak (FWHM ∼ 5°) was observed at
the centre of the figure with α = 90° (Fig. 6a). The figure taken
with 2θ = 31.47°, corresponding to the 1 0 1, exhibits a ring
with α = 9° (Fig. 6b). These results confirmed the <00l> pre-
ferred orientation in which the ab planes of the crystallites are
parallel with the substrate.
Scanning electron microscopy (SEM) images reveal that the
NbS films have a uniform morphology formed of microcrystal-
2
line platelets mainly lying flat on the substrate (Fig. 7), consist-
ent with the orientation inferred from the XRD data. EDX data
measured at an accelerating voltage of 15 keV show significant
Fig. 8 In plane XRD (blue), grazing incidence (incidence angle = 1°)
Si and O peaks in addition to peaks due to Nb and S, indicat- XRD (black) from the NbSe
2
thin film deposited by LPCVD using
)] at 650 °C; simulated XRD pattern from bulk NbSe
red). The broad feature at 2θ ∼22° is from the SiO substrate.
n
[NbSe
2
Cl
3
(Se Bu
2
2
ing that the films are thin. EDX data also shows there is no evi-
dence for any residual Cl in the films (Cl Kα = 2.621 keV).
Accurate quantification of the Nb : S ratio by EDX is difficult
27
(
2
due to the Nb L
α α
and S K peaks overlapping.
orientation (Fig. S3†). Lattice parameters determined by
Rietveld refinement of the grazing incidence XRD pattern are:
Films obtained from low pressure CVD using
n
n
[
NbSCl
patterns consistent with R3mh (3R-type NbS
lattice parameters a = 3.29(2) and c = 17.8(2) Å (Rwp = 5.54%,
= 3.47%). SEM images of these films are presented in the
3
{ BuS(CH
2
)
3
S Bu}] at 700 °C also present diffraction
a = 3.434(7) and c = 12.53(3) Å (Rwp = 2.48%, R
paring to the literature values for bulk NbSe
p
= 1.87%), com-
of a = 3.4446(2),
2
) (Fig. S1†), with
2
2
7
c = 12.5444(7) Å. The NbSe films appear to be air and moist-
2
R
p
ure stable. The precursor was also tested in LPCVD at 600 °C
however, there is no deposition observed. Scanning electron
ESI (Fig. S2†).
Low pressure CVD experiments were also performed using
n
microscopy (SEM) of the same NbSe film shows a polycrystal-
2
[NbSe
2
Cl
3
(Se Bu
2
)] at temperatures between 600 and 700 °C
line film formed of hexagonal platelets mostly oriented with
the c axis parallel to the substrate (Fig. 9), although the
absence of significant preferred orientation from the XRD data
suggests it is likely that there are different crystal orientations
within the film. Energy dispersive X-ray spectroscopy (EDX)
gives the ratio of Nb : Se in the films of 35.8% : 64.2%, with no
detectable Cl contamination.
(
0.05 mmHg). Films obtained at 650 °C present diffraction
patterns consistent with P6 /mmc (2H-type NbSe ) (Fig. 8).
3
2
n
8
Previously we obtained 3R-NbSe
2
from [NbCl
5
(Se Bu
by dual source
APCVD from NbCl and Se Bu . The 002 101 and 110 reflec-
2
)]. but
Parkin and co-workers have reported 2H-NbSe
2
t
6
5
2
tions are the three most intense in both grazing incidence and
in-plane XRD patterns, indicating that preferred orientation is
not significant in this case. However, using a reduced amount
of precursor produces thinner films with evidence of preferred
Conclusions
A series of thioether and selenoether complexes derived from
NbSCl
Lewis acid than NbCl
substituents have been used as single source precursors to
produce 3R-NbS thin films via low pressure CVD, with pre-
ferred <00l> orientation. In contrast, NbSeCl does not form
3
is reported. NbSCl
3
has been shown to be a weaker
n
5
. Selected complexes containing Bu
2
3
n
similar complexes, however treatment of [NbCl (Se Bu )] with
5
2
n
Se(SiMe
3
)
2
forms the complex [NbSe
2
Cl
3
(Se Bu
2
)] which has
been used as a single source precursor for low pressure CVD of
H-NbSe thin films.
2
2
Experimental
Syntheses were performed by using standard Schlenk and
glove-box techniques under a dry N atmosphere. NbCl and
2
Fig. 7 SEM image of a polycrystalline NbS film deposited by LPCVD
n
3 2
from [NbSCl (S Bu )] at 700 °C.
2
5
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n
2 2 3 2
Fig. 9 SEM images of the NbSe film deposited from [NbSe Cl (Se Bu )] at 650 °C.
S(SiMe
from Fluorochem and stored in the glovebox in ampoules orange to black immediately and was stirred for 30 min at
under N . Solvents were dried by distillation from CaH room temperature. The solvent was removed in vacuo, leaving a
3
)
2
were obtained from Sigma-Aldrich and Se(SiMe
3
)
2
(6 mL) was added with stirring. The solution changed from
2
2
−
1
(
CH
2
Cl
2
,
MeCN) or Na/benzophenone ketyl (n-hexane). dark green powder. Yield: 295 mg, 83%. IR (Nujol, cm ): 550s
ER (E = S, Se; n = 2, 3; R = Me, (NbvS).
Dichalcogenoethers, RE(CH )
Pr, Bu), were prepared via literature methods.
2 n
i
n
24,25
[NbSCl (MeCN) ]: Method 1: The complex was prepared by
3 2
1
6
a modified literature method. NbCl
dissolved in MeCN (30 mL) and cooled in an ice bath. A solu-
Infrared spectra were recorded on a PerkinElmer Spectrum 100 tion of (Me Si) S (260 mg, 1.5 mmol) in MeCN (20 mL) was
5
(405 mg, 1.5 mmol) was
Physical measurements
3
2
−
1
spectrometer in the range 4000–200 cm , and samples pre- added. The reaction mixture was then removed from the ice
pared as Nujol mulls between two CsI plates. H NMR spectra bath and the colour changed from yellow to green over a few
1
were recorded using a Bruker AV II 400 spectrometer and refer- minutes. The solution was stirred for 1 h giving a green solu-
enced to the residual protio-resonance of the solvent. tion. The solvent was then removed in vacuo leaving a yellow–
7
7
93
4 6 2 3
Multinuclear ( Se, Nb) NMR spectra were recorded from green solid. Yield: 337 mg, 72%. Required for C H N Cl NbS
CD
2
Cl
2
, CDCl
3
or CD
3
CN solutions using a Bruker AV II 400 (313.33): C, 15.33; H, 1.93; N, 8.94. Found: C, 15.26; H, 1.96; N,
and 8.82%. IR (Nujol, cm− ): 2316, 2287s (MeCN), 530s (NbvS),
1
spectrometer and referenced to neat external SeMe
Et N][NbCl ] in MeCN (δ = 0), respectively. Microanalyses on 355sh, 343s, 319s (Nb–Cl). H NMR (CD
2
1
[
2
Cl
2
, 295 K): δ = 1.97
4
6
9
3
new compounds were undertaken by London Metropolitan (s, MeCN). Nb NMR (CD
University. Thermogravimetric analysis (TGA) data for Method 2: NbSCl (83 mg, 0.35 mmol) was dissolved in
NbSCl (S Bu )] (ESI Fig. S4†), [NbSCl ( BuSCH CH CH S Bu)] MeCN (20 mL) with stirred for 30 min and giving a dark green
CN, 295 K): δ = 414.
3
3
n
n
n
[
(
3
2
5
2
2
2
n
2 3 2
ESI Fig. S5†) and [NbSe Cl (Se Bu
)] (ESI Fig. 6†) were col- solution. The solution was filtered and the filtrate taken to
lected via a Netzsch TG209 F1 Libra analyser under a flow of dryness in vacuo. Green powder. Yield: 100 mg, 90%. The
−
1
argon at 65 mL min , contained within a dry, nitrogen product was spectroscopically identical to that of
purged glovebox. The temperature was increased at a rate of [NbSCl (MeCN) ] produced by Method 1.
[NbSCl (SMe
in CH Cl (10 mL). SMe
3
2
1
0 °C min− . Samples were loaded in Al sample pans.
1
3
2
)]: NbCl
5
(135 mg, 0.5 mmol) was suspended
2
(1 mL) was added with stirring for
2
2
X-ray experimental
3
0 min, giving a dark brown solution. The solution was then
Data collections used a Rigaku AFC12 goniometer equipped cooled in an ice bath (0 °C) and a solution of S(SiMe (90 mg,
with an enhanced sensitivity (HG) Saturn724+ detector 0.5 mmol) in CH Cl (ca. 1 mL) was added slowly with stirring
mounted at the window of an FR-E+ SuperBright molybdenum for 30 min. The solution was removed from ice bath and
λ = 0.71073) rotating anode generator with VHF Varimax stirred for another 5 min and then the volatiles were removed
optics (70 micron focus) with the crystal held at 100 K (N
cryo- in vacuo, leaving a light yellow green solid. Yield: 55 mg, 38%.
stream). Crystallographic parameters are in the ESI Required for C Cl NbS (293.46): C, 9.19; H, 2.06. Found: C,
Table S1†). Structure solution and refinement were performed 9.29; H, 2.37%. IR (Nujol, cm ): 530 (NbvS), 369, 356, 322
3 2
)
2
2
(
2
H
2
6
3
2
−
1
(
1
93
using SHELX(S/L)97, SHELX-2014/7 and were mostly straight- (Nb–Cl). H NMR (CDCl
forward, except for the Cl and terminal S atoms of the (CD Cl , 295 K): δ = 651. Yellow–green crystals grew by allowing
NbSCl {MeSe(CH
SeMe}] which were disordered and there- CH Cl solution to evaporate slowly under nitrogen
atmosphere.
3 2
, 295 K): δ = 2.32 (s, SMe ). Nb NMR
2
2
[
3
2
)
3
2
2
a
2
8,29
fore refined with split occupancies giving a 50 : 50 ratio.
H atoms were added and refined with a riding model.
n
[NbSCl
(405 mg, in CH Cl
(20 mL) in an ice bath in CH Cl
0 °C). A solution of (Me Si) S (260 mg, 1.5 mmol) in CH Cl
3 2
orange solution formed. A solution of S(SiMe )
(S Bu
(10 mL) and a solution of S Bu
(3 mL) was added with stirring. After 15 min an
(179 mg,
)]: NbCl (270 mg, 1.0 mmol) was suspended
3
2 5
n
Complex/precursor preparations. NbSCl
.5 mmol) was suspended in CH Cl
3
: NbCl
5
2
2
2
(147 mg, 1.0 mmol)
1
(
2
2
2
2
3
2
2
2
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Paper
n
n
1
.0 mmol) and CH
2
Cl
2
(3 mL) was added with stirring. The
3 2 3
[NbSCl { BuS(CH ) S Bu}]: Was made similarly and iso-
colour changed to dark green after stirring for 30 min. The lated as a dark green oil after washing with n-hexane, decant-
solution was taken to dryness in vacuo, leaving a sticky oil ing off the washings and drying in vacuo. Yield: 76%. Required
which was washed with n-hexane (5 mL), before drying for C11
H
24Cl
3
NbS
3
(451.77): C, 29.24; H, 5.35. Found: C, 29.37;
−
1
in vacuo. Thick dark oil. Yield: 331 mg, 88%. Required for H, 5.45%. IR (Nujol, cm ): 529 (NbvS), 349, 322 (Nb–Cl).
9
3
C
8
H
18Cl
3
NbS
2
(377.62): C, 25.44; H, 4.80. Found: C, 25.58; H,
Nb NMR (CD
[NbSCl {MeSe(CH
H NMR (CDCl , 295 K): δ = 0.97 (t, [6H], Me), 1.48 (m, [4H], lated as a yellow brown powder. Yield: 58%. Required for
2
Cl
2
, 295 K): δ = 534.
−
1
4
.88%. IR (Nujol, cm ): 554 (NbvS), 387, 374, 359sh (Nb–Cl).
3
2 3
)
SeMe}]: Was made similarly and iso-
1
3
CH
2
Me), 1.74 (m, [4H], SCH
Nb NMR (CD Cl , 295 K): δ = 654.
NbSCl (Se Bu )]: NbCl (270 mg, 1.0 mmol) was suspended
2
CH
2
CH
2
), 2.94 (t, [4H], SCH
2
).
5 3 2
C H12Cl NbSSe (461.40): C, 13.02; H, 2.62. Found: C, 13.17;
9
3
−1
2
2
H, 2.74%. IR (Nujol, cm ): 521 (NbvS), 342, 320 (Nb–Cl).
n
1
[
H NMR (CD Cl , 295 K): δ = 2.25 (br, [8H], SeMe and CH CH Se),
3
2
5
2
2
2
2
n
77
1
in CH
.0 mmol) in CH
red solution, which was stirred for 1 h. S(SiMe3)2 (0.21 mL, δ = 547. Yellow crystals grew by allowing a CH Cl solution to
2
Cl
2
(10 mL) and a solution of Se Bu
2
(193 mg, 2.92 (br, [4H], CH
2
Se). Se{ H} NMR (CD
2
Cl
2
, 295 K): no
9
3
1
2
2
Cl (3 mL) was added with stirring, giving a resonance; (223 K): δ = 163, 70, 68. Nb NMR (CD
2
2
Cl , 295 K):
2
2
1
.0 mmol) was then added. The solution turned dark green, evaporate under a dinitrogen atmosphere.
and after stirring for 30 min the solvent was removed in vacuo [NbSeCl (MeCN) ]: NbCl (135 mg, 0.5 mmol) was dissolved
to leave a sticky oil. After washing with hexane (5 mL), the oil in MeCN (10 mL). A solution of Se(SiMe ) (113 mg, 0.5 mmol)
3
2
5
3
2
was dried in vacuo. Sticky black oil. Yield: 200 mg, 47%. in MeCN (5 mL) was then added and the reaction mixture was
Required for C NbSSe (424.52): C, 22.63; H, 4.27. stirred for 30 min. The colour changed to dark brown. The
Found: C, 22.52; H, 4.29%. IR (Nujol, cm ): 530 (NbvS), 380, solvent was removed in vacuo leaving a brown solid. Yield:
8 3
H18Cl
−
1
1
3
66, 355sh (Nb–Cl). H NMR (CDCl
3
, 295 K): δ = 0.93 (t, [6H], 150 mg, 83%. Required for C
4 6 3 2
H Cl N NbSe (360.33): C, 13.33;
Me), 1.42 (m, [4H], CH Me), 1.66 (m, [4H], SeCH
2
2
CH ), 2.61 H, 1.68; N, 7.77. Found: C, 13.25; H, 1.65; N, 7.57%. IR (Nujol,
2
7
7
93
−1
(
br, [4H], SeCH2). Se (CD Cl , 295 K): no resonance. Nb cm ): 2310, 2281 (MeCN), 397 (NbvSe?), 377, 344 (Nb–Cl).
2
2
9
3
NMR (CD
2
Cl
2
, 295 K): δ = 694.
Nb NMR (CD
2
Cl
2
, 295 K): δ = 923.
n
[
NbSCl
3
(MeSCH
2
CH
2
SMe)]: [NbSCl
3
(MeCN)
2
]
(94 mg,
[NbSe
2
Cl
3
(Se Bu )]: NbCl (235 mg, 0.88 mmol) was sus-
2
5
n
0
.3 mmol) was dissolved in CH Cl (10 mL) at room tempera- pended in CH Cl (20 mL). A solution of Bu Se (177 mg,
2
2
2
2
2
ture. A solution of MeSCH
2
CH
2
SMe (110 mg, 0.9 mmol) and 0.88 mmol) and CH
2
Cl
2
(ca. 1.5 mL) was added with stirring
CH
Some green-yellow powder formed in the solution. After filter- red and all the NbCl5 dissolved. A solution of Se(SiMe3)2
ing, the green solution was evaporated to dryness in vacuo. (0.22 mL, 0.88 mmol) and CH Cl (ca. 1.7 mL) was
2 2
Cl (1 mL) was added and the solution stirred for 30 min. for 1 hour. The reaction mixture changed colour to dark
2
2
n-Hexane (10 mL) was added to wash the solid which was sep- added, causing a colour change from dark red to black.
arated and dried in vacuo. Yield: 67 mg, 63%. Required for The solution was stirred for 15 min before it was taken to
C
4
H
10Cl
3
NbS
3
(353.58): C, 13.59; H, 2.85. Found: C, 13.64; H, dryness in vacuo. The resulting black solid was washed with
−
1
2
.93%. IR (Nujol, cm ): 526 (NbvS), 361sh, 349, 319 (Nb–Cl). n-hexane (15 mL) and then dried in vacuo. Yield: 298 mg,
1
H NMR (CD Cl , 295 K): δ = 2.22 (br, [3H], SMetrans Cl), 2.78 61%. Required for C H Cl NbSe (550.37): C, 17.46; H, 3.3.
2
2
8
18
3
3
−
1
(
(
(
(
br, [3H], SMetrans S) 3.04(s), 3.26(s) ([4H], CH
s, [6H], Me), 2.63 (s, [4H], CH ) (both ‘free’ dithoether), 2.12 (Nb–Cl). H NMR (CDCl , 295 K): δ 0.94 (t, [6H], Me), 1.44
s, [3H]), 2.18 (s, [3H]), 2.76, 2.94 (CH ) (coord. dithioether) (m, [4H], CH Me), 1.70 (m, [4H], SeCH CH CH ), 2.71 (t, [4H],
see text). Nb NMR (CD
2
); (183 K): 2.06 Found: C, 17.59; H, 3.38. IR (Nujol, cm ): 344, 319, 272
1
2
3
2
2
2
2
2
9
3
2
Cl
2
2
, 295 K): δ = 507. Green crystals SeCH ).
grew by allowing a CH
2
Cl
2
solution to evaporate under a dini-
LPCVD general procedure. The precursor (20–100 mg) was
trogen atmosphere.
loaded into the end of a silica tube in an N2 purged glove
S Pr)]: Was made similarly and isolated box. Then the silica substrates (∼1 × 8 × 20 mm ) were loaded
i
i
3
[
NbSCl
3
( PrSCH
2
CH
2
as a green powder. Yield: 76%. Required for C
8
H
18Cl
3
NbS
3
in the tube and placed end-to-end. The tube was set in a
(
409.69): C, 23.45; H, 4.43. Found: C, 23.27; H, 4.41%. furnace so that the substrates were in the heated zone and
−
1
IR (Nujol, cm ): 527 (NbvS), 365 (sh), 348, 318 (Nb–Cl). the precursor was ca. 2 cm away from the start of the heated
1
2 2
H NMR (CD Cl , 295 K): δ = 1.32 (br s, [6H], SMe), 1.59 (br s, zone. The tube was evacuated to 0.5 mmHg, and the furnace
[
6H], SMe), 3.01–3.28 (br, [4H], SCH ), 3.46 (br, [2H], SCH). was heated to the requisite temperature between 600 and
2
9
3
Nb NMR (CD
allowing a CH Cl
gen atmosphere.
NbSCl {MeS(CH
as a green solid. Yield: 68% Required for C
367.61): C, 16.34; H, 3.29. Found: C, 16.48; H, 3.21%. IR (Nujol,
2 2
Cl , 295 K): δ = 523. Green crystals grew by 800 °C. The tube was then moved into the furnace. The posi-
2
2
solution to evaporate slowly under a dinitro- tion of the sample was maintained until the all the precursor
had evaporated. The tube was then cooled to room tempera-
[
3
2
)
3
SMe}]: Was made similarly and isolated ture and the tiles were unloaded at ambient temperature and
NbS stored in air.
LPCVD from [NbSCl (S Bu )], [NbSCl { BuS(CH ) S Bu}]
5
H
12Cl
3
3
n
n
n
(
3
2
3
2 3
−
1
1
n
cm ): 524 (NbvS), 369 sh, 345, 323 (Nb–Cl). H NMR (CDCl
95 K): δ = 2.14 (br, [2H], SCH CH ), 2.45 (vbr, [6H], SMe), 2.96 black films on tiles positioned in the hotter region of the
vbr, [4H], SCH2). Nb NMR (CD Cl , 295 K): δ = 530.
3
,
2 3 2
and [NbSe Cl (Se Bu )] resulted in deposition of reflective
2
(
2
2
9
3
furnace (i.e. NbS2 actual deposition temperature ∼670 °C;
2
2
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NbSe
2
actual deposition temperature ∼625 °C – measured by
Inorg. Chem., 1998, 37, 418; S. D. Reid, A. L. Hector,
W. Levason, G. Reid, B. J. Waller and M. Webster,
Dalton Trans., 2007, 4769; S. L. Benjamin, C. H. de Groot,
C. Gurnani, A. L. Hector, R. Huang, K. Ignatyev,
W. Levason, S. J. Pearce, F. Thomas and G. Reid,
Chem. Mater., 2013, 25, 4719; N. D. Boscher,
C. J. Carmalt and I. P. Parkin, Chem. Vap. Deposition, 2006,
12, 54.
6 N. D. Boscher, C. J. Carmalt and I. P. Parkin, Eur. J. Inorg.
Chem., 2006, 1255.
7 E. S. Peters, C. J. Carmalt, I. P. Parkin and D. A. Tocher,
Eur. J. Inorg. Chem., 2005, 4179; C. J. Carmalt, E. S. Peters,
I. P. Parkin, T. D. Manning and A. L. Hector, Eur. J. Inorg.
Chem., 2004, 4470.
profiling the furnace).
Film characterisation. X-Ray diffraction (XRD) patterns were
collected in grazing incidence mode (θ
θ1 = 0.5°, 2θχ scan with the detector scanning in the film
plane) using a Rigaku SmartLab diffractometer (Cu-K , λ =
.5418 Å) with parallel X-ray beam and a DTex Ultra 250 1D
detector. Phase matching and lattice parameter refinement
1
= 1°) or in-plane mode
(
α
1
3
0
used the PDXL2 software package and diffraction patterns
3
1
from ICSD.
Scanning electron microscopy (SEM) was performed on
samples of NbSe using a Philips XL30 ESEM and with an
acceleration voltage of 10 kV or 15 kV, whilst SEM measure-
ments on NbS films used a JEOL JSM6500 and an accelerating
2
2
voltage of 10 kV.
8 S. L. Benjamin, Y.-P. Chang, C. Gurnani, A. L. Hector,
M. Huggon, W. Levason and G. Reid, Dalton Trans., 2014,
43, 16640.
9 S. L. Benjamin, Y.-P. Chang, M. Huggon, W. Levason and
G. Reid, Polyhedron, 2015, 99, 230.
2
Energy dispersive X-ray (EDX) data on NbSe samples were
obtained at accelerating voltage of 10 and 15 kV with a
Thermofisher Ultradry NSS 3 (XL30) detector or at an accelerat-
ing voltage of 15 kV with an Oxford INCA x-act X-ray detector
(
JSM6500) for NbS samples.
10 Y.-P. Chang, W. Levason, M. E. Light and G. Reid, Dalton
Trans., 2016, 45, 16262.
2
11 D. A. Rice, Coord. Chem. Rev., 1978, 25, 199; M. J. Atherton
and J. H. Holloway, Adv. Inorg. Chem. Radiochem., 1979, 22,
Acknowledgements
171.
We thank the EPSRC for funding the SmartLab diffractometer 12 Comprehensive Coordination Chemistry II, ed. T. J. Meyer
(
via EP/K00509X/1 and EP/K009877/1) and the University of
and J. A. McCleverty, Elsevier, Oxford, 2004, vol. 4 and 5.
Southampton for a VC Scholarship (to Y.-P. C).
13 U. Müller and P. Klingelhöfer, Z. Anorg. Allg. Chem., 1984,
5
10, 109.
4 M. G. B. Drew and R. J. Hobson, Inorg. Chim. Acta, 1983,
2, 233.
5 K. Behzadi, A. G. Baghlaf and A. Thomson, J. Less-Common
Met., 1987, 128, 195.
1
1
7
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