Po/yhedron Vol. 9, No. II, pp. 1389-1395,
Printed in Great Britain
1990
0
0277-5387/90
S3.OOf.00
1990 Pergamon Press plc
SYNTHESIS, STRUCTURE AND nSe/“gSn NMR
SPECTROSCOPY
OF THE NEW POLYSELENIDE,
TRIS(TETRASELENIDO)STANNATE(IV),
[Sn(Se4)3]zSONG-PING
HUANG, SANDEEP
DI-IINGRA and MERCOURI
G. KANATZIDIS*
Department of Chemistry, Michigan State University, East Lansing, MI 48824, U.S.A.
(Received
11 September
1989 ; accepted 18 January 1990)
Abstract-The reaction of sodium pentaselenide with SnCl, or SnC12* 2H20 in dimethylformamide (DMF), in a 3 : 1 ratio, forms the new soluble anion [Sn(SeJJ2- in high
(> 79%) yields. The compound (Ph,P)2[Sn(Se,),] (I) crystallizes in the monoclinic space
group P2,/c with unit cell dimensions, a = 13.320(2), b = 11.678(3), c = 34.817(9) A,
j? = 98.85(2)’ and V = 4535 A3. A single-crystal X-ray diffraction study of I shows that
three chelating Sed2- ligands provide an octahedral coordination about the central Sn4+
atom. The crystal structure was solved and refined with conventional techniques to R =
6.0% and R, = 7.0%. The average Sn-Se distance is 2.709(13) A, while the average
Se-Se bond distance is 2.324(12) A. The IR spectrum of I (CsI pellet) shows two sets of
absorptions at 273, 256 cm-’ and 181, 173 cm- ‘, respectively, assigned tentatively to
v(Se-Se) and v(Sn-Se) vibrations. The ‘19Sn NMR spectrum of I in DMF, shows a
single resonance at -723 ppm (vs Me4Sn). The 77Se NMR spectrum of I in DMF, shows
two resonances at 618 and 459 ppm. Thermal decomposition of I results in formation
of SnSe, at 510°C. Further heating, above 6OO”C,results in SnSe.
Interest in the synthesis of soluble transition-metal
polychalcogenide
compounds
remains intense
because of their astonishing tendency for structural
and stoichiometric diversity. As a result, a number
of polysulphide and to a lesser extent polyselenide
and polytelhuide complexes with transition metals
have been isolated and structurally characterized. ‘-*
By contrast, the preparation of soluble polychalcogenide compounds containing main-group
elements has not been pursued to any considerable
degree. The few existing examples are, the
Pi2S3414-,9
[~n(~4~2(~~)~.A~4)~.412-,‘”
l?n2~2114-,”
[In3Se15]3- ‘* and [T13Se,5]3-.‘2 Recently we
have undertaken a systematic investigation of
polychalcogenide chemistry of the late transition
and main group metals. “-” Except for some
cases, the solution chemistry of polyselenide or polytelluride complexes has proven to be at considerable variance from that of polysulphide chemistry. For example, while group 12 metals form
isostructural complexes with all types of Q42ligands, group 11 metals form different structures
with different polychalcogenide ligands3s13 The
*Author to whom correspondence should be addressed.
reasons for this deviation from polysulphide chemistry are not completely understood, although the
size difference between sulphur and the heavier
chalcogens is probably a strongly influencing factor.
It would be useful to understand the role of the
metal ion in determining similarities and differences
in the chemistry of the various polychalcogenide
ligands. 77Se NMR spectroscopy appears to be a
useful or even unique tool (not applicable to polysulphides) for the investigation of metal-polyselenide complexes. ‘3’ In this paper we report
the synthesis, molecular structure, 77Se, ‘19Sn
NMR and other spectroscopic characterization of
the new complex [Sn(Se4),12-, the first group 14
polyselenide.
EXPERIMENTAL
All work was done in a glovebox (Vacuum Atmospheres, Inc.) under a nitrogen atmosphere. Dimethylformamide (DMF) was stored over 4 w
Linde molecular sieves for several days and distilled
under vacuum. Ether was distilled over sodium (or
potassium)/benzophenone
under a nitrogen blanket. SnCl, (anhydrous) and SnC12* 2H20 were pur-
1389
1390
SONG-PING
chased from Alpha Products. Elemental analyses
were performed by Galbraith Laboratories, Knoxville, Tennessee. Satisfactory elemental analyses
were obtained. Sodium pentaselenide (Na$e,) was
prepared in liquid ammonia from sodium metal
and elemental selenium in a 2 : 5 ratio. The X-ray
powder diffraction patterns were recorded either
with a standard Debye-Scherrer powder camera
mounted on a Phillips Norelco XRG-5000 X-ray
generator operating at 40 kV/20 mA, or a Phillips
XRG-3000 computer-controlled
powder diffractometer. Nickel filtered, copper radiation was used.
Thermal gravimetric analyses were performed on a
Cahn TG System 121 under flowing nitrogen. A
typical heating rate of 5°C mine1 was used. IR
spectra were recorded as KBr and CsI pellets
on a Nicolet 740 FT-IR spectrometer. UV-vis
spectra were recorded on a Hitachi U-2000
spectrophotometer.
Synthesis of (Ph,P),[Sn(Se,),]
(Ph,P),[Sn(Se,),]
of
10
-1
0
10
11
-1
1
00
11
01
-1
1
01
10
-1
-2
-2
1
1
0
02
12
1
2
21
A. A 10 cm3 DMF solution of 0.051 g
(N 0.2 mmol) liquid SnCl, was added to a 50 cm3
DMF solution of 0.270 g (- 0.61 mmol) Na,Se,
in the presence of 0.150 g (0.40 mmol) Ph4PCl.
Filtration of NaCl precipitate, followed by slow
addition of ca 60 cm3 of ether, and storage at room
temperature for several days, afforded analyticallypure red-brown hexagonal platelets in 85%. The
X-ray diffraction (XRD) powder pattern obtained
from this material matches extremely well that
obtained from calculating the same pattern from
the single-crystal coordinates, confirming the purity
of the compound. A comparison between the calculated and observed d spacings for this material is
shown in Table 1.
Method B. A 20 cm3 DMF solution of 0.045 g
(0.2 mmol) SnCl,*2H,O was added to a 30 cm3
DMF solution of 0.270 g (0.61 mmol) Na,Se, in
the presence of 0.220 g (0.60 mmol) Ph4PCl. The
resulting red-brown solution was filtered to remove
NaCl and the filtrate was diluted with 50 cm3 ether
to incipient crystallization. Upon standing at room
temperature
for a week, red-brown
microcrystalline powder was obtained (0.275 g). Yield
79%. The product was recrystallized from DMFether to obtain large, hexagonal-shaped crystals.
The XRD powder pattern of this product is identical to that obtained in method A.
of
et al.
Table 1. Observed and calculated X-ray powder pattern
-1
-1
(I)
Method
Thermal decomposition
HUANG
to
SnSe,
This decomposition was carried out inside an
alumina boat in a tube furnace under flowing nitro-
-2
-2
0
2
03
31
03
22
-1
-2
2
3
32
23
-3
-2
-4
0
0
1
23
-3
2
22
-3
1
32
-4
1
23
33
50
24
2 1
-5
1
15
52
-1
4
0
2
2
0
1
4
1
3
2
4
4
4
1
4
2
1
6
3
3
6
5
1
3
3
5
8
1
2
0
8
10
1
3
7
8
10
6
8
7
5
2
5
12
8
1
5
13
W@‘MWkJ31
13.16
11.33
9.75
8.73
8.68
8.60
8.30
8.18
8.13
6.962
6.740
6.467
5.782
5.663
5.529
5.225
5.035
4.958
4.873
4.695
3.870
3.867
3.700
3.686
3.528
3.455
3.360
3.356
3.350
3.338
3.261
3.197
3.150
3.037
2.918
2.846
2.840
2.752
2.672
2.588
2.544
2.437
2.436
2.366
2.290
2.173
1.972
13.39
11.43
9.79
8.82
8.65
38
100
85
85
65
8.36
8.20
28
31
6.925
6.779
6.499
5.817
5.689
5.577
5.257
4.998
14
22
32
33
19
14
23
25
4.897
4.699
3.888
36
25
26
3.708
35
3.522
3.459
3.369
29
15
31
3.339
3.264
3.207
3.164
3.046
2.922
2.848
27
29
39
25
24
25
41
2.758
2.677
2.589
2.537
2.439
26
14
26
8
20
2.370
2.297
2.174
1.972
7
13
11
9
gen at 5 10°C. The final black-grey microcrystalline
product corresponds, by weight, to SnSez. It was
characterized by X-ray diffraction. X-ray diffraction powder pattern spacings (in A) follow ; intensities are shown in parentheses : 6.17 (100.0) 3.076
(7), 2.25 (21), 2.050 (40), 1.906 (6), 1.742 (13).
Tris(tetraselenido)stannate(IV)
Thermal decomposition of (Ph,P),[Sn(Se,),]
to SnSe
This decomposition was carried out inside an
alumina boat in a tube furnace under flowing nitrogen at 600°C. The final black-grey microcrystalline
is, by X-ray diffraction, SnSe. d Spacings (in A)
follow; intensities are shown in parentheses: 5.76
(I), 3.514(3), 3.033 (2), 2.934(10), 2.874(100), 2.380
(6), 2.087 (4) 2.042 (3), 1.920 (l), 1.833 (7) 1.761
(3), 1.684 (2).
X-ray crystallographic studies
The crystallographic data for I were collected on a
Nicolet four-circle diffractometer using a o-28 scan
mode and MO-K, radiation (at Crystalytics Co., Lincoln, Nebraska by Dr C. S. Day). The crystals were
mounted inside glass capillaries and sealed. Crystal
data and details for data collection and refinement
are shown in Table 2. The intensities of three check
reflections were monitored every 100 reflections and
did not show any appreciable decay during the data
collection period. An empirical absorption correction was applied to all data based on + scans
for seven reflections. The structure was solved with
direct methods using SHELXS-86’ 6and was refined
with the SDP17 package of crystallographic
programs, using a VAXstation 2000 computer. All
non-carbon and non-hydrogen atoms were refined
anisotropically. The carbon atoms were refined isotropically. The hydrogen atom positions were calculated and included in the structure factor calculation but were not refined. There were no
significant residual peaks in the final electron density difference map. The XRD powder pattern was
calculated using the atom coordinates determined
from the single-crystal data using the program
POWD lOI (see Table 1).
Table
2. Data
for
crystal
Formula
FW
a (A)
b (A)
c (A)
a(O)
B (“)
Y(“)
z V(A’)
Space group
&+l, (g cm- 3,
~(Mo-K,) (cm- ‘)
Crystal size (mm)
0 range (“)
Data collected
Number of data collected
Number of data unique
Data used [FO> 3a(F,J]
Min, max abs. correction
Number of variables
Number of atoms per asym.
unit (including H)
Final R/R,(%)
structure
analysis”
of
G8H40P2Snh
1744.6
13.320(2)
11.678(3)
34.817(9)
90.00
98.85(2)
90.00
4,5351(2)
P2 Jc (No. 14)
2.17
86.5
0.11 x 0.60 x 0.88
4.0-48.0
h, k fl
9412
9220
3898
0.41,0.99
328
103
6.017.0
aAt 25°C.
decays accumulated was 30,000 and 72,000 for 77Se
and ’ “Sri, respectively. A line broadening of 50 Hz
was typically applied.
The spectra were referenced to Me,Se for 77Se
and Me,Sn for ’ 19Sn at 6 = 0 ppm in DMF. Solutions of PhlSez (6 = 460 ppm) and Me$n in DMF
were used as external reference. The convention
used for the chemical shifts is that a positive sign
signifies a shift to high frequency compared to the
reference compound.
RESULTS
NMR spectroscopy
77Se (I= l/2, nat. abund. 7.58%) and ‘19Sn
(Z = l/2, nat. abund. 8.58%) NMR spectra were
obtained on a Varian VXR-500 (superconducting
cryomagnet
11.74 Tesla) pulse spectrometer
equipped with Sun/360 workstation. The spectra
were recorded at ambient temperature using a
broad band 5 mm probe (frequency range 50-202
MHz). The observing frequencies were 95.358 MHz
for 77Seand 186.250 MHz for ‘19Sn. The aquisition
time was 0.32 s with a spectral width of 38.35 KHz
for 77Seand 37.393 KHz for ‘19Sn which gave data
point resolution of 1.14 and 1.17 Hz, respectively.
The pulse width used in these experiments was 6 ps
for both 77Se and ‘19Sn spectra, and no relaxation
delay was applied. The number of free induction
1391
AND DISCUSSION
Synthesis
The preparation of (Ph,P),[Sn(Se&] was carried
out by reacting SnCl, with Na,Se, in DMF in the
presence of Ph.,P+ according to eq. (1) :
SnCl, + 3NazSes + 2Ph4PC1 (Ph,P),[Sn(Se&]
+ 6NaCl.
(1)
The reaction was accompanied by a sharp colour
change from dark green to red-brown. Interestingly
the same compound can be obtained by using
SnCl, 2Hz0 as starting material which indicates
that possible Sn2+-Sex2- (x > 1) complexes are
unstable towards internal redox chemistry resulting
in the formation of Sn4+ species. This is similar to
l
SONG-PING
1392
the behaviour of the corresponding Fe2+/Se,*-,*
Au+/Se,‘- 14*15and Tl+/Se,*- ‘* systems from
which only Fe3+, Au3+ and T13+ complexes have
been isolated.
The UV-vis spectrum of I in DMF solution has
no characteristic absorption bands (300-800 mn)
and features a rising absorbance at higher energies.
The absence of a band around 650 nm suggests that
the complex does not dissociate in this solvent to
form Se,- radical anions (as has been observed in
[In2Se2J4- ‘I) which are responsible for this absorption.“.” In the far-IR region of the spectrum we
observe two sets of two absorptions at 273, 256
cm-’ and 181, 173 cm- ‘, respectively. According
to other literature data***’ we assign these sets,
respectively, to Se-Se and Sn-Se vibrations.
The 77Se NMR spectrum of I in DMF solution
at room temperature, shows two peaks at 618 and
459 ppm, respectively, indicating that all three
Se4*- ligands in the complex are equivalent [Fig.
l(A)]. The various conformations of the SnSe, fivemembered rings (uide injkz) interconvert in solution
me
NMR
HUANG
et al.
at room temperature. This is common in complexes
containing
Se4*- ligands, as in the series
[MQ(Se,)d*- (Q = 0, S, Se)’ where the fluxional
behaviour persists down to -60°C. Table 3 summarizes pertinent 77Se NMR chemical shifts from
MSe, systems known thus far. In all cases but one,
the metal-bound selenium atom resonance occurs
at lower field than the corresponding ring-selenium
resonance.5T8 It was found in the isostructural (but
not isomorphous) [Pt(Se4)3]2-, the platinum-bound
77Se resonance occurs at higher field than the corresponding non-platinum-bound 77Se resonance.*’
Since we could not observe Sn-Se satellite peaks,
we cannot unequivocally assign the resonances for
[WSe4)31’-.
The “‘Sn
NMR spectrum of [Sn(Se4)3]2-, in
DMF solution at room temperature, shows a single
peak at - 723 ppm, as expected, consistent with the
notion that the integrity of the complex is maintained in solution [Fig. l(B)]. We did not observe
satellite peaks that could be attributed to ’ “Sn77Se coupling. The observed ’ “Sn NMR chemical
(A)
(B)
Fig. 1. (A) “Se NMR spectrum of (Ph,P),[Sn(Se.,),] in DMF at 25°C; (B) “‘Sn NMR spectrum of
(Ph,P),[Sn(Se,),] in DMF at 25°C.
Tris(tetraselenido)stannate(IV)
by other Ph,P+ salts of polyselenide complexes and
is due to the nucleophilic attack on the Ph4P+
cation by the Se, 2- ligands to generate the volatile
Ph3P, Ph,PSe, Ph,Se, Ph2Se2, etc. Following a
smooth and continuous weight loss, the decomposition of I results, at 52O”C, in the formation of
SnSez. Further heating results in the loss of one
selenium to yield SnSe at - 660°C. SnSe2 and SnSe
were unequivocally identified by X-ray powder
diffraction.
Table 3. “Se NMR chemical shifts (in ppm) for metalpolyselenide compounds containing Se4*- ligands in
DMF
Compound
(RtJWMoG(Se&l
(Rt4N)2[MoS(Se&.l
(I&N) JMoSe(Se.J 21
Ph4As)2WG(Se4)d
Ph&)DWW~1
(Ph4As)2WSe(Se&l
(PhJVW@e&J
(PhJ%[Zn(Se&l
(PhJ%[Cd(W,l
(Rt,N)JHg(Se&l
V’U’LW@e3~1
(Rt,N)JIn$e,(SeJJ
PWMWW31
(RhJ%[Pt(Se.JJ
%I*
Sed
Reference
946
1122
1163
828
993
1034
598
607
617
604
829
644
619
680
380
396
403
280
313
324
127
137
75
86
759
197
459
790
8
8
8
8
8
8
8
12
12
12
12
12
This work
21
1393
Description
of the structure of I
The monoclinic unit cell contains well-separated
[Sn(Se4),12- anions and Ph,P+ cations. The latter
have the usual tetrahedral structure and will not be
discussed further. The structure of the anion in I is
similar to the recently reported [Pt(Se,),]‘- 21 and
[Sn(S,),]‘-. lo However, the latter was not isolated
in pure form. It was found co-crystallized in the
same crystallographic
site (and therefore disordered) with [Sn(S,),(S,)]‘-, respectively, in a 4: 6
ratio. No such disorder was detected in the present
study. The structure of the [Sn(Se4),12- anion is
shown in Fig. 3, and consists of three four-membered selenium chains chelated to a central Sn4+.
The coordination geometry of the Sn4+ is octahedral approaching D3 symmetry, with an average
Sn-Se
bond distance of 2.709(13) A, and a
Se-Sn-Se
angle of roughly 90”. A listing of selected bond distances and angles for [Sn(Se4),12- is
given in Table 4. The observed Se-Se bonds are in
the normal range of single Se-Se bond distances
reported for other metal-polyselenide compounds.
To the best of our knowledge*[Sn(Se4)3]2- is the first
“Labelling scheme of the MSe, ring system :
shift for [Sn(Se&]2-, correlates well with those of
[SnSe312- and [SnSe414- anions” which occur at
-264.3 and -476.6 ppm, respectively. The successive shift of the “‘Sn resonance toward more
negative values with increasing tin coordination
number is evident and suggests increased shielding
on the tin centre. This is consistent with similar
trends observed for other tin complexes (e.g. the
tin-halide series). 23
TGA examination of the thermolysis of I under
flowing nitrogen shows that the compound begins
to lose weight at - 335°C as shown in Fig. 2. This
onset temperature of initial weight loss, is shared
(PhqP)z[Sn(Se&l
Decomposition
TEYP (C)
Fig. 2. Typical TGA diagram of I under flowing nitrogen.
SONG-PING HUANG et al.
Fig. 3. ORTEP representation and labelling scheme of
the structure of the [Sn(Se#- anion.
molecular example of a Sn4+ centre being coordinated in an octahedral fashion by six selenide
atoms. A solid-state analogue is SnSe*, in which the
tin is coordinated octahedrally. The Sn-Se bond
lengths in the anion of I are comparable to those
found in SnSe224 (2.683(2) A) but shorter than
those observed for SnSe” (2.793(2) and 2.744(3)
A). This difference is expected due to the Sn*+ oxidation state in SnSe. The Sn-Se bond, however,
in [Sn(SeJ,]*- is much longer than that found in
[Sn2SeJ4+ (av. 2.508 A) in which tin features a
tetrahedral
coordination. 26 The
SnSe( 1)Se
(2)Se(3)Se(4) ring adopts the envelope comformation while the other two SenSe(5)Se(6)Se(7)Se(8)
and SnSe(9)Se( lO)Se(1l)Se( 12) adopt puckered conformations. Both of these conformations are common in Q4*- chemistry. For example, the envelope
conformation is notable in the series [M(Se3,]*- 3
(M = Zn, Cd, Hg), while the puckered one is
characteristic in the [MQ(Se,),]*(M = MO,
Q = Q, S, Se) series.’
With three c&coordinated bidentate ligands, I
can exist as optical isomers. The complex is a
racemic mixture similar to the [Pt(S,),]*- 27 where
Table 4. Selected distances (A) and angles (“) in the [Sn(SeJ,]‘- anion. Standard
deviations are shown in parentheses
Sn-Se( 1)
Sn-Se(4)
Sn-Se(S)
Sn-Se(8)
Sn-Se(9)
Sn-Se( 12)
2.694(3)
2.705(3)
2.718(3)
2.697(3)
2.733(3)
2.708(3)
Sn-Se(mean)
2.709(13)
Intrachelate
Se(l)-Sn-Se(4)
Se(S)-Sn-Se(8)
Se(9)-Sn-Se( 12)
95.30(8)
96.73(8)
95.40(9)
Interchelate
Se(l)-Sn-Se(S)
Se(l)--Sn-Se(8)
Se(1)-Sn-Se(9)
Se(l)-Sn-Se(12)
Se(4)---Sn-Se(S)
Se(4)-Sn-Se(8)
Se(4)-Sn-Se(9)
Se(4)---Sn-Se( 12)
Se(S)-Sn-Se(9)
Se(S)-Sn-Se( 12)
Se(8)--Sn-Se(9)
Se(8)--Sn-Se( 12)
91.15(9)
91.31(9)
172.51(9)
87.53(9)
84.18(9)
173.31(9)
77.49(9)
79.91(9)
86.15(9)
177.62(9)
95.94(9)
81.32(9)
W%---Se(6)
~@---Se(7)
f+O-Se@)
Se(9jSe( 10)
Se(lO)---Se(l1)
Se(1l)--Se(12)
2.341(4)
2.302(4)
2.327(4)
2.337(4)
2.328(4)
2.320(4)
2.308(4)
2.332(4)
2.319(4)
Se-Se(mean)
2.324(12)
Se(ljSe(2)
fW+--Se(3)
Se(3jSe(4)
Sn-Se( l)---Se(2)
Sn-Se(4)-Se(3)
Sn-Se(SkSe(6)
Sn-Se(8pSe(7)
Sn-Se(9+Se( 10)
Sn-Se(l2FSe(ll)
100.6(1)
104.9(1)
101.9(l)
101.6(l)
101.9(l)
103.5(l)
Sn-Se-Se(mean)
102(2)
Se( l)-Se(2)-Se(3)
Se(2)-Se(3)-Se(4)
Se(5)-Se(6)-Se(7)
Se(6)-Se(7)--Se(8)
Se(9)-Se( lO)-Se( 11)
Se(lO)-Se(ll)-Se(12)
101.0(l)
103.1(l)
102.2(1)
101.0(l)
102.4(1)
100.5(l)
Se-Se-Se(mean)
101(l)
Tris(tetraselenido)stannate(IV)
partial resolution of the optical isomers using (+)as the counterion provided a carbon[Ru(Phen),]‘+
free optically active inorganic molecule. Although
we did not attempt it, the resolution of the optical
isomers of [Sn(Se.,)$by a similar method should
also be possible.
AcknowledgementsFinancial
support from the Donors
of the Petroleum Research Fund, administered by the
American Chemical Society, the Center for Fundamental
Materials Research (CFMR) at Michigan State University and the NSF (for a Presidential Young Investigator Award) is gratefully acknowledged.
Supplementary material. Tables of atomic coordinates
of all atoms and anisotropic and isotropic thermal parameters of all non-hydrogen atoms have been deposited
with the Cambridge Crystallographic Data Centre.
9.
10.
11.
12.
13.
14.
15.
16.
17.
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