Structural chemistry of (PPh4)2M(WS4) 2 materials

Article abstract of DOI:10.1039/b716407f

In this paper we discuss the structural chemistry of (PPh₄) ₂M(WS₄)₂ (M = Co, Ni, Zn) materials. For M = Ni we and others have been unable to grow single crystals and we report the structure determination from powder diffraction. The material is triclinic (PI, a = 9.3730(2), b = 12.4951(3), c = 12.5189(3) Ae, α = 65.814(1), β = 83.751(1), γ = 69.571(1)° at T = 293 K). It contains square-planar coordination around Ni. For M = Zn we have isolated two polymorphs. We describe new analysis of the complex superstructure and diffuse scattering observed in the tetragonal polymorph (I4, a = 18.723(4), c = 13.563(4) Ae at T = 120 K) and the bulk preparation of a monoclinic (P2 ₁/c, a = 18.6397(4), b = 15.3693(5), c = 18.9822(5) Ae, β = 109.239(2)° at T = 293 K) polymorph isostructural with the M = Co material. The Royal Society of Chemistry.

Full text of DOI:10.1039/b716407f

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Structural chemistry of (PPh ) M(WS ) materials†‡§
4
2
4 2
Clare J. Crossland, Ivana Radosavljevi c´ Evans and John S. O. Evans*
Received 24th October 2007, Accepted 22nd January 2008
First published as an Advance Article on the web 15th February 2008
DOI: 10.1039/b716407f
In this paper we discuss the structural chemistry of (PPh
4
)
2
M(WS
4
)
2
(M = Co, Ni, Zn) materials.
For M = Ni we and others have been unable to grow single crystals and we report the structure
¯
determination from powder diffraction. The material is triclinic (P1, a = 9.3730(2), b = 12.4951(3), c =
◦
˚
1
2.5189(3) A, a = 65.814(1), b = 83.751(1), c = 69.571(1) at T = 293 K). It contains square-planar
coordination around Ni. For M = Zn we have isolated two polymorphs. We describe new analysis of
¯
the complex superstructure and diffuse scattering observed in the tetragonal polymorph (I4, a =
˚
1
1
8.723(4), c = 13.563(4) A at T = 120 K) and the bulk preparation of a monoclinic (P2
1
/c, a =
◦
˚
8.6397(4), b = 15.3693(5), c = 18.9822(5) A, b = 109.239(2) at T = 293 K) polymorph isostructural
with the M = Co material.
Introduction
Experimental
The chemistry of transition-metal containing thiometallates has
been extensively investigated over many years and a number
of reviews of their chemistry are available. Thiomolybdate
and thiotungstate salts have also been investigated as precursor
(NH ) WS
4
2
4
1–5
(NH
4
)
2
WS
4
was prepared according to the method of
15
McDonald. NH
to solid H WO (5.0619 g) to form a suspension of white powder
in a colourless solution. The suspension was saturated by slow
addition of H S (g) for about 20 min at room temperature, then
3
(28% w/w aqueous solution, 40 ml) was added
2
4
materials to produce nano-structured MoS
2
/WS hydrodesul-
2
furization (HDS) catalysts; Ni/Co promoted systems being of
6–11
2
particular interest. We have been interested in thiometallates as
potential reagents for the low-temperature synthesis of metastable
metal chalcogenides, and have successfully prepared a range
filtered to remove a green solid. The bright yellow filtrate was
heated to 60 C with stirring and a continuous flow of H
◦
2
S (g)
−
1
bubbling through the solution (rate ∼1–2 bubbles s ) for 7 h,
of ternary A
Se) materials.
2
MX
4
(A = Cu, Ag; M = Mo, W; X = S,
During work aimed at preparing transition-
metal doped quaternary chalcogenides we have reinvestigated the
structural chemistry of a family of (PPh M(WS materials
which were first reported for M = Fe, Co, Ni and Zn by Muller,
though an improved synthesis was later reported by Callahan.
12,13
resulting in the formation of a yellow solid. The solution was
purged with N and cooled; the solid was isolated by filtration
and dried under vacuum. Yield 4.14 g, 59%. CHN analysis (%):
measured: C: 0, H: 2.32, N 7.90; calc.: C 0, H 2.32, N 8.05. Identity
2
4
)
2
)
4 2
16
14
was confirmed by comparison of the PXRD pattern to the PDF
(48-1663).
Such materials are potential single-source precursors for HDS
catalysts. In our hands the original synthetic route produces
only brown X-ray amorphous materials whereas the latter allows
isolation of essentially phase-pure (poly)crystalline materials. We
report the structure determination of the M = Ni phase by
powder diffraction methods, the identification of a new monoclinic
polymorph for M = Zn and describe the complex superstructure
and origins of diffuse scatter in the tetragonal form of the M = Zn
material.
(
PPh
4
)
2
Ni(WS
)
4 2
(
PPh
4
)
2
Ni(WS
4
)
2
was prepared using the method of
14,17
Muller/Callahan.
in a 1 : 1 (v/v) mixture of H
drops of glacial acetic acid, was added to a solution of (NH
A solution of NiCl
O–CH CN (5 ml), acidified with a few
WS
CN
PCl (0.7059 g,
O–CH CN (7 ml)
2
(0.0324 g, 0.25 mmol)
2
3
4
)
2
4
(
(
1
0.1758 g, 0.53 mmol) in a 1 : 3 (v/v) mixture of H
5 ml) to give a red solution. A solution of (C
.88 mmol) in a 1 : 1 (v/v) mixture of H
2
O–CH
3
6
H
)
5 4
2
3
was added to this mixture resulting in the formation of a pale
brown solid which showed some long-term instability in air. CHN
analysis (%): measured: C 40.16, H 2.84, N 0; calc.: C 42.34, H
2
.96, N 0.
Department of Chemistry, Durham University, South Road, Durham, UK
DH1 3LE. E-mail: john.evans@durham.ac.uk; Fax: 44 191 384 1297;
Tel:44 191 334 2093
(
PPh
4
)
2
Zn(WS
4
)
2
†
Dedicated to Kenneth Wade on the occasion of his 75th birthday.
‡
CCDC reference numbers 665202–665205. For crystallographic data in
(PPh ) Zn(WS ) was made using the same methodology. The
4
2
4 2
CIF or other electronic format see DOI: 10.1039/b716407f
Electronic supplementary information (ESI) available: Tables of
bond distances and angles for materials described; thermal expansion
data for (PPh Ni(WS and monoclinic (PPh Zn(WS . See DOI:
0.1039/b716407f
solution (solvents and volumes as above) formed from ZnCl
2
§
(0.0343 g, 0.25 mmol) and (NH
4
)
2
WS
4
(0.1749 g, 0.50 mmol)
was bright orange. Addition of (C
6
H
)
5 4
PCl (0.7517 g, 2.01 mmol)
4
)
2
4
)
2
4
)
2
4 2
)
1
resulted in the formation of a bright orange solid which showed
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some long-term instability in air. CHN analysis (%): measured:
C 39.27, H 2.80, N 0; calc.: C 42.13, H 2.95, N 0.
4 2 4 2
Table 1 Agreement factors for Rietveld refinement of (PPh ) Ni(WS )
◦
¯
Space group
P1
9.3730(2)
2h range/
2h step/
5–70
0.0144
27
3.92
1.62
2.23
74
◦
a/A˚
(
PPh
4
)
2
Co(WS
)
4 2
b/A˚
c/A˚
12.4951(3)
12.5189(3)
65.814(1)
83.751(1)
69.571(1)
Time per step/s
R
wp (%)
2Bragg (%)
Solutions (see above) of Co(NO
and (NH WS (0.1747 g, 0.50 mmol) were mixed to give a dark
brown solution. Addition of a solution of (C PCl (0.7511 g,
.0 mmol) gave a dark green solid. The solid showed long-term
instability in air. CHN analysis (%): measured: C 40.94, H 2.81, N
; calc.: C 42.33, H 2.96, N 0.
3
)
2
·6H
2
O (0.0728 g, 0.25 mmol)
◦
a/
b/
R
)
2
4
◦
4
v
◦
6
H
5
)
4
c /
No. of refined
parameters
2
0
¯
data was therefore performed in P1. A total of 74 parameters were
refined (18 coefficients of a Chebychev polynomial to describe
the background, sample displacement, an axial coefficient to
describe peak asymmetry, 6 pseudo-Voigt peak shape parameters,
14 coefficients of a spherical harmonic function to describe the
preferred orientation, 6 cell parameters, 15 atomic coordinates
Methods
Single-crystal diffraction experiments were performed on a Bruker
AXS Smart 6000 diffractometer equipped with a Mo tube on
samples cooled to 120 K using an Oxford Cryosystems nitrogen
18
+
cryostream. Structures were solved using SIR92 and refined
for the anion, 10 parameters to describe the rigid PPh4 unit and
19
using the Crystals package. Powder diffraction patterns were
collected on a Bruker d8 powder diffractometer equipped with a
Cu tube, a Ge(111) incident beam monochromator and a Braun
PSD-50M linear position-sensitive detector. Room-temperature
measurements were performed on samples mounted on “zero
background” Si single-crystal sample holders. Low-temperature
measurements were performed on samples sprinkled on an Al
plate and mounted in an Oxford Cryosystems pHeniX cryostat.
2 temperature factors, one each for the anion and cation; soft
restraints were applied to W–S (2.240 A˚ ) and Ni–S (2.296 A˚ )
bond lengths and to WS tetrahedral angles). Final agreement
4
factors are given in Table 1 and the Rietveld plot in Fig. 1.
We note that separate diffraction experiments on these materials
confirmed the presence of preferred orientation; the spherical
harmonic correction applied led to improvements in the quality of
the Rietveld fit but no significant changes in fractional coordinates.
20
21
24
Indexing, simulated annealing and Rietveld refinement were
performed using the Topas-Academic software suite.
(PPh ) Ni(WS ) is isostructural with (AsPh ) Ni(WS )
and
4
2
4
2
4
2
4 2
25
(PPh ) Ni(WSe )
4
2
4
2
materials. Two views of the structure of
(
PPh
4
)
2
Ni(WS
4
)
2
◦
are shown in Fig. 2. Bond angles around Ni
◦
of 2 × 83.4(4) and 2 × 96.6(4) reveal an essentially square
Results and discussion
˚
planar geometry around Ni. Ni–S (2.12(1)–2.25(2) A) and W–
˚
(
PPh
4
)
2
Ni(WS
4
)
2
S (2.03(2)–2.17(2) A) bond lengths are within the range expected
To the best of our knowledge the structure of (PPh
4
)
2
Ni(WS
4
2
) has
not been reported. As reported by earlier workers, we were unable
to prepare single crystals of this material, but were able to prepare
a brown polycrystalline solid which was stable in air for short
periods but showed some long-term instability. Powder diffraction
data were collected on a sample sprinkled on a Si zero-background
sample holder. All but two reflections could be indexed using a
˚
triclinic cell of a = 9.3730, b = 12.4951, c = 12.5189 A, a =
◦
22
6
5.814, b = 83.751, c = 69.571 . A structure-independent Pawley
refinement gave an excellent fit to the data. The structure could
Fig. 1 Observed, calculated and difference (lower curve) plots for
be solved using a real-space simulated annealing protocol in space
the Rietveld refinement of (PPh
4
)
2
Ni(WS
4
)
2
. Tick marks show allowed
+
group P1. PPh
4
groups were modelled as rigid bodies with a P–C
◦
reflection positions. A zoom of the region between 24 and 40 2h is shown.
+
˚
bond of 1.792 A (the mean bond length for P–C bonds of PPh
4
23
groups in the CSD ) with tetrahedral geometry at P and phenyl
˚
groups with C–C and C–H bond lengths of 1.39 and 0.998 A,
respectively. Four torsion angles of Ph groups around P–C bonds
were allowed to vary. The anion was originally described using
a Ni(WS
4
2
) rigid body with square-planar Ni and tetrahedral W,
though this geometry was allowed to relax in final refinements.
+
Simulated annealing was performed in which PPh
˚
4
cations were
◦
moved by up to ± 5 A, rigid-body rotations by ± 180 and torsion
◦
angles by ± 30 , followed by full Rietveld refinement. Since P1
has a floating origin the Ni atom was fixed at (0, 0, 0). Using this
protocol the same low R-factor solution was found approximately
every 4000 cycles of randomisation/refinement to convergence.
Examination of this structural model revealed an approximate
centre of symmetry at Ni and final Rietveld refinement using all
4 2 4 2
Fig. 2 The structure of (PPh ) Ni(WS ) viewed down the a axis (left) and
down the b axis (right). W tetrahedra are shown in green, square-planar
Ni ions in red, S in yellow, P in orange, C in blue and H in grey.
1
598 | Dalton Trans., 2008, 1597–1601
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for a structure of this type refined from powder data. The packing
Table 2 Crystallographic details for sub- and super-structure refinement
+
2−
4 2 4 2
of (PPh ) Zn(WS )
of PPh
Powder diffraction data were also recorded on cooling
PPh Ni(WS from 300 to 16 K. A smooth variation in cell
4
and Ni(WS
4
)
2
anions is discussed in more detail below.
Formula
[P(C
6
H
5
)
4
]
2
Zn(WS
4
)
2
[P(C
6
H
5
)
4
]
2
Zn(WS
4
)
2
(
4
)
2
)
4 2
parameters was observed suggesting no phase transitions (see
Mr
1368.38
Tetragonal
¯
I4
1368.38
Tetragonal
¯
I4
Crystal system
ESI§). Thermal expansion was relatively isotropic with thermal
Space group
expansion coefficients between 15 and 300 K of a
a
= 41.6(8) ×
a/A˚
b/A˚
c/A˚
V/A
T/K
13.2295(3)
13.2295(3)
6.7770(2)
1186.11(5)
120
1.916
5.793
20241
1292
1175
83
1.9
1.76
18.723(4)
18.723(4)
13.563(4)
4754(2)
120
1.912
5.781
82669
4564
2471
142
3.0
4.97
−
6
−6
−6
−1
10 , a
b
= 43.3(5) × 10 , a
c
= 38.5(6) × 10 K .
(
PPh
4
)
2
Zn(WS
4
)
2
: tetragonal polymorph
˚
3
◦
−
3
Orange single crystals of (PPh
4
)
2
Zn(WS
4
)
2
were grown at 4
C
D /g cm
c
−
1
by layering ethanol on a DMF solution of the polycrystalline
material. A small number of crystals of sufficient quality for
single-crystal structural analysis could be obtained.¶ Fig. 3 shows
a typical image collected from such a crystal. The most intense
l/mm
Total no. reflections
No. unique reflections
No. observed reflections
No. refined parameters
R
int (%)
sharp reflections could all be indexed on a tetragonal cell of a =
R (%)
(%)
Twin element parameter (%)
˚
1
3.2295, c = 6.7770 A. However between these layers weaker
R
w
3.96
—
5.94
24.5(5)
reflections could be observed superimposed on lines of significant
diffuse scatter. The supercell reflections could be indexed using
√
˚
a cell of a = b = 18.723, c = 13.563 A i.e. asup
∼
2asub, csup
shown. This places the Zn atom at the centre of the anion on the
original position occupied by the W atom. As such the S atoms
on the “lower half” of the ZnS
sites originally on the “upper half” of the WS
S positions are therefore, to a first approximation, unaffected by
this disorder.
∼
2csub (Table 2). Similar observations were made in the original
paper on this material, though no attempt was made to refine the
superstructure. An excellent fit to the subcell-only data (R/R
.76/3.96%) could be obtained using the disordered structural
4
tetrahedron are superimposed on
tetrahedron. The
26
w
=
4
1
model illustrated in Fig. 4 and final agreement factors are given in
2
−
¯
Table 2. In this model [Zn(WS
the tetragonal unit cell with PPh
4
)
2
]
anions lie along the 4 axes of
+
4
cations interspersed between
them. Note that Fig. 4 shows only one of two possible sets of anion
positions. An alternative set of sites is located at +c/2 from those
¶
Diffraction data were collected using a Bruker AXS Smart 6000
diffractometer on a crystal of dimensions 0.08 × 0.08 × 0.3 mm. Two full
◦
spheres of data were collected with a frame width of 0.3 and integrated
using the SAINT software package to give 20241 reflections for the
subcell and 82669 for the supercell. Correction for absorption using
29
30
SADABS and merging (Rint = 1.9/3.0%) resulted in 1292/4564 reflections
of which 1175/2471 had I > 3r(I). Systematic extinctions were consistent
¯
with space group I4.
Fig. 4 An ordered view of the substructure of the tetragonal polymorph
of (PPh ) Zn(WS ) , viewed down the c axis (left) and perpendicular to
4 2 4 2
the c axis (right) with the cations omitted. Note that only half of the anion
sites are shown. W is shown in green, Zn in red, S in yellow, P in orange,
C in blue and H in grey.
This disorder model is the origin of the supercell reflections and
diffuse scatter observed on the X-ray images. The superstructure
was solved using SIR92 and refined successfully to R/R
w
=
4.97/5.94%.* A twin law of the form (0 1 0; 1 0 0; 0 0 −1) was
applied, as is commonly required for structures in Laue group 4/m.
In the superstructure model there are two crystallographically
2
−
independent chains of [Zn(WS
4
)
2
]
anions in the unit cell. These
1
1
correspond to the chains at (0, 0, z) and ( , , z) of Fig. 4. Within
2
2
these chains we refine ∼ 64 : 36 and 77 : 23% disorder of anions
over two sets of positions related to those refined in the subcell
4 2 4 2
Fig. 3 Diffraction data for crystals of (PPh ) Zn(WS ) with predicted
*
For final cycles of refinement an optimal weighting scheme based on
reflections for the subcell overlaid. Predicted reflections are shown by
squares for reflections centred on this particular frame, crosses for
reflections centred a few frames before this one and circles for reflections
centred a few frames after this one.
a third-order Chebychev polynomial was applied. Soft restraints were
applied to maintain the planarity and regularity of phenyl rings. H atoms
were added geometrically and refined using the riding model. Isotropic
temperature factors were refined for all atoms.
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model (where occupancies are fixed at 50 : 50% by symmetry).
The two disordered positions and resulting average anion chain
structure are shown in Fig. 5. It can be seen from this figure
that the superposition of these two disordered sites leads to an
approximate superposition of atomic coordinates (e.g. metal sites
4 2 4 2
Table 3 Agreement factors for Rietveld refinement of (PPh ) Zn(WS )
◦
Space group
P2
1
/c
2h range/
2h step/
4.5–70
0.0144
90
◦
a/A˚
18.6397(4)
15.3693(5)
18.9822(5)
109.239(2)
97
b/A˚
c/A˚
Time per step/s
R
R
wp (%)
6.38
1.72
10.55
˚
◦
are separated by ∼1 A). If these sites superimpose precisely and the
b/
(%)
Bragg
2
No. refined parameters
v
site occupancies were 50 : 50% the tetragonal substructure would
2
−
result. Presumably within a given anion chain [Zn(WS
4
)
2
]
units
are fully ordered. As one moves to adjacent chains the registry is
rapidly lost as the sulfur atoms of the anion chains can “lock in”
+
to the PPh
4
cations in one of two possible positions along c. The
length scale of registry is reflected in the ∼30% refined occupancy
of the minor component of each chain and further manifests itself
as the streaks of diffuse scatter on all X-ray images. Full details of
the superstructure model have been deposited.
Fig. 6 Observed, calculated and difference (lower curve) plots for the
Rietveld refinement of monoclinic (PPh
allowed reflection positions. A zoom of the region between 24 and 40 2h
4
)
2
Zn(WS
4
)
2
. Tick marks show
◦
is shown.
has been deposited. Bond lengths and angles of Zn(WS
4
)
2
units
showed minor distortions from tetrahedral geometry. W–S bond
˚
lengths ranged from 1.89(3) to 2.29(3) A and angles from 102(1)
◦
to 119(1) . ZnS
4
tetrahedra showed more marked distortion with
˚
bond lengths from 2.22(4) to 2.43(4) A and angles from 91(1)
Fig. 5 Disordered chain in the superstructure of the tetragonal form of
◦
to 124(2) . ZnS
4
tetrahedra are, however, significantly distorted
in the tetragonal polymorph (Zn–S 2.387(1), S–Zn–S 96.95(6)
and 116.07(3) with the subcell model). CoS polyhedra in the
(
4 2 4 2
PPh ) Zn(WS ) viewed down the b axis. Major anion sites are shown in
red, minor anion sites in blue.
4
corresponding M = Co phase have bond angles from 101.8
◦
to 116.1 . The significant distortion is presumably caused by
2
+
6+
repulsion between formally Zn and W ions in edge-sharing
tetrahedra.
(
PPh
4
)
2
Zn(WS ) : monoclinic polymorph
4
2
Powder diffraction of the monoclinic material between 15
and 300 K revealed no phase transitions. Thermal expansion
Powder diffraction measurements on the polycrystalline sample
from which the tetragonal single crystal was grown revealed a
very different structure to that obtained by single-crystal methods.
The powder diffraction pattern could instead be indexed on a
−
6
coefficients between 15 and 300 K of a
a
= 44(1) × 10 , a
b
= 66(3) ×
−
6
−6
−1
10 , a
c
= 21(1) × 10
K showed slightly higher anisotropy than
the M = Ni material (see ESI‡).
˚
monclinic cell of a = 18.6397, b = 15.3693, c = 18.9822 A, b =
◦
1
09.239 close to that expected from the single-crystal structure
27
reported for the Co material. Rietveld refinement of the powder
data was performed using the Co structure as a starting model. A
total of 97 parameters were refined: 12 coefficients of a Chebychev
polynomial to describe the background, sample displacement, an
axial model parameter to describe peak asymmetry, a scale factor,
Conclusions
We have shown that there are three basic structural types available
to (PPh
4
)
2
M(WS
4
) materials. The Mn material is reported to have
2
28
6
peak shape parameters, 15 coefficients of a spherical harmonic
a tetragonal structure. Single crystals of the Co material are
27
function to describe preferred orientation, 4 cell parameters, 33
coordinates of atoms in the anion, and 4 temperature factors;
monoclinic. We have confirmed that the bulk powder has the
same structure as reported for a single crystal. Single crystals
of the Zn material are tetragonal yet the bulk polycrystalline
phase prepared here is monoclinic and isostructural with M =
Co. The M = Ni structure is distinct, driven by the preference of
Ni for square-planar geometry. The anion packing arrangements
are compared in Fig. 7. The cell volumes per formula unit are given
in Table 4. It can be seen that the Ni and monoclinic Zn structures
have significantly larger cell volumes than other materials. Since
both samples were characterised using powder diffraction we
PPh units were modelled as rigid bodies with P–C distances of
4
˚ ˚ ˚
1.79 A, C–C distances of 1.39 A and C–H distances of 0.998 A. Six
parameters were refined to describe the rotations and translations
of these units relative to the x, y and z axes, 4 torsion angles
were also refined for each unit to describe the rotation of the
phenyl rings around the P–C bonds. Final agreement factors of
R
wp = 6.38% and RBragg = 1.72% were obtained. The Rietveld plot
is shown in Fig. 6 and refinement details in Table 3. A .cif file
1
600 | Dalton Trans., 2008, 1597–1601
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Table 4 Cell volume per formula unit for (PPh
4
)
2
M(WS
unit/ A˚ 3
4 2
M(WS )
4
)
2
2 A. Muller and S. Sarkar, Angew. Chem., Int. Ed. Engl., 1977, 16, 705–
7
07.
3 S. H. Laurie, Eur. J. Inorg. Chem., 2000, 2443–2450.
Metal Crystal symmetry Cell volume per (PPh
4
)
2
4
5
D. Coucouvanis, Adv. Inorg. Chem., 1998, 45, 1–73.
Q. F. Zhang, W. H. Leung and X. Q. Xin, Coord. Chem. Rev., 2002,
Mn
Co
Ni
Zn
Zn
Tetragonal
Monoclinic
Triclinic
Monoclinic
Tetragonal
1210
1269
1361
1368
1186
2
24, 35–49.
6
G. Alonso, J. Espino, G. Berhault, L. Alvarez and J. L. Rico, Appl.
Catal., A, 2004, 266, 29–40.
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8
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−
Fig. 7 Packing of M(WS
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(
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Acknowledgements
The authors would like to thank Prof. Judith Howard for
the provision of single crystal diffraction facilities. CJC thanks
EPSRC/Durham University for a DTA studentship. IRE thanks
RCUK for an Academic Fellowship.
2
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30 G. S. Sheldrick, SADABS, University of Gottingen, 1996.
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