Synthesis, electrochemical behavior, spectral, and magnetic studies of copper(II) complexes with ferrocene-containing hydrazones

Article abstract of DOI:10.1081/SIM-120016464

A new series of copper(II) complexes of the stoichiometry [L₂Cu]·nH₂O and [(HL)₂ CuCl₂]·2H₂O, where HL is 1-acetylferrocene-benzoylhydrazone, 1-acetylferrocene-4-chlorobenzoylhydrazone, 1-acetylferrocene-4-hydroxy-benzoylhydrazone or 1-acetylferrocene-4-methylbenzoylhydrazone, HL¹, HL², HL³ or HL⁴, respectively, were synthesized and characterized. IR data showed that all ligands act as monobasic or neutral bidentates coordinated to copper ion via the oxygen and azomethine N atoms. ESR spectra and magnetic data showed that [(L¹)₂Cu]·H₂O and [(L³)₂Cu]·2H₂O are polymeric exhibiting magnetic exchange interaction. ESR data also indicate that all complexes are associated with a d_x2-y2 ground state. The electrochemical behavior of the free ligands and their copper(II) complexes were studied and are discussed.

Full text of DOI:10.1081/SIM-120016464

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SYNTHESIS, ELECTROCHEMICAL BEHAVIOR, SPECTRAL,
AND MAGNETIC STUDIES OF COPPER(II) COMPLEXES
WITH FERROCENE-CONTAINING HYDRAZONES
Taher S. Kassem a , Mohamed A. EI-Sayed a , Heba M. Refaat a & Ali El-Dissouky b
a Chemistry Department , Alexandria University , Alexandria, Egypt
b Chemistry Department , Kuwait University , P. O. Box 5969, Safat, 13060, Kuwait
Published online: 15 Feb 2007.
To cite this article: Taher S. Kassem , Mohamed A. EI-Sayed , Heba M. Refaat & Ali El-Dissouky (2002) SYNTHESIS,
ELECTROCHEMICAL BEHAVIOR, SPECTRAL, AND MAGNETIC STUDIES OF COPPER(II) COMPLEXES WITH FERROCENE-CONTAINING
HYDRAZONES, Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 32:10, 1769-1787, DOI: 10.1081/
SIM-120016464
To link to this article: http://dx.doi.org/10.1081/SIM-120016464
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 32, No. 10, pp. 1769–1787, 2002
SYNTHESIS, ELECTROCHEMICAL
BEHAVIOR, SPECTRAL, AND
MAGNETIC STUDIES OF COPPER(II)
COMPLEXES WITH FERROCENE-
CONTAINING HYDRAZONES
Taher S. Kassem,1 Mohamed A. El-Sayed,1
Heba M. Refaat,1 and Ali El-Dissouky2,*
1Chemistry Department, Faculty of Science,
Alexandria University, Alexandria, Egypt
2Chemistry Department, Faculty of Science,
Kuwait University, P. O. Box 5969,
13060 Safat, Kuwait
ABSTRACT
A new series of copper(II) complexes of the stoichiometry
[L2Cu]ꢀnH2O and [(HL)2CuCl2]ꢀ2H2O, where HL is 1-acetyl-
ferrocene-benzoylhydrazone, 1-acetylferrocene-4-chlorobenzoyl-
hydrazone, 1-acetylferrocene-4-hydroxy-benzoylhydrazone or
1-acetylferrocene-4-methylbenzoylhydrazone, HL1, HL2, HL3 or
HL4, respectively, were synthesized and characterized. IR data
*Corresponding author. E-mail: adissouky@yahoo.com
1769
DOI: 10.1081=SIM-120016464
Copyright # 2002 by Marcel Dekker, Inc.
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com

1770
KASSEM ET AL.
showed that all ligands act as monobasic or neutral bidentates
coordinated to copper ion via the oxygen and azomethine N
atoms. ESR spectra and magnetic data showed that [(L1)2Cu]ꢀ-
H2O and [(L3)2Cu]ꢀ2H2O are polymeric exhibiting magnetic
exchange interaction. ESR data also indicate that all complexes
are associated with a dx2ꢁy2 ground state. The electrochemical
behavior of the free ligands and their copper(II) complexes were
studied and are discussed.
INTRODUCTION
Metallocenes are considered to be redox-active materials. The fine-
tuning of the redox couple of the metal center was used as a probe for
chemical sensing.[1] Systems that are capable of displaying two or more
electron redox activity are of interest to the field of electrolysis.[2] Fer-
rocene (Fc) has been recognized since its first appearance on the chemical
stage as a reversible one-electron redox agent.[3] Ferrocene is oxidized to
the stable ferrocenium ion in an outer-sphere electron-transfer process.
Ferrocene was used for the preparation of several ligands. The presence of
the ferrocene moiety in an organic ligand causes it to act as a reversible,
one-electron redox center. When such ligands are coordinated to transi-
tion metal ions, multielectron complexes are formed and act as ‘‘electron
reservoirs’’.[477] If there is no electronic communication between the two
ferrocenes in L7M7L, L is a ferrocene containing ligand, and the distance
between the two ferrocene is large enough to minimize the electrostatic
repulsive interactions, the L7M7L system will exchange two electron in a
single step, i.e., through one electron processes whose potentials E1 and
E2 are separated only by the statistical term DE ¼ E2 ꢁ E1 ¼ 36 mV at 25
ꢂC. Electronic interactions (through a delocalized p-system) or electro-
static repulsive effects cause the DE value to increase. The larger is the
interaction, the larger is the DE value. If M in L7M7L shows redox
behavior, two consecutive redox steps will be observed, one being ascribed
to the oxidation of the ferrocene moiety and the second to the metal
center M.
This work was undertaken to study the incorporation of ferrocene into
the skeleton of the classical chelating N,O-donor ligands, Fig. 1. When such
a ligand coordinates to copper(II), a polynuclear metal complex containing
an easily oxidizable redox active centers has been prepared.

COPPER(II) COMPLEXES
1771
Figure 1. Structure of the ligands HL.
EXPERIMENTAL
Reagents and Solvents
benzoylhydrazine,
1-Acetylferrocene,
4-chlorobenzoylhydrazine,
4-hydroxybenzoylhydrazine and 4-methylhydrazine, CuCl2ꢀ2H2O and
Cu(OAc)2ꢀH2O, ethanol and methanol were obtained from commercial
sources and were used without further purification. Dimethyl sulfoxide
(DMSO) was of spectroscopic grade and was used as received.
Preparation of the Compounds
Preparation of 1-Acetylferrocenyl-aroylhydrazones[8]
A solution of acetylferrocene (4.56 g, 0.02 mol) in anhydrous ethanol
(50 mL) was added drop-wise to a solution of the corresponding
aroylhydrazine (2.7, 3.4, 3.0, 3.0 g; 0.02 mol for benzoyl, 4-chlorobenzoyl,
4-hydroxybenzoyl, 4-methylbenzoylhydrazine, respectively) in the same
solvent (30 mL). The reaction mixture was heated under reflux on a water
bath for about 6 h. After cooling to room temperature, the precipitate
formed in each case was filtered, washed several times with hot ethanol
followed by diethyl ether. After drying the products were recrystallized from
ethanol to obtain brown and dark brown crystalline solids. These were dried
under vacuo over P4O10. The purity of the products was confirmed by TLC
[plastic sheets of a silica gel F254 with 0.2 mm layer thickness, Merck eluent
was ethylacetate-n-hexane (3:2 v=v)].

1772
KASSEM ET AL.
Preparation of the Copper(II) Complexes
A solution of Cu(OAc)2ꢀH2O (1.99, 0.01 mol) or CuCl2ꢀ2H2O (1.70 g,
0.01 mol) in absolute ethanol (20 mL) was added drop-wise with stirring
to a solution of the corresponding ferrocenylaroylhydrazone (7.5, 8.4, 8.0,
7.9 g; 0.022 mol for 1-acetyl-ferrocenebenzoyl-, 4-chlorobenzoyl-, 4-hydrox-
ybenzoyl-, 4-methylbenzoylhydrazones, respectively) in the same solvent
(20 mL). The reaction mixture was heated under reflux on a water bath for
274 h and then cooled to room temperature. The isolated solid in each case
was removed by filtration, washed several times with hot ethanol followed
by diethyl ether and dried under vacuo over P4O10. The purity of the product
was confirmed by TLC.
Elemental Analyses
C, H, and N contents in each sample were determined at the Micro-
analysis Unit at Cairo University. The iron content in the free ligands was
determined titrimetrically with standard EDTA solution and salicylic acid as
indicator[9] after digestion with aqua regia.
Physical Measurements
The 1H NMR spectra were recorded in DMSO-d6 or CDCl3 solutions
on a high-resolution Bruker AM 300 L spectrometer with tetramethylsilane
(TMS) as internal standard at Cairo University. The vibrational spectra
were made on a Perkin Elmer 1430 ratio recording IR spectrometer in KBr
discs.[10] The electronic spectral measurements (Nujol mulls and=or as
CH2Cl2 solutions) in the UV-Vis region were carried out on a Shimadzu
160A UV-Vis recording spectrophotometer employing 1 cm matched silica
cells in the wave length ranges of 2007800 nm and 40071000 nm for the free
ligands and their copper(II) complexes, respectively. Magnetic suscept-
ibilities, wDC, have been measured at room temperature using a Faraday
balance at the Faculty of Science, Mansoura University (Demiatta). The
measured wDC per Cu(II) was corrected for diamagnetism using Pascal’s
constants.[11] The ESR (X-band) spectra for polycrystalline samples were
recorded at room temperature using a Radiation SE=X 2543 spectrometer
with a rectangular TE 102 cavity and 100 kHz modulation field. Spin con-
centrations were estimated by comparing the intensity of the standard
CuSO4ꢀ5H2O signal with that of our ESR results. Diphenylpicrylhydrazide
free radical (DPPH) was used as internal standard. Cyclic voltammetry

COPPER(II) COMPLEXES
1773
measurements were carried out using a BAS-27 Bioanalytical System elec-
trochemistry analyzer connected with a BAS X-Y recorder and in con-
junction with a three-electrode cell fitted with a purged dinitrogen gas inlet
and outlet. The two electrodes were a Beckman platinum working electrode
(flat circular sheet of 5 mm diameter) and a platinum wire auxiliary elec-
trode. All potentials were measured with respect to an Ag=Agþ electrode
(1610ꢁ 3 M AgNO3 in 0.1 M tetrabutylammonium perchlorate (TBAP) in
CH2Cl2) as non-aqueous reference electrode. The measurements were per-
formed at room temperature in CH2Cl2 as solvent containing 0.1 M TBAP,
5610ꢁ 4 M (HL or Cu complexes) and thoroughly deoxygenated by bub-
bling oxygen-free dinitrogen into the solution.
RESULTS AND DISCUSSION
Acetylferrocene reacts with benzoylhydrazine, 4-chloro-, 4-hydroxy-
or 4-methylbenzoylhydrazins to give the corresponding ligands HL1, HL2,
HL3 or HL4, respectively. The products are soluble in MeOH, EtOH,
DMSO or DMF but only slightly soluble in MeCOMe or CHCl3. The
reaction of these hydrazones with Cu(OAc)2ꢀ2H2O yielded the intense
coloured complexes [L2Cu]ꢀnH2O while with CuCl2ꢀ2H2O gave complexes of
the stoichiometry [(HL)2CuCl2]ꢀH2O, where L is the monobasic anion of the
corresponding ligand and n ¼ 1 or 2, according to the following equations:
1-acetylferrocene þ 4-X-phenylhydrazine ! HL
2HL þ CuðOAcÞꢀH2O ! ½L2CuꢃꢀnH2O þ 2HOAc
2HL þ CuCl2 ꢀ2H2O ! ½ðHLÞ2CuCl2 ꢀ nH2OꢃꢀH2O
ð1Þ
ð2Þ
ð3Þ
The neutral complexes obtained in case of using Cu(OAc)2ꢀH2O could
be explained on the basis of the existence of the strong conjugate base OAc
which has the ability to deprotonate the enolized HL proton while in case of
CuCl2ꢀH2O, the Cl ion acts as a weak conjugate base which could not
abstract the proton from HL thus giving cationic complexes.
All complexes are air-stable, insoluble in most non-polar solvents,
sparingly soluble in MeOH, EtOH, MeCOMe or CHCl3 and soluble in
DMSO or DMF. The melting and decomposition temperatures of the
ꢂ
complexes (over 300 C) are higher than those of their ligands (Table I)
indicating that the complexes are much more thermally stable than the free
ligands. This could be attributed to the formation of chelate rings upon
complexation.

1774
KASSEM ET AL.
Table I. Elemental Analyses, Color, and Melting Points Data of the Organic
Ligands and Their Complexes
% Calc. (Found)
Yield
F.Wa (%)
M.p.b
(ꢂC)
C
H
N
Fe
Compound
Color
HL1
C19H18N2OFe
345.85 78 Brown
155 65.9 5.2 8.1 16.1
(65.7) (5.0) (8.2) (16.3)
170 59.0 4.5 7.4 14.7
(59.5) (4.5) (7.3) (14.9)
200 63.0 4.9 7.7 15.4
(62.9) (4.6) (7.5) (15.5)
178 66.6 5.6 7.8 15.5
(66.8) (5.5) (7.8) (15.4)
>300 59.1 4.7 7.3
(59.3) (4.5) (7.4)
>300 54.0 4.5 6.6
(54.2) (4.5) (6.5)
>300 53.1 4.2 6.5
(52.8) (4.3) (6.4)
>300 49.9 3.9 6.1
(49.6) (4.3) (6.1)
>300 56.8 4.5 7.0
(57.1) (4.4) (7.2)
HL2
380.35 82 Dark
brown
361.85 65 Yellowish
brown
359.85 88 Brown
C19H17N2OClFe
HL3
C19H18N2O2Fe
HL4
C20H20N2OFe
[(L1)2Cu]ꢀH2O
771.24 58 Dark
brown
844.24 67 Dark
brown
858.24 70 Dark
brown
913.24 66 Dark
brown
803.24 71 Dark
brown
876.24 70 Dark
brown
817.24 66 Dark
Brown
872.24 76 Dark
Brown
C38H36N4O3Fe2Cu
[(HL1)2CuCl2]ꢀH2O
C38H38N4O3Cl2Fe2Cu
[(L2)2Cu]ꢀ2H2O
C38H36N4O4Cl2Fe2Cu
[(HL2)2CuCl2]ꢀH2O
C38H36N4O3Cl4Fe2Cu
[(L3)2Cu]ꢀH2O
C38H36N4O5Fe2Cu
[(HL3)2CuCl2]ꢀH2O
C38H38N4O5Cl2Fe2Cu
[(L4)2Cu]ꢀ2H2O
C40H42N4O4Fe2Cu
[(HL4)2CuCl2]ꢀH2O
C40H40N4O3Cl2Fe2Cu
>300 52.0 4.3 6.4
(52.1) (4.4) (6.2)
>300 58.7 5.1 6.9
(58.5) (5.0) (7.1)
>300 55.0 4.8 6.4
(55.1) (5.0) (6.5)
aFormula weight.
b
ꢂ
m.p. ꢄ 1 C.
1H NMR Spectral Studies
1
The H NMR spectra (Table II) of the free ligands, HL1, HL2 and
HL4, were recorded in DMSO-d6 or CDCl3 solutions in the presence and in
the absence of D2O. The spectra of the free ligands display two triplets at d
4.4074.20 and d 4.7574.25 ppm with the integration corresponding to 2H
and are due to the protons of the substituted cyclopentadienyl ring. Another
singlet signal with the integration corresponding to 5H at d 4.2074.10 ppm is
due to the unsubstituted cyclopentadienyl ring protons. Their relative

COPPER(II) COMPLEXES
Table II. 1H NMR Spectral Data (d ppm) of the Free Ligandsa
1775
d ppm
Phenyl
Ring
Compounds Solvents
CH3
C5H5
C5H4
N7H
HL1
HL3
HL4
CDCl3
2.3 (3H, s) 4.2 (5H, s) 4.4 (2H, t) 7.477.9
4.7 (2H, t) (5H, m)
7
DMSO-d6 2.2 (3H, s) 4.2 (5H, s) 4.4 (2H, s) 7.677.9 10.7 (1H, s)
4.7 (2H, s) (4H, m)
CDCl3
2.1 (3H, s) 4.1 (5H, s) 4.4 (2H, t) 7.477.9 9.1 (1H, s)
2.2 (3H, s) 4.8 (2H, t) (4H, m) 9.3 (1H, s)
as ¼ singlet; t ¼ triplet; m ¼ multiplet.
positions may be attributed to the deshielding effect of the azomethine
group. Furthermore, it was observed that there is no appreciable effect of
the substituents on the benzene ring. The methyl protons of the acetyl fer-
rocene moiety showed a singlet corresponding to 3H at d 2.4572.15 ppm.
The low-field position of this signal may be attributed to the deshielding
effect of the azomethine group. The shifts were found to be in the order
HL4 > HL2 > HL1 due to the hydrazonyl moiety effects. The aromatic
protons of the ligands gave multiplets at d 8.7577.35 ppm which integrate to
4H except in the case of HL1 which corresponding to 5H. The spectra of all
ligands display a low-intensity broad signal at d 10.779.1 ppm, which dis-
appeared in the presence of D2O: this signal is attributed to the imido NH.
The low field position of this signal may be attributed to the electronic effect
of the aroyl group, its participation in molecular association via inter-
molecular H-bonding and=or the enolization of the keto group followed by
intramolecular hydrogen bonding (Fig. 2).
In case of the ligand HL4, the NH proton displays two well-resolved
signals (disappeared in the presence of D2O) with the total integration
corresponding to one proton. The appearance of these two signals could be
attributed to the existence of this ligand as E- and Z-isomers in equilibrium
(Fig. 3) and=or an H-exchange phenomenon.
Infrared Spectra
The important IR frequencies of the ligands and their complexes along
with their relative assignments are collected in Table III. The spectra of the

1776
KASSEM ET AL.
Figure 2. Intermolecular (a) and intramolecular (b) H-bonding in the ligands.
free ligands display a broad split band with variable intensity in the range of
310073300 cmꢁ 1 due to the various vibrational modes of NH of the
hydrazone moiety. The existence of this group is confirmed by the medium-
intensity band at 154071545 cmꢁ 1 due to d(NH). These two bands are
absent in the spectra of the complexes [L2Cu]ꢀnH2O.
The spectra of [(HL)2CuCl2]ꢀH2O display
a broad band at
300073500 cmꢁ 1 due to n(NH) and n(OH). This band is found to be
unaffected upon complexation. The wave numbers at 158671614 and
164871669 cmꢁ 1 in the free ligands are assigned to n(C¼N) and n(C¼O),
respectively. In [L2Cu]ꢀnH2O the band at 164871669 cmꢁ 1 disappeared
completely with the appearance of a new one at 124071225 cmꢁ 1 due to
n(C7O), indicating the enolization of the carbonyl group followed by
deprotonation upon complexation. This is supported by the disappearance
of n(NH) and d(NH) and the appearance of a new band at 156071570 cmꢁ 1
Figure 3. The possible isomeric forms of HL4.

COPPER(II) COMPLEXES
1777

1778
KASSEM ET AL.
due to n(C¼N7N¼C). Therefore, the ligands undergo enolization in the
presence of Cu(OAc)2ꢀH2O and then react with copper(II) ion forming
neutral complexes with the release of HOAc. The frequencies due to
n(C¼N) and n(C¼O) in the spectra of [(HL)2CuCl2]ꢀH2O, where HL is the
non-deprotonated ligand and are shifted to lower wave numbers by 10715
and 10730 cmꢁ 1, respectively, with or without reduction in their intensities.
This indicates their participation in bonding to copper(II) ion without
changing their nature and the ligands coordinated in their neutral form. The
shift of the n(C¼N) to lower frequency may be also due to the conjugation
of the p-orbitals on the double bond with the d-orbitals on the copper ion
with reduction of the force constant. The band at 101271031 cmꢁ 1 in the
spectra of all complexes assignable to n(N7N) (at 9127923 cmꢁ 1 in the free
ligands) indicates the bonding of one of the hydrazone N atoms to the
copper ion. The shift of n(N7N) was found to be larger in [L2Cu]ꢀnH2O
than in [(HL)2CuCl2]ꢀH2O. This could be attributed to the larger conjuga-
tion upon complex formation in the former complexes. Furthermore, the
shift of d(NH) from 154071545 cmꢁ 1 in the free ligands to 155071556 cmꢁ 1
in the complexes suggests that the oxygen in the carbonyl group participates
in bonding with copper(II) in the keto form in [(HL)2CuCl2]ꢀH2O. The
spectra of the ligands display a medium-intensity band at 129671310 cmꢁ 1
attributed to d(C7N). This band is shifted to lower wave number by
8722 cmꢁ 1 in the spectra of all complexes, which may be attributed to the
induction effect resulting from the formation of the chelates. In addition to
these bands, the spectra of the ligands display three bands at 8317858,
112071132 and 146971496 cmꢁ 1, due to the ferrocenyl group. These bands
were found to be only slightly affected upon complexation. The spectra of all
complexes display a broad band centered at 340073500 cmꢁ 1, assigned to
the stretching frequency of H2O. The far-IR spectra of all complexes display
medium-strong bands at 3867411 and 293 cmꢁ 1 (absent in the free ligands)
due to n(Cu7O) and n(Cu7N), respectively. Based on these IR data and the
elemental analyses, we may conclude that the organic compounds behave as
bidentate ligands bonded to the copper(II) via the carbonyl-O (keto form)
and azomethine-N atoms in [(HL)2CuCl2]ꢀH2O [Fig. 4a] and enolized,
deprotonated carbonyl-O and the azomethine-N atoms in [L2Cu]ꢀnH2O
[Fig. 4b].
Electronic Spectral Studies
The spectra of the ligands (Table IV) display an intense band at
4507471 nm due to the transition of the 3d electrons of iron(II) to the non-
bonding or antibonding orbitals (d-p*) of the cyclopentadienyl ring. This

COPPER(II) COMPLEXES
1779
Figure 4. Suggested structures of the complexes.
band shows a bathochromic shift upon complexation in all complexes. This
shift suggests that there is a perturbation of the molecular orbitals of the
ferrocenyl moiety by the copper(II) and=or the hydrazone ligands. This
conclusion is consistent with the electronic spectral data of similar com-
pounds.[12,13] The band at 3007312 nm observed in the presence of the free
ligands is attributed to the K-band (p-p*) transitions.[14,15] This band
undergoes a bathochromic shift in all of complexes and appeared at
3127322 nm for [L2Cu]ꢀnH2O but at 3057316 nm for [(HL)2CuCl2]ꢀH2O.
The higher bathochromic shift in case of [L2Cu]ꢀnH2O relative to
[(HL)2CuCl2]ꢀH2O suggests that the whole molecule of [L2Cu]ꢀnH2O exists
in a strong conjugate system due to the chelation of the enolate form.[14] The
B-band of the cyclopentadienyl ring (2707293 nm) in the ligand[12,13]
undergoes a hypochromic shift (2657282 nm) in [(HL)2CuCl2ꢀH2O. This
phenomenon could be due to slightly enhanced bonding of the cyclo-
pentadienyl group in the complexes.[17,18] This means that the energy dif-
ference between the p and p* orbitals of the cyclopentadienyl ring became
large.[19] The spectra of the complexes [L2Cu]ꢀnH2O (except for complexes
of L1 and L3) are similar and display a band at 7007718 nm. These spectral
data are similar to the structurally characterized [L2Cu]ꢀnH2O, L ¼ N(o-
hydroxybenzylidene)ferrocenamine, in which copper(II) exists in a pseudo-
tetrahedral ligand field.[18,19] The band at 7007718 nm, accordingly, is
assigned to the dxy?dxz transition. The spectrum of [(L1)2Cu]ꢀH2O displays
a broad band at 625 nm and a shoulder at 820 nm, while that of

1780
KASSEM ET AL.
Table IV. Electronic Spectra (lnm) of the Free Ligandsa and Their Copper(II)
Complexesb and Room Temperature Magnetic Moments for the Copper(II)
Complexes
p-p*b
K
d-d
Transition
meff
Compounds
HL1
237
(3.77) (3.88) (3.81) (4.15) (3.87)
293
306
363
453
[(L1)2Cu]ꢀH2O
286
282
316
310
456
453
615,800
670,807
1.60
1.98
[(HL1)2CuCl2]ꢀH2O
HL2
238
(3.68) (3.90) (3.98) (4.01) (3.66)
284
306
372
452
[(L2)2Cu]ꢀ2H2O
[(HL2)2CuCl2]ꢀH2O
HL3
280
272
278
318
310
306
457
453
452
700
655,810
2.38
2.23
228
369
(3.90) (3.96) (4.02) (4.11) (3.71)
[(L3)2Cu]ꢀH2O
[(HL3)2CuCl2]ꢀH2O
HL4
270
266
272
318
310
302
456
452
450
615,820
660,805
1.56
2.01
239
361
(3.69) (3.81) (4.11) (4.06) (3.81)
[(L4)2Cu]ꢀ2H2O
268
260
316
308
455
451
710
670,820
2.33
1.98
[(HL4)2CuCl2]ꢀH2O
alnm (log e).
bAs saturated solutions (lnm).
[(L2)3Cu]ꢀH2O exhibits this band at 625 nm and a shoulder at 820 nm. These
data are similar to those reported for tetragonally distorted octahedral
copper(II) complexes.[19] These spectral data, together with the reduced
effective moments at room temperature (1.60 and 1.56 B.M., respectively),
indicate some sort of molecular association. Therefore, the six-coordination
around the copper(II) in these complexes could be achieved through the
oxygen atom via polymerization as shown in Fig. 5.
The electronic spectra of [(HL)2CuCl2]ꢀH2O display two bands at 8487
870 and 8007825 nm. These spectral features are similar to those reported
for six-coordinate copper(II) complexes in D4 or C4v symmetry.[20,21] In this
symmetry, there are three spin-allowed transitions in the visible and IR
2
2
2
2
regions due to B1g ! A2gðdx2ꢁy2 ! dz2 Þ, B1g ! B2gðdx2ꢁy2 ! dxyÞ and
2B1g ! Egðdx2ꢁy2 ! dxz; dyzÞ transitions in order of increasing energy. In
2
general, the energy level sequence depends upon the amount of distortion
due to the ligand field and Jahn-Teller effect.[20722] Accordingly, the main

COPPER(II) COMPLEXES
1781
Figure 5. Suggested structure of [L2Cu]ꢀH2O; L ¼ L1 or L3.
2
bands in the spectra of these complexes may be assigned to the 2B1g ! A2g
2
2
2
2
and B1g ! Eg transitions, respectively. The third band, the B1g ! B2g
transition, could not be observed perhaps due to its very low intensity
and=or the distortion from ideal symmetry.[23] Furthermore, these spectral
data are consistent with the data obtained for some ferrocene derivatives
containing copper(II) complexes with known crystal structure.[12,13]
Magnetic Susceptibility Studies
The room temperature magnetic moments (Table IV) were found to be
in the range of 1.9872.43 B.M. except for the complexes containing L1 and
L3, which have values of 1.60 and 1.56 B.M., respectively. These low values
indicate some sort of molecular association. The magnetic data of the rest of
the compounds is consistent with the presence of one unpaired electron in
monomeric complexes. Furthermore, the magnetic moment values indicate
that the complexes are of mixed-bond character. The high values of the
magnetic moments can also be attributed to the distortion from the ideal
symmetry, the tetrahedral structure for the [L2Cu]ꢀnH2O complexes, the
deviation of the cyclopentadienyl rings from coplanarity[24,25] and=or due to
spin-orbit coupling.
Electron Spin Resonance Spectral Studies
The X-band ESR spectra of polycrystalline samples are collected in
Table V. The spectra of [L2Cu]ꢀH2O, L ¼ L1 or L3, display a signal at 1656
and 1848 G, respectively. This signal is attributed to the DMs ¼ ꢄ 2 transi-
tion and further indicates the presence of magnetic exchange interaction

1782
KASSEM ET AL.
Table V. Room Temperature X-Band ESR Spectra of Polycrystalline Copper(II)
Complexes
g
?
c
g11
gz
A11
(G)
DMs ¼ ꢄ 1=2
a
Rb
g
gy
gx
Compound
hgi
G
[(L1)2Cu]ꢀH2O
[(L2)2Cu]ꢀ2H2O
[(L3)2Cu]ꢀH2O
[(L4)2Cu]ꢀ2H2O
2.36 2.17 2.09 2.21
2.17 2.05
2.16 2.09 2.04 2.10
7
0.42 227
0.71 238
4.07
3.65
2.09 3.04
7
2.17
2.05 2.09 3.40
2.09 2.14 2.60
2.09 2.15 3.00
2.10
[(HL1)2CuCl2]ꢀH2O 2.23
[(HL2)2CuCl2]ꢀH2O 2.27
[(HL4)2CuCl2]ꢀH2O
a
hgi ¼ 1=3 [g11þ2g ], hgi ¼ 1=3 [gxþgyþgz].
bG ¼ g11 ꢁ 2=g? ꢁ?2.
cR ¼ g2 ꢁ g1=g3 ¼ g2.
between the two copper ions. This is further supported by the presence of
parallel and perpendicular components of the signal (S0 ¼ 0, DMs ¼ ꢄ 0) to
triplet transitions (S0 ¼ 1, DMs ¼ ꢄ 1) characteristic for complexes contain-
ing intramolecular exchange interaction at 4603 and 5200 G for L1 and at
4466 and 5360 G for L3. The analysis of the spectra gave three g-values,
g3 > g2 > g1, with an average value hgi at 2.21 and 2.10, respectively. The
values of g gave R ¼ g2 ꢁ g1=g3 ꢁ g2 of 0.42 and 0.71, respectively, indicating
the dx2ꢁy2 ground state mixed with dz2. The spectra of both complexes also
display the hyperfine coupling constant in the parallel region due to the
copper ions of the values 227 and 238 G, respectively. This could be taken as
evidence for the decreased dipolar interaction due to the orientation of the
bulky ferrocenyl and benzoyl moiety in a manner to increase the separation
between the planes containing the CuN2O4 chromophore. The rhombic
nature of these two spectra can be attributed to the low crystal field sym-
metry, mixing of the dx2ꢁy2 and dz2 wave functions in the ground state[26]
and=or misalignment of the local crystal field symmetry in these com-
plexes.[25] The latter two factors dominate in most paramagnetic compounds
when the misalignment angle[28] is larger than 20 ꢂC and results in a
significant diminishing of the total g-tensor as in the case of the 4-hydrox-
ybenzoylhydrazone derivative.
The spectra of the other complexes are of the axial type with g11 > g ,
?
Table V. The average g-values are in the range of 2.1272.09. The extent of
interaction between the copper centers in the solid phase G, was calculated

COPPER(II) COMPLEXES
1783
to be 3.8373.40, indicating the presence of considerable exchange interac-
tion between the copper centers in all complexes in the solid state.
Cyclic Voltammetry
Voltammetry investigation of the free ligand and some of their cop-
per(II) complexes, [L2Cu]ꢀnH2O, were performed in CH2Cl2 solutions made
0.1 M in tetrabutylammonium perchlorate (TBAP) at a platinum working
electrode at 100 m Vsꢁ 1 scan rate and the data are summarized in Table VI.
The following observations were made:
1. Whether we start scanning from the positive potential ꢅ1.0 V, (to
reduce Fcþ formed at the electrode surface) or from the negative
potential, ꢅ1.0 V, (to oxidize Fc adsorbed at the electrode sur-
face), the volammograms are identical for all studied systems.
2. A reversible electron system of the ferrocene-ferroc0enium ion
couple, Fc=Fcþ, as the internal reference showed E0 (oxidation
potential) ¼ 0.18 V vs. Ag=Agþ, DE ¼ 150 mV and ipa=ipc ¼ 1.3 at
100 mVsꢁ 1 scan rate. This indicate the quasi reversible behaviour
of these systems.
3. All ligands showed only a single wave profile.
4. The voltammograms of the [L2Cu]ꢀnH2O complexes displayed a
single redox wave similar to that wave showed by the ligands but
with higher E0 and irreversible reduction peak at a very negative
potential which only appeared for [(L1)2Cu]ꢀH2O.
0
5. When the strength of the electron donating group on the 4-
substituent (X) of the benzoyl group is increased (from X ¼ 4-CH3
0
(HL4) to X ¼ 4-OH (HL3), E0 will be shifted to a lower value. The
same behavior occurred for X ¼ 4-Cl (HL2). The complexes
showed the same behavior as their corresponding ligands but with
0
higher E0 .
Reproducibility of the CV either by starting the scanning from Fcþ or
Fc indicate the existence of an electrochemically reversible system. In the
scan limits used, only the oxidation of the ferrocene moiety has been
0
detected. As the electron donating of the 4-substituent (X) increased, E0
shifted to a more negative value indicating that the oxidation of Fc is
0
getting easier. Furthermore, the E0 values are shifted to more negative
values in the order HL2 (X ¼ Cl) > HL1 (X ¼ H). This indicates that 4-Cl
acts as electron donor through the p-conjugated system, rather than electron
withdrawing through the s-bond.

1784
KASSEM ET AL.
Table VI. Cyclic Voltammetry Data for 5610ꢁ 4 M (HL1, HL2, HL3, HL4) and
5610ꢁ 4 M [L2Cu]ꢀnH2O Solutions in 0.1 M TBAP in CH2Cl2 at 25 C
ꢂ
Compound
HL1
S.R., mVsꢁ 1
Epc0 V
Epa0 V
E0, V
DE, V ipa=ipc
50
100
150
200
ꢁ 0.09
ꢁ 0.09
ꢁ 0.11
ꢁ 0.11
0.030
0.060
0.080
0.080
ꢁ 0.030
ꢁ 0.015
ꢁ 0.015
ꢁ 0.015
0.120
0.150
0.190
0.190
1.26
1.27
1.32
1.28
[(L1)2Cu]ꢀH2O
50
100
150
200
0.04
ꢁ 0.01
0.04
0.120
0.140
0.130
0.145
0.080
0.065
0.085
0.105
0.080
0.150
0.090
0.080
1.80
2.10
1.70
1.57
0.07
HL2
50
100
150
200
ꢁ 0.06
ꢁ 0.06
ꢁ 0.09
ꢁ 0.07
0.020
0.020
0.030
0.030
ꢁ 0.020
ꢁ 0.020
ꢁ 0.030
ꢁ 0.020
0.080
0.080
0.120
0.100
1.40
1.70
1.60
1.65
[(L2)2Cu]ꢀ2H2O
50
100
150
200
ꢁ 0.03
ꢁ 0.09
ꢁ 0.05
ꢁ 0.05
0.120
0.140
0.120
0.135
0.045
0.035
0.035
0.045
0.150
0.210
0.170
0.180
1.60
1.90
1.35
1.24
HL3
HL4
100
200
ꢁ 0.10
ꢁ 0.11
ꢁ 0.020
ꢁ 0.010
ꢁ 0.060
ꢁ 0.060
0.080
0.100
1.50
1.50
50
100
150
200
ꢁ 0.09
ꢁ 0.10
ꢁ 0.11
ꢁ 0.12
0.020
0.030
0.050
0.050
ꢁ 0.35
ꢁ 0.35
ꢁ 0.30
ꢁ 0.35
0.110
0.130
0.160
0.170
1.30
1.30
1.30
1.30
[(L4)2Cu]ꢀ2H2O
50
100
150
200
ꢁ 0.04
ꢁ 0.03
ꢁ 0.04
ꢁ 0.05
0.060
0.055
0.065
0.080
0.010
0.013
0.013
0.015
0.100
0.085
0.105
0.130
2.00
1.60
1.50
1.50
The two ferrocene centers in [L2Cu]ꢀH2O are oxidized in a single step,
i.e., through two one-electron processes indicating the absence of electronic
communication between the two ferrocene moieties. The oxidation difficulty
of ferrocene in these complexes is attributed to the electron-withdrawing
capability of the copper(II) center on the ferrocene moiety.[8] Furthermore,
the copper(II) centers show an irreversible reduction at EPc ¼ ꢁ 0.94 V for
[L2 Cu]ꢀH2O. Finally, the effect of electron donating of the 4-substituents on
1
the shifts of EPc for the reduction of copper(II) to more negative values is
outside our scanning limits.

COPPER(II) COMPLEXES
1785
CONCLUSION
This work describes the synthesis of acetylferrocene hydrazones with
variously substituted benzoylhydrazones and their copper(II) complexes. The
electrochemical spectral studies demonstrated that copper(II) behaves as
an efficient linking segment to generate bis(ferrocene). In particular, the
[L2Cu]ꢀnH2O core prevents any electronic interaction between the ferrocene
substituents, producing systems capable to release two electrons in a
single step.
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Received March 29, 2001
Accepted July 15, 2002
Referee I: E. Rosenberg
Referee II: F. A. Schultz