Cu(II) and Pd(II) complexes of N-(2-hydroxybenzyl)aminopyridines

Article abstract of DOI:10.1016/j.poly.2007.03.015

N-(2-Hydroxybenzyl)aminopyridines (Lⁱ) react with Cu(II) and Pd(II) ions to form complexes in the compositions Cu(Lⁱ)₂(CH₃COO)₂ · nH₂O (n = 0, 2, 4), Pd(Lⁱ)₂Cl₂ · nC₂H₅OH (n = 0, 2) and Pd(L²)₂Cl₂ · 2H₂O. In the complexes, the ligands are neutral and monodentate which coordinate through pyridinic nitrogen. Crystal data of the complexes obtained from 2-amino pyridine derivative have pointed such a coordinating route and comparison of the spectral data suggests the validity of similar complexation modes of other analog ligands. Cu(II) complex of N-(2-hydroxybenzyl)-2-aminopyridine (L¹), [Cu(L¹)₂(CH₃COO)₂] has slightly distorted square planar cis-mononuclear structure which is built by two oxygen atoms of two monodentate carboxylic groups disposed in cis-position and two nitrogen atoms of two pyridine rings. The remaining two oxygen atoms of two carboxylic groups form two Cu and H bridges containing cycles which joint at same four coordinated copper(II) ion. IR and electronic spectral data and the magnetic moments as well as the thermogravimetric analyses also specify on mononuclear octahedric structure of complexes [Cu(L²)₂(CH₃COO)₂ · 2H₂O] and [Cu(L³)₂(CH₃COO)₂ · 4H₂O] where L² and L³ are N-(2-hydroxybenzyl)-2- or 3-aminopyridines, respectively. X-ray analysis for [Pd(L¹)₂Cl₂ · 2C₂H₅OH] show square planar environment around Pd(II) ion formed by two chlorine atoms in trans position and two nitrogen atoms of pyridine rings. The spectral data indicate structural similarity in the complexes obtained via ligand exchange between PdCl₂(PhCN)₂ and 3-amino and 4-aminopyridine derivatives.

Full text of DOI:10.1016/j.poly.2007.03.015

Polyhedron 26 (2007) 3301–3309
www.elsevier.com/locate/poly
Cu(II) and Pd(II) complexes of N-(2-hydroxybenzyl)aminopyridines
a,
b
c
c
Bahattin Yalc¸ın *, Perizad A. Fatullayeva , Orhan Buyukgungor , Basak Kosar ,
¨ ¨
¨
¨
ß
ß
a
b
b
b
a
Sulin Taßscıog˘lu , Akif I. Israfilov , Zaur D. Ibayev , Ajdar A. Medjidov , Adnan Aydın
¨
a
Marmara University, Faculty of Science and Letters, Department of Chemistry, Go¨ztepe, Istanbul, Turkey
b
Institute of Chemical Problems of Azerbaijan Academy of Sciences, Baku, Azerbaijan
Ondokuzmayıs University, Faculty of Art and Science, Department of Physics, Samsun, Turkey
c
Received 8 January 2007; accepted 3 March 2007
Available online 21 March 2007
Abstract
N-(2-Hydroxybenzyl)aminopyridines (Li) react with Cu(II) and Pd(II) ions to form complexes in the compositions Cu(Li)2(CH3-
COO)2 Æ nH2O (n = 0, 2, 4), Pd(Li)2Cl2 Æ nC2H5OH (n = 0, 2) and Pd(L2)2Cl2 Æ 2H2O. In the complexes, the ligands are neutral and
monodentate which coordinate through pyridinic nitrogen. Crystal data of the complexes obtained from 2-amino pyridine derivative
have pointed such a coordinating route and comparison of the spectral data suggests the validity of similar complexation modes of other
analog ligands. Cu(II) complex of N-(2-hydroxybenzyl)-2-aminopyridine (L1), [Cu(L1)2(CH3COO)2] has slightly distorted square planar
cis-mononuclear structure which is built by two oxygen atoms of two monodentate carboxylic groups disposed in cis-position and two
nitrogen atoms of two pyridine rings. The remaining two oxygen atoms of two carboxylic groups form two Cu and H bridges containing
cycles which joint at same four coordinated copper(II) ion. IR and electronic spectral data and the magnetic moments as well as the
thermogravimetric analyses also specify on mononuclear octahedric structure of complexes [Cu(L2)2(CH3COO)2 Æ 2H2O] and
[Cu(L3)2(CH3COO)2 Æ 4H2O] where L2 and L3 are N-(2-hydroxybenzyl)-2- or 3-aminopyridines, respectively.
X-ray analysis for [Pd(L1)2Cl2 Æ 2C2H5OH] show square planar environment around Pd(II) ion formed by two chlorine atoms in trans
position and two nitrogen atoms of pyridine rings. The spectral data indicate structural similarity in the complexes obtained via ligand
exchange between PdCl2(PhCN)2 and 3-amino and 4-aminopyridine derivatives.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Aminopyridines; Mononuclear copper complexes; Mononuclear palladium complexes; Cu, H cycle
1. Introduction
Many works on transition metal complexes with Schiff
bases of aminopyridines have been reported [7–18]. In all
of these compounds metal ion is coordinated via phenolic
oxygen and azomethine nitrogen albeit endocyclic nitrogen
atom usually does not participate in coordination. In the for-
mer reports, there are very few data on the complexes of
‘‘hydrogenated’’ analogues of the above-stated compounds
[19,20]. The reduction of azomethine bond which interferes
p conjugation between phenolic oxygen and azomethine
nitrogen atoms should change the coordinating ability of
such compounds.
Aminopyridines and their derivatives in most cases act
as monodentate ligands which coordinate the metal ions
through the nitrogen of the ring [1–4], though there are sev-
eral works on 2-aminopyridine complexes in which the
amino group also participates in coordination [5,6]. The
2-amino group was reported to participate in H-bond with
phenol oxygen, which stabilizes the complex unit but no
direct coordination to metal ion was observed [6].
We have investigated the coordinating behaviour of
N-(2-hydroxybenzyl)aminopyridines which have been
received by the reduction of corresponding Schiff’s bases
obtained from salicylaldehyde and aminopyridines. Very
*
Corresponding author. Tel.: +90 216 348 77 59; fax: +90 216 349 25
81.
E-mail address: byalcin@marmara.edu.tr (B. Yalc¸ın).
0277-5387/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.03.015

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B. Yalc¸ın et al. / Polyhedron 26 (2007) 3301–3309
few complexes of N-(2-hydroxybenzyl)aminopyridines
have been reported in the chemical literature [19,20]. The
ligands have three electron donating atoms (NNO) and
mono- and dianionic forms of the ligands present in the
complexes. In our work, copper(II) acetate which is known
to have binuclear structure which partially decomposes in
the presence of water, is used to allow to keep the acetate
as ligand in the complexes, since the preservation of acetate
leads the formation of complexes with different coordina-
tion modes. Palladium(II) complexes of neutral ligands
have been synthesized by the ligand exchange reactions of
PdCl2(PhCN)2. The structures of complexes have been
elucidated by spectral means, TGA and magnetic measure-
ments. X-ray crystal data have also been obtained for the
copper(II) and palladium(II) complexes of N-(2-hydroxyb-
enzyl)-2-aminopyridine (L1).
The properties of the Schiff bases coincided with those of
given in the literature [17,18].
2.2.2. Borohydride reduction of Schiff bases
N-(2-Hydroxybenzyl)aminopyridines
have
been
obtained by the reduction of corresponding Schiff bases
by sodium borohydride in ethanolic solutions. A typical
procedure for the reduction is given below.
2.2.2.1. N-(2-Hydroxybenzyl)-2-aminopyridine (L1). Into a
solution of N-2-pyridylsalicylaldimine (25 mmol, 5 g) in
15 mL ethanol was added sodium borohydride in small
portions until initial yellow-orange colour of the solution
was discoloured. The mixture was poured into 60 mL
water, mixed well and left to crystallize for 3 h. Fine needle
crystals have been filtered, washed well with water up to
neutral reaction against litmus. The crystals have been
dried and recrystallized from ethanol to yield 3.2 g L1
1
(65%). White powder. Mp: 104 ꢁC. H NMR (DMSO-d6,
d): 10.55 (s, 1H, Ph–OH); 6.45–7.96 (m, 8H, arom.CH);
4.35 (s, 2H, CH2), 3.50 (s, 1H, NH). Anal. Calc. for
C12H12N2O: C, 71.98; H, 6.04; N, 13.99. Found: C,
71.55; H, 5.68; N, 13.59%.
NH
CH2
HO
N
L1 : 2-aminopyridine derivative
L2 : 3-aminopyridine derivative
L3 : 4-aminopyridine derivative
2.2.2.2. N-(2-Hydroxybenzyl)-3-aminopyridine (L2). White
powder. Mp: 196 ꢁC. 1H NMR (DMSO-d6, d): 9.65 (s, 1H,
Ph–OH); 6.25–8.15 (m, 8H, arom.CH); 4.25 (s, 2H, CH2);
3.4 (s, 1H, NH). Anal. Calc. for C12H12N2O: C, 71.98; H,
6.04; N, 13.99. Found: C, 71.12; H, 5.95; N, 13.73%.
2. Experimental
2.1. Physical and chemical measurements
2.2.2.3. N-(2-Hydroxybenzyl)-4-aminopyridine (L3). White
powder. Mp: 177 ꢁC. 1H NMR (DMSO-d6, d): 8.05 (s, 1H,
Ph–OH); 6.50–8.15 (m, 8H, arom.CH); 4.25 (s, 2H, CH2);
3.2 (s, 1H, NH). Anal. Calc. for C12H12N2O: C, 71.98; H,
6.04; N, 13.99. Found: C, 71.48; H, 5.45; N, 13.54%.
IR. IR spectra were recorded on a Specord-M80
(Charles Zeiss Jena) infrared spectrophotometer as
KBr tablets in the range of 4000–400 cmꢀ1
.
UV–Vis. The electronic spectra were recorded on
spectrophotometers Specord-M40 and Shimadzu UV–
Vis 240.
Magnetic susceptibility measurements were carried out
at room temperature on Faraday magnetic balance with
Hg[Co(SCN)4] as standard.
2.2.3. Copper(II) complexes of N-(2-hydroxybenzyl)-
aminopyridines
A typical procedure for copper(II) complexes of N-(2-
hydroxybenzyl)aminopyridines is given below.
Thermogravimetric measurements were made on deriva-
tograph MIM (Hungary).
Elemental analyses. The elemental analyses were per-
formed in the analytical laboratory Tubitak, Ankara
¨
on LECO CHNS 932.
X-ray data have been obtained on a STOE IPDS 2 dif-
fractometer with graphite monochromated MoKa radi-
ation at 296 K.
2.2.3.1. Diacetato-bis(N-(2-hydroxybenzyl)-2-aminopyridine)-
copper(II) [Cu(L1)2(CH3 COO)2]. L1 (1 mmol, 0.20 g) in
10 mL ethanol was mixed with copper acetate monohy-
drate (0.5 mmol, 0.10 g) solution in 5 mL water and the
mixture was heated at 50–60 ꢁC for 30 min. During cooling
to room temperature, dark blue rhombic crystals were col-
lected from dark green solution, washed with water and
dried in vacuo (0.27 g, 90% yield). Mp: 170–175 ꢁC
(decomp.). leff = 1.78. TGA data (ꢁC) (weight loss%)
(Calc. weight loss%) [Endo. peak temp. ꢁC]: (50–174 ꢁC)
(5.65) (5.15, calc. for ꢀ0.5AcOH); (174–244 ꢁC) (18.05)
(15.46, ꢀ1.5AcOH); (244–485 ꢁC) (32.39); (485–735 ꢁC)
(28.05); [170; 244; 465 ꢁC].
2.2. Syntheses of ligands and complexes
2.2.1. Reagents
Aminopyridines, salicylaldehyde, sodium borohydride
and the solvents used in the preparations were all Merck
p.a. products.
Schiff bases have been synthesized by the reaction of
aminopyridines with salicylaldehyde in ethanolic solutions
Anal. Calc. for C28H30N4O6Cu: C, 57.77; H, 5.19; N,
9.62; Cu, 10.91. Found: C, 57.86; H, 4.87; N, 9.77; Cu,
10.35%.

B. Yalc¸ın et al. / Polyhedron 26 (2007) 3301–3309
3303
2.2.3.2. Diacetato-bis(N-(2-hydroxybenzyl)-3-aminopyridine)-
copper(II)dihydrate [Cu(L2)2(CH3COO)2] Æ 2H2O. Green
powder. Mp: 160–165 ꢁC (decomp.). leff = 1.90. TGA data
(ꢁC) (weight loss%) (Calc. weight loss%) [Endo. peak temp.
ꢁC]: (50–130 ꢁC) (2.52) (2.91, calc. for –H2O); (130–175 ꢁC)
(2.87) (2.91, –H2O); (175– 251 ꢁC) (43.3); (351–819 ꢁC)
(36.52); [170, 296; 422 ꢁC]. Anal. Calc. for C28H34N4O8Cu:
C, 54.39; H, 5.54; N, 9.06; Cu, 10.28. Found: C, 53.42; H,
5.62; N, 8.85; Cu, 10.20%.
CH2); 3.15, 3.18 (s, 2H, NH). TGA data (ꢁC) (weight
loss%) (Calc. weight loss%) [Endo. peak temp. ꢁC]: (148–
284 ꢁC) (8.58) (8.87, calc. for –(HCl+H2O)); (284–329 ꢁC)
(3.19) (2.94, –H2O); (329–374 ꢁC) (27.90); (374–638 ꢁC)
(40.60); [240; 273; 329; 638; 832 ꢁC]. Anal. Calc. for
C24H28N4O4Cl2Pd: C, 46.96; H, 4.60; N, 9.13; Pd, 17.34.
Found: C, 46.66; H, 3.11; N, 9.62; Pd, 18.25%.
2.2.4.3. Dichloro-bis(N-(2-hydroxybenzyl)-3-aminopyridine)-
palladium(II) [Pd(L3)2Cl2]. Yellow powder. Mp: 303–
305 ꢁC (decomp). 1H NMR(DMSO-d6, d): 9.70 (s, 2H,
2.2.3.3. Diacetato-bis(N-(2-hydroxybenzyl)-4-aminopyri-
dine)copper(II)tetrahydrate[Cu(L3)2(CH3COO)2] Æ 4H2O. Ph–OH); 6.2–8.2 (m, 16H, arom.CH); 4.22 (s, 4H, CH2);
Blue powder. Mp: 121–125 ꢁC (decomp.). leff = 1.81. TGA
data (ꢁC) (weight loss%) (Calc. weight loss%) [Endo. peak
temp. ꢁC]: (50–130 ꢁC) (3.24) (2.75, calc. for –H2O); (130–
198 ꢁC) (6.82) (8.26, –3H2O); (198–268 ꢁC) (9.44) (9.17,
–AcOH); (778 ꢁC) (51.12); [130, 198, 268; 645 ꢁC]. Anal.
Calc. for C28H38N4O10Cu: C, 51.41; H, 5.85; N, 8.56; Cu,
9.71. Found: C, 51.17; H, 5.22; N, 8.11; Cu, 9.39%.
Refluxing the reaction mixture for 5 h yields Cu2O as
by-product. Oxidative dehydrogenations of the ligands to
give N-(2-pyridyl)salicylaldimines were not observed.
3.15, 3.18 (s, 2H, NH); TGA data (ꢁC) (weight loss%)
(Calc. weight loss%) [Endo. peak temp. ꢁC]: (69–198 ꢁC)
(6.34) (6.31, calc. for –HCl); (198–290 ꢁC) (7.31) (6.31, –
HCl); (290–411) (22.93); (411–651 ꢁC) (53.66); [242; 391;
476 ꢁC]. Anal. Calc. for C24H24N4O2Cl2Pd: C, 49.89; H,
4.18; N, 9.69; Pd, 18.42. Found: C, 49.84; H, 3.79; N,
9.15; Pd, 18.12%.
2.3. X-ray structural analyses of complexes
Blue plate [Cu(II) complex of L1] and colorless prism
[Pd(II) complex of L1] single crystals suitable for data col-
lection were mounted on a glass fiber and data collection
processes were performed on a STOE IPDS 2 diffractometer
with graphite monochromated MoKa radiation at 296 K.
Details of crystal data, data collection and refinement
results for the two crystals [21] are given in Table 1. The
structures were solved by direct-methods using SHELXS-97
[22] and refined by full-matrix least-squares methods on
F2 using SHELXL-97 [20]. Molecular drawings were obtained
using ORTEP-III [23] for Windows. Materials were pre-
pared for publication using software WinGX [24].
2.2.4. Palladium(II) complexes of N-(2-hydroxybenzyl)-
aminopyridines
A typical procedure for palladium(II) complexes of N-
(2-hydroxybenzyl)aminopyridines is given below.
2.2.4.1.
Dichloro-bis(N-(2-hydroxybenzyl)-2-aminopyri-
dine)palladium(II)diethanol [Pd(L1)2Cl2] Æ 2C2H5OH. L1
(2 mmol, 0.40 g) in 10 mL ethanol was mixed with
Pd(C6H5CN)2Cl2 (1 mmol, 0.383 g) solution in 15 mL eth-
anol. The mixture was heated at ꢁ40 ꢁC for 30 min, filtered
hot and left for crystallization. Light yellow crystals were
collected and dried in vacuo (0.44 g, 65% based on Pd).
Yellow crystals. Mp: 127–130 ꢁC (decomp.).
2.3.1. Crystal structure of diacetato-bis(N-(2-hydroxy-
benzyl)-2-aminopyridine)copper(II) [Cu(L1)2(CH3COO)2]
The compound, namely diacetato-bis[N-(2-hydroxyben-
zyl)-2-aminopyridine]copper(II), crystallize in triclinic
1H NMR (DMSO-d6, d): 10.55 (b, 1H, Ph–OH); 9.75 (s,
1H, Ph–OH); 8.61 (d, 1H, arom.CH); 8.3 (d, 1H, arom.CH);
6.25–7.60 (m, 14H, arom.CH); 4.55 (s, 4H, CH2–OH); 4.35
(s, 4H, CH2); 3.40, 3.42 (s, 2H, NH) 1, 17 (s, 6H, CH3).
Mass data (70 equiv) (m/z) (%): 623.95 (0.1,
M*ꢀEtOH); 577.9 (0.4, M*ꢀ2EtOH); 543 (25.9,
PdL2Cl+H); 542 (11.0, PdL2Cl); 541 (25.4, PdL2Cl–H);
540 (17.3, PdL2Cl–2H); 203.15 (1.2); 202.1 (13.6, L+2H);
201.1 (100.0, L+H); 130.2 (4.7); 107.1 (14.4, Pd); 96.1
(4.3). TGA data (ꢁC) (weight loss%) (Calc. weight loss%)
[Endo. peak temp. ꢁC]: (95–146 ꢁC) (14.07) (13.75, calc.
for –2C2H5OH); (146–345 ꢁC) (33.11); (345–926 ꢁC)
(39.42); [146; 213; 345 ꢁC]. Anal. Calc. for C28H36N4
O4Cl2Pd: C, 50.20; H, 5.42; N, 8.36; Pd, 15.89. Found:
C, 50.02; H, 4.61; N, 8.66; Pd, 15.93%.
ꢀ
space group P1 and molecular structure of this compound
is shown in Fig. 1. Title compound has intramolecular
and intermolecular hydrogen bonds; geometric parameters
are given in Table 2. In three-dimensional networks, the
molecules are linked by two intramolecular N–Hꢂ ꢂ ꢂO
and two intermolecular O–Hꢂ ꢂ ꢂO hydrogen bonds.
Fig. 2 shows the packing of molecules in unit cell. All
hydrogen atoms except for H4A and H5A were refined
using a riding model and H bond distances were set to
˚
˚
˚
˚
0.930 A for CH, 0.960 A for CH2, 0.970 A for CH3 and
0.820 A for OH (Table 3).
Crystal data and refinement results are listed in Table 1.
Atomic coordinates and equivalent isotropic displacement
parameters and the geometric parameters of molecule are
available from the Cambridge Crystallographic Data Cen-
ter, CCDC 605890.
2.2.4.2.
Dichloro-bis(N-(2-hydroxybenzyl)-3-aminopyri-
dine)palladium(II)dihydrate [Pd(L2)2Cl2] Æ 2H2O. Yellow
1
powder. Mp: 231–235 ꢁC (decomp). H NMR(DMSO-d6,
d): 9.75 (s, 2H, Ph–OH); 8.20 (d, 1H, arom.CH); 7.85 (d,
Data collection: X-AREA; Cell refinement: X-AREA;
Data reduction and absorption correction: X-RED32 [21].
1H, arom.CH); 6.7–7.4 (m, 14H, arom.CH); 4.20 (s, 4H,

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B. Yalc¸ın et al. / Polyhedron 26 (2007) 3301–3309
Table 1
Crystal data of compounds and structure refinement results
For Cu(II) complex
For Pd(II) complex
Moiety formula
Sum formula
Formula weight
Temperature (K)
C28H30CuN4O6
C28H30CuN4O6
582.10
C24H24Cl2N4O2Pd, 2(C2H5OH)
C28H36Cl2N4O4Pd
669.91
296
296
˚
Wavelength (A)
0.71073
0.71073
Crystal system
Space group
Unit cell dimensions
triclinic
monoclinic
P21/c
ꢀ
P1
˚
a (A)
9.8146 (6)
11.6563 (7)
14.7944 (9)
66.760 (5)
80.730 (5)
66.544 (5)
1426.65 (15)
2
10.3604 (7)
7.7407 (4)
19.9255 (14)
90
107.958 (5)
90
1520.11 (17)
2
1.464
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
Volume (A )
Z
Calculated density (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
1.369
0.812
606
)
0.825
688
Crystal size (mm)
h Range for data collection
Index ranges
0.69 · 0.42 · 0.14
1.50–26.11
ꢀ12 < h < 12,
ꢀ14 < k < 14,
ꢀ18 < l < 18
5466
0.57 · 0.37 · 0.18
2.01–27.24
ꢀ12 < h < 12,
ꢀ9 < k < 9,
ꢀ24 < l < 24
2988
Independent reflection
Measurement reflection
Absorption correction
Refinement method
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
12214
18906
integration
full-matrix least-squares on F2
1.164
R1 = 0.0467
R1 = 0.0615
0.881 and ꢀ0.339
integration
full-matrix least-squares on F2
1.068
R1 = 0.0258
R1 = 0.0697
0.400 and ꢀ0.591
ꢀ3
˚
Largest difference peak and hole (e A
)
2.3.2. Crystal structure of dichloro-bis(N-(2-
hydroxybenzyl)-2-aminopyridine) palladium(II) diethanol
Pd(L1)2Cl2 Æ 2C2H5OH
Dichloro-bis[N-(2-hydroxybenzyl)-2-aminopyridine]pal-
ladium(II)diethanol, crystallize in monoclinic space group
P21/c and molecular structure of this compound is shown
in Fig. 4. The asymmetric unit of the title compound con-
tains two independent molecules. Title compound has an
intramolecular and two intermolecular hydrogen bonds,
geometric parameters are given in Table 2. In three-dimen-
sional network, the molecules are linked by intramolecular
O–Hꢂ ꢂ ꢂO and intermolecular N–Hꢂ ꢂ ꢂO and O–Hꢂ ꢂ ꢂCl
hydrogen bonds. Fig. 5 shows the packing of molecules
in unit cell. All non-hydrogen atoms were refined with
Table 2
˚
Hydrogen-bonding geometries of compounds (A, ꢁ)
D–Hꢂ ꢂ ꢂA
D–H
Hꢂ ꢂ ꢂA
Dꢂ ꢂ ꢂA
D–Hꢂ ꢂ ꢂA
For Cu(II) complex
O1–H1Aꢂ ꢂ ꢂO4i
O2–H2Aꢂ ꢂ ꢂO6ii
N2–H3Aꢂ ꢂ ꢂO4
N4–H4Aꢂ ꢂ ꢂO6
0.82
0.82
0.78 (4)
0.79 (4)
1.91
1.94
2.21 (4)
2.18 (4)
2.630 (4)
2.679 (4)
2.985 (5)
2.959 (5)
146.2
149.7
170 (4)
174 (4)
i = ꢀx, 1 ꢀ y, ꢀz; ii = 2 ꢀ x, ꢀy, 1 ꢀ z
For Pd(II) complex
O2–H2Bꢂ ꢂ ꢂO1
N2–H2Aꢂ ꢂ ꢂO2i
O1–H1Aꢂ ꢂ ꢂCl1i
i = 1 ꢀ x, 1/2 + y, 1/2 ꢀ z
0.82
0.86
0.82
2.20
2.45
2.34
3.002 (3)
3.114 (3)
3.1342 (16)
166.8
134.0
162.2
Fig. 1. An ORTEP3 view of [Cu(L1)2(CH3COO)2], with the atom-
numbering scheme and 30% probability displacement ellipsoids. H atoms
are shown as small spheres of arbitrary radii.

B. Yalc¸ın et al. / Polyhedron 26 (2007) 3301–3309
3305
Fig. 2. A packed diagram of [Cu(L1)2(CH3COO)2]. Dashed lines show the intra- and intermolecular hydrogen bonds.
Table 3
depending on their positions in the pyridine ring, e.g.,
3328 cmꢀ1 for L1; 3360 cmꢀ1 for L2 and 3355 cmꢀ1 for
L3. Phenolic O–H stretching bands appear clearly at
3400 cmꢀ1 only for L3.
˚
Selected bond lengths and angles (A, ꢁ) of compounds
For Cu(II) complex
N1–Cu1
O3–Cu1
O5–Cu1–O3
O3–Cu1–N3
O5–Cu1–N1
2.001 (3)
1.979 (2)
89.53 (11)
91.77 (11)
90.88 (11)
N3–Cu1
O5–Cu1
O5–Cu1–N3
O3–Cu1–N1
N3–Cu1–N1
1.997 (3)
1.956 (3)
164.41 (11)
164.24 (11)
92.05 (11)
Prominent feature of N-(2-hydroxybenzyl)aminopyri-
dines is the presence of two broad absorption bands in
the region of 2500–1650 cmꢀ1, which notify the presence
of intramolecular hydrogen bond between phenolic hydro-
xyl and secondary amino group. Although position of the
band at around 2500 cmꢀ1 do not change for all ligands,
position of the low-frequency band shifts depending on
the basicity of secondary amino group. LogK of amino
group of aminopyridines depends on its position in the pyr-
idine ring and has the values of 7, 6; 6.1 and 1.5 for 2-
amino-; 4-amino- and 3-aminopyridine, respectively [25].
It can be inferred that similar sequence should be observed
for secondary amino groups in 2-hydroxybenzyl derivatives
of aminopyridines. L1 with the least basic amino group
For Pd(II) complex
N1–Pd1
N1–Pd1–N1ii
N1–Pd1–Cl1
2.0155 (16)
180.00
90.33 (5)
Cl1–Pd1
2.3052 (16)
89.67 (5)
180.00
N1–Pd1–Cl1ii
Cl1–Pd1–Cl1ii
ii = 1 ꢀ x, 1 ꢀ y, 1 ꢀ z
anisotropic parameters. All hydrogen atoms were refined
using a riding model and H bond distances were set to
0.930 A for CH, 0.960 A for CH2, 0.970 A for CH3,
˚
˚
˚
˚
shows maximum absorption at ꢁ1780 cmꢀ1
,
L3 at
˚
0.820 A for OH and 0.860 A for NH.
1840 cmꢀ1 and L2 at 1860 cmꢀ1. These bands, apparently,
may be attributed to the deformatiþon vibrations of proton-
The palladium ion is four coordinated by two Cl atoms
and N atoms of two pyridine rings. In Pd(II) complex, the
coordination environment of metal is very slightly distorted
square planar. There is no significantly deviation from
Pd1/Cl1/N1/Cl1i/N1i plane.
The N–Pd–N1 angle is 180ꢁ and N–Pd–Cl angles are
89.67ꢁ and 90.33ꢁ. Pd–N and Pd–Cl distances are
2.0155 A and 2.3052 A, respectively.
ated secondary amino group NH2
.
O–H bending and C–O stretching absorptions of phe-
nols appear at 1210–1270 cmꢀ1 and 1330–1360 cmꢀ1 range,
respectively.
˚
˚
3.2. Characterization of the complexes
Crystal data and refinement results, selected bond
lengths and angles are listed in Tables 1 and 3. Atomic
coordinates and equivalent isotropic displacement parame-
ters and the geometric parameters of molecule are available
from the Cambridge Crystallographic Data Center, CCDC
605890.
3.2.1. Cu(II) complexes of N-(2-hydroxybenzyl)-
aminopyridines
In the IR spectra of Cu(II) complexes, displacements of
absorption bands to lower frequencies were observed, by
which broad peaks assigned for O–H and N–H stretching
vibrations with maximum absorptions at ꢁ3328, ꢁ3260
and 3280 cmꢀ1 appeared for [Cu(L1)2(CH3COO)2],
[Cu(L2)2(CH3COO)2] Æ 2H2O and [Cu(L3)2(CH3COO)2]
Æ 4H2O complexes, respectively. 3420 and 3400 cmꢀ1 bands
in the spectra of L2-Cu(II) and L3-Cu(II) complexes
assigned for the coordination water O–H stretching appear
as weak and strong peaks, respectively.
3. Results and discussion
3.1. Infrared spectra of the ligands
The absorption bands of secondary amine N–H
stretching vibrations appear at different frequencies

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B. Yalc¸ın et al. / Polyhedron 26 (2007) 3301–3309
The broad bands of the ligands around 2500 and
dination routes with acetate and pyridine ligands in com-
plexes are same. For L2 and L3 complexes of Cu(II),
coordination of Cu(II) up to the extended octahedron is
possible due to the water molecules.
1850 cmꢀ1 which are assigned for proton transfer or hydro-
gen bonding between phenolic OH and secondary amine
NH disappear in the spectra of all complexes.
The carboxylic group stretching mas in the copper com-
plexes are obscured with ligand bands at 1624 and
1584 cmꢀ1. For complex [Cu(L1)2(CH3COO)2], msym of
Magnetic moments of the complexes are between 1.78–
1.90 BM which correspond to bivalent copper complexes
and specify the absence of antiferromagnetic interaction.
The X-ray study of [Cu(L1)2(CH3COO)2] obtained from
N-(2-hydroxybenzyl)-2-aminopyridine has shown that the
coordination environment around Cu(II) is slightly dis-
torted from square planar and is composed from two
oxygen atoms of two monodendate carboxylic groups,
disposed in cis-position and two nitrogen atom of two
pyridine rings. In complex L1-Cu(II), the remaining two
oxygen atoms of two carboxylic groups form two 8-mem-
bered cycles both of which contain Cu and H bridges
through hydrogen atoms of secondary amine groups. Ear-
lier such cycles with Cu and H bridges have been reported
for binuclear Cu(II) complexes of 2-aminopyridine such as
[Cu2(CH3COO)4(NH2C6H4N)2] and [Cu2(CH3COO)4 Æ
(NH2C6H4N)2 Æ C4H8O2] [28] in which acetate ion acted
as bidentate bridging ligand. However, mononuclear cop-
per(II) complex [Cu(L1)2(CH3COO)2] has two 8-membered
cycles which are joint at the same four coordinated copper
ion with square planar environment.
COOꢀ is observed at 1448 cmꢀ1
.
Dm = mas ꢀ msym
=
176 cmꢀ1 and corresponds to bridge structure [26] which
in the complex should be placed between Cu(II) ion and
secondary amino group. msym of COOꢀ in complexes
[Cu(L2)2(CH3COO)2] Æ 2H2O and [Cu(L3)2(CH3COO)2] Æ
4H2O are observed at 1392 cmꢀ1 and 1420 cmꢀ1 with
Dm = 192 and 204 cmꢀ1, respectively, by which monoden-
tate character of acetate and the absence of bridge struc-
tures in those complexes are noticed [27].
O–H bending and C–O stretching bands of phenol in
1220–1260 cmꢀ1 range and at 1340, 1350 cmꢀ1 frequencies,
respectively, do not change their position in Cu(II) com-
plexes to indicate the nonparticipation of phenolic O–Hs
in complexation which was also clearly observed in X-ray
studies of L1-Cu(II) complex.
According to the data of elemental analyses and thermo-
gravimetric measurements Fig. 3, ligands L2 and L3 form
Cu(II) complexes in the composition of [Cu(L2)2(CH3-
COO)2] Æ 2H2O and [Cu(L3)2(CH3COO)2] Æ 4H2O.
Electronic spectra of Cu(II) complexes in DMF solu-
tion contain three absorption bands around 400
(e 18 Mꢀ1 cmꢀ1), 488 (sh) (e 6 Mꢀ1 cmꢀ1) and 690 (e
4 Mꢀ1 cmꢀ1) nm which accordingly can be attributed to
charge transfer band and d–d transition. In the electronic
spectra of [Cu(L2)2(CH3COO)2] Æ 2H2O and [Cu(L3)2(CH3-
COO)2] Æ 4H2O taken in DMF the absorption bands at
410 (e 20 Mꢀ1 cmꢀ1), 488 (e 7 Mꢀ1 cmꢀ1) and 699
(e 5 Mꢀ1 cmꢀ1) nm and at 365 (e 25 Mꢀ1 cmꢀ1), 488
(e 6 Mꢀ1 cmꢀ1) and 730 (e 4 Mꢀ1 cmꢀ1) nm are observed,
respectively. The obtained data allow assuming that coor-
3.2.2. Pd(II) complexes of N-(2-hydroxybenzyl)-
aminopyridines
The spectral data of the Pd(II) complexes have been sup-
ported by the XRD data. In the IR spectra of Pd(II) com-
plexes, secondary amino group absorption of the ligand
does not shift by complexation and appears at 3373 cmꢀ1
for [Pd(L1)2Cl2] Æ 2C2H5OH and 3352 cmꢀ1 for [Pd(L2)2-
Cl2] Æ 2H2O and Pd(L1)2Cl2, by which nonparticipation of
amino group in coordination with palladium ion is
notified.
Fig. 3. TG, DTG and DTA diagrams of [Cu(L1)2(CH3COO)2] and [Pd(L1)2Cl2] Æ 2C2H5OH.

B. Yalc¸ın et al. / Polyhedron 26 (2007) 3301–3309
3307
Since the absorption bands of phenolic hydroxyl appear
in 3350–3500 cmꢀ1 range for stretching and 1210–
1270 cmꢀ1 range for bending modes in all Pd(II) complexes,
ligand coordination should be built through endocyclic
nitrogen atom which was also proved by XRD studies
(Figs. 4 and 5).
Another indication for the participation of pyridine
nitrogen in coordination has been shown earlier, the band
groups in the region of 1600–1340 cmꢀ1, referring to pyr-
idine ring absorption by complex formation displaces
aside high frequencies in comparison with the same bands
of free ligands [29,30]. However, in work [14], it has been
shown that high frequency shift of IR absorption bands
of pyridine ring not always can be a reliable indication
on the participation of pyridine nitrogen in coordination.
In [14] it was reported that in the Schiff bases of amino-
pyridine derivatives high-energy shift of pyridine ring
bands was observed, however the X-ray data have shown
the absence of coordination with endocyclic nitrogen.
Regarding those band groups, our studies showed
that the frequency shifts of the bands are not reliable in
discussions about the contribution of pyridinic nitrogen
into coordination. IR analysis of Pd complexes with
N-(2-hydroxybenzyl)aminopyridines shows that stretching
frequencies of pyridine rings decreased in [Pd(L1)2Cl2] Æ
2C2H5OH, while increased in [Pd(L3)2Cl2]. For com-
plex [Pd(L2)2Cl2] Æ 2H2O irregular band shifts were
observed.
Fig. 4. An ORTEP3 view of [Pd(L1)2Cl2] Æ 2C2H5OH, with the atom-numbering scheme and 30% probability displacement ellipsoids. H atoms are shown
as small spheres of arbitrary radii.
Fig. 5. A packed diagram of [Pd(L1)2Cl2] Æ 2C2H5OH. Dashed lines show the intra- and intermolecular hydrogen bonds. The hydrogen atoms which have
no contribution in bonding were omitted for clarity.

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B. Yalc¸ın et al. / Polyhedron 26 (2007) 3301–3309
Elemental analyses and TG data in Fig. 3 indicated the
Contrary to above mentioned results, our work showed
that, in both Pd(II) complexes and acetate containing com-
plexes of Cu(II), N-(2-hydroxybenzyl)-2-aminopyridine as
well as its 3-amino and 4-aminopyridine analogs behaved
as monodentate ligand coordinating only through pyridinic
nitrogen while the phenolic hydroxyl and secondary amino
groups have not participated in coordination. The ligands
form neutral ligand complexes. Neither secondary amine
NH nor aromatic hydroxyl is deprotonated. These groups
have been stabilized via intra- or intermolecular hydrogen
bonding. This coordinating behaviour is the basic differ-
ence from corresponding Schiff bases which coordinate
metal ions through phenolic oxygen and azomethine nitro-
gen while pyridine nitrogen has not any role in coordina-
tion. The crystal data of the complexes obtained from
2-aminopyridine derivative have supported these observa-
tions and comparison of the spectral data suggested the
validity of similar complexation modes with other analog
ligands.
presence of two ethanol solvate molecules in complex
[Pd(L1)2Cl2] Æ 2C2H5OH. In X-ray crystallography, the sec-
ond ethanol on the outside of the unit cell was not
observed. In the IR spectrum of L1-Pd(II) complex, O–H
stretching and methyl CH2 bands of ethanol which is
hydrogen bonded to phenolic oxygen and found in unit cell
appear at 3311 and 1392 cmꢀ1, respectively. The free etha-
nol O–H stretching appears at 3544 cmꢀ1 as a strong sharp
peak. The C–O stretching of alcohol absorbs at 1060 cmꢀ1
.
1H NMR data also indicate the presence of two ethanol
molecules in the complex.
In electronic spectra of Pd(II) complexes dissolved in
DMF, two weak absorption bands at 425 and 500 nm were
observed, which can be attributed to d–d transitions in
square planar complexes of palladium [26].
3.3. Discussion
The reactant copper(II) acetate Cu2(CH3COO)4 Æ 2H2O
is known to have binuclear structure which consists of four
three atom bridges of carboxylate groups uniting two con-
tiguous copper(II) ions [31]. Two water molecules occupy
the terminal positions. Although its dimeric structure is
destroyed in water to form monomeric hydrated Cu(II)
acetate in ionic and molecular form, this destruction can
be avoided in alcohol like organic solvents which have
much weaker coordinating power than the water molecule
[32]. The bonds between the carboxylate and Cu(II) ions
should be strong enough in such solvent systems.
In our work, we have used ethanol/water (2:1) solvent
mixture so that partial decomposition of dimeric structure
of copper(II) acetate may take place and the acetate bridges
are mainly cleaved by the attack of ligand’s pyridinic nitro-
gen, without elimination of acetates from simultaneously
formed mononuclear complex. In the working solution,
interaction between the free acetate which is in the low con-
centration and Ar–OH would be at minimum level and
consequently the bonding competition between acetate
and phenolate might be negligible. Thus, the participation
of deprotonated phenolic O–H in coordination is not
favored. XRD data confirmed such kind of coordinating
behaviour of the ligands in copper complexes.
N-(2-Hydroxybenzyl)aminopyridines (L) (L1: 2-amino;
L2: 3-amino; L3: 4-amino derivative) react with Cu(II) ace-
tate and Pd(C6H5CN)2Cl2 to give mononuclear complexes
in which accompanying anions and neutral ligands coordi-
nate the metal ions
Cu2ðCH3COOÞ4 ꢂ 2H2O þ 4L þ ð2n ꢀ 2ÞH2O
! 2ð½CuL2ðCH3COOÞ ꢃ ꢂ nH2OÞ ðn ¼ 0; 2; 4Þ
PdðC6H5CNÞ Cl2 þ 2L þ2nC2H5OH
2
! PdL2Cl2 ꢂ nC2H5OH þ 2C6H5CN ðn ¼ 0; 2Þ
PdðC6H5CNÞ Cl2 þ 2L2 þ 2H2O
! PdðL2Þ 2Cl2 ꢂ 2H2O þ 2C6H5CN
2
However, distinctive feature of N-(2-hydroxyben-
zyl)aminopyridines is their low coordinating ability. We
have attempted to obtain complexes with other metal ions
such as Co(II), Ni(II), Mn(II), etc., but because of instabil-
ity of these compounds, we could not succeed in their iso-
lation in pure state.
N-(2-Hydroxybenzyl)aminopyridines have three elec-
tron donating atoms (NNO): pyridinic nitrogen, secondary
amine nitrogen and phenolate oxygen. During complexa-
tion, aromatic hydroxyl and also secondary amine NH
can be deprotonated to give mono and dianionic ligands.
Pyridinic nitrogen can also participate in the coordination
of metal. Thus, complexation behaviour of ligands
depends on the reaction conditions as well as the kind of
the metal.
In alkaline solutions, N-(2-hydroxybenzyl)-2-aminopyri-
dine behave as tridentate ligand, as in the Ru-complex, in
which secondary amino NH also deprotonates to make
the ligand dianionic tridentate [19]. However, in acetone
solution of the reactants, as in the formation of Re-com-
plex, the secondary amino NH group has not been depro-
tonated, pyridinic nitrogen does not coordinate the metal
and consequently the ligand acts as a monoanionic diden-
tate chelate [20].
In Cu(II) complex of L1 (Fig. 1), hindering the Cu(II)
ion from phenolate coordination via the formation of Cu,
H eight membered two cycles through hydrogen bonding
between acetate oxygen and secondary amine NH, may
be an additional but minor reason. High yields (around
90%) of the acetatoCu(II) complexes of neutral ligands
support this reaction pathway. The complexes
[Cu(L2)2(CH3COO)2] Æ 2H2O and [Cu(L3)2(CH3COO)2] Æ
4H2O have similar structure with [Cu(L1)2(CH3COO)2],
but apparently without Me, H cycles.
In similar way, Pd(II) complexes are obtained in aque-
ous ethanol (90%) via the attack of pyridinic nitrogen
to substitute benzonitrile ligand of Pd(C6H5–CN)2Cl2.
N-(2-hydroxybenzyl)-aminopyridines yield light yellow

B. Yalc¸ın et al. / Polyhedron 26 (2007) 3301–3309
3309
complexes in compositions of [Pd(L1)2Cl2] Æ 2C2H5OH,
[Pd(L2)2Cl2] Æ 2H2O and [Pd(L3)2Cl2]. XRD data of
[Pd(L1)2Cl2] Æ 2C2H5OH indicate coordination through
pyridinic nitrogen. [Pd(L1)2Cl2] Æ 2C2H5OH with slightly
distorted square planar coordination of Pd(II) ion is
realized by two nitrogen atoms of pyridine rings and two
chlorine atoms in trans-position. Similar spectroscopic data
have been obtained for the other complexes.
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These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or
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