Ferrocenylpyrazole-A versatile building block for hydrogen-bonded organometallic supramolecular assemblies

Article abstract of DOI:10.1016/j.jorganchem.2006.11.011

The crystal architectures of 5-ferrocenylpyrazole (1) and its metal complexes were investigated. Compound 1 can form non-solvated and chloroform-solvated crystals. In both cases, 1 forms a zigzag one-dimensional architecture via NH?N hydrogen bonds. The hydrogen bond exhibits a twofold disorder, which was shown to be static by solid-state ¹³C NMR. In the solvated crystal, the chloroform is released at 415 K, associated with melting of the crystal. The reaction of 1 with metal salts provided metal-centered ferrocenyl clusters [Zn(NO₃)₂(1)₄] (4), [Co(NO₃)₂(1)₄] (5), [CoCl₂(1)₄] (6), [Zn(NCS)₂(1)₂] (7), cis-[Pt(NH₃)₂(1)₂](PF₆) ₂ (8), and trans-[Pt(NH₃)₂(1)₄](PF₆) ₂ (9). In all of these complexes, 1 acts as a monodentate ligand. In 4, 5, and 7, the multinuclear units are joined via hydrogen bonds to form supramolecular chains. Two polymorphs were found for the crystals of 4. Both are composed of the same hydrogen-bonded chains, but their arrangements are different. 5-Ferrocenyl-1-tritylpyrazole (2) and 4-ferrocenyl-1-methylpyrazole (3) were also crystallographically characterized.

Full text of DOI:10.1016/j.jorganchem.2006.11.011

Journal of Organometallic Chemistry 692 (2007) 1834–1844
www.elsevier.com/locate/jorganchem
Ferrocenylpyrazole—A versatile building block for
hydrogen-bonded organometallic supramolecular assemblies
a,b,
a
a
a
Tomoyuki Mochida
*, Fumiko Shimizu , Hirotaka Shimizu , Kazuya Okazawa ,
c
c
Fuminori Sato , Daisuke Kuwahara
a
Department of Chemistry, Faculty of Science, Toho University, Miyama, Funabashi, Chiba 274-8510, Japan
Research Center for Materials with Integrated Properties, c/o Faculty of Science, Toho University, Japan
b
c
The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan
Received 1 September 2006; received in revised form 7 November 2006; accepted 7 November 2006
Available online 16 November 2006
Abstract
The crystal architectures of 5-ferrocenylpyrazole (1) and its metal complexes were investigated. Compound 1 can form non-solvated
and chloroform-solvated crystals. In both cases, 1 forms a zigzag one-dimensional architecture via NHꢀ ꢀ ꢀN hydrogen bonds. The hydro-
gen bond exhibits a twofold disorder, which was shown to be static by solid-state 13C NMR. In the solvated crystal, the chloroform is
released at 415 K, associated with melting of the crystal. The reaction of 1 with metal salts provided metal-centered ferrocenyl clusters
[Zn(NO3)2(1)4] (4), [Co(NO3)2(1)4] (5), [CoCl2(1)4] (6), [Zn(NCS)2(1)2] (7), cis-[Pt(NH3)2(1)2](PF6)2 (8), and trans-[Pt(NH3)2(1)4](PF6)2
(9). In all of these complexes, 1 acts as a monodentate ligand. In 4, 5, and 7, the multinuclear units are joined via hydrogen bonds to
form supramolecular chains. Two polymorphs were found for the crystals of 4. Both are composed of the same hydrogen-bonded chains,
but their arrangements are different. 5-Ferrocenyl-1-tritylpyrazole (2) and 4-ferrocenyl-1-methylpyrazole (3) were also crystallographi-
cally characterized.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Crystal structure; Hydrogen bond; Pyrazole; Ferrocene; Metal complex
1. Introduction
its combination with hydrogen-bond donors leads to
hydrogen-bonded supermolecules with various dimensions
[4d]. We also prepared ferrocenyl tetrazoles and triazoles,
which exhibit one-dimensional crystal architecture based
on weak Nꢀ ꢀ ꢀHC hydrogen bonds [6]. In this study, to real-
ize the synergy of hydrogen bonds and coordination bonds
in an organometallic molecular assembly, we designed 5-
ferrocenylpyrazole (FcPz, 1). Pyrazole derivatives form
intriguing hydrogen-bonded assemblies, such as chains,
cyclic tetramers, trimers, and dimers (Fig. 1a), and they
often show disorder with respect to their NH protons [7].
The hydrogen bond in pyrazoles has drawn attention in
terms of intermolecular proton transfer [8]. Furthermore,
pyrazole derivatives are versatile ligands [9] that can act
as monodentate ligands in their neutral form (Fig. 1a)
and as bidentate bridging ligands in the form of pyrazolate
Various organometallic supramolecular assemblies have
been reported to date [1–3]. In the construction of supra-
molecular assemblies, hydrogen bonds and coordination
bonds play essential roles. Our approach toward the study
of organometallic supermolecules is to introduce heteroaryl
substituents into ferrocenes, which has led to the design of
versatile ligands such as 5-ferrocenylpyrimidine (FcPM) [4]
and relevant ligands [5]. FcPM gives various assembled
structures when combined with transition metal salts, and
*
Corresponding author. Address: Department of Chemistry, Faculty of
Science, Toho University, Miyama, Funabashi, Chiba 274-8510, Japan.
Tel./fax: +81 47 472 4406.
E-mail address: mochida@chem.sci.toho-u.ac.jp (T. Mochida).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.11.011

T. Mochida et al. / Journal of Organometallic Chemistry 692 (2007) 1834–1844
1835
showed a gradual decrease above 510 K, which corresponds
to degradation. The melting point of this crystal was deter-
mined to be 431.7 K by differential scanning calorimetry
(DH = 24.2 kJ molꢁ1). On the other hand, the TG trace of
the chloroform-solvated crystal exhibited a sudden weight
loss of 10% at 415 K, and with further increasing tempera-
ture, it showed a gradual decrease above 520 K. This obser-
vation suggests that the chloroform in the solvated crystals
is suddenly released at 415 K, associated with melting of the
crystal lattice. Thus, the guest molecule is held in the crystal
above its boiling point of 335 K.
Reaction of 1 with zinc and cobalt salts provided metal-
centered ferrocenyl clusters (Scheme 2), [Zn(NO3)2(1)4] (4),
[Co(NO3)2(1)4] (5), [CoCl2(1)4] (6), and [Zn(NCS)2(1)2] (7),
which were crystallographically characterized. Reaction of
1 with platinum salts in aqueous media produced cis-
[Pt(NH3)2(1)2](PF6)2 (8) and trans-[Pt(NH3)2(1)4](PF6)2
(9) in high yields. Compound 1 acted as a monodentate
ligand in all of these complexes.
Fig. 1. (a) Hydrogen bonding modes in pyrazoles and (b) assembly modes
of metal complexes with pyrazoles.
anions (Fig. 1b). The NH group in the neutral form can
form hydrogen bonds. For these reasons, 1 is an interesting
molecule with respect to the design of organometallic
supermolecules. Similar ligands 3-ferrocenylpyrazole [10]
and ferrocenylmethylpyrazole [11] have previously been
investigated, and intriguing metallocene ligands exhibiting
both hydrogen bonding and metal complexation [12] are
known to exist. Here we report the preparation and crystal
architecture of 1 and its metal complexes.
The redox potentials of 1, 2, 8, and 9 were measured
in acetonitrile by cyclic voltammetry. Compounds 1 and
2 exhibited quasi-reversible waves at E1/2 = ꢁ0.04 and
ꢁ0.03 V, respectively (vs. Cp2Fe/Cp2Fe+), which corre-
spond to the redox potentials of the ferrocenyl moieties.
This is much lower than those of other heteroarylferroc-
enes, e.g. 0.14, 0.21, and 0.27 V for ferrocenylpyrimidine
(FcPM), ferrocenyltetrazole, and ferrocenyltriazole,
respectively [4e,6], which is consistent with the substitu-
ent effect [14]. Platinum complexes 8 and 9 each showed
one redox wave, at E1/2 = 0.21 and 0.22 V, respectively,
which indicates that no electrochemical communication
occurs between the ferrocenyl groups through the metal
center. Metal complexation generally raises the redox
potential of the ligand [4e,15]. Despite the lower redox
potential of 1, the redox potentials of its platinum com-
plexes were comparable to those of FcPM complexes
(E1/2 = 0.20–0.21 V) [4e]. This result is probably ascrib-
able to the higher electron donating ability of 1 over
FcPM.
2. Results and discussion
2.1. Preparation and properties of 1 and its metal complexes
5-Ferrocenylpyrazole (1) was obtained by hydrolysis of
4-ferrocenyl-1-tritylpyrazole (2), which was prepared by
Negishi coupling [4a,13] of chlorozincated ferrocene and
iodotritylpyrazole (Scheme 1). Acetic acid was used for
hydrolysis to avoid oxidation of the ferrocenyl moiety.
We also prepared 4-ferrocenyl-1-methylpyrazole (3) by
methylation of 1. Recrystallization of 1 from acetonitrile
produced non-solvated crystals, while recrystallization
from chloroform produced solvated crystals (1 Æ 0.5CHCl3),
both of which were crystallographically characterized. To
examine the solvent desorption process from the solvated
crystal, we performed thermogravimetric (TG) analysis of
both crystal types. The TG trace of the non-solvated crystal
Scheme 1.
Scheme 2.

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T. Mochida et al. / Journal of Organometallic Chemistry 692 (2007) 1834–1844
Table 1
between the chains of 1 (Fig. 2b). The hydrogen-bonded
chains in both crystal forms have an almost identical
molecular arrangement. Fig. 3 shows the structure of the
chain in the chloroform-solvated crystal. The chain is made
up of two crystallographically independent molecules, A
and B. The Cp–Py rings in 1 are almost coplanar. The
chain consists of a repeating unit of –A–A–B–B–, with
inversion centers between A–A and also between B–B.
Therefore, the pyrazole rings of the A molecules related
by the inversion center are coplanar, which also holds for
the B molecules. The dihedral angle between the pyrazole
rings of molecules A and B is 74.4(3)ꢁ in the solvated crys-
tal, and 82.6(1)ꢁ in the non-solvated crystal. The inversion
center also imposes symmetry on the intermolecular hydro-
gen-bond potentials between A–A and between B–B. Thus,
the pyrazole NH protons are delocalized symmetrically
over two sites, with an equal statistical occupancy at 0.5.
The intramolecular bond lengths of the pyrazole moieties
in both crystals are shown in Fig. 4. The pyrazole rings
show apparent C2v symmetry, which is not crystallograph-
ically imposed, and no bond alternation was recognized.
This is consistent with the symmetrical distribution of the
hydrogen bond. Crystal structures of 4-ferrocenyl-1-trit-
ylpyrazole (2) and 4-ferrocenyl-1-methylpyrazole (3) were
also determined, and ORTEP drawings of the molecular
structures of 2 and 3 were deposited as Supplementary
materials. In these cases, clear bond alternation of the pyr-
azole ring was apparent (Fig. 4c and d). In these molecules,
the Cp–Pyrazole planes are twisted by 29.8(3)ꢁ and 3.0(2)ꢁ,
respectively.
˚
Hydrogen bond lengths (A) in 1 and its chloroform solvate
N(1)ꢀ ꢀ ꢀN(1)
2.899(3)
N(2)ꢀ ꢀ ꢀN(3)
2.879(3)
N(4)ꢀ ꢀ ꢀN(4)
2.888(3)
1
1 Æ 0.5CHCl3
2.865(7)
2.857(7)
2.940(7)
2.2. Structure and hydrogen bonding in 1 and its chloroform
solvate
The non-solvated and chloroform-solvated crystals of 1
are both composed of chains of 1 connected via NHꢀ ꢀ ꢀN
hydrogen bonds. These crystals exhibit disorder with
respect to their NH protons, as shown below. The hydro-
gen bond distances are listed in Table 1; they are within
the usual range of Nꢀ ꢀ ꢀN hydrogen-bond distances (2.8–
˚
3.2 A) found for pyrazole chain compounds [7], but are
rather shorter than average.
Packing diagrams of each crystal form, projected along
the chain direction (a-axes), are shown in Fig. 2. In the sol-
vated crystal, chloroform is accommodated in channels
The zig-zag hydrogen-bonded molecular arrangement,
as well as its delocalization, is similar to that observed in
4-(1-adamantyl)pyrazole and other materials [16]. Proton
Fig. 3. Hydrogen-bonded one-dimensional zig-zag arrangement of 5-
ferrocenylpyrazole (1) in the chloroform-solvated crystal. Dashed lines
indicate hydrogen bonds. Symbols A and B denote crystallographically
independent molecules. Hydrogen atoms are omitted for clarity.
Fig. 2. Packing diagrams of (a) 5-ferrocenylpyrazole (1) and (b) its
chloroform solvate. Symbols A and B denote crystallographically inde-
pendent molecules. Dashed lines indicate hydrogen bonds. Hydrogen
atoms are omitted for clarity.

T. Mochida et al. / Journal of Organometallic Chemistry 692 (2007) 1834–1844
1837
transfer in one-dimensional hydrogen-bonded systems is of
interest from the viewpoint of proton dynamics involving
the mechanism of solitonic excitation [17]. In pyraz-
oles, the disordered hydrogen bond is considered to be
dynamic only in some cyclic structures [9], but, interest-
ingly, 4-(1-adamantyl)pyrazole exhibits an exchange pro-
cess probably associated with molecular reorientation
[16]. To investigate proton dynamics and molecular motion
of 1 in the crystal, we performed 13C CP/MAS NMR mea-
surements on a polycrystalline sample of the non-solvated
form. Dipolar dephasing experiments and 13C spin–lattice
relaxation time (T1) measurements were also carried out.
Chemical shifts of the peaks and their assignments are
listed in Table 2. In the 13C CP/MAS spectrum, signals
for C3 and C5 (Fig. 1) appeared separately at around
135 and 125 ppm, which indicates that the disorder is sta-
tic. The line shape was invariant between 190 and 353 K.
T1 was long (ꢂ200 s) for C3 and C5, which further sup-
ports the static nature of the disorder. A short T1 (9 s)
was observed for the C5H5 carbons, which suggests that
the ring undergoes rotation at room temperature. Consis-
tently with this, dipolar dephasing for the C5H5 carbons
was not effective. No phase transitions were detected by
DSC measurement between 100 and 460 K except at the
melting point.
˚
Fig. 4. Intramolecular bond lengths (A) in (a) 5-ferrocenylpyrazole (1,
non-solvated form), (b) 5-ferrocenylpyrazole (1, chloroform solvate), (c) 4-
ferroceny-1-tritylpyrazole (2), and (d) 4-ferroceny-1-methylpyrazole (3).
Table 2
13C NMR chemical shifts (d, ppm) for 1 in the solid state
Assignmenta
Chemical shiftsb (T1)
C3
C5
C4
136.7, 135.3(198)
126.4, 123.8(179)
120.4, 119.8(15)
78.8, 77.4(39, 65)
70.3, 69.7(9)
Table 3
˚
C(C5H4)–Pz
C(C5H5)
C(C5H4)–H
Nꢀ ꢀ ꢀO distances (A) in hydrogen bonds in 4 and 5
Intramolecular
Intermolecular
67.5, 56.6(39)
4 (a-form)
4 (b-form)
5
2.862(2)
2.86(1)
2.848(3)
2.738(2)
2.76(1)
2.745(3)
Values of T1(s) are shown in parentheses.
a
Positions of C3, C4, and C5 are shown in Fig. 1.
b
Site splitting was observed.
Table 4
˚
Selected bond lengths (A) and angles (ꢁ) in 4–7
4 (a-form)
Zn(1)–N(1)
N(1)–Zn(1)–N(3)
Cp(Fe1)–Pza
2.112(1)
90.42(5)
17.7(1)
Zn(1)–N(3)
N(1)–Zn(1)–O(1)
Cp(Fe2)–Pza
2.132(1)
84.15(5)
30.0(1)
Zn(1)–O(1)
N(3)–Zn(1)–O(1)
2.178(1)
93.59(5)
4 (b-form)
Zn(1)–N(1)
N(1)–Zn(1)–N(3)
Cp(Fe1)–Pza
2.135(6)
90.6(2)
13.5(3)
Zn(1)–N(3)
N(1)–Zn(1)–O(1)
Cp(Fe2)–Pza
2.115(6)
83.6(2)
26.6(6)
Zn(1)–O(1)
N(3)–Zn(1)–O(1)
2.182(5)
93.1(2)
5
Co(1)–N(1)
Co(1)–N(3)
Cp(Fe1)–Pza
2.108(2)
2.108(2)
18.3(2)
Co(1)–O(1)
N(1)–Co(1)–N(3)
Cp(Fe2)–Pza
2.152(2)
90.54(8)
30.6(2)
N(3)–Co(1)–O(1)
N(1)–Co(1)–O(1)
93.34(7)
83.11(7)
6
Co(1)–N(1)
Co(1)–N(3)
Cp(Fe1)–Pza
2.130(2)
2.118(2)
17.0(2)
Co(1)–Cl(1)
N(1)–Co(1)–N(3)
Cp(Fe2)–Pza
2.526(5)
92.05(7)
13.9(2)
N(3)–Co(1)–Cl(1)
N(1)–Co(1)–Cl(1)
90.44(5)
87.99(5)
7
Zn(1)–N(1)
N(1)–Zn(1)–N(1)b
2.003(2)
103.55(9)
Zn(1)–N(3)
N(3)–Zn(1)–N(3)b
1.937(2)
112.4(1)
N(1)–Zn(1)–N(3)
Cp–Pza
103.68(8)
17.5(1)
a
Dihedral angle between the Cp and pyrazole rings.
Symmetry code: ꢁx + 1, y, ꢁz + 1/2.
b

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T. Mochida et al. / Journal of Organometallic Chemistry 692 (2007) 1834–1844
2.3. Structures of metal-centered ferrocenyl clusters 4–7
in Fig. 5a. The units form a chain structure via intermolec-
ular NHꢀ ꢀ ꢀO hydrogen bonds (Fig. 5b). In the molecule,
the Zn ion exhibits an octahedral coordination geometry,
and the nitrate anions are at the axial positions. In the unit
cell, intramolecular hydrogen bonds are formed between
the NH hydrogens of two ligands and two nitrate anions
Compounds 4–7 are metal-centered ferrocenyl clusters
in which 1 acts as a monodentate ligand. Three of these
clusters (4–6) are centrosymmetric pentanuclear complexes,
while 7 is a trinuclear complex. The ligand tends to form
assembled structures in which coordination bonds and
hydrogen bonds coexist. There are two crystallographically
independent molecules in each unit in 4–6, and one in 7.
Bond lengths around the metal atoms and Cp–Pz angles
are listed in Table 4.
˚
[N(2)ꢀ ꢀ ꢀO(2) distance: 2.862(2) A] (Fig. 5a). The NH
hydrogens of the other two ligands are involved in intermo-
lecular hydrogen bonding with the nitrate oxygens of adja-
˚
cent units [N(4)ꢀ ꢀ ꢀO(3) distance: 2.738(2) A], connecting
the unit along the a-axis. The structure of the hydrogen-
bonded chain in the b-form is almost the same. Hydro-
gen-bond lengths for both forms are comparable (Table 3).
[Zn(NO3)2(1)4] (4) has two polymorphs, the a-form and
the b-form. The molecular structure of the a-form is shown
Fig. 5. (a) ORTEP drawing (50% thermal probability ellipsoids) of [Zn(NO3)2(1)4] (4) (a-form). (b) Hydrogen-bonded one-dimensional arrangement of 4
in the a-form crystal. Dashed lines indicate hydrogen bonds. Hydrogen atoms are omitted.

T. Mochida et al. / Journal of Organometallic Chemistry 692 (2007) 1834–1844
1839
Fig. 6. Packing diagrams of (a) a-form and (b) b-form of [Zn(NO3)2(1)4] (4). Hydrogen atoms are omitted.
Packing diagrams of the a- and b-forms, projected along
the hydrogen-bonded chain direction, are shown in Fig. 6a
and b, respectively. The unit cell volume of the b-form is
twice that of the a-form, and in the b-form there is an addi-
tional chain at the center of the cell. This polymorphism is
attributed to the difference in the arrangement of the supra-
molecular chains. The calculated densities are comparable
(1.619 g cmꢁ3 (a-form) and 1.613 g cmꢁ3 (b-form)) at room
temperature.
units form a chain arrangement, as shown in Fig. 8. Inter-
molecular NHꢀ ꢀ ꢀS hydrogen bonds are formed between the
NH group of the ferrocenyl ligand and S(1) of the thiocy-
anate anion [Nꢀ ꢀ ꢀS distance: 3.336(2) A].
˚
[Co(NO3)2(1)4] (5) is isostructural with the a-form of 4.
Hydrogen bond lengths are also comparable (Table 3).
Reflecting the different ionic radii, the M–NFcPz distance
˚
in 5 (2.108(2) A) is slightly shorter than that in 4
˚
(2.112(1)–2.135(6) A), and the unit cell volume of 5 is smal-
ler than that of 4-b by 0.1%. We could not find polymor-
phs, but considering the structural similarity between 4
and 5, polymorphism may exist.
The molecular structure of [CoCl2(1)4] (6) is shown in
Fig. 7. The Co ion exhibits an octahedral coordination
geometry with the chloride ions at the axial positions.
The four NH hydrogens form intramolecular hydrogen
bonds with the chlorine atoms, with Nꢀ ꢀ ꢀCl distances of
˚
3.127(2) and 3.085(2) A. No intermolecular hydrogen
bonds are formed.
[Zn(NCS)2(1)2] (7) was the only example of a trinuclear
complex. In the molecule, the Zn ion adopts a tetrahedral
coordination environment, coordinated by the nitrogens
of two ferrocenyl ligands and two thiocyanate ions. The
Fig. 7. ORTEP drawing (50% thermal probability ellipsoids) of
[CoCl2(1)4] (6). Dashed lines indicate hydrogen bonds (NHꢀ ꢀ ꢀCl).
Hydrogen atoms are omitted.

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T. Mochida et al. / Journal of Organometallic Chemistry 692 (2007) 1834–1844
4. Experimental
4.1. General
All reagents and solvents were commercially available
except for 4-iodo-1-tritylpyrazole [20], which was synthe-
sized by following literature procedures. Solution NMR
spectra were recorded on a JEOL JNM-ECL-400 spec-
trometer. Solid-state NMR spectra were recorded using a
Bruker Avance 300 NMR spectrometer with a Bruker
MAS 4 mm probe head and a home-built NMR spectrom-
eter with a Tecmag Apollo console, a Doty MAS 7 mm
probe head, and an Oxford 7.05 T superconducting magnet
system. CP/MAS experiments were performed at
75.43 MHz for 13C with a sample spinning speed of
9 kHz and a CP time of 2 ms. Temperatures of the sample
were detected with a thermocouple on the inside near the
air inlet of the probe housing, which were corrected with
the chemical shift of the carboxyl carbon of samarium ace-
tate [21]. Dipolar dephasing experiments were performed
with a dephasing period of 100 ls [22]. 13C spin–lattice
relaxation times, T1, were measured using the method of
Torcha [23]. Infrared spectra were recorded on a Shimadzu
Prestige-21 FTIR-8400S spectrometer attached with an
AIM-8800 microscope in the 4000–400 cmꢁ1 range. Cyclic
voltammograms were recorded with an ALS/chi electro-
chemical-analyzer model 600 A in dichloromethane solu-
tions containing 0.1 mol dmꢁ3 nBu4NClO4 as the
supporting electrolyte, at a scan rate of 0.1 V sꢁ1. An Ag/
Ag+ reference electrode and a glassy carbon disk working
electrode were used, and the values were referenced to
Fig. 8. One-dimensional arrangement of [Zn(NCS)2(1)2] (7) via weak
hydrogen bonding (NHꢀ ꢀ ꢀS) in the crystal. Hydrogen atoms are omitted.
In all of these metal assemblies of 1, the NH group of
the ligand is involved in hydrogen bonding. Coexistence
of intramolecular and intermolecular hydrogen bonds
was observed in 4 (a-form), 4 (b-form), and 5, while 6
and 7 exhibited only intramolecular and intermolecular
hydrogen bonds, respectively. Similar to 1, FcPM forms
zinc-centered
ferrocenyl
cluster
complexes,
[Zn(NO3)2(FcPM)3] and [Zn(NCS)2(FcPM)2] [4b], but
hydrogen-bond interactions are absent in the FcPM com-
plexes. The stoichiometry and coordination environment
of the nitrate complexes are different for FcPM and 1;
the zinc ion is coordinated by three molecules of FcPM
and four molecules of 1, respectively. Flexibility of the
coordination environment of zinc ions allows such varia-
tion of the L:M ratio [18].
(Cp2Fe)+/0
. Powder X-ray diffraction patterns were
recorded on a MAC Science M03XHF22 diffractometer.
DSC measurements were performed using a Q100 differen-
tial scanning calorimeter (TA instruments) in the tempera-
ture range 100–460 K at
a
rate of 10 K minꢁ1
.
3. Conclusion
Thermogravimetric (TG) analysis was performed under a
nitrogen atmosphere at a heating rate 10 K minꢁ1 on a
Seiko TG/DTA 220U, in the temperature range 25–400 ꢁC.
We designed the 5-ferrocenylpyrazole ligand (1) as a
new building block for supramolecular organometallic
assembly. The crystal structure of 1 consists of zigzag
one-dimensional chains formed via NHꢀ ꢀ ꢀN hydrogen
bonds, which is a typical assembly mode for pyrazoles.
The ligand has proved useful for construction of supermol-
ecules containing both coordination bonds and hydrogen
bonds. The reaction of 1 with metal salts provided metal-
centered ferrocenyl clusters, which are further joined via
inter-unit hydrogen bonds to form chain structures. Poly-
morphism, derived from differing arrangements of the
chains, was also found.
In the metal complexes under discussion, 1 was used as a
neutral ligand. However, pyrazolate anions have been
shown to form cyclic metal complexes exhibiting interest-
ing photophysical properties [19]. A study on the synthesis
of metal complexes with the pyrazolate anion of 1 is cur-
rently in progress in our laboratory, but the desired com-
pounds have not yet been isolated.
4.2. 4-Ferrocenyl-1-pyrazole (1)
4-Ferrocenyl-1-tritylpyrazole (2, see below) (1.80 g,
3.63 mmol) was dissolved in a mixture of dichloromethane
and methanol (1:1 v/v, 80 mL), to which acetic acid
(12 mL) was added. The solution was refluxed for about
1 week. After removal of the solvent under reduced pres-
sure, the residue was dissolved in dichloromethane
(80 mL), and washed with an aqueous solution of sodium
bicarbonate (5 g, 60 mL) and water (80 mL · 3). The
organic layer was separated, dried with magnesium sulfate,
and the solvent was removed under reduced pressure. The
crude product was purified by column chromatography
(silica gel, eluent chloroform:acetone = 8:2). The second
band (Rf = 0.25) gave 4-ferrocenyl-1-pyrazole (1) as fine
needle crystals (0.87 g, yield 95%). The compound was
recrystallized from hexane and acetonitrile. UV–Vis

T. Mochida et al. / Journal of Organometallic Chemistry 692 (2007) 1834–1844
1841
(MeCN, k/nm, e): 207 (19796), 219 (19484), 270 (5532),
341 (101), 452 (214); IR (cmꢁ1): 3118s, 2934s, 1370m,
1147m, 1105m, 1012s, 957m, 865s, 802s, 3103s, 2949s,
1728m, 1597m, 1371s, 1317m, 1140m, 1105s, 1022s, 866s;
1H NMR (400 MHz, CDCl3): d 4.05 (s, 5H), 4.22 (t, 2H,
J = 1.8 Hz), 4.45 (t, 2H, J = 1.8 Hz), 7.63 (s, 2H); 1H
NMR (400 MHz, DMSO-d6): d 3.99 (s, 5H), 4.18 (t, 2H,
J = 1.8 Hz), 4.52 (t, 2H, J = 1.8 Hz), 7.61 (s, 1H), 7.81 (s,
1H), 12.67 (br, 1H). Anal. Calc. for C13H12FeN2: C,
61.94; H, 4.80; N, 11.11. Found: C, 61.83; H, 4.82, N,
11.22%. Orange plate crystals of 1 suitable for X-ray anal-
ysis were obtained by slow cooling of a hot acetonitrile
solution of 1. Crystals of the chloroform solvate,
1 Æ 0.5CHCl3, were obtained by slow evaporation of a
dichloromethane solution of 1. Crystals from hexane, con-
firmed to be in the non-solvated form by powder X-ray dif-
fraction, were used for calorimetric studies.
with water. The organic layer was dried over magnesium
sulfate and then evaporated. The crude product was
recrystallized from hexane. Yellow powder (31 mg,
1
49%). H NMR (400 MHz, CDCl3): d 3.89 (s, 3H), 4.04
(s, 5H), 4.20 (t, 2H, J = 1.8 Hz), 4.41 (t, 2H,
J = 1.8 Hz), 7.35 (s, 1H), 7.54 (s, 1H). Anal. Calc. for
C14H14FeN2: C, 63.19; H, 5.30; N, 10.53. Found: C,
63.15; H, 5.40; N, 10.72%. Orange prismatic crystals of
3 suitable for X-ray analysis were obtained by recrystalli-
zation from acetone.
4.5. [Zn(NO3)2(1)4] (4)
Methanol
solutions
and
(0.5 mL)
Zn(NO3)2 Æ 6H2O
of
1
(3 mg,
(3.9 mg,
1.2 · 10ꢁ2 mmol)
1.19 · 10ꢁ2 mmol) were mixed and left to stand at room
temperature. Orange plate crystals were formed in a week.
The results of elemental analysis indicated that a 1:3 M/L
complex was the major product. Anal. Calc. for
C39H36ZnFe3N8O6 [=Zn(NO3)2(1)3]: C, 48.61; H, 3.97;
N, 11.63. Found: C, 48.71; H, 4.03; N, 11.65%.
4.3. 4-Ferrocenyl-1-tritylpyrazole (2)
Under a nitrogen atmosphere, tert-butyllithium (11 mL,
16.0 mmol; 1.45 M in n-pentane) and a THF suspension
(22 mL) of zinc chloride (2.43 g, 17.8 mmol) were succes-
sively added slowly to a THF (11 mL) solution of ferrocene
(2.35 g, 12.6 mmol) cooled in an ice bath. The solution was
allowed to warm to room temperature, and stirred for 1 h.
To this solution, a THF suspension (12 mL) of bis(triphe-
nylphosphine)palladium chloride (0.455 g) and a THF
solution (30 mL) of 4-iodo-1-tritylpyrazole (5.479 g,
12.6 mmol) were added successively. After stirring the solu-
tion at room temperature for 1 day, water (5 mL) was
added, and insoluble materials were removed by filtration.
The filtrate was concentrated, and the residue was
extracted with diethyl ether (250 mL). The organic layer
was washed with water (150 mL · 4) and brine (100 mL),
and dried with magnesium sulfate. After removing the sol-
vent under reduced pressure, the residue was purified by
column chromatography (silica gel, eluent dichlorometh-
ane:hexane = 7:3). The first band gave ferrocene, and the
second band (Rf = 0.25) gave the desired product as brown
4.6. [Co(NO3)2(1)4] (5)
This complex was prepared as described for 4, using
Co(NO3)2 Æ 3H2O and acetonitrile as a solvent. Orange
plate crystals were obtained. Anal. Calc. for C52H48Cl2Co-
Fe4N8: C, 52.43; H, 4.06; N, 11.76. Found: C, 52.19; H,
4.11; N, 11.86%.
4.7. [CoCl2(1)4] (6)
This complex was prepared as described for 4, using
CoCl2 Æ 6H2O and ethanol as a solvent. Orange plate crys-
tals were obtained. Elemental analysis indicated that a 1:3
M/L complex was the major product. Anal. Calc. for
C39H36Cl2CoFe3N6 [=CoCl2(1)3]: C, 51.81; H, 4.24; N,
9.30. Found: C, 51.75; H, 4.36, N, 9.53%.
4.8. [Zn(NCS)2(1)2] (7)
1
powders (3.44 g, yield 55%). H NMR (400 MHz, CDCl3):
d 3.99 (s, 5H), 4.16 (t, 2H), 4.37 (t, 2H), 7.18–7.20 (m, 6H),
7.31–7.34 (m, 10H), 7.71 (s, 1H). The product was further
used for the preparation of 1. Orange plate crystals of 2
suitable for X-ray analysis were obtained by recrystalliza-
tion from acetonitrile.
This complex was prepared as described for 4, using
Zn(SCN)2 and methanol as a solvent. Orange plate crystals
were obtained. Anal. Calc. for C28H24Fe2N6S2Zn: C, 49.04;
H, 3.53; N, 12.26. Found: C, 48.66; H, 3.64; N, 11.96%.
4.9. cis-[Pt(NH3)2(1)2](PF6)2 (8)
4.4. 4-Ferrocenyl-1-methylpyrazole (3)
cis-[PtCl2(NH3)2] (18 mg, 0.060 mmol) and AgPF6
(33 mg, 0.131 mmol) were dissolved in water (4 mL). The
solution was heated at 60 ꢁC for 3 h in the absence of light,
and then filtered through Celite and added to a methanol
solution (2 mL) of 1 (30 mg, 0.12 mmol). After stirring at
room temperature for 1 day in the absence of light, the sol-
vent was removed under reduced pressure, giving a yellow-
brown powder (58 mg, 94%). The reaction afforded the
desired product almost quantitatively, and no by-products
Under a nitrogen atmosphere, sodium hydride (107 mg,
2.23–3.21 mmol; 50–72% in oil) was dispersed in THF
(20 mL), to which 1 (60 mg, 0.23 mmol) was added slowly
under stirring. After the evolution of hydrogen ceased,
methyl iodide (1 mL) was added to this solution, and stir-
ring continued overnight at room temperature. The sol-
vent was removed under reduced pressure, and the
residue was dissolved in dichloromethane and washed

1842
T. Mochida et al. / Journal of Organometallic Chemistry 692 (2007) 1834–1844
were observed. UV–Vis (MeCN, k/nm, e): 223 (28259), 264
(15216), 433 (948), 849 (17538). 1H NMR (DMSO-d6,
ppm): d 4.03 (s, 10H), 4.26 (s, 4H), 4.56 (s, 4H), 4.70 (br,
6H), 7.94 (s, 2H), 8.29 (s, 2H), 13.93 (s, 2H). Anal. Calc.
for C26H30N6F12P2Fe2Pt: C, 30.52; H, 2.96; N, 8.21%.
Found: C, 29.87; H, 3.10; N, 8.00%.
4.10. trans-[Pt(NH3)2(1)4](PF6)2 (9)
trans-[PtCl2(NH3)2] (31 mg, 0.103 mmol) and AgPF6
(53 mg, 0.208 mmol) were dissolved in water (4 mL). The
solution was heated at 60 ꢁC for 3 h in the absence of light,
and then filtered through Celite and added to a methanol
Table 5
Crystallographic data for 1–3
1
1 Æ 0.5CHCl3
2
3
Empirical formula
Formula weight
Crystal system
Space group
C
252.10
Triclinic
13H12FeN2
C27H25Fe2Cl3N4
623.56
Triclinic
C32H26FeN2
494.40
Triclinic
C14H14FeN2
266.12
Orthorhombic
P212121
5.7993(4)
12.0445(9)
16.5028(1)
ꢀ
ꢀ
ꢀ
P1
P1
P1
˚
a (A)
7.4330(8)
9.9266(1)
15.9111(2)
80.061(2)
87.867(2)
69.978(2)
1086.2(2)
4
7.456(2)
10.498(3)
16.990(5)
76.308(5)
89.620(5)
88.498(5)
1291.6(6)
2
9.4982(7)
12.382(1)
12.438(1)
112.971(2)
106.583(2)
103.675(2)
1186.3(2)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
1152.71(2)
4
1.533
173
1.284
Z
dcalc (g cmꢁ3
T (K)
)
1.542
173
1.357
1.603
120
1.46
1.384
296
0.66
l (cmꢁ1
)
Reflections collected
Independent reflections
Parameters
7913
5294
305
0.0354; 0.0787
0.0443; 0.0828
1.011
9042
6344
325
0.0593; 0.1179
0.1586; 0.1455
1.019
9015
5873
342
0.0627; 0.1254
0.1315; 0.1489
1.019
8602
2854
190
0.0338; 0.0776
0.0375; 0.0793
1.047
b
R1a, wR2 (I > 2r)
b
R1a, wR2 (all data)
Goodness-of-fit
P
P
a
R1 = iFoj ꢁ jFci/ jFoj.
h
i
1=2
P
P
2
2
b
wR2 ¼
wðF 2o ꢁ F c2Þ = wðF o2Þ
.
Table 6
Crystallographic data for 4–7
4 (a-form)
52H48Fe4N10O6Zn
1197.77
Triclinic
4 (b-form)
5
6
7
Empirical formula
Formula weight
Crystal system
Space group
C
C52H48Fe4N10O6Zn
1197.79
Monoclinic
P21/c
7.5111(8)
34.097(3)
C52H48CoFe4N10O6
1191.33
Triclinic
C52H48Cl2CoFe4N8
1138.21
Monoclinic
C2/c
35.881(3)
9.6608(8)
C28H24Fe2N6S2Zn
685.72
Monoclinic
P2/c
16.715(2)
6.2461(9)
14.421(2)
ꢀ
ꢀ
P1
P1
˚
a (A)
7.5127(4)
9.6742(6)
16.9404(1)
85.3640(1)
83.0270(1)
79.6820(1)
1200.15(1)
1
7.5230(7)
9.6502(1)
16.9190(2)
85.462(2)
82.978(2)
79.998(2)
1198.4(2)
1
˚
b (A)
˚
c (A)
11.3874(9)
14.2771(1)
a (ꢁ)
b (ꢁ)
c (ꢁ)
122.250(5)
109.377(2)
98.464(3)
3
˚
V (A )
2466.5(4)
2
1.613
293
1.690
4668.7(7)
4
1.723
173
1.723
1386.0(3)
2
1.643
293
2.072
Z
dcalc (g cmꢁ3
T (K)
)
1.657
173
1.736
1.651
173
1.584
l (cmꢁ1
)
Reflections collected
Independent reflections
Parameters
8939
5867
427
0.0251; 0.0628
0.0279; 0.0725
1.008
17672
6097
331
0.0876; 0.2071
0.1005; 0.2189
1.033
8934
5856
339
0.0379; 0.0782
0.0567; 0.0859
0.998
16839
5771
304
0.0363; 0.0776
0.0485; 0.0826
1.004
9803
3442
177
0.0338; 0.0901
0.0442; 0.0962
1.028
b
R1a, wR2 (I > 2r)
b
R1a, wR2 (all data)
Goodness-of-fit
P
P
a
R1 = iFoj ꢁ jFci/ jFoj.
h
i
1=2
P
P
2
2
b
wR2 ¼
wðF 2o ꢁ F c2Þ = wðF o2Þ
.

T. Mochida et al. / Journal of Organometallic Chemistry 692 (2007) 1834–1844
1843
solution (3 mL) of 1 (53 mg, 0.210 mmol). After stirring at
45 ꢁC for 17 h in the absence of light, the solvent was
removed under reduced pressure. The product was dis-
solved in acetone, filtered through Celite, and concen-
trated; chloroform was added to the concentrate, and the
solution was cooled in a refrigerator. A yellow-brown pow-
der was obtained (72 mg, 68%). The sample was purified by
recrystallization from acetone/chloroform. UV–Vis
(MeCN, k/nm, e): 227 (27132), 267 (16284), 445 (511),
849 (38). 1H NMR (DMSO-d6, ppm): d 4.11 (s, 10H),
4.31 (s, 4H), 4.51 (br, 6H), 4.62 (s, 4H), 8.07 (s, 2H), 8.38
(s, 2H), 14.21 (s, 2H). Anal. Calc. for C26H30N6F12P2Fe2Pt:
C, 30.52; H, 2.96; N, 8.21. Found: C, 29.87; H, 3.10; N,
8.00%.
retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.
ac.uk.
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