Structure and bonding of tetracyanopyrrolides

Article abstract of DOI:10.1002/ejic.201200790

Salts bearing the tetracyanopyrrolide anion (TCP) were synthesized from tetracyano-1,4-dithiin and sodium azide according to a modified synthetic protocol. The solid-state structures of HTCP, MeTCP, Me₄NTCP, NaTCP, and the ionic liquid EMIMTCP (EMIM = 1-ethyl-3-methylimidazolium) are discussed for the first time. According to experimental and computational data, the TCP anion can be regarded as a pseudohalide with π bonds highly delocalized over the entire anion including the four cyano groups. The planar anion is C _2v symmetric and represents a multifunctional binary CN ligand, which is capable of forming classic coordination bonds through the lone pairs of the CN groups or the ring nitrogen atom. In addition, noncovalent interactions such as π-π interactions are found and can be used to strengthen structural and electronic communication between organic ligands.

Full text of DOI:10.1002/ejic.201200790

Job/Unit: I20790
/KAP1
Date: 19-09-12 17:36:49
Pages: 11
FULL PAPER
DOI: 10.1002/ejic.201200790
Structure and Bonding of Tetracyanopyrrolides
Martin Becker,[a] Jörg Harloff,[a] Thomas Jantz,[a] Axel Schulz,*[a,b] and
Alexander Villinger[a]
Keywords: Coordination chemistry / Ligand design / N ligands / Main group elements / Pseudohalogen
Salts bearing the tetracyanopyrrolide anion (TCP) were syn-
anion including the four cyano groups. The planar anion is
thesized from tetracyano-1,4-dithiin and sodium azide ac- C2v symmetric and represents a multifunctional binary CN
cording to a modified synthetic protocol. The solid-state
structures of HTCP, MeTCP, Me4NTCP, NaTCP, and the ionic
liquid EMIMTCP (EMIM = 1-ethyl-3-methylimidazolium) are
discussed for the first time. According to experimental and
computational data, the TCP anion can be regarded as a
pseudohalide with π bonds highly delocalized over the entire
ligand, which is capable of forming classic coordination
bonds through the lone pairs of the CN groups or the ring
nitrogen atom. In addition, noncovalent interactions such as
π–π interactions are found and can be used to strengthen
structural and electronic communication between organic li-
gands.
Introduction
The chemistry of thiacyanocarbons (Scheme 1) was de-
veloped by Bähr and Schleitzer as early as 1955–1957.[1]
They started from CS2 and NaCN to yield sodium cyanodi-
thioformiate, which dimerizes under oxidizing conditions to
give disodium dimercaptomaleodinitrile (2) as shown in
Scheme 2. Both 1 or 2 can be oxidized to afford tetracyano-
1,4-dithiin (3) in high yield.[1,2] The reactive dithiin 3 ex-
trudes sulfur at elevated temperatures to give tetracya-
nothiophene 4, and also undergoes a remarkable reaction
with sodium azide in ethanol (Scheme 2) at 25 °C to form
sodium tetracyanopyrrolide (NaTCP).[3,4]
The free acid (HTCP) of the TCP ion is easily obtained
by ion exchange utilizing acidic Amberlite resin. HTCP,
which is a medium strong acid,[15] forms salts bearing the
tetracyanopyrrolide anion (TCP) upon addition of strong
bases such as MOH (M = R4N, alkali metal) or even am-
monia.[5]
Scheme 1. Thiacyanocarbons and tetracyanopyrrolides.
The parent anion of TCP, the pyrrolide anion [H4C4N]–
is composed of a five-membered ring with six delocalized π
electrons and represents a strong base (pKb = –3.51). In
comparison, pyrrole, the corresponding acid, is a very weak
acid (pKa = 17.51).[6] Substitution of all four H atoms by
cyano groups in [H4C4N]– dramatically decreases the basic-
ity of the anion (pKb = 11.29) and thus its conjugate acid
HTCP represents a medium–strong acid (pKa = 2.71),[15]
This situation resembles the situation in nonlinear reso-
nance-stabilized pseudohalides such as in the tricyanome-
thanide anion [C(CN)3]– [7] or dicyanoamide [N(CN)2]– [8]
compared to [CH3]– and [NH2]–.[9] The pseudohalogen con-
cept can be generalized and extended to planar highly delo-
calized heterocycle anions such as tetracyanopyrrolide or
the five-membered ring anion [CS2N3]–,[10,11] which can be
obtained in the reaction of carbon disulfide and sodium
azide as shown by Sommer[12] in 1915. Such heterocyclic
anions can also be classified as pseudohalides when they
fulfill the well-known criteria with respect to halogen-like
chemical behavior:[13,14] a pseudohalogen (X) forms a singly
charged anion (X–), a pseudohalogen hydrogen acid of the
type HX, and low solubility salts of the type M(X)n with
[a] Institut für Chemie, Universität Rostock,
Albert-Einstein-Str. 3a, 18059 Rostock, Germany
E-mail: axel.schulz@uni-rostock.de
Homepage: http://www.schulz.chemie.uni-rostock.de/
[b] Leibniz-Institut für Katalyse e. V. an der Universität Rostock,
Albert-Einstein-Str. 29a, 18059 Rostock, Germany
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201200790.
Eur. J. Inorg. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1

Job/Unit: I20790
/KAP1
Date: 19-09-12 17:36:49
Pages: 11
M. Becker, J. Harloff, T. Jantz, A. Schulz, A. Villinger
FULL PAPER
air, slow oxidation to yield the disulfide species 2_S2 was
observed as depicted in Scheme 3. Compound 2_S2 could
be isolated and characterized by X-ray crystallography (Fig-
ure 1). The final product of the oxidation process is dithiin
3. A much better alternative for the synthesis of dithiin 3 is
the direct oxidation of 2 in H2O with ammonium peroxodi-
sulfate as shown in Scheme 2 (yield Ͼ60%, Figure 2). De-
composition of 3 starts at 170 °C with the release of sulfur.
Scheme 2. Synthesis of sodium tetracyanopyrrolide (NaTCP).
silver, lead and mercury, etc. However, not all criteria are
always met. In case of TCP it is already known that it forms
a low solubility silver salt AgTCP.[15]
Scheme 3. Stepwise oxidation of 2.
We report here on the (modified) syntheses and full char-
acterization of tetracyanopyrrolide-based compounds along
with their first structural characterization including the
starting materials and the thiacyanocarbons 2 and 3. The
structure and bonding of the tetracyanopyrrolides are dis-
cussed on the basis of the pseudohalogen concept.
Results and Discussion
The TCP anion belongs to the class of resonance stabi-
lized binary CN anions such as tricyanomethanide
[C(CN)3]–,[7] dicyanoamide [N(CN)2]–, or its trimerization
product the melaminate [C3N6(CN)3]3–.[8,16,17] In the last
decade, these anions have been the object of great interest
by several groups,[14,16,18,19–22] especially in the fields of so-
lid state chemistry and coordination chemistry.[16,18,19]
Thus, it is was vital to have a feasible high-yielding synthe-
sis and to find ways to obtain single crystals suitable for a
single crystal structure elucidation.
Figure 1. Molecular structure of [Na(MeOH)1.5]2[C8N4S4] (2_S2).
Parts of the MeOH molecules are omitted for clarity. Selected bond
lengths [Å] and angles [°]: S1–C1 1.753(2), S1–S4 2.1031(7), S2–C2
1.689(2), S3–C5 1.695(2), S4–C6 1.755(2), C1–C2 1.377(3), C1–C3
1.421(3), C2–C4 1.454(3), C5–C6 1.377(3), C5–C7 1.459(3), C6–C8
1.426(3), N1–C3 1.148(2), N2–C4 1.144(2), N3–C7 1.143(2), N4–
C8 1.149(2); C1–S1–S4 100.81(6), C6–S4–S1 99.96(7), C2–C1–C3
118.0(2), C2–C1–S1 124.7(1), C3–C1–S1 117.3(2), C5–C6–S4
124.1(1), C8–C6–S4 117.8(2), N3–C7–C5 177.1(2), N4–C8–C6
177.9(2).
Synthesis
Starting from dithiin 3, different routes to salts bearing
The starting material for the synthesis of TCP salts, di- the TCP– ion were checked (Schemes 2 and 4). For practical
thiin 3, can be generated in a three-step synthesis. The path- reasons it is best to react tetracyano-1,4-dithiin with an
way as shown in Scheme 2 involves the synthesis of sodium equimolar amount of sodium azide in ethanol but without
cyanodithioformiate (1), which is obtained in good yields isolating NaTCP. Once the release of nitrogen is finished,
(Ͼ68%) as a DMF solvate. Slow decomposition of 1 occurs the dark red reaction mixture is filtered to remove elemental
at slightly elevated temperatures (Ͼ 80 °C) in the solid state. sulfur. The filtrate is evaporated to dryness and re-dissolved
Conversion of 1 into the dithiolate 2 is easily achieved in in water. This aqueous filtrate is decolorized with activated
CHCl3 (yield Ͼ 88%) under reflux conditions. Compound charcoal, and tetramethylammonium chloride is added as a
2 is easily prepared in bulk, almost indefinitely stable when saturated aqueous solution. The immediate precipitation of
stored in a sealed tube under argon, and decomposes at Me4NTCP is observed. Pure NaTCP can now be generated
temperatures above 374 °C. However, when 2 was stored in by utilization of an ion-exchange resin column. A similar
2
www.eurjic.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: I20790
/KAP1
Date: 19-09-12 17:36:49
Pages: 11
Structure and Bonding of Tetracyanopyrrolides
of all considered TCP species show sharp bands in the ex-
pected region between 2217–2256 cm–1, which can be as-
signed to the νCN stretching frequencies.
Table 1. Melting points, decompositions points [°C], and IR/Ra-
man data of the υCN stretching modes [cm–1].
M.p. [°C] Tdec. [°C] IR υCN [cm–1]
Raman υCN [cm–1]
2241(sh), 2226(s) 2247(10)
2220(s) 2228(10), 2229(sh)
2225(s), 2217(s) 2230(10)
2251(s), 2241(s) 2256(10)
2242(s), 2236(s) 2245(10)
NaTCP
Me4NTCP 119
EMIMTCP 30
HTCP
MeTCP
401
Ͼ600
423
230
202
362
Figure 2. ORTEP drawing of the molecular structure of 3. Thermal
ellipsoids with 50% probability at 173 K. Selected bond lengths [Å]
and angles [°]: S1–C1 1.762(2), S1–C4 1.763(2), S2–C2 1.762(2),
S2–C3 1.763(2), C1–C2 1.341(2), C1–C5 1.437(2), C2–C6 1.434(2),
C3–C4 1.338(2), C3–C7 1.434(2), C4–C8 1.433(2), N1–C5 1.142(2),
N4–C8 1.141(2), N2–C6 1.144(2), N3–C7 1.139(2); C1–S1–C4
96.95(8), C4–C3–S2 121.7(1), C2–S2–C3 97.24(8), C2–C1–C5
120.5(2), C2–C1–S1 121.70 (13), C5–C1–S1 117.8(1), N1–C5–C1
176.6(2), N2–C6–C2 176.8 (2), N3–C7–C3 179.4(2), N4–C8–C4
178.1(2).
202
187
X-ray Crystallography
As far as we know there are no structural data available
of the starting material or of any TCP species. The struc-
tures of the starting materials as well of the TCP species
HTCP, HTCP·2H2O, NaTCP, MeTCP, Me4NTCP, and the
ionic liquid EMIMTCP have been determined. Tables 2, 3,
and 4 present the X-ray crystallographic data. X-ray quality
crystals of all considered species were selected in Kel-F-oil
(Riedel deHaen) or Fomblin YR-1800 (Alfa Aesar) at am-
bient temperature. All samples were cooled to –100(2) °C
during the measurement.
procedure can be used to prepare HTCP when the ion ex-
change column is loaded with H+ instead of Na+. More-
over, HTCP can be obtained from NaTCP upon addition
of HClO4. Methylation of the TCP ion in Me4NTCP by
means of Me2SO4 yields MeTCP. The low solubility silver
salt AgTCP can be generated from NaTCP or Me4NTCP
dissolved in a water/acetone mixture when AgNO3 is added.
Table 2. Crystallographic details of 1, 2_S2, and dithiin 3.
1
2_S2
3
Formula
Fw [gmol–1]
Color
Cryst. system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C11H21N4NaO3S2 C11H12N4Na2O3S4 C8N4S2
344.43
yellow
422.47
orange
triclinic
216.24
brown
monoclinic
P21/n
6.8962(3)
18.3391(7)
6.9796(3)
90
90.345(2)
90
882.69(6)
4
hexagonal
¯
¯
P62c
P1
12.5185(6)
12.5185(6)
6.4790(4)
90
120
90
8.6772(3)
9.9270(4)
13.0318(5)
96.233(2)
106.649(2)
112.217(2)
965.40(6)
2
γ [°]
V [Å3]
879.31(7)
2
Z
μ [mm–1]
λ Mo-Kα [Å]
T [K]
0.34
0.55
0.56
0.71073
173
0.71073
173
0.71073
173
Scheme 4. Synthesis of TCP compounds.
Measured refl.
Ind. refl.
Refl. with IϾ2σ(I)
Rint.
6609
1000
848
0.029
364
28721
6151
3960
0.064
432
0.043
0.094
1.02
239
8219
2111
1610
0.031
432
0.033
0.071
1.06
127
891165
As ionic liquids are increasingly receiving attention be-
cause of their wide spectrum of applications (as reaction
media, as lubricants, or as electrolytes particularly for solar
and fuel cells),[23–31] the EMIM (1-ethyl-3-methylimidaz-
F(000)
R1 {R[F2Ͼ 2σ(F2)]} 0.033
wR2 (all data)
0.075
1.06
54
olium) salt of TCP was also prepared and fully charac- GooF
Parameters
CCDC
terized. By a salt metathesis reaction, the silver salt can be
transferred into EMIMTCP, an ionic liquid with a melting
point of 30 °C {cf. EMIM3[C3N6(CN)3]: –20 °C,[17] EM-
IM[N(CN)2]: –12 °C[32]}. EMIMTCP is thermally stable to
891163
891164
The molecular structures of disulfide species 2_S2, di-
over 230 °C {cf. EMIM3[C3N6(CN)3]: 253 °C,[17] EM- thiin species 3, and all TCP species are shown in Figures 1,
IM[N(CN)2]: 275 °C[33]}. The melting and decomposition 2, 3, 4, 5, 6, 7, 8, and 9, along with selected bond lengths
points of all TCP species along with selected vibrational and angles. More details are found in the Supporting Infor-
data are summarized in Table 1. The IR and Raman data mation including the data for compound 1, 2, and 2_S2.
Eur. J. Inorg. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3

Job/Unit: I20790
/KAP1
Date: 19-09-12 17:36:49
Pages: 11
M. Becker, J. Harloff, T. Jantz, A. Schulz, A. Villinger
FULL PAPER
Table 3. Crystallographic details of HTCP, HTCP·2H2O, and
MeTCP.
HTCP
HTCP·2H2O MeTCP
C8HN5·2H2O C9H3N5
Formula
Fw [gmol–1]
Color
Cryst. system
Space group
a [Å]
b [Å]
c [Å]
α [°]
C8HN5
167.14
203.17
181.16
colorless
colorless
colorless
orthorhombic orthorhombic orthorhombic
Pna21
11.4239(4)
7.5869(3)
9.6957(3)
90
Pna21
13.854(3)
10.023(2)
6.858(2)
90
Pca21
12.667(1)
6.4604(7)
10.9375(9)
90
Figure 3. Hydrogen bonding in solvent free HTCP [d(N1···N3Ј) =
2.897 Å] leading to planar chains of HCTP molecules.
β [°]
90
90
840.35(5)
4
0.09
0.71073
173
90
90
952.3(4)
4
0.11
0.71073
173
90
90
895.1(1)
4
0.09
0.71073
173
γ [°]
V [Å3]
Z
μ [mm–1]
λ Mo-Kα [Å]
T [K]
Measured refl.
Indep. refl.
Refl. with IϾ2σ(I)
Rint.
14732
2483
2258
0.029
336
6106
2283
1549
0.054
416
7164
2462
2101
0.027
368
F(000)
R1 {R[F2 Ͼ 2σ(F2)]} 0.036
0.043
0.089
0.95
0.037
0.089
1.09
wR2 (all data)
GooF
0.083
1.07
Parameters
CCDC
123
911668
156
891167
129
891168
Figure 4. Ball-and-stick representation of HTCP·2H2O displaying
hydrogen bonding around one TCP ion. Selected bond lengths [Å]
and angles [°]: N1–C4 1.348(3), N1–C1 1.361(3), N2–C5 1.136(3),
N3–C6 1.145(3), N4–C7 1.145(3), N5–C8 1.140(3), C1–C2
1.389(3), C1–C5 1.422(3), C2–C3 1.410(3), C2–C6 1.423(3), C3–C4
1.380(3), C3–C7 1.428(3), C4–C8 1.423(3), O1···O2 2.703(3); C4–
N1–C1 108.2(2), N1–C1–C2 109.2(2), N1–C1–C5 122.2(2), C2–
C1–C5 128.6(2), C1–C2–C3 106.1(2), C1–C2–C6 124.7(2), C3–C2–
C6 129.1(2), C4–C3–C2 106.8(2), C4–C3–C7 124.5(2), C2–C3–C7
128.7(2), N1–C4–C3 109.7(2), N1–C4–C8 124.0(2), C3–C4–C8
126.3(2), N2–C5–C1 178.0(3), N3–C6–C2 178.0(3), N4–C7–C3
177.2(3), N5–C8–C4 175.8(3).
Table 4. Crystallographic details of Me4NTCP, EMIMTCP and
NaTCP·2.33(THF).
Me4NTCP
EMIMTCP
NaTCP·2.33THF
Formula
Fw [gmol–1]
Color
Cryst. system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C12H12N6
240.28
colorless
orthorhombic
Cmca
6.6339(5)
20.819(2)
19.878(1)
90
90
90
2745.4(3)
8
0.08
C14H11N7
277.30
colorless
monoclinic
P21/c
7.1996(4)
11.4526(5)
17.5271(9)
90
92.885(2)
90
1443.4(1)
4
0.09
0.71073
173
11495
2805
2251
C8N5Na·2.33C4H8O
357.36
colorless
Sulfide Bridged 2_S2
triclinic
Compound 2_S2 was recrystallized from MeOH to yield
[Na(MeOH)1.5]2[C8N4S4]. Compound 2_S2 crystallizes in
the triclinic space group P1 with two formula units per unit
¯
P1
12.6752(3)
15.2851(4)
17.3205(5)
67.384(1)
70.118(1)
72.894(1)
2861.0(1)
6
0.11
0.71073
173
70690
15118
¯
cell (Figure 1). The sodium cations are octahedrally coordi-
nated by three O atoms of the MeOH solvent molecules
and three N atoms of the cyano groups leading to a two-
dimensional network. A slightly distorted C2 symmetry is
found for the [C8N4S4]2– anion with two almost planar
C4N2S2 moieties linked by the S–S bridge [d(S1–S4) =
2.1031(7) Å cf. Σrcov(S–S) = 2.06 Å].[34] Both cyano groups
are part of these planes. The sulfur–carbon bond lengths
amount to 1.762–1.763 Å, in accord with a typical S–N sin-
gle bond [cf. Σrcov(S–N) = 1.78 Å].[34] All C–CN units are
almost linear with angles between 177–179°.
γ [°]
V [Å3]
Z
μ [mm–1]
λ Mo-Kα [Å]
T [K]
0.71073
173
4349
989
698
Measured refl.
Indep. refl.
Refl. with IϾ2σ(I)
Rint.
10313
0.049
1124
0.037
1008
0.034
576
F(000)
R1 {R[F2Ͼ 2σ(F2)]} 0.042
0.056
0.044
wR2 (all data)
GooF
0.104
1.02
0.154
1.08
0.127
1.07
Dithiin 3
Parameters
CCDC
107
891169
217
891170
919
891171
The molecular compound 3 crystallizes in the monoclinic
space group P21/n (Z = 4, see Figure 1). There are only four
4
www.eurjic.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: I20790
/KAP1
Date: 19-09-12 17:36:49
Pages: 11
Structure and Bonding of Tetracyanopyrrolides
Figure 5. ORTEP drawing of the molecular structure of HTCP
(left) and MeTCP (right). Thermal ellipsoids with 50% probability
at 173 K. Selected bond lengths [Å] and angles [°]: HTCP: N1–C1
1.354(2), C1–C2 1.384 (2), N1–C4 1.354(2), C1–C5 1.424(2), C2–
C3 1.412(2), N2–C5 1.140(2), C2–C6 1.429(2), N3–C6 1.139(2),
C3–C4 1.386(2), N4–C7 1.144(2), C3–C7 1.422(2), N5–C8 1.143(2),
C4–C8 1.424(2); N1–C4–C3 108.9(1), N1–C1–C2 108.52(9), N1–
C4–C8 123.5(1), N1–C1–C5 123.5(1), C3–C4–C8 127.6(1), C2–C1–
C5 128.0(1), N2–C5–C1 176.0 (1), C1–C2–C3 107.0(1), N3–C6–
C2 179.9(2), C1–C2–C6 125.8(1), N4–C7–C3 177.9(1), C3–C2–C6
127.2(1), N5–C8–C4 177.2(1); MeTCP: N1–C4 1.353(2), N1–C1
1.361(2), N1–C5 1.465(2), N2–C6 1.137(2), N3–C7 1.137(2), N4–
C8 1.136(2), N5–C9 1.137(2), C1–C2 1.376(2), C1–C6 1.419(2),
C2–C3 1.406(2), C2–C7 1.419(2), C3–C4 1.381(2), C3–C8 1.421(2),
C4–C9 1.422(2); C4–N1–C1 108.1(1), C4–N1–C5 125.5(1), C1–
N1–C5 126.3(1), N1–C1–C2 109.1(1), N1–C1–C6 123.0(1), C2–
C1–C6 127.9(1), C1–C2–C3 106.9(1), C1–C2–C7 124.5(1), C3–C2–
C7 128.6(1), N2–C6–C1 177.4(2), N3–C7–C2 177.2(2), N4–C8–C3
177.4(2), N5–C9–C4 177.4(2).
Figure 6. View along the a axis in NaTCP displaying layers with
no significant interactions between these layers (THF molecules
omitted for clarity).
weak S···NC van der Waals interactions with intermo-
lecular distances between 3.27–3.4 Å [cf. ΣrvdW(S···N) =
3.4 Å].[35] A slightly distorted C2v symmetry is found for 3
with a strongly folded central six-membered S2C4 ring
(ϽC1–C2–S2–C3 45.03°). Both S2C2 moieties are planar
(deviation from planarity Ͻ0.6°). Interestingly, both cyano
groups are also part of these planes. The sulfur–carbon
bond lengths are in the range 1.762–1.763 Å, in accord with
a typical single bond [cf. Σrcov(S–C) = 1.78 Å]. The C–C
bonds within the ring amount to 1.338–1.341 Å indicating
double bonds, whereas the exocyclic C–C bonds are signifi-
cantly longer at 1.434–1.437 Å [cf. Σrcov(C–C) = 1.50 vs.
Σrcov(C=C) = 1.34 Å].[34]
Figure 7. Ball-and-stick representation of the coordination environ-
ment of the three independent NaTCP ion pairs (A, B, and C). For
the Na+ ions only the coordinating atoms are shown. Selected bond
lengths [Å] and angles [°]: N1–C1 1.355(2), N1–C4 1.356(2), N2–
C5 1.142(2), N3–C6 1.140(2), N4–C7 1.140(2), N5–C8 1.140(2),
N6–C9 1.356(2), N6–C12 1.358(2), N7–C13 1.142(2), N8–C14
1.139(2), N9–C15 1.142(2), N10–C16 1.144(2), N11–C17 1.354(2),
N11–C20 1.358(2), N12–C21 1.141(2), N13–C22 1.138(2), N14–
C23 1.138(2), N15–C24 1.139(2), C1–C2 1.394(2), C1–C5 1.432(2),
C2–C3 1.403(2), C2–C6 1.423(2), C3–C4 1.397(2), C3–C7 1.425(2),
C4–C8 1.432(2), C9–C10 1.397(2), C9–C13 1.429(2), C10–C11
1.405(2), C10–C14 1.424(2), C11–C12 1.401(2), C11–C15 1.420(2),
C12–C16 1.425(2), C17–C18 1.394(2), C17–C21 1.428(2), C18–C19
1.403(2), C18–C22 1.422(2), C19–C20 1.395(2), C19–C23 1.422(2),
C20–C24 1.428(2); N2–C5–C1 175.3(1), N3–C6–C2 177.5(1), N4–
C7–C3 177.7(2), N5–C8–C4 174.9(1), N7–C13–C9 176.5(2), N8–
C14–C10 178.4(2), N9–C15–C11 177.5(2), N10–C16–C12 175.9(1),
N12–C21–C17 176.6(1), N13–C22–C18 178.6(2), N14–C23–C19
179.5(2), N15–C24–C20 177.6(1).
HTCP and HTCP·2H2O
The free acid crystallizes either as a dihydrate or as a
solvent-free species in the orthorhombic space group Pna21
Eur. J. Inorg. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5

Job/Unit: I20790
/KAP1
Date: 19-09-12 17:36:49
Pages: 11
M. Becker, J. Harloff, T. Jantz, A. Schulz, A. Villinger
FULL PAPER
2.897 Å is found for HTCP in the solid state, which leads
to chains of planar HCTP molecules (Figure 3). A slightly
different picture is observed for HTCP·2H2O (Figure 4).
Here, both water molecules are linked by strong hydrogen
bonds (O1···O2 2.703 Å) and form a Zundel ion. Such a
dihydrate moiety is closely attached through O1 by a second
strong hydrogen bond with the acidic proton (H1) of the
TCP ion as illustrated in Figure 4 (N1···O1 2.595 Å). Ad-
ditionally, three of the four cyano groups also form weak
hydrogen bonds with heavy-atom distances between 2.96–
3.01 Å. The main molecular structural motif of HTCP and
HTCP·2H2O is the almost C2v-symmetric tetracyanopyrrol-
ide unit as shown in Figures 3, 4, and 5. All four cyano
groups are linearly attached to the five-membered ring with
NC–Cring distances between 1.422–1.423 Å, which are only
slightly longer than the Cring–Cring distances [e.g. C1–C2
1.389(3), C2–C3 1.410(3), and C3–C4 1.380(3) Å in
HTCP·2H2O] indicating partial double bond character and
delocalization of π-electron density along the carbon frame-
Figure 8. ORTEP drawing of the molecular structure of Me4NTCP
(left) and EMIMTCP (right). Thermal ellipsoids with 50% prob-
ability at 173 K. Selected bond lengths [Å] and angles [°]:
Me4NTCP: N1–C4 1.354(3), C2–C6 1.417(4), N1–C1 1.354(3), C3–
C4 1.405(4), N2–C5 1.141(4), C3–C7 1.409(4), N3–C6 1.150(4), work in HTCP (vide infra). The CN distances range from
C4–C8 1.433(4), N4–C7 1.150(4), N6–C11 1.486(4), N5–C8
1.136–1.145 Å in accord with the values for typical CN tri-
1.139(4), N6–C10 1.488 (3), N6–C9 1.491(4); N2–C5–C1 180.0(4),
ple bonds [cf. Σrcov(CϵN) = 1.14 Å].[34]
N3–C6–C2 179.5(3), N4–C7–C3 180.0(3), N5–C8–C4 179.8 (3);
EMIMTCP: N1–C4 1.355(3), N1–C1 1.355(3), N2–C5 1.148(3),
N3–C6 1.148(3), N4–C7 1.148(3), N5–C8 1.148(3); N2–C5–C1
177.5(2), N3–C6–C2 179.5(3), N4–C7–C3 178.1(2), N5–C8–C4 MeTCP
178.6(3).
In contrast to HTCP·2H2O, MeTCP crystallizes without
significant intermolecular interactions in the orthorhombic
space group Pca21 with four formula units in the unit cell.
The asymmetric unit consists of a planar C2v-symmetric
molecule with a disordered methyl group, which was split
into two parts (Figure 5, right). The metrical parameters
are very similar to those found in HTCP (vide supra).
NaTCP
Three independent NaTCP ion pairs are found within
¯
the triclinic unit cell of this compound (space group P1, Z
= 6), which only differ with respect to the coordination
modes around the Na+ and TCP– ions as depicted in Fig-
ure 6. Thus, the unit cell contains six NaTCP moieties and
in addition seven THF solvent molecules, which are linked
by numerous interactions. The Na+ ions have either a 4N +
2O or a 3N + 3O coordination leading to a distorted octa-
hedral environment for all sodium ions (Figure 7). Al-
though, the pyrrolide nitrogen atom always takes part in
the Na+ coordination, either one (Figure 7, structure A and
B) or two CN groups (structure C) remain uncoordinated.
Owing to these strong interactions, layers are formed, how-
ever, no interpenetration is observed as shown in Figure 6.
The C4N rings are superimposed but between these layers
neither considerable interionic interactions nor π-stacking
effects are observed. Two slightly different sets of Na–N
bond lengths are found: d(Na–Ncyano) = 2.44–2.53 and
d(Na–Npyrrolide) = 2.54–2.59 Å. It is interesting to note that
no significant difference in the CN bond lengths is observed
Figure 9. Top: view along the a axis displaying layers. Bottom: sig-
nificant van der Waals interactions between these layers (right).
Distances [Å] Ͻ 3.4: a = 3.384, b = 3.350, c = 3.384; cf.
ΣrvdW(C···C) = 3.4, ΣrvdW(C···N) = 3.3.
with four formula units per unit cell. One strong hydrogen depending on the coordination mode (1.138–1.144 Å) and
bond along N1–H1···N3Ј with a heavy-atom distance of even the uncoordinated cyano groups are within this range.
6
www.eurjic.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: I20790
/KAP1
Date: 19-09-12 17:36:49
Pages: 11
Structure and Bonding of Tetracyanopyrrolides
Although the coordination environment around the TCP veals a strong mixing of the three occupied, mainly bonding
ion does not support C2v symmetry, the coordinated anion MOs of the C4N ring as known from [H4C4N]– with the
retains almost local C2v symmetry. Again the metrical pa- out-of-plane π bond of the four cyano groups yielding seven
rameters compare well with those found in HTCP (vide su- occupied π-MOs with mainly bonding character as depicted
pra).
in Figure 10.
Me4NTCP and EMIMTCP
Me4NTCP crystallizes in the orthorhombic space group
Cmca with eight formula units per unit cell (Figure 8, left),
and EMIMTCP crystallizes in the monoclinic space group
P21/c with four formula units per unit cell (Figure 8, right).
In contrast to NaTCP, no coordinative interactions between
cations and anions are detected for Me4NTCP and EM-
IMTCP. However, as illustrated in Figure 9, anion···anion
π–π stacking[36,37] is observed in both compounds, which is
more pronounced in Me4NTCP as indicated by the shorter
distances between the TCP layers (Me4NTCP: 3.4–3.5, EM-
IMTCP: 3.5–3.6 Å). X-ray crystal structure analysis for
Me4NTCP and EMIMTCP showed that the TCP anion
possesses high planarity and nearly C2v symmetry (Fig-
ures 8 and 9). The atoms of the NC4 skeleton deviate by
only 0.009 (MeTCP) and 0.0011 (EMINTCP) Å, respec-
tively, from the least-squares plane. The TCP anions are
uniformly stacked along the a axis with an interplanar dis-
tance of about 3.4 Å in Me4NTCP, nearly equal to the sum
of the van der Waals radii of the carbon atoms of the two
TCP planes [cf. ΣrvdW(C) = 1.7, rvdW(N) = 1.6].[34,35] The
neighboring TCP columns are not linked with each other
and, therefore, no three-dimensional structure is observed
as found for NaTCP (vide supra). The cations are located
in vacant channels.
Figure 10. π MOs in the TCP ion displaying a strong delocalization
into the CN groups.
Computations
Calculations were carried out with the Gaussian 03 pack-
age of molecular orbital programs to gain further insight
into the electronic situation in the TCP ion.[38] The struc-
Conclusions
Salts bearing the tetracyanopyrrolide anion were synthe-
tures of the TCP ion and for comparison the parent ion sized in good yields starting from tetracyano-1,4-dithiin (3)
[H4C4N]– were optimized within the DFT approach at the and sodium azide. The structure and bonding of such salts
pbe1pbe level with an aug-cc-pVDZ basis set.[39] Vi- is discussed for the first time and the anion can be referred
brational frequencies were also computed to characterize to as a pseudohalide with π bonds highly delocalized over
all structures as minima on the potential energy surface. A the entire anion including the four cyano groups. The
natural bond orbital analysis (NBO)[40] was performed at planar anion is C2v symmetric and represents a multifunc-
the same level, to study the charge distribution, bond polar- tional binary CN ligand, which is capable of forming classic
ization, and hybridization effects. The C4N core in the par- coordination bonds through the lone pairs of the CN
ent anion [H4C4N]– possesses a charge of –1.74e which de- groups or the ring nitrogen atom. In addition, noncovalent
creases upon substitution of all H atoms by CN groups to interactions such as π–π interactions are found and can be
–0.80e corresponding to a total loss of 0.95e. In accord with used to strengthen structural and electronic communication
the pseudohalogen concept (vide supra), the basicity of the between organic ligands. With metal ions the multidentate
ring nitrogen atom also decreases as displayed by the TCP ligand forms a σ-conjugation network, with weakly
change in the partial charge (–0.63 vs. –0.45e). As the entire coordinating cations such as Me4N+ or EMIM+ isolated
TCP ion is planar, strong in-plane and out-of-plane delocal- ion pairs are observed, in which anion···anion π–π stacking
ization of π electrons is found in the MO and NBO picture, occurs, and in HTCP hydrogen bonds with water molecules
respectively, leading among other things to fairly short C– dominate the solid-state structure. Interestingly, all four cy-
CN and C–C distances, in accord with partial double bond ano groups are not always involved in the coordination
character (see above). A close inspection of the π MOs re- chemistry. It can be concluded that the utilization of TCP
Eur. J. Inorg. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
7

Job/Unit: I20790
/KAP1
Date: 19-09-12 17:36:49
Pages: 11
M. Becker, J. Harloff, T. Jantz, A. Schulz, A. Villinger
FULL PAPER
Tetramethylammonium Tetracyanopyrrolide (Me4NTCP): Tetracy-
ano-1,4-dithiin (10.8 g, 0.05 mol), sodium azide (3.25 g, 0.05 mol),
and 200 mL of ethanol was mixed and stirred overnight, and nitro-
gen slowly evolved. The dark red reaction mixture was filtered to
remove elemental sulfur (1.15 g), and the filtrate was evaporated to
dryness under reduced pressure. Water (200 mL) was added, and a
brown solid (1.1 g) that contained appreciable amounts of elemen-
tal sulfur was removed by filtration. The aqueous filtrate was decol-
orized with “Darco” and stirred at 0 °C, tetramethylammonium
chloride (11 g) was added as a saturated aqueous solution. Reddish
brown tetramethylammonium tetracyanopyrrolide (7.25 g, 62.5%)
was removed by filtration, washed with water, and dried under re-
duced pressure; m.p. (DSC): 118.7 °C, Tdec = 423 °C. C12H12N6
(240.27): calcd. C 59.99, H 5.03, N 34.98; found C 59.11, H 5.01,
N 34.13. 1H NMR ([D6]DMSO, 300 MHz, 25 °C): δ = 3.09 (s, CH3,
12 H) ppm. 13C NMR ([D6]DMSO, 75 MHz, 25 °C): δ = 119.8 (s,
ions in combination with transition metal ions will results
in supramolecular chemistry and for the paramagnetic met-
als even molecular magnetism can be expected.
Experimental Section
General Information: All substances were used as received: NaCN
(Alfa Aesar, 98%), CS2 (Riedel-de Haën, Germany), NaN3 (Acros
Organics, 99%), NMe4Cl (Merck, 98%), (NH4)2S2O8 (Roth, 98%).
1
NMR: H and 13C spectra were obtained with Bruker Avance 250
(250 MHz) and Avance 300 (300 MHz) spectrometers and were ref-
erenced externally. [D6]DMSO was dried with molecular sieves
(3 Å). IR spectra were recorded with a Nicolet 380 FTIR spectrom-
eter equipped with a Smart Orbit attenuated total reflectance
(ATR) device; Raman spectra were recorded with a Bruker Vertex
70 FTIR spectrometer with a RAM II FT-Raman module
equipped with a Nd:YAG laser (1064 nm), or Kaiser Optical Sys-
tems RXN1-785 nm microprobe. CHN analyses were conducted
with an Analysator Flash EA 1112 instrument from Thermo Quest
or C/H/N/S-Mikronalysator TruSpec-932 instrument from Leco.
Differential scanning calorimetry (DSC) measurements were re-
corded with a from Mettler–Toledo 823e calorimeter. A sample of
approximately 1 to 2 mg was placed in an aluminium crucible. The
closed crucible was placed in the furnace. The closed furnace was
flushed with nitrogen and the sampled was measured using a heat-
ing rate of 5 °C per minute. The heat flow was calculated based on
a two point calibration (melting points of In and Zn) using the
Metler software.
Cquat, 2 C), 114.5 (s, Cquat, 2 C), 112.5 (s, Cquat, 2 C), 102.0 (s,
Cquat, 2 C), 54.4 (s, CH , 4 C) ppm. IR (ATR): ν = 3039 (w), 2220
˜
3
(s), 1485 (s), 1475 (s), 1415 (m), 1372 (w), 1132 (w), 1074 (m), 948
(s), 677 (w) cm–1; Raman (500 mW, 5 scans, 25 °C): ν = 2229 (10),
˜
2228 (10) cm–1.
1-Ethyl-3-methylimidazolium Tetracyanopyrrolide (EMIMTCP): To
a solution of tetramethylammonium tetracyanopyrrolide (2.4 g,
10 mmol) in water/acetone was added AgNO3 (2.2 g, 13 mmol) in
water. After stirring for 2 h the brown silver salt was collected,
washed three times with 20 mL of water and suspended in another
30 mL of water. To the suspension was added 1-ethyl-3-methylimi-
dazolium iodide (1.9 g, 8 mmol) in water (20 mL). After stirring for
7 d, the suspension was filtered. Removal of the solvent of the
filtrate led to light brown ionic liquid; yield 61%; m.p. (DSC):
29.8 °C, Tdec. = 230.4 °C. C14H11N7·2.5H2O (322.32): calcd. C
52.17, H 5.00, N 30.42; found C 51.99, H 4.25, N 30.91. 1H
NMR ([D6]DMSO, 300 MHz, 25 °C): δ = 9.23 (s, NCHN, 1 H),
X-ray Structure Determination: X-ray quality crystals were selected
in Fomblin YR-1800 perfluoroether (Alfa Aesar) at ambient tem-
peratures. The samples were cooled to 173(2) K during measure-
ment. The data were collected with a Bruker Apex Kappa-II CCD
diffractometer using graphite-monochromated Mo-Kα radiation (λ
= 0.71073 Å). The structures were solved by direct methods
(SHELXS-97) and refined by full-matrix least-squares procedures
(SHELXL-97). Semi-empirical absorption corrections were applied
(SADABS).
3
7.77 (s, NCHCHN, 1 H), 7.69 (s, NCHCHN, 1 H), 4.20 (q, JH,H
3
= 7.4 Hz, 2 H, CH2), 3.85 (s, 3 H, NCH3), 1.41 (t, JH,H = 7.4 Hz,
3 H, CH3) ppm. 13C NMR ([D6]DMSO, 75 MHz, 25 °C): δ = 136.5
(s, NCHN, 1 C), 123.6 (s, NCHCHN, 1 C), 122.0 (s, NCHCHN, 1
C), 119.8 (s, Cquat, 2 C), 114.6 (s, Cquat, 2 C), 112.5 (s, Cquat, 2 C),
102.5 (s, Cquat, 2 C), 44.2 (s, CH2, 1 C), 35.7 (s, NCH3, 1 C), 15.1
Synthesis
(s, CH , 1 C) ppm. IR (ATR): ν = 3414 (br), 3152 (w), 3121 (w),
˜
3
2994 (w), 2755 (w), 2714 (w), 2225 (s), 2217 (s), 1598 (w), 1572 (m),
1471 (m), 1450 (m), 1347 (s), 1328 (s), 1167 (vs), 1076 (m), 1028
(w), 962 (w), 826 (s), 739 (s), 709 (w), 675 (w), 631 (m), 616 (vs)
Tetracyano-1,4-dithiin: A suspension of NaCN (49.0 g, 1 mol) and
DMF (300 mL) was stirred vigorously and CS2 (76.1 g, 1 mol) was
added dropwise over one hour. H2O (2.5 L) was added and the
mixture was stored overnight at 6 °C. The precipitate (sulfur) was
removed by filtration. A solution of H2O (500 mL) and (NH4)2-
S2O8 (228.0 g, 1 mol) was added to the filtrate over an hour, the
mixture was stirred over 30 min, and the product was collected by
filtration. The yield of the raw product was 40–50 g (80–90%) and
was contaminated with sulfur (5 weight percentage). The resulting
residue was applied to the top of an open-bed silica gel column.
The column was eluted with ethyl acetate/n-heptane (v:v = 3:1).
The resulting purified fractions were combined and evaporated un-
der reduced pressure; yield 34–39 g (60–70%); m.p. (DSC):
175.6 °C, Tdec = 257 °C. C8N4S2 (216.23): calcd. C 44.43, N 25.91,
S 29.66; found C 44.67, N 25.53, S 29.11. 13C NMR ([D6]DMSO,
63 MHz, 25 °C): δ = 125.4 (s, CN, 4 C), 112.4 (s, Cquat, 4 C) ppm.
cm–1; Raman (500 mW, 1000 scans, 25 °C): ν = 2230 (10), 1473 (1),
˜
1414 (2), 1309 (2) cm–1.
Tetracyanopyrrole (HTCP): A column containing Amberlyst 15
ion-exchange resin (200 g) was thoroughly washed with 10 mol-%
HCl, deionized water, acetone, and acetonitrile. A solution of tetra-
methylammonium tetracyanopyrrolide (2.4 g, 0.01 mol) in acetoni-
trile (25 mL) was slowly added to the top of the column. The free
pyrrole was eluted with acetonitrile and the eluent evaporated to
dryness under reduced pressure. The resulting residue was applied
to the top of an open-bed silica gel column. The column was eluted
with ethyl acetate/n-heptane (v:v = 3:1). The resulting purified frac-
tions were combined and evaporated under reduced pressure; yield
54%, Tdec. (DSC) = 202 °C C8HN5·2H2O (203.16): calcd. C 47.30,
IR (ATR): ν = 2921 (m), 2852 (s), 2226 (m), 2212 (s), 1532 (m),
H
2.48,
N 34.47; found C 47.08, H 2.69, N
34.33. 1H
˜
1486 (s), 1463 (s), 1455 (s), 1306 (s), 1160 (m), 1148 (m), 1122 (w),
NMR (CD3CN, 250 MHz, 25 °C): δ = 11.09 (s, 1 H, NH) ppm. 13
C
1927 (w), 997 (w), 926 (w), 869 (w), 825 (w), 805 (s), 677 (w), 623 NMR (CD3CN, 63 MHz, 25 °C): δ = 113.5 (s, Cquat, 2 C), 110.1 (s,
(m), 582 (s), 561 (s) cm–1; Raman (50 mW, 1500 scans, 25 °C): ν =
Cquat, 2 C), 109.0 (s, Cquat, 2 C), 107.0 (s, Cquat, 2 C) ppm. IR
˜
2283 (1), 2218 (10), 2185 (3), 1560 (4), 620 (1), 472 (1), 349 (1)
cm–1. MS m/z (%) = 216 (100) [M], 184 (11) [M – S], 70 (34) [M –
(NC–C–S)], 32 (31) [S].
(ATR): ν = 3572 (m), 3501 (m), 3161 (w), 3047 (w), 2939 (w), 2796
˜
(w), 2700 (m), 2557 (w), 2251 (s), 2241 (s), 1610 (m), 1493 (w), 1462
(m), 1443 (m), 1285 (m), 1083 (m), 893 (s), 673 (m) cm–1; Raman
8
www.eurjic.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: I20790
/KAP1
Date: 19-09-12 17:36:49
Pages: 11
Structure and Bonding of Tetracyanopyrrolides
(500 mW, 1000 scans, 25 °C): ν = 2256 (10), 1491 (4), 1445 (5), 1351
˜
Acknowledgments
(1), 1068 (1), 674 (1), 520 (1) cm–1. MS m/z (%) = 167 (100) [M].
HRMS (EI): calcd. for C8HN5 167.02265; found 167.02256.
Financial support by the Deutsche Forschungsgemeinschaft
(DFG) is gratefully acknowledged. We thank LONZA for supply
of chemicals and helpful advice.
N-Methyltetracyanopyrrole (MeTCP): To a solution of acetone and
tetramethylammonium tetracyanopyrolide (2.2 g, 9.16 mmol), di-
methyl sulfate (1.15 g, 9.16 mmol) was added, and the mixture was
stirred overnight. For purification, ethyl acetate was added, and the
mixture was filtered over a sintered glass filter filled with silica gel.
The product was crystallized from dichloromethane (135 mg); yield
8%; m.p. (DSC): 187.45 °C, Tdec. = 361.9 °C. C12H12N6 (240.27):
calcd. C 59.67, H 1.67, N 38.66; found C 59.53, H 1.59, N 37.59.
1H NMR ([D6]DMSO, 300 MHz, 25 °C): δ = 4.0 (s, 3 H, CH3)
ppm. 13CNMR ([D6]DMSO, 75 MHz, 25 °C): δ = 111.6 (s, 2 C,
Cquat), 109.5 (s, 2 C, Cquat), 108.1 (s, 2 C, Cquat), 104.3 (s, 2 C,
[1] G. Bähr, G. Schleitzer, Chem. Ber. 1955, 88, 1771.
[2] Du Pont Patent, US3008967, 1961.
[3] a) H. E. Simmons, D. C. Blomstrom, R. Vest, J. Am. Chem.
Soc. 1962, 84, 4746; b) H. E. Simmons, D. C. Blomstrom, R.
Vest, J. Am. Chem. Soc. 1962, 84, 4756; c) H. E. Simmons,
D. C. Blomstrom, R. Vest, J. Am. Chem. Soc. 1962, 84, 4772;
d) H. E. Simmons, D. C. Blomstrom, R. Vest, J. Am. Chem.
Soc. 1962, 84, 4782.
Cquat), 37.8 (s, 4 C, NCH ) ppm. IR (ATR): ν = 3083 (w), 2959 [4] M. Becker, Dissertationschrift, University of Rostock, Ger-
˜
3
many, 2012.
(w), 2830 (w), 2299 (w), 2242 (s), 2236 (s), 2194 (w), 1532 (w), 1503
(s), 1462 (s), 1377 (s), 1262 (w), 1224 (w), 1186 (m), 1126 (w), 1013
(w), 965 (w), 934 (w), 899 (w), 838 (m), 836 (w), 806 (w), 705 (w),
[5] H. E. Simmons, R. D. Vest, O. W. Webster, J. Org. Chem. 1980,
45, 5113.
[6] I. Heldt, U. Behrens, Z. Anorg. Allg. Chem. 2005, 631, 749.
[7] a) H. Schmidtmann, Ber. Dtsch. Chem. Ges. 1896, 29, 1168;
b) E. Cox, A. Fontaine, Bull. Soc. Chim. Fr. 1954, 948; c) W.
Middleton, V. Engelhardt, J. Am. Chem. Soc. 1958, 80, 2788;
d) W. Middleton, E. Little, D. Coffmann, J. Am. Chem. Soc.
1958, 80, 2795; e) S. Trofimenko, E. Little, H. Mower, J. Org.
Chem. 1962, 27, 433.
678 (m), 550 (w) cm–1; Raman (500 mW, 250 scans, 25 °C): ν =
˜
2961 (0.3), 2245 (10.0), 1505 (2.1), 1464 (2.2), 1424 (1.6), 1380 (0.7),
517 (0.5), 134 (0.8), 111 (0.9), 82 (1.3) cm–1. HRMS (ESI): calcd.
180.03157; found 180.03198.
Sodium Tetracyanopyrrolide (NaTCP): A column containing 200 g
of AMBERLYST 15 ion-exchange resin was used for ion exchange.
A solution of acetonitrile and tetramethylammonium tetracya-
nopyrrolide (1 g, 4.16 mmol) was added to the top of the column.
After the whole solution was run through the column, the column
was flushed with acetonitrile (100 mL) twice. All acetonitrile frac-
tions were collected, and the solvents were evaporated to dryness.
The yield of the raw product was 85%. For purification, the residue
was crystallized from hot THF and n-heptane and then dissolved
in hot ethanol. n-Heptane was added to form two phases (yellow/
red). The mixture was stored overnight at –40 °C. The red phase
with higher density evaporated until crystals formed at –40 °C. Af-
ter addition of diethyl ether, the precipitation of white NaTCP was
observed. The hygroscopic precipitate was collected by filtration
through a sintered glass funnel and was washed three times with
diethyl ether (yield 25%). Alternative route: Two equimolar solu-
tions of tetramethylammonium tetracyanopyrrolide in acetonitrile
and NaClO4 in water were united, the acetonitrile was evaporated,
and the solution was filtered. The filtrate was evaporated to dryness
and the precipitate was dissolved in THF. When diethyl ether was
slowly added the product crystallized. The crystallization step was
repeated four times; m.p. 400.5 °C. DSC: M.p. 400.5 °C. C8N5Na
(189.11): cald. C 50.81, N 37.03, found C 52.10, N 36.94. 13C NMR
([D6]DMSO, 63 MHz, 25 °C): δ = 119.8 (s, Cquat, 2 C), 114.5 (s,
Cquat, 2 C), 112.5 (s, Cquat, 2 C), 102.0 (s, Cquat, 2 C) ppm. IR
[8] W. Madelung, E. Kern, Justus Liebigs Ann. Chem. 1922, 427,
1.
[9] a) H. Brand, A. Schulz, A. Villinger, Z. Anorg. Allg. Chem.
2007, 633, 22; b) H. Brand, J. F. Liebman, A. Schulz, P. Mayer,
A. Villinger, Eur. J. Inorg. Chem. 2006, 4294; c) H. Brand, J. F.
Liebman, A. Schulz, Eur. J. Org. Chem. 2008, 4665; d) A.
Bernsdorf, H. Brand, R. Hellmann, M. Köckerling, A. Schulz,
A. Villinger, K. Voss, J. Am. Chem. Soc. 2009, 131, 8958; A.
Schulz, H. Brand, A. Villinger, Chem. Asian J. 2009, 4, 1588.
[10] A. W. Browne, A. B. Hoel, J. Am. Chem. Soc. 1922, 44, 2106.
[11] E. Lieber, E. Offentdahl, C. N. R. Rao, J. Org. Chem. 1957, 22,
1750.
[12] F. Sommer, Ber. Dtsch. Chem. Ges. 1915, 48, 1833.
[13] A. M. Golub, H. Köhler, Chemie der Pseudohalogenide, VEB
Deutscher Verlag der Wissenschaften, Berlin, 1979.
[14] a) A. Schulz, Habilitationsschrift, University of Munich
(LMU), Germany, 2001; b) A. M. Golub, H. Köhler, V. V. Sto-
penko, Chemistry of Pseudohalides, Elsevier, Amsterdam, 1986.
[15] Du Pont de Nemours & Co. patent, US3221024,1962.
[16] a) A. P. Purdy, E. Houser, C. F. George, Polyhedron 1997, 16,
3671; b) B. Jürgens, W. Milius, P. Morys, W. Schnick, Z. Anorg.
Allg. Chem. 1998, 624, 91; c) B. Jürgens, E. Irran, J. Schneider,
W. Schnick, Inorg. Chem. 2000, 39, 665; d) E. Irran, B. Jürgens,
W. Schnick, Chem. Eur. J. 2001, 7, 5372.
[17] K. Voss, M. Becker, A. Villinger, V. N. Emel’yanenko, R.
Hellmann, B. Kirchner, F. Uhlig, S. P. Verevkin, A. Schulz,
Chem. Eur. J. 2011, 17, 13526.
(ATR, 32 scans, 25 °C): ν = 3542 (w), 3131 (w), 2769 (vw), 2721
˜
(vw), 2241 (vs), 2226 (vs), 1681 (w), 1478 (s), 1417 (m), 1329 (w), [18] P. Starynowicz, Acta Crystallogr., Sect. C 1991, 47, 2198.
[19] H. Brand, P. Mayer, A. Schulz, T. Soller, A. Villinger, Chem.
Asian J. 2008, 3, 1050.
[20] a) B. Jürgens, E. Irran, W. Schnick, J. Solid State Chem. 2001,
157, 241; b) W. Schnick, S. Schmid, B. Jürgens, E. Irran, Z.
Anorg. Allg. Chem. 2005, 631, 1512.
[21] a) B. Jürgens, H. A. Höppe, E. Irran, W. Schnick, Inorg. Chem.
2002, 41, 4849; b) B. V. Lotsch, W. Kockelmann, J. Senker, W.
Schnick, J. Solid State Chem. 2003, 176, 180; c) B. V. Lotsch,
J. Senker, W. Schnick, Inorg. Chem. 2004, 43, 895; d) B. V.
Lotsch, W. Schnick, E. Naumann, J. Senker, J. Phys. Chem. B
2007, 111, 11680.
[22] B. V. Lotsch, W. Schnick, New J. Chem. 2004, 28, 1129.
[23] Reviews: a) I. Krossing, I. Raabe, Angew. Chem. 2004, 116,
2116; Angew. Chem. Int. Ed. 2004, 43, 2066; b) C. Reed, Acc.
Chem. Res. 1998, 31, 133; c) S. H. Strauss, Chem. Rev. 1993,
93, 927, and references cited therein.
1305 (vw), 1201 (vw), 1087 (m), 1043 (vw), 1012 (vw), 979 (vw),
728 (w), 692 (m), 679 (m), 536 (s) cm–1; Raman (500 mW, 400 scans,
25 °C): ν = 2247 (10.0), 1482 (2.1), 1420 (2.4), 1318 (1.5), 1310
˜
(1.6), 546 (0.5), 467 (0.4), 157 (0.6), 136 (1.6), 109 (0.7), 76 (0.8)
cm–1.
CCDC-891163 (for 1), -891164 (for 2_S2), -891165 (for 3), -891166
(for HTCP), -891167 (for HTCP·2H2O), -891168 (for MeTCP),
-891169 (for Me4NTCP), -891170 (for EMIMTCP) and -891171
(for NaTCP·2.33THF) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
Supporting Information (see footnote on the first page of this arti-
cle): Experimental and theoretical details.
Eur. J. Inorg. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
9

Job/Unit: I20790
/KAP1
Date: 19-09-12 17:36:49
Pages: 11
M. Becker, J. Harloff, T. Jantz, A. Schulz, A. Villinger
FULL PAPER
[24]
[25]
[26]
[27]
[28]
[29]
[30]
Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar,
J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P.
Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R.
Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R.
Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morok-
uma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzew-
ski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K.
Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V.
Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B.
Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L.
Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A.
Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.
Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian 03, Re-
vision E.01, Gaussian, Inc., Wallingford, CT, 2004.
P. Wasserscheid, T. Welton, Ionic Liquids in Synthesis, Wiley-
VCH, Weinheim, Germany, 2003.
H. Shobukawa, H. Tokuda, A. B. H. Susan, M. Watanabe,
Electrochim. Acta 2005, 50, 3872.
H. Shobukawa, H. Tokuda, S.-I. Tabata, M. Watanabe, Elec-
trochim. Acta 2004, 50, 1.
S. Seki, Y. Kobayashi, H. Miyashiro, Y. Ohno, A. Usami, Y.
Mita, M. Watanabe, N. Terada, Chem. Commun. 2006, 544.
P. Wang, S. M. Zakeeruddin, M. Shaik, R. Humphry-Baker,
M. Grätzel, Chem. Mater. 2004, 16, 2694.
P. Wang, S. M. Zakeeruddin, M. Shaik, R. Humphry-Baker,
M. Grätzel, Chem. Mater. 2004, 16, 2694.
F. Mazille, Z. Fei, D. Kuang, D. Zhao, S. M. Zakeeruddin, M.
Grätzel, P. Dyson, Inorg. Chem. 2006, 45, 1585.
[31] C. A. Angell, W. Xu, Science 2003, 302, 422.
[32] Y. Yoshida, K. Muroi, A. Otsuka, A. Saito, M. Takahashi, T.
Yoko, Inorg. Chem. 2004, 43, 1458.
[33] S. A. Forsyth, S. R. Batten, Q. Dai, D. R. MacFarlane, Aust. J.
Chem. 2004, 57, 121.
[34] P. Pyykkö, M. Atsumi, Chem. Eur. J. 2009, 15, 12770.
[35] A. Holleman, E. Wiberg, N. Wiberg, Lehrbuch der Anorgan-
ischen Chemie, vol. 102, Walter de Gruyter, Berlin, 2007, Ap-
pendices IV and V.
[36] S. Suzuki, Y. Morita, K. Fukui, K. Sato, D. Shiomi, T. Takui,
K. Nakasuji, Inorg. Chem. 2005, 44, 8197.
[39] a) T. H. Dunning, J. Chem. Phys. 1989, 90, 1007; b) D. E.
Woon, T. H. Dunning, J. Chem. Phys. 1993, 98, 1358; c) K. A.
Peterson, T. H. Dunning, J. Chem. Phys. 2002, 117, 10548.
[40] a) E. D. Glendening, A. E. Reed, J. E. Carpenter, F. Weinhold,
NBO Version 3.1; b) J. E. Carpenter, F. Weinhold, THEO-
CHEM 1988, 169, 41; c) F. Weinhold, J. E. Carpenter, The
Structure of Small Molecules and Ions, Plenum Press, New
York, 1988, p. 227; d) F. Weinhold, C. Landis, Valency and
Bonding. A Natural Bond Orbital Donor–Acceptor Perspective,
Cambridge University Press, 2005, and references cited therein.
Received: July 13, 2012
[37] B. Moulton, M. J. Zaworotko, Chem. Rev. 2001, 101, 1629.
[38] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T.
Published Online: ᭿
10
www.eurjic.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: I20790
/KAP1
Date: 19-09-12 17:36:49
Pages: 11
Structure and Bonding of Tetracyanopyrrolides
Coordination Chemistry
Salts containing the binary tetracyanopyr-
rolide anion (TCP) were synthesized from
tetracyano-1,4-dithiin and sodium azide.
The planar TCP anion, which might be re-
garded as a pseudohalide, is C2v symmetric
and represents a multifunctional binary
CN ligand as demonstrated in a series of
solid-state structures.
M. Becker, J. Harloff, T. Jantz,
A. Schulz,* A. Villinger .................. 1–11
Structure and Bonding of Tetracyanopyr-
rolides
Keywords: Coordination chemistry / Li-
gand design / N ligands / Main group
elements / Pseudohalogen
Eur. J. Inorg. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
11