Copper(II), nickel(II) and cobalt(II) complexes of 4-cyanobenzonic acid: Syntheses, crystal structures and spectral properties

Article abstract of DOI:10.1016/j.molstruc.2005.01.018

Three new metal complexes, Cu(4-Hcba)₂(4-cba) ₂(Py)₂ (4-Hcba=4-cyanobenzoic acid) 1 and M[H(4-cba) ₂]₂(Py)₂ (M=Ni 2, Co 3), have been prepared by the treatment of 4-Hcba with the respective

Full text of DOI:10.1016/j.molstruc.2005.01.018

Journal of Molecular Structure 740 (2005) 147–151
www.elsevier.com/locate/molstruc
Copper(II), nickel(II) and cobalt(II) complexes of 4-cyanobenzonic acid:
syntheses, crystal structures and spectral properties
a
a
a,b
a,
*
Fa-Kun Zheng , A-Qing Wu , Yan Li , Guo-Cong Guo ,
Ming-Sheng Wanga, Qiang Lia,b, Jin-Shun Huanga
aState Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter,
The Chinese Academy of Sciences, Yangqiao West Road 155, Fuzhou, Fujian 350002, People’s Republic of China
bGraduate School, The Chinese Academy of Sciences, Beijing 100039, People’s Republic of China
Received 12 November 2004; revised 9 January 2005; accepted 11 January 2005
Abstract
Three new metal complexes, Cu(4-Hcba)2(4-cba)2(Py)2 (4-HcbaZ4-cyanobenzoic acid) 1 and M[H(4-cba)2]2(Py)2 (MZNi 2, Co 3), have
been prepared by the treatment of 4-Hcba with the respective metal nitrate M(NO3)2 (MZCu, Ni, Co) in the presence of pyridine (Py).
Single-crystal X-ray diffraction analyses (3 is isostructural to 2) show that the obtained complexes are of isolated mononuclear and the metal
atoms have distorted octahedral coordination environment. Two different types of intramolecular hydrogen bonds exist: asymmetrical
O–H/O for 1 and symmetrical O/H/O for 2 and 3. The crystal packing between the molecular complexes is controlled mainly by
T-shaped C–H/p interactions between pyridine and phenyl rings. Preliminary discussions on IR, UV–VIS and fluorescent spectra have also
been carried out.
q 2005 Elsevier B.V. All rights reserved.
Keywords: 4-Cyanobenzoic acid; Metal complex; Hydrogen bond; Crystal structure; Spectral properties
1. Introduction
possesses two functional coordination groups and should
exhibit structural diversities on the formation of complexes. In
our laboratory the 3-cba-bridged rare earth-transition metal
complex [8] and transition metal complex of 4-Hcba [9] were
first synthesized. However, compared to benzoic acid,
chemistry of Hcba has been investigated limitedly so far
[10–13]. Asa partofour ongoing research, inthe present study
we report the syntheses, crystal structures and physical
properties of three new metal 4-cyanobenzoate complexes,
namely trans-dipyridine-bis(4-cyanobenzoato)-bis(4-cyano-
benzoic acid)-copper(II) 1, trans-dipyridine-bis[hydrogen
bis(4-cyanobenzoato)]-nickel(II) 2 and trans-dipyridine-
bis[hydrogen bis(4-cyanobenzoato)]-cobalt(II) 3.
The research on the metal carboxylates has always been
intriguing in that they play important roles not only in
synthetic chemistry with the essence of labile coordination
modes of carboxylate group, such as architecture of open and
porous framework [1,2], but also in biologic activities [3,4]
and physiological effects [5]. Especially, aromatic carboxylic
acids and their metal salts have been widely used in medicine
as non-steroidal anti-inflammatory drugs. Some of the simple
aromatic carboxylic acids (benzoic and cinnamic acid) are
known to have anti-bacterial and anti-fungal properties [6,7].
Therefore, it is necessary to gain more knowledge about the
structures and bonding relations of the aromatic carboxylates
for further pharmic study. We select 3- and 4-cyanobenzoic
acid (3- and 4-Hcba) as ligand to bind the metal ions, which
2. Experimental
2.1. General procedures
* Corresponding author. Tel.: C86 591 83705054; fax: C86 591
83714946.
All reagents were purchased commercially and used as
received without further purification. The elemental
E-mail address: zfk@ms.fjirsm.ac.cn (G.-C. Guo).
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2005.01.018

148
F.-K. Zheng et al. / Journal of Molecular Structure 740 (2005) 147–151
Table 1
analyses were performed on an Elementar Vario EL III
microanalyzer. The FT-IR spectra were measured using
KBr discs in the range of 4000–400 cmK1 on a Perkin–
Elmer Spectrum One spectrometer. The electronic spectra
in ethanol solution from 190 to 1000 nm were obtained on a
Perkin–Elmer Lambda-900. The emission spectra in the
solid state were recorded on an Edinburgh Instruments
FLS920P spectrofluorimeter.
Crystal data and structure refinement
1
2
3
Empirical
formula
C42H28CuN6O8
C42H28N6NiO8
C42H28CoN6O8
Formula weight 808.24
803.41
803.63
Crystal system
Crystal size
(mm)
Triclinic
0.35!0.35!
0.25
Triclinic
0.26!0.20!
0.10
Triclinic
0.45!0.30!
0.20
Space group
˚
a (A)
˚
b (A)
P-1 (No. 2)
7.4565(7)
9.7190(9)
13.4173(10)
96.907(3)
94.321(3)
107.290(4)
915.32(14)
1
P-1 (No. 2)
7.3473(2)
9.7528(2)
13.5785(6)
95.71(2)
97.30(2)
107.05(1)
913.05(5)
1
P-1 (No. 2)
7.3351(7)
9.7653(8)
13.6109(10)
95.340(3)
97.453(3)
107.074(3)
915.21(13)
1
2.2. Synthesis
˚
c (A)
The title complexes were prepared by mixing a 1:4:3
molar ratio of 4-Hcba, metal nitrate M(NO3)2$nH2O
(MZCu, nZ3; and MZNi and Co, nZ6) and pyridine in
anhydrous ethanol. The reaction solution was stirred at
about 70 8C for 1 h and then filtered. The filtrate was kept at
room temperature by slow evaporation of the solvent
yielding blue block crystals of 1 (72% based on Cu
compound), green prism crystals of 2 (68% based on
Ni compound) and blue prism crystals of 3 (70% based on
Co compound), respectively. Elemental analysis calcd
(found) for 1 (C42H28CuN6O8, %): C, 62.41(62.37); H,
3.49(3.51); N, 10.40(10.38), 2 (C42H28N6NiO8, %): C,
62.79(62.82); H, 3.51(3.52); N, 10.46(10.48) and 3
(C42H28CoN6O8, %): C, 62.77(62.80); H, 3.51(3.53); N,
10.46(10.43).
a (deg)
b (deg)
g (deg)
3
˚
V (A )
Z
Dcalcd (g cmK3
)
1.466
1.461
1.458
m (mmK1
)
0.662
0.597
0.534
F(000)
415
414
413
q range for data 3.04–27.48
3.06–27.48
3.05–27.48
collection (deg)
Index ranges
K7%h%9
K12%k%12
K17%l%16
7103/4136
(0.0121)
K8%h%9
K12%k%12
K17%l%17
7155/4141/
(0.0363)
K7%h%9
K12%k%10
K17%l%17
7090/4120
(0.0129)
Total reflec-
tions/unique
reflections (Rint
Completeness
to qmax
)
0.983
0.987
0.979
Observed data/
restraints/
3840/1/262
3238/2/263
3761/0/263
2.3. X-ray crystallography
parameters
Final R and wR
indices
0.0291 and
0.0704
0.0551 and
0.1085
0.0310 and
0.0754
The single-crystal X-ray diffraction experiments of the
three new complexes were performed on a Rigaku Mercury
CCD diffractometer with graphite monochromatic Mo Ka
[IO2s(I)]
R and wR indi-
ces (all data)
Goodness-of-fit
on F2
0.0321 and
0.0723
0.0772 and
0.1234
0.0350 and
0.0782
˚
radiation (lZ0.71073 A) under liquid dinitrogen atmos-
1.062
1.069
1.045
phere at 140 K. Absorption corrections Sphere [14] based
upon redundant reflections were applied to the data set. The
structures were solved by the direct methods (SHELXS-97
[15]) and subsequent successive difference Fourier maps,
and refined using full-matrix least-squares refinement on F2
(SHELXL-97 [16]). All non-hydrogen atoms were refined
anisotropically, and hydrogen atoms except for that of the
carboxyl were placed in geometrically calculated positions
and refined with temperature factors 1.2 times those of their
bonded carbon atoms. The carboxyl hydrogen atoms were
located from difference Fourier syntheses and fixed, and
refined isotropically. The detailed crystal data and structure
refinement are summarized in Table 1. The selected bond
lengths and angles are listed in Table 2. The final fractional
atomic coordinates of atoms, the anisotropic thermal
parameters and other details of the structure have been
deposited at the Cambridge Crystallographic Data-base
Centre, CCDC No. 239907, 255029 and 239908 for 1, 2 and
3, respectively. Copies of these data are available free of
charge on request from CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK (fax: C44 1223 336033; e-mail: deposit@
ccdc.ac.uk or www: http://www.ccdc.cam.ac.uk).
Largest differ-
ence peak and
0.375 and
0.353 and
0.292 and
K0.348
K0.390
K0.326
K3
˚
hole (e A
)
3. Results and discussion
3.1. Crystal structure
For complexes 2 and 3 are of isostructure, only molecular
structures of 1 and 3 will be discussed in details, as shown in
Figs. 1 and 2, respectively. These two complexes are
approximately isomorphic and of mononuclear isolate
skeleton. The metal atom in each complex is located at a
crystallographic inversion center and exists in distorted
octahedral coordination environments. Two trans 4-Hcba
ligands, two trans 4-cba ions and two trans pyridine
molecules have assembled around each Cu(II) atom in 1,
and four trans 4-cba ions and two trans pyridine molecules
around each Co(II) atom in 3. Such trans-arrangement can
minimize repulsion between the ligands. Each of four
carboxylates acts as monodentate terminal ligand.

F.-K. Zheng et al. / Journal of Molecular Structure 740 (2005) 147–151
149
Table 2
Selected bond lengths (A) and bond angles (deg)
˚
1
2
3
M–O(2)
2.475(1)
1.954(1)
2.013(1)
1.500(2)
1.311(2)
1.218(2)
1.447(2)
1.145(2)
1.515(2)
1.243(2)
1.267(2)
1.446(2)
1.145(2)
2.062(2)
2.083(2)
2.077(2)
1.506(4)
1.274(3)
1.243(3)
1.446(4)
1.145(4)
1.505(4)
1.276(3)
1.244(3)
1.448(4)
1.146(4)
2.078(1)
2.096(1)
2.128(1)
1.505(2)
1.269(2)
1.241(2)
1.448(2)
1.141(2)
1.503(2)
1.275(2)
1.241(2)
1.448(2)
1.142(2)
M–O(4)
M–N(3)
C(1)–C(2)
C(1)–O(1)
C(1)–O(2)
C(5)–C(8)
C(8)–N(1)
C(9)–C(10)
C(9)–O(3)
C(9)–O(4)
C(13)–C(16)
C(16)–N(2)
Fig. 2. Molecular structures of complex 2 and 3 with 30% probability
ellipsoid (MZNi, Co). Hydrogen atoms not involved with hydrogen bonds
are omitted for clarity, and the dotted line represents the intramolecular
hydrogen bonding.
O(2)–M–O(4)
O(2)–M–O(40)
98.66(4)
81.34(4)
94.28(4)
85.72(4)
91.92(5)
88.08(5)
97.69(8)
82.31(8)
92.58(8)
87.42(8)
92.48(8)
87.52(8)
96.27(4)
83.73(4)
92.23(4)
87.77(4)
92.38(4)
87.62(4)
180.08 in 1 and 3 for centro-symmetric structures. Other
bond angles around M centers range from 81.34(4) to
98.66(4)8 for 1 and from 83.73(4) to 96.24(4)8 for 3.
The most distinctive aspect in the two structures lies in
the carboxylic bonding. For protonated C(1)O(1)O(2)H(1)
˚
group in 1 the C(1)–O(1) bond distance of 1.311(2) A for
the hydroxyl O(1) is longer than the C(1)–O(2) bond
O(2)–M–N(3)
O(2)–M–N(30)
O(4)–M–N(3)
O(4)–M–N(30)
O(1)–C(1)–O(2)
C(2)–C(1)–O(1)
C(2)–C(1)–O(2)
C(5)–C(8)–N(1)
O(3)–C(9)–O(4)
C(10)–C(9)–O(3)
C(10)–C(9)–O(4)
C(13)–C(16)–N(2)
124.5(1)
113.5(1)
122.0(1)
178.8(2)
127.5(1)
117.6(1)
114.9(1)
179.8(2)
126.5(2)
115.6(2)
117.9(2)
179.1(3)
125.9(2)
115.5(2)
118.6(2)
179.0(4)
126.3(1)
116.0(1)
117.8(1)
179.9(2)
125.7(1)
115.4(1)
118.9(1)
178.3(2)
˚
distance of 1.218(2) A owing to weak Cu–O(2) bond, and
the latter has somewhat characteristic of double bond.
Similar to the structures of the reported carboxylic Cu(II)
complexes [9,20,21], two different C–O bond distances in
the axially coordinated carboxylic acid are also present.
Strong intramolecular asymmetrical O–H/O hydrogen
bonding is formed between the O(1) and O(3) atoms
(Table 3). As expected in the carboxylic monodentate
coordination mode, the C(9)–O(3) bond distance of
Symmetry code: 2Kx, Ky, 2Kz.
Comparatively, the octahedral geometry of Cu(II) in 1 is
˚
more distorted with a long Cu–O(2) distance of 2.475 A due
to the Jahn–Teller effect of Cu(II) ion with d9 electron
configuration. The elongated axial positions in the Cu
octahedral coordination polyhedron are occupied by two
trans 4-Hcba ligands. The other Cu–O and Cu–N distances,
˚
1.243(2) A in deprotonated C(9)O(3)O(4) group in 1 is
just slightly shorter compared to the C(9)–O(4) bond
˚
distance of 1.267(2) A. However, four carboxylate groups
are equal in 3. The carboxylate ions in the molecules of 3 are
held together by strong intramolecular symmetrical O/
H/O hydrogen bonds (Table 3). This leads to the fact that
˚
1.954(1) and 2.013(1) A, respectively, are in good agree-
ment with those reported in related complexes [9,17,18].
˚
The Co–O distances of 2.078(1) and 2.096(1) A and Co–N
˚
the C–O bond distances (1.269(2) and 1.275(2) A) involved
with the uncoordinated O atoms are surprisingly slightly
˚
distance of 2.128 A are comparable with those observed in
six-coordinated Co(II) complexes with the benzoic-like acid
and pyridine mixed ligands [19]. The O(2)–M–O(20), O(4)–
M–O(40) and N(3)–M–N(30) (MZCu, Co) angles should be
˚
longer than those (both being 1.241(2) A) concerned with
coordinated O atoms in 3. Finally, the carboxylic plane is
not coplanar with its bonded benzonitrile plane with the
dihedral angles of 7.52 and 8.718 for 1 and 5.01 and 8.728 for
3, respectively.
Interestingly, weak intermolecular C–H/p hydrogen
bonds between one hydrogen atom of the phenyl ring of
4-cba group and the pyridine ring can be observed in the
investigating complexes (Table 4) and responsible for
Table 3
˚
Symmetric and asymmetric hydrogen bond geometry (A and deg)
O(1)–H(1)/O(3) O(1)–H(1)
H(1)/O(3) O(1)/O(3) :(O(1)
H(1)O(3))
Fig. 1. Molecular structure of complex 1 with 30% probability ellipsoid.
Non-interacting hydrogen atoms are omitted for clarity, and the dotted line
represents the intramolecular hydrogen bonding and the dashed line shows
the weak coordination between Cu and O(2).
Asymmetric for 1 0.919(9)
Symmetric for 2
Symmetric for 3
1.62(1)
1.22(4)
1.21(3)
2.527(1)
2.418(3)
2.420(2)
169(2)
169(4)
170(3)
1.21(3)
1.22(3)

150
F.-K. Zheng et al. / Journal of Molecular Structure 740 (2005) 147–151
Table 4
a
˚
C–H/p hydrogen bonds (A and deg)
1
2
3
C–H/p contacts, H/p distances (and angles)
2.90(134.0)
2.92(124.5)
4.81(45.9)
3.61
2.96(137.8)
2.85(130.1)
4.93(50.3)
3.70
2.96(138.7)
2.84(131.4)
4.94(50.5)
3.71
Shortest intermolecular C–H/X (p) contacts, H/X distances (and angles)b
Shortest intermolecular rings centroid-to-centroid contacts (and interplanar angles)
Shortest intermolecular C–H/R2-centroid contacts
a
C–H from the phenyl ring (R1) of the 4-cba group, and p denoting the pyridine ring (R2).
X representing the N or C atoms of the pyridine ring.
b
formation of one-dimensional network (Fig. 3). Such
feature of strong symmetrical O/H/O hydrogen bonds.
The detailed assignments of D band will be carried out by
deuterium isotope effects [26]. The carboxylate vibration
out-of-plane bending vibration d(O–H) at 932 cmK1 in the
free 4-Hcba ligand vanishes on the formation of the
complexes, which can be attributed to the intramolecular
hydrogen bonding. One important characteristic in the IR
spectra of the investigating complexes is stretching
vibration n(COO) of carboxylate group. The asymmetrical
stretching frequency nasym(COO) of 1 at 1695 cmK1 is
similar to that of the free 4-Hcba ligand (1699 cmK1) thanks
to the existence of the short C–O bond, while
C–H/p interactions between aromatic rings, which are
referred to as a point-to-face or T-shaped configuration, play
an important role in crystal packing and non-covalent
framework structure in supramolecular chemistry [22]. The
˚
H/p distances (2.90–2.96 A) are slightly longer than
˚
generally observed average value (2.79 A [23]) and the
rings centroid-to-centroid contacts fall in the range of 4.81
˚
and 4.94 A. In the crystal structure of benzene, molecular
dynamic calculations show the benzene dimmer is bound by
˚
1.6 kJ/mol even with a 6 A distance of a benzene–benzene
center [24]. It’s evident that the interplanar angles lie
between 45.9 and 50.38 and the aromatic rings are not
perpendicular to each other. Therefore, the C–H/p
arrangement can be described as an intermediate between
parallel displaced and point-face geometry.
3.2. Spectral properties
The reliable assignments are made by comparing IR
spectra of complexes 1–3 with that of the free 4-Hcba
compound, as plotted in Fig. 4. For each complex, the cyano
n(ChN) stretching vibration occurs at the almost same
frequency, ca. 2230 cmK1, as that recorded for the free
4-Hcba ligand, which denotes that the cyano group does not
take part in coordination. The presence of the asymmetrical
O–H/O hydrogen bonds in complex 1 is manifested by a
broad absorption in the 2924–2482 cmK1 (so called ABC
bands [25]), which is associated with n(O–H) and also exists
Fig. 4. Infrared spectra of complexes 1–3 and 4-Hcba.
in the free 4-Hcba ligand between 2881 and 2555 cmK1
.
However, in the spectra of complexes 2 and 3 these bands
disappear and should be shifted to the lower frequency
below 1600 cmK1 (D band [25]), which is characteristic
Fig. 3. One-dimensional network in the crystal structure held by C–H/p
interactions (exemplified by 3).
Fig. 5. Emission spectra of 1–3 and 4-Hcba (solid) in the solid state.

F.-K. Zheng et al. / Journal of Molecular Structure 740 (2005) 147–151
151
symmetrical stretching frequency nsym(COO) around 1392
and 1380 cmK1 is in accordance with the occurrence of
COOH group and COOK ion. nasym(COO) of 2 and 3
(both at ca. 1650 cmK1) shift to lower frequency in contrast
Science Foundation of Fujian Province (2003I031,
A0420002).
with 1, and nsym(COO) are observed at 1407 cmK1
.
The differences in the frequencies of nasym(COO) and
nsym(COO) (303 and 305 cmK1 for 1, and 243 cmK1 for 2
and 3), which are larger than 200 cmK1, are indicative of
monodentate carboxylate coordination [27].
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and n/p* transitions. One or more additional less intense
peaks appearing in the region of 350–1000 nm corre-
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3A2g/3T1g(P) and A2g/3T1g transitions, respectively,
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3A2g/3T2g transition. A resolved peak at 516 nm and a
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4
4
from T1g/4T2g and T1g/4A2g, respectively.
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The emission spectra of complexes 1–3 in the solid state
under the same measurement environment at room tem-
perature, together with the 4-Hcba ligand, are illustrated in
Fig. 5. A broad peak in the region 365–385 nm for 1, and a
peak around 450 nm for 2 and 416 for 3 can safely be
assigned to intraligand p/p* transitions, and are red-
shifted compared to the free 4-Hcba ligand (in the range of
335–355 nm). The formed complexes display a smaller
luminescence quantum yield than 4-Hcba, which forms
dimmers by hydrogen bonds and have more conjugated
system [28]. It is noteworthy that a peak at 606 nm with a
shoulder of 558 nm for 3 is likely attributed to LMCT
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In summary, three mononuclear 4-cyanobenzoate com-
plexes has been synthesized and characterized by X-ray
single-crystal diffraction, and IR, electronic and fluorescent
spectra. Asymmetrical intramolecular O–H/O hydrogen
bonds exist in the Cu complex, while symmetrical
intramolecular O/H/O hydrogen bonds in the Ni and
Co complexes. Weak intermolecular C–H/p contacts
promote formation of infinite one-dimensional chains.
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Acknowledgements
This work was supported by National Natural Science
Foundation of China (20001007, 20131020) and Natural
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