Synthesis and X-ray diffraction study of Zn(II) complexes with o-phthalic acid and aromatic amines

Article abstract of DOI:10.1016/S0277-5387(01)00698-2

New zinc (II) complexes [Zn(Pht)A₂], where Pht^2- = dianion of o-phthalic acid, A= pyridine (1), 3-methylpyridine (2), 4-methylpyridine (3) and [Zn(Pht)A] (A = 4-methylpyridine (4)) have been synthesised and characterised by X-ray crystallography. The compounds have polymeric structures due to 1,6-bridging ability of the o-phthalate ligand. Polymeric chains exhibit three types of organisation in the crystal. Complexes 1 and 2 have similar structures, where Zn atom is coordinated by two oxygen atoms of two carboxylate groups and two nitrogen atoms of N-containing ligands. Two independent Zn atoms in 3 have different environments: tetrahedral N₂O₂ and distorted square-pyramidal N₂O₃. One of the acid residues behaves as bidentate 1,6-bridge, while the other acts as tridentate (1,6-bridging and 1,3-chelating) ligand. One of the Zn atoms in 4 has a tetrahedral NO₃ geometry, while the second is characterised by a distorted octahedral NO₅ coordination polyhedron. Both phthalate anions are tetradentate and act as syn-syn, syn-anti and monoatomic Zn-O-Zn bridging ligands. The IR spectra are discussed in relation to the crystal structures.

Full text of DOI:10.1016/S0277-5387(01)00698-2

Polyhedron 20 (2001) 831–837
www.elsevier.nl/locate/poly
Synthesis and X-ray diffraction study of Zn(II) complexes with
o-phthalic acid and aromatic aminesꢀ
Svetlana G. Baca a,*, Yurii A. Simonov b, Nicolae V. Gerbeleu a, Maria Gdaniec c,
Paulina N. Bourosh b, Grigore A. Timco a
a Institute of Chemistry, Academy of Sciences of RM, Academiei str. 3, MD-2028 Chisinau, Moldo6a
b Institute of Applied Physics, Academy of Sciences of RM, Academiei str. 5, MD-2028 Chisinau, Moldo6a
c Faculty of Chemistry, A. Mickiewicz Uni6ersity, Grunwaldzka str. 6, 60-780 Poznan, Poland
Received 24 March 2000; accepted 21 August 2000
Abstract
New zinc (II) complexes [Zn(Pht)A2], where Pht2− =dianion of o-phthalic acid, A=pyridine (1), 3-methylpyridine (2),
4-methylpyridine (3) and [Zn(Pht)A] (A=4-methylpyridine (4)) have been synthesised and characterised by X-ray crystallography.
The compounds have polymeric structures due to 1,6-bridging ability of the o-phthalate ligand. Polymeric chains exhibit three
types of organisation in the crystal. Complexes 1 and 2 have similar structures, where Zn atom is coordinated by two oxygen
atoms of two carboxylate groups and two nitrogen atoms of N-containing ligands. Two independent Zn atoms in 3 have different
environments: tetrahedral N2O2 and distorted square-pyramidal N2O3. One of the acid residues behaves as bidentate 1,6-bridge,
while the other acts as tridentate (1,6-bridging and 1,3-chelating) ligand. One of the Zn atoms in 4 has a tetrahedral NO3
geometry, while the second is characterised by a distorted octahedral NO5 coordination polyhedron. Both phthalate anions are
tetradentate and act as syn–syn, syn–anti and monoatomic Zn–O–Zn bridging ligands. The IR spectra are discussed in relation
to the crystal structures. © 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Zinc(II) complexes; Zinc(II) carboxylates; Phthalate complexes; Crystal structures
1. Introduction
We have recently reported the crystal structures of
copper(II) complexes with o-phthalic acid (H2Pht) [4,5].
These complexes revealed the monodentate as well as
chelating and bridging bonding modes. Other metal
complexes with phthalate ligands are also available
[6–23]. However, data on zinc(II) phthalate complexes
containing amines have not been reported yet (CSD
version 5.19 [24]).
Herein we report on the synthesis and X-ray diffrac-
tion study of zinc(II) complexes [Zn(Pht)A2] and [Zn-
(Pht)A], where A=pyridine, 3-, 4-methylpyridine (b-,
g-Pic).
The versatility of carboxylic acids as ligands and the
extraordinary reach binding facilities of carboxylate
groups are responsible for the existence of a huge
number of metal carboxylates. Carboxylate groups are
capable of binding a metal in either a monodentate,
bidentate or bridging mode leading to both mono- and
polynuclear molecular and polymeric structures [1–3].
Dicarboxylic acids have additional coordination abili-
ties for the formation of new types of polymers and
oligomers, which can considerably influence the mag-
netic, optical or catalytic properties of the ultimate
product.
2. Experimental
ꢀ This article was presented at the Second Contemporary Inorganic
Chemistry Conference (CIC-II) held at Texas A&M University, Col-
lege Station, TX, USA, on March 12–15, 2000.
* Corresponding author. Tel.: +373-2-725490; fax: +373-2-
739954.
2.1. General
Commercial starting materials were used without fur-
ther purification. The carbon, hydrogen and nitrogen
E-mail address: sbaca@mail.md (S.G. Baca).
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(01)00698-2

832
S.G. Baca et al. / Polyhedron 20 (2001) 831–837
contents were determined by standard micro-methods.
The zinc content was determined gravimetrically as
ZnO. Fourier transform infrared spectroscopy on KBr
pellets was performed on a Perkin–Elmer 1725 X FT-
IR instrument.
2.5. Synthesis of [Zn(Pht)(k-Pic)] (4)
To a solution of o-phthalic acid (3.4 g, 20 mmol) and
4-methylpyridine (4 cm3) in water (30 cm3) was added a
solution of Zn(O2CMe)2·2H2O (4.4 g, 20 mmol) in
water (20 cm3) at 70°C. The mixture was stirred and
refluxed for 30 min. After cooling to room temperature
the precipitated crystals were collected by filtration,
washed with water, ethanol and dried in air. Yield:
54%. Calc. for C14H11NO4Zn: C, 52.11; H, 3.44; N,
4.34; Zn, 20.27. Found: C, 52.16; H, 3.55; N, 4.31; Zn,
20.19%.
2.2. Synthesis of [Zn(Pht)Py2] (1)
Zinc(II) carbonate (1.25 g, 10 mmol) was added to a
solution of o-phthalic acid (4.98 g, 30 mmol) and
pyridine (10 cm3) in water (40 cm3) at 70°C. The
resulting mixture was stirred and heated for 30 min.
After cooling to room temperature the colourless crys-
tals were filtered off, washed several times with water,
ethanol and dried in air. Yield: 71%. Calc. for
C18H14N2O4Zn: C, 55.75; H, 3.64; N, 7.22; Zn, 16.86.
Found: C, 55.87; H, 3.64; N, 7.38; Zn, 16.94%.
Slow evaporation of the mother liquors of 1–4 af-
forded colourless crystals suitable for X-ray diffraction
analyses.
2.6. X-ray diffraction measurements
2.3. Synthesis of [Zn(Pht)(i-Pic)2] (2)
Experimental data were collected on a KUMA
KM4CCD s-axis diffractometer with graphite
monochromated Mo Ka radiation at 293 K for 1 and 3,
and at 180 and 150 K for 2 and 4, respectively. The
crystals were positioned at 60 mm from the KM4CCD
camera. 532 frames (in 4 runs) were measured, each for
45, 40, 20 and 24 s over 0.75 degree scan for 1–4,
respectively. The data were processed using the KUMA
Diffraction (Wroclaw, Poland) program. Crystal data,
details of data collection and refinement of the crystal
structures 1–4 are given in Table 1. The structures were
solved by direct methods (SHELXS-97 [25]) and refined
To a solution of o-phthalic acid (1.7 g, 10 mmol) and
3-methylpyridine (5 cm3) in water (40 cm3) was added a
solution of Zn(O2CMe)2·2H2O (2.2 g, 10 mmol) in
water (10 cm3). The crystalline product, precipitated
after 30 min, was filtered off, washed with water,
ethanol, ether and dried in air. Yield: 89%. Calc. for
C20H18N2O4Zn: C, 57.78; H, 4.36; N, 6.74; Zn, 15.28.
Found: C, 57.73; H, 4.36; N, 6.52; Zn, 15.44%.
2.4. Synthesis of [Zn(Pht)(k-Pic)2] (3)
This compound was synthesised analogously to the
complex 2 by using 4-methylpyridine as aromatic
amine. Yield: 65%. Calc. for C20H18N2O4Zn: C, 57.78;
H, 4.36; N, 6.74; Zn, 15.28. Found: C, 57.50; H, 4.39;
N, 6.82; Zn, 15.89%.
on F2
(SHELXL-97 [26]) in anisotropic approach for
non-hydrogen atoms. The hydrogen atoms were calcu-
lated and allowed to ride with isotropic displacement
parameters fixed at 1.2×Ueq. The methyl groups in 2
have been found disordered over two positions with the
Table 1
Crystal data and details of data collection for 1–4
1
2
3
4
Formula
Crystal system
Space group
C
18H14N2O4Zn
C20H18N2O4Zn
monoclinic
P21/c
C40H36N4O8Zn2
monoclinic
P21
C28H22N2O8Zn2
monoclinic
Cc
orthorhombic
Pbca
,
a (A)
15.730(3)
12.380(2)
17.650(4)
90
8.447(2)
17.659(4)
13.498(3)
104.64(3)
10.096(2)
15.848(3)
11.814(2)
92.61(3)
7.4220(10)
20.462(4)
17.865(4)
,
b (A)
,
c (A)
i (°)
100.67(3)
Z
8
4
2
4
Crystal size (mm)
0.05×0.05×0.4
3.12–25.04
13365/2285
2285/0/226
1.073
R1=0.0570,
wR2=0.1345
R1=0.1044,
wR2=0.1547
0.862 and −0.288
0.1×0.2×0.4
2.75–29.71
12812/4992
4992/0/249
1.120
R1=0.0443,
wR2=0.1181
R1=0.0585,
wR2=0.1269
0.969 and −0.631
0.6×0.35×0.15
3.45–29.26
11644/8658
8658/1/487
1.051
R1=0.0501,
wR2=0.1416
R1=0.0699,
wR2=0.1538
0.792 and −0.595
0.01×0.07×0.035
3.37–29.24
8574/4203
4203/2/361
0.810
R1=0.0385,
wR2=0.0904
R1=0.0751,
wR2=0.1024
0.720 and −0.431
q Range for data collection (°)
Reflections collected/unique
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I\2|(I)]
R indices (all data)
−3
,
Largest difference peak and hole (e A
)

S.G. Baca et al. / Polyhedron 20 (2001) 831–837
833
Table 2
,
Selected bond distances (A) and bond angles (°) for 1–4
a
1
2 a
3 b
4 c
Bond lengths
Zn(1)–O(4)c
Zn(1)–O(1)
Zn(1)–N(1a)
Zn(1)–N(1b)
1.965(5)
1.987(5)
2.073(5)
2.064(6)
1.929(2)
1.970(2)
2.070(2)
2.032(2)
Zn(1)–O(4b)c
Zn(1)–O(1a)
Zn(1)–N(21)
Zn(1)–N(11)
Zn(2)–O(1b)
Zn(2)–N(31)
Zn(2)–O(4a)
Zn(2)–N(41)
Zn(2)–O(3a)
1.921(3)
1.990(3)
2.046(4)
2.072(4)
1.940(4)
2.044(4)
2.047(4)
2.075(4)
2.405(4)
Zn(1)–O(4b)c1
Zn(1)–O(4a)c1
Zn(1)–N(1a)
Zn(1)–O(1a)
Zn(2)–N(1b)
Zn(2)–O(2b)
Zn(2)–O(1a)
1.945(3)
1.949(3)
2.002(4)
2.031(3)
2.072(4)
2.102(4)
2.100(3)
2.121(3)
2.158(3)
2.240(3)
Zn(2)–O(3b)c1
Zn(2)–O(3a)
Zn(2)–O(1b)
Bond angles
O(4)c–Zn(1)–O(1)
O(4)c–Zn(1)–N(1b)
O(1)–Zn(1)–N(1b)
O(4)c–Zn(1)–N(1a)
O(1)–Zn(1)–N(1a)
N(1b)–Zn(1)–N(1a)
141.7(2)
108.7(2)
95.5(2)
92.7(2)
110.0(2)
104.3(2)
109.02(7)
123.78(9)
110.66(9)
110.94(8)
97.54(8)
O(4b)c–Zn(1)–O(1a)
O(4b)c–Zn(1)–N(21)
O(1a)–Zn(1)–N(21)
O(4b)c–Zn(1)–N(11)
O(1a)–Zn(1)–N(11)
N(21)–Zn(1)–N(11)
O(4a)–Zn(2)–O(3a)
N(41)–Zn(2)–O(3a)
O(1b)–Zn(2)–N(31)
O(1b)–Zn(2)–O(4a)
N(31)–Zn(2)–O(4a)
O(1b)–Zn(2)–N(41)
N(31)–Zn(2)–N(41)
O(4a)–Zn(2)–N(41)
O(1b)–Zn(2)–O(3a)
N(31)–Zn(2)–O(3a)
110.66(16)
124.62(17)
110.03(15)
106.04(15)
100.04(16)
102.07(16)
57.11(14)
150.31(15)
127.64(18)
113.95(18)
109.19(18)
102.90(17)
102.72(16)
93.37(16)
88.30(16)
91.25(16)
O(4b)c–Zn(1)–O(4a)c
O(4b)c–Zn(1)–N(1a)
O(4a)c–Zn(1)–N(1a)
O(4b)c–Zn(1)–O(1a)
O(4a)c–Zn(1)–O(1a)
N(1a)–Zn(1)–O(1a)
N(1b)–Zn(2)–O(2b)
N(1b)–Zn(2)–O(1a)
O(2b)–Zn(2)–O(1a)
N(1b)–Zn(2)–O(3b)c
O(2b)–Zn(2)–O(3b)c
O(1a)–Zn(2)–O(3b)c
N(1b)–Zn(2)–O(3a)
O(2b)–Zn(2)–O(3a)
O(1a)–Zn(2)–O(3a)
O(3b)c–Zn(2)–O(3a)
N(1b)–Zn(2)–O(1b)
O(2b)–Zn(2)–O(1b)
O(1a)–Zn(2)–O(1b)
O(3b)c–Zn(2)–O(1b)
O(a)–Zn(2)–O(1b)
105.46(15)
103.99(16)
119.97(16)
96.46(15)
99.64(14)
127.27(15)
147.63(15)
96.75(16)
115.07(14)
98.24(15)
89.37(14)
87.44(13)
87.91(14)
89.88(13)
83.47(12)
169.57(13)
87.69(14)
61.15(13)
173.57(13)
87.32(14)
101.40(12)
101.54(9)
a Symmetry transformations used to generate equivalent atoms: for 1 c −x+1/2, y−1/2, z; for 2 c x, −y+1/2, z−1/2.
b Symmetry transformations used to generate equivalent atoms: c x, y, z−1.
c Symmetry transformations used to generate equivalent atoms: c x+1, y, z.
occupancy factors 0.69 (C(10b)) and 0.31 (C(10c)). Se-
lected bond distances and angles are listed in Table 2.
pyridines. As a consequence, compounds 1–4 belong to
three different structural types.
3.1.1. Compounds 1 and 2
Fig. 1(a) and (b) show a view of the fragment of the
polymeric chain [Zn(Pht)A2]ꢀ. Phtalate ligand acts as
1,6-bridging (I) in both structures. The same picture is
seen in the dimer [Fe2(TPA)2O(Pth)](ClO4)2·MeOH·
H2O [31], in the catena-aqua(1,10-phenanthroline)(m-
phthalato)copper(II) hemihydrate [32], catena-(m-phtha-
lato)bis(oxamideoxime)nickel(II) tetrahydrate [33] and
[Cu2(Pht)2(g-Pic)4H2O] [4]. In both 1 and 2 the phtha-
late ligand is coordinated by one of the oxygen atoms
of each of its carboxylate groups to the neighbouring
Zn atom. The Zn···Zn distance is 6.645(1) and 6.896(2)
3. Results and discussion
3.1. Crystal structures
It is worth noting the coordination mode of phtha-
late ligand, which exhibits a great variety of bonding
geometries such as monodentate [27], 1,3-chelating [6]
and 1,6-chelating [11,28–30], including various bridging
modes [7–12,31–37]. In complexes 1–4 the bridging
modes of phthalate coordination have been revealed,
which favour the formation of polymeric structures.
The compounds differ by the stoichiometric ratio metal:
acid: heterocyclic amine, which is 1:1:2 for 1–3 and
1:1:1 for 4, and by geometric peculiarities of substituted
,
A, respectively, for 1 and 2. Each Zn atom is in a
tetrahedral donor atom environment, which comprises
two nitrogen atoms of two pyridine molecules (3-
methylpyridine for 2) and two oxygen atoms of two

834
S.G. Baca et al. / Polyhedron 20 (2001) 831–837
Pht2− ligands. The Zn–N and Zn–O distances in the
coordination polyhedron of 1 and 2 are correspond-
2 (Zn–N 2.046(4) and 2.072(4) A, Zn–O 1.921(3) and
,
,
1.990(3) A), while bond angles differ significantly
,
ingly at 2.064(6), 2.073(5) and 1.965(5), 1.987(5) A, and
(Table 2). In the coordination polyhedron of Zn(2) the
Zn–O distances are longer compared to those in Zn(1)
tetrahedron (Zn–N 2.044(4) and 2.075(4) A, Zn–O
1.940(4), 2.047(4) and 2.405(4) A). The most distorted
angle in Zn(2) polyhedron is O(3a)Zn(2)O(4a) at
57.1(1)°, what is common for the carboxylate groups
coordinated in a 1,3-chelating manner, as found in a
number of 3d metal complexes, as for example,
,
2.032(2), 2.070(2) and 1.929(2), 1.970(2) A.
,
,
3.1.2. Compound 3
In 3 the polymeric chain is arranged along the c-axis
(Fig. 2(a) and (b)). Two adjacent zinc atoms in the
polymeric chain differ by their coordination geometry.
Zn(1) atom has a tetrahedral environment of N2O2
type, while Zn(2) atom is surrounded by the N2O3 set
of donor atoms, which form a distorted square-pyramid
(Table 2). One Pht2− ligand acts as bidentate 1,6-bridg-
ing (I), while the other behaves both as 1,6-bridging
and 1,3-chelating being coordinated to zinc atoms as is
shown by structure representation II.
[Cu(HPht)2Py2],
[Cu(HPht)2(g-Pic)2]
[4]
and
[Cu(Pht)Py2] [15].
3.1.3. Compound 4
Fig. 3(a) and (b) shows views of crystallographically
independent structure fragment and a part of the poly-
meric chain of 4. The chain includes two independent
Zn atoms with different coordination geometries. Zn(1)
is tetrahedral (NO3), while Zn(2) environment ap-
proaches to a distorted tetragonal bipyramid (NO5). In
the Zn(1) coordination core Zn(1)–N bond is at
,
2.002(4) A, whereas Zn(1)–O distances are at 1.945(3),
,
1.949(3) and 2.031(3) A, bond angles ranging from
96.5(2) to 147.63(2)°. The distances between Zn(2) and
surrounding donor atoms are increased dramatically
(Zn(2)–N=2.072(4), Zn(2)–O ranging from 2.100(3)
The bridging mode of phthalate coordination de-
picted by structures I and II does not significantly
influence the Zn···Zn distances which are at 6.358(2)
,
to 2.240(3) A. Bond angles deviate considerably from
90° (Table 2).
,
and 6.405(3) A in 3. The interatomic distances in Zn(1)
tetrahedral core are very close to those found in 1 and
Generally both phthalate ligands behave as 1,6-bridg-
ing ones (III and IV) in 4.
Fig. 1. (a) Polymeric chain in compound 1. (b) Polymeric chain in compound 2.

S.G. Baca et al. / Polyhedron 20 (2001) 831–837
835
Note, however, that these bridging phthalate groups
link two symmetry related zinc atoms (Zn(1) and
Zn(1)*, Zn(2) and Zn(2)* as displayed in Fig. 3(b). In
addition, there are bridges of different type between
nonequivalent Zn atoms. Zn(1) and Zn(2) atoms being
,
3.470(2) A from each other are bridged by the O(1a)
atom of the phthalate ligand a, with the corresponding
angle at O(1a) at 114.3(2)°. We also note that both Zn
atoms are linked by the bridging bidentate carboxylate
group, which adopts a syn–syn arrangement b. Such
behaviour is typical for the acetate ion and its deriva-
tives [38–41] and has been established for binuclear
copper(II) [42] and zinc(II) compounds [43–45]. The
second carboxylate group of the ligand (b) bind the
metal in 1,3-chelate manner. Another pair of Zn(1) and
,
Zn(2) atoms being at 3.467(2) A from each other is
bound to the Pht(b) ligand via syn–anti bridge (Fig.
3(b)). The formation of the seven-membered metallocy-
cle on coordination of Pht(a) to Zn(2) has also been
found in [11,28–30] and is a distinctive feature of
compound 4.
The phthalate ligand shows a high degree of self-or-
ganisation upon complex formation. Dihedral angles
between the carboxylate groups and aromatic rings
range from 12.5(3) to 101.3(3)°. Delocalisation of p
electron density over the carboxylate groups is ob-
served, which is typical for the deprotonated RCOO−
fragments. The C–O distances range from 1.223(9) to
1.233(8) (1), 1.230(3) to 1.288(3) (2), 1.202(6) to
,
1.299(6) (3) and 1.225(6) to 1.305(6) A (4). In 3 and 4
the redistribution of electon density occurs over both
chelating and bridging carboxylate groups. The C(sp2)–
,
COO distances ranging from 1.496(6) to 1.528(6) A can
be considered as single bonds. The mean C–C distances
in the aromatic rings are 1.382 (1), 1.390 (2), 1.383 (3)
Fig. 2. (a) Crystallographically independent structure fragment in
compound 3 with a numbering scheme. (b) Polymeric chain in
compound 3.
,
and 1.394 A (4).
Fig. 3. (a) Crystallographically independent structure fragment in compound 4 with a numbering scheme. (b) Polymeric chain in compound 4.

836
S.G. Baca et al. / Polyhedron 20 (2001) 831–837
The composition of 1–4 and full deprotonation of
case of amine deficient (1:1:1) complex the phthalate
ligand coordination capacity increases up to 4, display-
ing additional bridging facilities. Carboxylate groups
adopt different arrangements: syn–syn, syn–anti,
monoatomic Zn–O–Zn bridging. We consider the 1,6-
bridging mode as the most favoured for the transition
metal coordination with o-phthalic acid.
both carboxylate groups in o-phthalic acid makes im-
possible the formation of hydrogen bonds. Van der
Waals and weak C–H···O contacts are the only interac-
tions between the chains. The latter is also a source of
an additional binding within the polymeric chains. The
C–H···O contacts resemble those reported in Ref. [46].
In 1 (Fig. 1(a)) we mention the C(9a)–H···O(2) contact
,
with C···O=3.298 and O···H=2.59 A. Between the
chains two similar interactions were found: C(35)–
5. Supplementary data
,
H···O(3)=3.346, H···O(3)=2.52
H···O(3)=3.472, H···O(3)=2.54 A. In 2 a contact of
the same type has also been found (C(8a)–H···O(1)=
A
and C(6a)–
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 140711 (1), 140712 (2),
140713 (3), 140714 (4). Copies of this information may
be obtained from The Director, CCDC, 12 Union
Road, Cambridge, CB2 1EZ, UK (fax: +44-1233-
336033; e-mail: deposit@ccdc.cam.ac.uk or www: http:/
/www.ccdc.cam.ac.uk). Structure factors for 1–4 are
available from the authors on request.
,
,
3.341 and H···O(1)=2.39 A). Intermolecular contacts
H···O ranging from 2.23 to 2.54 A are also present in 3
,
and 4.
3.2. Spectroscopic properties
Complexes 1 and 2 have similar structures and their
spectra show broad wasym(CO2) absorptions at 1618 and
1567 cm−1 (with shoulders at 1590 and 1539 cm−1
)
References
and 1622 and 1590 cm−1, respectively, which can be
attributed to monodentate phthalate bridges [2,3,47].
The wasym(CO2) bands in 3 are slightly red shifted
relative to those in 1 and 2 (1610 and 1560 cm−1). The
symmetric CO2 stretching vibrations appear as a strong
band correspondingly at 1390, 1372 and 1388 cm−1 in
the spectra of 1–3. The IR spectrum of 4 shows several
bands in the wasym(CO2) and wsym(CO2) region at 1636,
1610, 1584, 1556 cm−1 and 1409, 1374 cm−1, respec-
tively. The absorptions at lower frequencies (1610–1556
cm−1) can be attributed to deformation vibrations of
the chelating and bridging carboxylate groups. Such
absorptions have already been reported for copper(II)
complexes with o-phthalic acid and aromatic amines
(1620–1520 cm−1) [4,5] and a number of other car-
boxylate bridged compounds [3]. The Dw values related
to the frequency differences between each wasym(CO2)
and wsym(CO2) at 1409 cm−1, range from 201 to 147
cm−1. The band at 1636 cm−1 can be assigned to
wasym(CO2) of the monodentate phthalate bridge (Zn–
O–Zn). Analogous assignment has been proposed for
other zinc carboxylate complexes containing the same
bridge (1630–1620 cm−1) [48]. Because of the non-
equivalence of the two oxygen atoms, a large Dw value
at 296 cm−1 is observed.
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