Dinuclear copper(II) complexes with different bridging connectors

Article abstract of DOI:10.1016/S0022-2860(03)00080-2

One novel triply-bridged dicopper(II) complex formulated as [Cu₂(dpa)₂(μ-Cl)(μ-OH)(μ-HCOO)] ·(ClO₄) 1 and two terephthalate anions bridged 2,2′-bipyridine (2,2′-bpy) dicopper(II) complexes with formulae of [Cu₂(

Full text of DOI:10.1016/S0022-2860(03)00080-2

Journal of Molecular Structure 649 (2003) 269–278
www.elsevier.com/locate/molstruc
Dinuclear copper(II) complexes with different bridging connectors
a
W. Huang , D. Hu , S. Gou , H. Qian , H.-K. Fun , S.S.S. Raj , Q. Meng
a
a,
b
c
c
a
*
aState Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, People’s Republic of China.
bCollege of Science, Nanjing University of Technology, Nanjing 210009, People’s Republic of China
cX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
Received 23 October 2002; accepted 20 January 2003
Abstract
One novel triply-bridged dicopper(II) complex formulated as [Cu2(dpa)2(m-Cl)(m-OH)(m-HCOO)]·(ClO4) 1 and two
terephthalate anions bridged 2,20-bipyridine (2,20-bpy) dicopper(II) complexes with formulae of [Cu2(2,20-bpy)4(m-
terephthalate)]·(NO3)2 2 and [Cu2(2,20-bpy)4(m-terephthalate)]·(terephthalate) 3, respectively, have been synthesized and
characterized by infrared and electrospray mass spectra as well as X-ray single-crystal determination. In addition, thermal
properties of all compounds have been studied.
q 2003 Elsevier Science B.V. All rights reserved.
Keywords: Copper complexes; dinuclear complexes; crystal structures
1. Introduction
coordination bonding as well as weak surpramolecu-
lar interactions [1–8]. Among these ligands, rigid bi-
functional linear ligands and tri-functional tripodal
ligands such as two or three pyridine-based bridging
ligands have been actively utilized as construction
units to obtain lots of supramolecular arrays with
certain metal ion connectors [9–12]. In addition,
transition metals with specific coordination geome-
tries have also been employed for the rational design
and construction of highly ordered structures. Fur-
thermore, the weak forces such as hydrogen bonding,
van der Walls forces, p–p interactions, and dipole–
dipole interactions are very common in constructing
these supramolecular systems.
Over the past two decades the use of transition
metal centers and coordination chemistry for directing
the high-yielding formation of complexes has gener-
ated one of the most widely used strategies for
organizing molecular building blocks into supramo-
lecular arrays. More and more supramolecular
coordination complexes with a wide range of sizes
and shapes have been prepared by this directional-
bonding approach due to their interesting topologic
structures and possible functions. The assembly of
well-designed ligands with metal ions possessing
certain coordination geometry has led to the gener-
ation of diversiform 1D, 2D and 3D networks via
In our recent study, we have designed and prepared
a few of bi-terminal tetradentate ligands containing
2,20-dipyridylamine (dpa) units, attempting to obtain
supramolecular compounds or ordered coordination
*
Corresponding author. Tel.: þ86-25-359-5068; fax: þ86-25-
331-4502.
E-mail address: sgou@netra.nju.edu.cn (S. Gou).
0022-2860/03/$ - see front matter q 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-2860(03)00080-2

270
W. Huang et al. / Journal of Molecular Structure 649 (2003) 269–278
polymers via self-assembly with transition metal ions.
It is known to us now that when N,N0-bis(2,20-
dipyridyl)isophthaloylamide is used to react with
copper(II) ions, a copper(II) complex formulated as
[Cu(dpa)2]·(ClO4)2 could be found as the major
product, which suggests that the amide C–N bonds
of the ligand which are longer than the normal value
have been broken [13]. But what will happen when
N,N0-bis(2,20-dipyridyl)trimesoylamide is assembled
with copper(II) ions. Once again, instead of an
expected supramolecular framework, a dinuclear
copper(II) complex with free dpa molecules which
come from the amide C–N bonds decomposition of
the N,N0-bis(2,20-dipyridyl)trimesoylamide has
proved to be yielded. In this paper, we report the
syntheses and the crystal structures of three dinuclear
copper(II) complexes by assembling CuII ions with bi-
or multi-dentate ligands containing N- or O-donors,
namely, one novel triply-bridged complex formulated
as [Cu2(dpa)2(m-Cl)(m-OH)(m-HCOO)]·(ClO4) 1, and
two terephthalate anions bridged 2,20-bipyridine (2,20-
bpy) dicopper(II) complexes with the formulae of
Caution: Although no problem was encountered in
all our experiments, transition metal perchlorates are
potentially explosive and should be handled in small
quantities.
2.2. Synthesis of complex 1
The syntheses of the ligand and its CuII complex 1
are shown in scheme 1. Trimesoyl chloride (1.03 g,
4 mmol) and 2,20-dipyridylamine (2.00 g, 12 mmol)
were dissolved in 80 cm3 dry DMF and stirred at
70 8C for one day, and the same amount of water was
added, then the solution was condensed to nearly dry
under reduced pressure. The residue was washed by
40 cm3 hot acetonitrile, and then the colorless crystals
came into being when the filtrate was cooled in an ice
bath. Finally the precipitate was collected and dried in
a vacuum to obtain N,N0-bis(2,20-dipyridyl)trimesoy-
lamide. Anal Calc for C39H27N9O3·H2O C: 68.11; H:
4.25; N: 18.33. Found: C: 68.32; H: 4.34; N: 18.61.
FT-IR: n[cm21]: 3353, 1666, 1602, 1560, 1506, 1482,
1453, 1248, 843 and 777.
[Cu2(2,20-bpy)4(m-terephthalate)]·(NO3)2
2
and
The resulting colorless crystals obtained above
(0.67 g, 1 mmol) and CuCl2·2H2O (0.17 g, 1 mmol)
were dissolved in CH3CN–C2H5OH (40 cm3), and
the mixture was refluxed for 1 h, then an ethanol
solution (10 cm3) of sodium perchlorate (0.12 g
1 mmol) was added dropwise. A deep green precipi-
tate formed immediately, which was filtered off,
washed with a small amount of ethanol, and dried in a
vacuum. The single crystal sample suitable for X-ray
diffraction measurements was grown from the mixed
solution of CH3CN/DMF (1:1) by slow evaporation at
room temperature. Anal. Calc for the green crystals
C21H20Cl2N6O7Cu2 (1): C, 37.85; H, 3.02; N, 12.61.
Found: C, 37.62; H, 3.21; N, 12.89. FT-IR data for the
green crystals: n [cm21]: 3296, 3207, 3141, 1634,
1585, 1525, 1477, 1432, 1383, 1230, 1157, 1118,
1083, 776 and 625. Es-ms: m=z 297 (100%),
[Cu(dpa)(m-HCOO)(H2O)]þ.
[Cu2(2,20-bpy)4(m-terephthalate)]·(terephthalate) 3,
respectively.
2. Experimental section
2.1. Materials and measurements
2,20-Bipyridine, terephthalic acid, trimesoyl chlor-
ide and 2,20-dipyridylamine were purchased as
commercial chemicals from Aldrich. All other
solvents and reagents were of analytical grade and
used without further purification. [Cu(2,20-
bpy)](NO3)2·3H2O was prepared by a literature
method [14].
Analyses for carbon, hydrogen and nitrogen were
performed on a Perkin-Elmer 1400C analyzer.
Infrared spectra (4000–400 cm21) were recorded
with a Nicolet FT-IR 170X spectrophotometer on
KBr disks. Electrospray (ES) ionization mass spectra
were recorded on a Finnigan MAT SSQ 710 mass
spectrometer in a scan range of 100–1200 amu. TGA-
DTA data were recorded by a CA Instrument DTA-
TGA 2960 type simultaneous analyzer in nitrogen
atmosphere.
2.3. Synthesis of complex 2
An aqueous solution of NaOH (0.08 g, 2 mmol)
and terephthalate acid (0.17 g, 1 mmol) was added to
the solution of [Cu(202-bpy)](NO3)2·3H2O (0.40 g,
1 mmol) in 20 cm3 ethanol (scheme 2). The liquid
immediately became dark blue, and the mixture was

W. Huang et al. / Journal of Molecular Structure 649 (2003) 269–278
271
Scheme 1. Synthesis of the ligand and its CuII complex 1.
Scheme 2. The synthetic routes for copper(II) complexes 2 and 3.

272
W. Huang et al. / Journal of Molecular Structure 649 (2003) 269–278
refluxed for 2 h, blue micro-crystals precipitated,
which were filtered out and dried in a vacuum. Single
crystals suitable for X-ray crystallography were
grown from the aqueous solution of 2. Anal Calc for
C48H40N10O12Cu2 C: 53.58; H: 3.75; N: 13.02.
Found: C: 53.42; H: 3.98; N: 13.29. FT-IR: n
[cm21]: 1688, 1616, 1604, 1593 and 1397. Es-ms:
m=z 190 (100%), [Cu(202-bpy)2]2þ/2.
and 3 is listed in Table 1, selected bond distances and
bond angles are given in Table 2. Further details are
provided in supporting information.
3. Results and discussion
3.1. Synthesis and spectral characterization
2.4. Synthesis of complex 3
In the process of preparing N,N0-bis(2,20-dipyr-
idyl)trimesoylamide ligand, the results of the micro-
analytical and the IR spectral data (a sharp CyO
stretching vibration band assigned to the amide group
at 1666 cm21 and the signals corresponding to the dpa
units and the benzene group) suggest that the expected
ligand has been yielded. But the elemental analyses of
complex 1 show that it is not an expected product. The
IR spectral data indicate that dpa molecules still exist
but the sharp CyO stretching vibration band has
disappeared compared with those of the ligand. In
addition, complex 1 is characterized by perchlorate
Complex 3 was prepared in the same way as 2
except that the molar ratio of sodium terephthalate salt
to [Cu(202-bpy)](NO3)2·3H2O was 2:1, namely,
NaOH (0.16 g, 4 mmol) and terephthalate acid
(0.34 g, 2 mmol) dissolved in 40 cm3 water were
added to the solution of [Cu(202-bpy)](NO3)2·3H2O
(0.40 g, 1 mmol) in 20 cm3 ethanol. Anal Calc for
C56H68N8O22Cu2 C: 50.49; H: 5.14; N: 8.41. Found:
C: 50.22; H: 5.08; N: 8.59. FT-IR: n [cm21]: 1688,
1614, 1604, 1592 1400. Es-ms: m=z 190 (100%),
[Cu(202-bpy)2]2þ/2. Green single crystals of 2 and 3
suitable for X-ray determination were developed from
their DMF (2) and water (3) solutions, respectively,
which were slowly evaporated at room temperature.
absorptions at 1118, 1083 and 625 cm21
.
As mentioned above, when Cu(ClO4)2·6H2O was
reacted directly with such a kind of ligands, only
[Cu(dpa)2]·(ClO4)2 could be obtained because of the
cleavage of imide C–N bond, but at this time
CuCl2·2H2O was used for comparison. As the X-ray
crystal structural study shown, the imide C–N bonds
of the ligand are broken and a triply-bridged dinuclear
copper(II) perchlorate complex with three kinds of
different bidentate bridging ligands (a chloride anion,
a hydroxy anion and a formate anion) [Cu2(dpa)2(m-
Cl)(m-OH)(m-HCOO)]·(ClO4) 1 has been yielded. It
is believed that chloride and perchlorate anions are
derived from the addition of CuCl2·2H2O and
NaClO4, respectively, and the hydroxy anions may
arise from the ionization of water molecules in
solution. Up till now, we could not specify certainly
where formate anions come from, but there have been
many reports in literature about metal-catalyzed (Cu,
Zn, Co, Fe, Ru, et al.) hydrogenation of carbon
dioxide to formic acids [18–21]. It is assumed that
formate anions in 1 could be resulted from the
catalytic reduction of copper(II) ions to carbon
dioxide in atmosphere absorbed by mother liquor
during the formation of single crystals. The IR
frequencies of the antisymmetric and symmetric O–
C–O stretching modes of the coordinated formate ion
2.5. Crystal structure determination
As crystals of 1, 2 and 3 are unstable in the absence
of their mother liquors, these single crystal samples
were glue-covered for measurements. Reflection data
for 1, 2 and 3 crystals were measured on a Bruker
SMART 1 K CCD diffractometer at 293(2) K using
graphite mono-chromated Mo Ka radiation
˚
(l ¼ 0.71073 A) at a detector distance of 4 cm and
swing angle of 2358. The collected data were reduced
by using the program SAINT [15] and empirical
absorption correction was done by using the SADABS
[16] program. Both structures were solved by direct
methods and refined by least squares method on Fo2bs
by using the SHELXTL-PC [17] software package,
with 3142 of 8728 (1), 3947 of 4722 (2) and 5508 of
8216 (3) [I . 2sðIÞ] unique absorption corrected
reflections, respectively. All non-H atoms were
anisotropically refined; other hydrogen atoms were
geometrically fixed and allowed to ride on the
attached atoms. The summary of the crystal data,
experimental details and refinement results for 1, 2

W. Huang et al. / Journal of Molecular Structure 649 (2003) 269–278
273
Table 1
Crystal and structure refinemental data for 1, 2 and 3
Compound
1
2
3
Empirical formula
Formula weight
Crystal size (mm)
Crystal system
Space group
C
21H22‘Cl2Cu2N6O8
C48H40Cu2N10O12
1075.98
C56H68Cu2N8O22
1332.26
684.43
0.46 £ 0.36 £ 0.22
0.65 £ 0.60 £ 0.40
Triclinic
0.20 £ 0.20 £ 0.30
Triclinic
P-1
Orthorhombic
Cmc21
P-1
˚
a; A
˚
b; A
˚
c; A
16.8109(3)
9.578(3)
10.432(2)
11.767(2)
14.278(2)
92.160(10)
106.300(10)
106.960(10)
1595.4(5)
1, 1.387
694
7.78600(10)
10.819(5)
12.030(6)
77.33(4)
19.31540(10)
a; deg
b; deg
g; deg
90
90
68.46(3)
90
89.98(3)
3
˚
V,A
2528.19(6)
1126.9(9)
1, 1.586
Z; Dcalcd; (Mg/m3)
4, 1.798
Fð000Þ
1384
552
m; M mm21
Temperature (K)
1.954
1.023
0.747
293(2)
293(2)
293(2)
h
min=hmax
min=kmax
min=lmax
222/13
210/10
21/11
212/12
210/12
213/13
k
l
225/24
8728/3142
213/14
4722/3947
331
216/12
8216/5508
397
Refl. collected/unique
Parameters
191
Max./min. transmissions
Final R indices [I . 2sðIÞ]
R indices (all data)
Goodness-of-fit on F2
0.6731/0.4668
R1 ¼ 0:0405; wR2 ¼ 0:1016
R1 ¼ 0:0435; wR2 ¼ 0:1030
1.020
0.6728/0.5193
R1 ¼ 0:0747; wR2 ¼ 0:1834
R1 ¼ 0:1112; wR2 ¼ 0:2087
1.047
0.861/0.836
R1 ¼ 0:0521; wR2 ¼ 0:1476
R1 ¼ 0:0573; wR2 ¼ 0:1508
1.080
23
˚
Max./min., Dr (e A
)
0.550/ 2 0.583
0.852/ 2 1.399
0.703/ 2 0.457
in 1 are assigned at na (CO2) ¼ 1585 cm21 and ns
(CO2) ¼ 1383 cm21, respectively. The separation
between them (D) is 202 cm21. Deacon and Phillips
[22] have reported that for bidentate carboxylates the
value is similar to, or less than, that found in the free
formate, taken as those for the sodium
spectral data of 2 and 3 reveals different products, but
their ES-MS spectral results are analogous, so it is
necessary for us to determine their crystal structures to
specify how they are arranged. Contrary to our
expectation, the X-ray diffraction structures of 2 and
3 are only five-coordinated dinuclear copper(II)
complexes in which two 2,20-bpy molecules are
bonded to each metal atom.
(D ¼ 241 cm21) [23] or potassium (D ¼ 233 cm21
)
[24] salts. Furthermore, a vibration of d (OCO) mode
at 776 cm21 has also been observed. Thus it is
suggested that what is observed experimentally for
complex 1 in this case has proved the existence of
bidentate formate bridging groups.
3.2. Crystal structure of [Cu2(dpa)2(m-Cl)(m-OH)
(m-HCOO)]·(ClO4) 1
[Cu(2,20-bpy)](NO3)2·3H2O is often used to gen-
erate coordinating polymers and supramolecular
compounds [25–27], in which two coordinating
sites of its copper(II) ions have been preoccupied by
2,20-bpy which serves as a shape-defining unit [28]. In
our experiments, equal or double molar ratios of
sodium terephthalate to [Cu(2,20-bpy)](NO3)2·3H2O
are performed to yield dissimilar infinite supramole-
cular arrays. The outcome of microanalytical and IR
An X-ray crystal structural study indicated that
compound 1 consists of discrete dimeric copper(II)
cations countered by a hydroxy anion, a chloride
anion, a formate anion and an independent perchlorate
anion (Fig. 1). The coordination environment around
each Cu(II) atom is five-coordinated distorted pyr-
imidal. A dpa molecule occupies two coordinating
positions of each copper atom and three different
ligands, i.e. a chloride anion, a hydroxy anion and

274
W. Huang et al. / Journal of Molecular Structure 649 (2003) 269–278
Table 2
˚
Selected bond lengths (A) and angles(8) for complexes 1, 2 and 3
1
2
3
Cu(1)–O(2)
Cu(1)–N(2)
Cu(1)–N(1)
Cu(1)–O(1)
Cu(1)–Cl(1)
O(1)–C(11)
1.913(2)
1.972(3)
2.024(3)
2.160(2)
2.4788(11)
1.256(3)
Cu(1)–N(1)
Cu(1)–O(1)
Cu(1)–N(3)
Cu(1)–N(2)
Cu(1)–N(4)
O(1)–C(21)
O(2)–C(21)
C(22)–C(24)a
1.993(5)
1.995(4)
2.007(5)
2.010(5)
2.198(5)
1.256(8)
1.230(8)
1.383(9)
Cu(1)–O(1)
Cu(1)–N(4)
Cu(1)–N(1)
Cu(1)–N(3)
Cu(1)–N(2)
C(4)–O(2)
C(4)–O(1)
C(28)–O(3)
C(28)–O(4)
1.980(2)
1.993(2)
2.017(2)
2.036(2)
2.199(2)
1.263(3)
1.271(4)
1.253(5)
1.254(5)
O(2)–Cu(1)–N(2)
O(2)–Cu(1)–N(1)
N(2)–Cu(1)–N(1)
O(2)–Cu(1)–O(1)
N(2)–Cu(1)–O(1)
N(1)–Cu(1)–O(1)
O(2)–Cu(1)–Cl(1)
N(2)–Cu(1)–Cl(1)
N(1)–Cu(1)–Cl(1)
O(1)–Cu(1)–Cl(1)
C(11)–O(1)–Cu(1)
Cu(1)–Cl(1)–Cu(1A)
O(1)–C(11)–O(1A)
Cu(1)–O(2)–Cu(1A)
173.32(12)
94.40(12)
91.81(11)
87.73(11)
86.19(10)
133.82(11)
82.75(9)
N(1)–Cu(1)–O(1)
N(1)–Cu(1)–N(3)
O(1)–Cu(1)–N(3)
N(1)–Cu(1)–N(2)
O(1)–Cu(1)–N(2)
N(3)–Cu(1)–N(2)
N(1)–Cu(1)–N(4)
O(1)–Cu(1)–N(4)
N(3)–Cu(1)–N(4)
N(2)–Cu(1)–N(4)
O(2)–C(21)–O(1)
C(23)–C(22)–C(24)a
91.9(2)
174.9(2)
92.0(2)
O(1)–Cu(1)–N4
O(1)–Cu(1)–N1
N(4)–Cu(1)–N1
O(1)–Cu(1)–N3
N(4)–Cu(1)–N3
N(1)–Cu(1)–N3
O(1)–Cu(1)–N2
N(4)–Cu(1)–N2
N(1)–Cu(1)–N2
N(3)–Cu(1)–N2
O(2)–C(4)–O1
O(3)–C(28)–O4
91.59(9)
88.59(9)
177.16(9)
158.88(10)
80.78(10)
98.09(10)
103.32(9)
104.28(10)
78.42(10)
97.66(10)
123.6(3)
80.8(2)
164.49(19)
94.6(2)
104.8(2)
95.08(19)
78.1(2)
96.46(9)
118.34(9)
107.71(8)
126.9(2)
100.0(2)
125.3(6)
118.9(6)
75.33(4)
123.9(3)
126.5(4)
104.72(17)
a
2x; 2y; 2z þ 1:
Fig. 1. A perspective view of the molecular structure of the complex cation (1) with the atom-numbering scheme, hydrogen atoms and
perchlorate anions are omitted for clarity.

W. Huang et al. / Journal of Molecular Structure 649 (2003) 269–278
275
a formate anion, all serve as bidentate ligands linking
Table 3
Table3 Hydrogen bonds (A, 8) in complexes 1, 2 and 3
˚
two copper(II) ions. Two nitrogen atoms of dpa
molecules, a chlorine atom and an oxygen atom of
hydroxy group offer the base plane, and the apical
position was placed by one oxygen atom of the
formate anion. The related bonds are Cu(1)–O(1)
D–H· · ·A
D–H
H–A
D· · ·A
/DHA
1
O(2)–H(2A)· · ·O(4)a
N(3)–H(3A)· · ·O(1)b
C(1)–H(1A)· · ·O(2)c
2
0.9300 2.5640 2.9280
0.8600 2.1278 2.8582
0.9300 2.3455 2.9109
103.76
142.47
118.80
˚
˚
2.160(2) A, Cu(1)–O(2) 1.913(2) A, Cu(1)–N(1)
˚
2.024(3) A, Cu(1)–N(2) 1.972(3) A, Cu(1)–Cl(1)
˚
O(1W)–H(1A)· · ·O(2)e
C(1)–H(1A)· · ·O(1)
C(7)–H(7A)· · ·O(2)d
C(10)–H(10A)· · ·N(3)
C(12)–H(12A)· · ·O(3)e
0.7581 2.2743 2.9081
0.9300 2.4898 3.0107
0.9300 2.3885 3.1186
0.9301 2.6259 3.1379
0.9300 2.5409 3.3973
141.82
115.59
135.27
115.29
153.27
170.02
˚
2.4788(11) A and O(1)–C(11) 1.256(3) A. The two
˚
˚
copper atoms are separated only by 3.0291(6) A with
a Cu(1)–O(2)–Cu(1A) bridge angle of 104.72(17)8
and Cu(1)–Cl(1)–Cu(1A) angle of 75.33(4)8. The
related angle of bridged formate anions are C(11)–
O(1)–Cu(1) 126.9(2)8 and O(1)–C(11)–O(1A)
126.5(4)8. Two pyridine rings of each dpa molecule
are nearly at the same plane, and the dihedral angle of
them is 6.98.
Hathaway has pointed out that triply-bridged
dimeric complexes are unusual in copper(II) chem-
istry [29], up till now there are several triply-bridged
copper(II) dimers reported. An early case is a
Cs3[Cu2Cl2(H2O)2] compound where three chloride
anions act as bridging connectors linking two
C(17)–H(17A)· · ·O(1A)f 0.9301 2.3957 3.3156
3
C(5)–H(5)· · ·O(2)
0.9304 2.5815 3.178(4) 122.36
0.9297 2.5410 3.365(5) 147.85
0.9306 2.5134 3.379(6) 154.75
0.9298 2.4078 3.324(3) 168.26
0.9295 2.4860 3.362(6) 157.12
0.9309 2.5218 2.997(4) 111.95
C(6)–H(6)· · ·O(12)g
C(15)–H(15)· · ·O(14)h
C(21)–H(21)· · ·O(2)i
C(23)–H(23)· · ·O(13)
C(24)–H(24)· · ·O(1)
a
1=2 2 x; 1=2 2 y; 21=2 þ z:
1=2 2 x; 21=2 þ y; z:
1=2 þ x; 1=2 2 y; 21=2 þ z:
2x; 1 2 y; 1 2 z:
b
c
e
d
f
1 2 x; 1 2 y; 1 2 z:
x; 21 þ y; 1 þ z:
˚
copper(II) ions with a Cu· · ·Cu separation of 3.45 A
g
h
i
21 þ x; y; z:
[30]. Recent examples are a [Cu2(dpa)2(m-OH)2(m-
H2O)]Cl2·2H2O complex containing two hydroxy
anions and one water molecule bridging two cop-
1 2 x; 1 2 y; 1 2 z:
x; 21 þ y; z:
˚
˚
per(II) ions which are separated by 2.799(1) A [31],
between adjacent pyridine rings is ca. 3.58 A. Under
the assistance of these above-mentioned weak inter-
actions, a two-dimensional network has been formed
(Fig. 3).
and a [Cu2(dpa)2(m-OMe)2(m-Cl)]Cl·MeOH complex
synthesized in anhydrous condition in which two
OMe2 and one Cl2 anions serve as bridging ligands
˚
with a Cu· · ·Cu distance of 2.792(2) A [32]. But
3.3. Crystal structures of [Cu2(2,20-bpy)4(m-
terephthalate)]·(NO3)2 2 and [Cu2(2,20-bpy)4(m-
terephthalate)]·(terephthalate) 3
dimeric copper(II) complex triply-bridged by three
different bridging ligands in our case is unique.
In the crystal packing of molecule 1 exists N–
H· · ·O type H-bonding interactions between two
oxygen atoms of each formate anion and two N–H
units in dpa molecules of neighboring bimetallic units
˚
(2.8582 A, 142.478) (Table 3). There are also O–
H· · ·O typed H-bonds between one oxygen atom of
perchlorate anion and the hydroxy group with the
The structure of 2 is made up of dinuclear cations
with two copper(II) centers bridged by terephthalic
dianions, coordinated in a monodentate fashion to
Cu(1) and Cu(1A), through the oxygen atoms of their
carboxylic groups, two NO23 anions and two water
molecules (Fig. 2).
˚
length of 2.9280 A and in an angle of 103.768.
Furthermore, weak C–H· · ·O kind hydrogen bonding
interactions have been observed between the hydroxy
anion and a-positioned hydrogen of pyridine rings,
The geometry of each copper(II) ion may be
described as a trigonal bipyramid with N(2), O(1) and
N(4) in the basal plane and N(1) and N(3) in axial
˚
˚
positions. The Cu ion deviates only by 0.0196 A from
such C–H· · ·O H-bonds are 2.9109 A, 118.808. In
addition, pyridine rings of complex 1 are all packed in
a parallel fashion via p–p interactions. The distance
the basal plane, and the trigonal axis does not show
too much deviation from linearity, N(1)–Cu(1)–N(3)

276
W. Huang et al. / Journal of Molecular Structure 649 (2003) 269–278
Fig. 2. Molecular structure of the complex cation (2) with the atom-numbering scheme, hydrogen atoms are omitted for clarity.
˚
vary from 1.994–2.198 A.
being 174.98. However, the angles in the basal plane
depart significantly from the theoretical 1208 value,
with values of 100, 164.5, and 95.18.
The Cu–Cu distance inside the same dinuclear unit
˚
is 11.027 A. The shortest Cu–Cu distance, equal to
It is worthwhile to point out, as listed in Table 2,
the existence of a hydrogen bond between the oxygen
atom O(3) of the carboxylic group and the carbon
atom C(12) of the 2,20-bpy. The distance between
˚
6.883 A, involves metal ions belonging to two
˚
C(12)–O(3) is 3.3973 A and C(12)–H· · ·O(3) angle is
different dinuclear units, as shown in Fig. 2. Both
pyridine planes in one 2,20-bpy molecule, staggered
with a dihedral angle of 11.78 and paralleled with their
counterparts which linked another copper(II) ion, are
nearly perpendicular to the adjacent 2,20-bpy (the
dihedral angle is 103.28). The bond lengths of
153.278. A 1D chain comes into being under the
assistance of these above-mentioned hydrogen-bond-
ing interactions (Fig. 4). Moreover, the p–p inter-
actions between two adjacent 2,20-bpy belonging to
two different units are also observed. The centroid–
0
˚
centriod distance of two different 2,2 -bpy is ca 3.6 A.
˚
C(21A)–O(1A) and C(21A)–O(2A) are 1.256(8) A
˚
and 1.230(8) A, respectively. The Cu–N distances
In complex 3, the coordination environments of the
metal atoms are similar to those of in 2, where
Fig. 3. View of the 2D network depicting the connection via hydrogen bonds and p–p interactions along c-axis in 1.

W. Huang et al. / Journal of Molecular Structure 649 (2003) 269–278
277
Fig. 4. View of the 2D network depicting the connection via hydrogen bonds and p–p interactions along c-axis in 2.
the geometry of a copper(II) ion is also trigonal
bipyramid and the angles of O(1)–Cu(1)–N(4),
O(1)–Cu(1)–N(2), N(4)–Cu(1)–N(2), O(1)–
Cu(1)–N(1), N(4)–Cu(1)–N(1), O(1)–Cu(1)–N(3),
N(4)–Cu(1)–N(3), N(1)–Cu(1)–N(3), N(1)–Cu(1)–
N(2), N(3)–Cu(1)–N(2) are 91.59(9), 103.32(9),
104.28(10), 88.59(9), 177.16(9), 158.88(10), 80.78(10),
98.09(10), 78.42(10) and 97.66(10), respectively. It is
interesting to note that only one simple terephthalic
divalentanionandsevenwatermoleculeswerefoundin
a unit cell, and NO23 that is present in 2 was absent. In
thecrystalpackingof3, a1Dchainstructure comesinto
being (Fig. 5) under the assistance of hydrogen bonds
between the oxygen atoms O(1) and O(2) of the
carboxylic group and the carbon atoms C(24) and C(5)
of the 2,20-bpy, respectively. The H-bond lengths and
co-workers [33], in which only the IR spectra of
[(VO)2(TPHA)(H2O)2(bpy)2](Ac)2, [(VO)2(-
TPHA)(H2O)2(Me2bpy)2](Ac)2 and [(VO)2(TPHA)(H2-
O)2(phen)2](Ac)2·0.5H2O were recorded. However, it is
regretted that crystal structures of three above-
mentioned complexes were not given, so the detailed
structural comparison could not be carried out here.
3.4. Thermal analyses
TGA-DTA analysis on 1 denotes that the com-
pound is stable in a large range of 293–568 K, then a
quick weight loss (68.73%) in a range of 569–596 K
indicating the decomposition of the compound. The
thermal analyses of 2 show that it loses coordinating
terephthalate molecules in the range of 398–428 K
(15.94% weight loss) and chelating 202-bpy units from
517 to 579 K (59.96% weight loss), respectively.
Compared with 2, the thermal property of 3 observed
is similar, namely, the sample can keep unchangeable
in the range of 298–368 K, then it loses coordinating
˚
relative angles are C(24)–O(1) 2.997(4) A and C(24)–
˚
H(24)· · ·O(1) 111.958, C(5)–O(2) 3.178(4) A and
C(5)–H(5)· · ·O(2) 122.368, respectively.
That m-terephthalato acting as a bi(monodentate)
bridging ligand has been reported by Ma and his
Fig. 5. View of the 2D network depicting the connection via hydrogen bonds along b-axis in 3.

278
W. Huang et al. / Journal of Molecular Structure 649 (2003) 269–278
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4. Supplementary material
[15] Siemens, SAINT v4 Software Reference Manual, Siemens
Analytical X-Ray Systems, Inc., Madison, Wisconsin, USA,
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Crystallographic data have been deposited to the
Cambridge Crystallographic Data center (CCDC) (12
Union Road, Cambridge, CB2 1EZ, UK) and are
available on request quoting the deposition number
195306 (1), 195307 (2) and 195308 (3).
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We want to thank Jiangsu Science & Technology
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Academy of Sciences (TWAS) for the financial
support. This work is also partly funded by National
Natural Science Foundation of China (project
20271026). W.H. is grateful to Nanjing University
Talent Development Foundation.
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