Structure and magnetic behaviour of a novel alternating one-dimensional chain compound {[Cu(phen)(μ1,1-N3)]2 (μ-ta)}n

Article abstract of DOI:10.1016/S0277-5387(01)00705-7

A new one-dimensional alternating chain compound {[Cu(phen)(μ_1,1-N₃)]₂ (μ-ta)}_n(phen = 1,10-phenanthroline, ta = terephthalato dianion) has been prepared and characterised by X-ray crystallography and magnetic measurements. The structure consists of copper chains in which the copper(II) ions are alternatively bridged by terephalato and double end-on azido bridges. In the temperature range 4-300 K, the variable temperature magnetic susceptibility of the title compound can be modelled as a dimeric copper species within which the exchange interaction is ferromagnetic.

Full text of DOI:10.1016/S0277-5387(01)00705-7

Polyhedron 20 (2001) 681–684
www.elsevier.nl/locate/poly
Structure and magnetic behaviour of a novel alternating
one-dimensional chain compound {[Cu(phen)(m1,1-N3)]2(m-ta)}n
Licun Li a,*1, Daizheng Liao b, Zonghui Jiang a,*2, Shiping Yan a
a Department of Chemistry, Nankai Uni6ersity, Tianjin 300071, People’s Republic of China
b State Key Laboratory of Structural Chemistry, Fujian Institute of research on Structure of Matter, Chinese Academy of Sciences,
Fujiian 350002, People’s Republic of China
Received 25 October 2000; accepted 14 December 2000
Abstract
A new one-dimensional alternating chain compound {[Cu(phen)(m1,1-N3)]2(m-ta)}n (phen=1,10-phenanthroline, ta=terephtha-
lato dianion) has been prepared and characterised by X-ray crystallography and magnetic measurements. The structure consists
of copper chains in which the copper(II) ions are alternatively bridged by terephalato and double end-on azido bridges. In the
temperature range 4–300 K, the variable temperature magnetic susceptibility of the title compound can be modelled as a dimeric
copper species within which the exchange interaction is ferromagnetic. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Azide; Copper(II) compound; Crystal structure; Magnetic properties; Terephthalate
1. Introduction
2. Experimental
A safe strategy in designing alternating chains is the
reaction of metal salts with a combination of different
ligands with multiple bridge capacity [1]. Terephthalato
and azide ligands, due to their versatile bonding modes
with metal ions, have been widely used in the synthesis
of one-dimensional [2], two-dimensional [3] and three-
dimensional [4] systems. A number of alternating chain
compounds with azide ligands have been reported [5].
In order to develop a new alternating chain with ferro-
and antiferromagnetic interactions, the reaction system
of copper(II) ion with terephthalato dianion and azide
as bridging ligands has been explored. Here we report
the synthesis, crystal structure and magnetic properties
of the compound {[Cu(phen)(m1,1-N3)]2(m-ta)}n (phen=
1,10-phenanthroline, ta=terephthalato dianion). To
our knowledge, no similar compound has been reported
and it is a novel structural mode of an alternating chain
compound.
2.1. Materials
1,10-Phenanthroline, copper(II) nitrate trihydrate
and sodium azide were purchased from commercial
sources and used as received.
2.2. Preparation of single crystals of the compound
{[Cu(phen)(v1,1-N3)]2(v-ta)}n
Single crystals of the compound {[Cu(phen)(m1,1
-
N3)]2(m-ta)}n were grown in aqueous solution by a
slow-diffusion method using an H-double-tube glass
vessel. The starting solution was aqueous solutions of
Cu(phen)(NO3)2 (0.01 M) in one arm, NaN3 (0.01 M)
and dipotassium terephthalate (0.01 M) in the other
one. After a month, bright green crystals were sepa-
rated. Anal. Found: C, 52.31; H, 2.75; N, 18.78; Cu,
16.34. Calc. for C32H20N10O4Cu2: C, 52.25; H, 2.74; N,
19.04; Cu, 17.28%.
2.3. Physical measurements
1 *Corresponding author. E-mail: coord@sun.nankai.edu.cn
2 *Corresponding author.
Elemental analysis for carbon, hydrogen and nitro-
gen were carried out on a Perkin–Elmer elemental
0277-5387/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0277-5387(01)00705-7

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L. Li et al. / Polyhedron 20 (2001) 681–684
analyser model 240. Metal contents were determined by
EDTA titration. Variable temperature magnetic suscep-
tibilities were measured on an MPMS-7 SQUID mag-
netometer. Diamagnetic corrections were made with
Pascal’s constants for all constitute atoms and the
magnetic moments were calculated by the equation
ware. A full matrix least-squares refinement on F2 was
carried out using SHELXL-97 and the goodness-of-fit on
F2 was 1.021. The final agreement factor values are
R1=0.0485, wR2=0.1021(I\2|), R1=ꢀ(ꢁꢁFoꢁ−ꢁFcꢁꢁ)/
wR2=(ꢀwꢁFo ꢁ−ꢁFc ꢁ)2/ꢀwꢁFo ꢁ)2,
w=1/
2
2
2
ꢀꢁFoꢁ,
[|2(Fo 2)+(0.0500P)2+0.000P] where P=(Fo
+
2
veff=2.828(MT)1/2
.
2Fc 2)/3. Significant bond parameters are given in Table
2.
2.4. Crystal structure determination and refinement
3. Results and discussion
A bright green single crystal of the title compound
having the approximate dimensions 0.20×0.1×0.05
mm3, was put on a Bruker Smart 1000 diffractometer
equipped with graphite-monochromated Mo Ka radia-
3.1. Description of the structure
A
perspective drawing of the basic unit of
,
tion (u=0.71073 A). Data were collected at room
{[Cu(phen)(m1,1-N3)]2(m-ta)}n is shown in Fig. 1. The
structure consists of neutral chains of copper(II) atoms
linked by azido and terephthalato bridges. Two azido
bridges link two copper(II) ions in end-on mode and
give an asymmetrical copper(II) pair(Cu(1)ꢀN(4)ꢀ
Cu(1A)ꢀN(4A)), which has a inversion centre. The cop-
per pairs are linked together through the terephthalato
bridge so that they form an infinite chain. The cop-
per(II) ion is in a 4+1 distorted square-pyramidal
environment. Basal plane positions are occupied by two
nitrogen atoms of phen, one carboxylatoꢀoxygen atom
of the ta ligand and one nitrogen atom of the azido
bridge. This basal plane is roughly perpendicular to the
plane of the terephthalato bridge. The apical position is
occupied by one nitrogen atom(N(4)) of the other azido
bridge ligand. The apical bond length Cu(1)ꢀN(4)=
temperature to a 2qmax value of 26.43°, with a total of
4175 reflections collected including 2918 independent
reflections (Rint=0.0420). A summary of the crystallo-
graphic data is given in Table 1. The structure was
solved with direct methods using the SHELXS-97 soft-
Table 1
Crystallographic data and processing parameters for {[Cu(phen)(m1,1
N3)]2(m-ta)}n
-
Formula
C32H20N10O4Cu2
735.66
triclinic
Formula weight
Crystal system
Space group
(
P1
Unit cell dimensions
,
a (A)
6.3398(13)
10.861(2)
11.399(2)
110.561(4)
96.751(4)
97.779(4)
716.5(2)
1
,
b (A)
,
2.461(4) A is longer than the equatorial ones. The
,
c (A)
h (A)
i (A)
k (A)
copper(II) atom is displaced towards the apical site by
,
,
,
0.0730 A. The azido group is quasi-linear (178.1(5)° for
,
N(4)ꢀN(2)ꢀN(3)) and the bond angle Cu(1)ꢀN(4)ꢀ
3
,
V (A )
Cu(1A) is 94.89(15)°. The value of Cu(1)ꢀO(1) bond is
Z
,
1.930(3) A, in agreement with analogous literature dis-
Dcalc (g cm−3
F(000)
R1
)
1.705
372
0.0485
tances [6]. The intrachain Cu···Cu distances through
double end-on azido bridges and the terephthalato
wR2
0.1021
,
bridge are 2.737 and 10.848 A, respectively. The short-
,
est interchain metal–metal separation is 7.887 A.
Table 2
3.2. Magnetic properties
,
Selected bond distances (A) and bond angles (°) for the compound
{[Cu(phen)(m1,1-N3)]2(m-ta)}n
Magnetic susceptibility measurements (4–300 K) in-
dicate the occurrence of weak ferromagnetic coupling in
the {[Cu(phen)(m-1,1-N3)]2(m-ta)}n complex. It is well
known that terephthalate as a bridge, in general, can
mediate weak magnetic exchange interactions between
first transition-metal ions [7] and that double end-on
azido bridges with bond angles such as observed in this
case are able to mediate a ferromagnetic interaction
between copper(II) ions [8]. Considering these magnetic
properties, two possibilities can be envisaged. The sim-
ple one corresponds to a copper (II) dimer, assuming
Bond distances
Cu(1)ꢀO(1)
Cu(1)ꢀN(9)
Cu(1)ꢀN(4)
1.930(3)
2.010(3)
2.461(4)
Cu(1)ꢀN(4A)
Cu(1)ꢀN(10)
Cu(1)ꢀO(4)
1.980(4)
2.038(4)
2.737(3)
Bond angles
O(1)ꢀCu(1)ꢀN(4A)
N(4A)ꢀCu(1)ꢀN(9)
N(4A)ꢀCu(1)ꢀN(10) 173.31(14) N(9)ꢀCu(1)ꢀN(10)
O(1)ꢀCu(1)ꢀN(4)
95.79(13) O(1)ꢀCu(1)ꢀN(9)
92.31(14) O(1)ꢀCu(1)ꢀN(10)
168.01(13)
90.45(13)
81.16(13)
86.77(13)
178.1(5)
102.69(12) N(9)ꢀCu(1)ꢀN(4)
94.89(15) N(4)ꢀN(2)ꢀN(3)
Cu(1)ꢀN(4)ꢀCu(1A)

L. Li et al. / Polyhedron 20 (2001) 681–684
683
Fig. 1. The labelled diagram of the compound {[Cu(phen)(m1,1-N3)]2(m-ta)}n. Thermal ellipsoids are at the 30% probability level.
Fig. 2. Molar susceptibility (ꢀ) and effective magnetic moment (ꢁ) for{[Cu(phen)(m-1,1-N3)]2(m-ta)}n as a function of temperature. The solid line
corresponds to the fit of the corrected Bleaney–Bowers expression.
Considering the compounds structural data, the un-
paired electron coming the copper(II) ion occupied a
d-type magnetic orbital pointing toward the four
nearest neighbours in the basal plane, i.e. the N(9),
N(10), O(1), and N(4A) atoms. This orbital is roughly
perpendicular to the plane of the terephthalate bridge.
It has been proved that coplanarity of the terephthalate
and the magnetic orbital is a prerequisite to observe an
interaction through this bridge between two magnetic
centres that are far apart from each other [11]. There-
that the magnetic coupling mediated by the terephtha-
lato bridge is negligible. In this case, we used the simple
Bleaney–Bowers expression to fit the magnetic data.
The fitting result is poor at low temperature. Taking
into account the molecular field approximation [9], the
corrected Bleaney–Bowers equation was used to fit the
experimental data now and the magnetic data fit the
model perfectly (Fig. 2). The best-fitting parameters
are: J=12.36 cm−1, zJ%= −1.46 cm−1, g=2.05 and
R=4.68×10−6 (R is an agreement factor defined as
R=ꢀ[(M)obs−(M)calc]2/ꢀ[(M)obs]2. Another possibil-
ity is that the terephthalato bridge mediates weak mag-
netic interaction and the magnetic behaviour of the
compound can be explained by the alternating ferro-
and antiferromagnetic Heisenberg chain model [10].
fore, the exchange coupling of the {[Cu(phen)(m1,1
-
N3)]2(m-ta)}n compound through the terephthalate
bridge is negligible and the alternating Heisenberg
chain model is not reasonable. In the title compound,
the magnetic interaction through asymmetrical double

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L. Li et al. / Polyhedron 20 (2001) 681–684
end-on azido bridges is +12.36 cm−1, which indicates
a weak ferromagnetic interaction. This is as expected
because the azido bridges connect an equatorial site
with a high spin density to an apical site which has a
weak spin density and that is less favourable to mediate
magnetic exchange [12]. There is weak antiferromag-
netic coupling between alternating chains.
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4. Supplementary data
Crystallographic data for the structural analysis have
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Acknowledgements
This project was supported by the Tianjin Natural
Science Foundation, Tianjin the 21st Century Science
Foundation for Youth (No. 983700511).
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