Monomer and cyclic tetramer of copper(II) complexes: Synthesis, characterization and crystal structure determination of [Cu(dm4bt)Cl(Hipht)] and [{Cu(dm4bt)(H2O)(ipht)}4·2H2O]

Article abstract of DOI:10.1016/j.poly.2010.05.007

Copper complexes, [Cu(dm4bt)Cl(Hipht)] (1) and [{Cu(dm4bt)(H ₂O)(ipht)}₄·2H₂O] (2) (where dm4bt is 2,2′-dimethyl-4,4′-bithiazole, Hipht is hydrogen isophthalate and ipht is isophthalate) have been synthesized. These two complexes were characterized by IR, UV?Vis and EPR spectroscopy. Moreover; their single- crystal structures were studied by the X-ray diffraction method. Complex 1 has a monomer structure and copper has accepted a distorted square pyramidal structure. Isophthalic acid in 1 lost one of its protons and produced one bidentate carboxylate and one free carboxylic acid. Controlled deprotonation in the presence of ethylene diamine results in self-assemblies of 1 to form a tetramer complex of 2. Complex 2 has two kinds of spatial isomers which are resolved by EPR and X-ray.

Full text of DOI:10.1016/j.poly.2010.05.007

Polyhedron 29 (2010) 2409–2416
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Monomer and cyclic tetramer of copper(II) complexes: Synthesis, characterization
and crystal structure determination of [Cu(dm4bt)Cl(Hipht)]
and [{Cu(dm4bt)(H2O)(ipht)}4ꢀ2H2O]
b
a
a
Radhiya Al-Hashemi a, Nasser Safari a, , Saeid Amani , Vahid Amani , Hamid Reza Khavasi
*
a Department of Chemistry, Shahid Beheshti University, G.C., Evin, Tehran 1983963113, Iran
b Department of Chemistry, Arak University, Dr. Beheshti Ave., Arak 38156, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Copper complexes, [Cu(dm4bt)Cl(Hipht)] (1) and [{Cu(dm4bt)(H2O)(ipht)}4ꢀ2H2O] (2) (where dm4bt is
2,20-dimethyl-4,40-bithiazole, Hipht is hydrogen isophthalate and ipht is isophthalate) have been synthe-
sized. These two complexes were characterized by IR, UV–Vis and EPR spectroscopy. Moreover; their sin-
gle-crystal structures were studied by the X-ray diffraction method. Complex 1 has a monomer structure
and copper has accepted a distorted square pyramidal structure. Isophthalic acid in 1 lost one of its pro-
tons and produced one bidentate carboxylate and one free carboxylic acid. Controlled deprotonation in
the presence of ethylene diamine results in self-assemblies of 1 to form a tetramer complex of 2. Complex
2 has two kinds of spatial isomers which are resolved by EPR and X-ray.
Received 13 March 2010
Accepted 11 May 2010
Available online 1 June 2010
Keywords:
Copper
2,20-Dimethyl-4,40-bithiazole
Isophthalic acid
Monomer
Ó 2010 Elsevier Ltd. All rights reserved.
Cyclic tetramer
Crystal structure
1. Introduction
methyl-2,20-bipyridine [24] and 4,7-diphenyl-1,10-phenanthroline
[25]. The coordination environment of Cu(II) with phthalate and
Self-assembly formations involving metal ions and organic
ligands of suitable geometry to build multi-component molecular
architectures has attracted intense interest; this is due to fascinat-
ing structural topologies, bioinorganic modeling, materials chemis-
try and catalysis [1–6]. In these regards, complexes of copper
carboxylate with nitrogen donor ligands were found to exhibit a
variety of pharmacological activities, super oxide dismutase activ-
ities and cytogenetic effects [7,8].
bidentate nitrogen donor ligands are common with five coordina-
tion numbers that consisted of two oxygen’s from half phthalate,
two nitrogen’s from bidentate nitrogen donor and one oxygen from
a water molecule [20–23]. In addition, some of them were four
coordinated consisting of two oxygen from half phthalate and
two nitrogen from bidentate nitrogen donor number [20,23].
Therefore, most Cu(II) phthalate complexes reported are polymers
[15,19–24].
Bithiazole moiety is part of the C terminus of bleomycins, which
plays an important role in the interaction with DNA [9]. This has
simulated coordination chemistry of bithiazole derivates [10–14].
On the other hand isophthalic acid (m-benzenedicarboxylic acid)
is a potential mono/bidentate, bridging ligand. Bis or monodentate
and combined mono and bis dentate, result in monomer, oligomer
or polymer formations. Furthermore the mode of coordination of
phthalic acids can be controlled by adjusting the pH or basicity
in the solution in order to reach special topology [15,16].
Furthermore, phthalate coordination formed chains or grids
structures with one, two or three dimensions [15,17–25] with
different bidentate nitrogen donor ligands such as 4,40-bipyridine
[15,19], 2,20-bipyridine [20], 1,10-phenanthroline [20–23], 4,40-di-
In addition, recently we reported the synthesis and crystal
structure of two copper complexes; monomer and polymer with
terephthalic acid (1,4-benzenedicarboxylic acid), H2tpht [26].
Herein we synthesized monomer and tetramer with isophthalic
acid. In these cases terephthalate and isophthalate are worked as
spacer ligands, one with the tendency to form a polymer and the
other a cyclic oligomer compound.
Taking advantage of the ability of both isophthalate ligand and
bithiazole moiety, we synthesize and characterize two new Cu(II)
complexes. One complex is a monomer, although monomer of
copper(II) containing carboxylate are quite limited [27]. The other
complex is self-assembled to form a diamond shape tetramer
with two pairs of distinct copper(II) ions in its structure. Both
complexes have bithiazole and isophthalate ligand which their
topologies were contorted by the presence of an ethylene diamine
base.
* Corresponding author. Tel.: +98 21 29902886; fax: +98 21 2243166.
E-mail address: n-safari@cc.sbu.ac.ir (N. Safari).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.05.007

2410
R. Al-Hashemi et al. / Polyhedron 29 (2010) 2409–2416
for another 20 min and 4 ml ethylene diamine (0.30 M in methanol
2. Experimental
2.1. Materials and instruments
solution, 0.40 mmol) was gradually added drop by drop until the
precipitation had completely dissolved. The resulting violet solu-
tion was stirred at (45–50) °C for 1 h; and the reaction vessel
was left aside. After one month, light blue crystals of 2 were iso-
lated (yield 0.10 g, 76.5%, m.p. 240 °C). Selected IR frequencies
(cmꢁ1) are reported in Table 1. UV–Vis kmax: 3.54 ꢂ 104 cmꢁ1. Anal.
Calc. for C64H60Cu4N8O22S8ꢀ2(H2O): C, 42.57; H, 3.32; N, 6.21.
Found: C, 42.41; H, 3.26; N, 6.14%.
All chemicals were purchased from Merck and Aldrich. Infrared
spectra (4000–250 cmꢁ1) of solid samples were taken as 1% disper-
sion in CsI pellets using a Shimadzu-470 spectrometer. UV–Vis
spectra were recorded on a Shimadzu 2100 spectrometer using a
1 cm path length cell. X-band EPR spectra were measured on an
IBM electron spin resonance (ESR) spectrometer using DPPH
(g = 2.0036) as a standard in methanol at room and liquid nitrogen
temperature. Melting point is uncorrected and was obtained by a
Kofler Heizbank Rechart type 7841 melting point apparatus. Ele-
mental analysis was performed using a Heraeus CHN-O Rapid
analyzer.
2.4. Crystal structure determination and refinement
TheX-ray diffractionmeasurements were madeona STOE IPDS-II
diffractometer with graphite monochromated Mo Ka radiation. For
1, a light green prismatic crystal of 0.22 ꢂ 0.20 ꢂ 0.12 mm and for
2, a light blue block crystal of 0.30 ꢂ 0.28 ꢂ 0.24 mm were mounted
on a glass fiber and used for data collection. Cell constants and an ori-
entation matrix for data collection were obtained by least-squares
refinement of diffraction data from 4456 for 1 and 20 429 for 2 un-
ique reflections. Data were collected at a temperature of 120(2) K
to a maximum 2h value of 58.32° for 1 and 298(2) K to a maximum
2.2. Synthesis of [Cu(dm4bt)Cl(Hipht)] (1)
Isophthalic acid (0.05 g, 0.29 mmol) was dissolved in a mixture
of 1 ml methanol, 1 ml water and 1 ml ethylene diamine (0.30 M in
methanol solution, 0.30 mmol). Then CuCl2ꢀ2H2O (0.05 g,
0.29 mmol) was added to the solution and the reaction mixture
was stirred. After 30 min 2,20-dimethyl-4,40-bithiazole (0.06 g,
0.30 mmol) was added to the stirred solution while precipitation
was formed. The precipitate disappeared after adding gradually
10 ml of water to the reaction vessel. The resulting bluish- green
solution was stirred at (40–45) °C for another half an hour and then
the vessel was left aside. After 1 month, light green crystals of 1
were isolated (yield 0.09 g, 67.4%, m.p. 290–292 °C). Selected IR
2h value of 58.58° for 2 in a series of
integrated using the STOE X-AREA [28] software package. The numerical
absorption coefficient, , for Mo K
radiation is 1.647 mmꢁ1 for 1
x scans in 1° oscillations and
l
a
and 1.535 mmꢁ1 for 2. A numerical absorption correction was ap-
plied using X-RED [29] and X-SHAPE [30] software. The data were cor-
rected for Lorentz and Polarizing effects. The structures were
solved by direct methods [31] and subsequent difference Fourier
maps and then refined on F2 by a full-matrix least-squares procedure
using anisotropic displacement parameters [31]. All of the hydrogen
atoms instead of OH and water hydrogen’s were positioned geomet-
rically, with C–H = 0.93 and 0.96 Å for aromatic and methyl H,
respectively, and constrained to ride on their parent atoms with Ui-
so(H) = 1.2Ueq(C). Subsequent refinement then converged with R fac-
tors and parameter errors significantly better than all attempts to
model the solvent disorder. Atomic factors are from the Interna-
tional Tables for X-ray Crystallography [32]. All refinements were
performed using the X-STEP32 crystallographic software package
[33]. A summary of the crystal data, experimental details and refine-
ment results are given in Table 2.
frequencies (cmꢁ1
) are reported in Table 1. UV–Vis kmax:
3.64 ꢂ 104 cmꢁ1. Anal. Calc. for C16H13ClCuN2O4S2: C, 41.70; H,
2.82; N, 6.08. Found: C, 41.57; H, 2.76; N, 6.01%.
2.3. Synthesis of [{Cu(dm4bt)(H2O)(ipht)}4ꢀ2H2O] (2)
Isophthalic acid (0.05 g, 0.29 mmol) was dissolved in a mixture
of 1 ml methanol, 1 ml water and 1 ml ethylene diamine (0.30 M in
methanol solution, 0.30 mmol). The solution was then stirred for
10 min until all acid dissolved completely. To the stirred solution;
solid CuCl2ꢀ2H2O (0.05 g, 0.29 mmol) was added and left to stir
until the copper salt had completely dissolved. When 2,20-di-
methyl-4,40-bithiazole (0.06 g, 0.30 mmol) was added to the reac-
tion mixture precipitation was formed. The solution was stirred
3. Results and discussion
3.1. Synthesis of 1 and 2
Table 1
Selected IR frequencies (cmꢁ1) for complexes 1 and 2.
Compound 1 was obtained from the reaction of 1 equiv. of
CuCl2ꢀ2H2O with 1 equiv. of 2,20-dimethyl-4,40-bithiazole, 1 equiv.
of isophthalic (1,3-benzenedicarboxylic) acid (H2ipht) and 1 equiv.
ethylene diamine in a mixture of methanol and water at (40–45) °C
during 30 min. Compound 1 is a monomer complex and one car-
boxylate group arm in isophthalic was not deprotonated at
pH ꢃ 3.80. However, removal of the remaining proton by increas-
ing the amount of the ethylene diamine base to pH ꢃ 8.28 results
in getting 2. Therefore, compounds 1 and 2 were prepared with
the appropriate ratio of the ethylene diamine with the same start-
ing materials. Yields of 67.4% for 1 and 76.5% for 2 were obtained. It
seems control of pH in these reactions is crucial for self-assembling
going form obtained monomer to oligomer or maybe polymer, as
shown in Scheme 1.
dm4bt
H2ipht
1
2
m
(C–H)cycle
3450,
3124,
3043
3017
1541
1507
1471
1158
881
3079,
3006
3078m,
3059m
3106br,
2970w
m
m
m
m
m
m
m
m
(C–H)Me
(C@C)
(C@N)
(C–C)
(C–N)
(S–C)
(Cu–N)
as(COO)un-ionized/un-coor
2904br
1606m
1513m
1485w
1154m
886m
2925w
1608s
1550s
1482w
1161m
887w
1582
1452
380w
375w
1698,
1486
1423,
1327,
1298
1706s,
1534m
1449m,
1374m,
1295m
3443br
1704w,
1571s
1424s,
1380s,
1358s
ms(COO)
m(O–H)
3089br
m
(O–H2)
3623m,
3455br
540br
3.2. Spectroscopic characterization of 1 and 2
m
(Cu–Opht
(Cu–OW
(Cu–Cl)terminal
)
)
582br
273m
Infrared spectra in Table 1 show the vibration frequencies for
free and coordinated dm4bt and H2ipht ligands in compounds 1
and 2. The IR frequencies are shifted to higher frequencies upon
m
473m
m

R. Al-Hashemi et al. / Polyhedron 29 (2010) 2409–2416
2411
show the strong bands corresponding to
m
as(COO) at 1534 cmꢁ1
Table 2
Crystallographic and structure refinements data for complexes 1 and 2.
for complex 1 and 1571 cmꢁ1 for complex 2; while,
m
s(COO) at
1449 cmꢁ1 and 1374 cmꢁ1 for complex 1 and 1424–1358 cmꢁ1
for complex 2. The ‘‘ criterion” which is based on the difference
in the as(COO) and s(COO) value of isophthalic acid carboxylate
group, was employed to determine the coordinating mode of the
carboxylate group [8,45,46]. The
are 85 cmꢁ1 and 160 cmꢁ1
for complex 1. These values are comparable to those of biden-
Complex
1
2
D
Formula
C
16H13ClCuN2O4S2 C64H60Cu4N8O22S8
m
m
Formula weight
T (K)
460.42
120(2)
1803.96
298(2)
k (Å)
0.71073
0.71073
D
m
Crystal system
Space group
Crystal size (mm3)
a (Å)
b (Å)
c (Å)
triclinic
P1
triclinic
P1
D
m
ꢀ
ꢀ
tate (chelating) complexes [19,40]. On the other hand, since the Dm
0.22 ꢂ 0.20 ꢂ 0.12 0.30 ꢂ 0.28 ꢂ 0.24
values for complex 2 are 147, 191 and 213 cmꢁ1; the ligand in this
complex appears to be unidentate [17,18,40,46]. This is also consis-
tent with the crystal structural analysis.
7.6885(7)
9.0443(8)
13.9613(12)
104.701(7)
96.323(7)
106.189(7)
884.55(14)
2
7.4202(6)
13.2494(11)
17.9548(14)
92.549(7)
98.564(6)
95.568(6)
1734.2(2)
1
a
(°)
In addition, complex 1 showed a very broad band for m(O–H)
b (°)
stretching at 3443 cmꢁ1 confirming the presence of one terminal
carboxylate group which is not coordinated [19,46]. Complex 2
also showed different narrow and broad absorption at 3623 and
3455 cmꢁ1 which confirm the presence of free and coordinated
water molecules in the complex [17,18].
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ3
)
1.729
1.727
h Ranges for data collection
F(0 0 0)
2.46–29.16
466
1.87–29.29
920
UV–Vis spectra were taken in the 200–900 nm range in DMSO
for both complexes. The intense band at higher energy near-UV re-
gion, 3.64 ꢂ 104 cmꢁ1 for complex 1 and 3.54 ꢂ 104 cmꢁ1 for com-
Absorption coefficient
Index ranges
1.647
1.535
ꢁ10 6 h 6 10
ꢁ11 6 k 6 12
ꢁ18 6 l 6 19
8827
4456 (0.0380)
241, 0
0.0385, 0.0938
0.0435, 0.0977
1.058
ꢁ10 6 h 6 9
ꢁ18 6 k 6 18
ꢁ24 6 l 6 24
9308
20 429 (0.0482)
502, 0
0.0420, 0.1089
0.0520, 0.1163
1.098
0.626, ꢁ0.913
plex 2, which are in agreement with absorption at about
Data collected
3.85 ꢂ 104 cmꢁ1 are assigned to intra-ligand
p
to
p
transitions
*
Unique data (Rint
)
of bithiazole. The visible region also contain broad with very low
Parameters, restrains
a
intensity absorbance at 1.25 ꢂ 104 cmꢁ1 for complex
1 and
Final R1, wR2 (observed data)
a
1.34 ꢂ 104 cmꢁ1 for complex 2, which are assigned to d–d transi-
Final R1, wR2 (all data)
Goodness of fit on F2 (S)
tion [8,47,48].
Largest difference in peak and hole 0.987, ꢁ0.725
(e Åꢁ3
)
EPR spectra of both complexes as powder and frozen solution
were recorded in X-band frequencies at room and liquid nitrogen
temperatures to provide evidence for the ground-state configura-
tion of copper(II) ions. In the solid state, the spectra were similar
and appear to be EPR silent, with only a weak and broad signal
(gave. = 2.06). Such behavior is also found in the literatures
[49,50]. The observed frozen solution (77 K) EPR spectra in metha-
P
P
2
2
1=2
|Fo|, wR2 ¼ ½ ðwðF2o ꢁ Fc2Þ Þ= wðFo2Þ ꢄ
.
a
R1
=
R
||Fo| ꢁ |Fc||/
R
coordination. Similar shifts have been observed for bipyridine and
other ligands coordinated to metals as well [15,34–37] and can be
explained by changing the geometry of the free ligand from syn to
anti orientation in the coordinated one.
nol of complex 1; Fig 1(A), show two bands located at g = 2.28 and
k
The IR spectra of 1 and 2 are distinguished from dm4bt mainly
g\ = 2.09 (2876 and 3080 gauss for
t = 8.880 GHz) and for complex
by the metal to ligand stretches. The band at 380 and 387 cmꢁ1
2; Fig 1(B), g = 2.33 and g\ = 2.07 (22 750 and 3090 gauss for
k
were assigned to the
tively [38]. The band at 273 cmꢁ1 was assigned to
plex 1 [39–43]. The band at 582 and 540 cmꢁ1 were assigned to
(Cu–Opht) in complexes 1 and 2, respectively. The band at
473 cmꢁ1 was assigned to
(Cu–OW) in complex 2 [40].
m
(Cu–Nthiazol) frequencies for 1 and 2, respec-
t
= 8.882 GHz) corresponding to the transition
DMS = 1. These
m(Cu–Cl) in com-
typical features for copper (II) complexes with g > g\ > 2.0023
k
and a large parallel hyperfine splitting, associate with dx
ground
2ꢁy2
m
state in distorted octahedral or square-pyramidal geometry [51–
53].
m
IR spectra of 1 and 2 distinguish the coordination modes of iso-
phthalic acid molecules; Table 1. Complex 1 showed a very strong
band at 1706 cmꢁ1 which is related to the un-ionized COOH group
[44], while this band is very weak at 1704 cmꢁ1 for complex 2,
indicating the loss of the carboxylic protons to form COOꢁ group
[40]. Therefore, in compound 1 one carboxylic acid in isophthalic
acids is intact while the other is in the form of deprotonated car-
boxylate. Finally, in compound 2 the totally deprotonated form of
isophthalate is used which results in a polynuclear structure.
Moreover, each complex showed an antisymmetric and sym-
metric ionized or coordinated (COO) group. The two complexes
In the spectrum of complexes 1 and 2, the parallel region is
clearly resolved and all four transitions derived from the Cu
(I = 3/2) hyperfine splitting can be directly observed. These hyper-
fine lines for complex 1 are on the g signal with spacing ranging
k
from 169 ꢂ 10ꢁ4 cmꢁ1 to 175 ꢂ 10ꢁ4 cmꢁ1 and an average spacing
of 168 ꢂ 10ꢁ4 cmꢁ1 [54,55]. The hyperfine lines for complex 2 start
from 141 ꢂ 10ꢁ4 cmꢁ1 to 187 ꢂ 10ꢁ4 cmꢁ1 and an average spacing
of 157 ꢂ 10ꢁ4 cmꢁ1. Two kinds of hyperfine coupling in the parallel
region indicate two different copper (II) ions in each molecule. This
is in agreement with the X-ray data. Four copper (II) ions in the tet-
ramer have two different geometries which provide two different
s
Scheme 1.

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R. Al-Hashemi et al. / Polyhedron 29 (2010) 2409–2416
Fig. 1. EPR spectra of 1 (trace A) and 2 (trace B) at solution liquid temperature.
factors in this region. While in the perpendicular region of both
complexes, the spectrum is not well resolved, some superhyperfine
structure is observed.
The peak–peak width of the derivative spectrum suggests a va-
lue of about 13 ꢂ 10ꢁ4 cmꢁ1 for AN\. The lack of clear resolution in
this spectral region is presumably due to the large number of over-
3.3. Description of the molecular structures of 1 and 2
Five-coordination Cu(II) species with different ligands are al-
most invariably distorted from regular trigonal bipyramidal
(TBP), D3h or square pyramidal (SP), C4v symmetry. This involves
a coupling between the electronic and vibration wave functions
that lowers the ground-state energy [58].
lapping
DMI = 0 and DMI > 0 transitions and to the large intrinsic
widths of the individual transitions. The structure observed in
the perpendicular region of the spectra is due to nitrogen superhy-
perfine splitting from the ligands. The AN\ value ꢅ 13 ꢂ 10ꢁ4 cmꢁ1
and the presence of three weak resolved peaks for the nitrogen
superhyperfine structure for both complexes agrees with two N
donors per copper(II) ions [56,57].
ORTEP views of 1 and 2 are shown in Figs. 2 and 3, respectively.
Selected bond lengths and angles are listed in Table 3. The struc-
ture of 1 consists of a Cu atom surrounded by one dm4bt, one
hydrogen isophthalate (Hipt) and one chloride. In this structure,
the basal plane is made up of two thiazoline nitrogen atoms and
two carboxylate oxygen atoms. The apical site is occupied by the

R. Al-Hashemi et al. / Polyhedron 29 (2010) 2409–2416
2413
chloride atom. Cu–N distances around 1.99 Å and Cu–O distances
around 2.02 Å. The Cu–Cl bond distance is 2.50 Å in the longer
range of Cu–Cl normal bond distances (Cu–Cl bond distances usu-
ally of 2.29–2.34 Å are seen for five coordination copper complexes
[59]) possibly due to the Jahn–Teller effect. In addition, the angle
O(1)(2)–Cu(1)–Cl(1) and N(2)–Cu(1)–Cl(1) are around 97° while
the angle of N(2)–Cu(1)–Cl(1) is around 99°. Therefore, the geom-
etry around copper can be described as a distorted square-pyrami-
an usual chelate ligand with typical Cu–N distances and a charac-
teristic N–Cu–N chelating angle.
Tetramer 2 has two independent copper atoms Cu(1) and Cu(2).
Both geometries consist of a centered Cu(II) ion which is coordi-
nated to one dm4bt, two different isophthalate ligands and one
water molecule. In each Cu(II) geometry: dm4bt ligands and water
molecules are set in the opposite direction. Isophthalate links Cu
atoms with monodentate mode in Cu(1) and monodentate and
bidentate modes in Cu(2). Only half of each isophthalate belongs
to the asymmetric unit. Therefore, the coordination numbers
around copper atoms are distinguishable in a way that one copper
is five coordinated and the other is six coordinated. There are two
different coordination structures according to bond distances and
angles shown in Table 3. Cu(1) center metal and the basal plane
is made up of two thiazoline nitrogen atoms N(1), N(2), water oxy-
gen O(1) and O(9); while the apical site is occupied by another car-
boxylate oxygen atom O(2). The apical Cu(1), O2 bond is around
0.3 Å longer than Cu(1) oxygen’s of the basal plane due to Jahn–
Teller effects. Cu(2) center metal and the basal plane is made up
of one thiazoline nitrogen atom N(3), O(5), water oxygen O(6)
and O(8); while the apical sites are occupied by another dm4bt
nitrogen atom N(4) and O(4). This N(4) distance from Cu(2) is again
around 0.3 Å longer than Cu(2)–N(3) and O(4) distance from Cu(2)
is around 0.7 Å longer than Cu(2) oxygen’s of the basal plane. The
long Cu–O4 bond distance that suggest strong Jahn–Teller distor-
tion in the Cu(2) ions, is 2.67 Å; comparable to those found in pre-
viously reported for copper(II) complexes [20,47,48,61–64]. The
geometry around Cu(2) ions are distorted octahedral or square
pyramidal that semi-bridged to an oxygen at the other apical view
(Cu–Osemi = 2.67 Å).
dal geometry; with trigonality index
s = 0.02 (s = 0 and 1 for
perfect square-pyramidal and trigonal-bipyramidal geometries,
respectively) [60].
An interesting point in the structure of 1 is that isophthalic acid
lost one proton thus forms one carboxylate anion and one carbox-
ylic acid group. The deprotonated arm is coordinated to Cu in
bidentate fashion and the other carboxylic acid group is left free;
this prevents the formation of a dimer or polymer structure. How-
ever, connection between monomer units is formed by hydrogen
bonding between adjacent molecules of O–H from one unit to
the Cl of the other, as shown in Table 4 and Fig. 4.
The atomic numbering scheme and atom connectivity for 2 are
shown in Fig. 3. The tetramer unit is further held together by iso-
phthalate ligands. The resulting 3D structure of 2 is ‘‘diamond”-like
and has diameters of approximately 17.4 and 9.0 Å. Copper atoms
lie outside the cavity and are connected with each other with O
bridges from two different isophthalate in a bent fashion. Interest-
ingly, coordinated waters on neighboring Cu are suited in anti ori-
entation to each other through the cycle, Fig. 3. The dm4bt acts as
Fig. 2. Graphical representations of 1 (30% probability for the thermal ellipsoids).

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R. Al-Hashemi et al. / Polyhedron 29 (2010) 2409–2416
Fig. 3. Graphical representations of 2 (30% probability for the thermal ellipsoids).
Table 3
Therefore, there are two different coordination structures in the
Selected bond distances (Å) and bond angles (°) for complexes 1 and 2.
cyclic tetramer; distorted square pyramidal and distorted octahe-
dral geometries. Overall, this cyclic complex has C2 rotation sym-
metry dividing the complex to two parts (dimer); each part
consists of both Cu(1) and Cu(2) geometries. The two repeating
adjacent dimer units are perpendicular to each other and show a
propeller-like side view. The distances between Cu(1) and Cu(2)
are 9.5 and 10.2 Å, these distances are consistent with different
copper tetramer structures [2,3,16,44,65,66].
1
Cu(1)–Cl(1)
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–O(1)
2.498(7)
1.992(19)
1.988(2)
2.032(2)
2.019(18)
65.35(7)
82.40(8)
97.38(6)
O(1)–Cu(1)–Cl(1)
N(1)–Cu(1)–Cl(1)
N(2)–Cu(1)–Cl(1)
O(3)–C(15)–O(4)
N(1)–Cu(1)–O(2)
N(2)–Cu(1)–O(2)
N(1)–Cu(1)–O(1)
N(2)–Cu(1)–O(1)
97.23(6)
97.08(6)
99.14(6)
124.38(2)
162.82(8)
104.34(8)
103.61(8)
161.72(9)
Cu(1)–O(2)
O(2)–Cu(1)–O(1)
N(2)–Cu(1)–N(1)
O(2)–Cu(1)–Cl(1)
The distances between copper atoms are distinguished accord-
ing to two different coordination structures in the cyclic tetramer.
The distances between copper centers with same geometries are
17.4 and 9.0 Å for Cu(1)ꢀ ꢀ ꢀCu(1) and Cu(2)ꢀ ꢀ ꢀCu(2), respectively.
While, the distances between copper centers with different geom-
etries are 9.5 and 10.2 Å for Cu(1)ꢀ ꢀ ꢀCu(2). Former one is through
the cavity while the later one is through the isophthalate bridge.
There are two kinds of water molecules in this complex; one is
coordinated and other is hanging. The coordinate H2O molecules
have two kinds of hydrogen bonds: Cu(1)–H2O has double hydro-
gen bond donor toward O(3) free COO group in the parallel cycle
and O(11)W free molecule. That makes both hydrogen bond (O1–
H1Eꢀ ꢀ ꢀO3) and (O1–H1Dꢀ ꢀ ꢀO11) intermolecular interactions.
Cu(2)–H2O has double hydrogen bond donor toward O(4) semi-
bridge atom (O6–H6Bꢀ ꢀ ꢀO4) and O(7) coordinate atom (O6–
H6Cꢀ ꢀ ꢀO7) which belong to ipht in the parallel cycle, Table 4. Both
H bonds are short and strong; indeed they increase the stability of
the crystal lattice and increase its insolubility. There is one hanging
water molecule which stays in the core of the cavity, this molecule
has one H bond donor toward O(5) coordinated atom (O11–
H11Bꢀ ꢀ ꢀO5) to the parallel cycle. Overall, free water molecules
are distributed between cycles in a zigzag fashion. These hydrogen
bonds work as a net which tries to hold the cycles in parallel layers.
The crystallographic structure shows cyclic tetramers molecules
2
Cu(1)–O(1)W
Cu(1)–O(2)
Cu(1)–O(9)
Cu(1)–N(1)
Cu(1)–N(2)
N(1)–Cu(1)–O(1)
N(2)–Cu(1)–O(1)
N(1)–Cu(1)–O(2)
N(2)–Cu(1)–O(2)
N(1)–Cu(1)–O(9)
N(2)–Cu(1)–O(9)
O(1)–Cu(1)–O(2)
O(1)–Cu(1)–O(9)
N(1)–Cu(1)–N(2)
O(2)–Cu1–O(9)
Cu(2)–O(6)W
Cu(2)–O(4)
1.979(19)
2.244(2)
1.940(18)
2.038(2)
2.051(2)
172.37(9)
93.09(8)
94.57(8)
96.49(8)
95.82(9)
159.61(8)
91.62(9)
87.00(9)
81.80(9)
103.89(8)
1.9809(19)
2.670(18)
2.0192(17)
Cu(2)–O(8)
Cu(2)–N(3)
Cu(2)–N(4)
1.960(17)
2.050(2)
2.3119(19)
178.25(9)
101.30(8)
93.17(8)
89.24(7)
88.04(8)
95.51(7)
94.86(7)
142.43(8)
54.06(8)
86.80(8)
121.27(7)
175.25(8)
88.24(8)
90.63(9)
N(3)–Cu(2)–O(6)
N(4)–Cu(2)–O(6)
N(3)–Cu(2)–O(5)
N(4)–Cu(2)–O(5)
N(3)–Cu(2)–O(8)
N(4)–Cu(2)–O(8)
N(3)–Cu(2)–O(4)
N(4)–Cu(2)–O(4)
O(4)–Cu(2)–O(5)
O(4)–Cu(2)–O(6)
O(4)–Cu(2)–O(8)
O(5)–Cu(2)–O(8)
O(6)–Cu(2)–O(5)
O(6)–Cu(2)–O(8)
Cu(2)–O(5)
Symmetry transformations used to generate equivalent.
are site parallel to each other through hydrogen bonds (Table 4
and Fig. 5).
However, why do these two copper atoms have different
structures in cyclic tetramer? There are reasons: one is due to

R. Al-Hashemi et al. / Polyhedron 29 (2010) 2409–2416
2415
Table 4
the steric hindrance of dm4bt ligand which indicates a slightly
tilted orientation. Thus, the angle between the mean planes of
adjacent dm4bt ligands is 60.00(10)°. This overcomes the steric
hindrance related to other bidentate ligands. The other reason
is due to the appropriate flexible or V-shaped exo-bidentate or-
ganic bridges (ipth) could be useful in the formation of cyclic
in the presence of aromatic chelate ligand such dm4bt. In addi-
tion, the length, the geometry and the coordination environment
of the bridging ligand, as well as the size of the aromatic chelate
ligand, lead to self-organized uniquely by supramolecular recog-
nition and attractions. In contrast, the transition metals are
likely to prevent the formation of highly distorted structures
[67]. Therefore, the competition between the metal and ligands
nature arrives to a special conformational rigidity such this cyc-
lic structure.
Geometry of the hydrogen bonds of complexes 1 and 2.
Complexes D–Hꢀ ꢀ ꢀA
d(D–H)
(Å)
d(Hꢀ ꢀ ꢀA)
d(Dꢀ ꢀ ꢀA)
(D–Hꢀ ꢀ ꢀA)
(°)
(Å)
(Å)
1
2
O3–
0.86(4)
0.87(3)
1.01(4)
0.83(4)
2.15(4)
1.89(3)
1.65(4)
1.89(4)
3.002(3)
2.745(3)
2.631(3)
2.688(3)
172(5)
171(3)
163(3)
159(4)
H3ꢀ ꢀ ꢀCl1#1
O1–
H1Dꢀ ꢀ ꢀO11
O1–
H1Eꢀ ꢀ ꢀO3#2
O6–
H6Bꢀ ꢀ ꢀO4#3
O6–
0.69(5)
0.80(4)
2.01(5)
2.03(4)
3.684(3)
2.809(3)
165(6)
164(4)
H6Cꢀ ꢀ ꢀO7#4
O1–
H11Bꢀ ꢀ ꢀO5#2
Symmetry codes: #1: ꢁ1 + X, ꢁ1 + Y, Z, #2: ꢁ1 + X, Y, Z, #3: 3 ꢁ X, 2 ꢁ Y, ꢁZ, #4:
1 + X,Y,Z.
Fig. 4. Unit cell-packing diagram of the complex 1 in c-direction. Hydrogen bonds are shown as dashed lines.
Fig. 5. Unit cell-packing diagram of the complex 2. Hydrogen bonds are shown as dashed lines.

2416
R. Al-Hashemi et al. / Polyhedron 29 (2010) 2409–2416
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Coord. Chem. accepted for publication.
This work demonstrates a pH-dependent self-assembly system
which a protonated building unit and it is deprotonated oligomer
or polymer were interconverted depending on the pH. According
to this, two copper (II) complexes were synthesized from the same
substances and with the same methodology, one is monomer and
the other is a cyclic tetramer. Moreover, the cyclic tetramer builds
up from two distinct copper centers clearly resolved by EPR and X-
ray studies.
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