Structure and magnetic properties of binuclear copper(II) complexes with 2,6-diformyl-4-tert-butylphenol bis(imidazolinyl)hydrazone

Article abstract of DOI:10.1134/S1070363213120153

Binuclear copper(II) complexes with bis(imidazolinyl)hydrazone of 2,6-diformyl-4-tert-butylphenol have been prepared and studied. In all complexes the antiferromagnetic exchange interaction between the copper(II) ions is observed.

Full text of DOI:10.1134/S1070363213120153

ISSN 1070-3632, Russian Journal of General Chemistry, 2013, Vol. 83, No. 12, pp. 2314–2319. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © L.D. Popov, S.I. Levchenkov, I.N. Shcherbakov, G.G. Aleksandrov, A.A. Tsaturyan, S.S. Beloborodov, O.V. Maevskii, V.A. Kogan,
2013, published in Zhurnal Obshchei Khimii, 2013, Vol. 83, No. 12, pp. 2030–2035.
Structure and Magnetic Properties of Binuclear Copper(II)
Complexes with 2,6-Diformyl-4-tert-butylphenol
Bis(imidazolinyl)hydrazone
L. D. Popova, S. I. Levchenkovb, I. N. Shcherbakova, G. G. Aleksandrovc,
A. A. Tsaturyana, S. S. Beloborodova, O. V. Maevskiia, and V. A. Kogana
a Southern Federal University, Rostov-on-Don, Russia
b Southern Scientific Center, Russian Academy of Sciences, ul. Chekhova 41, Rostov-on-Don, 344022 Russia
e-mail: s.levchenkov@gmail.com
cKurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
Received February 7, 2013
Abstract—Binuclear copper(II) complexes with bis(imidazolinyl)hydrazone of 2,6-diformyl-4-tert-butyl-
phenol have been prepared and studied. In all complexes the antiferromagnetic exchange interaction between
the copper(II) ions is observed.
DOI: 10.1134/S1070363213120153
Hydrazinoimidazoline and its hydrazone deriva-
tives are attractive due to their biological activity and
strong complexing ability. The antifungal and
anticancer activity as well as cytotoxicity of a series of
hydrazinoimidazoline hydrazones has been studied in
[1–3]. The complexes of Pt(II) and Pd(II) with
hydrazinoimidazoline have been described [4–6]; the
former has been considered a probable analog of
cisplatin [6]. The dimeric complex of copper(II) with
pyridine-2-carbaldehyde imidazolinylhydrazone is
known [7], containing two mononuclear [Cu(L)Br]
fragments connected via the sulfate bridge. However,
we are not aware of any systematic study of the
complexing ability of imidazolinylhydrazones.
Composition and structure of the isolated
compounds were confirmed by elemental analysis, IR
and NMR spectroscopy, magnetic properties, and X-
ray diffraction data.
1
In the H NMR spectrum of I, the singlet signal of
the methylene group as well as the broad singlet signal
of NH (4H, δ = 7.45 ppm) disappearing upon addition
of D2O were observed; therefore, we concluded that
the compound existed in the diazine form due to the
hydrazine proton transfer to the imidazoline nitrogen.
Noteworthily, the singlet of imidazoline CH2 group
was observed in the spectra of the other imidazol-
inylhydrazones [2, 3]; the diazine form of imidazol-
inylhydrazone of 3-hydroxy-5-pregnan-20-one was
confirmed by X-ray diffraction study [3].
Here we report on the preparation and physico-
chemical studies of bis(imidazolinyl)hydrazone of 2,6-
diformyl-4-tert-butylphenol I and its binuclear com-
plexes with copper(II). The complexes of transition
metals with azomethines and 2,6-diformylphenol
hydrazones, the so-called Robson’s ligands [8, 9], are
known as convenient models for the study of the
factors influencing the magnetic exchange interaction
of paramagnetic transition metal ions [10–12]. Such
information is of high importance in view of
development of new molecular magnetic materials
[13–15].
N
OH
N
N
N
NH
NH
NH
NH
I
2314

STRUCTURE AND MAGNETIC PROPERTIES OF BINUCLEAR COPPER(II) COMPLEXES
2315
The interaction of I dihydrobromide with copper(II)
perchlorate, of I with copper(II) bromide, and of I with
copper(II) acetate gave the following complexes:
[Cu2(H2L)Br2]·ClO4 (II), [Cu2(H2L)Br3] (III), and
[Cu2L(OCH3)] (IV). The thermogravimetric analysis
of the complexes revealed no endothermic effects
below 180°С, thus proving the absence of the solvent
molecules in the complexes structure [16, 17]. The
thermal oxidative destruction of the organic ligand
occurred at 290–310°С.
information from the referenced literature it was
suggested that in the case of II and III the ligand was
coordinated in the monodeprotonated form, whereas in
the case of IV, triply deprotonated form of the ligand
was more probable. Higher degree of deprotonation in
the case of I interaction with copper(II) acetate was
due to the deprotonating ability of the acetate ion in the
methanol solution [18–22]. In all previously described
cases of 2,6-diformylphenol bishydrazones interaction
with copper(II) halides or perchlorate the complexes
containing monodeprotonated bishydrazone were
formed [21–23].
In the IR spectra of II–IV the ν(ОН) band was
absent, whereas the ν(С=N) band assigned to the
azomethine fragment was shifted to lower wave-
numbers (1610–1620 cm–1), therefore, the coordination
of copper(II) ions to azomethine nitrogen atoms was
postulated. Based on the IR data, the deprotonation of
bishydrazone in the complexes could not be evaluated
unambiguously. In the spectra of all complexes the
bands assigned to NH group vibrations were observed:
at 3250 cm–1 (broad) in the case of II, at 3322 and
3169 cm–1 in the case of III, and at 3308 cm–1 in the
case of IV. From the elemental analysis data and the
The effective magnetic moments of complexes II–
IV significantly decreased upon cooling to –196°C,
thus evidencing the exchange interaction of the
antiferromagnetic type and proving the binuclear
structure of the compounds. The exchange interaction
parameters 2J as calculated in the frame of the
isotropic exchange model [24] using the Bleaney–
Bowers equation [25] were –108 cm–1 (II), –52 cm–1
(III), and –408 cm–1 (IV) (Table 1).
Br
N
O
O
N
N
O
N
N
N
NH
NH
HN
NH
Cu
Cu
Cu
Br
Cu
N
NH
NH
N
N
N
Br
CH3
IV
III
From the collected data the above shown structures
of III and IV were reliably assumed.
rather unusual; to the very best of our knowledge, the
complexes of 2,6-diformylphenol bishydrazone con-
taining both perchlorate and halide ions were not
mentioned either in the literature nor in the Cambridge
The significant difference in the strength of the
antiferromagnetic exchange interaction in the cases of
III and IV coincided with the known correlations
between the structure and the magnetic properties. The
bridged coordination of bromine led to a noticeable
distortion of the exchange fragment, whereas in the com-
plexes with the alkoxide bridge the exchange fragment
was almost planar, as was the overall structure of the
metal chelate macrocycle. The planar structure enhances
Table 1. Magnetic properties of II–IV
Comp.
a
Т, K
μeff, μB
2J, cm–1
g
f
no.
297
77.4
297
77.4
295
77.4
1.81
1.26
1.75
1.52
1.27
0.47
–108
2.24
0.068
II
–52
2.08
2.20
0.006
0.056
III
IV
the overlap of dx –y
2
2
copper ions orbitals, thus
improving the exchange interaction [10, 12, 19].
–408
Structure of II could be hardly elucidated from the
above presented data. The complex composition was
a μeff is calculated per one copper atom.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 12 2013

2316
POPOV et al.
Scheme 1. General view of molecule of II (thermal vibration ellipsoids correspond to 50% probability)
Structural Database. All known examples of cop-
per(II) perchlorate with the Robson’s ligands were
binuclear complexes with exogenous hydroxy or
alkoxide bridge [23, 26].
the N1C3N2C2C1 and N7C12N8C14C13 imidazoline rings
were turned with respect to the benzene ring by 28.15°
and 29.62°, respectively.
The perchlorate ion was located in the outer sphere
of the complex. In the crystal, each of the complex
ions formed two hydrogen bonds with perchlorate ions
(Table 3), thus giving the infinite zigzag one-
dimensional chains stretched along c crystallographic
axis.
Structure of II was found by the X-ray diffraction
analysis. The single crystal suitable for the analysis
was prepared by recrystallization from methanol. In II,
the bishydrazone was coordinated to copper ions in its
monodeprotonated hydrazone tautomeric form. The
coordination polyhedra of both copper ions were found
to be distorted squares formed by the phenoxide
oxygen atom, azomethine and imidazoline nitrogen
atoms, and bromine (see Shceme 1). The Br1 and Br2
atoms were off the O1N4N1 and O1N5N7 planes by
1.008 and 0.904 Å, respectively. Each of the bromine
atoms was bound to the second copper ion via weak
coordination bond [Br2–Cu1 3.1840(7) Å long and
Br1–Cu2 3.1388(7) Å long], thus supplementing copper
coordination polyhedron to the elongated square
pyramid (4+1). The distance between copper atoms
was 3.1222(7) Å; the Cu1O1Cu2 bond angle at the
bridging oxygen atom was 106.4(1)° (Table 2).
The bromine atoms coordination in II was
significantly different from that in the other known
halogen-containing complexes of transition metals
with 2,6-diformylphenol hydrazones. In the previously
described complexes of that type, the bridging
coordination of one of the halogen atoms was observed
by X-ray diffraction analysis [26–31]. If other halogen
atoms were present in the molecule, they were axially
coordinated to one or both copper atoms, supple-
menting their coordination polyhedron to the distorted
square pyramid.
Among the previously described copper(II)
complexes with the Robson’s ligands, the following
ones exhibited the coordination of the exogenous acido
ligands most similar to that observed in this work: bis-
μ2-chlorine bridged copper(II) complex with bis(2-
dimethylaminoethyl)pyridine-2,6-dicarboxamide-1-
The five-membered chelate rings, Cu1N4N3C3N1
and Cu2N5N6C12N7, were almost planar, whereas the
six-membered chelate rings were highly distorted due
to bending along the O1–N4 and O1–N5 lines. The
organic ligand fragment on the whole was not planar,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 12 2013

STRUCTURE AND MAGNETIC PROPERTIES OF BINUCLEAR COPPER(II) COMPLEXES
2317
Table 2. Selected interatomic distances and angles of the
copper coordination polyhedron in complex II
Table 3. Characteristics of the intermolecular hydrogen
bonds in the crystal of complex IIa
Bond
Br1–Cu1
Cu1–N4
d, Å
2.3661(7)
1.969(4)
1.923(4)
1.950(3)
3.1840(7)
ω, deg
Bond
Br2–Cu2
Cu2–N5
d, Å
D–H···A
D–H, Å
H···A, Å
D···A, Å ∠DHA, deg
N3–H3A···O2S 0.881(3) 2.095(3)
N6–H6B···O1Si 0.880(3) 2.064(4)
2.905(5)
152.5(2)
155.8(2)
2.3752(7)
1.981(4)
1.919(3)
1.949(3)
3.1388(7)
ω, deg
2.889(5)
Cu1–N1
Cu2–N7
a Symmetry code: (i) –x + 1/2, –y + 1/2, z – 1/2.
Cu1–O1
Cu2–O1
Br2–Cu1
Br1–Cu2
EXPERIMENTAL
Angle
Angle
Elemental analysis was performed on the Perkin-
Elmer 240C analyzer in the Laboratory of Micro-
analysis, Southern Federal University. IR spectra of the
suspensions in mineral oil were registered on a Varian
Scimitar 1000 FT-IR spectrometer at 400–4000 cm–1.
1H NMR spectra of the solutions in DMSO-d6 were
registered on a Varian Unity 300 (300 MHz)
spectrometer in the pulse Fourier mode, with
hexamethyldisiloxane as the internal reference.
Magnetic susceptibility was determined by the relative
Faraday method at 77.4–300 K; the calibration
reference was Hg[Co(CNS)4]. The thermogravimetric
analysis preformed on a Diamond TG/DTA (Perkin-
Elmer) instrument at the heating rate of 10 deg/min,
ramp to 650°С.
N1Cu1O1
N1Cu1N4
O1Cu1N4
N1Cu1Br1
O1Cu1Br1
O1Cu1Br2
N4Cu1Br1
Cu1Br1Cu2
166.08(15)
81.29(15)
87.98(13)
100.82(12)
91.96(9)
70.75(8)
163.80(10)
67.42(2)
N7Cu2O1
N7Cu2N5
O1Cu2N5
N7Cu2Br2
O1Cu2Br2
O1Cu2Br1
N5Cu2Br2
Cu1Br2Cu2
167.46(14)
81.57(15)
87.99(13)
99.40(11)
92.51(9)
71.24(8)
164.60(10)
66.50(2)
oxide [Cu2LCl2] [32] and the polymeric complex of
copper(II) with 2,6-bis[N-(2-pyridylethyl)formidoyl]-
4-ethylphenol [33]. It was suggested that in the
[Cu2L(NCS)2] binuclear fragments of the latter, the
copper atoms were only bound via the phenoxide
bridge, and the coordination surrounding of copper
atoms was as follows: N3OS and N4O. In the former
complex, the exchange interaction between copper(II)
ions was not noticeable [32], whereas in the latter
complex, strong antiferromagnetic exchange was
observed (2J –210 cm–1) [33].
Bishydrazone
I
was prepared from the
commercially available hydrazinoimidazoline dihydro-
bromide. 2,6-Diformyl-4-tert-butylphenol was prepared
as described in [36].
Bishydrazone I. The equimolar amount of sodium
acetate was added to the hot solution of 10 mmol of
hydrazinoimidazoline dihydrobromide in 20 mL of
ethanol, and the mixture was refluxed during 10 min.
Then, the hot solution of 5 mmol of 2,6-diformyl-4-
tert-butylphenol in 10 mL of ethanol was added; the
mixture was refluxed during 5 h and left overnight.
The yellow precipitate was filtered off and recrystal-
lized from acetonitrile–methanol, 1 : 1. Yield 75%, mp
256–258°C. IR spectrum, ν, cm–1: 3308 (OH), 3170
2
The J value in the case of II fell into a quite wide
range of the exchange parameters reported in the cases
of copper(II) complexes with various 2,6-di-
formylphenol hydrazones, containing copper atoms
bridged by phenoxide or by bromide (from –10 to
–160 cm–1) [10, 12]. At the same time, the
antiferromagnetic exchange in II was noticeably
weaker than that described in [33]. Taking into account
that in the case of II the exchange interactions could
only be translated via the phenoxide oxygen bridge, it
was suggested that the weakening of the exchange
interaction was due to the decrease in the bond angle
of the phenoxide bridge [106.4(1)° and 110.13(8)°,
respectively]. Indeed, that bond angle was shown to
affect the antiferromagnetic exchange in similar
systems [10–12, 34, 35].
1
(NH), 1660, 1625 (C=N). H NMR spectrum, δ, ppm:
12.188 s (1H, OH), 8.364 s (2H, CHazometh), 7.622 s
(2H, CHarom), 7.45 br.s (4H, NH), 3.529 s (8H, CH2),
1.293 s (9H, t-Bu). Found, %: C 58.90; H 6.79; N
30.54. C18H25N8O. Calculated, %: C 58.52; H 6.82; N
30.33.
Dihydrobromide of I was prepared similarly,
without addition of sodium acetate. Yield 80%, mp
>260°C. Found, %: C 40.87; H 5.29; N 20.99.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 12 2013

2318
POPOV et al.
C18H27Br2N8O. Calculated, %: C 40.69; H 5.12; N
21.09.
carbon and n = 1.2 in the case of other carbon atoms].
The final divergence factors were R1 0.0479 and wR2
0.1240 for 4933 independent reflections with I > 2σ(I);
and R1 0.0862 and wR2 0.1440 for the total 7524
independent reflections. With 325 of the refined
parameters, GOOF equaled 1.000. All calculations
were performed in the SHELXL-97 software package
[39]. The structure was analyzed in the PLATON [40]
software. The selected interatomic distances and bond
angles are collected in Table 2, the hydrogen bonds
parameters are given in Table 3. The atomic
coordinates and the temperature factors were deposited
to the Cambridge Structural Database under CCDC
908059.
Preparation of complex II. The hot solution of
2 mmol of copper(II) perchlorate in 10 mL of
methanol was added to the hot solution of 1 mmol of I
dihydrobromide in 20 mL of methanol. The mixture
was boiled during 1 h; the formed precipitate was
filtered off, washed with methanol, and dried in a
vacuum at room temperature. Yield 75%, mp >260°C
(decomp.). IR spectrum, ν, cm–1: 3250 (NH), 1619,
1598 (C=N), 1101 (ClO4). Found, %: C 28.12; H 3.49;
N 15.08; Cu 16.90. C18H25Br2ClCu2N8O5. Calculated,
%: C 28.61; H 3.33; N 14.83; Cu 16.82.
Preparation of complexes III and IV. The hot
solution of 2 mmol of either copper(II) bromide (III)
or copper(II) acetate (IV) in 20 mL of methanol was
added to the hot solution of 1 mmol of I in 20 mL of
methanol. The mixture was boiled during 1 h; the
precipitate was filtered off, washed with methanol, and
dried in a vacuum at room temperature.
ACKNOWLEDGMENTS
This work was financially supported by the Russian
Foundation for Basic Research (project no. 12-03-
31691-mol_a).
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