Syntheses, crystal structures and magnetic properties of two new 3-cyanobenzate coordination complexes

Article abstract of DOI:10.1016/j.inoche.2005.05.008

Two new 3-cyanobenzate complexes, [Cu(3-cba)₂(Py)(H ₂O)]_n 1 and [Cd(3-cba)₂(Py)₂(H ₂O)] 2 (3-cba = 3-cyanobenzate, Py = pyridine), were synthesized and structurally characterized by single-crystal X-ray diffraction. Three different coordination modes of 3-cba group exist in the two obtained complexes, which results in different molecular architectures: 1 with a 1-D chained structure and 2 with an isolated configuration. Variable-temperature magnetic susceptibility data show the presence of antiferromagnetic interactions in 1.

Full text of DOI:10.1016/j.inoche.2005.05.008

Inorganic Chemistry Communications 8 (2005) 708–712
www.elsevier.com/locate/inoche
Syntheses, crystal structures and magnetic properties
of two new 3-cyanobenzate coordination complexes
a
a,
a,b
Yan Li a,b, A-Qing Wu , Fa-Kun Zheng *, Ming-Lai Fu
,
a
Guo-Cong Guo ,a, Jin-Shun Huang
*
a
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Yangqiao West Road 155, Fuzhou, Fujian 350002, Peopleꢀs Republic of China
b
Graduate School, Chinese Academy of Sciences, Beijing 100039, Peopleꢀs Republic of China
Received 24 March 2005; accepted 7 May 2005
Available online 16 June 2005
Abstract
Two new 3-cyanobenzate complexes, [Cu(3-cba)2(Py)(H2O)]n 1 and [Cd(3-cba)2(Py)2(H2O)] 2 (3-cba = 3-cyanobenzate, Py = pyr-
idine), were synthesized and structurally characterized by single-crystal X-ray diffraction. Three different coordination modes of
3-cba group exist in the two obtained complexes, which results in different molecular architectures: 1 with a 1-D chained structure
and 2 with an isolated configuration. Variable-temperature magnetic susceptibility data show the presence of antiferromagnetic
interactions in 1.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: 3-Cyanobenzate complex; Crystal structure; Magnetic properties; Hydrogen bonds; p–p Stacking
Carboxylate coordination complexes have been exten-
sively investigated in past decades because of their excel-
lent coordination capability and the possibility of
offering new functional materials [1,2]. Especially, aro-
matic carboxylate coordination complexes, possessing
special physical properties and intriguing structural fea-
tures [2–4], have attracted increasing interest. Cyano-
benzate compounds having two functional coordination
groups can be used to bind metal atoms and should exhi-
bit versatile coordination modes. However, only carbox-
ylate group participates in coordination in most of the
reported cyanobenzate complexes [5–15]. So far the un-
ique example of cyanobenzate complex has been ob-
tained with both carboxylate and cyano groups bound
to the metal atoms [16]. Furthermore the magnetic prop-
erties of cyanobenzate complexes have not ever been
investigated. Herein, we report syntheses and crystal
structures of two new 3-cyanobenzate complexes, a coor-
dination polymer [Cu(3-cba)2(Py)(H2O)]n 1 showing
antiferromagnetic behaviour, a second instance in which
two functional coordination groups of 3-cba ligand are
both involved in coordination, and an isolated mono-
nuclear complex [Cd(3-cba)2(Py)2(H2O)] 2.
The blue prism crystals of 1 were obtained via solu-
tion synthetic methods [17]. However, the colorless
prism crystals of 2 were yielded via solvent-thermal
route [18]. The structures of 1 and 2 were determined
by single-crystal X-ray diffraction analyses [19].
As shown in Fig. 1(a), the structure of 1 consists of a
1-D coordination polymer with a basic unit [Cu(3-cba)2
(Py)(H2O)]. The coordination environment around the
Cu(II) atom can be described as a distorted square-
pyramid, with the equatorial positions occupied by two
carboxylate O atoms from two different 3-cba ligands
*
Corresponding author. Tel.: +86 591 8370 4827/5054; fax: +86 591
8371 4946
E-mail address: zfk@ms.fjirsm.ac.cn (F.-K. Zheng).
1387-7003/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2005.05.008

Y. Li et al. / Inorganic Chemistry Communications 8 (2005) 708–712
709
Fig. 1. (a) Structure of 1 with 50% probable thermal ellipsoid. The dashed lines show the weak coordination between Cu(1) and N(30). Hydrogen
˚
atoms are omitted for clarity. Selected bond lengths (A) and bond angles (ꢁ): Cu(1)–O(1), 1.921(3); Cu(1)–O(3), 1.929(3); Cu(1)–O(1W), 1.973(3);
Cu(1)–N(1), 2.018(3); Cu(1)–N(30), 2.442(3); N(2)–C(8), 1.140(5); N(3)–C(16), 1.140(5); O(1)–Cu(1)–O(3), 176.75(11); O(1)–Cu(1)–O(1W), 88.54(11);
O(3)–Cu(1)–O(1W), 89.73(11); O(1)–Cu(1)–N(1), 89.71(12); O(3)–Cu(1)–N(1), 92.49(12); O(1W)–Cu(1)–N(1), 169.27(12); O(1)–Cu(1)–N(30),
82.37(12); O(3)–Cu(1)–N(30), 95.04(11); O(1W)–Cu(1)–N(30), 95.08(11); N(1)–Cu(1)–N(30), 95.17(12). (Symmetry code0: 1 + x, y, z). (b) A double-
chained structure of 1 connected by hydrogen bonds. Hydrogen atoms are omitted for clarity. (Symmetry codei: 1 ꢁ x, ꢁy, 1 ꢁ z).
˚
(Cu(1)–O(1) = 1.921(3) A and Cu(1)–O(3) = 1.929(3) A),
˚
one pyridine N atom (Cu(1)–N(1) = 2.018(3) A), and one
˚
water O atom (Cu(1)–O(1W) = 1.973(3) A). The Cu–O
˚
ported complex also with both carboxylate and cyano
groups coordinating the metal atoms [16]. In the latter,
carboxylate groups of 3-cba ligand display a bridging
bis-monodentate coordination mode, bringing on dinu-
clear metals, which is further linked by carboxylate O
atoms and cyano N atoms of 3-cba ligands in pairs to
form infinite intersect double-chains. Notably, the car-
boxylate group O(1)C(1)O(2) is not coplanar with the
corresponding aromatic ring [dihedral angles 7.01(43)ꢁ],
while the carboxylate group O(3)C(9)O(4) and the
aromatic ring of the other 3-cba ligand constitute reason-
ably good plane (maximum deviation of atoms:
and Cu–N(equatorial) distances are similar to those in the
reported complexes [14,20]. The apical position is occu-
pied by one cyano 0N atom of 3-cba bridging ligand with
˚
a long Cu(1)–N(3 ) distance of 2.442(3) A due to the
Jahn–Teller effects of Cu(II) ions with a d9 electron con-
figuration (Symmetry code0: 1 + x, y, z). It is noteworthy
that the C–N distances of cyano groups of the two 3-cba
ligands are almost equal (mean value of the C–N dis-
˚
tances: 1.140 A), indicating that the C(16)–N(3) bond
˚
still bears the characteristic of triple bond. Meanwhile,
the cyano stretching vibration m(C„N) occurs at the al-
most same frequency as that recorded for the free 3-Hcba
ligand (see Fig. S1). This can be concluded by the matter
that the Cu atom bonds to the N atom of cyano group
with its lone electronic pair (mainly contributed by 2s2)
and the triple bond C„N is almost unperturbed. The
most interesting structural feature of 1 is the coordina-
tion modes of 3-cba ligands. One acts as a terminal li-
gand with the carboxylate O atom accomplishing the
coordination of the Cu(II) atom. The other serves as a
bridging ligand linking the neighboring copper(II) atoms
by the unidentated carboxylate O atoms and cyano N
atoms to form an infinite chain along the a-axis, which
is obviously different from the situation in the first re-
0.0250(23) A).
In 1 the two adjacent chains are further connected by
O–Hꢀ ꢀ ꢀO hydrogen bonds to give an infinite double-chain
i
˚
with the distances O(1W)ꢀ ꢀ ꢀO(2 ) = 2.680(4) A and
i
˚
O(1W)ꢀ ꢀ ꢀO(4 ) = 2.722(4) A, and the angles O(1W)–
H(1WB)ꢀ ꢀ ꢀO(2i) = 154(4)ꢁ and O(1W)–H(1WA)ꢀ ꢀ ꢀO(4i)
= 171(4)ꢁ (Symmetry codei: 1 ꢁ x, ꢁy, 1 ꢁ z), as depicted
in Fig. 1(b). The pyridine ligands are located on the two
sides of the double-chain. The nearest separation of
˚
Cu(II)ꢀ ꢀ ꢀCu(II) in interchains (4.6827(16) A) is much
˚
shorter than that in intrachains (10.327(4) A), which are
obviously longer than that in the presented complex
˚
(2.664(2) A) [16].
The complex 2 has a crystallographic two-fold axis
passing through the Cd(II) and water O atoms, as

710
Y. Li et al. / Inorganic Chemistry Communications 8 (2005) 708–712
illustrated in Fig. 2(a). The cyano group of 3-cba re-
mains uncoordinated and the carboxylate group adopts
a chelating bidentate fashion. The Cd atom is seven-
coordinated with four carboxylate O atoms from two
3-cba ligands, one water O atom and two pyridine N
atoms. The coordination geometry around the Cd atom
may be described as a distorted pentagonal bipyramid.
The O(1), O(2), O(10), O(20) and O(1W) atom all lie
close to a plane with a maximum deviation of atoms
N(1) and N(10) atoms with axial angle N(1)–Cd(1)–
N(10) of 169.54(8)ꢁ as opposed to the ideal angle of
180ꢁ (Symmetry code0: 1 ꢁ x, y, 3/2 ꢁ z). The Cd–
˚
O(3 ꢁ cba) distances of 2.3953(13) and 2.4680(14) A,
which are longer than those of Cd(1)–N(1)
˚
˚
(2.3384(16) A) and Cd(1)–O(1W) (2.281(2) A). The car-
boxylate group is not coplanar with the aromatic ring in
the 3-cba ligand [dihedral angles 11.23(19)ꢁ].
Besides covalent forces in 2, supermolecular interac-
˚
0.0589(13) A, while the axial positions are occupied by
tions also play an important role in crystal packing as
˚
Fig. 2. (a) Structure of 2 with 30% probable thermal ellipsoid. Hydrogen atoms are omitted for clarity. Selected bond lengths (A) and bond angles
(ꢁ): Cd(1)–O(1W), 2.281(1); Cd(1)–N(1), 2.3384(16); Cd(1)–O(1), 2.3953(13); Cd(1)–O(2), 2.4680(14); O(1W)–Cd(1)–N(1), 95.23(4); N(1)–Cd(1)–
N(10), 169.54(8); O(1W)–Cd(1)–O(1), 83.03(4); N(1)–Cd(1)–O(10), 92.86(6); N(1)–Cd(1)–O(1), 88.41(5); O(1)–Cd(1)–O(10), 166.07(7); O(1W)–Cd(1)–
O(2), 136.79(3); N(1)–Cd(1)–O(2), 82.59(5); N(1)–Cd(1)–O(20), 89.77(5); O(1)–Cd(1)–O(20), 140.10(5); O(1)–Cd(1)–O(2), 53.82(5); O(1W)–Cd(1)–
O(20), 136.79(3); O(2)–Cd(1)–O(2), 86.43(6). (Symmetry code0: 1 ꢁ x, y, 3/2 ꢁ z). (b) View of the layer structure formed by isolated molecules of 2
linked through hydrogen bonds p–p stacking interactions to give a 2-D structure. The atoms of the Py rings and hydrogen atoms have been omitted
for clarity.

Y. Li et al. / Inorganic Chemistry Communications 8 (2005) 708–712
711
in 1. Intermolecular hydrogen bonds occur via the car-
boxylate groups and coordinated water molecules with
is well interpreted based on the modified analytical
expression [21], which is derived from the Fisher clas-
sical Heisenberg model [22] for infinite linear chains.
By using a least-squares method, a very satisfactory
fit of the data at 20–300 K was obtained using the
set of parameters of J = 5.29 cmꢁ1, g = 1.95, and
ii
˚
the distances O(1W)ꢀ ꢀ ꢀO(2 ) of 2.755(2) A and the an-
gles O(1W)–H(1WA)ꢀ ꢀ ꢀO(2ii) of 154(2)ꢁ (Symmetry
codeii: 1 ꢁ x, ꢁ1 + y, 3/2 ꢁ z), resulting in a 1-D chain
parallel to the b-axis. Furthermore, the adjacent chains
are connected via p–p stacking interactions between
the aromatic groups of 3-cba, with a centroid-to-
J = ꢁ15.61 cmꢁ1 with R = 1.2 · 10ꢁ4
. The positive
J parameter may be assigned to the intrachained
ferromagnetic exchange interactions and the negative
J0 value to the interchained antiferromagnetic ex-
change interactions. Certainly, the shorter interchained
Cuꢀ ꢀ ꢀCu distance generates a stronger magnetic inter-
actions, which dominate the overall magnetic behavior
in 1. On the basis of this model, the antiferromagnetic
interactions are present in 1, in line with the minus
sign of the Weiss constant values, similar to those of
the 1-D copper (II) complexes bridged by terephtha-
lato dianions [23].
Thermogravimetric analyses (TGA) show that 1 and
2 undergo different thermal decomposition process, as
demonstrated in Figs. S2 and S3. The TGA curve of 1
reveals that the dehydration of one coordinated water
molecule occured in the range 108–128 ꢁC with a weight
loss of 4.05% (calcd. 3.98%); then the loss of pyridine li-
gands followed in the temperature range 128–187 ꢁC
with the weight loss of 17.19% (calcd. 17.47%). The
decomposition process of the 3-cba ligand occured
above 360 ꢁC and heating to 600 ꢁC gave black solid re-
side which is likely to be CuO with the weight loss of ca.
82.81%, close to the theoretical value of 82.45%. How-
ever, when 2 were heated, the weight loss of 29.41%
was observed from 99 to 318 ꢁC, which is attributed to
the release of both Py and coordinated water molecules
(calcd. 30.34%). The decomposition process of the 3-cba
ligand began from 318 ꢁC and the final inorganic reside
was formed above 463 ꢁC with a weight loss of ca.
41.29%.
˚
centroid distance of 3.77 A, giving a 2-D network
parallel to the bc plane, as shown in Fig. 2(b) The near-
˚
est Cd(II)ꢀ ꢀ ꢀCd(II) distance is 6.2547(5) A through
hydrogen bonds, much shorter than the value of
˚
12.1449(9) A through p–p stacking interactions.
Variable-temperature magnetic behavior of 1 is plot-
ted in Fig. 3. For 1, a non-linear fit vM = C/(T ꢁ h) + v0
above 20 K reveals a Curie-Wesis behavior with the
Curie constant C = 0.361(2) cm3 molꢁ1 K, the Weiss
constant h = ꢁ5.2(1) K, and background susceptibility
v0 = ꢁ7.7(1) · 10ꢁ4 cm3 molꢁ1. The vM value increases
with decreasing the temperature, reaching a maximum
of 0.02 cm3 molꢁ1 at around 8.5 K, and then decreases
very quickly. The value of vMT is 0.367 cm3 molꢁ1 K
at room temperature, which is somewhat smaller than
the value (0.38 cm3 molꢁ1 K) expected for a non-inter-
acting Cu(II) ion. On lowering the temperature, the va-
lue ofvMT decreases smoothly until approximately 50 K
and then decreases at a faster rate, reaching a value of
0.043 cm3 molꢁ1 K at 2 K. This is characteristic of sig-
nificant antiferromagnetic ordering (TN = 8.5 K).
According to the structure of 1, two possible mag-
netic exchange coupling pathways are taken into con-
sideration: one is via hydrogen bonds and the other
through 3-cba ligands. Since the shorter interchained
˚
Cuꢀ ꢀ ꢀCu distance (4.6827(16) A) connected by hydro-
gen bonds is less than half of the intrachained
˚
Cuꢀ ꢀ ꢀCu distance (10.327(4) A) bridged by 3-cba
groups, sizable magnetic exchange interactions would
occur in interchains. Actually, the magnetic behavior
In summary, two new 3-cba coordination complexes
have been synthesized and structurally characterized.
The coordination modes of 3-cba ligands in the two
complexes are different from each other, resulting in dif-
ferent structures: 1 with a 1-D chained structure and 2
with an isolated configuration. Variable-temperature
magnetic susceptibility data indicate that 1 exhibits
antiferromagnetic interactions through hydrogen bonds
owing to the shorter distance between the Cu(II) mag-
netic centers. The thermogravimetric analyses of the
two complexes have also been performed.
0.4
0.020
0.3
0.2
0.1
0.0
χ
0.020
0.015
0.010
0.015
0.010
0.005
0.000
χ
χ
5
15
T1/0K
Acknowledgements
0
50
100
150 200
T /K
250 300
We gratefully acknowledge the financial support of
the National Natural Science Foundation of China
(20131020) and Natural Sciences Foundation of Fujian
Province (2003I031, A0420002).
Fig. 3. Temperature dependence of vM and vMT for 1 with the solid
line showing the best fit obtained through vM values. Inset: low
temperature region of vM
.

712
Y. Li et al. / Inorganic Chemistry Communications 8 (2005) 708–712
Found: C, 55.93%; H, 3.53%; N, 9.09%. IR data (KBr): 3436w,
Appendix A. Supplementary data
2924m, 2854w, 2232s (m(CN)), 1630s (masym(CO2)), 1575m, 1488w,
1447m, 1433m, 1386s (msym(CO2)), 1376s (msym(CO2)), 1071w,
1046w, 766s, 696m, 678m, 641w, 565w, 469w, 444w (cmꢁ1).
[18] Synthesis of 2: a mixture of Cd(NO3)2 Æ 4H2O (0.5 mmol, 154 mg),
pyridine (0.8 mL, 2.5 mmol) and 3-cba (1.0 mmol, 147 mg) in
ethanol (10 mL) was sealed in a polyfluoro-ethylene-lined stainless
steel bomb, and kept at 100 ꢁC under autogenous pressure for 3
days. After slowly cooling at 1 ꢁC/h to room temperature, the
colorless prism crystals of 2 were obtained by filtration and air-
dried. Anal. Calc. for [Cd(3-cba)2(Py)2(H2O)]: C, 53.46%; H,
3.57%; N, 9.47%. Found: C, 53.71%; H, 3.47%; N, 9.64%. IR data
(KBr): 3409br, 2232s (m(CN)), 1601m, 1591m, 1551vs
(masym(CO2)), 1484w, 1443s, 1429s, 1393vs (msym(CO2)), 1215w,
1068w, 1038w, 1013w, 787m, 769s, 701s, 683w, 629w (cmꢁ1). Itꢀs
evident that the separation between masym(CO2) and msym(CO2)
frequencies for 1 (av. 249 cmꢁ1) with unidentate coordination
mode of carboxylate group is much larger than that for 2
(158 cmꢁ1) with chelating.
Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/
j.inoche.2005.05.008.
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V = 1907.3(13) A ,
˚
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