Structural diversity in Cd(NCS)2-3-cyanopyridine coordination compounds: Synthesis, crystal structures and thermal properties

Article abstract of DOI:10.1515/znb-2019-0175

Five new compounds with the compositions [Cd(NCS)₂(3-cyanopyridine)₂]_n · 3-cyanopyridine (1), [Cd(NCS)₂(3-cyanopyridine)₂]_n · 1/3 3-cyanopyridine (2), [Cd(NCS)₂(3-cyanopyridine)₂]_n (3), {[Cd(NCS)₂]₂(3-cyanopyridine)₃}_n (4), and {[Cd(NCS)₂]₃(3-cyanopyridine)₄}_n (5) have been obtained by the reaction of Cd(NCS)₂ with 3-cyanopyridine in different solvents. While large amounts of compounds 1-4 could be prepared as powders, only a few single crystals of 5 were accidently obtained. Thermoanalytical investigations have shown that 4 could also be obtained by annealing of 1 or 2 and that under slightly different conditions 5 could be obtained as part of a mixture with 4. The crystal structures of all compounds can be divided in two sets of compounds. Compounds 1, 2 and 3 consist of chains in which the Cd cations show three different coordination environments and in which the coligands are only terminally bonded. In the structures of 4 and 5 similar chains are observed, which are connected into layers via some of the 3-cyanopyridine coligands.

Full text of DOI:10.1515/znb-2019-0175

Z. Naturforsch. 2019; aop
Aleksej Jochim, Inke Jess and Christian Näther*
Structural diversity in Cd(NCS) -3-cyanopyridine
coordination compounds: synt2hesis, crystal
structures and thermal properties
https://doi.org/10.1515/znb-2019-0175
Mn(II), Fe(II), Co(II), and Ni(II) contain N-terminally coor-
dinated thiocyanate anions and are of interest because,
e.g. several of them show spin crossover [1–4]. On the
other hand, compounds with bridging thiocyanate anions
are of importance because they can form dimers as well
as 1D and 2D networks, in which significant magnetic
exchange can be observed [5–14]. For the metal cations
mentioned above the coordination to the sulfur atom of
the anionic ligand is energetically unfavorable and there-
fore, such compounds are frequently difficult to synthe-
size from solution [15]. However, there is an alternative
approach reported in the literature that is based on ther-
mally induced ligand removal from precursor complexes
with terminal thiocyanate anions [15–17].
All this is completely different for coordination com-
pounds based on Cd(NCS)2, because this cation prefers
to coordinate to sulfur, which means that in this case
compounds with terminally N-bonded anionic ligands
are more difficult to synthesize [18–21]. Especially this
chemical behavior is the reason why the structural chem-
istry of Cd(NCS)2 coordination compounds is much richer
than that of the paramagnetic late first row transition
Received November 5, 2019; accepted November 20, 2019
Abstract: Five new compounds with the compositions
[Cd(NCS)2(3-cyanopyridine)2]nꢀꢀ·ꢀꢀ3-cyanopyridine
(1),
[Cd(NCS)2(3-cyanopyridine)2]nꢀꢀ·ꢀꢀ1/3
3-cyanopyridine
(2), [Cd(NCS)2(3-cyanopyridine)2]n (3), {[Cd(NCS)2]2(3-
cyanopyridine)3}n (4),and{[Cd(NCS)2]3(3-cyanopyridine)4}n
(5) have been obtained by the reaction of Cd(NCS)2 with
3-cyanopyridine in different solvents. While large amounts
of compounds 1–4 could be prepared as powders, only a
few single crystals of 5 were accidently obtained. Ther-
moanalytical investigations have shown that 4 could also
be obtained by annealing of 1 or 2 and that under slightly
different conditions 5 could be obtained as part of a mix-
ture with 4. The crystal structures of all compounds can
be divided in two sets of compounds. Compounds 1, 2 and
3 consist of chains in which the Cd cations show three dif-
ferent coordination environments and in which the coli-
gands are only terminally bonded. In the structures of 4
and 5 similar chains are observed, which are connected
into layers via some of the 3-cyanopyridine coligands.
Keywords: 3-cyanopyridine; cadmium thiocyanate; chain metals mentioned above and that compounds with more
compounds; crystal structures; thermal properties.
condensed thiocyanate networks can be easily synthe-
sized from solution [22–24]. This includes a large number
of compounds with different chain structures. In most
of them the metal cations are linked by pairs of anionic
ligands into chains, in which the cations show either an
all-trans or a cis-cis-trans coordination [25–30]. Depend-
ent on the actual metal coordination these chains can be
linear or corrugated, and there are also examples where
within such chains an alternating 5-fold and 6-fold Cd(II)
coordination is present [31]. Moreover, two of such chains
can be condensed into double chains with μ-1,1,3(S,N)-
coordinating thiocyanate anions, a structure type that is
reminiscent of spin ladders [32, 33]. Also 2D networks are
observed, in which the Cd(II) cations are linked by pairs
of anionic ligands into chains that are further linked into
layers by single μ-1,3(N,S)-bridging thiocyanate anions
[30, 34]. With Cd(NCS)2 also a number of polymorphic
or isomeric compounds have been reported that can be
transformed into each other [33, 35]. Cd(NCS)2 coordina-
tion compounds show structural motifs that have also
Dedicated to: Professor Arndt Simon on the occasion of his 80th
birthday.
1 Introduction
The structural chemistry of transition metal thiocyanate
coordination compounds is characterized by a large vari-
ability and a versatile coordination behavior. Most com-
pounds with less chalcophilic metal cations like, e.g.
*Corresponding author: Christian Näther, Institut für Anorganische
Chemie, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Straße 2,
24118 Kiel, Germany, Fax: +49-431-8801520,
E-mail: cnaether@ac.uni-kiel.de
Aleksej Jochim and Inke Jess: Institut für Anorganische Chemie,
Christian-Albrechts-Universität zu Kiel, Max-Eyth-Straße 2, 24118
Kiel, Germany
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2ꢀ ꢀA. Jochim et al.: Structural diversity in Cd(NCS)2-3-cyanopyridine coordination compounds
been observed for the paramagnetic cations and in several
cases they were found to be isotypic. Summarizing,
Cd(NCS)2 coordination compounds with condensed thio-
cyanate structures can be easily synthesized and allow
conclusions, which compounds might be accessible with
the paramagnetic analogs, which is the reason why we
have been interested in the structural chemistry of this
class of compounds for several years.
In the course of our investigations we introduced
3-cyanopyridine as coligand, that can also act as a bridg-
ing ligand via the cyano N atom which might lead to the
formation of structures of enhanced dimensionality. With
this ligand no Cd(NCS)2 compounds had been reported in
the literature, but several thiocyanate complexes contain-
ing cobalt(II), nickel(II), copper(II) or zinc(II) have been
reported, most of which consist of ligand-rich discrete
complexes and contain additional solvent or uncoordi-
nated 3-cyanopyridine solvate molecules [36–39].
Fig. 1:ꢀTG curves for 1 measured with 16, 8, 4 and 1 K min−1 in
a 300 μL and with 1 K min−1 in a 120 μL crucible under nitrogen
atmosphere. The events at Tꢁ=ꢁ300°C and above result from the
decomposition of Cd(NCS)2.
2 Results and discussion
2.1 Synthesis and thermoanalytical
investigations
The reaction of Cd(NCS)2 with 3-cyanopyridine in water, and is always higher than that calculated for the removal
ethanol or methanol leads to the formation of two differ- of one of the 3-cyanopyridine ligands, indicating that
ent 3-cyanopyridine-rich compounds with the composi- a product of undefined stoichiometry or a mixture of
tions
[Cd(NCS)2(3-cyanopyridine)2]nꢀ·ꢀꢀ3-cyanopyridine compounds are formed. If the heating rate is lowered to
(1) and [Cd(NCS)2(3-cyanopyridine)2]nꢀ·ꢀꢀ1/3 3-cyanopyri- 1 K min−1 two mass losses are observed, with each of
dine (2). While compound 1 can be obtained after one them corresponding to the removal of 1.5 3-cyanopyri-
or two days from all three solvents if a ratio of Cd(NCS)2 dine ligands. Therefore, a compound with the composi-
to 3-cyanopyridine (“M:L ratio”) of 1:4 or higher is used, tion {[Cd(NCS)2]2(3-cyanopyridine)3}n might have formed.
a lower M:L ratio of 1:2 is needed for the synthesis of 2. Interestingly if a crucible of 300 μL is used, a mass loss
However, 2 could not be obtained from methanol, even if of 37.9% is observed, that is in rough agreement with that
a M:L ratio of 1:2 was used, because 1 was formed instead. calculated for the removal of about 1.8 coligands, which
To check if more ligand-deficient compounds can be points to the formation of an additional 3-cyanopyridine
obtained, the thermal properties of both solvates were deficient phase. The dependence on the size of the cruci-
investigated. Thermogravimetric measurements of 1 have ble can be explained by the fact that in larger crucibles the
shown that its decomposition behavior depends on the 3-cyanopyridine rich atmosphere that is generated in the
heating rate as well as on the size of the crucible (Fig. 1), first decomposition process is trapped for a longer period
which is used for the measurement, while for 2 only a of time, which stabilizes intermediates of the pyrolysis.
dependency on the heating rate was observed. Because
for 2 similar TG curves were obtained, they are not shown poorly resolved and depend strongly on the heating rate.
here, but are discussed below. The emission of the 3-cyanopyridine solvate molecules
The TG curves obtained for compound 2 are also very
If crucibles of 120 μL and heating rates between 4 cannot be resolved. However, at higher heating rates a dis-
and 16 K min−1 are used for 1, a discrete step is observed crete step is also observed, in which more than 1/3 of the
in the beginning, but upon further heating a series of coligands are emitted, but powder X-ray diffraction (PXRD)
steps follows that cannot be fully resolved (Fig. 1). The investigations of the residues obtained after these steps
mass loss in the first step depends on the heating rate revealed that only amorphous products were formed.
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A. Jochim et al.: Structural diversity in Cd(NCS)2-3-cyanopyridine coordination compoundsꢂ
The products formed after the first mass loss of 1 experiments were conducted, in which relatively low
at different heating rates were investigated by PXRD, amounts of 3-cyanopyridine compared to Cd(NCS)2 were
which showed that at higher heating rates always amor- used. In the course of these experiments single crystals of
phous products were obtained. In contrast, at the rate of additional compounds with the compositions [Cd(NCS)2(3-
1 K min−1 compound 1 was transformed into a new phase cyanopyridine)2]n (3) and {[Cd(NCS)2]2(3-cyanopyridine)3}n
of poor crystallinity if the 300 μL crucible was used. To (4) were obtained. Compound 3 could only be obtained
increase the crystallinity, compounds 1 or 2 were annealed from ethanol with M:L ratios of 1:1 and 2:1 and reaction
at Tꢀ=ꢀ120°C for several hours. In both cases a much better times of 1–3 h. If the same M:L ratio is used while the reac-
crystalline residue was obtained within 2 h that shows tion time is increased to one or more days, compound 4
reflections that are also observed in the pattern of the is obtained. It is noted that 3 is often contaminated with
residue obtained by thermogravimetric measurements. If compounds 1, 2, 4 or other unidentified phases. However,
annealing is continued to 5 h, no 3-cyanopyridine could comparison of the calculated patterns with those meas-
be detected by elemental analysis, which means that ured for the residues obtained during the thermoanalytical
Cd(NCS)2 was formed. Interestingly the powder pattern investigations proves that pure compound 4 is formed by
of this Cd(NCS)2 phase is different from that of the known annealing of compound 1. Moreover, the product obtained
modification of Cd(NCS)2, but similar to that of Ni(NCS)2 by thermogravimetry using a heating rate of 1 K min−1
(Fig. 2) [40].
in 300 μL crucibles could be identified as a mixture of 4
To check if the crystalline phases obtained by thermal and an unknown phase as major product (Fig. 3). To iden-
decomposition are also available from solution, additional tify the unknown phase, a large number of crystallization
Fig. 2:ꢀExperimental PXRD patterns of the residues obtained after
the first mass step of 1 using different heating rates and of those
obtained by annealing 1 for 2 h and 5 h, together with the pattern
calculated for Ni(NCS)2.
Fig. 3:ꢀExperimental and calculated PXRD patterns for 1–5
together with the experimental pattern of the residue obtained by
thermogravimetric measurements of 1 at 1 K min−1 using the 300 μL
crucible.
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4ꢀ ꢀA. Jochim et al.: Structural diversity in Cd(NCS)2-3-cyanopyridine coordination compounds
experiments were performed and accidently a few single
crystals of this phase were obtained, which proved that a
more 3-cyanopyridine deficient compound with the compo-
sition {[Cd(NCS)2]3(3-cyanopyridine)4}n (5) had formed. No
access to larger amounts of this compound was found. The
occurrence of mixtures of compound 4 and 5 that exhibit
an unusual stoichiometry might explain why in most cases
different mass losses are observed in the TG measurements.
2.2 Crystal structures
2.2.1 Crystal structures of the chain compound
[Cd(NCS)2(3-cyanopyridine)2]n (3) and its solvates
(1 and 2)
All three compounds crystallize in the triclinic space
̅
group P1 with Zꢀ=ꢀ2 (1), Zꢀ=ꢀ6 (2) or Zꢀ=ꢀ4 (3). The asym-
metric unit of compound 1 contains two crystallographi-
cally independent Cd cations that are located on centers
of inversion, that of compound 2 of three unique Cd
cations in general positions and that of compound 3 of
three unique Cd cations, of which two are located on
special positions. In all compounds the Cd cations are
coordinated octahedrally and are linked into chains by
pairs of thiocyanate anions. Compounds 1 and 2 repre-
sent solvates in which the chains are arranged in a way
that channels are formed along the crystallographic a
axis, in which the solvate 3-cyanopyridine molecules
are located (Fig. 4).
Fig. 4:ꢀView of the crystal structure of 1 (top) and of 2 (bottom)
along the crystallographic a axis (Cd: turquoise, N: blue, C: black, S:
yellow, H: gray).
Interestingly, in all three chain compounds dif-
ferent Cd coordination environments are observed. In
compound 1 the two S- and the two N-coordinating
thiocyanate anions as well as the two 3-cyanopyridine
coligands are in trans positions. In compound 2 two dif- Cd1 and λoctꢀ=ꢀ1.019 for Cd2 in 3 for the all-trans coordina-
ferent chains are present. One of them shows the usual tion environments. The corresponding values for the octa-
2
all-trans coordination whereas in the second one an hedral angle variance amount to σθ‹oct› ꢀ=ꢀ14.7 for Cd1 and
2
2
all-cis coordination of the thiocyanate anions and the
σ
θ‹oct›2ꢀ=ꢀ9.8 for Cd2 in 1, to σθ‹oct› ꢀ=ꢀ17.2 for Cd1 and σθ‹oct› ꢀ=ꢀ16.5
2
2
3-cyanopyridine molecules is observed, which to the best for Cd2 in 2 and to σθ‹oct› ꢀ=ꢀ20.3 for Cd1 and σθ‹oct› ꢀ=ꢀ20.7 for
of our knowledge has never been observed before in such Cd2 in 3 [41]. This shows that the degree of longitudinal as
thiocyanate coordination polymers. In compound 3, also well as of the angular distortions increases with decreas-
an all-cis coordination is found, but because this com- ing amounts of the 3-cyanopyridine molecules, if only the
pound shows disordering for some of the thiocyanate all-trans coordination environments are considered. For
anions a cis-cis-trans coordination is also observed, the other coordination environments values of λoctꢀ=ꢀ1.011
in which the N-bonding thiocyanate anions are trans, in 2, λoctꢀ=ꢀ1.020 for all-cis in 3 as well as λoctꢀ=ꢀ1.033 for
while the S-bonding thiocyanate anions as well as the cis-cis-trans in 3 are found. The corresponding values for
2
coligands are cis (Fig. 5).
the octahedral angle variance amount to σθ‹oct› ꢀ=ꢀ18.1 in 2,
2
Inallcasesthecoordinationenvironmentsarestrongly
σ
θ‹oct›2ꢀ=ꢀ23.9 for all-cis in 3 as well as σθ‹oct› ꢀ=ꢀ47.8 for cis-cis-
distorted with values of the mean quadratic elongation of trans in 3. Similarly to the values found for the all-trans
λoctꢀ=ꢀ1.016 for Cd1 and λoctꢀ=ꢀ1.015 for Cd2 in 1, λoctꢀ=ꢀ1.018 for coordination environments, the degree of distortion is
Cd1 and λoctꢀ=ꢀ1.018 for Cd2 in 2 as well as λoctꢀ=ꢀ1.020 for higher in the solvate deficient compounds.
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ꢂ5
A. Jochim et al.: Structural diversity in Cd(NCS)2-3-cyanopyridine coordination compoundsꢂ
Fig. 6:ꢀSide view (top) and top-down view (bottom) of a linear
chains in 3, in which only all-trans coordination environments are
present, as a representative for the linear chains found in 1, 2 and 3
(Cd: turquoise, N: blue, C: black, S: yellow, H: gray).
Fig. 5:ꢀDifferent coordination environments of the Cd cations as
observed in 1, 2 and 3 (Cd: turquoise, N: blue, C: black, S: yellow, H:
gray).
The different Cd coordinations in the three chain
compounds lead to different chain geometries. The occur-
rence of an all-trans coordination in compound 1 leads to
the formation of linear chains (Fig. 6), while in compound
2 two different Cd environments are present with the
all-trans coordination leading to the formation of linear
chains, whereas the all-cis coordination results in corru-
gated chains (Figs. 6 and 7). Corrugated chains are also
observed in compound 3, because both, the all-cis and cis-
cis-trans coordination, lead to this chain geometry (Fig. 7).
The crystal structures of the linear chains are similar
in all three compounds. The 6-membered ring planes of the
opposing 3-cyanopyridine coligands are parallel and ori-
ented nearly perpendicular to the chain direction (Fig. 6).
Moreover, along the chains the distances between
adjacent 3-cyanopyridine coligands alternate, which
Fig. 7:ꢀZig-zag chains found in the crystal structure of 2 (top) and
in the substructure (middle) as well as the superstructure of 3
(bottom). Disordered thiocyanate anions are indicated by dotted
bonds; Cd: turquoise, N: blue, C: black, S: yellow, H: gray.
means that always a very long and a relatively short dis- the deviation of the chains from linearity, which is espe-
tance are observed, indicating π–π interactions for the cially the case in compound 2. In contrast to compounds
latter (Fig. 6 and Table 1). This arrangement also leads to 1 and 3, in compound 2 the dihedral angle between two
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6ꢀ ꢀA. Jochim et al.: Structural diversity in Cd(NCS)2-3-cyanopyridine coordination compounds
Table 1:ꢀDistances between adjacent coligand molecules and angles
between neighboring (NCS)2 planes in compounds 1, 2 and 3.
chains by pairs of thiocyanate anions. In contrast to the
former compounds some of the 3-cyanopyridine coligands
connect adjacent chains into layers by coordinating via
the 3-cyano group. This means that in compounds 4 and
5, both, terminal and bridging coligands are present.
In contrast to 5, compound 4 consists of three crystal-
lographically independent chains, which contain either
exclusively Cd1 (chain 1), Cd2 and Cd3 (chain 2) or Cd4
and Cd5 (chain 3). Furthermore, they differ in the way, in
which the 3-cyanopyridine molecules are coordinated to
the Cd cations. While in chains 1 and 2 each Cd cation is
bonded to a bridging as well to a terminal 3-cyanopyridine
Compoundꢁ
Dist. 1/Å
ꢁ
Dist. 2/Å
ꢁ
∠ plane 1
and 2/deg
1
2
3
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
7.5084(5)
ꢃ 4.0218(2)
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
0.00(8)
0.00(8)
24.35(11)
24.35(11)
0.00(10)
0.00(10)
ꢃ
7.2586(3)
7.4212(3)
7.3390(3)
ꢃ 3.9891(1)
ꢃ 4.0687(1)
ꢃ 3.9251(2)
ꢃ
neighbored (NCS)2 planes amounts to 24.353° (Fig. 6 and molecule, the bridging ligands in chain 1 are always
Table 1).
linked via the pyridine N atom, whereas in chain 2
The geometries of the corrugated chains in com- they are always bound via the cyano N atom (Fig. 8).
pounds 2 and 3 with an all-cis arrangement of the coordi- In chain 3 all 3-cyanopyridine ligands are coordinated
nating ligands are also similar (Fig. 7). What is special in via the pyridine N atom, but here the Cd cations are
these chains is the fact that the Cd–N–C angles in the all- coordinated by either only bridging or only terminal
cis coordination environments deviate very strongly from 3-cyanopyridine ligands (Fig. 8). In chains 1 and 2 every
linearity with values between 151 and 131°, much smaller Cd cation is linked to one neighboring chain, whereas in
than the values for most other transition metal thiocy- chain 3 each second Cd cation is connected to two neigh-
anates, especially those with an all-trans coordination. It boring chains leading to a ratio between bridging and ter-
is noted that in compound 3 disorder is observed, which minal coligands of 1:2.
means that in every second (NCS)2 unit the direction of the
In contrast, for 5 only one crystallographically inde-
thiocyanate anions is reversed (Fig. 7: middle). For this pendent chain is found, in which the two Cd cations are
compound additional reflections are observed leading to coordinated differently. While both coligands connected
a 4-fold larger unit cell, in which each fourth (NCS)2 unit to Cd2 are involved in bridging adjacent chains, only one
of the 3-cyanopyridine molecules coordinated to Cd1 is
bridging, while the other is bound terminally (Fig. 8).
This leads to a ratio between bridging and terminal coli-
gands of 1:1, which means that compound 5 shows a more
condensed thiocyanate network as compared to that in
compound 4. Furthermore both of the coligands bound to
Cd2 coordinate via the pyridine N atom, while the bridg-
ing coligand molecule bound to Cd1 is coordinated via the
cyano N atom (Fig. 8). This is probably one of the reasons
for the relatively high degree of angular distortion of the
coordination octahedron of Cd1 compared to that of Cd2
is disordered (Fig. 7: bottom), but we decided to refine this
structure in the subcell for several reasons (see Section 4).
2.2.2 Crystal structures of the layered compounds
{[Cd(NCS)2]2(3-cyanopyridine)3}n (4) and
{[Cd(NCS)2]3(3-cyanopyridine)4}n (5)
Compounds 4 and 5 crystallize in the triclinic space
̅
group P1 and the monoclinic space group P21/c with Zꢀ=ꢀ4
and Zꢀ=ꢀ2 formula units in the unit cell, respectively. The
asymmetric unit of compound 4 contains five crystallo-
2
2
(σ
θ‹oct› ꢀ=ꢀ25.8 and λoctꢀ=ꢀ1.017 for Cd1, and σθ‹oct› ꢀ=ꢀ4.5 and
graphically independent 3-cyanopyridine ligands, eight λoctꢀ=ꢀ1.014 for Cd2).
thiocyanate anions and three Cd(II) cations in general
positions as well as two unique Cd(II) cations that are
located on centers of inversion. In compound 5 the asym-
metric unit consists of two crystallographically inde- 3 Conclusions
pendent 3-cyanopyridine ligands and three thiocyanate
anions in general positions as well as two unique Cd(II) Several new compounds based on Cd(NCS)2 and
cations, of which one is located on a center of inversion. 3-cyanopyridine have been presented, in which the ratio
Similarly to those in compounds 1, 2 and 3 the Cd cations between metal salt and coligand is always different. In com-
in both compounds are octahedrally coordinated by two pound 3 this ratio is 1:2 leading to the formation of chains
3-cyanopyridine ligands and two N-bonding and two in which the metal cations are linked by pairs of anionic
S-bonding thiocyanate anions and are linked into linear ligands, while in 1 and 2 similar chains are accompanied
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A. Jochim et al.: Structural diversity in Cd(NCS)2-3-cyanopyridine coordination compoundsꢂ
same linear thiocyanate chains are present as in 1–3, the
ratio between bridging and terminal coligands is 1:2, but in
compound 5 it is 1:1, leading to the formation of 2D instead
of 1D networks. However, in the chain compound 3 only
terminally coordinating coligands are present. If half of
the coligands would be removed from compound 3, a com-
pound with an Cd(NCS)2:3-cyanopyridine ratio of 1:1 would
be obtained in which all terminal coligands would be trans-
formed into bridging coligands. This would lead to the most
condensed network in which each Cd cation is linked to a
Cd cation of a neighboring chain. Compounds 4 and 5 thus
represent structural intermediates between the chain and
the “ideal” layered structures. Surprisingly from all of our
investigations there is no hint that a 1:1 compound with a
composition of [Cd(NCS)2(3-cyanopyridine)]n exists, and
such a compound could also not be prepared by ligand
removal via thermal annealing of 3-cyanopyridine-rich
precursors.
4 Experimental section
4.1 Synthesis
4.1.1 General
CdSO4ꢀꢀ·ꢀꢀ8/3H2O was obtained from Merck and
Ba(NCS)2ꢀ·ꢀ3H2O as well as 3-cyanopyridine were obtained
from Alfa Aesar. All chemicals were used without further
purification. Cd(NCS)2 was prepared by the reaction of
equimolar amounts of CdSO4ꢀ·ꢀ8/3H2O and Ba(NCS)2ꢀ·ꢀ3H2O
in water. The precipitated BaSO4 was filtered off and the
filtrate was concentrated to complete dryness resulting
in a colorless residue of Cd(NCS)2. If not noted otherwise
the reactions were carried out in snap cap vials at ambient
conditions. After the reaction the residue was filtered off
and dried in air.
Fig. 8:ꢀView onto a layer as observed in the crystal structure
of compounds 4 (top) and 5 (bottom). For clarity, the terminal
3-cyanopyridine coligands are shown using a wire stick model (Cd:
turquoise, N: blue, C: black, S: yellow, H: gray).
by different amounts of additional 3-cyanopyridine solvate 4.1.2 Synthesis of [Cd(NCS)2(3-
molecules. In these compounds three different Cd coordi-
nation environments are observed with the all-trans coor-
cyanopyridine)2]nꢂꢂ·ꢂꢂ3-cyanopyridine (1)
dination leading to the formation of linear chains, whereas A mixture of Cd(NCS)2 (114.4 mg, 0.50 mmol) and
all-cis and the cis-cis-trans coordination result in the forma- 3-cyanopyridine (208.3 mg, 2.00 mmol) in 2 mL of water
tion of corrugated chains. However, the 3-cyanopyridine was stirred for one day. Single crystals were obtained
molecules can also act as bridging ligands and therefore in a similar way from a mixture of Cd(NCS)2 (57.1 mg,
structures with more condensed networks are possible. 0.25 mmol) and 3-cyanopyridine (52.1 mg, 0.50 mmol) in
This is realized in the crystal structures of 4 and 5, in which 1 mL of methanol. – Elemental analysis for C20H12CdN8S2
the ratio between Cd(NCS)2 and 3-cyanopyridine is 2:3 and (540.9009 g mol−1): calcd. C 44.41, H 2.24, N 20.72, S 11.86;
3:4, respectively. This means that in compound 4 where the found C 42.26, H 2.05, N 20.17, S 11.06.
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8ꢀ ꢀA. Jochim et al.: Structural diversity in Cd(NCS)2-3-cyanopyridine coordination compounds
4.1.3 Synthesis of [Cd(NCS)2(3-cyanopyridine)2]nꢂꢂ·ꢂꢂ1/3
3-cyanopyridine (2)
could be synthesized, but mixtures containing 5 could be
obtained by thermal degradation of 1 in nitrogen atmos-
phere using a heating rate of 1 K min−1 in a crucible with a
Cd(NCS)2 (114.4 mg, 0.50 mmol) and 3-cyanopyridine volume of 300 μL.
(52.1 mg, 0.50 mmol) were stirred in 2 mL of water for one
day. Single crystals were synthesized by layering a mixture
of Cd(NCS)2 (34.3 mg, 0.15 mmol) in 1 mL of water with 4.2 Elemental analysis
2 mL of diethylether and carefully adding a solution of
3-cyanopyridine (3.9 mg, 0.04 mmol) in 1 mL diethylether. CHNS analyses was performed using an EURO EA elemen-
The diethylether was evaporated slowly and after one day tal analyzer, fabricated by EURO VECTOR Instruments.
colorless crystals were obtained. – Elemental analysis for
C16H9.33CdN6.67S2 (471.4934 g mol−1): calcd. C 40.76, H 2.00, N
19.80, S 13.60; found C 40.59, H 1.98, N 19.90, S 14.19.
4.3 Single-crystal structure analyses
Data collections were performed with an imaging plate dif-
fraction system IPDS-2 from STOE & Cie using MoKα radia-
tion. Structure solutions were performed with Shelxt [42]
4.1.4 Synthesis of [Cd(NCS)2(3-cyanopyridine)2]n (3)
A powder was obtained by the reaction of Cd(NCS)2 (compound 3) or Shelxs-97 [43] (compounds 1, 2, 4 and 5)
(114.4 mg, 0.50 mmol) with 3-cyanopyridine (52.1 mg, and structure refinements performed against F2 using
0.50 mmol) in 2.0 mL ethanol. After 3 h the mixture was Shelxl-2018 [44]. A numerical absorption correction was
filtered and a colorless solid was obtained. Single crystals applied using the programs X-Red and X-Shape of the
were synthesized using the same method as described in program package X-Area [45–47]. All non-hydrogen atoms
4.1.3, but with different amounts of Cd(NCS)2 (68.6 mg, were refined with anisotropic displacement parameters.
0.30 mmol) and 3-cyanopyridine (15.6 mg, 0.15 mmol) and The hydrogen atoms were positioned with idealized geom-
without evaporation of the diethylether. Elemental anal- etry and were refined isotropically with Uiso(H)ꢀ=ꢀ1.2 Ueq(C)
ysis for C14H8CdN6S2 (436.7897 g mol−1): calcd. C 38.50, H using a riding model.
1.85, N 19.24, S 14.68; found C 38.92, H 1.91, N 19.22, S 14.40.
In compound 3 one of the thiocyanate anions is dis-
ordered leading to a centrosymmetric Cd-(NCS)2-Cd pair,
in which each Cd cation is coordinated by the S or N atom
of this ligand. For this structure super structure reflec-
tions are observed that lead to a 4-fold larger triclinic unit
4.1.5 Synthesis of {[Cd(NCS)2]2(3-cyanopyridin)3}n (4)
A mixture of Cd(NCS)2 (228.8 mg, 1.00 mmol) and cell with aꢀ=ꢀ13.8420(8), bꢀ=ꢀ22.1948(15), cꢀ=ꢀ23.5542(14) Å,
3-cyanopyridine (52.1 mg, 0.50 mmol) was stirred in 2 mL αꢀ=ꢀ112.178(5),βꢀ=ꢀ93.435(5),γꢀ=ꢀ97.248(5)°andVꢀ=ꢀ6601.7(8)Å3
ethanol. After one day a colorless powder was obtained. with Zꢀ=ꢀ16 and 9 crystallographically independent Cd
Single crystals were synthesized by layering a suspen- cations. In this unit cell the disorder is reduced but still
sion of Cd(NCS)2 (68.6 mg, 0.60 mmol) with 2 mL diethy- one Cd-(NCS)2-Cd pair is disordered. The refinement led to
lether and carefully adding a solution of 3-cyanopyridine much poorer reliability factors than that in the subcell and
(7.8 mg, 75 μmol) in 1 mL diethylether. After one day very the displacement parameters of some of the thiocyanate
small needles precipitated. – Elemental analysis for anion were enlarged. For this unit cell the ADDSYM option
C22H12Cd2N10S4 (769.4683 g mol−1): calcd. C 34.34, H 1.57, N in Platon [48] suggests a pseudo-translation, which is
18.20, S 16.67; found C 34.62, H 1.40, N 18.63, S 16.78.
valid for 97% of the structure. The super cell can be trans-
formed into the subcell using the matrix 0.25 −0.25 −0.25;
−0.75 −0.25 −0.25; 0.25 0.75 −0.25 (1 −1 −2; −1 0 −1; 0 1 −1
is the matrix for the transformation of the atomic coordi-
nates) and therefore structure refinement was performed
4.1.6 Synthesis of {[Cd(NCS)2]3(3-Cyanopyridin)4}n (5)
Single crystals could be obtained by layering a mixture in the subcell.
of Cd(NCS)2 (137.2 mg, 0.60 mmol) in 1 mL of water with
The crystals of compound 4 are of very poor quality,
2 mL of diethylether with a solution of 3-cyanopyridine which is obvious from a view of its diffraction pattern
(15.6 mg, 0.15 mmol) in 1 mL diethylether. After one day that is far from that expected for a single crystal (Fig. 9).
colorless crystals had formed, which were suitable for However, indexing leads to a reasonable triclinic unit cell,
the structure determination. No phase pure powder of 5 for which the structure could not be solved, obviously
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ꢂ9
A. Jochim et al.: Structural diversity in Cd(NCS)2-3-cyanopyridine coordination compoundsꢂ
reasonable R values. Selected crystal data and details of
the structure refinements can be found in Table 2.
CCDC 1963757 (1), 19637578 (2), 1963759 (3), 1963760
(4) and 1963761 (5) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained
free charge from the Cambridge Crystallographic Data
Centre via http://www.ccdc.cam.ac.uk/data_request/cif.
4.4 X-ray powder diffraction (XRPD)
The measurements were performed using a STOE Trans-
mission Powder Diffraction System (STADI P) with CuKα1
radiation (λꢀ=ꢀ1.540598 Å) equipped with a MYTHEN 1K
detector from Dectris and a Ge(111) monochromator from
STOE & Cie.
Fig. 9:ꢀReciprocal space plot of compound 4 along [100].
4.5 Thermogravimetry and differential
scanning calorimetry (TG-DSC)
because inaccurate intensities were extracted. Therefore,
the mosaic spread and the integration box was varied sys- TG-DSC measurements were performed in a dynamic nitro-
tematically until the structure was solved and refined to gen atmosphere in Al2O3 crucibles using a STA-PT1600
Table 2:ꢀSelected crystal data and details of the structure determinations for 1, 2, 3, 4 and 5.
1
2
3
4
5
Formula
MW/g mol−1
Crystal system
Space group
a/Å
C14H8CdN6S2ꢁꢁ·ꢁꢁC6H4N2
540.90
C14H8CdN6S2ꢁꢁ·ꢁꢁ1/3 C6H4N2
471.49
C14H8CdN6S2
436.78
C22H12Cd2N10S4
769.46
C30H16Cd3N14S6
1102.13
Monoclinic
P21/n
10.3722(3)
15.6932(5)
12.2003(3)
90
Triclinic
Triclinic
Triclinic
Triclinic
̅
̅
̅
̅
P1
P1
P1
P1
7.4045(5)
11.5175(7)
13.1054(9)
90.050(5)
91.259(5)
90.609(5)
1117.31(13)
298(2)
7.6199(2)
11.3461(4)
32.3632(10)
97.976(2)
94.854(2)
90.805(3)
2760.05(15)
200(2)
7.7426(3)
11.2597(5)
19.6070(8)
102.283(3)
98.893(3)
91.599(3)
1646.84(12)
200(2)
11.4395(7)
14.7433(10)
17.5518(12)
74.555(5)
79.720(5)
89.278(5)
2805.6(3)
200(2)
b/Å
c/Å
α/deg
β/deg
γ/deg
96.259(2)
90
V/Å3
1974.04(10)
200(2)
T/K
Z
2
6
4
4
2
D
calcd/g cm−3
1.61
1.70
1.76
1.82
1.85
μ/mm−1
θmax/deg
1.2
1.4
1.6
1.9
2.0
28.067
19 118
25.000
32 813
26.005
14 394
25.100
20 148
26.999
22 704
4307
Refl. collected
Refl. unique
Rint
5338
9698
6432
9840
0.0410
0.634; 0.855
3976
0.0547
0.610; 0.805
8295
0.0219
0.672; 0.790
5271
0.1139
0.641; 0.836
6841
0.0466
0.570; 0.740
3862
Transm. min; max
Refl. [F0ꢁ>ꢁ4 σ(F0)]
Parameters
R1 [F0ꢁ>ꢁ4 σ(F0)]
wR2 (all unique data)
GOF
283
695
446
688
241
0.0368
0.0775
1.036
0.0455
0.1294
1.064
0.0337
0.0814
1.063
0.0959
0.2911
1.053
0.0353
0.0937
1.067
Δρmax; min/e Å−3
0.68; −0.56
1.05; −1.17
0.95; −2.11
3.18; −2.88
0.57; −0.74
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10ꢀ ꢀA. Jochim et al.: Structural diversity in Cd(NCS)2-3-cyanopyridine coordination compounds
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Acknowledgements: This project was supported by
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Z. Naturforsch.ꢂ
ꢂ2019 | Volume x | Issue x(b)
Graphical synopsis
Aleksej Jochim, Inke Jess and Christian
Näther
Structural diversity in Cd(NCS)2-
3-cyanopyridine coordination compounds:
synthesis, crystal structures and thermal
properties
https://doi.org/10.1515/znb-2019-0175
Z. Naturforsch. 2019; x(x)b: xxx–xxx
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