Synthesis of complexes of Pb(II), Cd(II), Zn(II), Ni(II), La(III) and Cu(II) with a Schiff base macrocyclic ligand containing pyridine

Article abstract of DOI:10.3184/030823410X12744563061343

1,5-bis(2-formylphenyl)pentane (synthesised from 1,5 dibromopentane and salicylaldehyde). reacts with 2,6-diaminopyridine to give a new macrocyclic ligand that gives Cu(II), Ni(II), Pb(II), Zn(II), Cd(II) and La(III) complexes by reaction with Cu(NO₃

Full text of DOI:10.3184/030823410X12744563061343

304 RESEARCH PAPER
JUNE, 304–306
JOURNAL OF CHEMICAL RESEARCH 2010
Synthesis of complexes of Pb(II), Cd(II), Zn(II), Ni(II), La(III) and Cu(II) with
a Schiff base macrocyclic ligand containing pyridine
a
b
˙
Salih Ilhan * and Hamdi Temel
aDepartment of Chemistry, Faculty of Arts and Sciences, Siirt University, Siirt, Turkey
bDepartment of Chemistry, Faculty of Education, Dicle University, 21280 Diyarbakir, Turkey
1,5-bis(2-formylphenyl)pentane (synthesised from 1,5 dibromopentane and salicylaldehyde). reacts with 2,6-
diaminopyridine to give a new macrocyclic ligand that gives Cu(II), Ni(II), Pb(II), Zn(II), Cd(II) and La(III) complexes by
reaction with Cu(NO3)2·3H2O, Ni(NO3)2·6H2O, Pb(NO3)2, Zn(NO3)2·6H2O, Cd(NO3)2·4H2O and La(NO3)3·6H2O respectively.
The ligand and its metal complexes have been characterised by elemental analysis, IR, 1H and 13C NMR, UV-Vis spec-
tra, magnetic susceptibility, conductivity measurements and mass spectra. All complexes are diamagnetic and the
Cu(II) complex is binuclear.
Keywords: macrocyclic Schiff base complexes, 1,5-bis(2-formylphenyl)pentane, 2,6-diaminopyridine
1
Schiff base metal complexes have widely been studied because
of their industrial, antifungal, and biological applications.1,2
Schiff base macrocycles have been of great importance
in macrocyclic chemistry.3 The chemistry of macrocyclic
complexes has received much attention in recent years
on account of its applications in bioinorganic chemistry,4,5 in
fundamental and applied sciences4–6 and its general importance
in coordination chemistry.6,7 In the present work, we have
synthesised a dialdehyde, 1,5-bis(2-formylphenyl)pentane,
derived from 1,5-dibromopentane with salicylaldehyde and
K2CO3, then a macrocyclic Schiff base (L) by reaction of 2,6-
diaminopyridine and 1,5-bis(2-formylphenyl)pentane. Cu(II),
Ni(II), Pb(II), Zn(II), Cd(II) and La(III) complexes of L have
been synthesised by reaction of L and Cu(NO3)2·3H2O,
Ni(NO3)2·6H2O, Pb(NO3)2, Zn(NO3)2·6H2O, Cd(NO3)2·4H2O
and La(NO3)3·6H2O respectively. Spectral and magnetic
properties of the new compounds are reported in detail.
128.03, 136.86, 161.53. H NMR (DMSO-d6, δ ppm): 1.66 (q, 2H,
J = 8.4 Hz, CH2CH2CH2:), 1.87 (p, 4H, J = 7.6 Hz, CH2CH2O), 4.16
(t, 4H, J = 6.4 Hz, CH2CH2O), 7.03–7.70 (m, 8H, ArH), 10.39 (s, 2H,
HC=N). Selected IR data (KBr, ν cm−1): 3074, 3039 ν(Ar-CH),
2947, 2873 ν(Alf.-CH), 1682 ν(C=O), 1485, 1458 ν(Ar-C=C), 1284,
1242 ν(Ar-O), 1188, 1052 ν(R-O), 752 ν(substituted benzene). Mass
spectra: 312 [M]+
Synthesis of macrocyclic Schiff Base L
The macrocyclic ligand (L) was prepared by the dropwise addition of
a solution of 2,6-diaminopyridine (0.22 g, 2 mmol) in methanol
(40 mL) to a stirred solution of 1,5-bis(2-formylphenyl)pentane
(0.63 g, 2 mmol) in methanol (60 mL). After the addition was com-
plete, stirring was continued for 2h. The yellow-coloured precipitate
was filtered, washed with methanol and dried (Fig. 2). Yield: 0.31 g
(38.5%). Anal. Calcd for C24H23N3O2.H2O: C, 74.8, H, 6.0, N, 10.9.
Found: C, 75.0, H, 6.1, N, 10.8%. 13C NMR (DMSO-d6, δ ppm):
CH2CH2CH2: 22.59, CH2CH2O: 28.66, CH2CH2O: 68.65, HC=N:
189.60, Aromatic: 112.68, 113.95, 120.99, 124.68, 128.06, 136.90,
1
155.60, 159.71, 161.53. H NMR (DMSO-d6, δ ppm): 1.66 (2H,
Experimental
Methods
CH2CH2CH2), 1.86 (4H, CH2CH2O), 4.16 (4H, CH2CH2O), 7.05–7.68
(m, 11H, ArH), 10.40 (s, 2H, HC=N). Selected IR data (KBr, ν cm−1):
3383 (H2O), 3066, 3039 ν(Ar-CH), 2935, 2866 ν(Alf.-CH), 1683
ν(C=N), 1597 (C=N(pyridine)), 1489, 1454 ν(Ar-C=C), 1284, 1242
ν(Ar-O), 1160, 1053 ν(R-O), 752 ν(substituted benzene). UV-Vis
(λmax, nm) (DMSO)): 265, 321, 373. Mass spectra: 385 [L]+.
1,5-bis(2-formylphenyl)pentane was prepared from 1,5-dibromopen-
tane, salicylaldehyde and K2CO3 by a literature method.8–10 All other
chemicals and solvents were of analytical grade and used as received.
Elemental analysis was carried out on a LECO CHNS model 932
1
elemental analyser. H NMR and 13C NMR spectra were recorded
Synthesis of complexes
using a Bruker Avance DPX-400 NMR spectrometer. IR spectra were
recorded on a Midac 1700 FTIR spectrometer as KBr discs in the
wave number range 4000–400 cm−1. Electronic spectral studies were
conducted on a Shimadzu model 160 UV/visible spectrophotometer
in the wavelength 200–800 nm. Molar conductivity was measured
with a WTW LF model 330 conductivity meter, using a solution of
the complex 10−3 M in DMSO. Electrospray ionisation mass spectro-
metric analysis (ESI–MS) was obtained on an Agilent 1100 MSD
Spectrometer. Magnetic susceptibilities were determined on a
Sherwood Scientific magnetic susceptibility balance (Model MK1)
at room temperature (20 °C) using Hg[Co(SCN)4] as calibrant;
diamagnetic corrections were calculated from Pascal’s constants.11
To a stirred solution of L in chloroform (60 mL) was added dropwise
M(NO3)n·nH2O (2 mmol, if M = Cu 4 mmol) in methanol (40 mL).
After the addition was complete, stirring was continued for 2 h, then
the precipitate was filtered off, washed with CHCl3 and methanol
respectively and dried in air (Fig. 3).
[Cu2(L)(NO3)2][NO3]2·H2O: Brown. Yield: 0.65 g (42.1%). Anal.
Calcd for Cu2C24H23N7O14·H2O : C, 37.0, H, 3.2, N, 12.6. Found:
C, 37.4, H, 3.4, N, 12.3%. 1H NMR (DMSO-d6, δ ppm): 1.68
(CH2CH2CH2), 1.84 (CH2CH2O), 4.15 (CH2CH2O), 7.02–7.74 (ArH),
10.41 (HC=N). Selected IR data (KBr, ν cm−1): 3346 (H2O), 3067
ν(Ar-CH),2933,2864ν(Alf.-CH),1616ν(C=N),1598(C=N(pyridine)),
1488, 1453 ν(Ar-C=C), 1243 ν(Ar-O), 1105 ν(R-O), 753 ν(substituted
benzene), 1384 ionic ν(NO3−). ΛM = 193 Ω−1.mol−1 cm2. UV-Vis
(λmax, nm) (DMSO): 274, 324, 374. Mass spectra (m/z): 715
[[Cu2(L)(NO3)2][NO3]-H]+. (M.W. = 778 g mol−1).
[Ni(L)(NO3)2]·2H2O: Yellow. Yield: 0.44 g (35.2%). Anal. Calcd
for NiC24H23N5O8·2H2O: C, 47.7, H, 4.5, N, 11.6. Found: C, 48.1, H,
4.7, N, 11.7%. 1H NMR (DMSO-d6, δ ppm): 1.66 (CH2CH2CH2), 1.93
(CH2CH2O), 4.16 (CH2CH2O), 6.96–7.68 (ArH), 10.41 (HC=N).
Selected IR data (KBr, ν cm−1): 3367 (H2O), 3066 ν(Ar-CH), 2928,
2866 ν(Alf.-CH), 1653 ν(C=N), 1598 (C=N(pyridine)), 1489, 1453
ν(Ar-C=C), 1286, 1246 ν(Ar-O), 1106, 1048 ν(R-O), 752 ν(substituted
benzene), ΛM = 39 Ω−1.mol−1.cm2. UV-Vis (λmax, nm) (in DMSO):
276, 328, 376. Mass spectra(m/z): 603 [Ni(L)(NO3)2-H]+. (M.W.
= 604 g mol−1).
Synthesis of 1,5-bis(2-formylphenyl)pentane
To a stirred solution of salicylaldehyde (24.4 g, 0.2 mol) and
K2CO3 (13.8 g, 0.1 mol) in DMF (80 mL) was added dropwise 1,5-
dibromopentane (23.0 g, 0.1 mol) in DMF (20 mL). The reaction was
continued for 4h at 150–155 °C and 4 h at room temperature (Fig. 1).
After the addition was completed, distilled water (200 mL) was added
and the mixture was put in a refrigerator; 1h later the precipitate was
filtered and washed with water (500 mL), dried in air and recrystal-
lised from EtOH. Yield: 24.3 g (78%), m.p. 66–67 °C, Colour: white.
Anal. Calcd for C19H20O4: C, 73.1, H, 6.5. Found: C, 73.3, H, 6.6%.
13C NMR (DMSO-d6, δ ppm): CH2CH2CH2: 22.57, CH2CH2O: 28.66,
CH2CH2O: 68.67, HC=O: 189.55, Aromatic: 113.98, 120.98, 124.71,
[Pb(L)(NO3)][NO3]·H2O: Yellow. Yield: 0.41 g (28.0%). Anal.
Calcd for PbC24H23N5O8·H2O: C, 39.2, H, 3.4, N, 9.5. Found: C, 39.5,
* Correspondent. E-mail: salihsiirt@gmail.com

JOURNAL OF CHEMICAL RESEARCH 2010 305
Fig. 1 Synthesis of 1,5-bis(2-formylpheyl)pentane.
H, 3.4, N, 9.7%. 1H NMR could not be taken because of the low solu-
bility. Selected IR data (KBr, ν cm−1): 3429 (H2O), 3068 ν(Ar-CH),
2932, 2877 ν(Alf.-CH), 1635 ν(C=N), 1598 (C=N(pyridine)), 1486,
1467 ν(Ar-C=C), 1243 ν(Ar-O), 1105 ν(R-O), 751 ν(substituted
benzene), 1384 ionic ν(NO3−). ΛM = 86 Ω−1 mol−1 cm2. UV-Vis (λmax,
nm) (in DMSO): 274, 327, 377. Mass spectra (m/z): 654 [Pb(L)(NO3)]+.
(M.W. = 734 g mol−1).
they are 1:1 and 1:2 electrolytes respectively in DMSO. These results
verify different binding modes of L in the case of the Cd(II) and Pb(II)
metal ions. As expected, in the case of the relatively small Ni(II) and
Zn(II)) metal ions, the ligand behaves as a bidentate ligand using the
lone electron pairs of the azomethine nitrogen atoms with NO3− ligands
also. The conductivity measurements showed that these complexes
are nonelectrolytes.12–14
[Cd(L)][NO3]2.2H2O: Yellow. Yield: 0.43 g (32.4%). Anal. Calcd
for CdC24H23N5O8·2H2O : C, 43.8, H, 4.1, N, 10.6. Found: C, 44.5, H,
4.2, N, 10.8%. 1H NMR (DMSO-d6, δ ppm): 1.67 (CH2CH2CH2), 1.92
(CH2CH2O), 4.17 (CH2CH2O), 7.03–7.72 (ArH), 10.39 (HC=N).
Selected IR data (KBr, ν cm−1): 3378 (H2O), 3069 ν(Ar-CH), 2932,
2874 ν(Alf.-CH), 1639 ν(C=N), 1598 (C=N(pyridine)), 1486, 1455
ν(Ar-C=C), 1243 ν(Ar-O), 1092 ν(R-O), 754 ν(substituted benzene),
1384 ionic ν(NO3−). ΛM = 168 Ω−1 mol−1 cm2. UV-Vis (λmax, nm)
(DMSO): 274, 325, 377. Mass spectra: 657 [[Cd(L)](NO3)2]+. (M.W.
= 657 g mol−1).
[La(L)(NO3)3(H2O)]·H2O: Yellow. Yield: 0.57 g (39.0%). Anal.
Calcd for LaC24H25N6O12·H2O: C, 38.6, H, 3.6, N, 11.3. Found: C,
39.1, H, 3.9, N, 11.4%. 1H NMR (DMSO-d6, δ ppm): 1.68
(CH2CH2CH2), 1.91 (CH2CH2O), 4.17 (CH2CH2O), 6.97–7.66 (ArH),
10.41 (HC=N). Selected IR data (KBr, ν cm−1): 3356 (H2O), 3066
ν(Ar-CH),2933,2863ν(Alf.-CH),1646ν(C=N),1597(C=N(pyridine)),
1488, 1453 ν(Ar-C=C), 1286, 1243 ν(Ar-O), 1096, 1048 ν(R-O), 753
ν(substituted benzene). ΛM = 27 Ω−1.mol−1.cm2. UV-Vis (λmax, nm) (in
DMSO): 274, 326, 376. Mass spectra(m/z): 648 [La(L)(NO3)2]+.
(M.W. = 746 g mol−1).
FTIR spectra
The IR spectrum of the ligand (L) shows ν(C=N) at 1683 cm−1,
absence of a (C=O) peak at around 1700 cm−1 and ν(NH2) at around
3300 cm−1, indicative of Schiff’s base condensation. The IR spectra of
all complexes show ν(C=N) at 1666–1653 cm−1 and it is found that the
ν(C=N) in the complexes is shifted by about 67–30 cm−1 to lower
energy compared to that in the free ligand.12–14 This phenomenon
appears to be due to the coordinated of azomethine nitrogen to the
metal ion.15 A strong (H2O) band at about 3380 cm−1 is observed in L
and its complexes.16 Also, the ionic metal complexes exhibit an intense
band at 1384 cm−1 assigned to NO3−.17 The IR spectra of the complexes
clearly demonstrated that the COC and CCO stretching vibrations are
altered compared to L due to conformational changes. The fact that
the C–O–C absorptions of the complexes are shifted to lower wave
numbers compared to those of L also confirms the complex forma-
tion.18 The spectra of all the metal complexes are dominated by bands
between 2955 and 2828 cm−1 due to ν(Alph.-CH). A band appearing
in the 1598 cm−1 region is assigned to ν(C=N)(pyridine) and is value
19
did not change in the complexes, thus the azomethine group in the
pyridine did not bind the metal ions.20
[Zn(L)(NO3)2]·2H2O: Yellow. Yield: 0.52 g (42.6%). Anal. Calcd
for ZnC24H23N5O8·2H2O: C, 47.2, H, 4.4, N, 11.5. Found: C, 47.5, H,
4.8, N, 11.4%. 1H NMR (DMSO-d6, δ ppm): 1.67 (CH2CH2CH2), 2.01
(CH2CH2O), 4.16 (CH2CH2O), 6.94–7.69 (ArH), 10.40 (HC=N).
Selected IR data (KBr, ν cm−1): 3371 (H2O), 3067 ν(Ar-CH), 2938,
2874 ν(Alf.-CH), 1644 ν(C=N), 1598 (C=N(pyridine)), 1488, 1454
ν(Ar-C=C), 1292, 1242 ν(Ar-O), 1105, 1048 ν(R-O), 756 ν(substituted
benzene),. ΛM = 34 Ω−1.mol−1.cm2. UV-Vis (λmax, nm) (in DMSO):
276, 326, 374. Mass spectra: 575 [Zn(L)(NO3)2+H]+. (M.W. =
610 g/mol).
NMR spectra
1H NMR and 13C NMR of the 1,5-bis(2-formylphenyl)pentane and
ligand and 1H NMR of the complexes in DMSO-d6 solution show that
they are NMR active. The 1H NMR spectra of the complexes exhibited
almost the same values as L. Although we expected a shift on the posi-
tion of the CH=N signal for the NMR spectra of the complexes, no
significant shift could not be observed, but this resonance is observed
in very low intensity owing to solubility problems.19
Electronic spectra
The electronic spectrum of L in DMSO shows absorption bands at ca
280, 320 and 370 nm arising from benzene and other chromophore
moieties present in the ligand. The absorption bands of the complexes
are shifted to longer wave numbers compared to those of L as
expected.18–20 No d–d transitions for the complexes were observed
probably due to the low solubility of complexes. A moderately inten-
sive band observed in the range of 320–380 nm is due to n─π* transi-
tions, and the strong band observed in the range of 270–280 nm is due
to π─π* transitions 21 for these complexes.
Result and discussion
Macrocyclic Schiff base complexes
The ligand and its complexes have been synthesised and characterised
1
by elemental analysis, IR, H and 13C-NMR data, electronic spectra,
magnetic susceptibility measurements, molar conductivity and mass
spectra. The complexes have no clearly defined melting point and
begin to decompose in the temperature range 250–350 °C. Ligand L
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 but insoluble in CHCl3, CH2Cl2 and CH3CN and
the crystals were unsuitable for single-crystal X-ray structure
determination.
Magnetic measurements and mass spectra
The observed room-temperature magnetic moment value for the binu-
clear Cu(II) compound and the mononuclear complexes show them to
be diamagnetic. The diamagnetic behaviour of the binuclear complex
may be explained by a very strong anti-ferromagnetic interaction in
the Cu–Cu pair.22 Their mass spectra confirm the monomeric [1+1]
(dicarbonyl and diamine) nature of the complexes.23
Molar conductivity
The conductivities of the Pb(II) and Cd(II) complexes in DMSO are
86 Ω−1mol−1cm2 and 168 Ω−1mol−1cm2 respectively, which indicate that
Fig. 2 Synthesis of L.

306 JOURNAL OF CHEMICAL RESEARCH 2010
Fig. 3 Suggested structures of the complexes.
2
3
R. Herzfeld and P. Nagy, Spectrosc. Lett., 1999, 31 (1), 57.
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Conclusion
Compound L and its six complexes have been prepared and
characterised. The binding mode of L in the Pb(II), Cd(II) and
Cu(II) complexes in the solid state differs from the other com-
plexes (Fig. 3). In the first case, L behaves as a tetradentate
ligand using the lone electron pairs of the azomethine nitrogen
atoms the two oxygens in the ether groups. In the second case,
the ligand behaves as a bidentate ligand using only the azome-
thine nitrogen atoms. The long distance binding process can be
favoured for the large Cd(II) and Pb(II) metal ions but not for
smaller metal ions where coordination is then satisfied by, for
example, two or three NO3− and one H2O for the La(III) com-
plex. Similar binding modes were observed in the literature for
Pb(II) and Cd(II) metal ions.12 The general structures proposed
for the solid complexes are shown in Fig. 3. Most probably
the La(III) complexes show octahedral geometry, the Zn(II)
and Cd(II) complexes tetrahedral geometry, the Ni(II) complex
square planar geometry and the Pb(II) complex square
pyramidal geometry around the central metal ions.23–25
4
5
6
7
8
9
10 İ. Yılmaz, S. İlhan, H. Temel and A. Kılıç, J.Inc. Phenom Macrocyclic
Chem., 2009, 63, 163.
11 A. Earnshaw, Introduction to magnetochemistry, Academic Press, London,
1968, p.4.
12 S. İlhan, J.Coord. Chem., 2009, 62, 456.
13 S. İlhan, H. Temel, I. Yilmaz and M. Sekerci, J. Organomet. Chem., 2007,
692, 3855.
14 S. İlhan, H. Temel and S. Paşa, Chin. Chem. Lett., 2009, 20, 339.
15 S. İlhan, H. Temel and A. Kılıç, Chin. J.Chem., 2007, 25, 1547.
16 S. İlhan, H. Temel, İ. Yılmaz and A. Kılıç, Trans. Metal Chem., 2007,
32, 3.
17 S. İlhan and H. Temel, Trans. Metal Chem., 2007, 32, 1039.
18 H. Temel, H. Hoşgören and M. Boybay, Spectrosc. Lett., 2001, 34, 1.
19 S. İlhan, H. Temel, A. Kılıç and E. Tas, Trans. Metal Chem., 20007, 32,
1012.
Received 29 December 2009; accepted 7 May 2010
Paper 100970 doi: 10.3184/030823410X12744563061343
Published online: 1 July 2010
20 S. İlhan, Indian J. Chem., A (IJC-A), 2008, 47A, 374.
21 S. İlhan, Russ. J. Coord. Chem., 2009, 35, 347.
22 S. İlhan, J. Coord. Chem., 2008, 61, 2884.
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2007, 32, 584.
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