New magnetically active metal complexes of tridentate Schiff bases of phenylazosalicylaldehyde

Article abstract of DOI:10.1134/S1070328409070045

The bidentate chelate Cu(II) complexes of phenylazosalicylaldehyde azomethines are synthesized for the first time and their magnetic properties are studied. The complexes with the intermetallic bridge of the nitrogen atoms are characterized by the antifer

Full text of DOI:10.1134/S1070328409070045

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2009, Vol. 35, No. 7, pp. 486–491. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © A.S. Burlov, S.A. Nikolaevskii, A.S. Bogomyakov, I.S. Vasil’chenko, Yu.V. Koshchienko, V.G. Vlasenko, A.I. Uraev, D.A. Garnovskii, E.V. Sennikova, G.S.
Borodkin, A.D. Garnovskii, V.I. Minkin, 2009, published in Koordinatsionnaya Khimiya, 2009, Vol. 35, No. 7, pp. 495–500.
New Magnetically Active Metal Complexes of Tridentate Schiff
Bases of Phenylazosalicylaldehyde
A. S. Burlova, S. A. Nikolaevskiia*, A. S. Bogomyakovb, I. S. Vasil’chenkoa, Yu. V. Koshchienkoa,
V. G. Vlasenkoc, A. I. Uraeva, D. A. Garnovskiid, E. V. Sennikovaa, G. S. Borodkina,
A. D. Garnovskiia*, and V. I. Minkina,d
a Research Institute of Physical and Organic Chemistry, Southern Federal University, Rostov-on-Don, Russia
b International Tomography Center, Siberian Division, Russian Academy of Sciences, Novosibirsk, Russia
c Research Institute of Physics, Southern Federal University, Rostov-on-Don, Russia
d Southern Scientific Center, Russian Academy of Sciences, Rostov-on-Don, Russia
*E-mail: garn@ipoc.rsu.ru
Received September 24, 2008
Abstract—The bidentate chelate Cu(II) complexes of phenylazosalicylaldehyde azomethines are synthesized
for the first time and their magnetic properties are studied. The complexes with the intermetallic bridge of the
nitrogen atoms are characterized by the antiferromagnetic interaction, whereas the ferromagnetic exchange is
typical of analogous coordination compounds with the sulfur bridge.
DOI: 10.1134/S1070328409070045
INTRODUCTION
(3.05 g, 0.025 mol) in methanol (7 ml) with vigorous
stirring. The azocoupling was ceased 45 min after, and
the resulting solution was stirred for 30 min. When the
temperature of the solution became ambient, the pH
value was brought to 7 by the addition of Na2CO3. The
brown precipitate formed was filtered off, washed with
a large amount of water, and dried in air. The product
was purified by chromatography on a column packed
with Al2O3 (chloroform as eluent), chloroform was dis-
tilled off from the eluate, and the resulting precipitate
was recrystallized from benzene. The yield of L1 was
70% (mp = 128–129°C).
Azo ligands are most important objects of the mod-
ern coordination chemistry [1–4]. In the most cases,
metallochelates with five-, six- or five-, and six-mem-
bered coordination modes were obtained from the azo-
ligating compounds. At the same time, complexes,
whose azo group of the ligand is not in the composition
of the coordination mode, are of considerable interest
for the synthesis and study of magnetically active mate-
rials [5, 6]. This position of the azo group makes it pos-
sible to use its ability for the photoinduced E/Z- isomer-
ization in the creation of coordination compounds with
the properties of molecular switchers [7]. We synthe-
sized earlier undescribed binuclear copper chelates (I)
from 2-hydroxy-5-phenylazobenzaldehyde (L1) and
For C13H10N2O2
anal. calcd, %:
Found, %:
C, 69.01;
C, 69.11;
H, 4.46;
H, 4.48;
N, 12.39.
N, 12.40.
related
2-((E)-{[2-(ethylamino)-5-nitrophe-
nyl]imino}methyl)-4-(phenylazo)phenol (L2). Their
magnetic properties were studied in the temperature
interval from 2 to 300 K.
IR, cm–1: 1664 vs (C=O). 1H NMR (CDCl3), δ, ppm:
7.12–8.22 (m, 8H, CAr–H), 10.04 (s, 1H, CHO), 11.33
(s, 1H, OH).
EXPERIMENTAL
Synthesis of L2. A solution of 2-ethylamino-5-
nitroaniline (0.544 g, 3 mmol) [8] in toluene (15 ml)
was added to a solution of L1 (0.679 g, 3 mmol) in tol-
uene (20 ml). The mixture was refluxed under argon for
3 h. Then 1/3 of the toluene volume was distilled off on
a rotary evaporator. A yellow-orange precipitate was
formed on cooling, filtered off, washed with cold etha-
nol (4 × 5 ml), and recrystallized from a chloroform–
ethanol (4 : 1) mixture. The yield of L2 was 65% (mp =
Synthesis of L1 was carried out by the dinitration of
aniline and the coupling of the obtained diazonium salt
with salicylaldehyde. Dry NaNO2 (1.82 g, 0.026 mol)
was added during 45 min with vigorous stirring at a
temperature not higher than –5°C to a solution of
aniline (2.33 g, 0.025 mol) in a 12% solution of HCl
(15 ml). Subsequent procedures were carried out at this
temperature. After the end of the dinitration, the result-
ing solution was stored for 30 min. The diazonium salt
was slowly added to a solution of salicylaldehyde 233–234°C).
486

NEW MAGNETICALLY ACTIVE METAL COMPLEXES
487
N N
OH
COH
N N
OH
N
H
N
C
H
C H
2
5
(L1)
(L2)
Ph
N
O N
2
N
R
HC
N
H
X
N C
O2N
O
Cu Cu
O
Ph N N
O
Cu
X
Cu
O
N N Ph
X
C N
H
X
N
NO2
CH
R
(Ib) X = S, R = H
N
N
Ph
(I‡) X = NC2H5, R = NO2
For C42H34N10O6Cu2
anal. calcd, %: C, 55.93; H, 3.80; N, 15.53; Cu, 14.09.
Found, %: C, 56.10; H, 3.47; N, 15.75; Cu, 14.11.
For C21H19N5O3
anal. calcd, %:
Found, %:
C, 64.77;
C, 65.06;
H, 4.92;
H, 4.85;
N, 17.98.
N, 17.91.
IR, cm–1: 1602 s (C=N), 1344 w (Ph–O).
Synthesis of bis[2-{(E)-[(2-mercaptophe-
IR, cm–1: 1605 (C=N), 1293 (Ph–O), 3408 (N–H).
1H NMR (CDCl3), δ, ppm: 1.37 (t, 3H, J = 7.22 Hz,
CH3), 3.37 (m, 2H, ëç2), 5.06 (br.s, 1H, NH), 6.66 (d,
nyl)imino]methyl}-4-(phenyldiazenyl)phenolato]di-
1H, J = 9.1 Hz, CAr–H), 7.17 (d, 1H, J = 8.7 Hz, CAr–H), copper(II) (Ib). A hot solution of o-aminothiophenol
(0.125 g, 0.001 mol) in methanol (10 ml) and a solution
of copper acetate dihydrate in the same solvent (10 ml)
were added to a hot solution of L1 (0.226 g, 0.001 mol)
in dioxane (10 ml). The resulting mixture was refluxed
for 15 ml, and then a hot solution of copper acetate
dihydrate (0.200 g, 0.001 mol) in methanol (10 ml) was
added. Then the mixture was refluxed for 1.5 h. A black
precipitate was formed during reflux. The mixture was
cooled down, filtered off, washed with hot methanol
(4 × 5 ml) and then with hexane (5 ml), and dried in a
vacuum drying oven at 100°ë. The yield of compound
Ib was 60% (mp > 250°C).
7.47–7.57 (m, 3H, CAr–H), 7.90–8.17 (m, 6H, CAr–H),
7.90–8.17 (m, 6H, CAr–H), 8.84 (s, 1H, CH=N), 12.78
(s, 1H, OH).
Synthesis of bis[2-((E)-{[2-(ethylamino)-5-nitrophe-
nyl]imino}methyl)-4-(phenylazo)phenolato]dicop-
per(II) (Ia). A boiling solution of copper acetate dihy-
drate (0.119 g, 0.00058 mol) in methanol (10 ml) was
added to a hot solution of azomethine L2 (0.232 g,
0.00058 mol) in a dioxane–methanol (3 : 1) mixture
(20 ml). The resulting mixture was refluxed for 2.5 h. A
brown precipitate of compound Ia was formed during
reflux. After cooling, the precipitate was filtered off,
washed with hot methanol (4 × 5 ml) and hexane (5 ml),
and dried in a vacuum drying oven at 100°ë. The yield
of compound Ia was 45% (mp > 250°C).
For C38H26N6O2S2Cu2
anal. calcd, %: C, 57.78; H, 3.32; N, 10.64; Cu, 16.09.
Found, %:
C, 57.61; H, 3.41; N, 10.71; Cu, 16.20.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 35 No. 7 2009

488
BURLOV et al.
N/O
S
1.5
1.0
0.5
Cu
2
1
0
1
2
3
4
5
6
r, Å
Fig. 1. The FTM EXAFS of the X-ray K-edge absorption of complexes (1) Ia and (2) Ib. Solid line is experiment, and circles show
theoretical calculation.
IR, cm–1: 1611 vs (C=N), 1324 w (Ph–O).
The Cuä-edge EXAFS spectra of the studied com-
pounds were detected on an EXAFS laboratory spec-
trometer based on a DRON-3 diffractometer. A BSV-
21-Mo tube was used as an X-ray radiation source at
the voltage U = 17 kV and the current I = 30 mA. The
X-ray radiation was decomposed into the spectrum
1H NMR spectra were recorded on a Varian Unity-
300 instrument (300 MHz) in the mode of internal sta-
2
bilization of the H polar resonance line in CDCl3. IR
spectra were measured on a Nicolet Impact-400 instru-
ment (suspensions in Nujol).
using a SiO2(134 0) monochromating crystal.
Samples for detection were thoroughly mixed with
the Apiezon lubricant and placed between thin lavsan
films. The thickness of the samples was selected in such
a way that the intensity of the passed X-ray beams
decreased by 2.5–3.0 times. After standard procedures
on the isolation of the background, normalization to the
ä-edge jump, and isolation of the atomic absorption µ0
[9], the Fourier transformation of the obtained EXAFS
spectra was performed in the interval of wave vectors of
photoelectrons k from 3.0 to 13 Å–1 with the weight
function k2. The threshold ionization energy E0 was
chosen by the value of the maximum of the first deriv-
ative of the K-edge and further was varied during fit-
ting. The exact values of the structure parameters of the
nearest environment of metal atoms were determined
by the nonlinear fitting of the parameters of the corre-
sponding coordination spheres by the comparison of
the calculated EXAFS signal and that isolated from the
full EXAFS spectrum by the Fourier filtration method
of the Fourier transformant modules (FTM). This non-
Structure parameters of the nearest environment of the Cu at-
oms obtained from the multisphere fitting of the EXAFS data
(R are the interatomic distances, N is the coordination num-
ber, σ2 is the Debye–Waller factor, and Q is the fitting quality
function)
Compound
N
R, Å
σ2, Å2
0.0035 O/N
0.0037
0.0074 Cu
Atom Q, %
Ia
2
2
1
2
2
1
1.87
1.99
2.79
1.92
2.24
2.99
5.1
N
Ib
0.0040
0.0057
N
S
4.3
0.0060 Cu
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 35 No. 7 2009

NEW MAGNETICALLY ACTIVE METAL COMPLEXES
489
µeff, µB
2.8
µeff, µB
3.6
2.6
2.4
2.2
2.0
3.4
3.2
3.0
2.8
2.6
1.8
0
50
100
150
200
250
300
0
50
100
150
200
250
300
T, K
T, K
Fig. 2. Temperature plot of the effective magnetic moment
for complex Ia.
Fig. 3. Temperature plot of the effective magnetic moment
for complex Ib.
linear fitting was carried out using the IFFEFIT-1.2.10 areAvogadro’s number, Bohr’s magneton, and the Bolt-
programs [10]. The photoelectron wave scattering zmann constant, respectively.
phases and amplitudes, being necessary for the con-
struction of theoretical spectra, were calculated using
RESULTS AND DISCUSSION
According to the data of the IR and 1H NMR spec-
the FEFF7 program [7] and the X-ray structural data for
the model compounds. The model compounds were
bis((µ2-azido-N,N)-(7-amino-4-methyl-5-aza-3-hep- tra, the enolimine form can be ascribed to the Schiff
tyl-2-onato-N,O)-copper(II) (C14H26Cu2N10O2) [12] and base L2 as to other Ó-hydroxyazomethines [14–17]. The
N,N-(2,6-dimethylene-4-methylthiophenyl)-1,3-diami- intense peak of the absorption band of stretching vibra-
nopropane)-bis(methanol-copper(II)) nitrate hexafluo- tions of the HC=N bond appears at 1605 cm–1 in the IR
rophosphate ethanol solvate (C29H43Cu2F6N5O6.5PS2) spectrum, whereas the band corresponding to vibra-
[13] for compounds Ia and Ib, respectively. They have tions of the NH groups appears at 3408 cm–1.
The enolimine tautometic form of L2 is also con-
local environment of the metal atoms close to the
assumed one in the compounds under study.
1
firmed by the H NMR signals at 5.06 (NH), 8.84
(HC=N), and 12.78 (OH) ppm.
The fitting quality function Q, which was minimized
by finding the structure parameter of the nearest envi-
ronment, was calculated by the formula
The formation of chelate structure of type I by anal-
ogy to [18, 19] is confirmed by the disappearance of the
ν(NH) stretching vibrations in the IR spectrum of the
complexes and the signals of the NH groups in their
1H NMR spectra and by an insignificant decrease in the
frequencies of vibrations of the HC=N bond.
For the first time the dimeric structure can be
ascribed to synthesized complexes I, which is con-
firmed by the EXAFS spectral data.
The FTM of the copper K-edge EXAFS spectra of
compounds Ia and Ib are shown in Fig. 1. The parame-
ters of the nearest environment of the copper atom in
these compounds obtained by the fitting of theoretically
calculated χtheor(k) of the chosen models to χexp(k) are
given in the table.
As can be seen from Fig. 1, the FTM of the EXAFS
spectra of the both samples consist of the main peak
(r ≈ 1.48–1.50 Å) corresponding to the first coordination
sphere of the light N and O atoms and the peaks with
the lower amplitude (r = 2.43 (Ia), 2.64 (Ib) Å). The
main FTM peak of sample Ib (X = S) also has an addi-
[kχexp(k) – kχtheor(k)]2
∑
--------------------------------------------------------------
Q(%) =
100,
[kχexp(k)]2
∑
where χexp and χtheor are the experimental and theoreti-
cal EXAFS values, respectively; k is the wave vector of
a photoelectron.
The magnetic properties of the compounds were
measured on an MPMSXL SQUID magnetometer
(Quantum Design) in the temperature interval from 2 to
300 K and a magnetic field of 5 kOe. The paramagnetic
components of the magnetic susceptibility (χ) were
determined with allowance for the diamagnetic contri-
bution estimated from Pascal’s constants. The effective
magnetic moment (meff) was calculated by the formula
1/2
3kB
⎛
⎝
⎞
⎠
------------
µeff(T) =
2χT
≈ (8χT)1/2, where NÄ, β, and kÇ
NAβ
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 35 No. 7 2009

490
BURLOV et al.
tional shoulder (r ≈ 1.77 Å) corresponding to the photo-
Thus, the main structural factor determining the
electron wave scattering on two different coordination type of magnetic interactions in the binuclear copper
spheres. We interpreted the second peak as the manifes- complexes with azosalicylaldehyde anils is the nature
…
tation of the Cu Cu distance in the complexes. As of the bridging atoms.
found by the analysis of the FTM of the EXAFS spectra
on the basis of the proposed models of the local atomic
structure of the copper atoms in the complexes under
study, metallochelates Ia and Ib have a dimeric struc-
It is known that the compounds containing the azo
group are characterized by cis–trans-isomerization,
which was observed under external effects [22–24].
Taking into account the crossover effect [25–27] and
based on the ligand systems L2 and the data presented,
we can assume a possibility of the synthesis of other
metal complexes (for Fe2+, Fe3+, Cr3+, Co2+) with both
thermo- and photocontrolled magnetic properties.
…
ture with a Cu Cu distance of 2.79 Å, two sets of bond
…
…
lengths Cu N/O 1.87 Å and Cu N 1.99 Å in Ia, and
…
…
the distances Cu Cu 2.99 Å, Cu N/O 1.92 Å, and
…
Cu S 2.24 Å in Ib.
The temperature magnetochemical studies made it
possible to determine the dependence of the character
of exchange interactions on the type of bridging atoms
in dimeric complexes Ia and Ib.
ACKNOWLEDGMENTS
This work was supported by the program of the
The experimental curves µeff(í) for complexes Ia Ministry of Education and Science of the Russian Fed-
and Ib are presented in Figs. 2 and 3. Taking into eration “Development of Scientific Potential of the
account the dimeric structure of the complexes, we Higher School” (grant RNP nos. 2.2.1.1/2348,
used the Bleaney–Bowers equation for the magnetic 2.1.1/2371), the program of the Presidium of the Rus-
susceptibility of the dimer [20] in the theoretical mod- sian Academy of Sciences (project “Molecular Design
eling of the obtained dependences [20]
of Magnetically Active Substances and Materials
(Molecular Magnetics), the Russian Foundation for
Basic Research (project nos. 07-03-00710, 08-03-
00154, 08-03-00223), the program “Development of
the Network of National Universities” (internal grants
YuFU 2008), and the President of the Russian Federa-
tion (grant no. NSh-363.2008.3).
NAβ2g2
3kBT
–1
1
3
–2J
---------
kBT
⎛
⎝
⎞
⎠
-----------------
--
1 + exp
χ(Cu–Cu)
=
+ Nα;
with allowance for intermolecular exchange interac-
tions zJ'
χ(Cu–Cu)
χ' = ------------------------------------------------------------------- ;
(1 – (2zJ'/NAg2β2)χ(Cu–Cu)
)
REFERENCES
1. Garnovskii, A.D., Vasil’chenko, I.S., and Garnovskii, D.A.,
Sovremennye aspekty sinteza metallokompleksov.
Osnovnye ligandy i metody (Modern Aspects of Synthe-
sis of Metal Complexes. Key Ligands and Methods),
Rostov-on-Don: LaPO, 2000.
2. Synthetic Coordination and Organometallic Chemistry,
Garnovskii, A.D. and Kharisov, B.I., Eds., New York:
Marcel Dekker, 2003.
and a possible admixture of the monomer p with the
spin S = 1/2
NAβ2g2S(S + 1)
--------------------------------------
χ = χ'(1 – p) +
p.
3kB(T – θ)
Here NÄ, Nα, kÇ, β, J, g, and θ are Avogadro’s num-
ber, van Vleck paramagnetism, the Boltzmann con-
stant, Bohr’s magneton, the exchange interaction
parameter, the Lande factor, and the Weiss constant,
respectively.
The introduction of the azophenyl group into the
azomethine fragment induces no basic changes in the
magnetic behavior of the binuclear copper complexes
with the NC2H5 intermetallic bridges: compound Ia, as
similar chelates containing no N=NPh group [18, 19,
21], is characterized by the exchange interaction of the
ferromagnetic type (Fig. 2).
3. Kogan, V.A. and Shcherbakov, I.N., Ross. Khim. Zh.,
2004, vol. 48, no. 1, p. 69.
4. Burlov, A.S., Uraev, A.I., Lysenko, K.A., et al., Koord.
Khim., 2008, vol. 34, no. 12, p. 916 [Russ. J. Coord.
Chem. (Engl. Transl.), vol. 34, no. 12, p. 904].
5. Khandar, A.A. and Nejati, K., Polyhedron, 2000, vol. 19,
no. 6, p. 607.
6. Pucci, D., Bellusci, A., Crispini, A., et al., Inorg. Chim.
Acta, 2004, vol. 357, no. 2, p. 495.
7. Gütlich, P., Garcia,Y., and Woike, T., Coord. Chem. Rev.,
2001, vols. 219–221, p. 839.
The comparison of the characteristics of magnetic
exchange in complex Ia and in the analogous chelate
without the azo fragment [19, 21] indicates that the
introduction of the N=NPh group increases the zJ'
parameter by 2 cm–1.
Complex Ib is characterized by the ferromagnetic
exchange (Fig. 3).An analog of this compound contain-
ing no azo group in the aldehyde fragment is diamag-
netic [18, 19, 21].
8. Foster, R., J. Chem. Soc., 1957, no. 11, p. 4687.
9. Kochubei, D.I., Babanov, Yu.A., Zamaraev, K.I., et al.,
Rentgenospektral’nyi metod izucheniya struktury amor-
fnykh tel: EXAFS-spektroskopiya (X-Ray Spectral
Method for Study of the Structure ofAmorphous Bodies:
EXAFS Spectroscopy), Novosibirsk: Nauka, Sib. Otd.,
1988.
10. Newville, M., EXAFS Analysis using FEFF and FEFFIT,
J. Synchrotron Rad., 2001, vol. 8, p. 96.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 35 No. 7 2009

NEW MAGNETICALLY ACTIVE METAL COMPLEXES
491
11. Zabinski, S.I., Rehr, J.J., Ankudinov, A., andAlber, R.C., 19. Burlov, A.S., Ikorskii, V.N., Uraev, A.I., et al., Zh.
Phys. Rev., B: Condens. Matter., 1995, vol. 52, p. 2995.
12. Costes, J.P., Dahan, F., Ruiz, J., and Laurent, J.P., Inorg.
Chim. Acta, 1995, vol. 239, nos. 1-2, p. 53.
Obshch. Khim., 2006, vol. 76, no. 8, p. 1337 [Russ. J.
Gen. Chem. (Engl. Transl.), vol. 76, no. 8, p. 1282].
20. Kalinnikov, V.T. and Rakitin, Yu.V., Vvedenie v magne-
tokhimiyu (Introduction to Magnetochemistry), Mos-
cow: Nauka, 1980.
13. Branscombe, N.D.J., Blake, A.J., Marin-Becerra, A.,
et al., Chem. Commun., 1996, p. 2573.
14. Hernandez-Molina, R and Mederoz, A, Comprehensive 21. Garnovskii, A.D., Ikorskii, V.N., Uraev, A.I., et al., J.
Coordination Chemistry, Lever, A.B.P., Ed., Amster-
dam-Oxford: Elsevier–Pergamon Press, 2003, vol. 1,
p. 411.
Coord. Chem., 2007, nos. 12–14, p. 1493.
22. Fujino, M., Amano, T., Akutsu, H., et al., Chem. Com-
mun., 2004, p. 2310.
15. Yang, C.-T. and Vital, J., Inorg. Chim. Acta, 2003,
23. Amano, T., Fujino, M., Akutsu, H., et al., Polyhedron,
vol. 344, no. 1, p. 65.
2005, vol. 24, nos. 16–17, p. 2614.
16. Lo, W.-K., Wong, W.-K., Cuo, J., et al., Inorg. Chim.
Acta, 2004, vol. 357, no. 15, p. 4510.
24. Fujino, M., Hasegava, S., Akutsu, H., et al., Polyhedron,
2007, vol. 26, no. 12, p. 2614.
17. Garnovskii, A.D. and Vasil’chenko, I.S., Usp. Khim.,
25. Sato, O., Acc. Chem. Res., 2003, vol. 36, no. 9, p. 692.
26. Nakatsuji, S., Chem. Soc. Rev., 2004, vol. 33, p. 348.
2005, vol. 74, no. 3, p. 211.
18. Burlov, A.S., Koshchienko, Yu.V., Ikorskii, V.N., et al.,
Zh. Neorg. Khim., 2006, vol. 51, no. 7, p. 1143 [Russ. J. 27. Brefuel, N., Vang, I., Shova, S., et al., Polyhedron, 2007,
Inorg. Chem. (Engl. Transl.), vol. 51, no. 7, p. 1065].
no. 8, p. 1745.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 35 No. 7 2009