Synthesis and magnetic property of a dual μ-[N(CN)2] bridged copper(II) supramolecule with dinuclear unit

Article abstract of DOI:10.1016/j.inoche.2005.09.022

A dicyanamide (dca) Cu(II) supramolecular complex constructed by hydrogen-bond interactions and weak Cu-N bond interactions has been prepared and the structure was determined by X-ray diffraction analysis. The magnetic studies indicate that strong antiferromagnetic interactions exist between two Cu(II) ions of the dca-bridged dimer.

Full text of DOI:10.1016/j.inoche.2005.09.022

Inorganic Chemistry Communications 8 (2005) 1169–1172
www.elsevier.com/locate/inoche
Synthesis and magnetic property of a dual l-[N(CN)2]
bridged copper(II) supramolecule with dinuclear unit
*
Qian Shi , Mao-Lin Hu, Hong-Ping Xiao, Xin-Hua Li
School of Chemistry and Materials Science, Wenzhou Normal College, Wenzhou Zhejiang 325027, PR China
Received 14 July 2005; accepted 10 September 2005
Available online 2 November 2005
Abstract
A dicyanamide (dca) Cu(II) supramolecular complex constructed by hydrogen-bond interactions and weak Cu–N bond interactions
has been prepared and the structure was determined by X-ray diffraction analysis. The magnetic studies indicate that strong antiferro-
magnetic interactions exist between two Cu(II) ions of the dca-bridged dimer.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Dicyanamide; Supramolecule; Crystal structure; Magnetic material
Dicyanamide-bridged 1D to 3D extended systems are
attracting much attention in the field of crystal engineering
and the design of inorganic coordination polymers, because
of their fascinating structures and long-range magnetic
ordering in the binary a-M(dca)2 (dca = dicyanamide)
compounds [1]. More generally, dca is also a very interest-
ing ligand due to the presence of three potential donor
centers and varieties of possible bridging fashions [2]. Inter-
esting types of structures such as rutile-like networks and
interpenetration have been already observed in dca bridged
compounds. However, in most of the dca-bridged coordi-
nation polymers reported, dca acts both as network-
constructed factor and as counter-anion to balance the
charge on the metal. Neutral monodentate, chelated and
bridging ligands have been used as coligands, for the con-
struction of multiform topologies and architectures with
potential applications as functional materials, while the
examples of ionic ligand as coligand are limited [3]. Herein,
a novel Cu(II) supramolecular complex was reported,
which is constructed by two anion ligands, dca and pcl
(Hpcl = picolinic acid).
The title complex [Cu(N(CN)2)(C6H4NO2)(H2O)]2 was
prepared by mixing the methanol solution of CuCl2 Æ 2H2O
(0.5 mmol) 10 mL and aqua solution of picolinic acid
(0.5 mmol) 10 mL, and stirring for 30 min at room temper-
ature. The aqua solution of sodium dycyanamide
(0.5 mmol) 10 mL dropped into the above mixture, and
adjusted the pH value to 5 using 10% NaOH aqua solution,
further stirring for 30 min. Blue-green solution was filtered
and standing at room temperature, and block blue-green
crystals were obtained and washed with methanol solution
(yield 78%). At the same time, a few of blue crystals of
Cu(pcl)2 (determined by X-ray diffraction analysis) were
obtained as by-product, which can be separated from the
title complex manually, due to the differences in the color
and shape of the crystals.
The single X-ray crystallographic analysis [4] reveals
that the Cu(II) anion is surrounded by three N atoms from
a pcl ligand and two dca ligands, two O atoms from a pcl
ligand and an aqua molecule as depicted in Fig. 1. The dca
ligand has a dual l1,5-coordination fashion, and two dca
molecules link two Cu(II) into a porous dinuclear unit,
while the pcl ligand coordinates to the metal ion with a
bidentate mode using the N atom of pyridine ring and
the O atom of the carboxylate group. The N1, N2, N4A
and O1 atoms are in the equatorial plane (average devia-
*
Corresponding author. Tel.: +86 577 88373111; fax: +86 577
88373113.
E-mail address: shiq@wznc.zj.cn (Q. Shi).
1387-7003/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2005.09.022

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Q. Shi et al. / Inorganic Chemistry Communications 8 (2005) 1169–1172
Fig. 1. The coordination environment of Cu(II) in the title complex, thermal ellipsoids are shown in 50% probability.
tion: 0.0201) and the deviation of Cu(II) from the above
plane is 0.1691 A. The O1W atom occupies the axial posi-
unit) of two adjacent dinuclear units, with the distance of
3.856 and 3.353 A, respectively. Besides of the weak bond
˚
˚
tion. The bond distances of Cu–N1, Cu–N2, Cu–N4A and
Cu–O1 are 1.986(3), 1.979(3), 1.984(3) and 1.955(2) A
interactions, there are hydrogen-bond interactions between
˚
the O1w(aqua) ÆÆÆ O2(carboxylate) with the distance of
˚
respectively, in which both of the two Cu–N (dca) bonds
distances are with slightly difference, and also nearly to
the corresponding value in some Cu–dca systems reported
[5]. The O1W atom occupies the axial position, and the
bond distance of Cu–O1W is somewhat longer with the
2.782 A, forming a one dimensional chain. The chains are
also assembled by the hydrogen-bond interactions between
˚
O1w(aqua) ÆÆÆ O2(carboxylate) with the distance of 2.766 A.
Viewing down the c axis, it is interesting to find that the
hydrogen-bond interactions constructed by two O atoms
of aqua molecules and two O atoms of carboxylate groups,
link into a regular square plane as shown in Fig. 2. The title
complex forms a channel-like supramolecular structure
(Fig. 3), due to the construction of normal coordination
bonds along with the hydrogen-bond interactions and the
weak interactions of the Cu–Cu and Cu–N4 bonds.
Variable temperature magnetic susceptibilities were
determined in the temperature range of 4–300 K on a
Quantum Design MPMS SQUID magnetometer at the
applied magnetic field of 10 T. All data were corrected
for diamagnetism of the ligands estimated from Pascalꢀs
˚
value of 2.257(3) A. The bond angles of N1–Cu–N2, N2–
Cu–N4A, N4A–Cu–O1 are in the range of 82.59(10)–
91.49(12)ꢁ, and those of N1–Cu–N4A and N2–Cu–O1
are 167.92(14)ꢁ and 171.14(13)ꢁ respectively. The angles
of the bond N1–Cu–O1W, N2–Cu–O1W, N4A–Cu–
O1W, and O1–Cu–O1W are in the range of 93.45(11)–
95.87(11)ꢁ, indicating the distorted square–pyramidal
environment of the Cu(II) anion. The bond distances of
˚
N3–C7 and N3–C8 are 1.297(5) and 1.301(5) A, while the
bond angle of C7–N3–C8 is 118.8(3)ꢁ, lightly smaller than
120ꢁ, indicating the N3 atom of the dca ligand has hybrid
sp2 orbitals. The dca ligand has an end to end coordination
mode and links two Cu(II) anions forming a porous struc-
ture with dinuclear unit.
constants [6]. Effective magnetic moments were calculated
pffiffiffiffiffiffiffiffiffiffiffi
by the equation leff
¼
8vMT, where vM is the magnetic
susceptibility per Cu(II) moiety. The plots of the molar
magnetic susceptibility versus T and the effective magnetic
moment leff versus T for the title complex are shown in
In this system, there exist weak interactions between the
Cu–Cu and Cu–N4 (from the dca ligand of the symmetric
Fig. 2. A perspective view down the c-axis of the hydrogen-bond interactions.

Q. Shi et al. / Inorganic Chemistry Communications 8 (2005) 1169–1172
1171
Fig. 3. A perspective view down the b-axis of the channel-like network of the title complex.
Fig. 4. The plots of vM vs T (hhh) and leff vs T (nnn) for the title complex.
Fig. 4. The leff value at room temperature, 2.03 lB, exceeds
the spin-only value for Cu(II) anion (1.73 lB), increases
smoothly from 300 to 140 K, and decreases sharply to
reach 0.06 lB at 9 K. On further lowering the temperature,
the value increases gradually to 0.18 lB at 5 K. This beha-
vior indicates the presence of antiferromagnetic interaction
between two Cu(II) ions of the dimer.
The magnetic data of the title complex were fitted to the
modified Bleaney–Bowers equation shown below [7], allow-
ing for the presence of paramagnetic impurity, where P is
the mole fraction of the non-coupled Cu(II) impurity,
J is somewhat higher than the relative dca complexes re-
ported [2a], which may be due to effective supercoupling
change via the Cu–Cu and picolinate ÆÆÆ H2O pathways
rather than the dca bridges.
In conclusion, a novel Cu(II) supramolecular complex
composed of two anion ligands (dca and pcl) was prepared
by solution synthesis, in which the channel-like network is
constructed by O(aqua) ÆÆÆ O(carboxylate) hydrogen-bond
interactions and Cu–N weak bond interactions among
the dca-bridged Cu(II) dimers. The magnetic studies shown
that there exist strong antiferromagnetic interactions bet-
ween two Cu(II) ions, and the Cu–Cu and picolinate ÆÆÆ
H2O pathways might acts as the effective supercoupling
exchange media rather than the dca ligand.
2Ng2b2
kT
Ng2b2
2kT
2
kT
vM
¼
½3 þ eꢀ2J ꢁꢀ1ð1 ꢀ PÞ þ
P.
The best fit parameters are: J = ꢀ34.8 cmꢀ1, g = 2.65, P =
P
m
2
0.17% and R = 3.43 · 10ꢀ8, where R ¼ i¼1ðvicalc ꢀ vei xpÞ =
Acknowledgement
P
m
i¼1
2
ðvei xpÞ , which conforms the existing of antiferromag-
netic supercoupling exchange interactions between two
Cu(II) ions. However, the value of the coupling parameter
We thank the National Natural Science Foundation of
China (20471043) for financial support of this study.

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Q. Shi et al. / Inorganic Chemistry Communications 8 (2005) 1169–1172
(c) Y.M. Chow, Inorg. Chem. 10 (1971) 1938;
Appendix A. Supplementary data
(d) J.L. Manson, C.D. Incarvito, A.L. Rheinhold, J.S. Miller, J. Chem.
Soc., Dalton Trans. (1998) 3705;
(e) J.L. Manson, C.R. Kmety, Q. Huang, J.W. Lynn, G. Bendele, S.
Pagola, P.W. Stephens, L.M. Liable-Sands, A.L. Rheingold, A.J.
Epstein, J.S. Miller, Chem. Mater. 10 (1998) 2552.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.inoche.2005.
09.022.
[3] A.M. Madalan, C. Paraschiv, J.-P. Sutter, M. Schmidtmann, A.
Muller, M. Andruh, Crystal Growth Design 5 (2004) 707.
¨
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