Synthesis, crystal structure and redox properties of dihydropyrazole- bridged ferrocene-based derivatives

Article abstract of DOI:10.1016/j.molstruc.2012.05.026

Dihydropyrazole-bridged ferrocene-based derivatives were prepared by corresponding chalcones with hydrazine hydrate, then acylation with 3-(ethoxycarbonyl)propionyl chloride directly in high yields and purity. All of these compounds were characterized by

Full text of DOI:10.1016/j.molstruc.2012.05.026

Journal of Molecular Structure 1024 (2012) 40–46
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, crystal structure and redox properties of dihydropyrazole-bridged
ferrocene-based derivatives
a,b,
Heng-Dong Li a, Zai-He Ma a, Kun Yang a, Li-Li Xie a,b, , Yao-Feng Yuan
⇑
⇑
a Department of Chemistry, Fuzhou University, Fuzhou 350108, China
b Fujian Provincial Key Laboratory of Photocatalysis, State Key Laboratory Breeding Base, Fuzhou University, Fuzhou 350002, China
h i g h l i g h t s
"
"
Two dihydropyrazole-bridged ferrocenyl-substituted derivatives were synthesized in high yields.
Ordered two-dimensional structure was promoted by weak hydrogen-bonding interactions and
molecules.
p–p stacking interactions between neighboring
"
DFT calculation results explain the electron transfer mechanism of typical compound.
a r t i c l e i n f o
a b s t r a c t
Article history:
Dihydropyrazole-bridged ferrocene-based derivatives were prepared by corresponding chalcones with
hydrazine hydrate, then acylation with 3-(ethoxycarbonyl)propionyl chloride directly in high yields
and purity. All of these compounds were characterized by MS, IR, 1H NMR, 13C NMR and elemental anal-
ysis. The relationship between the structure and redox properties was investigated based on the results of
single crystal X-ray structure determinations and cyclic voltammetry. The mechanism of the electron
transfer for representative compound 4b was verified by density functional theory (DFT) calculations.
Ó 2012 Elsevier B.V. All rights reserved.
Received 11 February 2012
Received in revised form 8 May 2012
Accepted 8 May 2012
Available online 16 May 2012
Keywords:
Ferrocene (Fc)
Dihydropyrazole (Pz)
Crystal structure
Cyclic voltammetry
DFT
1. Introduction
substituted derivatives in high yields. The relationship between
the structure and redox properties was investigated based on the
Recently, great interest has been generated in the synthesis and
study of heterocyclic derivatives containing one or more ferrocenes,
since these derivatives have potential applications as new func-
tional materials in several areas [1–5]. It is well known that pyrazole
derivatives have been arousing lots of interest for the construction
of new heterocyclic compounds in which dihydropyrazole (Pz) com-
poses the core structure of various compounds [6–11]. As a stable
and readily oxidizable organometallic complex, ferrocene has been
widely employed in multifunctional systems [12], which have
exhibited potential utilizations in electrochemical sensors [13,14],
molecular recognition [15,16] and highly efficient burning rate
catalysts [17].
results of single crystal X-ray structure determinations, electro-
chemical investigations and theoretical calculations (DFT). The
mechanism of the electron transfer for typical compound 4b was
studied during the redox process [18].
2. Experimental
2.1. General
All experiments were carried out under an atmosphere of dry
nitrogen. All solvents employed were dried by routine procedures.
Melting points are uncorrected. NMR spectra were obtained on a
Bruker AV600 spectrometer at ambient temperature in CDCl3.
Combining the considerations above, we designed a simple and
general approach to synthesis dihydropyrazole-bridged ferrocenyl-
Infrared spectra were measured on
a Spectrum 2000 FTIR
spectrometer in KBr pellets and reported in cmꢀ1. Electrospray ion-
ization mass spectrometry (ESI-MS) was performed using an X7
ICP-MS instrument. 1-Aryl-3-ferrocenyl-2-propen-1-on (2) was
prepared according to the previously reported methods [17,19].
⇑
Corresponding authors. Address: Department of Chemistry, Fuzhou University,
Fuzhou 350108, China. Tel./fax: +86 591 22866161.
E-mail addresses: xielili@fzu.edu.cn (L.-L. Xie), yaofeng_yuan@fzu.edu.cn
(Y.-F. Yuan).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.05.026

H.-D. Li et al. / Journal of Molecular Structure 1024 (2012) 40–46
41
X-ray structural measurements were made using a Rigaku RAX-
IS-IV CCD diffractometer with graphite-monochromated Mo K
2.2.1. Synthesis of 5-(4-bromophenyl)-1-(3-
(ethoxycarbonyl)propionyl)-3-ferrocenyl-4,5-dihydro-1H-pyrazole
a
radiation (k = 0.071073 nm) at 293(2) K. All diffraction data were
collected by scanning in a certain mode and refined in Lp factor.
The structures were solved by the direct method and refined by
the full-matrix least-squares method on F2 using the SHELX-97
program suite [20].
Cyclic voltammetry (CV) was performed with a CHI620C elec-
trochemical workstation in a conventional three-electrode electro-
chemical cell using glassy carbon as the working electrode,
platinum electrode as counter electrode, and Ag/AgCl (3.0 M KCl)
as reference electrode at room temperature. The bare glassy carbon
(4a)
Elution of the chromatogram with 25% ethyl acetate in petro-
leum ether afforded 4a as a brown solid, 1.06 g (82.2%); m.p.
110–112 °C. 1H NMR (600 MHz, CDCl3) d 7.48 (2H, d, J = 7.7 Hz,
PhAH), 7.13 (2H, d, J = 7.6 Hz, PhAH), 5.49 (1H, HX, dd,
JXB = 11.2 Hz, JXA = 4.8 Hz, PzAH), 4.67 (1H, s, CpAH), 4.57 (1H, s,
CpAH), 4.42 (2H, s, CpAH), 4.14 (5H, m, CpAH), 3.65 (1H, HB, dd,
JBA = 17.1 Hz, JBX = 11.2 Hz, PzAH), 3.09 (2H, m,CH2), 2.94 (1H, HA,
dd, JAB = 17.2 Hz, JAX = 4.8 Hz, PzAH), 2.68 (2H, m, CH2), 2.63 (2H,
m, CH2), 1.26 (3H, t, CH3). 13C NMR (150 MHz, CDCl3) d 173.12
(C@O), 169.14 (C@O), 156.08 (PzAC), 141.04 (PhAC), 132.06
(PhAC), 127.16 (PhAC), 121.47 (PhAC), 75.01 (CpAC), 70.58
(CpAC), 70.48 (CpAC), 69.43 (CpAC), 67.74 (CpAC), 67.31 (CpAC),
60.57 (PzAC), 58.97 (ACH2A), 43.41 (PzAC), 29.06 (ACH2A), 28.83
electrode was polished successively with 0.3 and 0.05 lm a-Al2O3
slurry on emery paper and rinsed with doubly distilled water. Ace-
tonitrile containing [n-Bu4N] PF6 (c = 0.10 M) was applied as a sup-
porting electrolyte. Before each electrochemical measurement, the
experimental solution in the cell was purged with highly purified
nitrogen gas for at least 10 min to remove dissolved oxygen and
then a nitrogen atmosphere was kept over the solution during
measurements.
(ACH2A), 14.20 (ACH3). IR (KBr) m
, cmꢀ1: 2980, 1732, 1656, 1497,
1440, 1375, 1211, 1161, 820. MS (ESI) m/z: 537.16, [M + 1]+ calcd.
537.23. Analysis (%): C, 55.72; H, 4.78; N, 5.41 (C25H25BrFeN2O3 re-
quires C, 55.89; H, 4.69; N, 5.21).
Theoretical calculations were performed at the DFT level using
the B3LYP functional [21–23]. Geometry optimization of the sin-
glet ground state was calculated using the 6–31G(d,p) basis set
for H C N O atoms and the ECP Lanl2dz basis set for the Fe atom
[24–26]. Vibrational frequency calculations were performed at
the same level of theory to verify the nature of the stationary
points. The DFT calculations were carried out with the Gaussian
03 program package [27].
2.2.2. Synthesis of 1-(3-(ethoxycarbonyl)propionyl)-3,5-diferrocenyl-
4,5-dihydro-1H-pyrazole (4b)
Elution of the chromatogram with 25% ethyl acetate in petro-
leum ether afforded 4b as a brown solid, 1.10 g (80.9%); m.p.
157–158 °C. 1H NMR (600 MHz,CDCl3):
d 5.44 (1H, HX, dd,
JXB = 11.2 Hz, JXA = 2.8 Hz, PzAH), 4.68 (2H, d, CpAH), 4.50 (1H, s,
CpAH), 4.44 (2H, s, CpAH),4.23 (5H, s, CpAH), 4.18 (5H, m, CpAH),
4.15 (2H, m, CpAH), 4.05 (1H,s, CpAH), 3.56 (1H, HB, dd,
JBA = 17.1 Hz, JBX = 11.2 Hz, PzAH), 3.32 (1H, HA, dd, JAB = 17.2 Hz,
JAX = 2.8 Hz, PzAH), 2.99 (2H, m,CH2), 2.68 (2H, m, CH2), 1.66
(2H, s, CH2), 1.26 (3H, t, CH3). 13C NMR (150 MHz, CDCl3) d
173.24 (C@O), 168.99 (C@O), 155.95 (PzAC), 87.69 (CpAC), 75.58
(CpAC), 70.39 (CpAC), 69.50 (CpAC), 68.68 (CpAC), 68.20 (CpAC),
67.56 (CpAC), 65.22 (CpAC), 60.44 (PzAC), 54.99 (ACH2A), 40.93
2.2. Synthesis of the 5-aryl-1-(3-(ethoxycarbonyl)propionyl)-3-
ferrocenyl-4,5-dihydro-1H-pyrazole derivatives
To a stirred solution of 3-(4-bromophenyl)-1-ferrocenyl-2-pro-
pen-1-on or 1,3-diferrocenyl-2-propen-1-on (2a or 2b, 2.4 mmol)
in ethanol (10 mL), 98% hydrazine hydrate (100.0 mmol) was
added at room temperature. After addition the reaction mixture
was further stirred at 80 °C for 0.5 h. The solvent and excess hydra-
zine hydrate was evaporated under reduced pressure to give an or-
ange viscous substance. The unstable compounds 3a and 3b were
not purified but directly used for the following reaction. The or-
ange viscous solid was dissolved in CH2Cl2 (10 mL), and a solution
of 2.8 mmol 3-(ethoxycarbonyl)propionyl chloride of CH2Cl2
(10 mL) was added dropwise at room temperature. After addition,
the mixture was further stirred for 10 min. The solution was
poured into water (100 mL) and extracted with CH2Cl2
(3 ꢁ 10 mL). Combined organic phases were dried with magne-
sium sulfate and evaporated. The product was purified by column
chromatography.
(PzAC), 29.22 (ACH2A), 29.03 (ACH2A), 14.23 (ACH3). IR (KBr) m,
cmꢀ1: 3098, 2920, 1732, 1656, 1425, 1166, 1105, 858, 823. MS
(ESI) m/z: 567.11,[M + 1]+ calcd. 566.25. Analysis (%): C, 61.39; H,
5.41; N, 5.02 (C29H30Fe2N2O3 requires C, 61.51; H, 5.34; N, 4.95).
3. Results and discussion
3.1. Synthesis and characterization
The strategy (Scheme 1) for the preparation of compounds 3a
and 3b was the cyclization reaction of
a,b-unsaturated ketones
with hydrazine hydrate [28]. Such cyclization is well documented
for the synthesis of 3a and 3b, which were unstable and could not
Reaction conditions: (i) 4-bromobenzaldehyde or ferrocenecarboxaldehyde, NaOH, 40°C; (ii)
NH2NH2 H2O, 80 °C; (iii) 3-(ethoxycarbonyl)propionyl chloride, CH2Cl2
Scheme 1. Synthesis of compounds 4a and 4b.

42
H.-D. Li et al. / Journal of Molecular Structure 1024 (2012) 40–46
4b have approximated position in 1H NMR spectra [29]. We
concentrate our attention on d: 5.49–5.44 ppm (ACHA of the 4,5-
dihydropyrazole ring) and d: 3.65–2.94 ppm (ACH2A of the 4,5-
dihydropyrazole ring), which belong to the characteristic ABX
proton spin systems. The presence of the 4-bromophenyl substitu-
ent at position 5 of the dihydropyrazole ring 4a is typical of the
pronounced upfield shift of the H(A) proton (d: 2.94 ppm), the dif-
ference (dH(B) ꢀ dH(A)) being equal to 0.71 ppm. In the spectra of
dihydropyrazole 4b with the ferrocenyl group at position 5, the
H(A) proton was present at lower fields (d: 3.32 ppm).
Scheme 2. Electron transfer mechanism of 4b.
Analysis of the 13C NMR spectra of compounds 4a and 4b (see
Supporting information) also allows one to reveal characteristic
differences for 3-ferrocenyl and 3,5-diferrocenyl-substituted pyr-
azoline. Thus signal for CipsoAFc of 4a are located at 75.01 ppm
while 4b contains two types of signals for CipsoAFc, viz. d: 75.58
and 87.69 ppm, respectively [29].
B
A
4
5
3
X
N
N
2
1
C
CH2CH2COOEt
O
3.2. Crystal structure
Brown crystals of 4a and 4b suitable for X-ray single crystals
analysis were crystallized by slow diffusion of petroleum ether into
a solution of 4a or 4b in acetonitrile. The molecular structures of 4a
and 4b are showed in Fig. 2. A summary of the key crystallographic
information of 4a and 4b are given in Table 1. The selected bond
distances and bond angles are given in Tables 2 and 3, respectively.
Two conformations in the crystal structure of compound 4a
have been defined with respect to the flexible aliphatic chain
(Fig. 2a). The two cyclopentadienyl rings of the ferrocene moiety
are parallel in both crystal structures. Interestingly, the Cp ring
of FcI is almost coplanar with the pyrazoline ring with a dihedral
angle of 13.24°, while the Cp ring of FcII is nearly orthogonal to
the pyrazoline ring with a dihedral angle 88.30° in the crystal
Fig. 1. Molecular structure of compounds 4a and 4b.
be purified by conventional methods. The initial substances were
directly acylated for the formation of the desired compounds 4a
and 4b in high yield 82.2%, 80.9%, respectively.
The structures of 4a and 4b were characterized by IR, 1H, and
13C NMR spectral data. In the IR spectrum, the ester carbonyl
absorptions were seen at 1732 cmꢀ1
. The strong bands at
1656 cmꢀ1 of all the compounds can be attributable to the car-
bonyl group stretching vibrations. The NMR spectra also confirmed
the structures of compounds 4a and 4b (Fig. 1). The signals of
unsubstituted cyclopentadiene (Cp) ring protons of both 4a and
Fig. 2. (a) The molecular structure of 4a. (b) The molecular structure of 4b.

H.-D. Li et al. / Journal of Molecular Structure 1024 (2012) 40–46
43
Table 1
Crystallographic data and structure refinement details for 4a and 4b.
Table 2
Selected bond lengths (Å) and angles (°) for compound 4a.
Compound
4a
4b
Bond
Dist.
Bond
Dist.
Empirical formula
Crystal size (mm)
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C
25H25BrFeN2O3
C29H30Fe2N2O3
0.20 ꢁ 0.20 ꢁ 0.20
566.25
Br(1)AC(17)
N(1)AC(11)
N(1)AN(2)
N(2)AC(20)
N(1)AC(3)
O(1)AC(11)
O(3)AC(27)
N(2)AC(24)
O(1)AC(24)
C(9)AC(11)
C(12)AC(13)
1.896(6)
1.288(5)
1.402(5)
1.342(6)
2.060(6)
1.296(5)
1.328(5)
1.358(5)
1.223(5)
1.464(5)
1.532(5)
Br(2)AC(42)
Fe(2)AC(28)
Fe(2)AC(28)
Fe(2)AC(28)
Fe(2)AC(28)
N(1)AN(2)
O(3)AC(28)
N(2)AC(13)
O(2)AC(27)
C(11)AC(12)
C(13)AC(14)
1.891(4)
2.054(6)
2.054(6)
2.054(6)
2.054(6)
1.402(4)
1.444(5)
1.475(5)
1.191(6)
1.496(5)
1.507(5)
0.20 ꢁ 0.20 ꢁ 0.20
537.22
293(2)
293(2)
0.71073
Triclinic
P(ꢀ1)
0.71073
Triclinic
P(ꢀ1)
10.909(4)
11.491(4)
20.917(9)
93.531(13)
97.845(16)
112.977(12)
2372.5(15)
4
10.387(2)
10.813(2)
13.215(3)
95.03(3)
106.25(3)
117.20(3)
1226.4(4)
2
b (Å)
c (Å)
a
(°)
b (°)
Angles
(°)
Angles
(°)
c
(°)
C(18)AC(17)ABr(1)
C(16)AC(17)ABr(1)
C(20)AN(1)AN(2)
C(20)AN(2)AC(13)
N(1)AN(2)AC(13)
C(11)AN(1)AN(2)
C(23)AO(2)AC(24)
N(1)AC(11)AC(1)
N(1)AC(11)AC(12)
C(1)AC(11)AC(12)
C(11)AC(12)AC(13)
N(2)AC(13)AC(14)
N(2)AC(13)AC(12)
C(14)AC(13)AC(12)
O(1)AC(20)AN(2)
O(1)AC(20)AC(21)
N(2)AC(20)AC(21)
C(22)AC(21)AC(20)
C(21)AC(22)AC(23)
O(3)AC(23)AO(2)
O(3)AC(23)AC(22)
O(2)AC(23)AC(22)
C(24)AC(25)AO(2)
121.0(6)
117.8(6)
122.2(4)
125.5(4)
112.3(4)
107.3(4)
118.9(5)
123.0(4)
113.2(4)
123.8(4)
102.1(4)
111.6(4)
99.7(4)
110.9(4)
120.3(4)
122.6(4)
117.1(4)
113.0(4)
113.1(4)
123.7(5)
125.5(5)
110.8(5)
112.4(4)
C(43)AC(42)ABr(2)
C(41)AC(42)ABr(2)
C(36)AN(3)AN(4)
C(45)AN(4)AN(3)
C(45)AN(4)AC(38)
N(3)AN(4)AC(38)
C(48)AO(5)AC(49)
N(3)AC(36)AC(26)
N(3)AC(36)AC(37)
C(26)AC(36)AC(37)
C(36)AC(37)AC(38)
N(4)AC(38)AC(39)
N(4)AC(38)AC(37)
C(39)AC(38)AC(37)
O(4)AC(45)AN(4)
O(4)AC(45)AC(46)
N(4)AC(45)AC(46)
C(45)AC(46)AC(47)
C(48)AC(47)AC(46)
O(6)AC(48)AO(5)
O(6)AC(48)AC(47)
O(5)AC(48)AC(47)
C(50)AC(49)AO(5)
120.2(3)
118.6(4)
107.4(3)
122.7(4)
125.6(4)
111.6(3)
116.8(6)
122.6(4)
113.2(4)
124.1(4)
101.9(3)
110.7(4)
100.4(3)
111.7(4)
120.2(4)
124.2(4)
115.6(4)
111.9(4)
113.8(5)
122.8(6)
126.2(5)
111.0(5)
114.3(8)
V (Å3)
Z
Dcalc (g/cm3)
1.504
2.349
1.533
1.218
Absorption coefficient
(mmꢀ1
)
F(000)
Index ranges
1096
720
ꢀ14 6 h 6 14
ꢀ17 6 k 6 17
ꢀ27 6 l 6 27
22,833
ꢀ12 6 h 6 13
ꢀ14 6 k 6 13
ꢀ17 6 l 6 12
10,313
5415 RAll = 0.0353
96.2%
Multi-scan
R1 = 0.0537,
wR2 = 0.1613
R1 = 0.0651,
wR2 = 0.1878
0.921
Reflections collected
Independent reflections
Completeness to h = 27.50° 97.5%
Absorption correction Multi-scan
Final R indices [I > 2
10,580 RAll = 0.0419
r(I)]
R1 = 0.0672,
wR2 = 0.1771
R1 = 0.1290,
wR2 = 0.2095
1.013
R indices (all data)
Goodness-of-fit on F2
structure of compound 4b. The bond length (4b) of N(2)AC(24)
is 1.358 Å, which is shorter than the N(2)AC(13) single bond
distance (1.475 Å) and longer than the N(1)=C(11) double bond
distance (1.296 Å), at the same time the N(1)AN(2) distance
(1.402 Å) is shorter than the corresponding NAN single bond
(1.460 Å). Similarity, the C(9)AC(11) distance is 1.465 Å shorter
than the length of C(13)AC(14) (1.507 Å).Thus, it can indicate
that there is a conjugated system in 4b between the C(24),
N(2), N(1), C(11) and the Cp ring of FcI, owing to the strong
electron-withdrawing carbonyl group has a greater effect on FcI
than on FcII.
Table 3
Selected bond lengths (Å) and angles (°) for compound 4b.
Bond
Dist.
Bond
Dist.
N(1)AC(11)
O(3)AC(27)
N(2)AC(24)
O(1)AC(24)
C(9)AC(11)
C(12)AC(13)
1.296(5)
1.328(5)
1.358(5)
1.223(5)
1.464(5)
1.532(5)
N(1)AN(2)
1.402(4)
1.444(5)
1.475(5)
1.191(6)
1.496(5)
1.507(5)
O(3)AC(28)
N(2)AC(13)
O(2)AC(27)
C(11)AC(12)
C(13)AC(14)
Crystal packing of 4b is shown in Fig. 3b. It can be seen that the
adjacent molecules are stacked along the c axis through the edge-
Angles
(°)
Angles
(°)
C(11)AN(1)AN(2)
C(24)AN(2)AN(1)
N(1)AN(2)AC(13)
N(1)AC(11)AC(12)
C(11)AC(12)AC(13)
N(2)AC(13)AC(12)
O(1)AC(24)AN(2)
N(2)AC(24)AC(25)
C(27)AC(26)AC(25)
O(2)AC(27)AC(26)
O(3)AC(28)AC(29)
106.2(3)
122.2(3)
112.2(3)
114.4(3)
101.1(3)
100.2(3)
121.0(4)
115.9(4)
112.8(4)
125.4(4)
107.1(4)
C(27)AO(3)AC(28)
C(24)AN(2)AC(13)
N(1)AC(11)AC(9)
C(9)AC(11)AC(12)
N(2)AC(13)AC(14)
C(14)AC(13)AC(12)
O(1)AC(24)AC(25)
C(24)AC(25)AC(26)
O(2)AC(27)AO(3)
O(3)AC(27)AC(26)
115.8(4)
125.3(3)
122.4(3)
123.3(3)
110.6(3)
110.4(3)
123.1(4)
111.6(4)
122.6(5)
112.0(4)
to-face interactions (the distance of CAHꢂ ꢂ ꢂ
p is 2.703 Å) and the
weak hydrogen bond of C(2)AH(2)ꢂ ꢂ ꢂO(2) (the length of
H(2)ꢂ ꢂ ꢂO(2) is 2.493 Å). Meanwhile 4b is self-assembled by the off-
set face-to-face interactions between C(10) and C(11) of neighbor-
ing molecules (the distance of C(10)ꢂ ꢂ ꢂC(11) is 3.284 Å) to form 2D
supramolecular structure along the a axis. A similar structural
arrangement of 4a was seen in Fig. 3a, the adjacent molecules
are held together by the hydrogen bond of C(19)AH(19)ꢂ ꢂ ꢂO(4) or
C(44)AH(44)ꢂ ꢂ ꢂO(1) (the length of H(19)ꢂ ꢂ ꢂO(4) and H(44)ꢂ ꢂ ꢂO(1)
is 2.461 Å, 2.504 Å, respectively) and the
(the distance of Pzꢂ ꢂ ꢂCp is 3.365 Å).
pꢂ ꢂ ꢂp stacking interaction
As it can be seen from Fig. 4 and Table 4, the redox potentials of
4b were slightly influenced by the scan rate in a range from 0.1 to
0.8 V/s. The cyclic voltammogram of compound 4b shows two qua-
3.3. Electrochemistry and quantum-chemical calculations
The electrochemical behaviors of compounds 4a (see Support-
ing information) and 4b (c = 10ꢀ3 M) were investigated by the cyc-
lic voltammetric technique in acetonitrile containing [n-Bu4N]PF6
(c = 0.10 M) as a supporting electrolyte at 25 °C. In order to explain
the two redox processes of compound 4b, we focused our attention
on its electrochemical behaviors (Scheme 2).
si-reversible oxidation waves at EII of 0.472 V and E1I =2 of 0.605 V.
1=2
II
The first one-electron wave (E ) corresponds to FeII(II) M FeII(III)
1=2
oxidation and the second one-electron wave (EI1=2) to FeI(II) M
FeI(III) oxidation. The difference between the values of these two
potentials is arising from the strong electron-withdrawing effect
of the carbonyl group.

44
H.-D. Li et al. / Journal of Molecular Structure 1024 (2012) 40–46
Fig. 3. (a) Cell packing diagram of 4a (viewed down the a axis). (b) Cell packing diagram of 4b (viewed down the c axis).
Table 4
The electrochemical data at the scan rate of 0.1 V/s.
a
b
c
d
e
Compound
Epa (V)
Epc (V)
E1/2 (V)
D
Ep (V)
DE1/2 (V)
Fc
4a
4b
0.517
0.652
0.641
0.507
0.404
0.579
0.569
0.437
0.461
0.616
0.605
0.472
0.113
0.073
0.072
0.070
I
II
0.133
a
b
c
Epa: anodic oxidation potential.
Epc: cathodic reduction potential.
E1/2: half-wave potential, E1/2 = (Epa + Epc)/2.
d
e
D
D
Ep = Epa ꢀ Epc
.
II
1=2
E1=2 ¼ EI1=2 ꢀ E
.
representation of the molecular frontier orbitals of 4b was exhib-
ited in Fig. 5b. From Fig. 5b, we can see that the HOMO
(ꢀ5.34 eV) and HOMO-1 (ꢀ5.36 eV) of 4b are dominated by the
ferrocene unit II, while the HOMO-2 (ꢀ5.68 eV) and HOMO-3
(ꢀ5.81 eV) consist of orbitals on the ferrocene unit I moiety. These
results conform to the electrochemical behavior of 4b.
Fig. 4. Cyclic voltammetry of compound 4b at different scan rates (0.1, 0.2, 0.4, 0.6,
0.8 V/s) in acetonitrile.
In addition, the effect of scan rate was investigated (Fig. 4), both
the anodic and cathodic peak currents are linear to the square root
DFT computational studies were performed to verify the
electron transfer mechanism of 4b (Fig. 5a). The schematic
of scan rates (
diffusion-controlled process [30].
v
1/2) in the range of 0.1–0.8 V/s, which indicating a

H.-D. Li et al. / Journal of Molecular Structure 1024 (2012) 40–46
45
Fig. 5. (a) The structure of compound 4b optimized by theoretical calculations. (b) Energy diagram of the first four HOMOs of compound 4b (B3LYP/LANL2DZ).
Foundation for the Returned Overseas Chinese Scholars, State Edu-
cation Ministry (No. 20111568).
4. Conclusion
Two dihydropyrazole-bridged ferrocenyl-substituted deriva-
tives were successfully synthesized in high yields. The crystal
arrangements of title compounds were promoted by weak hydro-
Appendix A. Supplementary material
gen-bonding interactions and
p–p stacking interactions between
General experimental procedure and spectroscopic data for the
synthesized compounds see Supporting Information. Crystallo-
graphic data for the structural analysis have been deposited with
the Cambridge Crystallographic Data Center, CCDC 853434 and
800388 for compounds 4a and 4b, respectively. Copies of this
information can be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44 1223
336033; email: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.
ac.uk). Supplementary data associated with this article can
be found, in the online version, at http://dx.doi.org/10.1016/j.
molstruc.2012.05.026.
neighboring molecules to form 2D supramolecular structure.
Furthermore, electrochemical investigations showed that two
quasi-reversible oxidation waves were controlled by diffusion.
The difference between the values of two potentials in compound
4b is arising from the strong electron-withdrawing effect of the
carbonyl group. DFT calculation results explain the electron trans-
fer mechanism of typical compound 4b.
Acknowledgments
We are grateful for the financial support from the National Nat-
ural Science Foundation of China (No. 21172036), the Research
Fund for the Doctoral Program of Higher Education of China (No.
20113514110002), the Natural Science Foundation of Fujian Prov-
ince (No. 2009J05028, 2010J01036) and the Scientific Research
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