Facile Reduction of Tungsten Halides with Nonconventional, Mild Reductants. I. Tungsten Tetrachloride: Several Convenient Solid-State Syntheses, a Solution Synthesis of Highly Reactive (WCI4)x, and the Molecular Structure of Polymeric Tungsten Tetrachloride

Article abstract of DOI:10.1021/ic9801286

Polymeric (WCl₄)_X has been prepared in crystalline form from WCl₆ by three new, safer solid-state approaches via mercury (in 83% yield), bismuth (82% yield), or antimony (97% yield) reduction. A modification of a published procedure for reduction of WCl₆ with red phosphorus, which improves (WCl₄)_x purity, is also described. Highly reactive (WCl₄)_xpowder can be prepared in 99% yield via tin reduction of WCl₆ in 1,2-dichloroethane. (WCl₄)_x powder was readily converted in high yields to the known WCl₄(MeCN)₂ and W₂Cl₄(OMe)₄(HOMe)₂. The molecular structure of (WCl₄)_x, as determined by single-crystal X-ray diffractometry, consists of a polymer of opposite-edge-sharing bioctahedra with alternating short (W(1)-W(1A), 2.688(2) ?) and long (W(1)?W(1B), 3.787(3) ?) tungsten - tungsten distances. The acute W(1)-Cl(2)-W(1A) angle (69.4(2)°), obtuse C1(1)-W(1)W(1A) angle (94.99(12)°), short axial Cl(1)?Cl(1A) nonbonded distance (3.085(10) ?, substantially less than twice the Cl van der Waals radius), and short W(1)-W(1A) distance are consistent with a strong W(1)-W(1A) interaction best described as a W=W bond for this d²-d² compound. Crystal data: Cl₄W, a = 11.782(3) ?, b = 6.475(1) ?, c = 8.062(2) ?, β= 131.14(1)°, V = 463.2(2) ?³, monoclinic, C2/m, Z = 4.

Full text of DOI:10.1021/ic9801286

Inorg. Chem. 1998, 37, 3257-3262
3257
Facile Reduction of Tungsten Halides with Nonconventional, Mild Reductants. I. Tungsten
Tetrachloride: Several Convenient Solid-State Syntheses, a Solution Synthesis of Highly
Reactive (WCl4)x, and the Molecular Structure of Polymeric Tungsten Tetrachloride
Vladimir Kolesnichenko, Dale C. Swenson, and Louis Messerle*
Department of Chemistry, The University of Iowa, Iowa City, Iowa 52242
ReceiVed February 2, 1998
Polymeric (WCl4)x has been prepared in crystalline form from WCl6 by three new, safer solid-state approaches
via mercury (in 83% yield), bismuth (82% yield), or antimony (97% yield) reduction. A modification of a published
procedure for reduction of WCl6 with red phosphorus, which improves (WCl4)x purity, is also described. Highly
reactive (WCl4)x powder can be prepared in 99% yield via tin reduction of WCl6 in 1,2-dichloroethane. (WCl4)x
powder was readily converted in high yields to the known WCl4(MeCN)2 and W2Cl4(OMe)4(HOMe)2. The
molecular structure of (WCl4)x, as determined by single-crystal X-ray diffractometry, consists of a polymer of
opposite-edge-sharing bioctahedra with alternating short (W(1)-W(1A), 2.688(2) Å) and long (W(1)‚‚‚W(1B),
3.787(3) Å) tungsten-tungsten distances. The acute W(1)-Cl(2)-W(1A) angle (69.4(2)°), obtuse Cl(1)-W(1)-
W(1A) angle (94.99(12)°), short axial Cl(1)‚‚‚Cl(1A) nonbonded distance (3.085(10) Å, substantially less than
twice the Cl van der Waals radius), and short W(1)-W(1A) distance are consistent with a strong W(1)-W(1A)
2
2
interaction best described as a WdW bond for this d -d compound. Crystal data: Cl4W, a ) 11.782(3) Å, b
3
)
6.475(1) Å, c ) 8.062(2) Å, â ) 131.14(1)°, V ) 463.2(2) Å , monoclinic, C2/m, Z ) 4.
Introduction
with CCl4.10 Newer synthetic routes are based on reduction of
11
WCl6 with red phosphorus (95% yield based on WCl6), Al
Tungsten tetrachloride is an important starting reagent in
lower-valent tungsten and organotungsten chemistries. (WCl4)x
12
(
100% yield based on Al), C2Cl4 (95% yield based on WCl6,
13
with brief preparative details; 50% yield in an earlier detailed
procedure ), W(CO)6 in refluxing PhCl (96% yield based on
1
is a common synthon in tungstenocene, multiply bonded
14
2
3
ditungsten, and hexatungsten(II) halide cluster chemistries and
has been used to prepare important compounds/materials, e.g.,
3d,15
16
W(CO)6),
and WO2. Most synthetic routes entail experi-
mental complexities, including high pressures of reactants or
byproduct, specialized equipment, slow reactions, high temper-
atures, careful temperature control, expensive reactant, difficulty
in filtration of product, chlorohydrocarbon byproducts, a need
for a two-zone furnace, or appreciable impurities if the reaction
is not run under optimal conditions. Irreproducibility can be a
problem; for example, in our hands the reaction of WCl6 with
C2Cl4 gave predominantly WCl5. In the two most common
routes (employing red P or W(CO)6), care must be exercised in
order to minimize residual levels of W phosphides, P, or PhCl,
all of which can affect subsequent chemistry. The suitability
of (WCl4)x for a particular synthetic use can be critically
4
5
porphyrin complexes, nanophase W2C, reactive WCl2(ligand)4
6
7
complexes, ring-opening metathesis polymerization catalysts,
and alkyne complexes.8 The earliest preparations of (WCl4)x
9
involved reduction of WCl6 with H2 or chlorination of WO2
(
(
1) Persson, C.; Andersson, C. Organometallics 1993, 12, 2370.
2) (a) Chisholm, M. H.; Martin, J. D. Inorg. Syn. 1992, 29, 137. (b)
Sattelberger, A. P.; McLaughlin, K. W.; Huffman, J. C. J. Am. Chem.
Soc. 1981, 103, 2880. (c) Schrock, R. R.; Sturgeoff, L. G.; Sharp, P.
R. Inorg. Chem. 1983, 22, 2801. (d) Chisholm, M. H.; Eichhorn, B.
W.; Folting, K.; Huffman, J. C.; Ontiveros, C. D.; Streib, W. E.; Van
Der Sluys, W. G. Inorg. Chem. 1987, 26, 3182. (e) Cotton, F. A.;
Mandal, S. K. Inorg. Chem. 1992, 31, 1267. (f) Chisholm, M. H.;
Cotton, F. A.; Extine, M.; Stults, B. R. J. Am. Chem. Soc. 1976, 98,
2a,11b,15a,c
dependent on the preparative route.
Crystalline product
4
477. (g) Cotton, F. A.; Falvello, L. R.; Fredrich, M. F.; DeMarco,
has been reported only from reduction of WCl6 with Al via
chemical transport in a two-zone furnace (475, 225°) with
careful temperature control because of the circulating AlCl3.12
D.; Walton, R. A. J. Am. Chem. Soc. 1983, 105, 3088. (h) Boorman,
P. M.; Gao, X.; Freeman, G. K. W.; Fait, J. F. J. Chem. Soc., Dalton
Trans. 1991, 115. (i) Cotton, F. A.; Koch, S. A.; Schultz, A. J.;
Williams, J. M. Inorg. Chem. 1978, 17, 2093. (j) Cotton, F. A.; Koch,
S.; Mertis, K.; Millar, M.; Wilkinson, G. J. Am. Chem. Soc. 1977, 99,
(9) (a) Voight, A.; Blitz, W. Z. Anorg. Allg. Chem. 1924, 133, 277. (b)
Blitz, W.; Fendius, C. Z. Anorg. Allg. Chem. 1928, 172, 385.
(10) Michael, A.; Murphy, A. Am. Chem. J. 1910, 44, 365 (cited in ref
12).
4
989.
3) (a) Lindner, K.; K o¨ hler, A. Ber. Dtsch. Chem. Ges. 1922, 55, 1461.
b) Lindner, K.; K o¨ hler, A. Z. Anorg. Allg. Chem. 1924, 140, 357. (c)
(
(
Hogue, R. D.; McCarley, R. E. Inorg. Chem. 1970, 9, 1354. (d) Zhang,
X.; McCarley, R. E. Inorg. Chem. 1995, 34, 2678.
4) Berreau, L. M.; Hays, J. A.; Young, V. G., Jr.; Woo. L. K. Inorg.
Chem. 1994, 33, 105.
5) Zeng, D.; Hampden-Smith, M. J. Chem. Mater. 1993, 5, 681.
6) (a) Sharp, P. R. Organometallics 1984, 3, 1217. (b) Bryan, J. C.; Geib,
S. J.; Rheingold, A. L.; Mayer, J. M. J. Am. Chem. Soc. 1987, 109,
(11) Novikov, G. I.; Andreeva, N. V.; Polyachenok, O. G. Russ. J. Inorg.
Chem. 1961, 6, 1019.
(
(12) McCarley, R. E.; Brown, T. M. Inorg. Chem. 1964, 3, 1232.
(13) McCann, E. L., III.; Brown, T. M. Inorg. Syn. 1970, 12, 181.
(14) Brown, T. M.; McCann, E. L., III. Inorg. Chem. 1968, 7, 1227.
(15) (a) Schaefer-King, M. A.; McCarley, R. E. Inorg. Chem. 1973, 12,
1972. (b) Santure, D. J.; Sattelberger, A. P. Inorg. Synth. 1989, 26,
219. (c) Schrock, R. R.; Sturgeoff, L. G.; Sharp, P. R. Inorg. Chem.
1983, 22, 2801.
(
(
2826.
(
(
7) Balcar, H.; Pacovska, M. J. Mol. Catal. A: Chem. 1997, 115, 101.
8) Bott, S. G.; Clark, D. L.; Green, M. L. H.; Mountford, P. J. Chem.
Soc., Dalton Trans. 1991, 471.
(16) Malysheva, L. E.; Eliseev, S. S. Dokl. Akad. Nauk Tadzh. SSR 1982,
25, 403; Chem. Abstr. 1983, 98, 100118m.
S0020-1669(98)00128-1 CCC: $15.00 © 1998 American Chemical Society
Published on Web 05/30/1998

3258 Inorganic Chemistry, Vol. 37, No. 13, 1998
Kolesnichenko et al.
A polymeric, octahedral chain structure17 has been assigned12
to solid (WCl4)x on the basis of isomorphism of the powder
X-ray diffraction data to that for (NbCl4)x. In the (NbCl4)x
structure, each octahedron shares a pair of opposite edges, with
alternating short and long Nb‚‚‚Nb separations.18 An alternate19
structural view is a close-packed array of chlorides with metal
atoms in adjacent octahedral holes, filling half the octahedral
holes in every second layer. To our knowledge, there has been
no single-crystal X-ray diffractometry performed on (WCl4)x.
During the course of our studies on tungsten halide cluster
chemistry, we found an improved approach (in terms of purity)
to the synthesis of (WCl4)x via reduction of WCl6 with red
phosphorus. Because of the high pressures of PCl3 which can
be generated during this reaction, we examined other reductants.
We found that mercury, antimony, and bismuth were convenient
reductants in safer sealed-tube furnace reactions for preparation
of crystalline (WCl4)x in good to excellent yields, and that Sn
is an effective reductant for solution preparation of highly
reactive (WCl4)x in high yield. We report here preparative
details for these improved and new synthetic routes, preparation
of known derivatives to test the suitability of the highly reactive
Figure 1. Ampule design for preparation of (WCl
WCl with P (not to scale).
4 x
) via reduction of
6
solution and precipitated BaWO
4
were heated at 100 °C for ∼20 min
and allowed to sit at room-temperature overnight. The precipitate was
removed with a glass fritted funnel and washed with distilled water.
The mother liquor volume was adjusted to 75-80 mL and neutralized
by adding 12 drops of concentrated (∼70%) HNO
3
. A 0.5 M solution
of AgNO (5.5 mL) was then added dropwise with stirring. The
3
resulting solution and precipitated AgCl were heated at 100 °C for ∼20
min and allowed to sit overnight at room temperature while protected
from light. The AgCl precipitate was filtered with a glass fritted funnel,
washed with distilled water, oven-dried for 1-2 h at 150 °C, and
weighed. Chlorine analyses are the average of two determinations.
Far IR spectra were recorded on a Perkin-Elmer 983G dispersive
IR spectrometer on samples in KBr pellets. Powder X-ray diffraction
was performed on a Siemens D5000 automated diffractometer, with
samples protected from hydrolysis by a thin sheet of poly(vinyl
chloride).
(WCl4)x, and the results of a single-crystal X-ray diffraction
study on (WCl4)x.
Preparation of (WCl
4
)
x
via Reduction of WCl
6
with Red
Phosphorus. Note: Dangerous pressures of PCl
3
deVelop during this
Experimental Section
reaction, and glass Vessels are unreliable at pressures in excess of 1
atm, particularly those which haVe not been thoroughly annealed during
construction and seal-off or which haVe been scratched. IndiViduals
General. Compounds were manipulated in a Vacuum Atmospheres
glovebox under prepurified N
recirculation blower). A Thermolyne 21100 single-zone tube furnace
e1200 °C) with positionable thermocouple was used in syntheses.
2
/He (He to assist cooling of the
who repeat this procedure are urged to calculate the PCl Vapor
3
(
pressure under their conditions (ampule Volume, quantities of reactants,
Borosilicate glass ampules of 25 mm OD with a standard taper 14/20
outer joint were sealed at one end, constricted at two or three locations
temperature) before proceeding, and to adjust these experimental
3
conditions to lower the PCl pressure which could be generated.
(depending on the synthetic approach), and then oven-dried overnight
Appropriate and conserVatiVe safety precautions, including shielding
of the tube furnace, enclosure of the apparatus within a fume hood,
and use of face shield and protectiVe gloVes, must be followed.
A straight borosilicate glass ampule of 25 mm OD with total inner
volume of ∼70 mL was constructed with three adjacent chambers: the
first, in which the reactants were loaded and which had a standard taper
at 130 °C. To ensure temperature uniformity throughout the reaction
zone and to preclude lower temperature zones (where intermediate
reduction products such as WCl could form), the ratio of lengths of
5
tube furnace to glass ampule was kept at g1.6. Precursors were
introduced into the ampule in the glovebox, the ground jointed end
closed off with a stopcock-equipped adapter, and the tube flame sealed
under dynamic vacuum from a Schlenk line. Reductions in 1,2-
dichloroethane were performed in Schlenk glassware.
1
4/20 outer joint on its end, the second (similar size), in which sublimed
impurities were collected at the end of the reaction, and the third
smaller than first and second), in which PCl was to be collected
(
3
WCl
powder, Aldrich), and Sn (325 mesh powder, Aldrich) were used as
received. 1,2-Dichloroethane (Aldrich) and CH Cl (Fisher) were
thoroughly degassed with argon and distilled from granular P
6
(Cerac), red P (Aldrich), Bi (325 mesh, Cerac), Sb (100 mesh
(Figure 1). The first and second chambers were separated by a wide
constriction which was plugged with borosilicate glass wool. The third
chamber was separated from the second chamber by a narrower
constriction (ID 1.5-2 mm).
The first chamber was loaded with 24.12 g (60.8 mmol) of WCl6
and 1.256 g (40.5 mmol) of red P through the ground-joint end. A
vacuum adapter was attached and the entire tube evacuated. The
ampule was then flame sealed at the constriction between the ground
joint and first chamber and the reagents mixed by shaking. The entire
ampule was placed in the center of the tube furnace such that WCl5
could not leave the reaction zone. The temperature was raised to 200
°C during 12 h, and then to 300 °C during 12 h. Assuming ideal gas
behavior for PCl3 at 300 °C (above its critical temperature), the
2
2
2
5
O .
MeCN (Aldrich, anhydrous) was used as received. MeOH (Aldrich,
anhydrous) was stored over 4 Å molecular sieves. Triply distilled Hg
was purified by filtration through a pinched paper filter into a glass
cylinder containing ∼1 M aqueous HNO
3
.
Tungsten content was determined gravimetrically as WO
3
by treating
followed by ignition. Qualitative microanalyses
for Hg, Bi, Sb, and Sn were performed according to published
12
samples with HNO
3
20
procedures. Chlorine analysis was performed by gravimetric methods
after removal of tungsten content according to the following proce-
dure: An accurately weighed sample of (WCl
decomposed in 5 mL of 1 M KOH at room temperature. The resulting
suspension was oxidized by adding 2 drops of 30% H After
4
)
x
(0.17-0.19 g) was
estimated PCl pressure was 27 atm based on the ampule volume. After
the furnace was shut off and cooled to 100 °C, the ampule was removed
from the furnace and its smaller third chamber immersed in liquid
3
2 2
O .
approximately 1 h, the solution was diluted to ∼50 mL volume and
nitrogen for trapping PCl . After 5 min, the frozen chamber was sealed-
3
heated at 100 °C for ∼20 min in order to complete oxidation of tungsten
off by torch, and the first chamber returned to the furnace in order to
sublime WOCl and WCl into the cool second chamber. A temperature
3 2
and decompose traces of peroxides. A 0.1 M solution of Ba(NO ) (7
4
5
mL) was added dropwise with stirring to the hot sample solution. The
of 230-240 °C was maintained for 1 day, then, after cooling, the
ampule was removed from the furnace and opened in the glovebox.
The yield of black, nonvolatile crystalline product was 18.69 g (94%
based on phosphorus).
(
(
(
(
17) Wells, A. F. Structural Inorganic Chemistry, 5th ed.; Clarendon
Press: Oxford, U.K., 1984; p 424.
18) Taylor, D. R.; Calabrese, J. C.; Larsen, E. M. Inorg. Chem. 1977, 16,
Powder X-ray diffraction data was consistent with (WCl
or WCl were detected. Anal. Calcd for WCl : W, 56.45. Found:
W, 56.6.
Preparation of (WCl
Note: This reaction should be performed in a fume hood with shielding
4 x 6
) ; no WCl
721.
5
4
19) Kepert, D. L. The Early Transition Metals; Academic Press: London,
U.K., 1972; pp 26-27.
20) Svehla, G. Vogel’s QualitatiVe Inorganic Analysis, 6th ed.; Long-
man: Essex, U.K., 1987.
4 x 6
) via Reduction of WCl with Mercury.

Facile Reduction of Tungsten Halides
Inorganic Chemistry, Vol. 37, No. 13, 1998 3259
of the furnace in order to preVent release of toxic, Volatile Hg and
and opened in the glovebox. The yield of black, nonvolatile, crystalline
HgCl
2
should the ampule seal fail or the ampule shatter. Mercury
product was 7.99 g (97% yield based on WCl
Anal. Calcd for WCl : W, 56.45; Cl, 43.55. Found: W, 56.5; Cl,
43.39. No Sb was detected by qualitative microanalysis.
Preparation of (WCl via Reduction of WCl with Sn in 1,2-
Dichloroethane. A 100 mL Schlenk flask was loaded with WCl
6
6
).
has appreciable Vapor pressure at eleVated temperatures. A dual
chamber borosilicate glass ampule, with standard taper 14/20 outer joint
on one end, constrictions in the middle and between the joint and the
4
)
4 x
6
first chamber, and total volume of ∼80 mL was loaded with WCl
6
(
10.00 g, 25.22 mmol) and Hg (5.00 g, 24.93 mmol) in the first
(12.00 g, 30.26 mmol), Sn powder (1.796 g, 15.13 mmol), and 60 mL
of 1,2-dichloroethane. The mixture was stirred at room temperature
for 17 h, yielding a gray suspension. A reflux condenser was attached
and the mixture heated and stirred at 80-90 °C for 2 days. The
graphitic suspension did not change appearance during heating. After
cooling, the flask was transferred to the glovebox and the suspension
centrifuged in a compact centrifuge. The supernatant was removed,
chamber. After evacuation, the ampule was flame-sealed between the
first chamber and joint and the reagents mixed by shaking. A reaction
was readily apparent after mixing, as the crystalline WCl changed from
6
purple-gray to brownish-gray, and Hg was consumed. No appreciable
temperature rise was noted.
The ampule was placed in the center of the furnace and the
temperature raised slowly (∼2 h) to 205 °C. After 1 day, the
temperature was raised slowly (∼2 h) to 360 °C. The estimated
the solid resuspended in CH
supernatant was removed and the resuspension in CH
process repeated four times. The solid was washed into a 125 mL
flask with fresh CH Cl , the supernatant decanted, and the precipitate
dried under dynamic vacuum at room temperature. The yield was 9.812
g (99.6% based on WCl ). The product was a graphitic fine powder
with poor crystallinity (by X-ray diffractometry) and high reactivity.
Anal. Calcd for WCl : W, 56.45; Cl, 43.55. Found: W, 56.6; Cl,
3.27. No Sn was detected by qualitative microanalysis.
In a smaller scale reaction, 3.00 g WCl (7.57 mmol) and 0.449 g
Sn (3.78 mmol) in 15 mL C Cl gave 2.405 g powdered (WCl
98% yield based on WCl ). SnCl was recovered from the supernatant
2
Cl
2
, and the mixture centrifuged. The
2
Cl /centrifugation
2
2
1
pressure in the ampule at 360 °C was 3.4 atm. After ∼10 h, the
temperature was lowered slowly (2-2.5 h) to 205 °C. The ampule
2
2
was partially slid out of the furnace in order to sublime HgCl
2
as well
as any WOCl and WCl into the cool second chamber. After heating
4
5
6
for ∼8 h, the ampule was removed, cooled, and opened in the glovebox.
The nonvolatile, black microcrystalline product weighed 6.82 g (83%
4
4
yield based on WCl
crystals was isolated from an ampule zone at intermediate temperature.
Colorless crystals of HgCl in the cold ampule end were mixed with a
4 x
small quantity of black needles of transported (WCl ; this (WCl )
6
). A small quantity (∼0.2 g) of large (WCl
4 x
)
6
H
2 4
2
4 x
)
2
(
6
4
)
4 x
as the insoluble bis-pyridine adduct. Yield ) 1.511 g (95% based on
Sn).
was not isolated, but differential sublimation to remove HgCl
possible and would improve the final yield.
2
is
Reaction of (WCl
Acetonitrile. Preparation of WCl
WCl (0.200 g, 0.61 mmol) in 7 mL of acetonitrile was stirred at
)
4 x
(Prepared in Solution via Sn Reduction) with
Anal. Calcd for WCl
3.52. According to powder X-ray diffraction, both the black micro-
crystals and transported black crystals were (WCl , and no WCl or
WCl was detected. No Hg was detected in either by qualitative
microanalysis.
4
: W, 56.45; Cl, 43.55. Found: W, 56.5; Cl,
4
(MeCN) A suspension of
2
.
4
(
4 x
)
4
)
x
6
room temperature. The suspension turned gray-purple after 1 day of
stirring and red-brown after an additional day. The supernatant was
decanted and the precipitate washed with MeCN, in which it was
5
In another experiment using the same quantities of starting materials,
insoluble, and dried in vacuo. The yield of red-brown WCl
powder was 0.202 g (81% based on WCl ).
Anal. Calcd for C Cl W: W, 45.09. Found: W, 45.15. The
IR spectrum (4000-250 cm ) matched literature values.
Reaction of (WCl (Prepared in Solution via Sn Reduction) with
Methanol. Preparation of W Cl (OMe) (HOMe) . An exothermic
reaction was noted upon mixing 0.300 g (0.92 mmol) of (WCl with
mL of MeOH at room temperature. The (WCl dissolved completely
4 2
(MeCN)
all steps of the above synthesis were conducted at 200-210 °C. Weight
4
of (WCl
Preparation of (WCl
A borosilicate glass ampule (similar to that used for the synthesis with
Hg) was loaded with WCl (10.00 g, 25.2 mmol) and Bi (3.51 g, 16.8
4
)
x
) 6.16 g (75% yield based on WCl
6
).
4
H
6
4 2
N
4
)
x
via Reduction of WCl with Bismuth.
6
-
1
15a,22
4 x
)
6
2
4
4
2
mmol). After evacuation, the ampule was sealed and the reagents mixed
by shaking. The ampule was placed in the center of the furnace and
the mixture heated for 1 day at 210-220 °C. The temperature was
raised to 290 °C and the ampule repositioned so that the empty chamber
was in a cooler zone (if the empty chamber is removed from the furnace,
then BiCl will plug the ampule constriction). After 3 days the receiver
3
chamber was repositioned partially outside of the furnace and heating
continued for 17 h. After cooling, the ampule was withdrawn, but a
4 x
)
4
4 x
)
in less than 1 min, forming a transparent green solution. After 4-5
min, the solution became cloudy and a greenish-yellow precipitate was
noted. After sitting overnight, green crystalline precipitate formed. The
precipitate was resuspended, heated at 65 °C for one minute, and cooled
to 20°. The supernatant was decanted, the solid washed with MeOH,
and the solid dried in vacuo. The yield of crystalline W
HOMe) was 0.234 g (73% based on WCl ).
Anal. Calcd for C Cl W: W, 52.72. Found: W, 52.05. The
far-IR spectrum matched literature values.
Single-Crystal Diffractometry on (WCl
crystal with 0.24 × 0.04 × 0.04 mm dimensions, from reduction of
WCl with Hg, was used in data collection. Crystals with larger cross-
2 4 4
Cl (OMe) -
3
small quantity of white crystals (BiCl ) was noted in the product. To
(
2
4
reduce the level of BiCl contamination, the ampule was returned to
3
3
H
11
O
3
2
the furnace and heated for 6 days at 290-295 °C, with a portion of
the receiver chamber outside of the furnace. After cooling, the ampule
was removed and opened in the glovebox. The yield of black,
23
4 x
) . A black needle-shaped
nonvolatile, crystalline (WCl
based on WCl ).
Anal. Calcd for WCl
4 x
) in the first chamber was 6.74 g (82%
6
6
sections appeared fibrous at the ends, consistent with multiple crys-
tallites and/or twinning. The crystal was examined while immersed in
oil with low oxygen solubility, mounted via grease onto a glass fiber
4
: W, 56.45. Found: W, 57.2. Trace levels
of bismuth-containing species were detected in the product by qualita-
tive microanalysis.
(epoxied to a brass pin) under inert gas purge, and cooled with a stream
Preparation of (WCl
A borosilicate glass ampule was loaded with 10.00 g (25.2 mmol) of
WCl and 2.04 g (16.7 mmol) of Sb. After evacuation, the ampule
4 x 6
) via Reduction of WCl with Antimony.
of gaseous dinitrogen. The crystal was placed in the diffractometer
cold stream with the long dimension (b axis) approximately parallel to
the diffractometer φ axis.
6
was sealed, the reagents mixed, and the ampule placed in the center of
The data were collected on an Enraf-Nonius CAD-4 diffractometer,
using Mo KR radiation and a graphite monochromator, at 210 K using
ω scans. Intensity standards were measured at 2 h intervals; no changes
in the standards were detected. Net intensities were obtained by profile
analysis of the 661 data. Data reduction was performed with computer
programs from the MolEN (Enraf-Nonius) package. Lorentz and
polarization corrections were applied, as was an empirical absorption
correction based on three ψ scans measured at 10° intervals. The
the furnace. After heating at 75-80 °C for 12 h, 105 °C for 12 h, and
3
130 °C for 12 h (calculated vapor pressure of SbCl , 46 Torr), the empty
chamber of the ampule was removed from the tube furnace in order to
distill SbCl and sublime WOCl and WCl . A temperature of 125-
30 °C was maintained for 1 day to distill SbCl , then the temperature
was raised to 160 °C (for 1 day) and 215 °C (for 1 day) in order to
remove any WOCl and WCl . After cooling, the ampule was removed
3
4
5
1
3
4
5
(
21) Gmelin’s Handbuch der Anorganischen Chemie, Verlag Chemie,
(22) Blight, D. G.; Kepert, D. L. J. Chem. Soc. A 1968, 534.
(23) Reagan, W. G.; Brubaker, C. H. Inorg. Chem. 1970, 9, 827.
GmbH.: Weinheim, Germany, 1967; Hg, 34, Tl. B, Lfg. 2, p 489.

3260 Inorganic Chemistry, Vol. 37, No. 13, 1998
Kolesnichenko et al.
transmittance range was 0.313-0.985, with an average value of 0.561.
Equivalent data were averaged, yielding 438 unique data (Rint ) 0.094,
volatility of Hg at reduced pressure ensures diffusion of the
reductant throughout the reaction tube and easy removal at the
end of the reaction. The potential reduction byproducts, HgCl2
and Hg2Cl2, are volatile and thus separable from (WCl4)x but
exert lower vapor pressures (∼3.4 atm at 360 °C). Finally, the
formation of W/Hg intermetallics is unlikely, and mercuric
chlorotungstates such as HgWCl6 did not form under our
reaction conditions. We obtained >83% yield of crystalline
3
68 data > 4σ(F)). Two reflections were excluded from the final
refinement cycles after inspection of their profiles revealed small
extraneous peaks of unknown origin. On the basis of preliminary
examination of the crystal, the space group C2/m was assigned.
Structure solution and refinement was performed with software
programs from the SHELXTL v. 5.0 software package (XS, direct
methods; XL, refinement; XP, for thermal ellipsoid illustrations; XCIF,
preparation of tables). The preliminary structure model was obtained
by direct methods. Refinement was performed using a rigid bond
restraint for the anisotropic thermal parameters. A I > 2σ(I) cutoff
was used in selecting data to calculate R1 for comparison purposes.
The molecule consists of a linear one-dimensional polymer with the
W(1) atom situated on a crystallographic 2-fold axis and the bridging
chlorine atoms (Cl(2), Cl(3)) positioned on crystallographic mirror
planes (y ) 0.0, y ) 0.5, respectively).
(WCl4)x by the Hg reduction route.
Because of the toxicities of mercury and mercuric chloride
and the effect of residual amounts of Hg or HgCl (neither
x
detected qualitatively) on some applications of (WCl ) derived
4 x
from Hg reduction, we decided to examine alternate low-cost
reductants which would form volatile byproducts.
Reduction of WCl6 with Bismuth. We obtained a good
yield (82%) of crystalline (WCl4)x from reduction with bismuth,
though the (WCl4)x contained detectable levels of bismuth by
qualitative microanalysis. The W analysis of this material was
also slightly high (57.2% found, 56.46% theory); as the W
analysis procedure does not remove involatile Bi-containing
impurities, contamination with bismuth-containing species may
account for the higher W analysis. We conclude that bismuth
is a less desirable reductant under our reaction conditions
because of the Bi contamination and the lengthy time (>6.5
3
Results and Discussion
Modification of the Procedure Employing Red Phosphorus
as Reductant. The reduction of WCl6 with red phosphorus is
an economical synthetic route but suffers from the need for
careful stoichiometric control in order to avoid contamination
of (WCl4)x with residual phosphorus or tungsten phosphides.
We find that the risk of this increases with the use of the
11a
apparatus and approach described by Novikov, et al., i.e., a
multichamber L-shaped glass tube with a receiver end outside
of the furnace for collection of PCl3 (along with POCl3 from
reduction of residual WOCl4). With a portion of the tube outside
of the furnace, some of the WCl6 (and WCl5) can sublime from
the reaction zone. This would result in an increase of the
P:WCl6 ratio at the reaction zone and thus greater contamination
with phosphorus.
days at ∼290 °C) needed to sublime BiCl .
Reduction of WCl with Antimony. Antimony proved to
6
be the best reductant of those examined by solid-state ap-
proaches, because (1) the yield was virtually quantitative, (2)
the SbCl pressure at 130 °C was considerably less than 1 atm,
3
(3) SbCl distillation required only 1 day, and (4) no Sb-
3
containing species could be detected in the (WCl ) by qualita-
4 x
tive microanalysis.
We find that use of a triple-chamber straight ampule, with
the third chamber for removal of PCl3, improves the (WCl4)x
quality. By heating the entire ampule during the reduction, the
nonstoichiometry from sublimation of WCl6 and WCl5 is
eliminated. After reduction, the ampule is withdrawn from the
furnace, the PCl3 collected by distillation into a liquid-nitrogen-
cooled collection chamber, and the collection chamber sealed
off. Then the ampule is partially returned to the furnace and
residual WCl6 and WCl5 is sublimed away from the (WCl4)x.
A significant safety drawback of this modified red P route is
the substantial PCl3 pressure (calculated at 27 atm at 300 °C
for the tube diameter and quantity of reactants employed; critical
T ) 290 °C) developed within the sealed tube prior to collection
of the PCl3. Therefore, we sought a safer, lower pressure
synthetic route involving a main group reductant which was
easily removable by distillation/sublimation. To achieve a
convenient vapor pressure of 10 Torr for sublimation/distillation,
Reduction of WCl with Tin in 1,2-Dichloroethane. We
6
expected that the reaction of Sn with WCl in the solid-state
6
would be too exothermic, which would exacerbate the high
vapor pressure (bp 112 °C) from SnCl ; thus, reduction of WCl6
4
in the solid-state with tin would have little safety advantage
over that of red phosphorus. In a trial experiment, we verified
that tin powder was too active a reductant for a sealed ampule
reduction in the solid state.
Solution reduction methods often lead to products with
smaller particle size and thus higher reactivity, while facilitating
temperature control during an exothermic reaction. There have
been several reports of in situ reduction of WCl , in the presence
6
of ligands (L), to WCl L compounds. For example, WCl -
4
2
4
2
5
(PPh ) was prepared by zinc reduction of WCl in CH Cl ,
3
2
6
2
2
and WCl (dme) (dme ) 1,2-dimethoxyethane) was prepared by
4
1
26
cyclopentene reduction of WCl . In these and other studies,
6
there was no attempt to characterize the reduced tungsten
product(s) prior to addition of ligand. We therefore examined
the use of tin as a reductant in solution, and chose a solvent
2
4
the following main group chlorides require temperatures of
.4 °C for SnCl4, 95 °C for SbCl3, 180 °C for HgCl2, 247 °C
for Hg2Cl2, and 257 °C for BiCl3. By comparison, WCl5 exerts
0 Torr of vapor pressure at 169 °C, WCl6 requires 198 °C,
3
with appropriate boiling point and in which the SnCl byproduct
4
1
would be soluble.
and PCl3 requires only -21 °C. Therefore, we examined the
use of mercury and antimony in solid-state reductions, and also
the less toxic bismuth (despite the high temperature needed to
remove BiCl3).
Reduction of WCl6 with Mercury. Despite its toxicity,
elemental mercury offers several important advantages as a
reductant for WCl6. First, the mild reductant mercury lessens
the chance for overreduction of WCl6 to tungsten metal. The
The reduction of WCl with tin powder in 1,2-dichloroethane
solution is facile; in fact, a graphitic suspension is evident within
6
1-2 h at room temperature after mixing. The graphitic
suspension after heating was isolated by centrifugation (without
centrifugation, 1 day is needed to allow settling) and washing
multiple times with CH Cl . (WCl ) can be isolated in virtually
2
2
4 x
quantitative yield and is free of tin contamination as shown by
qualitative microanalysis. Powder X-ray diffractometry showed
(
24) Yefimov, A. I.; Belorukova, L. P.; Vasilkova, I. V.; Chechev, V. P.
Properties of Inorganic Compounds. Handbook; Khimiia: Leningrad,
USSR, 1983.
(25) Butcher, A. V.; Chatt, J.; Leigh, G. J.; Richards, P. L. J. Chem. Soc.,
Dalton Trans. 1972, 1064.
(26) Persson, C.; Andersson, C. Inorg. Chim. Acta 1993, 203, 235.

Facile Reduction of Tungsten Halides
Inorganic Chemistry, Vol. 37, No. 13, 1998 3261
Figure 2. Thermal ellipsoid plot (50% probability ellipsoids) of a
portion of the polymeric molecular structure of (WCl ) .
4 x
that the (WCl4)x was poorly crystalline. SnCl4 can be recovered
quantitatively from the supernatant by precipitation as the bis-
(pyridine) adduct.
Comparative Reactivities of Various Forms of (WCl4)x.
We found that crystalline (WCl4)x obtained from the solid-state
methods is substantially less reactive than the powder formed
by solution-phase Sn reduction. In general, the lowest reactivity
was observed for crystalline (WCl4)x obtained at the highest
temperature, though microcrystalline (WCl4)x synthesized by
reduction with red phosphorus at 300 °C or with Hg at 350 °C
demonstrated similar reactivity.
Figure 3. Unit cell plot (spheres of arbitrary dimensions) of (WCl
down the polymer chain axis (b axis).
4 x
)
4 x
Table 1. Crystallographic Data for (WCl )
empirical formula ) Cl
a ) 11.782(3) Å
b ) 6.475(1) Å
4
W
fw ) 325.65
space group ) C2/m (No. 12)
T ) 210°K
c ) 8.062(2) Å
λ ) 0.71073 Å (Mo KR)
To characterize the (WCl4)x powder obtained in this work
by solution-phase reduction of WCl6 with Sn, we performed
syntheses similar to those described in the literature with
conventionally prepared (WCl4)x. (WCl4)x powder reacted
readily with methanol, acetonitrile, and tetrahydrofuran (thf) to
yield known compounds, which supports its chemical composi-
tion. (WCl4)x powder also reacted with diethyl ether to yield a
presently uncharacterized substance; WCl4(OEt2)2 is reported
to be either unisolable26 or stable only at low temperature.
Interestingly, thf and diethyl ether are often used as “inert”
solvents in reactions of conventionally prepared (WCl4)x, so the
ready reaction of the powdered (WCl4)x with these solvents
suggests that the tin-derived powder is a far more reactive form
of (WCl4)x.
-
3
â ) 131.14(1)°
F
calcd ) 4.670 g cm
3
-1
V ) 463.2(2) Å
µ ) 2.704 cm
a
Z ) 4
R1 (F
o
) ) 0.0523
2) ) 0.1301
wR2 (F
o
a
2
2)2]/∑[w(F
2 2 1/2
R1 ) ∑||F
o
| - |F
c
||/∑|F
o
|. wR2 ) {∑[w(F
o
- F
c
o
) ]} .
4
Table 2. Fractional Coordinates (×10 ) and Equivalent Isotropic
2f,27
2
3
Displacement Parameters (Å × 10 ) for (WCl
4 x
)
U(eq)a
x
y
z
W(1)
Cl(1)
Cl(2)
Cl(3)
0
2076(2)
2382(7)
0
0
11(1)
15(1)
14(1)
13(1)
227(5)
2179(6)
1832(6)
3025(8)
1906(10)
1581(10)
5000
The reaction of powdered (WCl4)x with neat methanol rapidly
gave, in 73% isolated yield, the known2 ditungsten compound
W2Cl4(OMe)4(HOMe)2, with identical color, solubility proper-
ties, and far IR spectrum. The acetonitrile adduct WCl4(MeCN)2
was obtained in 81% yield, and matched solubility, appearance,
and IR characteristics of the reported compound.15a,22
The reactivity of (WCl4)x may be related to the value of x,
with reactivity decreasing for crystalline samples with larger
values of x. The powdered (WCl4)x may also be a different
a
(
U(eq) is defined as one-third of the trace of the orthogonalized
3,28
U
ij tensor).
Table 3. Selected Bond Distances (Å), Intramolecular Contacts
Å), and Bond Angles (deg) for (WCl )
4 x
a
(
W(1)-W(1A)
W(1)-Cl(1)
W(1)-Cl(2)
W(1)-Cl(3)
2.688(2)
2.280(5)
2.359(5)
2.500(4)
Cl(1)-W(1)-Cl(1C)
Cl(1)-W(1)-Cl(2)
Cl(1)-W(1)-Cl(2C)
Cl(1)-W(1)-Cl(3)
Cl(2)-W(1)-Cl(3)
Cl(2)-W(1)-Cl(2C)
Cl(3)-W(1)-Cl(2C)
Cl(3)-W(1)-Cl(3C)
Cl(1)-W(1)-W(1A)
W(1)-Cl(2)-W(1A)
W(1)-Cl(3)-W(1B)
170.0(2)
92.4(2)
93.3(2)
86.2(2)
83.97(13)
110.6(2)
165.48(13)
81.5(2)
94.99(12)
69.4(2)
structural form, since MoCl4 exists in two forms, a linear
W(1)‚‚‚W(1B)
Cl(1)‚‚‚Cl(1A)
Cl(1)‚‚‚Cl(1B)
3.787(3)
3.085(10)
3.390(10)
oligomeric R-form1
4,29
with the same structure as that of
30
(
NbCl4)x, and a cyclic hexameric â-form.
Molecular Structure of (WCl4)x. Figure 2 shows a thermal
ellipsoid plot of a portion of the polymeric chain of (WCl4)x,
and Figure 3 shows a unit cell packing diagram. Tables 1-3
list crystallographic data, fractional coordinates and isotropic
thermal parameters, and selected bond and nonbonded distances
and angles. The structure consists of a polymeric chain of edge-
shared, distorted bioctahedra with alternating short (W(1)-
W(1A), 2.688(2) Å) and long (W(1)‚‚‚W(1B), 3.787(3) Å)
98.5(2)
a
Symmetry transformations used to generate equivalent atoms: A,
x, -y, z; B, x, -y + 1, z; C, -x, y, -z.
tungsten-tungsten distances. The W-Cl distances increase
from 2.280(5) Å (W(1)-Cl(1)) for the axial chlorine to 2.359(5)
Å for the bridge chlorine (W(1)-Cl(2)) within the bonded
bioctahedron portion to a long 2.500(4) Å for the bridge chlorine
(
27) (a) Grahlert, W.; Thiele, K.-H. Z. Anorg. Allg. Chem. 1971, 383, 144.
b) Castellani, L.; Gallazzi, M. C. Trans. Met. Chem. 1985, 10, 194.
(
W(1)-Cl(3)) between tungsten atoms which are not interacting
(
significantly. The acute W(1)-Cl(2)-W(1A) angle of 69.4(2)°
and obtuse Cl(2)-W(1)-Cl(2C) angle of 110.6(2)° are typical
of edge-shared bioctahedra in discrete dinuclear compounds of
the early transition metals with significant metal-metal bonding
(
28) (a) Anderson, L. B.; Cotton, F. A.; DeMarco, D.; Fang, A.; Ilsley, W.
H.; Kolthammer, B. W. S.; Walton, R. A. J. Am. Chem. Soc. 1981,
1
8
03, 5078. (b) Clark, P. W.; Wentworth, R. A. D. Inorg. Chem. 1969,
, 1223.
(
(
29) Kepert, D. L.; Mandyczewsky, R. Inorg. Chem. 1968, 7, 2091.
30) M u¨ ller, U. Angew. Chem., Int. Ed. Engl. 1981, 20, 692.
3
1
interaction. By contrast, the bridge chlorine angle (W(1)-

3262 Inorganic Chemistry, Vol. 37, No. 13, 1998
Kolesnichenko et al.
Cl(3)-W(1B)) for the long tungsten-tungsten separation
and Cl(2C) which bridge W(1) and W(1A) are all consistent
with a WdW double bond description for the W(1)-W(1A)
interaction.
(
W(1)‚‚‚W(1B)) is an obtuse 98.5(2)°. The axial chlorine atoms
Cl(1), Cl(1A)) on the bioctahedron with the short W(1)-W(1A)
(
distance are bent away from each other (Cl(1)-W(1)-W(1A),
4.99(12) Å), and these chlorine atoms are appreciably closer
3.085(10) Å) than twice the Cl van der Waals radius, 1.70-
9
(
1
Conclusion
The most convenient, highest yield methods for preparation
of polymeric WCl4 were found to be solid-state reduction of
WCl6 with antimony and reduction of WCl6 with tin in
dichloroethane. Mercury reduction of WCl6 is also a useful
method for preparation, despite toxicity concerns, in that the
yield is high and unreacted mercury and HgCl2 can be removed
easily. Reduction with bismuth gives a lower yield of product
with bismuth contamination, and requires substantially greater
time to sublime BiCl3. The solution-phase reduction with tin
affords highly reactive (WCl4)x powder, which can be used to
make the known compounds WCl4(MeCN)2 and W2Cl4(OMe)4-
3
2
.90 Å.
The molecular structures of related molecules can provide
insight into the structure of (WCl4)x. The higher-valent halide
WCl5)2 (i.e., W2Cl8(µ-Cl)2) has a discrete, more ideal biocta-
(
hedral structure as a solid with a long, nonbonded W‚‚‚W
separation of 3.814(2) Å, a W-Cl(axial) distance of 2.254(4)
Å, a W-Cl(terminal, equatorial) distance of 2.243(3) Å, a
W-Cl(bridge) distance of 2.519(3) Å, and a (µ-Cl)-W-(µ-
Cl) angle of 81.5(1)°.33 The tungsten atoms are displaced from
each other, consistent with the lack of a W-W bond, and the
axial chlorines in each “hemisphere” of the bioctahedron are
thus bent toward each other. The W-Cl(axial) distance for
(HOMe)2. Crystalline (WCl4)x, as obtained from the reduction
of WCl6 with Hg, possesses a polymeric chain structure of
opposite edge-linked octahedra with alternating short (WdW)
and long W‚‚‚W distances, an acute W-Cl-W angle for the
chlorine atoms bridging the short WdW distance, and ap-
preciable repulsive interaction between adjacent axial chlorines
on each side of the short WdW bond.
(WCl5)2 is marginally smaller than that for (WCl4)x as would
be expected for the increase in formal valence.
Crystalline (WCl4)x is remarkably isostructural with (NbCl4)x,
as was postulated by McCarley and Brown.12 In the (NbCl4)x
structure, the edge-sharing bioctahedra have significant distor-
tions from ideal bioctahedral geometry, and there are alternating
18
short (3.029(2) Å) and long (3.794(2) Å) Nb‚‚‚Nb separations.
Acknowledgment. This work was supported by a grant from
Nycomed, Inc. The CAD-4/ MicroVAX II X-ray diffractometer
system was purchased with National Science Foundation
(CHE85-07623) and University of Iowa funds. The Siemens
D5000 automated powder diffractometer was purchased with
Carver Foundation funds.
There is a small but significant bending of the axial chlorine
atoms away from the bonded niobium atoms (possibly because
of van der Waals repulsions).
Taken together with comparative structural data for (WCl5)2
and (NbCl4)x, the (1) bending away of the axial chlorine atoms
bonded to W(1) and W(1A), (2) short contact between the axial
chlorine atoms, (3) short W(1)-W(1A) distance in the double-
Supporting Information Available: Alternate thermal ellipsoid
plots of molecular structure, tables listing detailed crystallographic data,
anisotropic displacement parameters, and bond lengths and angles (4
pages). Ordering information is given on any current masthead page.
bond range34 for d -d W(IV)-W(IV), particularly with
2
2
chloride bridges, and (4) acute angle at the chlorine atoms Cl(2)
(
31) (a) Cotton, F. A.; Walton, R. A. Multiple Bonds between Metal Atoms,
IC9801286
2nd ed., Clarendon Press: Oxford, U.K., 1993. (b) Cotton, F. A.
Polyhedron 1987, 6, 667. (c) Messerle, L. Chem. ReV. 1988, 88, 1229.
(
(
32) Bondi, A. J. Phys. Chem. 1964, 68, 441.
(34) Cotton, F. A.; Walton, R. A. Multiple Bonds between Metal Atoms,
33) Cotton, F. A.; Rice, C. E. Acta Crystallogr. 1978, 34b, 2833.
2nd ed., Clarendon Press: Oxford, U.K., 1993; p 597.