Synthesis and characterization of copper(II) and cobalt(II) complexes with two new potentially hexadentate Schiff base ligands. X-ray crystal structure determination of one copper(II) complex

Article abstract of DOI:10.1016/j.jorganchem.2008.07.012

Two new potentially hexadentate N₂O₄ Schiff base ligands 2-((z)-(2-(2-(2-((z)-3,5-di-tert-butyl-2-hydroxybenzylideneamino) phenoxy) phenoxy) phenylimino) methyl)-4,6-di-tert-butylphenol [H₂L¹] and 2-((z)-(2-(2-(2-((z)-3,5-di-tert-butyl-2-hydroxybenzylideneamino) phenoxy)-5-tert-butylphenoxy) phenylimino) methyl)-4,6-di-tert-butylphenol [H₂L²] were prepared from the reaction of 3,5-di-tert-butyl-2-hydroxy benzaldehyde with 1,2-bis(2′-aminophenoxy)benzene or 1,2-bis(2′-aminophenoxy)-4-t-butylbenzene, respectively. From the direct reaction of ligands [H₂L¹] and [H₂L²] with copper(II) and cobalt(II) salts in methanolic solution and in the presence of N(Et)₃ the neutral [CuL¹], [CuL²], [CoL¹] and [CoL²] complexes were prepared. All complexes were characterized by IR spectra, elemental analysis, magnetic susceptibility, mass spectra, molar conductance (Λ_m), UV-Vis spectra and in the case of [CuL²] with X-ray diffraction. X-ray crystal structure of [CuL²] showed that the complex contains copper(II) in a distorted square planar environment of N₂O₂ donors. Three CH/π interactions were observed in the molecular structure of latter complex.

Full text of DOI:10.1016/j.jorganchem.2008.07.012

Journal of Organometallic Chemistry 693 (2008) 3179–3187
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and characterization of copper(II) and cobalt(II) complexes with two
new potentially hexadentate Schiff base ligands. X-ray crystal structure
determination of one copper(II) complex
a
a
a
Hassan Keypour a, , Maryam Shayesteh , Abdolhossein Sharifi-Rad , Sadegh Salehzadeh ,
*
Hamidreza Khavasi b, Laura Valencia c
a Faculty of Chemistry, Bu-Ali Sina University, Hamedan 65174, Iran
b Department of Chemistry, Shahid Beheshti University, Evin, Tehran 1983963113, Iran
c Departamento de Química Inorgánica, Facultad de Química, Universidade de Vigo, 36310 Vigo, Pontevedra, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new potentially hexadentate N2O4 Schiff base ligands 2-((z)-(2-(2-(2-((z)-3,5-di-tert-butyl-2-
hydroxybenzylideneamino) phenoxy) phenoxy) phenylimino) methyl)-4,6-di-tert-butylphenol [H2L1]
and 2-((z)-(2-(2-(2-((z)-3,5-di-tert-butyl-2-hydroxybenzylideneamino) phenoxy)-5-tert-butylphenoxy)
phenylimino) methyl)-4,6-di-tert-butylphenol [H2L2] were prepared from the reaction of 3,5-di-tert-
butyl-2-hydroxy benzaldehyde with 1,2-bis(20-aminophenoxy)benzene or 1,2-bis(20-aminophenoxy)-4-
t-butylbenzene, respectively. From the direct reaction of ligands [H2L1] and [H2L2] with copper(II) and
cobalt(II) salts in methanolic solution and in the presence of N(Et)3 the neutral [CuL1], [CuL2], [CoL1]
and [CoL2] complexes were prepared. All complexes were characterized by IR spectra, elemental analysis,
magnetic susceptibility, mass spectra, molar conductance (Km), UV–Vis spectra and in the case of [CuL2]
with X-ray diffraction. X-ray crystal structure of [CuL2] showed that the complex contains copper(II) in a
Received 12 February 2008
Received in revised form 16 June 2008
Accepted 15 July 2008
Available online 19 July 2008
Keywords:
Schiff base
Copper(II) complexes
Cobalt(II) complexes
X-ray structure
distorted square planar environment of N2O2 donors. Three CH/
molecular structure of latter complex.
p interactions were observed in the
3,5-Di-tert-butyl-2-hydroxy benzaldehyde
CH/p interaction
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
hexadentate Schiff base ligands [H2L1] and [H2L2] (Scheme 1) and
their Cu(II) and Co(II) complexes are described. X-ray crystal struc-
ture [CuL2] complex showed that the oxygen donor atoms and
nitrogen donor atoms are trans to each other.
Schiff bases have played an important role in the development
of coordination chemistry as they readily form stable complexes
with most of the transition metals. In the area of bioinorganic
chemistry interest in Schiff base complexes has centered on the
role of such complexes in providing synthetic models for the metal
containing sites in metallo-proteins and enzymes [1–5]. Schiff base
ligands are potential anticancer drugs [6] and the anticancer activ-
ity of this metal complexes is enhanced in comparison to the free
ligand [7]. 2-Hydroxy Schiff base ligands and their complexes de-
rived from the reaction of derivatives of salicylaldehyde with
amines have been extensively studied in great details for their
various crystallographic, structural and magnetic features [8–10].
The cobalt(II) and manganese(II) Complexes with tetra dentate
Schiff base ligands which coordinate through N2O2 donor atoms
have been extensively studied as oxygen carriers and also as
catalyst for water splitting system [11,12]. In the present paper,
the synthesis of diamines [1,2-bis(20-aminophenoxy)benzene(III)
and 1,2-bis(20-aminophenoxy)-4-t-butylbenzene(IV)], potentially
2. Experimental
2.1. Starting materials
3,5-Di-tert-butyl-2-hydroxy benzaldehyde was synthesized
according to the literature procedure [13]. Solvents, Catechol, 4-
tert-butylcatechol, 1-fluoro-2-nitrobenzene and metal salts were
purchased from Merck and were used without further purification.
2.2. Physical measurements
Infrared spectra were collected using KBr pellets on a BIO-RAD
FTS-40A spectrophotometer (400–4000 cmꢀ1). A Perkin–Elmer,
Lambda 45 (UV–Vis) spectrophotometer was used to record the
electronic spectra. Electron impact (20 ev) mass spectra for ligands
were recorded on a Shimadzu, QP1100EX spectrometer. FAB mass
spectra were recorded using a Kratos-MS- 50T spectrometer con-
nected to a DS90 data system using 3-nitrobenzyl alcohol as the
* Corresponding author. Tel.: +98 811 8257407.
E-mail address: haskey1@yahoo.com (H. Keypour).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.07.012

3180
H. Keypour et al. / Journal of Organometallic Chemistry 693 (2008) 3179–3187
NH2
O
H2N
O
O
OH
O
HO
O
OH
2
+
N
N
(H3C)3C
C(CH3)3
R
R
H2L1 R=H
H2L2 R=C(CH3)3
Scheme 1.
matrix. The Magnetic susceptibility measurements were per-
formed at 25 °C using a Johnson Matthey Alfa MSBMKI Gouy bal-
of EtOH was heated to boiling and zinc dust (2 g, 30 mmol) in
0.1 g portions at intervals of several minutes was added. The mix-
ture was then refluxed for 5 h. The resulting solution was filtered,
extracted with 300 ml H2O and dried. The precipitate was dis-
solved in CH3CN, The solution was filtered and the solvent was
then removed. Yield: 2.1 g (73%). M.p. 110 °C. Anal. Calc. for
ance. CHN analyses were carried out using
a Perkin–Elmer,
CHNS/O elemental analyzer model 2400. Conductance measure-
ments were performed using a Hanna HI 8820 conductivity meter.
1H and 13C NMR spectra were taken in CDCl3 on a Bruker Avance
300 MHz and Jeol 90 MHz spectrometer using Si(CH3)4 as an inter-
nal standard.
C
18H16N2O2.0.25H2O: C, 72.8; H, 5.6; N, 9.4. Found: C, 72.7; H,
5.5; N, 9.5%. IR(cm-1, KBr): 3426, 3408, 3313 (NH str).
2.3. X-ray crystallography
2.4.4. Synthesis of 1,2-bis(20-aminophenoxy)-4-t-butylbenzene (IV)
A mixture of 1,2-bis(20-nitrophenoxy)-4-t-butylbenzene (4.09 g,
10 mmol), NH4Cl (1.07 g, 20 mmol) and 10 ml of H2O in 100 ml of
EtOH was heated to boiling and zinc dust (2 g, 30 mmol) in 0.1 g
portions at intervals of several minutes. The mixture was refluxed
for 5 h. The solution was evaporated to dryness and the residue ex-
tracted with H2O/CHCl3. The organic layer was evaporated to yield
an organic solid. Yield: 2.7 g (77%). M.p. 89–91 °C. Anal. Calc. for
Single crystal of [CuL2] complex was obtained from toluene by
acetonitrile diffusion method. The single crystal X-ray diffraction
analyses were performed on a STOE IPDS-II two circle diffractom-
eter at 293(2) K, using graphite monochromated Mo Ka X-ray radi-
ation (k = 0.7107 nm). Details of the X-ray experiments and crystal
data are summarized in Table 1.
C
22H24N2O2.H2O: C, 72.1; H, 7.1; N, 7.6. Found: C, 72.2; H, 7.1; N,
2.4. Synthesis
7.7%. IR(cmꢀ1, KBr): 3461, 3405, 3376, 3304 (-NH2), 3041 (C–
H)ar, 2962, 2867 (C–H)aliph.
2.4.1. Synthesis of 1,2-bis(20-nitrophenoxy)benzene (I)
Catechol (11 g, 0.1 mol) was dissolved in DMF/Xylene mixture
before K2CO3 (42 g, 0.3 mol) and 1-fluoro-2-nitrobenzene (28.2 g,
0.2 mol) were added. The mixture, refluxed at 130–135 °C under
a dinitrogen atmosphere for 12 h with stirring, was then allowed
to cool and poured into 500 ml of H2O. The precipitate was isolated
by filtration. After drying, the crude product was recrystallized
from EtOH to give pure 1,2-bis(20-nitrophenoxy)benzene. Yield:
31.3 g (89%). M.p. 110 °C. Anal. Calc. for C18H12N2O6: C, 61.4; H,
3.4; N, 7.9. Found: C, 61.3; H, 3.5; N, 7.8%. IR(cmꢀ1, KBr): 1524,
2.4.5. H2L1
1,2-bis(20-aminophenoxy) benzene (0.292 g, 1 mmol) in metha-
nol (20 ml) was added dropwise with stirring to a solution of 3,5-
di-tert-butyl-2-hydroxy benzaldehyde (0.468 g, 2 mmol) in metha-
nol (30 ml). The mixture was stirred and heated to reflux for 4 h. A
yellow precipitate was obtained that was filtered off and washed
with cold methanol and dried in vacuo. Yield: 0.5 g (69%). M.p.
176 °C. Anal. Calc. for C48H56N2O4: C, 79.5; H, 7.8; N, 3.9. Found:
C, 79.1; H, 7.2; N, 4.3%. IR (cmꢀ1, KBr): 1620 (s,
(nm),
(Mꢀ1 cmꢀ1)]: 279(45390), 338(33600), 365(sh). Mass spec-
mC@N). UV–Vis [k
1348 (s,
m
NO2).
e
tral parent ion; m/z 724.
2.4.2. Synthesis of 1,2-bis(20-nitrophenoxy)-4-t-butylbenzene (II)
4-tert-Butylcatechol (16.6 g, 0.1 mol) was dissolved in DMF/Xy-
lene mixture before K2CO3 (42 g, 0.3 mol) and 1-fluoro-2-nitroben-
zene (28.2 g, 0.2 mol) were added. The mixture was refluxed at
130-135 °C under a dinitrogen atmosphere for 12 h with stirring,
The obtained mixture was poured into 500 ml of MeOH/H2O (vol
ratio 10:1) and left overnight in 0 °C to give a solid, which was col-
lected, washed thoroughly with MeOH and H2O and dried under
vacuum. After drying, the crude product was recrystallized with
EtOH to give pure 1,2-bis(20-nitrophenoxy)-4-t-butylbenzene.
Yield: 37.2 g (91%). M.p. 52 °C. Anal. Calc. for C22H20N2O6: C,
64.7; H, 4.9; N, 6.9. Found: C, 64.7; H, 4.9; N, 6.9%. IR(cmꢀ1, KBr):
2.4.6. H2L2
In a manner similar to the above–mentioned a methanol solution
(20 ml) of 1,2-bis(20-aminophenoxy)-4-t-butylbenzene (0.348 g,
1 mmol) was added dropwise with stirring to a solution of 3,5-di-
tert-butyl-2-hydroxy benzaldehyde (0.468 g, 2 mmol) in methanol
(30 ml). The mixture was stirred and heated to reflux for 4 h. A yel-
low solid product was formed that washed with cold methanol and
dried in vacuo. Yield: 0.6 g (77%). M.p. 105 °C. Anal. Calc. for
C
52H64N2O4: C, 79.9; H, 8.3; N, 3.6. Found: C, 79.3; H, 8.2; N, 2.9%.
IR (cmꢀ1, KBr): 1620 (s, (Mꢀ1 cmꢀ1)]:
mC@N). UV–Vis [k (nm),
e
278(29040), 345(21390), 362(sh). Mass spectral parent ion; m/z
2964, 2868 (C–H)aliph, 1524, 1348 (s,
mNO2).
781.
2.4.3. Synthesis of 1,2-bis(20-aminophenoxy)benzene (III)
mixture of 1,2-bis(20-nitrophenoxy) benzene (3.52 g,
10 mmol), NH4Cl (1.07 g, 20 mmol) and 10 ml of H2O in 100 ml
2.4.7. [CuL1]
A
A methanol solution (15 ml) of Cu(ClO4)2 ꢁ 6H2O (0.3704 g,
1 mmol) and a moderate excess of N(Et)3 were added to a warm

H. Keypour et al. / Journal of Organometallic Chemistry 693 (2008) 3179–3187
3181
solution of [H2L1] (0.724 g, 1 mmol) in methanol (50 ml). The mix-
ture was stirred and heated to reflux for 4 h. The resultant green
solid product was collected by filtration and washed with cold
methanol. Green crystals of [CuL1] were obtained by liquid diffu-
sion of acetonitrile into a solution of the complex in toluene. Yield:
0.5 g (64%). M.p. 328 °C. Anal. Calc. for C48H54CuN2O4: C, 73.3; H,
6.9; N, 3.6. Found: C, 72.8; H, 6.9; N, 4.2%. IR (cmꢀ1, KBr): 1613
to a warm solution of [H2L1] (0.724 g, 1 mmol) in methanol
(50 ml). The resultant red solid was collected by filtration and
washed with cold methanol. Red crystals of [CoL1] were obtained
by liquid diffusion of methanol into a solution of the complex in
toluene. Yield: 0.6 g (77%). M.p. 309 °C. Anal. Calc. for C48H54Co-
N2O4: C, 73.7; H, 6.9; N, 3.6. Found: C, 72.9; H, 6.9; N, 2.9%. IR
(cmꢀ1, KBr): 1615 (s,
mC@N), 445–472 (M–O), 537 (M–N). UV–Vis
(s,
m
C@N), 443–470 (M–O), 535 (M–N). UV–Vis [k (nm),
e
[k (nm), e
(Mꢀ1 cmꢀ1)]: 289(28430), 336(19310), 429(14600),
(Mꢀ1 cmꢀ1)]: 244(41090), 306(30330), 427(11620), 692(104).
578(179), 885(29). Km = 2.5 cm2 ꢀ1 molꢀ1
X . FAB-MS (m/z):
Km = 5 cm2
X
ꢀ1 molꢀ1. FAB-MS (m/z): 785([CuL1 + H]+, 100%).
782([CoL1], 100%).
2.4.8. [CuL2]
2.4.10. [CoL2]
Similarly, [H2L2] (0.780, 1 mmol) and Cu(ClO4)2 ꢁ 6H2O yielded
the product as green crystals. Yield: 0.7 g (83%). M.p. 316 °C. Anal.
Calc. for C52H62CuN2O4: C, 74.1; H, 7.4; N, 3.3. Found: C, 74.6; H,
Similarly, [H2L2] (0.780, 1 mmol) and CoCl2 ꢁ 6H2O (0.2378 g,
1 mmol) yielded the product as red crystals. Yield: 0.7 g (84%).
M.p. 290 °C. Anal. Calc. for C52H62CoN2O4: C, 74.5; H, 7.5; N, 3.3.
7.1; N, 3.8%. IR (cmꢀ1, KBr): 1613 (s,
m
C@N), 445–470 (M–O), 535
Found: C, 74.8; H, 7.8; N, 2.9%. IR (cmꢀ1, KBr): 1614 (s,
m
C@N),
(Mꢀ1 cmꢀ1)]:
288(30600), 335(21900), 436(15760), 567(186), 897(26).
Km = 1.8 cm2 ꢀ1 molꢀ1. FAB-MS (m/z): 837([CoL2 + H]+, 100%).
(M–N). UV–Vis [k (nm),
e
(Mꢀ1 cmꢀ1)]: 245(44740), 296(31740),
443–477 (M–O), 538 (M–N). UV–Vis [k (nm), e
425(13490), 688(110). Km = 4.2 cm2
X
ꢀ1 molꢀ1. FAB-MS (m/z):
841([CuL2 + H]+, 100%).
X
2.4.9. [CoL1]
3. Results and discussion
In the same way, a methanol solution (15 ml) of CoCl2 ꢁ 6H2O
(0.2378 g, 1 mmol) and a moderate excess of N(Et)3 were added
Two new potentially hexadentate N2O4 Schiff base ligands
[H2L1] and [H2L2] have been easily prepared from the reaction of
3,5-di-tert-butyl-2-hydroxy benzaldehyde with 1,2-bis(20-amino-
phenoxy) benzene or 1,2-bis(20-aminophenoxy)-4-t-butylbenzene,
respectively. The analytical and spectral data are completely con-
sistent with the proposed formulation. The 1H NMR and 13C{1H}
NMR assignments for 1,2-bis(20-nitrophenoxy)benzene (I), 1,2-
bis(20-nitrophenoxy)-4-t-butylbenzene (II), 1,2-bis(20-aminophen-
oxy)benzene (III), 1,2-bis(20-aminophenoxy)-4-t-butylbenzene
(IV), [H2L1] and [H2L2] are given in Table 4. The neutral Cu(II) and
Co(II) complexes of these ligands, were also synthesized. All com-
plexes were characterized by IR spectra, elemental analysis, mag-
netic susceptibility measurements, mass spectra, molar
conductance(Km), UV–Vis spectra and in the case of [CuL2] with
X-ray diffraction. The corresponding data for the ligands and their
complexes are presented in Tables 2–6.
Table 1
Crystal data and structure refinement for the [CuL2]
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C52H62CuN2O4
842.59
293(2)
0.71073
Monoclinic
P21/c
19.043(4)
14.744(3)
18.667(4)
90
119.35(3)
90
4568 (2)
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
Volume (Å3)
Z
4
3.1. IR spectra
Calculated density (Mg/mꢀ3
)
1.225
0.524
1796
Absorption coefficient (mmꢀ1
F(000)
)
1,2-Bis(20-nitrophenoxy)benzene (I) and 1,2-bis(2’-nitrophen-
oxy)-4-t-butylbenzene (II) can be prepared by SNAr between
1-fluoro-2-nitrobenzene and simple aromatic diols (catechol or
4-tert-butylcatechol). The IR spectrum of (I) and (II) reveals absorp-
tion bands appearing at ca. 1348 and 1524 cmꢀ1 due to symmetric
and asymmetric stretching of –NO2 group [14–16]. Aromatic nitro
compounds can be reduced in high yield to the corresponding dia-
mines using zinc metal and NH4Cl in H2O/EtOH [17–26]. After
reduction, the characteristic absorptions of nitro groups disap-
peared and the amino groups showed NH stretching bands at
3313, 3408, 3426 cmꢀ1 and 3304, 3376, 3405, 3461 cmꢀ1 for (III)
and (IV), respectively. The infrared spectra of [H2L1] and [H2L2] in
the region 400–4000 cmꢀ1 show a strong absorption band at
Crystal size (mm)
h Range for data collection (°)
Limiting indices
0.4 ꢂ 0.22 ꢂ 0.08
1.85–30.58
ꢀ27 6 h 6 27, ꢀ21 6 k 6 21,
ꢀ26 6 l 6 26
54823/12352 [0.1142]
98.0
Reflections collected/unique [R(int)
]
Completeness to
H = 30.58 (%)
Absorption correction
Maximum and minimum transmission 0.97 and 0.87
Refinement method
Numerical
Full-matrix least-squares on F2
12352/0/533
1.078
R1 = 0.0804, wR2 = 0.1847
R1 = 0.1074, wR2 = 0.2014
0.797 and ꢀ1.262
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I>2
R indices (all data)
r(I)]
Largest difference peak and hole (e Åꢀ3
)
Table 2
Physical characterization, analytical, molar conductance, mass spectra and magnetic susceptibility data of the complexes
Compound
Found (calc.)
%C
Yield (%)
Color
Mol weight
KM
(
X
ꢀ1 cm2 molꢀ1
)
Fab-MS
Assignment
leff (BM)
%H
%N
C
48H56N2O4
(79.5)79.1
(79.9)79.3
(73.3)72.8
(73.7)72.9
(74.1)74.6
(74.5)74.8
(7.8)7.2
(8.3) 8.2
(6.9)6.9
(6.9)6.9
(7.4)7.1
(7.5)7.8
(3.9)4.3
(3.6)2.9
(3.6)4.2
(3.6)2.9
(3.3)3.8
(3.3)2.9
69
77
64
77
83
84
Yellow
Yellow
Green
Red
Green
Red
724.97
781.08
786.49
781.89
842.59
837.99
724
781
785
782
841
837
[H2L1+H]+
[H2L2]
C52H64N2O4
CuL1
5
[CuL1+H]+
[CoL1]
1.54
4.48
2.02
4.38
CoL1
2.5
4.2
1.8
CuL2
[CuL2+H]+
[CoL2+H]+
CoL2

3182
H. Keypour et al. / Journal of Organometallic Chemistry 693 (2008) 3179–3187
Table 3
Comparison of IR data (cm-1) for [H2L1] and [H2L2] ligands and related complexes
[H2L1]
[H2L2]
[CuL1]
[CoL2]
[CoL1]
[CuL2]
1620(s)
1620(s)
1613(s)
1614(s)
1615(s)
1613(s)
1581(s)
1489(s)
1470(m), 1453(m)
1441(m), 1390(m)
1361(s), 1315(w)
1263(s)
1581(s), 1503(m)
1489(s),
1588(s), 1545(m)
1527(s), 1490(s)
1454(s), 1426(s)
1407(w), 1384(s)
1359(s), 1324(m)
1274(w), 1256(s)
1230(s),
1203(s), 1185(w)
1164(s), 1134(m)
1109(m)
1582(s), 1542(m)
1526(s), 1487(s)
1459(s), 1424(s)
1400(m), 1384(s)
1361(s), 1331(m)
1268(w), 1255(s)
1241(w), 1227(s)
1201(s), 1183(w)
1162(s), 1133(m)
1109(m)
1580(s), 1545(m)
1526(s), 1489(s)
1455(s), 1423(s)
1410(w), 1386(s)
1360(s), 1331(m)
1274(w), 1256(s)
1242(w), 1227(s)
1201(s), 1182(w)
1162(s), 1133(m)
1109(m)
1588(s), 1544(m)
1527(s), 1486(s)
1458(s), 1427(s)
1413(w), 1385(s)
1360(s), 1326(m)
1271(w), 1255(s)
1244(w), 1230(s)
1203(s), 1183(w)
1164(s), 1133(m)
1106(m)
1467(m), 1453(m)
1440(m), 1393(m)
1363(s), 1319(w)
1272(s), 1250(m)
1230(m)
1203(w)
1168(s), 1128(w)
1109(m)
1230(m)
1209(w), 1192(m)
1169(s), 1131(w)
1109(m)
1042(w), 1026(w)
982(w), 927(w)
900(w), 882(w)
865(w)
849(w), 821(w)
795(w), 774(w)
745(s)
1041(w), 1027(w)
981(w), 943(w)
901(w), 880 (w)
844(m)
844(w), 822(w)
803(w), 774(w)
749(s)
1037(w), 1027(w)
976(w), 933(w)
918(w), 875(m)
861(w)
834(m), 811(w)
788(m), 761(w)
749(w), 740(s)
694(w), 658(w)
637(w)
1046(w), 1027(w)
974(w), 941(w)
920(w), 887(w)
876(m), 848(w)
832(m), 810(w)
790(m),
753(w), 745(s)
695(w), 667(w)
636(w)
1048(w), 1028(w)
971(w), 932(w)
917(w), 885(w)
870(m)
836(m), 810(w)
790(m)
747(s)
693(w)
634(w)
1037(w), 1025(w)
977(w), 943(w)
907(w), 885(w)
873(w), 850(w)
833(m), 817(w)
788(m)
753(s)
699(w)
636(w)
693(w), 670(w)
645(w)
694(w), 666(m)
645(w)
Table 4
1H NMR and 13C{1H} NMR data for dinitro and diamine compounds, [H2L1] and [H2L2] ligands
Hydrogen atoms
Carbon atoms
(I)
6.975–7.999
(m, 12H, aromatics)
(aromatic rings)
118.880, 121.641, 123.117
125.476, 126.279, 134.263
140.007, 145.816, 150.095
(II)
6.846–7.848
1.312
(m, 11H, aromatics)
(s, 9H, H1)
C1,
C2,
31.095
34.557
(aromatic rings)
117.995, 118.480, 119.807
121.666, 122.579, 122.794
123.448, 125.404, 134.117
139.511, 139.782, 143.250
144.682, 150.308
(III)
6.616–7.042
3.663
(m, 12H, aromatics)
(s, 4H, NH2)
(aromatic rings)
116.820, 117.811, 118.858
120.088, 124.162, 137.492
144.336, 147.209
(IV)
6.659–7.147
3.658–3.664
1.279
(m, 11H, aromatics)
(b, 4H, NH2)
(s, 9H, H1)
C1,
C2,
31.689
35.119
(aromatic rings)
116.937, 118.133, 118.529
119.224, 119.757, 122.107
124.948, 125.363, 139.697
140.073, 144.571, 145.169
146.374, 147.312, 148.507
H2L1
13.209
8.336
6.816–7.330
1.349
(s, 2H, OH)
C1, C7
C2, C6
C8
C11
31.632, 29.576
35.184, 34.263
158.474
165.123
(s, 2H, CH@N)
(m, 16H, aromatics)
(s, 18H, H7)
1.229
(s, 18H, H1)
(aromatic rings)
118.298, 118.602, 121.254
121.537, 123.700, 124.950
126.938, 127.183, 127.845
136.984, 139.299, 140.268
147.290, 149.927
H2L2
13.342
8.409
8.428
6.865–7.430
1.470
1.351
(s, 2H, OH)
C1, C7, C22, C37, C41
C2, C6, C21, C36, C40
C8, C42
29.592, 31.562, 31.617
34.236, 34.571, 35.160
158.436
(s, 1H, CH@N)
(s, 1H, CH@N)
(m, 15H, aromatics)
C
11, C32
165.123
(s, 9H, H22
(s, 18H, H7,
)
(aromatic rings)
117.531, 117.960, 118.618
119.171, 121.259, 121.995
123.314, 123.442, 126.926
127.066, 127.732, 136.936
138.942, 139.123, 140.204
144.772, 146.023, 148.639
150.087
)
41
1.314
(s, 18H, H1,37)
s, singlet; m, multiplet, b, broad.

H. Keypour et al. / Journal of Organometallic Chemistry 693 (2008) 3179–3187
3183
Table 5
Electronic spectroscopy data (nm) for H2L1–2 and related complexes
a
Compound
kmax (nm) (e)
Intraligand (LL)
CT
d–d
[H2L1]
[H2L2]
[CuL1]
[CuL2]
[CoL1]
[CoL2]
279 (45,390)
278 (29,040)
244 (41,090)
245 (44,740)
289 (28,430)
288 (30,600)
338 (33,600), 365(sh)
345 (21,390), 362(sh)
306 (30,330)
296 (31,740)
336 (19,310)
427 (11,620)
425 (13,490)
429 (14,600)
436 (15,760)
692 (104)b
688 (110)b
578 (179)b
567 (186)b
885 (29)
897 (26)
335 (21,900)
a
Molꢀ1 cmꢀ1
Shoulder.
.
b
[H2L1] and 1168 cm-1 for [H2L2] are ascribed to the phenolic C-O
stretching vibrations. These bands are shifted to lower frequencies
due to O-metal coordination. The coordination of the azomethine
nitrogen is confirmed with the presence of a new band between
Table 6
Selected bond lengths (Å) and bond angles (ꢀ) for [CuL2]
Bond lengths
Cu(1)–O(1)
Cu(1)–O(4)
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–O(2)
Cu(1)–O(3)
1.849(2)
1.884(2)
2.024(3)
2.038(3)
2.846(3)
3.161(2)
532 and 559 cmꢀ1, assignable to
m(M–N) for the Co(II) and Cu(II)
complexes [29,30]. Several medium to strong absorption bands ap-
pear in the far-IR spectra of mentioned complexes (between 443
and 477 cmꢀ1), due to
m(M–O) [31,32]. The full IR spectral data
(600–1700 cmꢀ1) for ligands and related complexes are compared
in Table 3. As can be seen, the IR spectra of the copper complexes
are very similar to each other and this is the case for corresponding
cobalt complexes, indicating the same structures [33].
Bond angles
O(1)–Cu(1)–O(4)
O(1)–Cu(1)–N(1)
O(4)–Cu(1)–N(1)
O(1)–Cu(1)–N(2)
O(4)–Cu(1)–N(2)
N(1)–Cu(1)–N(2)
152.01(10)
89.80(11)
92.96(11)
94.77(11)
89.89(11)
164.59(11)
3.2. Magnetic measurements
1620 cmꢀ1 assigned to the C@N stretching vibration, indicating the
formation of the Schiff base linkages. Furthermore, the absence of
C@O and N–H stretching vibrations in the spectra of the ligands,
related to aldehyde and diamine, respectively, indicate occurrence
of Schiff base condensation. The reaction of copper(II) or cobalt(II)
salts with the Schiff base ligands ([H2L1] and [H2L2]) yields [CuL1],
[CuL2], [CoL1] and [CoL2] complexes. Deprotonation of all phenolic
functions is confirmed by the lack of O–H stretching bands in the IR
region 3300–3400 cmꢀ1 for all the complexes [27,28]. The infrared
spectra of these complexes provide some information about the
Room temperature magnetic moments of the Cu(II) complexes are
1.54 and 2.02 BM for [CuL1] and [CuL2], respectively. The observed va-
lue for [CuL2] is typical for mononuclear compounds of Cu(II) with a
S = 1/2 spin state and does not indicate antiferromagnetic coupling
of the spins at this temperature [34]. The smaller value of the mag-
netic moment of [CuL1] isprobablydue to a weak intermolecularanti-
ferromagnetic exchange interaction between the copper centers in
the crystal structure [35]. Note that such interactions between the
copper centers mononuclear [CuL1] complex is due to the lack of
bulky t-butyl group in this compound, in contrast to [CuL2]. Magnetic
susceptibility studies reveal complexes [CoL1] and [CoL2] to be para-
bonding in the complexes. The strong m(C@N) bands are shifted to-
wards lower frequencies compared with free imine bonds, indicat-
ing coordination of the ligands to the copper(II) and cobalt(II) ions
via the azomethine nitrogen atoms. The bands at 1169 cm-1 for
magnetic, with leff values of 4.48 and 4.38 BM, respectively. The ob-
served magnetic moments are consist whit that expected for four
coordinate Co(II) tetrahedral complexes [36–38].
O2N
NO2
NH2
H2N
9
8
6
7
O
O
O
O
4
3
5
2
1
NO2
O2N
NH2
H2N
11
11'
13'
11
13
11'
13'
10
10
10'
10'
12'
12
12'
12
O
O
O
O
9
9'
9'
9
4
3
4
3
14'
14'
14
14
13
8
5
8
5
6
6
7
7
2
2
1
1
Fig. 1. Structure of dinitro and diamine compounds along with NMR numbering.

3184
H. Keypour et al. / Journal of Organometallic Chemistry 693 (2008) 3179–3187
3.3. NMR spectra
The NMR numbering of the atoms is shown in Fig. 1. for dinitro
and diamines compounds and Fig. 2. for ligands. In the 1H NMR
spectrum, the absorption signals of aromatic protons of (I) and
(II) appeared in the region of 6.975–7.999 ppm and 6.846–
The 1H and 13C NMR spectra of the dinitro compounds, diamines
and ligands in CDCl3 solution confirm their proposed structures.
41
7
6
7
4
38
4
36
35
34
5
39
5
1
37
1
2
40
42
6
2
3
3
8
8
10
10
OH
HO
OH
HO
O
9
33
32
9
11
11
N
N
N
N
31
12
12
30
29
13
14
17
13
14
17
26
O
O
O
18
18
25
27
16
16
24
19
20
28
15
19
15
23
20
21
22
a
b
Fig. 2. Structure of (a) [H2L1] and (b) [H2L2], along with NMR numbering.
Fig. 3. 1H NMR spectra of (a) [CoL1] and (b) [CoL2].

H. Keypour et al. / Journal of Organometallic Chemistry 693 (2008) 3179–3187
3185
the non-equivalance of the two imine environments. As it can be
seen in Fig. 3, most of observed hydrogen resonances in [CoL1], as
expected, are doubled for corresponding asymmetric [CoL2]
complex.
3.4. Electronic absorption spectroscopy
The electronic spectra of the ligands and their metal complexes
were recorded in CHCl3. The bands below 365 nm are attributable
*
*
to intraligand
p
?
p
and n ?
p
transitions. In the electronic
spectra of the complexes, the intraligand transitions are slightly
shifted as a result of coordination.
The complexes of the Co(II) and Cu(II) show the low intensity
shoulders at ca. 567–692 nm, which are assigned as dꢀd transition
of the metal ions. The former bands is probably due to the
4A2(F) ? 4T1 (P) and 4A2(F) ? 4T1 (F) for [CoL1] and [CoL2] com-
plexes transition of tetrahedral geometry [40]. All spectra of the
Co(II) and Cu(II) complexes show an intense band at ca. 425–
436 nm, due to charge transfer transition [41–44]. The electronic
spectral details of the complexes are given in Table 5.
Fig. 4. Molecular structure of the [CuL2]. Hydrogen atoms are omitted for clarity.
3.5. Molar conductivity
The molar conductivities (KM) of the Cu(II) and Co(II) metal
complexes in CH2Cl2 at 10ꢀ3 M were found to be in the range
1.8–5
X
ꢀ1 cm2 molꢀ1. These low values indicate that all their
7.848 ppm, respectively, and the t-butyl group of (II) appeared in
1.312 ppm. In 13C NMR spectrum should be exhibited 20 main
peaks for (II). However, there are 16 main signals appeared, it
complexes are non-electrolytes due to the absence of any counter
ions in their structures [45,46]. The molar conductance values of
these complexes indicate that the [H2L1] and [H2L2] Schiff bases
are coordinated to the copper(II) and cobalt(II) ions as a doubly
negatively charged anions. Therefore, it seems two phenolic OH
have been deprotonated and bonded to the metal ions as oxygen
anion [47].
0
seems the carbon C9, C10, C11 and C13 are overlapping with C9 ,
0
0
0
C
10 , C11 and C13 , respectively, and the numbers of C were still con-
formed to (II). The 13C NMR in (I) showed nine aromatic signals, the
number of carbons was conformed to the (I). In the 1H NMR spec-
tra, all the aromatic protons of (III) and (IV) resonated in the 6.616–
7.042 ppm and 6.659–7.147 ppm region, respectively. Hydrogens
of the t-butyl group appeared in 1.279 ppm and the signal appear-
ing at 3.658–3.664 ppm corresponding to the amine group. Com-
paring the 13C NMR spectra of (III) and (IV) with the spectra of
it’s precursor (I) and (II), the 13C absorptions of the central three
benzene rings move upfield as a result of the transfer of elec-
tron-withdrawing nitro groups to the electron-donating amino
groups [14,15]. The 1H NMR spectrum of the ligand [H2L1] shows
only a single 1H imine resonance at ca. 8.336 ppm, demonstrating
the equivalence of the two imine environments. The 13C NMR spec-
trum shows that the imine carbon atoms, (165.123 ppm), are
chemically equivalent in the region corresponding to the signals
of aromatic ring carbons (118.298–158.474 ppm), fifteen peaks
are observed as expected. The 1H NMR spectrum of the ligand
[H2L2] shows two single 1H imine resonances at ca. 8.409 and
8.428 ppm, supporting the non-equivalence of the two imine envi-
ronments. 13C NMR spectrum of this ligand shows that in the re-
gion corresponding to the signals of aromatic rings carbons
(117.531–158.436 ppm) 20 peaks instead of thirty expected peaks
are observed, due to high similarity of carbons and low resolution
of instrument.
3.6. X-ray structures
The molecular structure of [CuL2] complex is shown in Fig. 4.
Selected bond distances and bond angles are listed in Table 6.
The X-ray structure analysis of [CuL2] complex shows only four
atoms of the donor set having considerate bonding interaction
with copper(II) atom. The four-coordinate Cu(II) is defined by the
two phenolate oxygen atoms O(1) and O(4) and the two imino
nitrogen atoms N(1) and N(2) in a distorted square-planar fashion
On N2O2 donor set ligand, the two Cu–O bonds are in trans config-
uration, the Cu–O(1) and Cu–O(4) distances are 1.849(2) and
1.884(2) Å. The O(1)–Cu(1)–O(4) bond angle is 152.01(10)° and
two N donor atoms are also in trans positions with a bond angle
164.59(11) showing an angular deviation of 15.4° from an exact
trans coordination [48]. The plane containing N(2), O(1), N(1) and
O(4) has an r.m.s. of 0.3615 and the metal atom is displaced from
this plane by 0.090 Å toward O(2). The Cu–O(3) distance of 3.161 Å
is too long to be considered as a bond. In contrast Cu–O(2) is rela-
tively short (2.846 Å) to be considered as a very weak coordinative
bond.
The 1H NMR paramagnetic spectra of [CoL1] and [CoL2], were
measured in the range from +120 to ꢀ120 ppm. The spectra of the
complexes are different with those of free ligands due to their para-
magnetism, which complicated spectra interpretation. It has been
reported that in the NMR spectra of Co(salen) complexes, the most
upfield shifted resonances which are usually weak and broad, can be
assigned to the hydrogen in –CH@N– group [39]. In the 1H NMR
spectra of present Co(II) complexes the latter signal was observed
at ꢀ36.103 ppm for [CoL1] and ꢀ38.601 ppm and ꢀ30.976 ppm
for [CoL2]. Two single 1H imine resonances for [CoL2] are due to
It is interesting that the ligand L2 is considerably folded, so three
CH/p interactions are established (see Fig. 5). For surveying CH/p
interactions in compounds bearing an arene ring, several kinds of
distance and angle parameters have been defined. Fig. 6 illustrates
a number of such parameters for a six-membered arene ring [49].
The corresponding values of h, Dlin and Datm for [CuL2] are also
shown in latter figure. As can be seen the substituted t-butyl
groups on both initial amine and aldehyde precursors are involved
in CH/p interactions in resulting Schiff base complex.

3186
H. Keypour et al. / Journal of Organometallic Chemistry 693 (2008) 3179–3187
Fig. 5. Illustration of CH/
p
interactions in molecular structure of [CuL2]. The interactions with nearest sp2 carbon atom are shown.
C
H
θ
Dlin (Å)
3.04
Datm (Å)
3.07
θ (˚)
20.1
Dlin
Datm
H5b
X1
H27a
H51b
3.19
3.26
43.9
17.1
2.95
3.02
X2
Fig. 6. Some distance and angle parameters for surveying CH/
between H and line X1X2; Datm: interatomic distance (H/X1).
p
interactions. X1 and X2: nearest and second nearest sp2 atoms, respectively, to H; h: HCX1; Dlin: distance
can be found, in the online version, at doi:10.1016/j.jorganchem.
2008.07.012.
4. Conclusion
We report here a study of the coordination capability of two
new potentially hexadentate N2O4 Schiff base ligands [H2L1] and
[H2L2] towards Cu(II) and Co(II). It was found that due to the rigid-
ity of the ligands and/or sizes of the present metal ions, only N2O2
donor set having bonding interaction. The ligand L2 is considerably
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