10.1002/chem.201604190
Chemistry - A European Journal
mixture was allowed to warm to room temperature gradually and stirred overnight. The
THF was evaporated under reduce pressure and the residue was extracted with toluene
(15 ml). The toluene solution was leaved to crystallize at -20 °C. Crystal suitable for X-
ray diffraction analysis were obtained and identified as compound 3. Remaining solid
insoluble in toluene was re-dissolved in THF-hexane solution (1:1, 15 ml) and the
filtrate was leaved to crystalize at 4°C. Crystal suitable for X-ray diffraction analysis
were obtained and identified as compound 4.
obtained values fall into the regions reported for the GaS materials
prepared by different techniques.
Experimental Section
General methods for preparation of 1 - 4.
for 3. Yield: 0.72 g (75 %); m.p. = 112-114 °C; Anal. Calcd. for C12H19GaN2S4 (Mw
389.28) C 37.0 %; H 4.9 %; Found: C 37.0 %; H 4.9 %. 1H NMR (C6D6, 400.13 MHz):
(ppm) 2.04 (12H, s, N(CH3)2), 3.03 (2H, s, CH2N), 6.75 (2H, d, ArH), 7.12 (1H, m,
ArH). 13C NMR (C6D6, 100.61 MHz): (ppm) 45.5 (N(CH3)2), 63.2 (CH2N), 124.5
(C(2,6)), 128.1 (C(3,5)), 143.1 (C(4)), 144.7 (C(1)).
Solvents were dried by standard methods and distilled prior to use. All moisture and air
sensitive reactions were carried out in an argon atmosphere using standard Schlenk
techniques. Starting compounds L2Br and L1GaCl2 were prepared according to
literature.[25-26] Starting materials S, nBuLi, Li[HBEt3] and GaCl3 were purchased from
Sigma Aldrich.. The 1H and 13C NMR spectra were acquired on Bruker 400 NMR
spectrometer. The 1H, 13C, NMR chemical shifts δ are given in ppm and referenced to
external Me4Si (13C, 1H).
for 4: Yield: 0.04 g (5 %); m.p. = 215 °C; Anal. Calcd. for C28H46Ga2N2O2S2 (Mw
646.24) C 52.0 %; H 7.2 %; Found: C 52.4 %; H 7.8 %. 1H NMR (C6D6, 400.13 MHz):
(ppm) 0.78 (6H, t, CH3(CH2)3CH), 1.18 (4H, m, CH3(CH2)3CH), 1.69 (4H, m,
CH3(CH2)3CH), 1.94 (4H, m, CH3(CH2)3CH), 2.02 (6H, s, N(CH3)2), 2.09 (2H, m,
CH3(CH2)3CH), 2.36 (6H, s, N(CH3)2), 2.67 (2H, AX system, CH2N), 3.45 (2H, AX
system, CH2N), 5.79 (2H, s, OH), 6.81 (2H, d, ArH), 7.13 (2H, d, ArH), 7.29 (2H, t,
ArH). 13C NMR (C6D6, 100.61 MHz):
(ppm) 16.5 (CH3(CH2)3CH), 23.3
(CH3(CH2)3CH), 24.0 (CH3(CH2)3CH), 38.7 (CH3(CH2)3CH), 43.7 (N(CH3)2), 44.2
(N(CH3)2), 64.1 (CH2N), 73.2 (CH3(CH2)3CH), 123.9 (C(3)), 126.7 (C(4)), 129.1 (C(5)),
134.5 (C(6)), 141.0 (C(2)), 152.5 (C(1)).
Synthesis of L2GaCl2
1.6M nBuLi solution in hexane (2.75 mL, 4.41 mmol) was added to a 20 ml Et2O
solution of L2Br (1.3 g, 3.67 mmol) at -80 °C and the reaction mixture was allowed to
warm to room temperature gradually and stirred for 3 hours. Formed lithium salt L2Li
was added to the 15 ml Et2O solution of GaCl3 (0.65 g, 3.67 mmol) under – 78 °C and
the reaction mixture was allowed to warm to room temperature gradually and stirred for
3 hours. The Et2O was filtered and evaporated under reduce pressure to give L2GaCl2.
Yield: 1.36 g (89 %). m.p. = 148 - 149 °C; Anal. Calcd. for C19H32Cl2GaN (Mw 415.09)
C 55.0 %; H 7.8 %; Found: C 54.5 %; H 7.6 %;. 1H NMR (C6D6, 400.13 MHz): (ppm)
0.65 (6H, t, CH2CH3), 1.31 (9H, s, C(CH3)3), 1.59 (9H, s, C(CH3)3), 2.30 (2H, m,
CH2CH3), 2.90 (2H, m, CH2CH3), 3.26 (2H, s, CH2N), 6.79 (1H, s, ArH), 7.59 (1H, s,
ArH). 13C NMR (C6D6, 100.61 MHz): (ppm) 7.9 (CH2CH3), 31.3 (C(CH3)3), 32.3 (
C(CH3)3), 34.6 (C(CH3)3), 36.7 (C(CH3)3), 45.4 (CH2CH3), 59.0 (CH2N), 119.4 (C(3)),
122.8 (C(5)), 129.0 (C(4)), 140.9 (C(6)), 152.4 (C(2)), 158.3 (C(1)).
General method for the preparation of GaS thin films by spin coating.
0.3 g organogallium precursor 1 was dissolved in 5 ml of propylamine to give solution
with c = 0.08 M. The above mentioned GaS thin layers were prepared by spin coating of
as-prepared solution (1 ml per sample) on single-crystalline silicon wafer substrates (ca
10 mm x 10 mm x 0.3 mm) using SpinMaster spincoater using one step – 500 - 10k rpm
for 60 sec. After spin coating, the layers were vacuum dried at 150°C using vacuum
oven at 1 mBar. Afterwards, the layers were subject of thermal annealing for 12 hours at
250°C. The thickness of the as-dried layers was approximately 0.2 – 0.3 m as
determined by SEM.
Synthesis of [L1Ga(-S)]3 (1)
1M Li[HBEt3] solution in THF (25.6 mL, 25.6 mmol) was added to a 25 ml THF
solution of S (0.41 g, 12.8 mmol) at room temperature and stirred for 2 hours. The
formed lithium sulfide Li2S was added to 25 ml THF solution of L1GaCl2 (4.25 g, 12.8
mmol) at -78°C. The reaction mixture was allowed to warm to room temperature
gradually and stirred overnight. The THF was evaporated under reduce pressure and the
residue was extracted with toluene-hexane solution (10 ml toluene and 20 ml hexane).
This toluene-hexane solution was leaved to crystallize at room temperature to yield
colourless crystals of 1 suitable for X-Ray diffraction analysis. Yield: 3.16 g (86 %).
m.p. = 160-162 °C; Anal. Calcd. for C36H57Ga3N6S3 (Mw 879.25) C 49.2 %; H 6.5 %;
Found: C 49.1 %; H 6.7 %; 1H NMR (C6D6, 400.13 MHz): (ppm) 2.35 (6H, s,
N(CH3)2), 2.46 (6H, s, N(CH3)2), 3.44 (2H, AB system, CH2N), 3.67 (2H, s, CH2N),
7.07 (2H, d, ArH), 7.19 – 7.21 (1H, m, ArH). 13C NMR (C6D6, 100.61 MHz): (ppm)
45.8 (N(CH3)2), 45.8 (N(CH3)2), 65.4 (CH2N), 65.4 (CH2N), 125.1 (C(3)), 125.3 (C(5)),
128.7 (C(4)), 144.0 (C(2)), 144.8 (C(6)), 149.4 (C(1)).
Characterization methods of GaS material.
The surface of the GaS films and their chemical composition were studied using
scanning electron microscopy (SEM, JSM-5 500 LV Jeol) linked with energy-dispersive
x-ray analyzer (EDX). Standard uncertainty of EDX measurements is ±1 at. %.
Typically, the EDX measurements were performed at 3 spots per sample and averaged.
Optical functions of prepared GaS layers as well as their thicknesses were obtained
from the analysis of spectroscopic ellipsometry data measured using an ellipsometer
with automatic rotating analyzer (VASE, J. A. Woollam Co., Inc.) on samples grown on
silicon substrates. The measurement parameters are as follows: spectral region 190–
1770 nm (i.e., 6.49 – 0.7 eV) with wavelengths steps of 10 nm and angles of incidence
65°, 70° and 75° (see Figure S6 in SI). The measured ellipsometric Ψ, Δ data were fitted
using the following layered model: “Substrate / Thin Film / Roughness”. The optical
constants of substrate were known from previous measurement. Optical constants of
spin-coated film were determined using the Cody-Lorentz model. This model is
appropriate for the description of amorphous chalcogenides optical functions.[27] Atomic
force microscopy (Solver NEXT, NT-MDT) was used to study topography of GaS thin
films within typical scanned area 10 μm × 10 μm in semicontact mode. Phase behavior
of all four compounds was studied in the temperature range of 183 to 373 K using DSC
Thermal Analysis Q1000 using a heating rate of 2 K∙min-1 and hermetic aluminium
pans, however no phase transitions were observed in this temperature range. TG
analysis has been measured at thermogravimetric analyzer SETARAM Setsys Evolution
in an open platinum 100 liters crucible employing temperature range 298 to 573 K or 25
to 500 °C with temperature gradient 10K/min in inert He atmosphere. The crystalline or
amorphous state of deposited thin films was studied by X-ray diffraction (XRD)
analysis employing a diffractometer Bruker AXE D8-Advance using Cu Kα radiation
with secondary graphite monochromator. Elemental analyses were performed on an
LECO-CHNS-932 analyzer.
Synthesis of [L2Ga(-S)]2 (2)
1M Li[HBEt3] solution in THF (5.10 mL, 5.10 mmol) was added to a 25 ml THF
solution of S (0.08 g, 2.55 mmol) at room temperature and stirred for 2 hours to
generate Li2S that was added to 25 ml THF solution of L2GaCl2 (1.06 g, 2.55 mmol) at -
78°C. The reaction mixture was allowed to warm to room temperature gradually and
stirred overnight. The THF was evaporated under reduce pressure and the residue was
extracted with toluene-hexane solution (10 ml toluene and 20 ml hexane). The solution
was leaved to crystallize at room temperature and provided colourless crystals of 2
suitable for X-ray diffraction analysis. Yield: 0.75 g (78 %). m.p. = 270-273 °C; Anal.
Calcd. for C38H64Ga2N2S2 (Mw 752.50) C 60.6 %; H 8.6 %; Found: C 60.4 %; H 8.7 %;
.
1H NMR (C6D6, 400.13 MHz): (ppm) 0.93 (6H, t, CH2CH3), 1.41 (9H, s, C(CH3)3),
1.93 (9H, s, C(CH3)3), 3.23 (4H, m, CH2CH3), 3.54 (2H, s, CH2N), 6.79 (1H, s, ArH),
7.59 (1H, s, ArH). 13C NMR (C6D6, 100.61 MHz): (ppm) 9.4 (CH2CH3), 31.4
(C(CH3)3), 33.3 (C(CH3)3), 34.6 (C(CH3)3), 37.6 (C(CH3)3), 48.2 (CH2CH3), 59.2
(CH2N), 119.6 (C(3)), 121.1 (C(5)), 141.8 (C(4)), 142.7 (C(6)), 150.6 (C(2)), 157.6
(C(1)).
Crystallography: The X-ray data for colorless crystals of 1 - 4 were obtained at 150K
using Oxford Cryostream low-temperature device on
a Nonius KappaCCD
diffractometer with Mo K radiation ( = 0.71073 Å), a graphite monochromator, and
the and scan mode. Data reductions were performed with DENZO-SMN.[28] The
absorption was corrected by integration methods.[29] Structures were solved by direct
methods (Sir92)[30] and refined by full matrix least-square based on F2 (SHELXL97).[31]
Hydrogen atoms were mostly localized on a difference Fourier map, however to ensure
uniformity of treatment of crystal, all hydrogen were recalculated into idealized
positions (riding model) and assigned temperature factors Hiso(H) = 1.2 Ueq (pivot atom)
or of 1.5Ueq (methyl). H atoms in methyl, methylene, methine moieties and hydrogen
atoms in aromatic rings were placed with C-H distances of 0.96, 0.97, 0.98 and 0.93. In
4, the hydrogen atoms belonging to the OH group were placed according to the maxima
observed on the Fourier difference density map. Crystallographic data for structural
Synthesis
of
L1Ga(-S4)
(3)
and
[{2-[CH{(CH2)3CH3}(-OH)]-6-
CH2NMe2}C6H3]GaS (4)
1M Li[HBEt3] solution in THF (5 mL, 5 mmol) was added to a 15 ml THF solution of S
(0.32 g, 10 mmol) at room temperature and stirred for 2 hours to give Li2S4 that was
added to 15 ml THF solution of L1GaCl2 (0.82 g, 2.5 mmol) at -78°C. The reaction
5
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