A Comprehensive Study on the Full Series of Alkali-Metal Selenocyanates AI[SeCN] (AI=Li?Cs)

Article abstract of DOI:10.1002/chem.202102058

The full series of quasibinary alkali-metal selenocyanates was synthesized either by oxidation of the respective cyanides (A=Li?Rb) or by metathesis (A=Cs). For Li[SeCN] only ball-milling and subsequent annealing led to the isolation of the quasibinary selenocyanate. Their structures were refined from single-crystal and powder X-ray data. The respective solid-state IR and Raman spectra were interpreted with the aid of solid-state quantum-mechanical calculations and DSC-TGA measurements allowed for extraction of melting points. Only for Li[SeCN] a possible phase transition was observed that is discussed on the basis of VT-PXRD experiments. It is also the only quasibinary selenocyanate to form a hydrate (Li[SeCN] ? 2H₂O).

Full text of DOI:10.1002/chem.202102058

Accepted Article
Accepted Article
Title: A Comprehensive Study on the Full Series of Alkali Metal
Selenocyanates AI[SeCN] (AI = Li – Cs)
Authors: Alena Shlyaykher, Marvin Ehmann, Antti J. Karttunen, and
Frank Tamborino
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To be cited as: Chem. Eur. J. 10.1002/chem.202102058
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A Comprehensive Study on the Full Series of Alkali-Metal
Selenocyanates AI[SeCN] (AI = Li – Cs)
Alena Shlyaykher,[a] Marvin Ehmann,[a] Antti J. Karttunen[b] and Frank Tambornino*[a]
Dedication ((optional))
[a]
Alena Shlyaykher, Marvin Ehmann, and Dr. Frank Tambornino
Fachbereich Chemie and Wissenschaftlichen Zentrum für Materialwissenschaften (WZMW)
Philipps-Universität Marburg
Hans-Meerwein-Strasse 4, D-35043 Marburg, Germany
E-mail: frank.tambornino@chemie.uni-marburg.de
Dr. Antti J. Karttunen
[b]
Department of Chemistry and Materials Science
Aalto University
Kemistintie 1, 02150 Espoo
Supporting information for this article is given via a link at the end of the document.
Abstract: The full series of quasibinary alkali-metal selenocyanates
was synthesized either by oxidation of the respective cyanides
(A = Li–Rb) or by metathesis (A = Cs). For Li[SeCN] only ball-milling
and subsequent annealing led to the isolation of the quasibinary
selenocyanate. Their structures were refined from single-crystal and
powder X-ray data. The respective solid-state IR and Raman spectra
were interpreted with the aid of solid-state quantum-mechanical
calculations and DSC-TGA measurements allowed for extraction of
melting points. Only for Li[SeCN] a possible phase transition was
observed that is discussed on the basis of VT-PXRD experiments. It
is also the only quasibinary selenocyanate to form a hydrate
(Li[SeCN] • 2H2O).
confirming the linear structure of the anion.[5] Nowadays, K[SeCN]
is commercially available and the selenocyanate starting material
of choice for inorganic and organic chemists. The heavier
tellurocyanate was first synthesized in 1968 and is, probably
owing to its instability, the least studied of all
chalcogenocyanates.[6,7]
Up until now, research on selenocyanates has been focussing on
its use as ligand in complex compounds. All chalcogenocyanates
are potentially ambidentate and will form N- or Ch-bonded
complexes depending on the metal ion. Additionally, they also
exhibit a range of bridging modes which has been used in the
construction of metal organic frameworks.[8–10] In organic
chemistry, both the R–Se–C≡N and R–N=C=Se forms are known.
Especially substances comprising the latter motif have received
considerable attention as key intermediates towards the synthesis
of Se-containing heterocycles. Such compounds are potential
chemotherapeutic agents against cancer or infection diseases.[11]
Introduction
Chalcogenocyanates are archetypical pseudohalide anions with
the general formula ChCN− (Ch = chalcogen). Of the potential six
candidates (including Po and Lv), only the lightest four
homologues have been synthesized so far: Cyanate (OCN−),
thiocyanate (SCN−), selenocyanate (SeCN−), and tellurocyanate
(TeCN−). Especially the chemistry of the cyanate and thiocyanate
anions has been researched extensively and features in
introductory and general chemistry textbooks. Due to their
stability, ease of handling and ready availability, they have been
widely used in coordination and organic chemistry. In contrast,
selenocyanates and tellurocyanates are less stable and handling
of these anions on air results in decomposition and deposition of
elemental selenium and tellurium, respectively.
Fusion of potassium hexacyanoferrate(II) with sulphur had been
shown to yield potassium thiocyanate. Consequently, reaction
with–the by that time new element–selenium led to the synthesis
of K[SeCN], probably the first selenocyanate containing
compound, albeit with low yields.[1] Showing that the
selenocyanate anion was in principle stable, the synthesis of
K[SeCN] by oxidation from readily available KCN with Se was
soon thereafter developed, proceeding in aqueous[2] and non-
aqueous[3] solvents, as well as in melt,[4] yielding mostly pure
product. Its crystal structure was studied decades later,
Considering
the
historical
and
recent
interest
in
(iso)selenocyanates it is all the more surprising how little is known
about the simple quasibinary salts of the selenocyanate anion.
While reports on the syntheses of Na[SeCN][3] and Cs[SeCN][12,13]
can be found in literature, their crystal structures have not been
reported. In fact, the only other reported crystal structure of a
quasibinary selenocyanate is that of Hg(SeCN)2,[14] which was
reported alongside the homoleptic complexes M2[Hg(SeCN)4]
(M = K, Cs).[14]
In this contribution we present the full series of alkali-metal
selenocyanates. Their syntheses, crystal structures, and thermal
behaviours are discussed alongside vibrational spectroscopy (IR,
Raman) which is corroborated by solid-state quantum mechanical
calculations.
Results and Discussion
Syntheses
K[SeCN] is easily synthesized by oxidizing KCN with grey
selenium, as has been reported before.[15] The starting materials
are combined and refluxed in dry ethanol yielding a solution of
1
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K[SeCN] alongside insolubles e.g. surplus selenium or common
impurities of KCN. If freshly precipitated red selenium is used
instead, the reaction proceeds in solution at r.t. within minutes.
Filtration and concentration of the resulting solution under
reduced pressure affords K[SeCN] as an off-white powder in 98%
isolated yield containing single crystals suitable for XRD.
Na[SeCN] is obtained similarly from NaCN and is also obtained in
very good yields up to 99% as an off-white powder. Crystals
suitable for SC-XRD were prepared by dissolution of 3.5 g
Na[SeCN] in 1 ml degassed water at r.t. and subsequent slow
evaporation of the solvent in a stream of argon.
Synthesis of Cs[SeCN] via salt metathesis reaction starting from
CsCl has been reported and was replicated by us in good yields
up to 75%. Attempted synthesis of Rb[SeCN] from K[SeCN] and
RbCl resulted in incomplete metathesis reaction and formation of
KxRb1−x[SeCN] with x = 0.1–0.3. Pure samples of Rb[SeCN] in
good yields were obtained by similar conditions as applied for the
syntheses of Na[SeCN] and K[SeCN].
The synthesis of Li[SeCN] was somewhat more challenging as
the identification of a suitable solvent for salt metathesis was not
straightforward. Reactions starting from K[SeCN] and LiCl in
acetonitrile proceeded under formation of KCl (identified by
PXRD) indicating a successful metathesis reaction. However,
upon concentrating the solution under reduced pressure, a gloopy
liquid was obtained which solidifies around 5 °C. 13C- and 77Se-
NMR spectroscopy showed signals for selenocyanate alongside
larger amounts of solvent and SC-XRD indicated the formation of
[Li(NCMe)3(SeCN)]. Not unsurprisingly, coordinated acetonitrile
could not be removed under reduced pressure. Application of
elevated temperatures led to decomposition of the material under
deposition of red Se. Salt metathesis reactions in other solvents
had similar outcomes.
Oxidation of LiCN with grey or red selenium performed in various
solvents suffered from similar formation of solvated compounds
(e.g. Li[SeCN] • 2H2O, see below) which led us to explore solvent-
free synthetic methods. Mechanochemical synthesis of Li[SeCN]
in a ball-mill (from LiCN and grey selenium) allowed isolation of a
grey, initially X-ray amorphous powder after only 5 minutes. 13C-
and 77Se-NMR alongside vibrational spectroscopy indicated
absence of cyanide and formation of the selenocyanate anion. An
endothermic signal in DSC-TGA measurements at 228 °C was
accompanied by steady loss of mass over time and thus assigned
to the melting point coinciding with a high vapour pressure.
Heating a sample in fused borosilicate glass ampoules to 250 °C
with subsequent slow cooling to r.t. resulted in formation of crystal
needles several millimetres long (identified as Li[SeCN] by SC-
XRD) alongside minor amounts of a grey powder (identified as
Li2Se by PXRD).
Figure 1. The crystal structure of Li[SeCN] (Na[SeCN] crystallizes isotypically).
a: Coordination around the cation in the form of a clinched octahedron. b: Stack
of octahedra with rod group symmetry pb 1 21/m 1. c: 2×1×2 supercell
emphasizing the distorted pseudohexagonal rod packing. Thermal
displacement ellipsoids drawn at 75% probability level. White: C, blue N, red:
Se, grey: A.
Cations occupy the Wyckoff position 4b (site symmetry −1) and
they are surrounded by six SeCN− anions occupying position 4c
(site symmetry .m.) in the form of a clinched octahedron. Four
SeCN− anions coordinate with their selenium (d(Li–Se) = 2.8316(4)
and 2.9186(4) Å, d(Na–Se) = 3.0457(1) and 3.0744(2) Å) two with
their nitrogen terminus (d(Li–N) = 2.143(3), d(Na–N) = 2.4635(8) Å) as
shown in Figure 1 a, leading to CN = 6.
In the extended crystal structure the octahedra share faces thus
forming columns along [010] (see Figure 1 b). The columns exhibit
rod group symmetry pb1 21/m 1 (no. 12) and its lattice periodicity
is the b axis of the parent space-group. The rods pack in the form
of a distorted pseudohexagonal rod packing (see Figure 1 c).
However, the structural description can be simplified if only the
centres of the octahedra, the cation positions, are considered. In
this case those form the distorted motif of a hexagonal primitive
packing where the SeCN− anions occupy the trigonal prismatic
voids thus forming a distorted variant of the NiAs-type.
Crystal structures of Li[SeCN] and Na[SeCN]
The crystal structures of Li[SeCN] and Na[SeCN] are isotypical in
the orthorhombic system with space-group Pnma (no. 62,
Li[SeCN]:
a = 7.8873(4),
b = 6.2442(4),
c = 5.4941(3) Å;
Na[SeCN]: a = 8.1745(4), b = 7.0647(3), c = 5.7171(3) Å) with 4
formula units in the unit cell (see Table S1 for details on data
collection and structure refinement). Phase purity was confirmed
by PXRD (for Li[SeCN] small amounts of Li2Se were identified as
side phase) and subsequent Rietveld refinement confirmed the
model within small margins (see Table S3 and Figures S1 & S2).
The structures do not correspond to a known structure type.
Crystal structure of K[SeCN]
The crystal structure of K[SeCN] has been described previously[5]
and was here redetermined with higher precision of lattice
parameters, atomic coordinates, interatomic distances and
angles. K[SeCN] crystallizes in its own structure type in the
monoclinic system with space-group P21/c (no. 14, a = 4.4211(9),
b = 7.502(2), c = 11.781(2) Å, β = 101.63(3)°), see Table S1 for
2
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details on data collection and structure refinement. Phase purity
was confirmed by PXRD and subsequent Rietveld refinement
confirmed the model within small margins (see Table S3 and
those pack in the type of a distorted hexagonal rod packing (see
Figure 2 c).
Crystal structures of Rb[SeCN] and Cs[SeCN]
Rb[SeCN] and Cs[SeCN] crystallize isotypically in the Cs[SCN]-
type in space-group Pnma (no. 62, Rb[SeCN]: a = 7.9241(2),
b = 6.0678(2), c = 8.0988(3) Å, Cs[SeCN]: a = 8.1188(6),
b = 6.3387(3), c = 8.4813(5) Å) with 4 formula units in the unit cell
(see Table S1 for details on data collection and structure
refinement). Phase purity was confirmed by PXRD and
subsequent Rietveld refinement confirmed the model within small
margins (see Table S3 and Fig. S4 & S5). Cell parameters for
Cs[SeCN] have been reported previously, albeit without refined
data or a structure model.[13] We were able to confirm the
parameters and rule out the suggested space-group type Pn21a.
Figure 3. Crystal structure of Rb[SeCN] (Cs[SeCN] crystallizes isotypically). a:
Coordination around the cation in the form of a severely distorted cube. b:
Coordination sphere around the SeCN− anion. c/d: Extended unit cells viewed
along [010] and [001], respectively. Thermal displacement ellipsoids drawn at
75% probability level. White: C, blue N, red: Se, grey: A.
Figure S3).
Figure 2. The crystal structure of K[SeCN]. a: Coordination around potassium
in the form of a capped trigonal prism. b: formation of distorted K2N2 squares
stacked along [100] with rod group symmetry pa −1. c: 1×2×2 supercell
emphasizing the distorted pseudohexagonal rod packing. Thermal
displacement ellipsoids drawn at 75% probability level. White: C, blue N, red:
Se, grey: A.
The structure consists of layers (see Figure 3 d) in the ab plane
which are stacked along [010]. Each cation is surrounded by four
SeCN− anions from this plane (d(Rb–N) = 3.005(6) and 3.001(5) Å,
d(Rb–Se) = 3.5959(8) and 3.6344(8) Å, d(Cs–N) = 3.176(5) and
3.195(5) Å, d(Cs–Se) = 3.7570(6) and 3.7975(6) Å). From the
planes above and below four additional SeCN− anions are in close
proximity two of which connect via their selenium terminus (d(Rb–
Se) = 3.7625(5) Å and d(Cs–Se) = 3.9097(4) Å) and two via their
nitrogen terminus (d(Rb–N) = 3.274(2) Å and d(Cs–N) = 3.397(2) Å).
In total this results in a coordination polyhedron with 8 vertices
which can be best described as a highly distorted cube (see
Figure 3 a).
All atoms occupy the general position with Wyckoff symbol 4e.
The potassium ion is coordinated by seven selenocyanate anions
forming a capped trigonal prism (Figure 2 a). The four the K–Se
distances are in the expected range (3.339(1) to 3.444(1) Å). Two
of the three K–N distances are 2.813(3) and 3.010(3) Å which is
in the expected range for the sum of their ionic radii, and one
distance is considerably larger (3.810(1) Å) leading to (6+1)
coordination of the potassium ion.
The selenocyanate anions are located in between the potassium
ions with each nitrogen terminus connecting to three, each
selenium terminus to four other potassium cations. When only the
K–N contacts are taken into account, one can construct a ladder
In contrast to A[SeCN] (A = Li–K) the extended structures of
Rb[SeCN] and Cs[SeCN] cannot be rationalized by packing of
rods but are better described by the cation positions. In the ab-
plane the cations form a rectangular motif which is stacked in an
A–B–C–D sequence along [001] (see Figure S7). The individual
rectangular motifs are then interconnected by selenocyanate ions.
The structure is related to the CsI3 type where the cation positions
are similar and atoms from the selenocyanate anion occupy
halogen atom positions. Here, the nitrogen atom occupies the
of distorted K2N2 squares (∢K–N–K = 108.02(9)° and
∢
N–K–
N = 71.98(8)°, see Figure 2 b) which extends along [100]. The rod
itself exhibits rod group symmetry pa −1 (no. 2) and its lattice
periodicity is the a axis of the parent space-group. Due to space-
group symmetry there are two orientations of this ladder and
−
more ionic position of the unsymmetric I3 anion, evident by the
3
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near tetrahedral coordination with four cations in close contact
(see Figure 3 b). The less ionic C–Se part is surrounded by six
cations in total, two of which show long interatomic distances
(d(Se–Rb) = 3.9588(5) Å, d(Se–Cs) = 4.0757(4) Å) and are also in the
coordination sphere of the N atom.
network (d(Se–H) = 2.56(2) Å, see Figure 4 c). Within the rods there
are also weak Se–H hydrogen bonds with d(Se–H) = 2.90(2) Å.
Geometry of the SeCN− anion
For all structures discussed here the SeCN− anion is almost linear
with angles 176.7(5)–179.8(1)°. The Se–C bond lengths range
from 1.8073(4)–1.8176(1) Å and are longer than the C=Se double
bond in CSe2 (1.692(2) Å) and shorter than the C–Se single bond
in Se(Ph)2 (1.924(3) Å).[17,18] C–N distances in the SeCN− anion
range from 1.1571(2)–1.1648(2) Å and are thus comparable to a
C≡N triple bond (1.16 Å).
Crystal structure of Li[SeCN] • 2H2O
Of all alkali-metal selenocyanates, only Li[SeCN] forms a hydrate.
Li[SeCN] • 2H2O crystallizes isotypical with Li[SCN] • 2H2O[16] in
the orthorhombic system with space-group Pnma (no. 62,
a = 5.7131(2), b = 8.3814(2), c = 9.8823(3) Å) with Z = 4 (see
Table S2 for details on data collection and structure refinement).
Li, N, C, and Se atoms occupy the position with Wyckoff symbol
4c, whereas the H2O molecules occupy the general position 8d.
Each cation is surrounded by four H2O molecules (d(Li–
O) = 2.116(3) and 2.071(3) Å, see Figure 4 a) and two SeCN−
anions which both coordinate via their N-terminus.
Vibrational spectra
For all quasibinary alkali-metal selenocyanates their structures in
the solid state were optimized with the DFT-PBE0-D3 method and
IR and Raman spectra were calculated. Experimental structures
were reproduced within small margins. The calculated vibrational
frequencies have been obtained within the harmonic
approximation and they are systematically overestimated in
comparison to the experimental frequencies. Details on
methodology, calculated band positions and assignments are
given in the Supporting Information.
The IR spectra of all selenocyanates are dominated by the ν1
(“antisymmetric”) stretching mode of the selenocyanate anion
(2055–2089 cm−1, see Table 1). Only for Li[SeCN] also the ν2
(“symmetric”) stretching mode can be observed at 588 cm−1.
Table 1. Comparison and assignment of IR-active bands for A[SeCN] with
A = Li–Cs. All values given in cm−1, literature value for K[SeCN] given in
parentheses.
Compound
Li[SeCN]
ν1 stretching
2089
ν2 stretching
588
Reference
this work
2224, 2214
2057
638, 632
not obs.
DFT-PBE0-D3
this work
Na[SeCN]
K[SeCN]
2232, 2227
2069 (2070)
2202, 2199
2057
605, 600
not obs. (558)
604, 604
not obs.
DFT-PBE0-D3
this work, [19]
DFT-PBE0-D3
this work
Rb[SeCN]
Cs[SeCN]
Figure 4. Crystal structure of Li[SeCN] • 2H2O. a: Coordination around the
cation in the form of an unsymmetrical square bipyramid. b: Rod of face sharing
polyhedral with rod group symmetry pa 1 21/m 1. c: Extended unit cell viewed
along [100] emphasizing the distorted pseudohexagonal rod packing and the
Se–H network (dashed contacts). Thermal displacement ellipsoids drawn at
75% probability level. White: C, blue N, red: Se, magenta: O, small white: H
grey: A.
2181, 2178
2055
604, 604
not obs.
DFT-PBE0-D3
this work
2189, 2181
603, 601
DFT-PBE0-D3
Similarly, the Raman spectra are also dominated by the ν1
stretching mode of the selenocyanate anion which here are a
combination of B3g and Ag modes (2101–2055 cm−1, see Table 2).
In all cases the ν2 mode is also observed (571–586 cm−1). While
the δ1 rocking mode of SeCN− calculated for ~450 cm−1 is
unobserved for all compounds, lattice vibrations can be observed
at low wavenumbers for A[SeCN] (A = Li−Rb) selenocyanates.
Lattice vibrations for Cs[SeCN] are out of the range of Raman
spectroscopy and calculated to be at 100 cm−1.
However, one anion is significantly farther away (d(Li–
N) = 2.871(5) Å) than the other (d(Li–N) = 2.080(5) Å) leading to a
5+1 coordination of the cation in the form of a distorted
unsymmetrical square bipyramid.
Both the selenocyanate anion and the water molecules serve as
bridging ligands connecting the cations into rods with rod-group
type pa 1 21/m 1 that extend along [100] (see Figure 4 b). The rods
form the motif of a distorted pseudohexagonal rod packing and
are themselves interconnected by a Se–H hydrogen bonding
4
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Figure 5. PXRD patterns of Li[SeCN] at 70 °C (front) and from 100 °C to 240 °C
(back) in 20K increments. * marks reflections of the proposed metastable phase,
# the strongest reflection for the Pnma phase.
Table 2. Comparison and assignment of Raman-active bands for A[SeCN] with
A = Li–Cs. All values given in cm−1, literature value for K[SeCN] given in
parentheses.
Compound
LiSeCN]
ν1
ν2
lattice
vibration
Reference
stretching
stretching
For as-synthesized Li[SeCN], the amorphous–to–crystalline
phase transition is a slow process starting at ca. 80 °C which was
verified by variable temperature powder X-ray diffraction (VT-
PXRD). If stored for prolonged (>6 months) time at ambient
temperature, however, samples of Li[SeCN] show broad
reflections (marked with asterisk in Figure 5) which do not
coincide with reflections for the Pnma-phase. The DSC-TGA data
also shows additional features at 115 and 154 °C. VT-PXRD
showed that upon heating to 80 °C the expected reflections for
the structural model in Pnma appear and the broad reflections
gradually disappear and are fully absent at T>160 °C. The DSC-
signal at 115 °C does not coincide with changes in the PXRD
pattern. Thus, we attribute the reflections to a still unknown
modification of Li[SeCN] the structure of which we were unable to
obtain thus far. Additionally, the molten Li[SeCN] shows a rather
high vapor pressure as evident by the constant mass-loss
observed in the TGA. If heated above the melting point in a sealed
capillary as used for PXRD measurements, the increased
pressure led to the bursting of the capillary around ca. 300 °C.
2090
586
150
this work
2215, 2204
2101
622, 619
573
166, 162
148
DFT-PBE0-D3
this work
Na[SeCN]
K[SeCN]
2230, 2224
2074 (2075)
2205, 2194
2064
602, 599
588 (558)
605, 604
564
163, 156
160
DFT-PBE0-D3
this work, [19]
DFT-PBE0-D3
this work
172, 166
153
Rb[SeCN]
Cs[SeCN]
2180, 2168
2057
605,604
571
161, 150
not obs.
100
DFT-PBE0-D3
this work
2180, 2172
601, 601
DFT-PBE0-D3
Thermal behaviour
Melting points for A[SeCN] (A = Li–Cs) have been obtained by
differential scanning calorimetry and thermal gravimetric analysis
(DSC-TGA) measurements. Initial experiments with 10 K/min
heating rates were conducted from r.t. to 1000 °C to find melting
points. Subsequent measurements with 1 K/min heating rates
were conducted to accurately determine the melting points, see
Table 3.
Conclusion
A[SeCN] (A = Li–Rb) were prepared by oxidation of the respective
cyanides with selenium either mechanochemically (Li[SeCN]) or
in solution (A = Na–Rb). Cs[SeCN] was prepared by metathesis
starting from CsCl and K[SeCN]. The coordination numbers of the
cations in the solid state increase with increasing ionic radius from
Li[SeCN]/Na[SeCN] (CN = 6), over K[SeCN] (CN = 6+1) to
Rb[SeCN]/Cs[SeCN] (CN = 8). Their crystal structures can be
rationalized by distorted hexagonal rod packings (for
Table 3. Melting points (onset) for A[SeCN] (A = Li–Cs) as measured from DSC-
TGA, values in °C. Literature value Cs[SeCN] given in parentheses.
Li[SeCN][a]
212
Na[SeCN]
273
K[SeCN]
155
Rb[SeCN]
133
Cs[SeCN]
224 (228)
Li[SeCN]/Na[SeCN]
and
K[SeCN]).
In
contrast,
Rb[SeCN]/Cs[SeCN] form a layered structure. Solely lithium
selenocyanate forms a hydrate with the formula Li[SeCN] • 2H2O.
Quantum chemical calculations of A[SeCN] allowed for complete
assignment of the recorded solid-state vibration spectra which are
dominated by the ν1 (“antisymmetric”) stretching mode of the
selenocyanate anion. Melting points were extracted from DSC-
TGA data. Amorphous as-synthesized Li[SeCN] stored for >6
[a] The amorphous–to–crystalline phase transition starts at ca. 80 °C.
We were able to reproduce previously reported melting point for
Cs[SeCN].[13] Possibly due to the different crystal structures, the
melting points do not follow a general trend. However, in the
isostructural pairs Li[SeCN]/Na[SeCN] and Rb[SeCN]/Cs[SeCN]
the respective heavier homologue exhibits the higher melting
point.
months shows broad reflections indicative for
metastable polymorph, which is currently under investigation.
a possibly
Experimental Section
Supporting Information. Experimental details, tables for SCXRD and
PXRD data incl. refinements, Raman and IR spectra, computational data,
and DSC-TGA data can be found in the Supporting Information.
Deposition Numbers 2080507 (for Li[SeCN]), 2080515 (for Na[SeCN]),
2080510 (for K[SeCN]), 2080509 (for Rb[SeCN]), 2080514 (for Cs[SeCN]),
2080516 (for [Li@12-crown-4][SeCN]), 2080518 (for [Li(MeCN)3SeCN]),
and 2080517 (for Li[SeCN]
• 2H2O) contain the supplementary
crystallographic data for this paper. These data are provided free of charge
by the joint Cambridge Crystallographic Data Centre and
Fachinformationszentrum Karlsruhe http://www.ccdc.cam.ac.uk/structures.
5
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Acknowledgements
FT thanks the Fonds der Chemischen Industrie for a Liebig
fellowship. FT thanks Prof. Dehnen for excellent support, Prof.
Müller and Prof. Kraus for discussions on the crystal structures.
Dr. Radostan Riedel is gratefully acknowledged for measuring the
single crystal dataset of Na[SeCN] and Jonathan Pfeiffer for
collecting Raman spectra.
Keywords: Selenocyanates • Crystallography • Solid-phase
synthesis • Vibrational spectroscopy • Alkali-metals
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10.1002/chem.202102058
Chemistry - A European Journal
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AI[SeCN] with AI = Li–Rb were synthesized by oxidation of cyanides with selenium or by metathesis (AI = Cs). Whereas all reactions
proceed in solution, LiSeCN can only be obtained solvent free by ball milling. All compounds were crystallographically characterized,
their structures optimized by DFT methods and their vibrational spectra recorded. DSC measurements showed congruent melting
and allowed for extraction of the melting points.
Institute and/or researcher Twitter usernames: @Uni_MR
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