Two new pseudohalide-bridged Cu(II) complexes with a hydrazone ligand: Syntheses, crystal structures and magnetic studies

Article abstract of DOI:10.1016/j.ica.2008.01.020

Two new pseudohalide-bridged copper(II) complexes [{Cu(PBH)(μ_1,1-CNO)}₂] (1) and {Cu(PBH)(μ_1,5-NCNCN)}_n (2) (where HPBH = 2-pyridinecarboxaldehyde benzoyl hydrazone) have been synthesised and characterised by elemental analysis, CV, IR and UV-Vis spectral studies. The tridentate hydrazone pro-ligand (HPBH) was obtained by the condensation of benzhydrazide and pyridine-2-carboxaldehyde. Structures of both complexes have been established by X-ray crystallography which shows that 1 is a μ_1,1-CNO^--bridged dimer whereas 2 is a μ_1,5-dca-bridged (dca = dicyanamide) linear polynuclear structure. Variable temperature magnetic susceptibility studies indicate weak antiferromagnetic interactions with J values -0.50 cm^-1 and -0.10 cm^-1 for 1 and 2, respectively.

Full text of DOI:10.1016/j.ica.2008.01.020

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Inorganica Chimica Acta 361 (2008) 2707–2714
www.elsevier.com/locate/ica
Two new pseudohalide-bridged Cu(II) complexes with a
hydrazone ligand: Syntheses, crystal structures and magnetic studies
a
a
a
a,
*
Sambuddha Banerjee , Soma Sen , Subhra Basak , Samiran Mitra ,
b
c
´
David L. Hughes , Cedric Desplanches
a Department of Chemistry, Jadavpur University, Kolkata 700 032, India
b School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, UK
`
´ ´
Institut de Chimie de la Matiere Condensee de Bordeaux – CNRS, Universite Bordeaux 1, Avenue du Dr. Schweitzer, F-33608 Pessac, France
c
Received 3 July 2007; received in revised form 22 January 2008; accepted 23 January 2008
Available online 1 February 2008
Abstract
Two new pseudohalide-bridged copper(II) complexes [{Cu(PBH)(l1,1-CNO)}2] (1) and {Cu(PBH)(l1,5-NCNCN)}n (2) (where
HPBH = 2-pyridinecarboxaldehyde benzoyl hydrazone) have been synthesised and characterised by elemental analysis, CV, IR and
UV–Vis spectral studies. The tridentate hydrazone pro-ligand (HPBH) was obtained by the condensation of benzhydrazide and pyri-
dine-2-carboxaldehyde. Structures of both complexes have been established by X-ray crystallography which shows that 1 is a l1,1
-
CNOꢀ-bridged dimer whereas 2 is a l1,5-dca-bridged (dca = dicyanamide) linear polynuclear structure. Variable temperature magnetic
susceptibility studies indicate weak antiferromagnetic interactions with J values ꢀ0.50 cmꢀ1 and ꢀ0.10 cmꢀ1 for 1 and 2, respectively.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Copper(II) complexes; Tridentate hydrazone ligand; Pseudohalide bridged; Crystal structures; Variable temperature magnetic studies
1. Introduction
pseudohalides and other spacer ligands. With this in mind
we prepared two new Cu(II) complexes with the hydrazone
ligand (PBHꢀ) and two different pseudohalides, cyanate
and dicyanamide [dca, NðCNÞ2ꢀ], to observe the variations
in structures and magnetic properties.
Aroylhydrazone complexes of transition metal ions are
known to provide useful models for the elucidation of the
mechanism of enzyme inhibition by hydrazine derivatives
[1] and for their possible pharmacological applications
[2]. Additionally, hydrazone complexes have been the sub-
ject of studies for many years due to their antimicrobial
and antitumor activities [3–9]. Copper and cadmium com-
plexes using a tridentate hydrazone ligand, the condensa-
tion product of 2-acetylpyridine and benzhydrazide, have
been reported by our group [10,11]. In continuation of pre-
vious work, we have prepared a similar type of tridentate
ligand, HPBH, from the condensation of pyridine-2-car-
boxaldehyde and benzhydrazide.
Compound 1, [{Cu(PBH)(l1,1-CNO)}2] is an end-on
l1,1-cyanato-bridged dimeric Cu(II) complex, whereas 2 is
a dca-bridged polynuclear Cu(II) complex. The larger
pseudohalide ligand, dicyanamide, has been extensively
used during the last few years to generate a wide variety
of polynuclear compounds of different topologies and mag-
netic properties partly due to the discovery of long range
magnetic ordering in the a-M(dca)2 compounds [12,13].
A particular feature of the dca ligand is the versatility of
its coordination modes [14–18] shown to generate com-
pounds with a large variety of architectures, binding one
[19], two [20,21], three [22] or four [23] metal centers. We
therefore now wish to prepare high-dimensional metal
complexes with dca as bridging ligand and polyamines as
coligands. There are few reports of dca-bridged metal com-
Our group is mostly concerned with the magnetic inter-
actions between paramagnetic metal centers bridged by
*
Corresponding author. Tel.: +91 33 2668 2017; fax: +91 33 2414 6414.
E-mail address: smitra_2002@yahoo.com (S. Mitra).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.01.020

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S. Banerjee et al. / Inorganica Chimica Acta 361 (2008) 2707–2714
plexes with a Schiff base as the coligand [24–26]. In this
paper, we describe the syntheses, X-ray crystal structures,
variable temperature magnetic (VTM) susceptibility mea-
surements, spectroscopic results and cyclic voltammetric
studies of the two new Cu(II) complexes 1 and 2.
Anal. Calc for C28H20Cu2N8O4: C, 50.99; H, 3.06; N,
16.99. Found: C, 50.87; H, 3.02; N, 16.92%.
2.3.3. Synthesis of {Cu(PBH)(l1,5-NCNCN)}n (2)
Compound 2 was prepared in an analogous way;
1 mmol (0.089 gm) dca in minimum volume of water was
used in place of sodium cyanate. Crystals suitable for X-
ray diffraction were obtained on overnight standing in
refrigerator. Yield: 65%.
2. Experimental
2.1. Materials
Anal. Calc. for C15 H10 Cu N6 O: C, 50.92; H,2.85; N,
23.75. Found: C, 50.89; H, 2.83; N, 23.71%.
Benzhydrazide, pyridine-2-carboxaldehyde, copper(II)
perchlorate hexahydrate, sodium cyanate and dicyanamide
(Fluka) were used as received without further purification.
All the solvents were of reagent grade.
2.4. X-ray crystallography
The determination of the unit cells and the intensity data
collection for 1 and 2 were performed on an Oxford Dif-
fraction Xcalibur-3 CCD diffractometer equipped with
Mo Ka radiation and graphite monochromator. Data were
processed using the CRYSALIS-CCD and -RED [28] programs.
The structures of both complexes were determined by
direct methods procedures in SHELXS [29a], and refined by
full-matrix least-squares methods, on F2’s, in SHELXL
[29b]. Carbon-bonded hydrogen atoms were included in
idealised positions and set to ride on the parent atoms.
The crystallographic data and the refinement results are
listed in Table 1.
2.2. Physical measurements
Elemental analyses were carried out using a Perkin–
Elmer 2400 II elemental analyzer. The infrared spectra
were recorded on a Perkin–Elmer RX 1 FT-IR spectropho-
tometer with a KBr disc. The electronic spectra were
recorded, in acetonitrile, on a Perkin–Elmer Lambda 40
(UV–Vis) spectrophotometer. Electrochemical studies were
carried out with a Versastate II cyclic voltammeter using
tetrabutylammonium perchlorate as supporting electrolyte.
Magnetic susceptibility measurements for 1 and 2 were car-
ried out with a Quantum Design MPMS-5S SQUID mag-
netometer under an applied magnetic field of 5000 Oe. The
temperature dependence of the molar magnetic susceptibil-
ity for 1 and 2 was measured on polycrystalline samples in
the temperature range 2–300 K. Diamagnetic corrections
were estimated from Pascal tables and magnetic data were
corrected for diamagnetic contributions of the sample
holder.
Table 1
Crystallographic and refinement data for complexes 1 and 2
Complex
1
2
Chemical formula
Formula weight
Crystal system
Space group
C
659.6
28H20N8O4Cu2
C15H10N6OCu
353.8
triclinic
monoclinic
P21/n (equiv. to
no. 14)
2
7.2133(9)
11.2710(6)
16.896(2)
90
103.799(11)
90
1334.0(3)
140(1)
ꢀ
P1 (no. 2)
2.3. Synthesis
Z
2
˚
a (A)
7.5489(8)
9.4986(16)
10.1997(13)
86.824(12)
76.482(11)
85.064(11)
707.99(17)
140(1)
˚
2.3.1. Synthesis of the pro-ligand
[C6H5C(O)NHN@C(H)C5H4N] (HPBH)
The pro-ligand was synthesised by condensing benzhy-
b (A)
˚
c (A)
a (°)
b (°)
c (°)
drazide with pyridine-2-carboxaldehyde following
a
method reported elsewhere [27]. The resulting light yellow
liquid solution was used without further purification.
Caution! Perchlorate salts are potentially explosive and
should be prepared in small quantities and handled with
much care.
3
˚
V (A )
Temperature (K)
Density (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
1.642
1.646
668
1.660
1.556
358
)
Crystal size (mm)
h Range for data collection (°)
Reflections collected
0.51 ꢁ 0.08 ꢁ 0.02 0.7 ꢁ 0.08 ꢁ 0.02
3.8–30.0
23883
3.6–30.0
10962
2.3.2. Synthesis of [{Cu(PBH)(l1,1-NCO)}2] (1)
To a methanolic solution (20 ml) of copper perchlorate
hexahydrate (0.370 g, 1 mmol), the solution of the hydra-
zone pro-ligand (HPBH) (1 mmol) was added, followed
by the addition, with constant stirring, of a solution of
sodium cyanate (0.065 g, 1 mmol) in minimum volume of
water–methanol mixture. The final solution was kept at
refrigerator temperature yielding dark green, square crys-
tals suitable for X-ray diffraction after 1 day. Crystals were
isolated by filtration and were air-dried. Yield: 72%.
Independent reflections (Rint
Number of ‘observed’
reflections
)
3879 (0.062)
2746
4027(0.058)
2974
Goodness-of-fit, F2
R indices (all data)
0.944
0.961
R1 = 0.065;
wR2 = 0.069
R1 = 0.033;
wR2 = 0.063
0.50 and ꢀ0.41
R1 = 0.066;
wR2 = 0.076
R1 = 0.040;
wR2 = 0.071
0.66 and ꢀ0.63
Final R indices [I > 2r(I)]
Largest difference in peak and
ꢀ3
˚
hole (e A
)

S. Banerjee et al. / Inorganica Chimica Acta 361 (2008) 2707–2714
2709
Table 2
3. Results and discussion
˚
Molecular dimensions (bond lengths in A and angles in °) about the
copper atoms in complexes 1 and 2
3.1. Description of the crystal structures
1
2
Bond lengths
Cu–O(1)
Cu–N(3)
Cu–N(42)
Cu–N(51)
Cu–N(510)
3.1.1. Description of the structure of the pro-ligand (HPBH)
An X-ray analysis of the hydrazone molecule by Pasc-
halidis et al. [30] shows that HPBH, in the free state, exists
in the keto tautomeric form and the structural conforma-
tion of the molecule is E with respect to the imine double
bond. It is during complexation the molecule switches to
its enol form and is then deprotonated to act as a poten-
tially tridentate NNO donor with subsequent change of
conformation from E to Z.
1.9785(13)
1.9326(16)
2.0232(16)
1.9458(16)
2.3571(17)
Cu–O(1)
Cu–N(3)
Cu–N(2)
Cu–N(22)
Cu–N(340)
1.9746(16)
1.9660(18)
1.9414(18)
2.0148(19)
2.2031(19)
Bond angles
N(3)–Cu–O(1)
O(1)–Cu–N(42)
N(51)–Cu–O(1)
O(1)–Cu–N(510)
N(3)–Cu–N(42)
N(3)–Cu–N(51)
N(3)–Cu–N(510)
N(51)–Cu–N(42)
N(42)–Cu–N(510)
N(51)–Cu–N(510)
Cu–N(51)–Cu0
79.07(6)
159.13(6)
99.36(6)
93.81(6)
80.55(6)
170.66(7)
100.46(6)
100.02(7)
94.27(6)
88.81(6)
91.19(6)
N(2)–Cu–O(1)
O(1)–Cu–N(22)
N(3)–Cu–O(1)
O(1)–Cu–N(340)
N(2)–Cu–N(22)
N(2)–Cu–N(3)
N(2)–Cu–N(340)
N(22)–Cu–N(340)
N(3)–Cu–N(340)
N(3)–Cu–N(22)
78.87(7)
158.42(7)
98.21(7)
94.30(7)
80.32(7)
154.52(7)
106.23(7)
96.94(7)
99.22(7)
98.09(7)
3.1.2. Description of the structure of [{Cu(PBH)(l1,1
NCO)}2] (1)
-
An ORTEP diagram of 1 with atom numbering scheme
is given in Fig. 1. Bond dimensions about the copper atom
are listed in Table 2. The structural study reveals that 1 is a
centrosymmetric dimer in which the copper centers are five-
coordinate, bonded to three coordinating atoms [N2O]
from the PBHꢀ ligand and the nitrogen atoms from two
bridging cyanato anions. Each cyanato anion bridges in
end-on fashion and this leads to a relatively small Cu—
bridging cyanato group (with the longer Cu–N distance) is
at the apex.
The dimensions in the hydrazone ligand confirm that
this is in the enolate form. The whole ligand is approxi-
mately planar, with the normals to the two six-membered
rings differing by 4.00(13)°. Each ligand is overlapped by
a neighbouring ligand, related by an inversion center; the
planes are ca. 3.38 A apart. The dimer molecules are thus
linked, through the p–p interactions, to form staggered
chains through the crystal, Fig. 2.
˚
Cu (3.0874(6) A) separation. A similar structure with ace-
tato and chloro bridging has been reported earlier [31].
The cyanato ion bridges in an asymmetric (basal–apical)
fashion so that the Cu–N bond lengths are significantly dif-
˚
˚
ferent (Kd = 0.411 A). The cyanate ions are nearly linear
with N–C–O angle of 177.7(2)°. The geometry of the Cu(II)
centers is close to square pyramidal with s = 0.192,
[s = jb ꢀ aj/60°, where b and a are the two largest angles
around the central atom; s = 0 and 1 for the perfect square
pyramidal and trigonal bipyramidal geometries, respec-
tively] [32]. The square base is formed by pyridyl and imine
nitrogen atoms, a benzoyl oxygen atom and one bridging
cyanato nitrogen atom and the Cu(II) atom is shifted from
3.1.3. Description of the structure of {Cu(PBH)(l1,5
NCNCN)}n (2)
-
An ORTEP diagram of the Cu(PBH)+ fragment of 2
and the NCNCN ligands which are bonded to it, with atom
numbering scheme, is shown in Fig. 3. Bond dimensions
about the copper atom are listed in Table 2. The copper
atoms are five-coordinate, with a square pyramidal bond-
ing pattern, s = 0.065. The tridentate hydrazone ligand
(PBHꢀ) is, again, in the enolate form and close to planar;
the normals to the two six-membered rings are 6.84(9)°
apart. It coordinates through its O1, N2, N22 donor atoms
in the basal plane, and the remaining basal position is occu-
pied by a nitrogen (N3) of a bridging dca ion. The apical
position is occupied by the nitrogen atom of a second
dca ion with slightly longer Cu–N340 bond length. The
trans-base angles [N2–Cu1–N3 = 154.52(3)° and O1–
Cu1–N22 = 158.42(7)°] correspond to the displacement of
˚
this base by 0.1320(8) A. The nitrogen atom from the other
˚
the Cu atom by 0.3052(9) A from the mean basal plane.
The bridging Cu–N–C–N–C–N–Cu0 unit adopts a ‘‘V”
shaped conformation resulting from the sp2 hybridisation
of the central N atom of the dca, where the C31–N32–
C33 angle is 122.3(3)°. The ½NðCNÞ2ꢀꢂ ligand has pseudo
C2v symmetry with average C–N and C@N bond lengths
Fig. 1. View of a dimer molecule of complex 1 indicating the atom
numbering scheme. Thermal ellipsoids are drawn at the 50% probability
level.
˚
of 1.303(3) and 1.151(3) A, respectively, as commonly
observed [33]. The sp hybridised C atoms of the dca ligand

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S. Banerjee et al. / Inorganica Chimica Acta 361 (2008) 2707–2714
Fig. 2. A series of dimer molecules of complex 1, connected in chains through overlapping p–p interactions. Hydrogen atoms have been omitted for
clarity. Thermal ellipsoids are drawn at the 30% probability level.
Fig. 3. View of the Cu(PBH)+ unit and its coordinated l1,5 bridging dca ligands in complex 2, indicating the atom numbering scheme. Thermal ellipsoids
are drawn at the 50% probability level.
show near linearity whereas the C–N–Cu angles of
152.0(2)° and 136.4(2)° show different degrees of bending.
Structure 2 is a chain polymer of Cu(PBH)+ units
bridged by dca anions in l1,5 fashion. Pairs of these chains
form a double-stranded chain, running parallel to the a
axis, by the overlap of PBH ligands arranged alternately
from the two chains, Fig. 4. Within each double-stranded
chain, each hydrazone is overlapped on both sides by sym-
metry-related molecules. On one side, the overlap extends
over the whole ligand, and the ligand mean-planes are ca.
3.2. Infrared spectra
The IR spectra of the complexes in the region 4000–
250 cmꢀ1 were analysed in comparison with that of the
pro-ligand. The data give evidence for the coordination
of the ligand PBH to the metal ion via two nitrogen atoms
and one oxygen atom. The infrared spectra of complexes 1
and 2 display IR absorption bands at 1608 and 1605 cmꢀ1
,
respectively, which can be assigned to the C@N stretching
frequency of the coordinated ligand PBHꢀ whereas for the
free ligand the same band is observed at 1663 cmꢀ1. The
shift of this band on complexation towards lower wave
˚
3.46 A apart; on the other side, only the edges of the rings
˚
are involved in the overlap, ca. 3.37 A apart.

S. Banerjee et al. / Inorganica Chimica Acta 361 (2008) 2707–2714
2711
the imine nitrogen atom is involved in coordination to
the metal ion [38]. The visible spectra of 1 and 2 display
a single broad band at 673 and 663 nm, respectively. These
spectral features are consistent with the five-coordinate
geometry of the Cu(II) complex. In general typical five
coordinated Cu(II) complexes of SP or distorted SP geom-
etries exhibit a band in the range 550–660 nm, whereas the
corresponding TBP complexes usually show a maximum at
k > 800 nm with a higher energy shoulder [39]. This indi-
cates that the solution spectrum of the complex ion is ade-
quately explained by a d–d transition for the Cu(II) ion in a
distorted SP geometry where the absorption maximum
band observed in the visible region results from a
2E ? 2B1 transition.
3.4. Redox potential
The electrochemical studies of 1 and 2 were performed
in acetonitrile using tetrabutylammonium perchlorate as
supporting electrolyte at a scan rate of 50 mV/s. 1 shows
two metal centered irreversible reduction peaks. The first
reductive response for 1 is observed at ꢀ0.6 V (w.r.t.
SCE) and the second is at ꢀ0.828 V. Compound 2 shows
only one reversible reductive response, at ꢀ0.177/
ꢀ0.122 V. The two metal centers in 1 can communicate
electrically through the shorter pseudohalide cyanate but
for 2, with the larger dca, this was not possible and only
one peak was observed.
Fig. 4. Portion of a double strand of a {Cu(PBH)(dca)} chain in
complex 2.
1
number indicates coordination of the azomethine nitrogen
to the metal center [34]. The low energy pyridine ring in-
plane and out-of-plane vibrations observed in the spectrum
of the pro-ligand at 625 and 406 cmꢀ1, respectively, com-
pared with the corresponding bands for the complexes
which are shifted to higher frequencies at 638–640 and
419–422 cmꢀ1, respectively, are good indications of the
coordination of the heterocyclic nitrogen atom[35]. In the
spectra of 1 a strong bifurcated band at 2172 and
2224 cmꢀ1 indicates the presence of bridging cyanato
groups [36]. The dicyanamide anion in NaN(CN)2 shows
three sharp and strong characteristic bands in the fre-
quency region 2290–2170 cmꢀ1 attributed to ms (C„N)
combination modes (2286 cmꢀ1), ms(C„N) (2232 cmꢀ1) and
ms(C@N) (2179 cmꢀ1), respectively [37]. The infrared spectra
of 2 shows strong absorption bands in the region 2372–
2174 cmꢀꢀ11. The splitting of the maxima is found at 2372,
2294 cm (mas + ms(C„N)), 2257, 2228 cmꢀ1 (mas(C@N)) and
2174 cmꢀ1 (ms(C@N)). The shift towards higher frequencies
of these peaks in 2 as compared to the free dca anion is
due to the bridging coordination modes of dca in the com-
plex. The ligand coordination to the metal center is sub-
stantiated by two bands appearing for each complex, at
3.5. Magnetic properties
The curve of vMT = f(T) for 1 is almost constant above
40 K with a value near 0.78 cm3 K molꢀ1, in good agree-
ment with the expected value for two Cu(II) ions. Below
40 K, vMT decreases to reach a value of 0.73 cm3 K molꢀ1
at 4 K, thus the dinuclear complex exhibits a very small
antiferromagnetic interaction. According to the dimeric
structure of the compound, the vMT curve has been fitted
using a classical Bleaney and Bowers law, using the phe-
nomenological Hamiltonian H = ꢀJSA ꢃ SB. The resulting
law used for fitting has the following form:
2Ng2b2
k½3 þ expðꢀJ=kTÞꢂ
vMT ¼
410, 379 and 479, 360 cmꢀ1 attributable to mCu–N, mCu–O
respectively, for complexes 1 and 2.
,
Best fit was obtained for Lande factor g = 2.03, isotropic
interaction parameter J = ꢀ0.50 cmꢀ1. The temperature
dependence of vMT for 1 is depicted in Fig. 5.
The temperature dependence of vMT for 2 is shown in
Fig. 6. Due to the chain structure of the complexes, the
model of equally spaced copper(II) ions has been used.
3.3. Electronic spectra
The electronic spectra of 1 and 2 in acetonitrile solution
show two strong absorption bands in the region 267 and
299 nm. These bands are clearly charge-transfer in origin
[38]. The band around 382 nm is assigned to the n–p* tran-
sition of the azomethine group. In the spectrum of the com-
plex, the bands of the azomethine chromophore n–p*
transition are shifted to lower frequencies indicating that
The
spin
Hamiltonian
in
where the summation runs over
iþ1
zero-field
is
P
H ¼ ꢀJ nꢀ1SA ꢃ SA
i
i¼1
the n sites of the chain. When n tends to infinity, there is
no analytical method to determine the magnetic suscepti-
bility. However, the results can be fitted using the numeri-
cal expression for J < 0 [40]

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S. Banerjee et al. / Inorganica Chimica Acta 361 (2008) 2707–2714
Table 3
0.78
0.77
0.76
0.75
0.74
0.73
0.72
Structural and magnetic properties of bis(cyanato) copper(II) dimers
Formula of the complex
h/R
J (cmꢀ1
)
[Cu2(l1,1-NCO)2(NCO)2(dpyam)2]
[Cu2(l1,1-NCO)2(NCO)2(phen)]
[Cu2(l1,1-NCO)2(Medien)2](ClO4)2
[{Cu(PBH)(l1,1-CNO)}2]
37.57
6.03
13.75
ꢀ4.6
ꢀ0.5
37.405
40.626
37.678
reported to show any such interactions. This is due to the
fact that in the latter geometry the magnetically active
[dx2ꢀy2 orbital in case of Cu(II)] orbitals on each monomeric
unit are orthogonal to each other and there is no suitable
orbital on the part of ligand, which participates in the
bridging, through which magnetic interaction can take
place. As a consequence greater distortion from the perfect
square pyramidal geometry will give rise to greater mag-
netic interaction between the paramagnetic metal centers.
Of the structures, where cyanate acts as a bridging ligand
[43], as far as our search goes, very few had variable temper-
ature magnetic studies. Due to lack of magnetic data no def-
inite conclusion could be drawn about the magneto
structural correlation in penta-coordinated cyanate bridged
Cu(II) dinuclear structures. Of the three data available with
VTM studies two showed ferromagnetic interactions [44]
and the other one showed antiferromagnetism [45]. We take
the h/R ratio [where h is the Cu–N–Cu bridge angle and R is
the longer Cu–N separation in the axial bond length in Cu
and bridging NCOꢀ] as an authentic parameter for magneto
structural correlation as done by Marsh et al. [46]. For the
complex [Cu2(l1,1-NCO)2(NCO)2(dpyam)2] (dpyam = di-
2-pyridylamine), h/R is 37.57 and J = 6.03 cmꢀ1 where as
for [Cu2(l1,1-NCO)2(NCO)2(phen)] the same ratio is
37.405 and the J is 13.75 cmꢀ1. The only previous report that
0
50
100
T / K
150
200
Fig. 5. Experimental (j) and calculated (—) temperature dependence of
MT for 1.
v
0.420
0.418
0.416
0.414
0.412
0.410
0.408
χ
0
50
100
150
T (K)
200
250
300
Fig. 6. Experimental (h) and calculated (—) temperature dependence
MT for 2.
v
we found where antiferromagnetism is operative is [Cu2(l1,1
-
NCO)2 (Medien)2](ClO4)2 (Medien = 4-Methyldiethylene-
triamine). But there are two independent types of dimmers
with different bond parameters, one symmetric and the other
asymmetric. Considering the h/R for the symmetric unit it
comes out to be 40.626 where as the J is ꢀ4.6 cmꢀ1. For com-
plex 1 that we are reporting here the h/R is 37.678 and J is
ꢀ0.5 cmꢀ1. All the above data are summarized in Table 3.
So it could be stated that with increase in h/R ratio the inter-
action changes from ferromagnetic to antiferromagnetic
gradually.
Ng2b2
k
vMT ¼
0:25 þ 0:074975x þ 0:075235x2
ꢁ
with x
1:0 þ 0:9931x þ 0:172135x2 þ 0:757825x3
¼ ꢀJ=kT :
For complex 2, the best fit was obtained with a Lande fac-
tor
g of 2.11, and isotropic interaction parameter
J = ꢀ0.10 cmꢀ1. This small value is in line with those for
similar reported structures [25,33,41].
4. Conclusions
The weak coupling inside the chain is due to the longer
distance between the copper(II) ions as dicyanamide acts as
Two new Cu(II) complexes with a tridentate hydra-
zone ligand, PBHꢀ and with CNOꢀ and dca as counter
ions, have been prepared. Complex 1 is dimeric with the
isocyanate ligands bridging in l1,1 mode; the dimer units
are linked through p–p interactions to form chains
through the crystal. Complex 2, however, is a double-
stranded coordination polymer in which each strand
comprises Cu(PBH)+ units linked through l1,5 bridging
dca ligands; the PBHꢀ ligands from the two strands
alternate in p-stacks parallel to the a axis. Both the com-
l1,5-bridging ligand. The weak interaction can also be
explained by the fact that one end of the dca bridge is in
the apical position of the square pyramidal copper. Since
the magnetic orbital (dx2ꢀy2 , again) is perpendicular to that
direction, no overlap between magnetic orbitals is
expected. This explains the low absolute value of J for 2.
It has been reported earlier [42] that dinuclear distorted
square pyramidal structures of Cu(II) can show magnetic
interactions whereas the perfect square pyramids are not

S. Banerjee et al. / Inorganica Chimica Acta 361 (2008) 2707–2714
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plexes show the copper atoms with distorted square
pyramidal geometry which can be verified from the
UV–Vis spectra and X-ray crystallography. Magnetic
studies of the complexes show that both are antiferro-
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Acknowledgements
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C.R. Acad. Sci. II C 4 (2001) 125;
We acknowledge DRDO New Delhi, India for funding
this research work and Prof. S. Bhattacharya, Jadavpur
University, Kolkata for electrochemical studies.
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Appendix A. Supplementary material
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CCDC 638165 and 643521 contain the supplementary
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