Synthesis of a highly reactive form of WO2Cl2, its conversion into nanocrystalline mono-hydrated WO3 and coordination compounds with tetramethylurea

Article abstract of DOI:10.1039/c6dt02997c

A new form of WO₂Cl₂ was obtained by modification of a literature procedure. Both the newly prepared WO₂Cl₂ and the commercial yellow WO₂Cl₂ exhibited an orthorhombic structure (powder X-ray diffraction, P-XRD), and their air exposure at room temperature afforded light green and lemon yellow WO₃·H₂O (orthorhombic phase), respectively. These materials were characterized by P-XRD, high-resolution transmission electron microscopy (HR-TEM) and scanning transmission electron microscopy (S-TEM). The analyses revealed the nanocrystalline nature of light green WO₃·H₂O, and the prevalent amorphism of lemon yellow WO₃·H₂O. The reactions of grey WO₂Cl₂ with one and two equivalents of tetramethylurea (tmu), in CH₂Cl₂ at room temperature, led to the isolation of the trinuclear complex [WO₂Cl₂(tmu)]₃, 1 (45% yield), and the mononuclear one WO₂Cl₂(tmu)₂, 2 (64%), respectively. Compounds 1 and 2 were fully characterized by analytical and spectroscopic methods, single crystal X-ray diffraction (SC-XRD) and DFT calculations.

Full text of DOI:10.1039/c6dt02997c

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Synthesis of a highly reactive form of WO2Cl2, its
conversion into nanocrystalline mono-hydrated
WO3 and coordination compounds with
tetramethylurea†
Cite this: DOI: 10.1039/c6dt02997c
Marco Bortoluzzi,a Claudio Evangelisti,b Fabio Marchetti,*c Guido Pampaloni,c
Fabio Piccinellid and Stefano Zacchinie
A new form of WO2Cl2 was obtained by modification of a literature procedure. Both the newly prepared
WO2Cl2 and the commercial yellow WO2Cl2 exhibited an orthorhombic structure (powder X-ray dif-
fraction, P-XRD), and their air exposure at room temperature afforded light green and lemon yellow
WO3·H2O (orthorhombic phase), respectively. These materials were characterized by P-XRD, high-resolu-
tion transmission electron microscopy (HR-TEM) and scanning transmission electron microscopy
(S-TEM). The analyses revealed the nanocrystalline nature of light green WO3·H2O, and the prevalent
amorphism of lemon yellow WO3·H2O. The reactions of grey WO2Cl2 with one and two equivalents of
tetramethylurea (tmu), in CH2Cl2 at room temperature, led to the isolation of the trinuclear complex
[WO2Cl2(tmu)]3, 1 (45% yield), and the mononuclear one WO2Cl2(tmu)2, 2 (64%), respectively. Compounds
1 and 2 were fully characterized by analytical and spectroscopic methods, single crystal X-ray diffraction
(SC-XRD) and DFT calculations.
Received 28th July 2016,
Accepted 19th August 2016
DOI: 10.1039/c6dt02997c
www.rsc.org/dalton
ing suitable methods for the production of WO3-based thin
films.4
Introduction
Tungsten(VI) dioxide dichloride, WO2Cl2, has aroused consider-
WO2Cl2 can be efficiently obtained as yellow flakes by WO3/
able interest due to the possible applications in solid state WCl6 metathesis, performed in a sealed tube at a high temp-
chemistry1 and as a catalytic precursor for a variety of organic erature.5 A more convenient laboratory method, affording a
transformations.2 On the other hand, as an air sensitive, oxo- yellow solid, was published in 1990, and consisted of the reac-
philic metal chloride, WO2Cl2 is a potential precursor for the tion of WOCl4 with hexamethyldisiloxane in octane at 80 °C
deposition of films of the corresponding metal oxide, WO3.3 (eqn (1)).6 It should be remarked also that several chemical
The latter is hugely investigated in view of technological appli- suppliers have yellow-WO2Cl2 in their product catalogues:
cations, and indeed there is currently high interest in develop-
WOCl4 þ OðSiMe3Þ2 ! WO2Cl2 þ 2ClSiMe3
ð1Þ
aUniversità di Venezia Ca’ Foscari, Dipartimento di Scienze Molecolari e
Nanosistemi, Via Torino 155, I-30170 Mestre, VE, Italy
bIstituto di Scienze e Tecnologie Molecolari (ISTM-CNR), Via G. Fantoli 16/15,
I-20138 Milano, Italy
cUniversità di Pisa, Dipartimento di Chimica e Chimica Industriale, Via Moruzzi 13,
I-56124 Pisa, Italy. E-mail: fabio.marchetti1974@unipi.it; http://www.dcci.unipi.it/
fabio-marchetti.html; Tel: +39 050 2219245
dUniversità di Verona, Dipartimento di Biotecnologie, Laboratorio di Chimica dello
Stato Solido, Strada Le Grazie 15, I-37134 Verona, Italy
The structure of WO2Cl2 was previously investigated by
single crystal X-ray diffraction and powder neutron diffraction
experiments.7 The structure revealed to be orthorhombic
(space group Immm), showing sheets of rectangular WO4 units
spaced by layers of chloride anions.7a
The polymeric network of WO2Cl2 may be cleaved by the
addition of group 15 and group 16 donor ligands, leading to
the formation of mononuclear metal compounds.8
In the framework of our interest in the chemistry of high
valent transition metal halides,9 herein we report the straight-
forward synthesis of a new form of WO2Cl2, obtained by modi-
fication of the literature procedure (eqn (1)).6 A comparative
description will be provided for the hydrolytic conversion into
WO3 of novel and commercially available WO2Cl2, respectively.
eUniversità di Bologna, Dipartimento di Chimica Industriale “Toso Montanari”,
Viale Risorgimento 4, I-40136 Bologna, Italy
†Electronic supplementary information (ESI) available: Fig. S1–S5 show P-XRD
and HR-TEM representations, while Fig. S6 and Tables S1, S2 show the details
related to DFT calculations. Cartesian coordinates of the DFT-optimized com-
pounds are collected in a separated .xyz file. CCDC 1494264 (1·CH2Cl2) and
1494265 (2). For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/c6dt02997c
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Furthermore, we were interested to check whether the oxi-
Although the two forms of WO2Cl2, i.e. grey and yellow,
dative chemistry of WCl6 towards some classes of organic com- display an orthorhombic structure, they exhibit considerably
pounds could be extended to WO2Cl2. In particular, WCl6 may different behaviours when allowed to come into contact with
act as a monoelectron abstractor from tetraalkylureas10 and air.12 This feature might be ascribable to a difference in the
amines,11 thus promoting unusual activation pathways average size of the respective crystalline domains in the two
through the intermediate formation of radical cation species. solid materials.13 Thus, grey WO2Cl2 was found to be much
Upon considering that the reactivity of tungsten(VI) dioxide more sensitive than the homologous yellow material. Indeed,
dichloride with alkylureas has never been described hereto- in the absence of oil protection, rapid degradation of the
fore, the reactions of WO2Cl2 with limited amounts of tetra- sample of grey WO2Cl2 could be monitored by P-XRD
methylurea (tmu) were studied in a weakly coordinating (Fig. S3†). The degradation was fast and complete in less than
medium (dichloromethane).
one hour from air exposure, resulting in the formation of a
light-green solid.14 Otherwise, the P-XRD peaks related to the
orthorhombic phase (Immm) were the only ones detected after
two hours from air exposure of the yellow WO2Cl2 sample;
complete degradation of this compound required 72 h,
affording a lemon yellow solid (Fig. S3†).
Results and discussion
We obtained analogous solid compounds in the laboratory,
by allowing the two forms of WO2Cl2, respectively, to keep in
contact with moist air for 3 days. The resulting products con-
tained only traces of chlorine, thus indicating the occurrence
of prevalent hydrolysis (eqn (3)). They were both identified as
WO3·H2O by means of P-XRD and electron microscopy
analyses.
WO2Cl2 was obtained as a light grey solid in 75% yield, by the
direct reaction of WCl6 with two equivalents of hexamethyl-
disiloxane in heptane at 80 °C (eqn (2)):
WCl6 þ 2OðSiMe3Þ2 ! WO2Cl2 þ 4Me3SiCl
ð2Þ
A tentative explanation for the different outcomes of the
reactions reported in eqn (1) and (2), respectively, is that the
direct synthesis of WO2Cl2 from WCl6 (eqn (2)) might not
proceed via the intermediacy of WOCl4 (eqn (1)).
WO2Cl2 þ 2H2O ! WO3ꢀH2O þ 2HCl
ð3Þ
grey
light‐green
The isolated material (eqn (1)) was characterized by Cl
elemental analysis, IR spectroscopy and P-XRD diffraction. The
IR spectrum (solid state) displays strong bands centred at 846,
800 and 760 cm−1, ascribable to the [WvO] moieties within
the polynuclear structure.6
yellow
lemon yellow
The P-XRD pattern related to light-green WO3·H2O (from
grey WO2Cl2, see eqn (3)) indicated the presence of nanocrys-
talline WO3·H2O (orthorhombic Pmnb space group, Fig. 2), the
estimated average crystal size being 9(1) nm. High-resolution
transmission electron microscopy (HR-TEM) and scanning
transmission electron microscopy (S-TEM) analyses were in
agreement with the P-XRD data. They showed partially rolled
nanosheets containing small nanocrystalline domains ranging
The P-XRD pattern was recorded by protecting the sample
from air with a thin layer of inert paraffin oil, and was found
to be consistent with the presence of orthorhombic WO2Cl2
(Immm space group), see Fig. S1 within the ESI.† The presence
of traces of impurities, possibly contributing to the grey
colour, could not be definitely ruled out. The orthorhombic
structure was detected also for commercial (Sigma Aldrich),
yellow WO2Cl2, in agreement with previous findings (see
Introduction).7 The P-XRD pattern of yellow WO2Cl2 is shown
in Fig. S1;† the related transmission electron micrographs
revealed the presence of large WO2Cl2 crystals (Fig. S2†). Fig. 1
compares a commercial sample of WO2Cl2 (Sigma Aldrich,
99%) with a sample obtained according to eqn (2).
Fig. 2 Observed X-ray pattern (black crosses) and Rietveld refinement
(red solid line) of the solid obtained from grey WO2Cl2 upon air exposure
for 3 days. The structural model used for the refinement was the ortho-
rhombic phase of WO3·H2O (space group Pmnb, PDF card 04-011-
6930). Final Rw = 8.02%.
Fig. 1 Samples of WO2Cl2: (A) commercial; (B) prepared according to
eqn (2).
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Fig. 3 Representative HRTEM (left side) and STEM (right side) micro-
graphs of light-green WO3·H2O derived from grey WO2Cl2.
in size between 3 and 10 nm (Fig. 3 and S4†); the electron-
diffraction patterns were successfully indexed on the basis of
the WO3·H2O structure (orthorhombic unit cell,
a
=
0.5235 nm, b = 1.0688 nm and c = 0.5123 nm).15
Scheme 1 Formation of coordination complexes from the reactions of
WO2Cl2 with tmu, and comparison with the parallel chemistry of WCl6.10
The P-XRD pattern collected for lemon yellow WO3·H2O
(from yellow WO2Cl2, see eqn (3)) showed a lower degree of
crystallinity compared to light-green WO3·H2O (from grey
WO2Cl2, Fig. S3†). The presence of a large amount of an amor-
phous phase was confirmed by HR-TEM analysis (Fig. S5†).
To the best of our knowledge, the non-incidental formation
of tungsten oxide from WO2Cl2 is reported here for the first
time.16 It has to be noted that the hydrolytic conversion of
high valent metal oxide halides to metal oxides might be a
complicated issue.17
The faster hydrolytic degradation of grey WO2Cl2, compared
to that of the traditional, yellow WO2Cl2, suggested that the
former may be a preferential starting material for studying the
reactivity with organic species. As a matter of fact, WO2Cl2 is
known to be a quite inert polymeric substance,8a,18 thus its
coordination compounds have been more often prepared from
molecular precursors, such as WCl6 and WO2Cl2(1,2-
dimethoxyethane),19 rather than by direct addition of the
ligands to WO2Cl2.8,20
We moved further to study the reactivity of grey WO2Cl2
with stoichiometric amounts of tetramethylurea. The
1 : 1 molar reaction afforded a mixture of compounds, and a
complex of the formula WO2Cl2(tmu) could be isolated in 45%
yield by fractional crystallization (Scheme 1). SC-XRD analysis
allowed us to identify this product as the trimer
[WO2Cl2(tmu)]3, 1 (Fig. 4 and Table 1). The three W(VI) centres
exhibit a distorted octahedral geometry, and are linked by
three asymmetric μ-O ligands. The latter display a short
π-bond to one W [1.753(6)–1.763(6) Å] and a longer bridging
bond to the adjacent tungsten [2.211(6)–2.226(6) Å]. Complex 1
is a very rare polynuclear WO2Cl2 coordination complex, the
only other example being the tetramer [WO2Cl2(thf)]4.21
The DFT calculated structure of 1 is depicted in Fig. 5,
together with the corresponding electron density surface
(selected bonding parameters are given in the caption). Also
the geometry of the hypothetical WO2Cl2(tmu) monomer
Fig. 4 Molecular structure of 1 with key atoms labelled. Thermal ellip-
soids are at the 50% probability level. H-bonds are drawn with dashed
lines.
hypothetical oligomerization of 1-mono to give 1 is a strongly
exergonic process (eqn (4)):
3WO2Cl2ðtmuÞð1‐monoÞ ! ½WO2Cl2ðtmuÞꢁ3
ΔH ¼ ꢂ40:4 kcal molꢂ1 ðEDF2Þ
ð4Þ
ΔH ¼ ꢂ22:8 kcal molꢂ1 ðC‐PCM=ωB97XÞ
The quite different electron densities exhibited by 1 along
(1-mono) was optimized at the DFT level, and this is shown in the different W–O bonds prompted us to study these bonds by
the inset of Fig. 5; 1-mono possesses a distorted square pyra- means of Mayer bond order analysis (Table S1†). As expected,
midal geometry. From a thermodynamic point of view, the the highest orders refer to the terminal WvO bonds, while the
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Table 1 Selected bond distances (Å) and angles (°) for 1
The 1 : 2 molar reaction of WO2Cl2 with tmu afforded the
monomeric complex WO2Cl2(tmu)2, 2, in 64% yield.
Computed thermodynamic data indicate that the conversion
of 1 to 2 upon tmu addition should be a highly favourable
process (eqn (5)):
W(1)–O(1)
W(2)–O(2)
W(3)–O(3)
W(1)–O(4)
W(2)–O(5)
W(3)–O(6)
W(1)–Cl(1)
W(2)–Cl(3)
W(3)–Cl(5)
C(1)–O(7)
C(11)–O(9)
C(1)–N(4)
C(6)–N(6)
C(11)–N(2)
2.220(6)
2.226(6)
2.211(6)
1.774(7)
1.701(7)
1.725(7)
2.321(3)
2.324(2)
2.347(2)
1.297(11)
1.287(12)
1.317(12)
1.347(12)
1.315(14)
W(2)–O(1)
W(3)–O(2)
W(1)–O(3)
W(1)–O(7)
W(2)–O(8)
W(3)–O(9)
W(1)–Cl(2)
W(2)–Cl(4)
W(3)–Cl(6)
C(6)–O(8)
C(1)–N(3)
C(6)–N(5)
C(11)–N(1)
1.763(6)
1.753(6)
1.758(6)
2.096(6)
2.136(6)
2.088(7)
2.338(3)
2.354(2)
2.333(2)
1.276(11)
1.336(12))
1.331(12)
1.329(13)
½WO2Cl2ðtmuÞꢁ3 þ 3tmu ! 3WO2Cl2ðtmuÞ2
ΔH ¼ ꢂ11:5 kcal molꢂ1 ðEDF2Þ
ð5Þ
ΔH ¼ ꢂ9:6 molꢂ1 ðC‐PCM=ωB97XÞ
Compound 2 represents a non-common case of a crystallo-
graphically characterized WO2Cl2L2 complex, where L is a
monodentate ligand (Fig. 6 and Table 2).20b,22 Coherently with
the π-character, the W(1)–O(1) [1.684(10) Å] and W(1)–O(2)
[1.718(9) Å] bonds are considerably shorter than W(1)–O(3)
[2.194(8) Å] and W(1)–O(4) [2.172(8) Å], the latter showing a
pure coordinative nature. The computed Mayer bond orders
for the WvO interactions are 1.909 and 1.936, i.e. comparable
to the average value found for the terminal WvO bonds in
1 (1.933, see Table S1†). On the other hand, the W–tmu Mayer
bond orders in 2 are 0.369 and 0.397, meaningfully lower than
the average value obtained for 1, 0.507. The weaker coordi-
nation of tmu in 2 with respect to 1 can be explained on the
basis of a reduced trans-influence of the bridging oxide
O(1)–W(1)–O(4)
O(1)–W(2)–O(8)
O(2)–W(3)–O(9)
Cl(1)–W(1)–Cl(2)
Cl(5)–W(3)–Cl(6)
W(2)–O(2)–W(3)
W(1)–O(7)–C(1)
W(3)–O(9)–C(11)
Sum at C(6)
175.3(3)
166.6(3)
164.5(3)
161.79(9)
162.02(9)
152.3(3)
136.9(7)
141.6(7)
359.9(16)
O(3)–W(1)–O(7)
O(5)–W(2)–O(2)
O(3)–W(3)–O(6)
Cl(3)–W(2)–Cl(4)
W(1)–O(1)–W(2)
W(3)–O(3)–W(1)
W(2)–O(8)–C(6)
Sum at C(1)
164.1(3)
173.1(3)
173.1(3)
158.79(9)
154.8(4)
156.5(3)
137.0(6)
360.0(16)
360.0(11)
Sum at C(11)
Fig. 5 DFT calculated structure of 1 with electron density surface (iso-
value = 0.05 a.u.). Inset: Structure of 1-mono. Selected computed
average bond lengths for 1 (Å, C-PCM/ωB97X, corresponding EDF2 data
in parenthesis): WvO(terminal) 1.677(1.710); WvO(bridging) 1.731
(1.762); W–O(bridging) 2.263(2.229); W–O(tmu) 2.093(2.138); W–Cl
2.360(2.368). Selected computed average bond lengths for 1-mono (Å,
C-PCM/ωB97X, corresponding EDF2 data in parenthesis): WvO(axial)
1.674(1.705); WvO(equatorial) 1.689(1.707); W–O(tmu) 2.096(2.172);
W–Cl 2.370(2.355).
Fig. 6 Molecular structure of 2 with key atoms labelled. Thermal ellip-
soids are at the 50% probability level.
bond order calculated for the bridged WvO units is about
25% lower. The partial loss of multiple bond character is
accompanied by an increase of the negative partial charge on
the oxygen atoms. Thus, the average Mulliken charge is
−0.515 a.u. on the terminal oxide ligands (C-PCM/ωB97X;
−0.541 a.u. at the EDF2 level), and −0.688 a.u. on the μ-O
atoms (−0.690 a.u. at the EDF2 level).
Table 2 Selected bond distances (Å) and angles (°) for 2
W(1)–O(1)
W(1)–O(3)
W(1)–Cl(1)
C(1)–O(3)
C(1)–N(1)
C(6)–N(3)
1.684(10)
2.194(8)
2.385(3)
1.311(15)
1.334(17)
1.313(17)
W(1)–O(2)
W(1)–O(4)
W(1)–Cl(2)
C(6)–O(4)
C(1)–N(2)
C(6)–N(4)
1.718(9)
2.172(8)
2.357(4)
1.281(14)
1.323(17)
1.358(17)
O(1)–W(1)–O(3)
Cl(1)–W(1)–Cl(2)
O(3)–W(1)–O(4)
W(1)–O(4)–C(6)
Sum at C(6)
168.7(4)
163.83(12)
74.6(3)
136.2(8)
360(2)
O(2)–W(1)–O(4)
O(1)–W(1)–O(2)
W(1)–O(3)–C(1)
Sum at C(1)
164.2(4)
101.2(4))
132.6(8)
360(2)
The salient IR data of 1 (solid state) are represented by two
absorptions at 1575 and 1531 cm−1, that have been attributed
to mixed CvO and C–N stretching vibrations, with the assist-
ance of DFT simulations.
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ligands. The DFT-optimized geometry of 2 is shown in products (Alfa Aesar) stored under an argon atmosphere as
Fig. S6.† The IR spectrum of 2 (solid state) displays a diagnos- received. Solvents (Sigma Aldrich) were distilled from appropri-
tic absorption at 1540 cm−1, due to the mixed CvO and C–N ate drying agents before use. Infrared spectra were recorded in
stretching vibrations.
the 4000–650 cm−1 range at 298 K with a FT IR-Perkin Elmer
The synthesis of W(VI) coordination complexes from the Spectrometer, equipped with a UATR sampling accessory.
reactions of WO2Cl2 with different ratios of tetramethylurea NMR spectra were recorded at 298 K on a Bruker Avance II
contrasts with what is observed for the WCl6/tmu reaction DRX400 instrument equipped with a BBFO broadband probe.
system. In the latter case, the presumable, initial formation of The chemical shifts for 1H and 13C were referenced to the non-
the tmu radical cation besides [WCl6]− is followed by C–H acti- deuterated aliquot of the solvent. The spectra were fully
vation and intermolecular H-migration, leading to the iso- assigned via 1H,13C correlation measured through gs-HSQC
lation of a protonated urea salt in moderate yield (Scheme 1).10 and gs-HMBC experiments.24 Carbon, hydrogen and nitrogen
The absence of electron interchange between WO2Cl2 and analyses were performed on a Carlo Erba mod. 1106 instru-
tmu indicates that the presence of two oxide ligands signifi- ment. The chloride content was determined by the Mohr
cantly weakens the oxidative power of the W(VI) metal method25 on solutions prepared by dissolution of the solid in
centre.11,23
aqueous KOH at boiling temperature, followed by cooling to
Interestingly, the 1 : 1 molar reaction of yellow WO2Cl2 with room temperature and addition of H2SO4 up to neutralization.
tmu was slightly less selective with respect to the analogous
Synthesis of WO2Cl2
reaction performed using the homologous grey material
(Scheme 1). A light green precipitate was recovered from the di- A suspension of WCl6 (5.198 g, 13.11 mmol) in heptane
chloromethane reaction mixture. IR analysis of this solid evi- (60 mL) was treated with O(SiMe3)2 (5.85 mL, 27.52 mmol).
denced the presence of three bands in the carbonyl region The mixture was stirred at 80 °C for 16 h. The resulting green-
(1762, 1649, 1609 cm−1), other than the absorptions due to 1.
ish grey precipitate was isolated, washed with hexane (2 ×
30 mL) and dried in vacuo. Yield 2.82 g, 75%. Anal. Calcd for
Cl2O2W: Cl, 24.73. Found: Cl, 24.61. IR (solid state): ν =
846s-sh, 800vs, 760s-sh (νWvO) cm−1
.
Conclusions
Synthesis of WO3·H2O
Modification of a known laboratory procedure allowed us to
obtain a new form of WO2Cl2 as a light grey solid. Instead, the
General procedure. WO2Cl2 (0.60 mmol) was layered over a
yellow colour is typical of commercial WO2Cl2. The hydrolytic watchglass and left in contact with air. A progressive colour
degradation of “grey” WO2Cl2 upon air exposure occurs fast at change was observed. After 72 h, the resulting solid material
room temperature, affording nanocrystalline WO3·H2O (light was collected and then characterized by elemental analysis,
green). Conversely, the yellow WO2Cl2 to WO3·H2O conversion TEM and P-XRD.
is a slower process resulting in the formation of a partially
amorphous material. The synthesis of tungsten oxide from Calcd for H2O4W: H, 0.81; Cl, 0.00. Found: H, 1.08; Cl, 0.28.
WO2Cl2 was not reported previously. Grey and yellow WO2Cl2, (B) From yellow WO2Cl2 (commercial): lemon yellow solid,
(A) From grey WO2Cl2: light green solid, yield 94%. Anal.
respectively, show some differences even when allowed to yield 95%. Anal. Calcd for H2O4W: H, 0.81; Cl, 0.00. Found: H,
interact with tetramethylurea (tmu), the reaction with grey 1.20; Cl, 0.36.
WO2Cl2 appearing slightly more selective. Two coordination
complexes were obtained by the reactions of grey WO2Cl2 with
limited amounts of tmu, and crystallographically character-
Reactions of WO2Cl2 with tetramethylurea (tmu): synthesis of
[WO2Cl2(tmu)]3, 1, and WO2Cl2(tmu)2, 2
ized, thus providing the first information available on the reac-
tivity of WO2Cl2 with alkylureas.
General procedure. Tetramethylurea (tmu) was added to grey
WO2Cl2 suspended in CH2Cl2 (ca. 15 mL), and the resulting
mixture was stirred at room temperature for 5 d. Then the reac-
tion solution was concentrated up to ca. 5 mL, layered with
hexane and set aside at −30 °C. The product was collected as a
crystalline material after ca. 1 week.
Experimental
General
[WO2Cl2(tmu)]3, 1. Green solid, from WO2Cl2 (0.250 g,
Warning: the metal products reported in this paper are highly 0.872 mmol) and tmu (0.105 mL, 0.872 mmol). Yield 0.158 g,
moisture-sensitive, thus rigorously anhydrous conditions were 45%. Anal. Calcd for C5H12Cl2N2O3W: C, 14.91; H, 3.00;
required for the reaction and crystallization procedures. The N, 6.95; Cl, 17.60. Found: C, 14.84; H, 3.05; N, 6.90; Cl, 17.45.
reaction vessels were oven dried at 140 °C prior to use, evacu- IR (solid state): ν = 2962w, 2862w, 1575m and 1531s (νCvO
+
ated (10−2 mmHg) and then filled with argon. WCl6 (Strem, νCN), 1471m, 1425m, 1409m-s, 1399s, 1322m, 1267w, 1234w,
99.9%) and WO2Cl2 (Sigma Aldrich, 99%) were purchased and 1165m, 1068w, 975w-m (νWO,terminal+bridging), 903w, 866vs
stored in sealed glass tubes under an argon atmosphere. Once (νWO,terminal+bridging), 762s, 747m-s, 730m, 700w-m cm−1 1H
.
isolated, the metal products were conserved in sealed glass NMR (CD3CN): δ = 3.06 (s, CH3) ppm. 13C NMR (CD3CN): δ =
tubes under argon. The organic reactants were commercial 163.0 (CvO), 39.4 (CH3) ppm.
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Table 3 Crystal data and details of the structure refinement for 1 and 2
WO2Cl2(tmu)2, 2. Colourless solid, from WO2Cl2 (0.240 g,
0.837 mmol) and tmu (0.21 mL, 1.8 mmol). Yield 0.278 g,
64%. Anal. Calcd for C10H24Cl2N4O4W: C, 23.14; H, 4.66; N,
10.79; Cl, 13.66. Found: C, 23.07; H, 4.74; N, 10.84; Cl, 13.50.
IR (solid state): ν = 2960w, 2886w, 1540s-br (νCvO + νNCN),
1470w-m, 1420m, 1397s, 1325w-m, 1260w, 1235w, 1163m,
1067s, 1018s, 960vs (νOvWvO, symm), 915vs (νOvWvO, asymm),
1·CH2Cl2
2
Formula
Fw
λ, Å
Temperature, K
Crystal system
Space group
a, Å
b, Å
c, Å
C16H88Cl8N6O9W3
1293.67
0.71073
100(2)
Orthorhombic
P212121
11.249(2)
11.476(2)
28.300(5)
90
3653.4(11)
4
2.352
10.055
2424
0.21 × 0.16 × 0.13
1.44–26.00
33 756
7163 [Rint = 0.0577]
7163/129/379
C10H24Cl2N4O4W
519.08
0.71073
100(2)
Monoclinic
P21/n
14.211(3)
22.418(5)
18.094(4)
113.063(3)
5304(2)
12
1.950
6.854
3024
0.21 × 0.16 × 0.12
1.22–26.00
51 807
10 547 [Rint = 0.0830]
10 547/279/569
873s, 798s, 765s, 746s cm−1 1H NMR (CD2Cl2): δ = 2.99 (s,
.
CH3) ppm. 13C NMR (CD2Cl2): δ = 165.9 (CvO), 39.2 (CH3)
ppm.
β, °
Cell volume, Å3
Z
TEM studies
Dc, g cm−3
Transmission electron microscopy (TEM) analyses were carried
out with a ZEISS LIBRA 200FE HRTEM instrument, equipped
with a FEG source operating at 200 kV and EDS probe for
chemical analysis. The samples were prepared by vigorously
rubbing the solid between two clean glass slides, and then
they were dispersed onto holey-carbon films supported on a
copper grid (300 mesh) by adherence.26
μ, mm−1
F(000)
Crystal size
θ limits, °
Reflections collected
Independent reflections
Data/restraints/
parameters
Goodness of fit on F2
R1 (I > 2σ(I))
wR2 (all data)
Largest diff. peak and
hole, e Å−3
1.048
0.0357
0.0726
2.100/−1.502
1.053
0.0544
0.1576
2.445/−3.752
P-XRD studies
The powder X-ray-diffraction patterns were measured with a
Thermo ARL X’TRA powder diffractometer, operating in the
Bragg–Brentano geometry and equipped with a Cu-anode X-ray
source (Kα, λ = 1.5418 Å), using a Peltier Si(Li) cooled solid
state detector. The patterns were collected with a scan step of
0.03° and an exposure time of 15 s in the 20°–90° 2θ range.
The phase identifications were performed with the PDF-4+
2013 database provided by the International Centre for
Diffraction Data (ICDD). The air-sensitive polycrystalline
samples of WO2Cl2 were ground in a mortar, transferred to a
low-background sample holder for the data collection and
then protected by using a film of the inert paraffin oil. Rietveld
refinement calculations were performed on WO3·H2O samples,
in order to calculate the cell parameters and the average
crystal size, by means of the MAUD computer program.27 This
program precisely takes into account the instrumental broad-
ening resolution and performs the separation of the lattice
narily located in the Fourier difference map. Several restraints
were applied to the C and N atoms of 1·CH2Cl2 during refine-
ment. In particular, all the atoms were restrained to have
similar U parameters [SIMU command in SHELXL, s.u. 0.01].
Similar U restraints [SIMU command in SHELXL, s.u. 0.02]
were applied to the C, O and N atoms of 2. The crystals of
2 are pseudo-merohedrally twinned with twin matrix −1 0 0 0
−1 0 1 0 1 and refined batch factor 0.4254(13). The asymmetric
unit of the unit cell of 2 contains three independent molecules
(located at general positions), with very similar geometries and
bonding parameters.
Computational studies
strain contribution from the broadening originated as a result The computational geometry optimizations were carried out
of crystallite size reduction. MAUD implemented a peak broad- without symmetry constrains using the hybrid-GGA EDF2 func-
ening description of the analytical Pseudo-Voigt lines, simi- tional,31 in combination with the 6-31G** basis set (ECP-based
larly to the pioneering Williamson Hall plot used in multiple LANL2DZ basis set for elements beyond Kr).32 The “restricted”
profile analysis.28
formalism was applied in all cases. The software used was
Spartan 08. Further computational geometry optimizations
were carried out without symmetry constrains, using the
SC-XRD studies
Crystal data and collection details of 1·CH2Cl2 and 2 are listed range-separated DFT functional ωB97X,33 in combination with
in Table 3. The diffraction experiments were carried out on a a polarized basis set composed by the 6-31G(d,p) set on the
Bruker APEX II diffractometer equipped with a CCD detector light atoms and the ECP-based LANL2TZ(f) on the metal
and using Mo-Kα radiation (λ = 0.71073 Å). Data were corrected centre.34 The C-PCM implicit solvation model (ε = 9.08) was
for Lorentz polarization and absorption effects (empirical considered for ωB97X calculations.35 Gaussian ‘09 was used as
absorption correction SADABS).29 The structures were solved software.36 All the stationary points were characterized by
by direct methods and refined by full-matrix least-squares IR simulations (harmonic approximation), from which zero-
based on all data using F2.30 All non-hydrogen atoms were point vibrational energies and thermal corrections (T =
refined with anisotropic displacement parameters. All hydro- 298.15 K) were obtained.37 The vibrational simulation sup-
gen atoms were fixed at calculated positions and refined by a ported the interpretation of the experimental IR data. Bond
riding model, except N-bonded hydrogens which were prelimi- orders were estimated on the basis of Mayer’s approach.38
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Cartesian coordinates of the optimized geometries are col-
lected in a separated .xyz file.
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Acknowledgements
The Universities of Pisa and Verona are gratefully acknowl-
edged for financial support.
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