Download IJCA 47A(4) 560-564

Indian Journal of Chemistry
Vol. 47A, April 2008, pp. 560-564
Synthesis, structural characterization of
new macrocyclic Schiff base derived
from 1,6-bis(2-formylphenyl)hexane
and 2,6-diaminopyridine and its
metal complexes
Salih İlhana,*, Hamdi Temelb, Murat Sunkurc &
İbrahim Teğina
a
Siirt University, Faculty of Art and Sciences,
Chemistry Department, Siirt, Turkey
b
Dicle University, Faculty of Education, Chemistry Department,
21280 Diyarbakır, Turkey
c
Batman University, Faculty of Technical Education,
Batman, Turkey
Email: [email protected]; [email protected]
Received 25 January 2008; revised 17 March 2008
A macrocyclic ligand has been synthesized by reaction of
2,6-diaminopyridine and 1,6-bis(2-formylphenyl)hexane. Its
complexes with Cu(II), Ni(II), Pb(II), Zn(II), Cd(II) and La(III)
have been synthesized by the reaction of ligand and
Cu(ClO4)2.6H2O,
Ni(ClO4)2.6H2O,
Pb(ClO4)2.6H2O,
Zn(ClO4)2.6H2O,
Cd(ClO4)2.6H2O
and
La(ClO4)3.6H2O,
respectively. The ligand and its metal complexes have been
characterized. All complexes are diamagnetic while the Cu(II)
complex is binuclear.
IPC Code: Int. Cl.8 C07F1/08; C07F3/06; C07F3/08; C07F5/00;
C07F7/00; C07F15/04
The coordination chemistry of macrocyclic ligands is a
fascinating area in inorganic chemistry1. Transition
metal macrocyclic complexes have received much
attention as active part of metalloenzymes as biomimic
model compounds due to their resemblance with
natural proteins like hemerythrin and enzymes2,3.
Schiff base macrocycles have been of great importance
in macrocyclic chemistry4. There is a continued
interest to synthesize macrocyclic complexes5-7
because of their potential applications in fundamental
and applied sciences7-9 and importance in the area of
coordination chemistry10,11. The development of the
field of bioinorganic chemistry has been another
important factor in spurring the growth in interest in
macrocyclic compounds12.
We report herein the synthesis of a new dialdehyde
1,6-bis(2-formylphenyl)hexane
derived
from
1,6-dibromohexane with salicylaldehyde and K2CO3.
The new macrocyclic Schiff base has been synthesized
by reaction of 2,6-diaminopyridine and 1,6-bis-
(2-formylphenyl)hexane. Its Cu(II), Ni(II), Pb(II),
Zn(II), Cd(II) and La(III) complexes have been
synthesized by template effect by reaction of the
ligand
and
Cu(ClO4)2.6H2O,
Ni(ClO4)2.6H2O,
.
.
Pb(ClO4)2 6H2O, Zn(ClO4)2 6H2O, Cd(ClO4)2.6H2O
and La(ClO4)3.6H2O, respectively. Spectral and
magnetic properties of the new compounds have also
been studied in detail.
Experimental
Elemental analysis was carried out on a LECO
CHNS (model 932) elemental analyzer. 1H NMR and
13
C NMR spectra were recorded using a Bruker
Avance DPX-400 NMR spectrometer. IR spectra were
recorded on a Midac 1700 FTIR spectrometer on KBr
discs in the range 4000-400 cm-1. Electronic spectral
studies were conducted on a Shimadzu (model 160)
UV-vis spectrophotometer in the range 200-800 nm,
using 10-3 M solution of the complex in DMSO. Molar
conductivity was measured with a WTW LF
(model 330) conductivitymeter, using 10-3 M solution
of the complex in DMSO. Electrospray ionization
mass spectrometric analyses (ESI–MS) were obtained
on the Agilent 1100 MSD spectrometer. 1,6-Bis(2-formylphenyl)hexane was prepared derived from
1,6-dibromohexane with salicyaldehyde and K2CO3 as
reported in literature13. All the other chemicals and
solvents were of analytical grade and used as received.
Synthesis of 1,6-bis(2-formylphenyl)hexane
To a stirred solution of salicylaldehyde (24.4 g, 0
.2 mol) and K2CO3 (13.8 g, 0, 1 mol) in DMF(100 mL),
was added dropwise 1,6-dibromohexane (24.4 g
0.1 mol) in DMF (40 mL). The reaction was continued
for 4 h at 150-155 °C and then for 4 h at room
temperature (Scheme 1). Then, 200 mL distilled water
was added and the mixture kept in a refrigerator. After
1 h, the precipitate was filtered and washed with 500
mL water. It was dried in air and recrystalized from
EtOH and filtered under vacuum. Yield: 49 g (75%),
M. pt: 75-77 °C, Color: white. Anal.: Calcd for
C20H22O4: C, 73.60, H, 6.79. Found: C, 73.75, H, 6.73.
13
C NMR (DMSO-d6, δ ppm): CH2CH2CH2: 25.64,
CH2CH2O: 28.87, CH2CH2O: 68.71, HC=O: 189.59,
Aromatic: 113.99, 120.99, 124.71, 128.03, 136.89,
161.55. 1H NMR (DMSO-d6, δ ppm): 1.54 (t, 4H,
J = 7.4 Hz, CH2CH2CH2:), 1.81 (p, 4H, J = 6.2 Hz,
CH2CH2O), 4.14 (t, 4H, J = 6.4 Hz, CH2CH2O),
NOTES
7.04-7.69 (m, 8H, Ar-H), 10.39 (s, 2H, HC=N).
Selected IR data (KBr, ν cm-1): 3070, 3035 ν(Ar-CH),
2951, 2854 ν(Alf.-CH), 1681 ν(C=O), 1489, 1458
ν(Ar-C=C), 1284, 1246 ν(Ar-O), 1192, 1046 ν(R-O),
760 ν(substituted benzene).
Synthesis of the macrocyclic Schiff base (L)
The macrocyclic ligand (L) was prepared by
the dropwise addition of a solution of the
2,6-diaminopyridine (0.22 g, 2 mmol) in methanol
(40 mL) to a stirred solution of 1,6-bis(2formylphenyl)hexane (0.65 g, 2 mmol) in methanol
(60 mL). After the addition was completed, stirring
was continued for 2 h. A yellow colored precipitate
(Scheme 2) was filtered and washed with methanol.
Yield: 0.44 g (55.14%). Color: yellow. Anal.: Calc. for
C25H25N3O2.H2O: C, 75.16, H, 6.31, N, 10.52. Found:
C, 75.38, H, 6.41, N, 10.44. 13C NMR (DMSO-d6,
δ ppm): CH2CH2CH2: 22.59, CH2CH2O: 28.66,
CH2CH2O: 68.65, HC=N: 189.60, Aromatic: 112.70,
113.95, 120.99, 124.69, 128.06, 136.90, 157.55,
159.71, 161.53. 1H NMR (DMSO-d6, δ ppm): 1.52
(4H, CH2CH2CH2), 1.81 (4H, CH2CH2O), 4.16 (4H,
CH2CH2O), 6.99-7.69 (m, 11H, Ar-H), 10.41 (s, 2H,
HC=N). Selected IR data (KBr, ν cm-1): 3379 (H2O),
3062, 3035 ν(Ar-CH), 2935, 2862 ν(Alf.-CH), 1689
ν(C=N), 1598 (C=N(pyridine)), 1489, 1454
ν(Ar-C=C), 1288, 1238 ν(Ar-O), 1161, 1045 ν(R-O),
752 ν(substituted benzene). UV-vis (λmax, nm)
(DMSO)): 267, 323, 378. Mass spectra (m/z): 399 [L]+.
Synthesis of the complexes
To a stirred solution of ligand in chloroform (60 mL),
was added dropwise M(ClO4)n.6H2O (2 mmol, if M =
Cu, 4 mmol) in methanol (40 mL). After the addition
was completed, the stirring was continued for 2 h.
561
Then, the precipitate was filtered and washed with
CHCl3, and then methanol, and dried in air (Fig. 1).
Characterization of [Cu2(L)(ClO4)2][ClO4]2.H2O
Color: brown. Yield: 0.43 g (22.8%). Anal.: Calc.
for Cu2C25H25N3Cl4O18.H2O: C, 31.85, H, 2.87, N,
4.46. Found: C, 32.04, H, 3.01, N, 4.37. 1H NMR
(DMSO-d6, δ ppm): 1.55 (CH2CH2CH2), 1.83
(CH2CH2O), 4.15 (CH2CH2O), 7.06-7.67 (Ar-H),
10.39 (HC=N). Selected IR data (KBr, ν cm-1): 3348
(H2O), 3066 ν(Ar-CH), 2931, 2862 ν(Alf.-CH), 1651
ν(C=N), 1598 (C=N(pyridine)), 1489, 1454
ν(Ar-C=C), 1242 ν(Ar-O), 1103 ν(R-O), 756
ν(substituted benzene), 1103, 621 ν(ClO4-).
ΛM = 197 Ω-1.mol-1.cm2. UV-vis (λmax, nm) (DMSO):
271, 325, 377. Mass spectra (m/z): 824
[[Cu2(L)(ClO4)2][ClO4]2-H]+.
Characterization of [Ni(L)(ClO4)2].2H2O
Color: yellow. Yield: 0.16 g (11.6%). Anal.: Calc.
for NiC25H25N3Cl2O10.2H2O: C, 43.35, H, 4.19, N,
6.07. Found: C, 43.46, H, 4.31, N, 5.96. 1H NMR
(DMSO-d6, δ ppm): 1.56 (CH2CH2CH2), 1.92
(CH2CH2O), 4.17 (CH2CH2O), 6.93-7.70 (Ar-H),
10.40 (HC=N). Selected IR data (KBr, ν cm-1): 3383
(H2O), 3069 ν(Ar-CH), 2935, 2866 ν(Alf.-CH), 1646
ν(C=N), 1598 (C=N(pyridine)), 1489, 1454
ν(Ar-C=C), 1292, 1242 ν(Ar-O), 1091, 1046 ν(R-O),
752 ν(Substituted benzene), 1113, 629 ν(ClO4-).
ΛM = 25 Ω-1.mol-1.cm2. UV-vis (λmax, nm) (in DMSO):
274, 326, 375. Mass spectra (m/z): 658
[Ni(L)(ClO4)2+2H]+.
Characterization of [Pb(L)(ClO4)][ClO4].2H2O
Color: yellow. Yield: 0.48 g (28.5%). Anal.: Calc.
for PbC25H25N3Cl2O10.2H2O: C, 35.67, H, 3.45,
N, 4.94. Found: C, 35.82, H, 3.79, N, 4.99. 1H NMR
INDIAN J CHEM, SEC A, APRIL 2008
562
Fig. 1 – Proposed structure of the complexes (X=ClO4).
could not be taken because of the low solubility
Selected IR data (KBr, ν cm-1): 3348 (H2O), 3070
ν(Ar-CH), 2931, 2858 ν(Alf.-CH), 1651 ν(C=N), 1598
(C=N(pyridine)), 1489, 1454 ν(Ar-C=C), 1288, 1238
ν(Ar-O), 1161, 1099 ν(R-O), 751 ν(Substituted
benzene), 1108, 621 ν(ClO4-). ΛM = 88 Ω-1.mol-1.cm2.
UV-vis (λmax, nm) (in DMSO): 274, 326, 377. Mass
spectra (m/z): 594 [Pb(L)(ClO4)]-H]+.
Characterization of [Cd(L)][ClO4]2.3H2O
Color: yellow. Yield: 0.63 g (44.7%). Anal.: Calc.
for CdC25H25N3Cl2O10.3H2O: C, 42.61, H, 4.40, N,
5.97. Found: C, 42.77, H, 4.67, N, 6.03. 1H NMR
(DMSO-d6, δ ppm): 1.68 (CH2CH2CH2), 1.92
(CH2CH2O), 4.18 (CH2CH2O), 7.06-7.69 (Ar-H),
10.39 (HC=N). Selected IR data (KBr, ν cm-1): 3371
(H2O), 3070 ν(Ar-CH), 2931, 2858 ν(Alf.-CH), 1647
ν(C=N), 1598 (C=N(pyridine)), 1489, 1454
ν(Ar-C=C), 1288 1238 ν(Ar-O), 1161, 1099 ν(R-O),
756 ν(Substituted benzene), 1106, 621 ν(ClO4-).
ΛM = 169 Ω-1.mol-1.cm2. UV-vis (λmax, nm) (DMSO
(1:1)): 273, 376. Mass spectra: 668 [[Cd(L)](ClO4)2]+.
Characterization of [La(L)(ClO4)3(H2O)].H2O
Color: yellow. Yield: 0.55 g (31.6%). Anal.: Calc.
for LaC25H27N3Cl3O15.H2O: C, 34.44, H, 3.33, N, 4.82.
Found: C, 34.56, H, 3.61, N, 4.89. 1H NMR (DMSOd6, δ ppm): 1.55 (CH2CH2CH2), 1.91 (CH2CH2O), 4.18
(CH2CH2O), 7.07-7.67 (Ar-H), 10.39 (HC=N).
Selected IR data (KBr, ν cm-1): 3363 (H2O), 3070
ν(Ar-CH), 2931, 2862 ν(Alf.-CH), 1651 ν(C=N), 1598
(C=N(pyridine)), 1489, 1454 ν(Ar-C=C), 1292, 1242
ν(Ar-O), 1103, 1049 ν(R-O), 756 ν(Substituted
benzene), 1106, 625 ν(ClO4-). ΛM = 34 Ω-1.mol-1.cm2.
UV-vis (λmax, nm) (in DMSO): 273, 323, 377. Mass
spectra (m/z): 752 [La(L)(ClO4)2(H2O)-H]+.
NOTES
Characterization of [Zn(L)(ClO4)2].2H2O
Color: yellow. Yield: 0.18 g (12.9%). Anal.: Calc.
for ZnC25H25N3Cl2O10.2H2O: C, 42.92 H, 4.15, N, 6.
10. Found: C, 43.09, H, 4.21, N, 6.04. 1H NMR
(DMSO-d6, δ ppm): 1.56 (CH2CH2CH2), 1.90
(CH2CH2O), 4.16 (CH2CH2O), 6.06-7.71 (Ar-H),
10.40 (HC=N). Selected IR data (KBr, ν cm-1): 3363
(H2O), 3074 ν(Ar-CH), 2935, 2862 ν(Alf.-CH), 1647
ν(C=N), 1598 (C=N(pyridine)), 1489, 1454
ν(Ar-C=C), 1292, 1242 ν(Ar-O), 1049 ν(R-O), 756
ν(Substituted benzene), 1107, 625 ν(ClO4-).
ΛM = 24 Ω-1.mol-1.cm2. UV-vis (λmax, nm) (in DMSO):
276, 323, 374. Mass spectra: 664 [Zn(L)(ClO4)2+H]+.
Result and discussion
The ligand and complexes (Schemes 1 and 2) have
been synthesized and characterized by elemental
analysis, IR, 1H and 13C-NMR data, electronic spectra,
magnetic
susceptibility
measurements,
molar
conductivity measurements and mass spectra.
The IR spectra of the ligand (L) show a ν(C=N)
peak at 1689 cm-1 and the absence of a ν(C=O) peak at
around 1700 cm-1 is indicative of Schiff’s base
condensation. The IR spectra of all complexes shows
ν(C=N) bands at 1646-1651 cm-1 and it is found that
the ν(C=N) bands in the complexes are shifted by
about 43-38 cm-1 to lower energy regions compared to
that in the free ligand (L). This phenomenon appears
to be due to the coordination of azomethine nitrogen to
the metal ion14. Also, a weak ν(H2O) band of free
ligand at about 3380 cm-1 is observed because of
hydrated water molecule. The IR spectra of the
complexes are characterized by the appearance of a
broad band in the region at 3328- 3383 cm-1 due to
H2O groups21. Also, infrared spectra of the metal
complexes exhibit an intense band at approximately
1110 cm-1 along with a weak band at ca. 620 cm-1
which is assigned to ν(Cl-O) of perchlorate anions16.
The IR spectra of the complexes clearly demonstrate
that the COC and CCO stretching vibrations are
altered compared to ligands due to conformational
changes. The fact that the C-O-C absorptions of the
complexes are shifted to lower wave numbers
compared to that of the ligand also confirms the
complex formation17. The spectra of all the complexes
are dominated by bands between 2955-2828 cm-1 due
to ν(Alph.-CH) groups and a strong band appearing in
the 1598cm-1 region is assigned to ν(C=N)pyridine mode.
The ν(C=N)pyridine did not change in the
complexes, indicating that azomethine group in
the pyridine does not bind the metal ions18.
563
1
H NMR and 13C NMR of the 1,6-bis(2formylphenyl)hexane, ligand and 1H NMR of the
complexes in DMSO-d6 solution show that they are
NMR active. The 1H NMR spectrum of the 1,6-bis(2formylphenyl)hexane showed a singlet at 10.39 ppm
due to the aldehyde protons, multiplet in the range
approximately 7.03-7.70 ppm due to the aromatic
protons, at 1.66 ppm due to CH2CH2CH2 protons, at
1.87 ppm due to CH2CH2O protons and at 4.16 ppm
due to CH2CH2O protons (Scheme 1). 13C NMR
spectrum of the aldehyde showed at 189.55 ppm due
to the imine carbon, at 22.57 ppm due to CH2CH2CH2
carbon, 28.66 ppm due to CH2CH2O carbon, at 68.67
ppm due to CH2CH2O carbon, and at 133.98-161.53
ppm due to aromatic carbon. The 1H NMR spectrum of
the ligand showed a singlet at 10.40 ppm due to the
imine protons, multiplet in the range approximately
7.05-7.68 ppm due to the aromatic protons, at 1.66
ppm due to CH2CH2CH2 protons, at 1.86 ppm due to
CH2CH2O protons and at 4.16 ppm due to CH2CH2O
protons. 13C NMR spectrum of the ligand showed at
189.60 ppm due to the imine carbon, at 22.59 ppm due
to CH2CH2CH2 carbon, at 28.66 ppm due to CH2CH2O
carbon, at 68.65 ppm due to CH2CH2O carbon and at
112.68-161.53 ppm due to aromatic carbon. The 1H
NMR spectra of the complexes exhibited almost the
same values as that of the ligand. Although we
expected a shift on the position of CH=N signal for the
NMR spectra of the complexes, no significant shift
could not be observed. But the CH=N signal is
observed in low intensity compared to the ligand19.
The electronic spectra of the ligand (L) in DMSO
showed absorption bands at ca. 280, 320 and 370 nm.
The bands are indicative of benzene and other chromophore moieties present in the ligand. The absorption bands of the complexes were shifted to longer
wave numbers compared to that of ligand as expected.
No d-d transitions for the complexes were observed
probably due to low solubility of complexes. A moderately intensive band observed in the range of 320380 nm is due to π-π* transition, and the strong band
observed in the range of 270-280 nm is due to n-π* for
these complexes20.
The observed room-temperature magnetic moment
values for the binuclear Cu(II) and the other
mononuclear complexes were found to be
diamagnetic. The diamagnetic behaviour of the
binuclear complex may be explained by a very strong
anti-ferromagnetic interaction in the Cu-Cu pair18-20.
The conductivity data in DMSO are reported in the
range for 1:2 and 1:1 electrolytes. The complexes,
564
INDIAN J CHEM, SEC A, APRIL 2008
[Cu2(L)(ClO4)2][ClO4]2.2H2O, [Cd(L)][ClO4]2.3H2O
and [Pb(L)(NO3)][NO3].2H2O have values of 197, 169
and 88 ohm-1 cm2 mol-1 indicating 1:2 and 1:1
electrolytes, respectively. The other complexes are
nonelectrolytes18-20.
The mass spectra of complexes with ligand play
an important role in confirming the monomeric
[1+1] (dicarbonyl and diamine) nature of the complexes. The MS peaks are attributable to the molecular
ions: 399 [L]+, 824 [[Cu2(L)(ClO4)2][ClO4]2-H]+, 658
[Ni(L)(ClO4)2+2H]+, 594 [Pb(L)(ClO4)]-H]+, 668
[[Cd(L)](ClO4)2]+, 752 [La(L)(ClO4)2(H2O)-H]+, 664
[Zn(L)(ClO4)2+H]+ (refs 21-23) .
The complexes have no clearly defined melting point
and begin to decompose in the temperature range 250350 °C. The ligand is soluble in DMSO, DMF, CHCl3,
CH2Cl2 and CH3CN but insoluble in H2O, EtOH and
MeOH. The complexes are air stable, partly soluble in
DMF, DMSO and insoluble CHCl3, CH2Cl2 and
CH3CN and the crystals were unsuitable for singlecrystal X-ray structure determination. It is seen that the
complex formation reaction between ligand and
relatively large Cd(II) and Pb(II) metal ions result in the
Cd(II) and Pb(II) complexes. The binding mode of the
ligand for the Pb(II), Cd(II) and Cu(II) complexes are
different than that of the other complexes. In the first
case, the ligand behaves as a tetradentate ligand with the
lone electron pairs of azomethine nitrogen atoms and
the lone electron pairs of two oxygen in ether groups. In
the second case, the ligand behaves as a bidentate ligand
with the lone electron pairs of azomethine nitrogen
atoms. The long distance binding process can be
favored for very large Cd(II), Pb(II) metal ions but not
other metal ions due to having smaller ion size than
Pb(II) and Cd(II) metal ion. So, its coordination is
satisfied with two or three ClO4- and one H2O for
La(III) complex in the second case. Similar binding
mode is known for Pb(II) and Cd(II) metal ions18-20, 24,25.
Also, infrared spectra of the metal complexes exhibit an
intense band at approximately 1110 cm-1 along with a
weak band at ca. 620 cm-1 which have been assigned to
the perchlorate complexes are due to ν(Cl-O) of
perchlorate anions18-20. Also, the conductivity
measurements of the Pb(II) and Cd(II) complexes in
DMSO resulted in ΛM value 88 Ω-1mol-1cm2 and 169 Ω1
mol-1cm2, which indicate that they are 1:1 and 1:2
electrolyte type, respectively. These results clearly
verify different binding mode of ligand in the case of
the Cd(II) and Pb(II) metal ions. As expected, in the
case of the relatively smaller (Ni(II) and Zn(II)) metal
ions, the ligand behaves as a bidentate ligand with the
lone electron pairs of azomethine nitrogen atoms and
the inner coordination sphere is donated with ClO4ligands. The conductivity measurements showed that
these complexes are nonelectrolyte. On the other hand,
the diamagnetic behaviour of the binuclear complex can
be explained by a very strong anti-ferromagnetic
interaction in the Cu-Cu pair18-20,22. Structure of the
binuclear complex is given in Scheme 2. Some Co(II),
Ni(II), Ag(II), Zn(II) or Pb(II) complexes prepared with
similar ligands are already known21. Suggested structure
for Cu(II) complex is bipyramidal, for La(III) complex
it is octahedral, for Pb(II) complex it is square pyramid,
for Zn(II) and Cd(II) complexes it is tetrahedral and that
for Ni(II) complex is square planar18-20,22.
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