Liquid ammonia mediated metathesis: Synthesis of binary metal chalcogenides and pnictides

Article abstract of DOI:10.1021/ic010648s

Addition of stoichiometric amounts of low valent metal halides to liquid ammonia solutions of disodium chalcogenide (Na₂E; E = S, Se, Te) afforded a range of both crystalline (PbE (E = S, Se, Te), TIE (E = S, Se), Tl₅Te₃, Ag₂E (E = S, Se, Te)) and X-ray amorphous (MS (M = Ni, Cu, Zn, Cd, Hg), M₂E₃ (M = Ga, In; E = S, Se, Te), HgE (E = Se, Te), CuE (E = S, Se, Te), Cu₂S) metal chalcogenides in good yield (95%). Reactions between metal halides and sodium pnictides (Na₃Pn; Pn = As, Sb) in liquid ammonia also afforded X-ray amorphous material (M₃Pn₂, M = Zn, Cd; MPn, M = Fe, Co, Ni) in good yield (95%). Isolation of the metal chalcogenides and pnictides was achieved through washing with CS₂ and distilled water. All reactions were complete within 36 h. Products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDXA), electron probe analysis, FR-IR spectroscopy, Raman spectroscopy, microanalysis, and band gap measurements. Annealing amorphous material at 250-300 °C for 48 h induced sufficient crystallinity for analysis by X-ray powder diffraction.

Full text of DOI:10.1021/ic010648s

6940
Inorg. Chem. 2001, 40, 6940-6947
Liquid Ammonia Mediated Metathesis: Synthesis of Binary Metal Chalcogenides and
Pnictides
G. A. Shaw and I. P. Parkin*
Department of Chemistry, Christopher Ingold Laboratories, University College London,
20 Gordon Street, London, U.K., WC1H 0AJ
ReceiVed June 18, 2001
Addition of stoichiometric amounts of low valent metal halides to liquid ammonia solutions of disodium
chalcogenide (Na2E; E ) S, Se, Te) afforded a range of both crystalline (PbE (E ) S, Se, Te), TlE (E ) S, Se),
Tl5Te3, Ag2E (E ) S, Se, Te)) and X-ray amorphous (MS (M ) Ni, Cu, Zn, Cd, Hg), M2E3 (M ) Ga, In; E )
S, Se, Te), HgE (E ) Se, Te), CuE (E ) S, Se, Te), Cu2S) metal chalcogenides in good yield (95%). Reactions
between metal halides and sodium pnictides (Na3Pn; Pn ) As, Sb) in liquid ammonia also afforded X-ray amorphous
material (M3Pn2, M ) Zn, Cd; MPn, M ) Fe, Co, Ni) in good yield (95%). Isolation of the metal chalcogenides
and pnictides was achieved through washing with CS2 and distilled water. All reactions were complete within 36
h. Products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-
dispersive X-ray analysis (EDXA), electron probe analysis, FT-IR spectroscopy, Raman spectroscopy, microanalysis,
and band gap measurements. Annealing amorphous material at 250-300 °C for 48 h induced sufficient crystallinity
for analysis by X-ray powder diffraction.
Introduction
position of precursors,11 and elemental combination reactions
at elevated temperature.12 Recent work has focused on the
synthesis of nanoparticulate chalcogenides and has used confined
environments such as zeolites and micelles to restrict particle
size.13 We have shown that traditional elemental combination
reactions can be improved by utilizing liquid ammonia as
solvent.14 Some elemental metals react with chalcogenide/
ammonia solutions to form crystalline metal chalcogenides at
room temperature.15 The reactions often form single-phase
materials in common mineral modifications but were, however,
restricted to chalcophilic metals such as Zn, Cd, Hg, Ag, Pb,
and Sn. Self-propagating elemental combination reactions have
also been used to form metal sulfides in a process known as
SHS (self-propagating high-temperature synthesis).16
Binary metal chalcogenides function as catalysis, secondary
batteries, lubricants, and semiconductors.1 Band gap energies
of group 12-16 materials are important for the emission,
detection, and modulation of light in the visible and near-UV
regions;2 group 13-15 materials are suitable for red to near-IR
radiation. Applications include coatings, gratings,3 and a wide
range of optical windows.4 Group 13-16 materials fall into two
different compound typessM2E3 and ME (M ) Ga, In; E ) S,
Se, Te); both materials are direct band gap semiconductors and
of interest as photovoltaic and optoelectronic materials. Gallium
and indium sesquichalcogenides (M2E3) have a wide band gap,
offering an alternative to group 12-16 materials.4 Catalytic
activity of transition metal sulfides is well documented; for
example, MoS2 is used as a petrochemical catalyst.5 The
disulfides of tin, titanium, molybdenum, zirconium, and hafnium
all crystallize as two-dimensional lattices exhibiting weak
interlayer bonding and find commercial applications as high-
temperature lubricants,3 battery cathodes,2,3 and hydrodesulfur-
ization catalysts.6 The sulfides and selenides of zinc and
cadmium are used in reflective coatings, as well as in the
pigmentation of paints, rubber, and porcelain.3,7
SHS is a process that utilizes highly exothermic reactions to
obtain a sustainable combustion wave.17 The reaction becomes
self-propagating, thereby greatly reducing processing time and
(7) Fielder, I.; Bayard, M. Artists Pigments, A Handbook of their History
and Characteristics; Feller, R. L., Ed.; Cambridge University Press:
Cambridge, 1986; Vol. 1, p 65.
(8) Schleich, D. M.; Martin, M. J. J. Solid State Chem. 1986, 64, 359.
(9) Sriram, M. A.; Kumta, P. N. J. Mater. Chem. 1998, 8, 2453.
(10) Massacces, S.; Sanchez, S.; Vedel, J. J. Electroanal. Chem. 1996, 412,
95. Bensalem, R.; Schleich, D. M. Mater. Res. Bull. 1988, 23, 857.
(11) Nomura, R.; Konishi, K.; Futenma, S.; Matsuda, H. Appl. Organomet.
Chem. 1990, 4, 607.
Various established syntheses exist for the preparation of bulk
binary chalcogenides. These include reaction of silyl sulfides,8
sol-gel processing,9 electrodeposition from solution,10 decom-
(12) Coustal, R. J. Chim. Phys. 1931, 31, 277. Braver, G. Handbook of
PreparatiVe Inorganic Chemistry, 2nd ed.; Academic Press: New
York, 1965; Vols. 1, 2.
(13) (a) Petit, C.; Pileni, M. P. J. Phys. Chem. 1988, 92, 2282. (b) Lianos,
P.; Thomas, J. K. Chem Phys. Lett. 1986, 125, 299. (c) Wang, Y.;
Herron, N. J. Phys. Chem. 1987, 91, 257.
* To whom correspondence should be addressed.
(1) (a) Lewis, K. L.; Savage, J. A.; Marsh, K. J.; Jones, A. P. C. New
Optical Materials. Proc. SPIE-Int. Soc. Opt. Eng. 1983, 400, 21. (b)
Kilbourne, B. T. A Lanthanide Lanthology- Part 1; Molycorp Inc.:
White Plains, NY, 1993.
(2) Nicolau, Y. F.; Dupuy, M.; Brunel, M. J. Electrochem. Soc. 1990,
137, 2915.
(3) Greenwood, N. N.; Earnshaw, E. A. Chemistry of the Elements;
Pergamon Press: Oxford, 1990; pp 1403-6.
(4) O’Brien, P.; Ryoˆki, J. J. Mater. Chem. 1995, 5, 1761.
(5) Tsigdinos, G. A.; Moh, G. W. Aspects of Molybdenum and Related
Chemistry; Springer: New York, 1978; Vol. 76.
(14) (a) Henshaw, G.; Shaw, G. A.; Hector, A.; Parkin, I. P. Main Group
Metal Chem. 1996, 1, 183. (b) Parkin, I. P.; Henshaw, G.; Shaw, G.
A. J. Mater. Sci. Lett. 1996, 15, 1741. (c) Omar, B.; Parkin, I. P.;
Shaw, G. A. J. Chem. Soc., Dalton Trans. 1997, 9, 1385.
(15) (a) Parkin, I. P.; Shaw G. A.; Henshaw, G J. Chem. Soc., Dalton Trans.
1997, 231. (b) Parkin, I. P. Henshaw, G.; Shaw, G. A. J. Chem. Soc.,
Chem. Commun. 1996, 1095.
(6) Hasse, M. A.; Qiu, J.; DePuydt J. M.; Cheng, H. Appl. Phys. Lett.
1991, 59, 1272.
(16) Merzhanov, A. G. Russ. Chem. Bull. 1997, 1, 8.
(17) Crider, J. F. Ceram. Eng. Sci. Proc. 1982, 3 (9-10), 519.
10.1021/ic010648s CCC: $20.00 © 2001 American Chemical Society
Published on Web 12/06/2001

Liquid Ammonia Mediated Methathesis
Inorganic Chemistry, Vol. 40, No. 27, 2001 6941
Table 1. XRD Data for Crystalline Binary Transition Metal Chalcogenides Synthesized by Metathetical Reactions in Liquid Ammonia at
Room Temperature
products formed
from reaction
phases obtained
after annealing
washed mater
product
color
reagentsa
(identified by XRD)b
lattice params, Å (( 0.01)
a ) c ) 4.48
lit.36 lattice params, Å
a ) c ) 4.46
2AgF + Na2S
2AgF + Na2Se
2AgF + Na2Te
2TlCl + Na2S
TlCl + Na2Se
Ag2S (acanthite) + NaF
Ag2Se (naumannite) + NaF
Ag2Te (hessite) + NaF
Tl[TlS2] + NaCl
black
black
black
black
black
black
black
black
black
Ag2S (acanthite)
Ag2S (naumannite) a ) 4.33, b ) 7.06, c ) 7.76 a ) 4.33, b ) 7.06, c ) 7.76
Ag2S (acanthite)
Tl[TlS2]
Tl[TlSe2]
Tl5Te3
PbS (galena)
PbSe (clausthalite)
PbTe (altaite)
a ) 8.07, b ) 4.47, c ) 8.94 a ) 8.09, b ) 4.47, c ) 8.96
a ) 7.79, c ) 6.80
a ) 8.02, c ) 7.00
a ) 8.93, c ) 12.62
a ) c ) 5.93
a ) c ) 6.12
a ) c ) 6.46
a ) 7.79, c ) 6.80
a ) 8.02, c ) 7.00
a ) 8.92 (5), c ) 12.61 (5)
a ) c ) 5.93
a ) c ) 6.12
a ) c ) 6.46
Tl[TlSe2] + NaCl
2TlCl + Na2Te Tl5Te3 + NaCl
PbCl + Na2S
PbCl + Na2Se
PbCl + Na2Te
PbS (galena) + NaCl
PbSe (clausthalite) + NaCl
PbTe (altaite) + NaCl
a Reagents (expressed with molar ratios) stirred in liquid ammonia at room temperature for 36 h. b Phases characterized by X-ray powder diffraction
prior to workup of reaction product.
Table 2. XRD Data for Amorphous Binary Transition Metal Chalcogenides Synthesized by Metathetical Reactions in Liquid Ammonia at
Room Temperature
prewash
mater
product
color
phases obtained after
lattice params, Å
reagentsa
annealing washed materb
(( 0.01)
lit. lattice params,36
Å
NiCl2 + Na2S
ZnCl2 + Na2S
CdCl2 + Na2S
2CuBr + Na2S
CuCl2 + Na2S
NaCl
NaCl
NaCl
NaBr
NaCl
black
NiS (millerite)
ZnS (wurzite)
a ) c ) 3.42
a ) c ) 3.42
yellow
yellow
black
a ) 3.82, c ) 6.25
a ) 4.14, c ) 6.72
a ) 3.96, c ) 6.78
a ) 3.76, c ) 16.21
Mc
a ) 3.82, c ) 6.26
a ) 4.14, c ) 6.72
a ) 3.96, c ) 6.78
CdS (greenockite)
Cu2S (chalcocite) + [Cu1.8S, Cu1.9S]
CuS (covelite)
Cu1.8S (diginite)
CuSe (klockmannite) + [CuSe2 (krutaite)]
Cu2.72Te2 + Cu4Te3
â-HgS (metacinnebar)
HgSe (tiemannite)
HgTe (coloradoite)
Ga2S3
Ga2Se3
Ga2Te3
In2S3
In2Se3
black
a ) 3.76, c ) 16.19
CuCl2 + Na2Se
CuCl2 + Na2Te
HgCl2 + Na2S
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
black
black
black
black
black
black
black
black
black
black
black
a ) 3.93, c ) 17.20
a ) 3.93, c ) 17.22
Mc
a ) c ) 5.85
a ) c ) 5.85
HgCl2 + Na2Se
HgCl2 + Na2Te
2GaCl3 + 3Na2S
2GaCl3 + 3Na2Se
2GaCl3 + 3Na2Te
2InCl3 + 3Na2S
2InCl3 + 3Na2Se
2InCl3 + 3Na2Te
a ) c ) 6.08
a ) c ) 6.07
a ) c ) 6.46
a ) c ) 6.45
a ) 3.68, c ) 6.03
a ) 6.66, c ) 11.65
a ) c ) 5.90
a ) 3.68, c ) 6.03
a ) 6.66, c ) 11.65
a ) c ) 5.90
a ) c )10.78
a ) 7.12, c ) 19.37
a ) c ) 18.51
a ) c ) 10.78
a ) 7.12, c ) 19.37
a ) c ) 18.49
In2Te3
a Reagents (expressed with molar ratios) stirred in liquid ammonia at room temperature for 36 h. b Phases characterized by X-ray powder diffraction
after annealing at 250-300 °C for 48 h. All minor phases (< ca. 10%) represented by square brackets. c M ) matched stick pattern to database
standard.
applied energy when compared to conventional sintering.18
However, high reaction rates also result in a lack of control of
grain size and density.19 Calculated adiabatic reaction temper-
atures for such reactions often exceed 1525 °C,20 restricting them
to the synthesis of refractory transition metal dichalcogenides:
MoS2, NbS2, WSe2, and TaSe2.21
A variant of SHS has been developed by R. Kaner’s group22
and ourseleves23 and is known as solid-state metathesis, SSM.22
This new reaction type has been primarily undertaken in ampules
or sealed containers. It involves the reaction of metal halides
with alkali metal chalcogenides and pnictides, eq 1. The driving
force for the reaction is the co-formation of a salt along with
the desired metal chalcogenide.
Maximum reaction temperature can be controlled to some
extent in SSM by altering the co-formed salt. Solid state
metathesis reaction of anhydrous metal chlorides with sodium
sulfide yielded a range of transition metal, lanthanide, actinide,
and main-group metal chalcogenides.23 Reactions were initiated
thermally inside a heated sealed ampule,24 by a heated filament,
known as point source initiation,25 by mechanical grinding of
low melting point solids,26 or by simple mixing of highly volatile
components at room temperature.27 SSM reactions often initiate
at relatively low temperatures and are frequently self-propagat-
ing. Total heat of formation of the product mixture is frequently
in excess of ca. 250 kcal/mol-1 generating temperatures
exceeding 1000 °C. The reactions once initiated are extremely
rapid (1-5 s)23 and often associated with the emission of clouds
of vaporized co-formed salt. Unlike many precursor reactions,
these byproduct salts are highly ionic in character and so are
easily removed from the markedly less ionic metal sulfide (to
<0.01%)24 simply by trituration with a suitable solvent such as
water, THF, or methanol. It is the formation and subsequent
melting of this coproduced salt that ultimately gives control of
MCl4 + 2Na2E f ME2 + 4NaCl
(1)
(18) Munir, Z. A.; Anselmi-Tamburini, U. Mater. Sci. Rep. 1989, 3 (7-
8), 277.
(19) Rice, R. W.; McDonough, W. J. J. Am. Ceram. Soc. 1985, 68 (5),
C122.
(20) Novikov, N. P.; Borovinskaya, I. P.; Merzhanov, A. G. Combustion
processes in chemical technology and metallurgy; Russ. Acad. Sci.:
Chernogolovka, 1975; p 174.
(21) (a) Sheppard, L. M. AdV. Mater. Process. 1986, 2, 25-32. (b) Moore,
J. J.; Feng, H. J. Prog. Mater. Sci. 1995, 39, 243.
(22) Bonneau, P. R.; Shibao, R. K.; Kaner, R. B. Inorg. Chem. 1990, 29,
2511.
(24) (a) Fitzmaurice, J. C.; Hector, A. L.; Parkin, I. P. J. Chem. Soc., Dalton
Trans. 1993, 2435. (b) Fitzmaurice, J. C.; Hector, A. L.; Parkin, I. P.
Polyhedron 1993, 12, 1295.
(25) Treece, R. E.; Conklin, J. A.; Kaner, R. B. Inorg. Chem. 1994, 33,
5701.
(26) Treece, R. E.; Macala, G. S.; Kaner, R. B. Chem. Mater. 1992, 4, 9.
(27) Hector, A. L.; Parkin, I. P. J. Chem. Soc., Chem. Commun. 1993, 1096.
(23) Parkin, I. P. Chem. Soc. ReV. 1996, 199.

6942 Inorganic Chemistry, Vol. 40, No. 27, 2001
Shaw and Parkin
the reaction temperature since it is the molten salt that sustains
the propagation wave.
Recent developments in SSM have included the synthesis of
binary main-group pnictide materials,23,28 as well as conducting
the process in mediating solvents. These have included both
toluene29 and diglyme solvents.28 The reaction proceeds either
in solution or at a solution-solid interface. To date gallium,
cobalt, and nickel pnictides28 and titanium chalcogenides29 have
been synthesized by solution-phase metathesis.
We report here the synthesis of a wide range of binary
chalcogenide and pnictide materials by metathetical reactions
in liquid ammonia. This process enables isolation of crystalline
nanoscaled materials. The new route also offers an advantage
over conventional SSM reactions in that the reactions occur
essentially at room temperature, thus allowing synthesis of
products with minimal thermal defects.
Results
Figure 1. Scanning electron micrograph of triturated Ag2S synthesized
from the reaction of Na2S and AgF in liquid ammonia, 25 °C, 36 h.
Binary Metal Chalcogenides: Synthesis and Character-
ization. Addition of stoichiometric amounts of metal halides
to liquid ammonia solutions of disodium chalcogenide at room
temperature afforded a range of both crystalline (Table 1, eqs
2-5) and X-ray amorphous (Table 2, eqs 6-11) metal chal-
cogenides in good yield, ca. 95%. Reactions were completed
within 36 h.
material with broad bands centered at 600-150 cm-1; no N-H
stretches were observed. Annealing of the X-ray amorphous
chalcogenides at 250-300 °C for 2-48 h induced sufficient
crystallinity for analysis by X-ray powder diffraction. Energy-
dispersive analysis by X-rays (EDAX) of the unwashed solids
showed regions of sodium halide (NaCl, NaBr) as well as the
metal chalcogenide. Trituration with water and CS2 removed
the co-formed salt, leaving only metal chalcogenide. Composi-
tion analysis both by electron-probe line analysis and by EDAX
spot analysis were in agreement with the products identified
by X-ray diffraction (within 1-2%); see Table 4. SEM of the
as-formed powders showed submicron roughly spherical par-
ticles of size ca. 200 nm (Figure 1). Annealing of the samples
encouraged particle agglomeration.
PbCl2(s) + Na2E f PbE(s) + 2NaCl(s) (E ) S, Se, Te) (2)
2AgF(s) + Na2E f Ag2E(s) + 2NaF(s) (E ) S, Se, Te) (3)
4TlCl(s) + 2Na2E(am) f Tl[TlE2](s) + 2Tl(s) + 2NaCl(s)
(E ) S, Se) (4)
6TlCl(s) + 3Na2Te(s/am) f Tl5Te3(s) + 2NaCl(s) + Tl(s) (5)
Raman patterns were obtained from the as-formed solids and
the triturated materials. These showed bands that were diagnostic
of the required material. This is illustrated in Figure 2 for ZnS.
The band gap measurements of the metal chalcogenides were
also determined by optical measurements; these showed evi-
dence for blue shifts corresponding with nanoparticle formation.
The laser induced fluorescence spectra of CdS showed a marked
shift to higher frequency compared to bulk CdS (480 nm); see
Figure 3.
MCl2(am) + Na2S(am) f MS(s) + 2NaCl(s)
(M ) Ni, Zn, Cd, Hg) (6)
HgCl2(am) + Na2E(am) f HgE(s) + 2NaCl(s) (E ) Se, Te) (7)
2CuBr(am) + Na2S(am) f Cu2S(s) + 2NaBr(s) + Cu2-xS(s)
(x ) 0.1, 0.2) (8)
Reactions involving lead and silver salts produced crystalline
metal chalcogenides at room temperature in familiar mineral
forms without recourse to annealing (Table 1). Figure 4 shows
the XRD pattern obtained for the triturated, as-formed PbSe
and PbTe products. Reaction of a 2:1 ratio of TlCl and Na2E in
liquid ammonia afforded crystalline thallium chalcogenides,
TlI[TlIIIE2] (E ) S, Se), and thallous telluride, Tl2-xE (x ) 1;
E ) Te).
Synthesis of cupric and mercuric chalcogenides by metathesis
reactions in ammonia, as well as the sulfides of nickel, zinc,
cadmium, and copper(I), afforded X-ray powder diffraction
patterns for the coproduced salt (NaCl or NaBr) only, with no
evidence of crystalline metal chalcogenide, (6)-(11). Washing
the X-ray amorphous chalcogenide materials with CS2 and water
followed by annealing at 250 °C for 48 h produced crystalline
material (Table 2). The X-ray diffraction patterns of ZnS (Figure
5), CdS (Figure 6), HgS, and HgSe showed significantly
broadened peaks indicative of the formation of nanometer
particles. The Scherrer equation31 gave particle sizes of 10 (ZnS),
39 (CdS), 24 (HgS), and 53 nm (HgSe).
CuCl2(am) + Na2S(am) f CuS(s) + 2NaCl(s) + Cu2-xS(s)
(x ) 0.2) (9)
CuCl2(am) + Na2Se(am) f CuSe(s) + CuSe2(s) + 2NaCl(s)
(10)
CuCl2(am) + Na2Te(am) f CuTe1-x(s)* + xTe(s) + 2NaCl(s)
(11)
[*In eq 11, two phases of nonstoichiometric (tellurium-deficient)
copper(II) telluride were characterized by XRD: Cu2.72Te2 and
Cu4Te3.]
In all cases (2)-(11), X-ray powder diffraction analysis of
the preannealed material showed the presence of crystalline
alkali metal halide. Washing of the product with CS2 and water
resulted in removal of the coproduced salt and isolation of
single-phase metal chalcogenides. IR studies of the washed
products showed absorptions characteristic of the desired
(28) (a) Kher, S. S.; Wells, R. L. Chem. Mater. 1994, 6, 2056. (b) Carmalt,
C. J.; Morrison, D. E.; Parkin, I. P. J. Mater. Chem. 1998, 8, 2209.
(29) Chianelli, R. R.; Dines, M. B. Inorg. Chem. 1978, 17, 2758.
(30) Bley, R. A.; Kauzlarich, S. M. J. Am. Chem. Soc. 1996, 118, 12461.

Liquid Ammonia Mediated Methathesis
Inorganic Chemistry, Vol. 40, No. 27, 2001 6943
Table 3. XRD Data for Binary Transition Metal Pnictides Synthesized by Liquid Ammonia Mediated Metathesis Reactions at Room
Temperature
XRD of
prewashed
mater
product
color
phases obtained after
reagentsa
annealing washed materb
lattice params, Å (( 0.01)
lit.36 lattice params, Å
3FeCl2 + 2Na3As
3FeCl2 + 2Na3Sb
3CoCl2 + 2Na3As
3CoCl2 + 2Na3Sb
3NiCl2 + 2Na3As
3NiCl2 + 2Na3Sb
3ZnCl2 + 2Na3As
3ZnCl2 + 2Na3Sb
3CdCl2 + 2Na3As
CdCl2 + 2Na3Sb
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
black
black
black
black
black
black
black
black
black
black
FeAs
FeSb
a ) 5.39, b ) 5.93, c ) 3.27
M
a ) 5.39, b ) 5.93, c ) 3.27
CoAs (orthorhombic)
CoSb (hexagonal)
NiAs (hexagonal) + [Ni]
NiSb (hexagonal) + [Ni]
Zn3As2 + [Zn, As]
Zn3Sb2 + [Zn, Sb]
Cd3As2 + [Cd, As]
Cd3Sb2 + [Cd, Sb]
a ) 3.46, b ) 5.87, c ) 5.29
a ) 3.88, c ) 5.19
a ) 3.62, c ) 5.01
a ) 3.93, c ) 5.13
a ) c ) 5.81
a ) 3.46, b ) 5.87, c ) 5.29
a ) 3.88, c ) 5.19
a ) 3.62, c ) 5.01
a ) 3.93, c ) 5.13
a ) c ) 5.81
M
a ) 8.93, c ) 12.68
M
a ) 8.93, c ) 12.68
a Reagents (expressed with molar ratios) stirred in liquid ammonia at room temperature for 36 h. b Phases characterized by X-ray powder diffraction
after annealing at 250-300 °C for 48 h. All minor phases (< ca. 10 %) represented by square brackets.
Table 4. SEM/EDXA Data of Binary Metal Chalcogenides Synthesized by Metathetical Reaction in Liquid Ammonia at Room Temperature
ratio of elementsc (exptl error ( 2-3 atom %)
reagentsa
particle morphologyb
elem. ratio
exptl values
theor values
NiCl2 + Na2S
ZnCl2 + Na2S
CdCl2 + Na2S
2CuBr + Na2S
1-5 µm aggregates; irregular particles < 50 nm
1-5 µm aggregates; spherical particles < 50 nm
1-5 µm aggregates; spherical particles < 50 nm
1-8 µm aggregates; irregular particles < 100 nm
Ni:S
Zn:S
50:50
50:50
50:50
67:33
64:36
50:50
67:33
50:50
42:58
67:33
67:33
67:33
50:50
50:50
50:50
40:60
40:60
40:60
40:60
40:60
40:60
50:50
50:50
63:37
50:50
50:50
50:50
60:40
60:40
50:50 (NiS)
50:50 (ZnS)
50:50 (CdS)
Cd:S
Cu:S
Cu:S
Cu:S
Cu:S
Cu:Se
Cu:Te
Ag:S
Ag:Se
Ag:Te
Hg:S
Hg:Se
Hg:Te
Ga:S
Ga:Se
Ga:Te
In:S
In:Se
In:Te
Tl:S
Tl:Se
Tl:Te
Pb:S
Pb:Se
Pb:Te
M:Pne
M:Pne
67:33 (Cu2S)
Cu2-xS (2 phases)
50:50 (CuS)
67:33 (Cu2S)
50:50 (CuSe)
Cu4Te3 (2 phases)
67:33 (Ag2S)
67:33 (Ag2Se)
67:33 (Ag2Te)
50:50 (HgS)
50:50 (HgSe)
50:50 (HgTe)
40:60 (Ga2S3)
40:60 (Ga2Se3)
40:60 (Ga2S3)
40:60 (In2S3)
40:60 (In2Se3)
40:60 (In2S3)
50:50 (TlS)
CuCl2 + Na2S
1-8 µm aggregates; spherical particles < 100 nm
CuCl2 + Na2Se
CuCl2 + Na2Te
2AgF + Na2S
1-8 µm aggregates; irregular particles < 100 nm
1-8 µm aggregates; spherical particles < 100 nm
1-5 µm aggregates; spherical particles < 50 nm
1-5 µm aggregates; spherical particles < 50 nm
1-5 µm aggregates; spherical particles < 50 nm
1-5 µm aggregates; spherical particles < 50 nm
1-5 µm aggregates; spherical particles < 50 nm
1-5 µm aggregates; spherical particles < 50 nm
1-5 µm aggregates; spherical particles < 50 nm
1-5 µm aggregates; spherical particles < 50 nm
1-5 µm aggregates; spherical particles < 50 nm
1-5 µm aggregates; spherical particles < 50 nm
1-5 µm aggregates; spherical particles < 50 nm
1-5 µm aggregates; spherical particles < 50 nm
1-8 µm aggregates; irregular particles < 200 nm
1-8 µm aggregates; irregular particles < 200 nm
1-8 µm aggregates; irregular particles < 200 nm
1-5 µm aggregates; spherical particles < 50 nm
1-5 µm aggregates; spherical particles < 50 nm
1-5 µm aggregates; spherical particles < 50 nm
1-5 µm aggregates; irregular particles 50-100 nm
1-8 µm aggregates; irregular particles 50-100 nm
2AgF + Na2Se
2AgF + Na2Te
HgCl2 + Na2S
HgCl2 + Na2Se
HgCl2 + Na2Te
2GaCl3 + 3Na2S
2GaCl3 + 3Na2Se
2GaCl3 + 3Na2Te
2InCl3 + 3Na2S
2InCl3 + 3Na2Se
2InCl3 + 3Na2Te
2TlCl + Na2S
2TlCl + Na2Se
2TlCl + Na2Te
PbCl + Na2S
PbCl + Na2Se
PbCl + Na2Te
3MCl2 + 3Na3Pnd
3MCl2 + 3Na3Pnf
50:50 (TlSe)
63:37 (Tl5Te3)
50:50 (PbS)
50:50 (PbSe)
50:50 (PbTe)
40:60 (M3Pn2)
40:60 (M3Pn2)
a Molar ratios of reagents given for the room-temperature, liquid ammonia metathesis reaction of transition metal halides with sodium chalcogenides.
Subsequent analyses were obtained from samples washed with distilled water, and refer to both preannealed and annealed material (unless stated).
b Assessed by SEM at maximum magnification. c Elemental composition of phase assessed by EDXA (spot size 1 µm). Approximately surface
abundance of multiple phases (assessed qualitatively using backscattered electrons) is expressed either as a percentage or as major/minor phases.
d M ) Fe, Co, Ni; Pn ) As, Sb. e Free elements (M, Pn) detected as minor phase. f M ) Zn, Cd; Pn ) As, Sb.
Equation 12 describes the synthesis of X-ray amorphous
group 13 sesquichalcogenides. As before, annealing of the
isolated product at 250-300 °C for 2-48 h induced sufficient
crystallinity for X-ray characterization of the powders (Table
2).
a metal oxide) with retention of the metal to chalcogen
composition (2:3):
M2E3 (s) + 4.5O2 (g) f M2E3O9 (s) (M ) Ga, In; E ) Se, Te)
(13)
Prior to annealing the product from the metathesis of tin(II)
or tin(IV) halides and sodium chalcogenides showed only
crystalline ammonium halide by X-ray powder diffraction. This
suggests that tin halide reactions are indicative of the lighter
group 14 halides (Ge, Si) in preferentially undergoing am-
monolysis upon addition to liquid ammonia rather than a
metathetical reaction. It is well documented that silicon tetra-
halides undergo sequential ammonolysis in liquid ammonia,
affording Si(NH)(NH2)2 up to 100 °C in conjunction with four
2MCl3(s) + 3Na2E f M2E3(s) + 6NaCl(s)
(M ) Ga, In; E ) S, Se, Te) (12)
Interestingly, annealing the selenide/telluride material in the
presence of oxygen afforded a metal chalcogenate (rather than
(31) (a) Bawendi, B. M.; Kortan, A. R.; Steigerwald, M. L.; Brus, L. E. J.
Chem. Phys. 1989, 91, 7282. (b) West, A. R. Solid State Chemistry
and its Applications; J. Wiley and Sons: Chichester, 1992; p 174.

6944 Inorganic Chemistry, Vol. 40, No. 27, 2001
Shaw and Parkin
Figure 2. Raman pattern for ZnS made from reaction of ZnCl2 and Na2S in liquid ammonia, 25 °C, 36 h.
analysis prior to workup showed the presence of only alkali
metal halide (NaCl), suggesting that a metathetical reaction had
taken place. After repeated washings with distilled water, a black
material was isolated and shown to be X-ray amorphous. EDXA
of the isolated black material showed the presence of two
phases: metal pnictide and a minority metal phase. SEM
analysis using backscattered electrons enabled the mixed phases
to be quantified; typically micron-sized particles of each phase
were observed. These phases showed little change in either
number or distribution after annealing the samples at 250-300
°C for 48 h. However, XRD analysis of the annealed samples
showed the presence of a single binary pnictide phase which
was fully characterized as MPn (M ) Ni, Co, Ni; Pn ) As,
Sb); see Table 3. In most of the XRD patterns the free metal
was not seen; however, its presence in the annealed powder
was confirmed by EDAX. Presumably the low temperature
annealing conditions employed were suitable to encourage
crystallization of the metal chalcogenide but not the co-formed
metal. In the NiAs and NiSb samples XRD analysis did show
minor peaks associated with nickel metal. A combination of
the XRD and EDAX results indicates that the reaction proceeds
in accordance with eq 16.
Figure 3. Laser induced fluoresence spectra of CdS synthesized from
reaction of CdCl2 and Na2S in liquid ammonia, 25 °C, 36 h.
molar equivalents of ammonium halide (eqs 14 and 15).32
3MCl2(s) + 2Na3Pn(s) f 2MPn(s) + 6NaCl(s) + M(s)
(M ) Co, Fe, Ni; Pn ) As, Sb) (16)
SiCl4 + 8NH3 f Si(NH2)4 + 4NH4Cl
(14)
Si(NH2)4 f SiNH(NH2)2 + NH3 0 °C e T e 100 °C (15)
Group 12 Pnictides (Zn3Pn2 and Cd3Pn2): Synthesis and
Characterization. XRD analysis of the products from reaction
of MCl2 and Na3Pn also showed a mixture of coproduced salt
(NaCl) and black, X-ray amorphous material. SEM/EDAX of
the isolated black material showed variable elemental composi-
tion resulting from the presence of three intimately mixed
phases, whose relative distributions seemed unaffected by
annealing at 250-300 °C for 48 h. XRD analysis of the annealed
material showed the presence of a single binary metal pnictide
Pnictides of Iron, Cobalt, and Nickel: Synthesis and
Characterization. Stoichiometric quantities of MCl2 (M ) Fe,
Co, Ni) and Na3Pn (Pn ) As, Sb) were stirred in liquid ammonia
for 36 h at room temperature. Each product was observed to be
inhomogeneous, containing both white and black material. XRD
(32) Billy, M. Ann. Chim. (Paris) 1959, 4, 795. Billy, M. Compt. Rend.
1958, 246, 433.

Liquid Ammonia Mediated Methathesis
Inorganic Chemistry, Vol. 40, No. 27, 2001 6945
Figure 4. X-ray powder diffraction patterns of (i, top trace) product from the reaction of PbCl2 and Na2Se in liquid ammonia, 25 °C, 36 h, where
stick pattern is for PbSe (clausthalite); (ii, bottom trace) product from the reaction of PbCl2 and Na2Te in liquid ammonia, 25 °C, 36 h, where stick
pattern is for PbTe (altaite). * indicates co-formed NaCl.
Figure 5. X-ray powder diffraction pattern of ZnS synthesized from reaction of ZnCl2 and Na2S in liquid ammonia, 25 °C, 36 h. Product was
triturated with water and CS2 and annealed at 250 °C for 2 h. Crystallite size of 100 Å from line broadening studies. Stick pattern for wurtzite-2H
ZnS.
(of stoichiometry M3Pn2), in addition to both elemental metal
and pnictogen (as described by eq 17).
only â-HgS after annealing (2 h, 250 °C), a less thermodynami-
cally stable phase than the more common R-HgS,8 suggests
kinetic phases can be obtained in some metathetical reactions.
The chalcogenides that could be synthesized were restricted to
group 10-14 elements. Attempts at using group 6 salts such as
MoCl5 to form MoS2 in ammonia resulted in destruction of the
containment vessel. The reaction was repeated on three occa-
sions, and in each attempt the reaction was too exothermic for
the thick-walled containment vessel, resulting in vessel cracking
and loss of ammonia. It is possible that the particle sizes of the
metal halides play a dominant role in determining the course
of the reaction, and care should be taken in repeating some of
these reactions with very finely divided reagents.
3MCl2(s) + 2Na3Pn(s) f (1 - x)M3Pn2(s) + 2NaCl(s)
+
(3 - x)M(s) + (2 - x)Pn(s) (M ) Zn, Cd; Pn ) As, Sb) (17)
Discussion
Reaction Scope. A wide range of binary metal chalcogenides
and pnictides can be synthesized from the reaction, at room
temperature, of metal halides and Na2E/Na3Pn in liquid am-
monia. In most cases the products were the most thermody-
namically stable forms, often in common mineral modifications.
However, in the case of mercury sulfide (eq 6) the presence of

6946 Inorganic Chemistry, Vol. 40, No. 27, 2001
Shaw and Parkin
in sufficient heat being generated to either vaporize or liquefy
most of the reagents and products.33 Consequently, solid state
diffusion is no longer rate limiting and the rate of reaction
greatly exceeds the rate of heat dissipation. The high reaction
temperature also expels volatile impurities.23 Reactions observed
in liquid ammonia metathesis proceed at room temperature
without the need of an external heat source. It is possible that
the liquid ammonia initiates the reactions by creating a change
in state of the precursors, by dissolution of the disodium
chalcodenide, or by formation of metallo-ammonia adducts.
The reaction is likely to proceed both in the solid state, through
surface-limited reactions, and in solution via solvent-mediated
reactions. The solvent may serve to facilitate the reactions in
two ways. Surface area of the reaction interface is greatly
increased by the formation of solvated species. Furthermore,
efficient stirring of insoluble reagents results in exposure of new
reactive surfaces.
Figure 6. X-ray powder diffraction pattern of CdS synthesized from
reaction of CdCl2 and Na2S in liquid ammonia, 25 °C, 36 h. Product
was triturated with water and CS2 and annealed at 250 °C for 2 h.
Crystallite size of 240 Å from line broadening studies. Stick pattern
for greenockite CdS.
Product Morphology. Conducting the metathesis reactions
in liquid ammonia rather than in the solid state produces greatly
different product morphology. Completion of these highly
exothermic reactions at room temperature shows the liquid
ammonia to act as a heat sink. The high heat capacity of liquid
ammonia allows efficient dissipation and absorption of reaction
enthalpy, while the unreactive nature of the solvent toward the
majority of precursors allows effective dispersion of insoluble
particles. Consequently, product annealing is reduced and so
particle size becomes restricted. This leads to the synthesis of
nanocrystalline group 12-16 semiconductors (ZnS, CdS).
Liquid ammonia metathesis affords spherical nanocrystallites
agglomerated into aggregates of <1 µm, whereas SSM char-
acteristically results in a fused massstypically with sharp angles
and facessin excess of 10 µm in diameter.23 In conventional
solid state metathesis the product is invariably crystalline,
whereas in the ammonia-mediated reactions crystallinity of the
product is dependent on the specific reaction. Those that involve
the most chalcophilic elements, silver, thallium, and lead, formed
crystalline chalcogenides directly from the metathesis in am-
monia. All of the other elements produced X-ray amorphous
products that could be readily crystallized in a single step by
facile heating (250-300 °C, 2-48 h). This route opens up the
possibility for larger crystal growth with longer annealing times
or slightly higher temperatures. Further such routes are likely
to offer products with very low thermodynamic defect densities
(although kinetic defects are still likely). The synthetic approach
reported here not only requires less energy and processing time
than conventional synthesis but can offer an effective, reproduc-
ible conversion from X-ray amorphous to crystalline materials.
We have not directly studied the effect of particle size of the
reactants on the relative rates of the reactions. However, we
did note that freshly formed finely divided reagents (Na2S and
Na3As) did react quicker than those that had been left to
agglomerate. It would be anticipated that higher surface area
reagents would promote faster reactions. The minimum anneal-
ing temperatures required to induce crystallinity in the X-ray
amorphous powders was not specifically determined. It was
noted that 250 °C was sufficient in all of the systems reported
here. It is possible that crystallinity could be induced at lower
temperatures.
We have tried to extend the scope of the ammonia-mediated
SSM reaction to metal phosphides. A wide variety of transition
metal halides were reacted with sodium and lithium phosphides
in liquid ammonia at room temperature. In no case was there
evidence for a direct metathesis reaction. For example, no co-
formed salt was found and unreacted metal halide was obtained
from the reaction. We can see no thermodynamic reason for
these reactions to fail as the comparable SSM reaction is known
to form phosphide products. Further investigations in this system
are underway.
Recent developments in metathesis reactions have resulted
in a variety of mediating solvents, such as toluene, glyme ethers,
benzene, and THF, being studied at reflux.35 To date, liquid
ammonia offers the only room temperature route to metathesis
reactions. It is restricted in some respects through the formation
of kinetically stable ammonia adducts of some of the metal
halide precursors. For example, dissolution of both nickel and
zinc bromide afforded Ni(NH3)6Br2 and Zn(NH3)2Br2, which
persisted as unreacted reagents, even after annealing the reaction
mixture. However, the corresponding insoluble nickel and zinc
chlorides did react with sodium sulfide to form NiS and ZnS,
respectively. Also, the tin halide precursors were shown to be
unsuitable due to preferential ammonolysis reactions.
Reaction Mechanism. Solid state metathesis reactions have
been speculated to proceed either via simple exchange of the
ions or via elemental intermediates.33 The presence of unreacted
elements in the metal pnictide products, eqs 16 and 17, support
an elemental recombination pathway with departure from a salt
balanced equation and subsequent inhomogeneous products. In
the metal chalcogenide reactions unreacted elements were not
observed in the products.
Comparison with Solid State Metathesis Reactions. The
metal chalcogenide materials reported here may be considered
as products of solvent mediated metathetical reactions. Although
the reactions were observed to be largely solid state in nature
and their products comply with metathetical predictions, there
are marked differences from purely solid state metathesis
reactions. With SSM reactions, initiation of a region of the
reaction mixture (typically by a localized heat source) results
Conclusions
(33) Bonneau, P. R.; Jarvis, R. F.; Kaner, R. B. Inorg. Chem. 1992, 31,
2127.
Solvent mediated metathesis reactions of metal halides and
sodium chalcogenides and pnictides offer a simple route to a
range of binary metal chalcogenides and pnictides. The reactions
proceed at room temperature in liquid ammonia and can afford
(34) Munir, Z. A.; Anselmi-Tamburini, U. Mater. Sci. Rep. 1989, 3, 277.
(35) Zavitsanos, P. D.; Morris, J. R. Ceram. Eng. Sci. Proc. 1983, 4, 624.
(36) Optional literature lattice parameters: JCPDS Files, PDF2-Database;
International Center for Diffraction Data: Swarthmore, PA.

Liquid Ammonia Mediated Methathesis
Inorganic Chemistry, Vol. 40, No. 27, 2001 6947
chalcogenide was freshly prepared from direct combination of the
elements in liquid ammonia. Condensation of the ammonia over either
sodium sulfide or sodium selenide resulted in complete dissolution
(partial dissolution of sodium telluride).
both crystalline and amorphous products together with co-
formed salt. The salt is readily removed by trituration, and the
amorphous products are crystallized by annealing at 250-300
°C. Solvent mediation produces nanometer-sized crystallites that
are agglomerated into micron-sized particles; these particles are
somewhat smaller than those formed by conventional solid state
metathesis.
Preparation of Zinc Sulfide from the Reaction of Sodium Sulfide
with Zinc Chloride. Ammonia (15 mL) was condensed over disodium
sulfide (100 mg, 1.28 mmol) in a Youngs-type pressure tube at ca.
-78 °C. Zinc chloride (175 mg, 1.28 mmol) was added. The tube was
sealed and allowed to warm to room temperature with continuous
magnetic stirring. Although liquid ammonia was observed to change
color upon addition of the reagents, the zinc halide was not observed
to dissolve in the ammonia. After 12-18 h the solution was cooled to
-77 °C and the ammonia was evaporated under a nitrogen flow. Part
of the product was triturated with 3 × 20 cm3 of distilled water, typically
yielding a black material, before being dried under vacuum. The isolated
product was then annealed for 2 h at 250 °C. Product analysis (before
and after annealing) involved XRD, SEM/EDXA (Table 4), and Raman,
IR, and UV/vis spectroscopies (Tables 1-3). XRD analysis was also
carried out on the prewashed product.
Experimental Section
All reagents (99.9% purity) were purchased from Aldrich Chemical
Co. and used without further purification. Ammonia was purchased
from BOC and used without drying. All manipulations were carried
out in a dinitrogen-filled glovebox. Reactions were carried out using
Schlenk techniques in thick-walled (3-4 mm), Teflon-in-glass, sealed
Youngs-type tubes that were surrounded by safety netting. X-ray powder
diffraction patterns were determined on a Siemens D5000 transmission
powder diffractometer using germanium monochromated Cu KR1
radiation (λ ) 1.5405 Å). They were indexed using either TREOR or
METRIC-LS programs, with lattice parameters typically matched to
within 0.02 Å of literature values. The SEM/EDXA measurements were
determined on a JEOL JSM820 microscope, equipped with a Kevex
Quantum Delta 4 detector and a Hitatchi SEM S-570 camera. The
electron beam was focused (1 µm spot at surface) with an excitation
energy of 20 keV. Electron-probe analyses were conducted on a JEOL
EMA, using polished samples, and compared to metal and chalcogen
standards. Infrared spectra were recorded on a Nicolet 205 spectrometer
using KBr pressed disks. Raman spectra were recorded on a Dilor XY
spectrometer. The 514.53 nm line of an argon laser (50 mW) was the
excitation source; the slit width was 300 µm. Thermolysis studies were
performed in a Lenton Thermal Designs tube furnace.
Caution! Liquid ammonia generates a pressure of about 7 atm at
room temperature. Care should be exercised in the use of liquid
ammonia in thick-walled glass vessels. All reactions should be
conducted behind a safety screen with blast-proof netting around the
reaction vessel. Reactions involving MoCl5 and sodium chalcogenide
and pnictides resulted in destruction of the containment vessel. Great
care should be exercised in using very finely divided reagents in these
syntheses.
Acknowledgment. The EPSRC is thanked for support of
the Raman machine through Grant GR/M82592. D. Morrisen
and C. Courtail are thanked for useful discussions.
All reaction and product workup procedures were carried out in the
manner described below for the zinc sulfide synthesis. Alkali metal
IC010648S