Solid-state structure of a tetrazole-substituted ferrocenium salt with weak intermolecular C-H...N hydrogen bonds

Article abstract of DOI:10.1016/j.ica.2011.11.032

A perchlorate salt of ferrocenylphenyltetrazole has been prepared and characterized crystallographically. In the crystal, tape-like one-dimensional molecular arrangements are formed by weak CH...N intermolecular hydrogen bonds between the tetrazole moieties (H...N distance: 2.49 ). A layer-like structure was formed, composed of neutral layers of phenyltetrazole moieties and ionic layers of ferrocenium moieties and anions.

Full text of DOI:10.1016/j.ica.2011.11.032

Inorganica Chimica Acta 382 (2012) 207–209
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Note
Solid-state structure of a tetrazole-substituted ferrocenium salt with weak
intermolecular C–Hꢀ ꢀ ꢀN hydrogen bonds
⇑
Tomoyuki Mochida , Yusuke Funasako
Department of Chemistry, Graduate School of Science, Kobe University, Rokkodai, Nada, Hyogo 657-8501, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 July 2011
Received in revised form 9 November 2011
Accepted 12 November 2011
Available online 19 November 2011
A perchlorate salt of ferrocenylphenyltetrazole has been prepared and characterized crystallographically.
In the crystal, tape-like one-dimensional molecular arrangements are formed by weak CHꢀ ꢀ ꢀN intermo-
lecular hydrogen bonds between the tetrazole moieties (Hꢀ ꢀ ꢀN distance: 2.49 Å). A layer-like structure
was formed, composed of neutral layers of phenyltetrazole moieties and ionic layers of ferrocenium moi-
eties and anions.
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Crystal engineering
Ferrocenium salt
Tetrazole
Crystal structure
Weak hydrogen bond
1. Introduction
interactions of ferrocenylazole salts. Ferrocenium salts with conju-
gated heterocyclic substituents are interesting because of their
Crystal engineering of organometallic crystals has attracted
considerable attention in recent years [1]. C–Hꢀ ꢀ ꢀX intermolecular
interactions, where X is an electronegative atom such as oxygen,
nitrogen, and halogens, are regarded as weak hydrogen bonds
[2,3], and their importance in crystal engineering is well recog-
nized [1,4,5]. As part of our continuous investigation into ferro-
cene-based organometallic supramolecular assemblies [6,7], we
have previously prepared tetrazoles and triazoles with ferrocenyl
substituents, and investigated their structures and properties [8].
X-ray crystallography revealed that short intermolecular C–Hꢀ ꢀ ꢀN
contacts are formed between the azole moieties. Ferrocenyl-tetra-
zoles and -triazoles exhibit one-dimensional molecular arrange-
ments via these interactions (Fig. 1). The Hꢀ ꢀ ꢀN distances are
about 2.3 Å and are 0.4 Å shorter than the sum of the van der Waals
radii. Intermolecular C–Hꢀ ꢀ ꢀN contacts have been found in tetra-
zole [9] and related compounds [5], and play an important role
in their crystal architectures. Although heteroaryl ferrocenes form
a variety of organometallic supramolecular complexes when re-
acted with metal salts [10], only a few complexes of ferrocenylaz-
oles have been reported [11], despite the versatile metal
coordination properties of triazole and tetrazole [12].
optical and electronic properties, and several have been character-
ized crystallographically [13]. Here, we report the X-ray crystal
structure of 1, which exhibits weak C–Hꢀ ꢀ ꢀN interactions between
the tetrazole moieties and Coulombic interactions between the
cations and anions. The structure is compared with those of ferr-
ocenyl- and ferrocenylphenyl-azolium salts [14], which have been
prepared as part of our studies on ferrocene-based ionic liquids
[15]. To our knowledge, this is the first example of the structural
characterization of an azole-substituted ferrocenium salt, whereas
there is a report on a carbazole derivative of a ferrocenium salt
[13].
2. Results and discussion
A small amount of the crystalline salt of 1 was produced by the
reaction of ferrocenylphenyltetrazole and Fe(ClO4)2ꢀ6H2O in meth-
anol followed by vapor diffusion of ether. Considering the redox
potential of ferrocenylphenyltetrazole (E1/2 = 0.09 V, versus
+
FeCp2/FeCp2 [8]), Fe(III) species formed by air oxidation might
be acting as an oxidant.
The molecular structure of 1 determined at 100 K is shown in
Fig. 3 and its crystallographic parameters are listed in Table 1. The
average intramolecular Fe–C distance in the ferrocenium moiety
(2.083 Å) corresponds to the value for the ferrocenium cation
(2.095 Å) [16], and is longer than in neutral ferrocenylphenyltetraz-
ole (2.034 Å) [8]. Among the Fe–C bonds, the bond involving the car-
bon connected to the phenylene ring is the longest [2.112(5) Å]. The
In this study, we isolated and determined the crystal structure
of a perchlorate salt of ferrocenylphenyltetrazole, [Fe(C5H5)(C5H4
PhN4CH)](ClO4) (1; Fig. 2), to investigate the intermolecular
⇑
Corresponding author. Tel./fax: +81 78 803 5679.
E-mail address: tmochida@platinum.kobe-u.ac.jp (T. Mochida).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.11.032

208
T. Mochida, Y. Funasako / Inorganica Chimica Acta 382 (2012) 207–209
Table 1
Crystallographic parameters for 1.
Formula
Formula weight
T (K)
C17H14ClFeN4O4
429.62
100
Crystal system
Space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/c
16.311(5)
8.053(3)
13.118(4)
101.229(4)
1690.0(9)
4
Fig. 1. Schematic illustration of weak C–Hꢀ ꢀ ꢀN hydrogen bonds in azole derivatives
b (°)
(X = CH or N).
V (Å3)
Z
Dcalc (g cmꢁ3
)
1.688
1.084
l
(mmꢁ1
)
Reflections collected
Independent reflections
F(000)
7986
3190
876
Parameters
244
0.0643, 0.1659
0.0918, 0.1883
b
Final R1a, wR2 (I > 2
r)
Final R1a, wR2 (all data)
b
Fig. 2. Chemical diagram of [Fe(C5H5)(C5H4PhN4CH)](ClO4) (1).
a
R1
=
R
||Fo| ꢁ |Fc||/
R|Fo|.
P
P
2
1=2
wR2 ¼ ½ wðF2o ꢁ Fc2Þ= wðF2oÞ ꢂ
.
b
dihedral angles between the Cp–Cp, Cp–phenylene, and phenylene–
tetrazole rings are 1.8(4)°, 14.7(3)°, and 19.7(3)°, respectively. The
Cp rings in the cation adopt a staggered conformation. The bond
lengths in the azole moiety are almost the same as those observed
for ferrocenylphenyltetrazole [8] and N-aryl-tetrazoles [5a,17],
which is consistent with the charge localization in the ferrocenium
moiety.
The packing diagram of 1 projected along the b-axis is shown in
Fig. 4. The ionic moieties and the neutral moieties form layer-like
structures. The perchlorate anions are located between the ferroce-
nium cations, exhibiting a short CCpHꢀ ꢀ ꢀOanion contact [Hꢀ ꢀ ꢀO dis-
tance: 2.365(8) Å]. The cations and anions form ionic layers, in
which p–p interactions exist between the Cp rings of the neighbor-
ing ferrocenium unit. The ionic layers are separated by the neutral
layers of phenyltetrazole moieties. The azole moieties form a tape-
like one-dimensional arrangement via weak C–Hꢀ ꢀ ꢀN hydrogen
bonds (Fig. 5). The molecular arrangement closely resembles those
of ferrocenyl-tetrazole and -triazole (Fig. 1), whereas the arrange-
ment in ferrocenylphenyl-tetrazole and -triazole are somewhat
different [8]. The C–Hꢀ ꢀ ꢀN distance of 2.485(4) Å in 1 is 0.27 Å
shorter than the sum of the van der Waals radii (2.75 Å). The dis-
tance is comparable to those in ferrocenylphenyl-tetrazole and -
triazole (2.5 Å), but longer than those in ferrocenyl-tetrazole and
-triazole (2.3 Å) [8]. The ferrocenylphenyl moieties are arranged
as pendants with respect to the one-dimensional tape structure
of the neutral moieties, and adjacent phenylene-tetrazole moieties
overlap via p–p interactions.
Ferrocenyl- and ferrocenylphenyl-azolium salts also generally
exhibit layer-like structures [14]. The azolium cations and anions
form ionic layers, with the azole hydrogens interacting with the
anion and the ferrocenyl moieties aggregating to form neutral
Fig. 4. Packing diagram of 1 viewed along the b-axis. Hydrogen atoms are omitted
for clarity. C–Hꢀ ꢀ ꢀN contacts are indicated by dashed lines.
layers. Hence, despite the different location of the cation within
the molecules, the azolium salts and 1 have similar structures.
In summary, the importance of weak C–Hꢀ ꢀ ꢀN hydrogen bonds
in the salt of ferrocenylazole has been revealed. This study may
lead to the future construction of magnetic organometallic supra-
molecules involving ferrocenium cations.
3. Experimental
Ferrocenylphenyltetrazole
[4-(4-ferrocenylphenyl)-1H-tetra-
zole] was prepared according to the literature [8]. Other chemicals
were commercially available. Vapor diffusion of ether into a meth-
anol solution of ferrocenylphenyltetrazole and Fe(ClO4)2ꢀ6H2O pro-
duced a small amount of black crystals of 1 together with
Fig. 3. ORTEP drawing of the molecular structure of 1 with the numbering scheme.
Thermal ellipsoids are shown at the probability level of 50%.

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209
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Appendix A. Supplementary material
CCDC 832625 contains 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.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2011.11.032.
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