The layered coordination polymer Bi(SCN)3·H2O

Article abstract of DOI:10.1002/zaac.201000154

Yellow crystals of Bi(SCN)₃·H₂O are obtained by reacting (BiO)2CO3 and HSCN in aqueous solution. X-ray diffraction on a single-crystal revealed a triclinic lattice (space group P1) with a = 843.6(2) pm, b = 920.4 (2) pm, c = 1210.7(2) pm, α = 109.16(3) °, β = 109.06(3) °, γ = 90.22(3) °, V = 832.8(3)·10 pm, and Z = 4. All thiocyanate anions bind with both ends to different cations. The coordination network expands in plane layers parallel (1 1 0). The water molecule coordinates one of the two independent Bi³⁺ cations. Dehydration sets in at 100 °C, followed by stepwise thermal decomposition to Bi₂S₃.

Full text of DOI:10.1002/zaac.201000154

ARTICLE
DOI: 10.1002/zaac.201000154
The Layered Coordination Polymer Bi(SCN)3·½H2O
Gregor Koch[a] and Michael Ruck*[a]
Keywords: Bismuth; Coordination polymers; Hydrates; Thiocyanates; X-ray diffraction
Abstract. Yellow crystals of Bi(SCN)3·½H2O are obtained by reacting All thiocyanate anions bind with both ends to different cations. The
¯
(BiO)2CO3 and HSCN in aqueous solution. X-ray diffraction on a sin- coordination network expands in plane layers parallel (1 1 0). The
gle-crystal revealed a triclinic lattice (space group P1) with a = water molecule coordinates one of the two independent Bi3+ cations.
¯
843.6(2) pm, b = 920.4 (2) pm, c = 1210.7(2) pm, α = 109.16(3) °, Dehydration sets in at 100 °C, followed by stepwise thermal decompo-
β = 109.06(3) °, γ = 90.22(3) °, V = 832.8(3)·106 pm3, and Z = 4. sition to Bi2S3.
Introduction
Experimental Section
Synthesis
The thiocyanate anion belongs to the so-called pseudo-halo-
genides. Salts with such monovalent bi- or triatomic anions
show extensive chemical similarity to the corresponding halo-
genides. In the context of metal-rich compounds, however, the
number of corresponding low-valent pseudo-halogenides is
much smaller than would be expected. Most examples are
found with thiocyanate or azide as terminal ligands of Nb6Cl12
cluster cores [1]. In analogy to the chemistry of bismuth-rich
halogenides [2], the synproportionation of bismuth with
Bi(SCN)3 could be a potential synthetic approach to low-valent
thiocyanates. Surprisingly, reliable information on Bi(SCN)3,
including its crystal structure, is not available.
Bi(SCN)3·½H2O was synthesized from (BiO)2CO3 and HSCN accord-
ing to [7]:
(BiO)2CO3 + 6HSCN → 2Bi(SCN)3·½H2O + CO2 + 2H2O.
In a three-necked flask (NH4)2SO4 (40 g, Grüssing, 99.5 %) was dis-
solved in H2O (10 mL). Two dropping funnels with (a) NH4SCN
(75 g, Grüssing, 99 %) dissolved in H2O (300 mL) and (b) an aqueous
solution of H2SO4 (100 g, 120 mL, Biesterfeld, 95–97 %) were
mounted. H2SO4 (30 g, 95–97 %) was added to the (NH4)2SO4 solu-
tion and the flask was heated to 60 °C. Simultaneously, both solutions
were added dropwise. The freshly produced HSCN was distilled at
reduced pressure (20–50 Pa) and condensed into an ice-cooled re-
ceiver. Addition of (BiO)2CO3 (Schering) to the distillate resulted in
the evolution of gas and the solution turned orange. After 1 h of stir-
ring, the solution was separated from the excess (BiO)2CO3.
The existence of bismuth thiocyanate has already been sug-
gested in the 19th century by Bender [3]. In 1906, Rosenheim
and Vogelsang mentioned a hydrate with the (unlikely) compo-
sition Bi(SCN)3·14H2O [4]. Later, the structures of complex
salts like RbBi(SCN)4 [5] or Cs2Na[Bi(SCN)6] [6] were re-
ported. In accordance to the HSAB principle, the bismuth cat-
ion is coordinated by the “soft” sulfur atom, whereas the
“hard” nitrogen atom binds preferably to the alkaline metal
cation. The first structural information on Bi(SCN)3, which
was synthesized by the method of Gallais and Familiades [7],
was provided by Bensch et al., who proposed a triclinic cell
Fractions of the orange solution were used for probing several crystalli-
zation methods. Evaporation at ambient conditions yielded yellow
crystals, the use of a rotary evaporator resulted in yellow powder. Yel-
low crystals and orange powder were obtained by extraction with
MeCN, DMF, THF, Et2O, or ethyl acetate and subsequent evaporation
of the solvent. Tests with DMSO, toluene, or hexane were not success-
ful.
Alternatively, the metathesis reaction of bismuth halogenides with thio-
cyanates of the alkaline metals [9] in the eutectic mixture
n(NaSCN):n(KSCN) = 7:3 (melting point 122 °C) [10], following the
reaction
¯
(space group P1, a = 662.9(3) pm, b = 1178.4(6) pm, c =
1200.8(5) pm, α = 114.18(4) °, β = 102.33(5) °, γ = 98.59(5) °,
V = 805.9·106 pm3) [8].
In view of this, we attempted to grow crystals of bismuth
thiocyanate following diverse synthetic strategies. What we
were able to characterize by single-crystal diffraction turned
out to be the hemihydrate Bi(SCN)3·½H2O.
BiX3 + 3MSCN → Bi(SCN)3 + 3MX,
as well as the corresponding Finkelstein reaction in dry acetone were
tested. In both cases, the precipitation of MX was observed, but suitable
crystals of bismuth thiocyanate were not obtained.
* Prof. Dr. M. Ruck
Vibrational Spectroscopy
Fax: +49-351-463-37287
E-Mail: michael.ruck@chemie.tu-dresden.de
[a] Fachrichtung Chemie und Lebensmittelchemie
Technische Universität Dresden,
01062 Dresden, Germany
The infrared spectrum of a pressed pellet of Bi(SCN)3·½H2O with KBr
was recorded with a Nicolet Magna-IR 550 Series II spectrometer. The
spectrum of a pure KBr sample was subtracted. The Raman spectrum
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G. Koch, M. Ruck
ARTICLE
Table 1. Coordinates and equivalent isotropic displacement parameters
of the atoms in Bi(SCN)3·½H2O at 293(2) K. Ueq (in pm2) is defined
as one third of the trace of the orthogonalized tensor Uij.
of a Bi(SCN)3·½H2O crystal was measured using a Raman microscope
Renishaw RM 2000 equipped with a CCD detector and an 800 L·mm–1
lattice monochromator. The wavelength of the laser was 632.9 nm, the
power of the beam on the sample was 0.3 mW.
Atom
x
y
z
Ueq/Uiso
Bi1
Bi2
S1
0.30158(3) 0.26911(2) 0.07828(2) 281.7(7)
0.23536(3) 0.19707(2) 0.44276(2) 309.4(7)
Thermal Analysis
–0.0248(2) 0.2613(2)
–0.0659(2) 394(4)
–0.1091(1) 388(3)
S2
0.3864(2)
0.6741(2)
0.5234(2)
0.4844(2)
0.0470(3)
0.0909(2)
0.3516(2)
0.2272(2)
0.1659(2)
0.3175(2)
Bi(SCN)3·½H2O was heated to 700 °C (rate 5 °C·min–1) in an open
Al2O3 crucible inside a thermobalance (Netzsch STA 409 PC Luxx).
The atmosphere was a stream (100 mL·min–1) of Ar (99.999 %).
S3
0.1469(2)
0.3392(1)
0.6417(2)
0.5810(2)
385(4)
315(3)
429(4)
498(5)
S4
S5
S6
N1
N2
N3
N4
N5
N6
C1
C2
C3
C4
C5
C6
O
–0.1971(7) –0.0102(6) –0.0843(6) 434(14)
0.0704(8)
0.6991(8)
0.6647(7)
0.7020(9)
–0.1674(8) 0.0551(6)
–0.1220(8) 0.0992(7)
–0.0653(7) –0.2804(5) 517(15)
X-ray Crystallography
0.5413(7)
0.5370(6)
0.4406(7)
0.0139(6)
0.4637(5)
0.7361(6)
0.5349(6)
–0.0729(6) 320(14)
–0.2081(6) 346(14)
0.0669(6)
0.4133(5)
0.6958(6)
0.5526(6)
0.2731(5)
0.249(6)
468(15)
378(12)
544(17)
447(14)
Intensity data of a single-crystal (yellow flat needle) were collected at
293(2) K with an imaging plate diffraction system IPDS-II (Stoe) using
graphite-monochromated Mo-Kα radiation. The raw-data were cor-
rected for background, polarization and Lorentz factors. The micro-
scopic description of the crystal shape, which was later used in the
numerical absorption corrections (μ(Mo-Kα) = 21.9 mm–1; max./ min.
transmission: 0.864/0.161) [11], was optimized using sets of reflections
that are equivalent in the triclinic Laue class [12]. The structure was
solved with direct methods [13] and subsequent difference Fourier syn-
0.1978(9)
0.6862(8)
0.6080(8)
0.6118(9)
0.0001(7)
0.4642(7)
0.4092(7)
0.3276(7)
305(13)
269(12)
383(15)
359(15)
484(13)
470(150)
–0.0806(9) 0.1628(7)
0.1044(7)
0.111(9)
0.005(11)
0.3237(6)
0.416(8)
0.306(9)
¯
H1
H2
theses in the space group P1 (no. 2). Even the hydrogen atoms could
0.235(7)
Uiso(H1)
be localized, although with high standard deviations of their parame-
ters. For the hydrogen atoms a common isotropic displacement param-
eter could be refined, whereas anisotropic displacement parameters
were determined for the other atoms. Atomic parameters are listed in
Table 1, selected interatomic distances in Table 2. Data in brief: 15033
reflections measured, 5406 unique; –12 ≤ h ≤ 12, –13 ≤ k ≤ 13, –17
≤ l ≤ 17, 2θmax = 64°; Rint = 0.043, Rσ = 0.076; extinction parameter:
145(6)·10–5; 198 parameters; R1 = 0.033 for 3444 Fo > 4σ(Fo), R1 =
0.066 for all Fo, wR2 = 0.045; residual electron density 1.5 to –1.9
e·10–6 pm–3). The experimental powder diffractogram, which was
measured with a Stadi-P powder diffractometer (Stoe) using Cu-Kα1
radiation, nicely matches the calculated pattern. Further data, in the
form of a CIF, have been deposited with the Fachinformationszentrum
Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (E-Mail: crys-
data@fiz-karlsruhe.de), as supplementary publication no. CSD-
421612, and can be obtained by contacting the FIZ quoting the article
details and the CSD number. Graphic representations of the crystal
structure were developed with the program Diamond [14].
Table 2. Selected interatomic distances (in pm) for Bi(SCN)3·½H2O.
Symmetry operators: (i): x, y, z; (ii): 1 –x, 1–y, –z; (iii): –x, –y, –z; (iv):
1–x, 1–y, 1–z; (v): –x, –y, 1–z.
Bi1–
N3ii
N1iii
S2i
235.9(5) Bi2–
256.9(5)
N4iv
N6v
Oi
235.1(5)
250.8(5)
262.6(5)
266.2(2)
266.3(6)
273.0(2)
312.4(2)
264.1(2)
S1i
272.2(2)
S6i
N5iv
S3i
288.0(7)
N2iii
S5i
300.1(2)
S4i
325.2(2)
S4i
S–
C
164.0(7)– N–
166.3(6)
C
112.8(7)–
114.8(8)
The crystal structure of Bi(SCN)3·½H2O consists of two-di-
mensional coordination networks that form plane layers paral-
Results and Discussion
¯
lel (1 1 0). The full width of one layer is 623 pm, which in-
Yellow transparent crystals of bismuth trithiocyanate hemi- cludes an estimated van der Waals gap of about 237 pm. Two-
hydrate, Bi(SCN)3·½H2O, were crystallized following the dimensional coordination networks were also found for
route of Gallais and Familiades [7]. Single-crystal X-ray dif- M(SCN)2 with M = Zn [16], Sn [17], and Hg [18], whereas
¯
fraction revealed a triclinic lattice (space group P1) with a = M(SCN)2 with M = Eu, Sr, Ba [9], Ni [19], Cd [20], and Pb
843.6(2) pm, b = 920.4 (2) pm, c = 1210.7(2) pm, α = [21] prefer three-dimensional connectivity.
109.16(3) °, β = 109.06(3) °, γ = 90.22(3) °, V =
The thiocyanate anions and the water molecules constitute
832.8(3)·106 pm3, and Z = 4. The powder pattern of the yellow the surface of the layer, whereas the Bi3+ cations are situated
crystals, which matches the results of the single-crystal struc- inside (Figure 1). The axes of thiocyanate anions are inclined
ture determination, deviates significantly from the pattern of to the plane with the nitrogen atoms pointing to the interior.
the microcrystalline orange by-product, which was described All thiocyanate anions coordinate with both ends to different
by Bensch et al. [8]. The unit cell volumes of the probably cations. Except for S4, which is μ2-bridging, all sulfur and
water-free orange powder and the yellow hemihydrate differ nitrogen atoms are non-bridging. The bond angle in the thiocy-
by 26.9·106 pm3, which corresponds to 8.1 cm3·mol–1 (H2O). anate anions differs by 1.2(7) ° to 4.7(6) ° from 180 °. The S–
Biltz has listed volume increments between 8 and 11 cm3·mol–1 C bond lengths range from 164.0(7) to 166.3(6) pm, the N–C
(H2O) [15].
bond lengths from 112.8(7) to 114.8(8) pm. Considering the
1988
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Z. Anorg. Allg. Chem. 2010, 1987–1990

The Layered Coordination Polymer Bi(SCN)3·½H2O
given accuracy, these distances and angles agree with literature nitrogen atoms. Bi2 binds to three sulfur and three nitrogen
data [9].
atoms, and to one oxygen atom. The application of the bond
length bond-strength concept [22] in the version of Brese and
O’Keeffe [23] and bond valence parameters RBiS = 255 pm,
RBiN = 224 pm, and RBiO = 209 pm, results in bond valence
sums of 3.17(3) for Bi1 and 3.34(3) for Bi2. Even in view of
the error limits of the concept, the formula, and the parameters,
the calculated valence sum of Bi2 is too large (the given stand-
ard deviation is based only on the standard deviations of the
distances). It can be argued that the dative bond of the oxygen
atom, which contributes about 0.23 to the sum, is not properly
handled. In particular, the hydrogen atoms do not bind to any
other atom and thus, in strict application of the principle, the
oxygen atom of the water molecule should have no remaining
valence.
The vibrational spectra of Bi(SCN)3·½H2O (Figure 3) can be
interpreted in analogy to the detailed analysis of the Ba(SCN)2
spectra by Wickleder [9]. The low-frequency Raman bands be-
low 250 cm–1 are attributed to modes that include bismuth at-
oms. The bands at higher frequencies in both spectra can be
assigned to internal vibrations of the thiocyanate anion:
δ(SCN) between 432 cm–1 and 460 cm–1; ν(CS) between
719 cm–1 and 787 cm–1; 2δ(SCN) between 889 cm–1 and
997 cm–1; ν(CN) between 2003 cm–1 and 2144 cm–1. The IR
absorption at 1620 cm–1 originates from the bending mode of
the H2O molecule [24].
¯
Figure 1. Layered coordination network parallel (1 1 0) in the crystal
structure of Bi(SCN)3·½H2O. The sulfur atoms of the thiocyanate ani-
ons and the water molecules constitute the layer surface.
For the orientation of the water molecule, the bonding of the
oxygen atom to the Bi2 cation seems to be the determining
factor; the secondary bond to Bi1 is almost 60 pm longer (Fig-
ure 2). The hydrogen atoms, which were (approximately) lo-
calized by X-ray diffraction, are situated on the reverse site of
the donating lone-pairs of the oxygen atom and point in the
opposite direction of the Bi2–O bond. Thus, the potential hy-
drogen bridge O–H1···N5, which is strongly bend (O···N5
276 pm, H1···N5 ~200 pm, angle at H1 < 135°), is most likely
not essential for the structure.
Figure 3. IR (top) and Raman spectra (below) of Bi(SCN)3·½H2O.
In contrast to the water-free thiocyanates M(SCN)2 with M =
Eu, Sr, Ba [9], the hemihydrate Bi(SCN)3·½H2O does not melt
congruently, but decomposes in several steps in the course of
heating. In a dynamic thermogravimetric heating experiment
(Figure 4) the sample lost 1.9 wt.-% above 70 °C, which is
assigned to adherent moisture. The following weight loss of
again 1.9 wt.-% is probably caused by the coordination water
(calcd. 2.3 wt.-%). The product of the dehydration step, which
is completed at 190 °C, proved to be amorphous in the X-ray
diffraction experiment. Above 260 °C, the thiocyanate anions
decompose successively into sulfide anions and gas phase spe-
cies, probably CS2, (CN)2, and N2 [25]. For the decay of one
Figure 2. Coordination of the Bi3+ cations in Bi(SCN)3·½H2O. Ellip-
soids indicate 70 % probability. Distances are given in pm.
The coordination number of both symmetry independent Bi3+ of the six crystallographically distinct thiocyanate anions, a
cations is seven. Bi1 is coordinated by four sulfur and three weight loss of 5.35 wt.-% is anticipated. Starting at 260 °C,
Z. Anorg. Allg. Chem. 2010, 1987–1990
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
1989

G. Koch, M. Ruck
ARTICLE
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310 °C, and 610 °C, one, another three, and the last two
groups undergo decomposition. The product after heating to
700 °C and cooling to room temperature is Bi2S3, which was
identified by powder diffraction. The integral weight loss
matches quite nicely.
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Bi(SCN)3·½H2O was characterized as one product of the
aqueous synthesis of bismuth thiocyanate. Thermal dehydra-
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der. Nevertheless this material can be used for further synthe-
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Acknowledgement
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Received: April 1, 2010
Published Online: June 2, 2010
1990
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© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2010, 1987–1990