Synthesis and characterization of nitro-Schiff bases derived from 5-nitro-salicylaldehyde and various diamines and their complexes of Co(II)

Article abstract of DOI:10.1080/00958970903225866

Some neutral tetradentate N₂O₂ type complexes of Co(II) have been synthesized using Schiff bases formed by condensation of 5-nitro-salicylaldehyde with various diamines in alcohol. The nature of the ligands and complexes was establis

Full text of DOI:10.1080/00958970903225866

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Synthesis and characterization of nitro-
Schiff bases derived from 5-nitro-
salicylaldehyde and various diamines
and their complexes of Co(II)
Hossein Naeimi a & Mohsen Moradian a
a Department of Chemistry, Faculty of Science, University of
Kashan, Kashan 87317, Iran
Version of record first published: 10 Sep 2009.
To cite this article: Hossein Naeimi & Mohsen Moradian (2010): Synthesis and characterization of
nitro-Schiff bases derived from 5-nitro-salicylaldehyde and various diamines and their complexes of
Co(II), Journal of Coordination Chemistry, 63:1, 156-162
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Journal of Coordination Chemistry
Vol. 63, No. 1, 10 January 2010, 156–162
Synthesis and characterization of nitro-Schiff bases
derived from 5-nitro-salicylaldehyde and various diamines
and their complexes of Co(II)
HOSSEIN NAEIMI* and MOHSEN MORADIAN
Department of Chemistry, Faculty of Science,
University of Kashan, Kashan 87317, Iran
(Received 19 February 2009; in final form 2 July 2009)
Some neutral tetradentate N2O2 type complexes of Co(II) have been synthesized using Schiff
bases formed by condensation of 5-nitro-salicylaldehyde with various diamines in alcohol.
The nature of the ligands and complexes was established by spectroscopic techniques. The
Schiff bases are bivalent anions with tetradentate ONNO donors derived from phenolic oxygen
and azomethine nitrogen. IR and UV-Vis spectral data suggest that all the complexes are
square-planar.
Keywords: Synthesis; Nitro-Schiff base; Ligand; Complex; Salicylaldehyde
1. Introduction
Schiff-base macroligands synthesized from reaction of dialdehydes and amino
compounds [1–6] form stable complexes, perhaps selective to specific metallic ions
with applications in electrochemistry, bioinorganic, antimicrobial activity, fluorescence
properties, catalysis, metallic deactivators, separation processes, and environmental
chemistry among others [7–14].
Preparation of new ligands is an important step in development of metal complexes,
which exhibit unique properties and reactivity. For example, in asymmetric catalyst
systems, small changes in donating ability of the ligand or the size of its substituents can
have a dramatic effect on catalyst efficiency and enantioselectivities [15–18]. The nitro
group is a strong electron-withdrawing group and due to its steric effects it has played
an important role in affecting the reactivity and enantioselectivities in asymmetric
cyclopropanation and allylic alkylation reactions [19].
In continuation of our research on preparation of Schiff bases [20–22] and their
complexes [23–26], we decided to prepare new Schiff bases containing electron-
withdrawing substituents.
This article describes the synthesis and spectroscopic characterization of several
nitro-Schiff bases and their complexes with transition metal ions. The corresponding
*Corresponding author. Email: naeimi@kashanu.ac.ir
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2010 Taylor & Francis
DOI: 10.1080/00958970903225866

Nitro-Schiff bases
157
1
materials were characterized by spectroscopic (IR, UV-Vis, H- and 13C-NMR, mass
spectra) and physical (melting point) data.
2. Experimental
2.1. Materials
Chemicals were purchased from Fluka and Merck Chemical Companies. Solvents were
purified by standard methods and dried before use by conventional methods. 5-Nitro-
salicylaldehyde has been prepared and characterized by our previously reported
procedure [26].
2.2. Physical measurments
IR spectra were recorded as KBr pellets on a Perkin-Elmer 781 spectrophotometer and
an Impact 400 Nicolet FTIR spectrophotometer. 1H- and 13C-NMR spectra were
recorded in d6-DMSO on a Bruker DRX-400 spectrometer with tetramethylsilane as
internal reference. Mass spectra were recorded on a Finnigan MAT 44S by electron
ionization (EI) mode with an ionization voltage of 70 eV. Melting points were obtained
with a Yanagimoto micromelting point apparatus and are uncorrected. Purity
determination of the substrates and reaction monitoring were accomplished by thin
layer chromatography (TLC) on silica–gel polygram SILG/UV 254 plates (from Merck
Company).
2.3. Synthesis of ligands
To prepare N,N0-bis(5-nitro-salicylidene)-1,3-propanediamine (L2), a solution of
5-nitro-salicylaldehyde (0.67 g, 4 mmol) in methanol (20 mL) was slowly added over a
solution of 1,3-diaminopropane (0.15 g, 2 mmol) in the same solvent (20 mL). The
mixture was stirred at 30ꢀC for 45 min and the precipitated product was obtained as a
yellowish orange solid. The crude solid was filtered off and washed with ethanol twice
(2 ꢁ 20 mL) and recrystallized from a dichloromethane/methanol mixed solvent to give
pure crystals, conversion 98%, yield 90.5% (0.67 g), m.p. 210–213ꢀC.
2.4. Synthesis of Schiff-base complexes of Co(II)
A flask containing a stirred suspension of cobalt(II) acetate tetrahydrate (0.25 g,
1 mmol) in methanol (20 mL) was purged with nitrogen, warmed to 50ꢀC, N,N0-bis(5-
nitrosalicylidene)-1,6-hexanediamine (L4) (0.42 g, 1 mmol) was added in one portion,
and the resulting black suspension was stirred at room temperature for 90 min. Then the
mixture was filtered under reduced pressure and the collected solid was washed with
diethyl ether and dried in air to give dark green crystalline complex (L4-M) which was
purified by recrystallization from chloroform, yield 87.0% (0.43 g).

158
H. Naeimi and M. Moradian
3. Results and discussion
The tetradentate Schiff bases were prepared by condensation of 5-nitro-salicylaldehyde
with various diamines in methanol (scheme 1). When 2 mol of 5-nitro-salicylaldehyde
and 1 mol diamine were reacted, the corresponding products (L1–L9) were obtained
under mild conditions; confirmation of these products was demonstrated by spectro-
scopic and physical data (table 1).
To prepare complexes, the Schiff bases were treated with cobalt(II) acetate in equal
mole amounts at low temperature in methanol (scheme 2). The reactions proceeded
without reflux under mild conditions preventing oxidation of metal(II) to metal(III).
The progress of reaction was monitored by TLC. After disappearance of the ligand on
TLC, the products were collected (table 2).
Complexes were insoluble in water and most organic solvents, but soluble in DMF
and DMSO. The electron-withdrawing paranitro substituents on phenyl cause the
6
O2N
2
CHO
OH
O2N
R
NO2
1
R
N
MeOH
r.t.
N
5
+
H2N
NH2
4
2
OH
HO
3
L1–L9
Scheme 1. Synthesis of nitro-Schiff bases from nitro-salicylaldehyde.
Table 1. Reactions for preparation of nitro-Schiff bases.
R
Ligand
Time (min)
Yield (%)a
m.p (ꢀC)
(CH2)2
(CH2)3
(CH2)4
(CH2)6
(CH2)8
L1
L2
L3
L4
L5
45
45
45
45
45
91.0
90.5
88.5
88.0
85.0
272–274
210–213
173–176
159–161
161–164
L6
L7
40
50
92.0
92.0
261–264
193–195
O
O
S
L8
L9
50
50
93.0
91.5
281–283
204–206
O
aIsolated yields.
R
R
N
NO2
NO2
O2N
O2N
N
N
N
Co(OAc)2.4 H2O
MeOH, rt
Co
O
O
HO
OH
L1– L9
L1–L9–M
Scheme 2. Preparation of complexes from nitro-Schiff bases.

Nitro-Schiff bases
159
Table 2. Reactions for preparation of nitro Schiff-base complexes with Co(II) acetate.
Ligands
Products
Time (min)
Yield (%)a
m.p (ꢀC)
L1
L2
L3
L4
L5
L6
L7
L8
L9
L1-M
L2-M
L3-M
L4-M
L5-M
L6-M
L7-M
L8-M
L9-M
80
85
90
90
100
75
90
89.0
90.0
88.5
87.0
85.0
91.5
88.0
88.5
90.0
4350
4350
312–315
295–300
282–286
4330
274–276
4350
255–258
100
100
aIsolated yields.
Table 3. UV-Vis spectral data (DMF, nm) and IR bands (cmꢂ1) of ligands and their complexes with Co(II).
n ! ꢀ*
(C¼N)
ꢀ ! ꢀ*
Entry
(arom. ring) d ! d ꢁ(C¼N) ꢁ(Ph–O) ꢁ(O–H)
ꢁ(NO2)
ꢁ(M–N,M–O)
L1
L1[Co(II)]
L2
L2[Co(II)]
L3
L3[Co(II)]
L4
L4[Co(II)]
L5
L5[Co(II)]
L6
L6[Co(II)]
L7
L7[Co(II)]
L8
L8[Co(II)]
L9
L9[Co(II)]
416
433
408
429
420
414
409
430
411
419
412
432
401
428
405
430
414
426
282
274
287
280
285
272
284
271
295
285
287
282
298
284
289
279
308
302
–
576
–
570
–
563
–
581
–
574
–
584
–
561
–
570
–
1649
1624
1643
1617
1658
1625
1640
1602
1647
1615
1641
1600
1642
1603
1648
1607
1645
1614
1328
1332
1325
1338
1333
1324
1326
1339
1321
1329
1327
1334
1328
1338
1322
1336
1322
1335
3384
–
3353
–
3338
–
3355
–
3340
–
3359
–
3294
–
3358
–
1521, 1334
1522, 1347
1530, 1342
1534, 1352
1524, 1351
1520, 1343
1533, 1340
1537, 1350
1527, 1355
1529, 1353
1534, 1348
1527, 1349
1531, 1357
1529, 1352
1531, 1343
1530, 1354
1538, 1356
1537, 1359
470–496
–
464–490
–
460–487
–
469–484
–
458–494
–
462–481
–
459–495
–
460–490
–
462–487
3354
–
587
phenolic OH to become more acidic, affecting the conditions of synthesis. Basically, the
aldehyde group becomes more active, increasing yields of the obtained Schiff bases.
Furthermore, formation of complexes ocurred in short reaction times and without
reflux. Ligands involving nitro are more stable in acidic and basic solution with
solubility in hot water. The UV-Vis and IR data of ligands and their complexes are
indicated in table 3.
3.1. Electronic spectra
Electronic spectra of complexes show intense absorptions in UV-region assigned to
charge transfer from ꢀ orbitals of the donor to d orbitals of the metal, d ! ꢀ* [27], and
intraligand n ! ꢀ* transition [28].

160
H. Naeimi and M. Moradian
In complexes, the n ! ꢀ* transitions due to azomethine shift to lower energy,
indicating the atom of imine group appears to be coordination of nitrogen [29]. The
bands due to the n ! ꢀ* transition of the C¼N appear between 380 and 410 nm in
ligands and shift to lower energy upon complexation. The bands between 320 and
350 nm are assigned as an n ! ꢀ* transition involving C¼N and benzene. The
remainder of the observed bands at about 290–320 nm are assigned as ꢀ ! ꢀ* type
transitions involving molecular orbital located on the phenolic chromophore.
A common feature of these spectra is the presence of three absorptions, two at lower
frequencies ascribed to ꢀ ! ꢀꢃ1 and ꢀ ! ꢀ2ꢃ transitions, in increasing energy [30].
Theoretical analysis of transitions of salicylidenimine suggests that the additional peak
found at higher frequencies corresponds to the ꢀ ! ꢀꢃ3 transition, where ꢀ3ꢃ is the third
unoccupied ꢀ molecular orbital [31]. For the nitro-substituted ligands, considerable
overlap between ꢀ ! ꢀꢃ2 and ꢀ ! ꢀ3ꢃ is observed. The ꢀ ! ꢀꢃ1 transition has been
assumed to be localized mainly on the azomethine chromophore [32, 33] and ꢀ ! ꢀ2ꢃ
band has been assigned to a transition involving mainly ꢀ molecular orbitals of the
aromatic ring of salicylidenimine moiety [34, 35].
In the ligands, these bands were observed at 280–320 nm. This blue shift in the
complexes may be due to electron donation from oxygen of the phenoxy group to the
metal [36]. An apparent bathochromic shift of the ꢀ ! ꢀ* transitions is observed upon
metal complex formation. All spectra of the metal complexes exhibit a d ! d band in
the visible region whose maximum absorption lie in the wavelength range 555–595 nm
(table 3).
3.2. IR spectra
Infrared spectra of the ligands and their respective metal complexes were very similar
(table 3). The ligands and complexes were characterized mainly using imine and
phenolic bands. The band at 1610–1640 cm–1 is characteristic of the azomethine
nitrogen in the free ligand. The lowering in this frequency to 1590–1615 cm–1 in all the
complexes indicates involvement of the azomethine nitrogen in coordination with metal
[37, 38]. The disappearance of ꢁO–H in spectra of all complexes indicates that chelation
takes place via the phenolic OH.
The compounds containing water exhibit characteristic medium intensity absorption
bands in the region 3200–3500 cmꢂ1, while these are absent in unsolvated compounds.
Spectra of the ligands exhibit medium intensity bands at 2500–3360 cmꢂ1 assigned to
intramolecular H-bonding (O–H ꢄ ꢄ ꢄ N). In spectra of the complexes (table 3) these
bands disappear. In the ligands, bands at 1311–1350 cmꢂ1 can be assigned to phenolic
(C–O) vibrations [39–41]. In the metal complexes, these bands displace to higher or
lower frequency, indicating chelation of oxygen to the metal. Upon coordination bands
at 1512 and 1341 cmꢂ1 that are typical of nitro in nitro ligands undergo minor changes,
suggesting that the nitro is not coordinated to cobalt. In all the complexes, bands at
617–461 cmꢂ1 and 461–420 cmꢂ1 can be attributed to the ꢁM–N and ꢁM–O modes,
respectively.
3.3. Magnetic properties of complexes
Magnetism of transition metal complexes is strongly influenced by coordination
geometry and electron configuration [42]. It should be noted that simple paramagnetism

Nitro-Schiff bases
161
will be found only if there is sufficient magnetic dilution. This is the case if, due to the
presence of large organic ligands, the paramagnetic centers are well separated, thus
avoiding cooperative interactions of the ferro and antiferromagnetic types.
Magnetic susceptibility amounts of the complexes, summarized in Supplementary
material, show different magnetic behavior, also evident in magnetization curves, which
show the net magnetization, M, of a sample versus applied field strength, H. Two
hysteresis loops for L1[Co(II)] complex is provided in Supplementary material.
3.4. 1H- and 13C-NMR spectra
Spectra of all the complexes (Supplementary material) were recorded in DMSO-d6
solution at 400 MHz and chemical shifts are in units of ppm relative to TMS. DMSO
1
resonates near 2.0 ppm. The H NMR spectra of the Schiff bases show the following
signals: a broad singlet for phenolic O–H group at ꢂ 14.0–14.5 ppm, a singlet for
azomethine hydrogen (HC¼N) at ꢂ 8.9 ppm, a doublet for Ar–H at ꢂ 8.5–8.6 ppm, a dd
for Ar–H at ꢂ 8.1–8.2 ppm and a doublet for Ar–H at ꢂ 6.9–7.1 ppm. The absence
of peak near 14.0 ppm in the metal(II) complexes indicates loss of –OH on
complexation [43].
Intramolecular hydrogen bonding accounts for the high frequency of the ortho-
phenolic hydrogen signals in all the Schiff bases. By comparing the 1H-NMR spectra of
all the Schiff bases with those of their corresponding cobalt(II) complexes, there is a
downfield shift in the frequency of azomethine protons of aromatic bridge and upfield
shift in the aliphatic bridge, confirming coordination of cobalt to both groups.
4. Conclusions
We have synthesized and characterized new nitro-Schiff-base complexes derived from
the Co(II) acetate and new N2O2 donor nitro-Schiff bases. Advantages for preparation
of these complexes are simplicity of synthesis and high stability of complexes in the
presence of nitro groups on ligands. Magnetic properties for all complexes confirm
presence of Co(II) without oxidation during complex formation.
Acknowledgment
The authors gratefully acknowledge partial support of this work by the Research
Affairs Office of the University of Kashan, I.R. Iran.
References
[1] N. Raman, S.J. Raja, A. Sakthivel. J. Coord. Chem., 62, 691 (2009).
[2] S. Brooker. Eur. J. Inorg. Chem., 2535 (2002).
[3] A.E. Martell, J. Perutka, D. Kong. Coord. Chem. Rev., 55, 216 (2001).

162
H. Naeimi and M. Moradian
[4] R. Ziessel. Coord. Chem. Rev., 195, 216 (2001).
[5] A.D. Garnovskii, I.S. Vasilchenko, D.A. Garnovskii, B.I. Kharisov. J. Coord. Chem., 62, 151 (2009).
[6] N.J. Parmar, S.B. Teraiya. J. Coord. Chem., 62, 2388 (2009).
[7] N. Alizadeh, S. Ershad, H. Naeimi, H. Sharghi, M. Shamsipur. Polish J. Chem., 73, 915 (1999).
[8] R.S. Joseyphus, M.S. Nair. J. Coord. Chem., 62, 319 (2009).
[9] Q.H. Wang, W. Weng, J.-M. Liu, L.-Z. Cai, G.-C. Guo. J. Coord. Chem., 59, 485 (2006).
[10] E. Tas, M. Aslanoglu, M. Ulusoy, H. Temel. J. Coord. Chem., 57, 677 (2004).
[11] M. Shamsipur, A.R. Ghiasvand, H. Sharghi, H. Naeimi. Anal. Chim. Acta, 408, 271 (2000).
[12] P. Buhlmann, E. Pretsch, E. Bakker. Chem. Rev., 98, 1593 (1998).
[13] H. Sharghi, H. Naeimi. Bull. Chem. Soc. Japan, 72, 1525 (1999).
[14] N. Matsumoto, Y. Sunatsuki, Y. Motoda. Coord. Chem. Rev., 226, 199 (2002).
[15] O. Pouralimardan, A. Chamayou, C. Janiak, H. Hosseini-Monfared. Inorg. Chim. Acta, 360,
1599 (2007).
[16] N. Raman, J.D. Raja, A. Sakthivel. J. Chem. Sci., 119, 303 (2007).
[17] J.K. Whitesell. Chem. Rev., 89, 1581 (1989).
[18] I. Ojima (Ed.). Catalytic Asymmetric Synthesis, VCH, New York (1994).
[19] E.J. Jacobsen, W. Zhang, M.L. Guler. J. Am. Chem. Soc., 113, 6703 (1991).
[20] H. Naeimi, H. Sharghi, F. Salimi, Kh. Rabiei. Heteroatom Chem., 19, 43 (2008).
[21] H. Naeimi, Kh. Rabiei. J. Chin. Chem. Soc., 54, 1293 (2007).
[22] H. Naeimi, J. Safari, A. Heidarnezhad. Dyes Pigm., 73, 251 (2007).
[23] H. Naeimi, M. Moradian. Polyhedron, 27, 3693 (2008).
[24] H. Naeimi, F. Salimi, Kh. Rabiei. J. Coord. Chem., 61, 3659 (2008).
[25] H. Naeimi, Kh. Rabiei, F. Salimi. J. Coord. Chem., 62, 1199 (2009).
[26] M. Moradian. Synthesis of new nitro-Schiff bases and their applications as catalyst in the synthesis of
halo alcohols and hydroxy propane nitriles. MSc thesis, University of Kashan, Kashan, Iran (2005).
[27] S. Karabocek, N. Karabocek. Polyhedron, 16, 1771 (1997).
[28] M.M. Mostafa, A. El-Hammid, M. Shallaby, A.A. El-Asmy. Trans. Met. Chem., 6, 303 (1981).
[29] M.J.M. Campbell. Coord. Chem. Rev., 15, 279 (1975).
[30] T. Tanaka. J. Am. Chem. Soc., 80, 4108 (1958).
[31] E.N. Bakers, D. Hall, T.N. Waters. J. Chem. Soc. A, 406 (1970).
[32] Y. Song, Z. Xu, Q. Sun, B. Su, Q. Gao, H. Liu, J. Zhao. J. Coord. Chem., 61, 1212 (2008).
[33] M.D. Hobday, T.D. Smith. Coord. Chem. Rev., 9, 311 (1972).
[34] A. Pasini, M. Gullotti, R. Ugo. J. Chem. Soc., Dalton Trans., 4, 346 (1977).
[35] H.E. Smith, J.R. Neergaard, E.P. Burrows, F.M. Chen. J. Am. Chem. Soc., 96, 2908 (1974).
[36] R.K. Sharma, R.V. Singh, J.P. Tandon. J. Inorg. Nucl. Chem., 42, 1382 (1980).
[37] G.A. Kolawole, A.A. Osowole. J. Coord. Chem., 62, 1437 (2009).
[38] H.H. Freddman. J. Am. Chem. Soc., 83, 2900 (1961).
[39] A. Seminara, S. Giuffrida, A. Musumei, I. Fragala. Inorg. Chim. Acta, 95, 201 (1984).
[40] F. Dianzhong, W. Bo. Trans. Met. Chem., 18, 101 (1993).
[41] R.S. Downing, F.L. Urbach. J. Am. Chem. Soc., 91, 5977 (1969).
[42] O. Kahn. Molecular Magnetism, VCH, New York (1993).
[43] D.N. Kumar, B.S. Garg. Spectrochim. Acta A, 64, 141 (2006).