Synthesis, characterization and structures of copper(II) complexes with amide-based ligands: Unusual formation of a linear trimer and a zig-zag chain and their contrast magnetic behaviour

Article abstract of DOI:10.1016/j.poly.2007.04.021

The present work illustrates the versatile coordination modes of the amide-based ligands towards copper(II) ion. The reaction of the deprotonated form of the ligand, [L¹]^2- with CuCl₂ affords a linear trinuclear complex, [Cu₃(L¹)₂(Cl)₂(H₂O)] (1) which has been characterized thoroughly including single crystal structure analysis. The structure of 1 shows that one of the arm of the flexible ligand flips to coordinate second copper(II) centre, resulting in the formation of a trinuclear complex. On the other hand, ligand H₂L² in its deprotonated form reacts with Cu(II) ion to give complex 2 with general formula, [Cu(L²)]_n (2). The crystal structure of the complex 2 shows that each copper is square-pyramidal with 5th coordination coming from the O-atom of the amide group from a neighbouring complex. This results in the generation of an one-dimensional zig-zag chain. The variable temperature magnetic measurements of the complexes, 1 and 2 show that while Cu ions in the former are antiferromagnetically coupled (J = -110.34 cm^-1), a weak ferromagnetic interaction (J = +3.08 cm^-1) exists in the later. A rationale, based on the orbital overlap from the copper ions and associated ligands, is provided for the observed magnetic coupling between the copper ions.

Full text of DOI:10.1016/j.poly.2007.04.021

Polyhedron 26 (2007) 3893–3903
www.elsevier.com/locate/poly
Synthesis, characterization and structures of copper(II) complexes
with amide-based ligands: Unusual formation of a linear trimer
and a zig-zag chain and their contrast magnetic behaviour
a
b
c,
a,
*
Jyoti Singh , Geeta Hundal , Montserrat Corbella *, Rajeev Gupta
a
Department of Chemistry, University of Delhi, Delhi 110 007, India
Department of Chemistry, Guru Nanak Dev University, Amritsar 143 005, Punjab, India
` `
´
Departament de Quı´mica Inorganica, Universitat de Barcelona, Martı I Franques 1-11, E-08028-Barcelona, Spain
b
c
Received 9 March 2007; accepted 14 April 2007
Available online 30 April 2007
Abstract
The present work illustrates the versatile coordination modes of the amide-based ligands towards copper(II) ion. The reaction of the
deprotonated form of the ligand, [L1]2ꢀ with CuCl2 affords a linear trinuclear complex, [Cu3(L1)2(Cl)2(H2O)] (1) which has been char-
acterized thoroughly including single crystal structure analysis. The structure of 1 shows that one of the arm of the flexible ligand flips to
coordinate second copper(II) centre, resulting in the formation of a trinuclear complex. On the other hand, ligand H2L2 in its deproto-
nated form reacts with Cu(II) ion to give complex 2 with general formula, [Cu(L2)]n (2). The crystal structure of the complex 2 shows that
each copper is square-pyramidal with 5th coordination coming from the O-atom of the amide group from a neighbouring complex. This
results in the generation of an one-dimensional zig-zag chain. The variable temperature magnetic measurements of the complexes, 1 and
2 show that while Cu ions in the former are antiferromagnetically coupled (J = ꢀ110.34 cmꢀ1), a weak ferromagnetic interaction
(J = +3.08 cmꢀ1) exists in the later. A rationale, based on the orbital overlap from the copper ions and associated ligands, is provided
for the observed magnetic coupling between the copper ions.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Copper(II) complexes; Amide ligands; X-ray structures; Magnetic properties
1. Introduction
mononuclear and dinuclear copper centres [10]. The exact
nature of the ligands present and their coordination mode
is not clear due to the limitations of the 2.8 A resolution of
the crystal structure. In this context, appropriate synthetic
model helps in better understanding to the elucidation of
the active site structure [11].
Another reason of interest into multi-copper systems
resides in the inherent magnetic interactions these systems
offer. Numerous examples of magnetic interaction in exog-
enous ligand(s) bridged copper(II) binuclear and polynu-
clear complexes have been reported [12–14]. On the other
hand, when the endogenous ligand(s) is involved in
providing the bridge for the magnetic superexchange;
examples are mainly limited to alkoxide- [15–17] and
phenoxide-based [18–20] ligands. There are comparatively
fewer examples when a endogenous ligand(s) capable of
˚
Multinuclear metal clusters are ubiquitous to a number
of biological systems. Particular interest in multi-copper
complexes has been sparked in recent years by the
characterization of several metalloenzymes that contain
multi-copper centres [1–4], including particulate methane
monooxygenase (pMMO) [5] and nitrous oxide reductase
(NOR) [6]. The recently solved crystal structure of NOR
shows the presence of a l4-sulfide bridged tetranuclear cop-
per cluster [7–9]. Whereas, very recently, the crystal struc-
ture of pMMO reveals interesting sub-units having
*
Corresponding authors. Tel.: +91 11 2766 7624; fax: +91 11 2766 6605
(R. Gupta).
E-mail address: rgupta@chemistry.du.ac.in (R. Gupta).
0277-5387/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.04.021

3894
J. Singh et al. / Polyhedron 26 (2007) 3893–3903
simultaneously coordinating two or more metal centers
also provide the bridge for the magnetic interaction; espe-
cially when the metal ions are relatively far from each
other. In this category, X2C2Y2 bridge, where X and Y
atoms bound to different metal ions may be O, N, or S,
has been used efficiently to propagate the magnetic interac-
tions between two and in very few cases three metal centers.
The examples include highly symmetrical bridge oxalato,
O2C2O22ꢀ [21–23], oxamido, N2C2O22ꢀ [24–27], and dithio-
analysis data were obtained from Elementar Analysensys-
teme GmbH Vario EL-III instrument. The NMR measure-
ments were done using an Avance Bruker (300 MHz)
instrument. The infra-red spectra (either as KBr pellet or
as a mull in mineral oil) were recorded using the Perkin–
Elmer FTIR 2000 spectrometer. The absorption spectra
were recorded using the Perkin–Elmer Lambda-25 spectro-
photometer. The mass spectra were obtained on a Jeol
SX102/DA-6000 instrument. The thermal analyses were
performed with a Shimadzu DTG-60 instrument in the
temperature range of 25–800 ꢁC. EPR spectra of the poly-
crystalline samples were recorded at X-band (9.4 GHz) fre-
quencies with a Bruker ESP-300E spectrometer, from room
temperature to 4 K at the Servei de Magnetoquimica of the
Universitat de Barcelona. Room temperature solution EPR
spectra were recorded with a Jeol JES-3XG spectrometer.
2ꢀ
oxamido, N2C2S2 [28–30]. In particular, the oxamido
ligand provide two planar NCO bridge between the metal
centres and the result is a very strong antiferromagnetic
coupling [24–27].
In this paper, we describe the design and synthesis of
two amide-based ligands and their copper coordination
chemistry. The ligands coordinate the copper ion via
deprotonated Namidate and neutral Namine donors. Interest-
ingly, in one case, flipping of the amide containing arm
take place to afford a linear copper trinuclear complex.
This is a rare example, where deprotonated amide group
coordinate via both ends, Namidate as well as Oamidate
[31,32]. The second complex also shows sharing of the
amide group between copper centres affording a one-
dimensional zig-zag chain. The bridging ligand present
between the copper(II) ions is NCO, thus we have chopped
off one unit (one NCO fragment) of the oxamido ligand.
The result of this alteration on the structure and magnetic
properties of the copper complexes is presented.
2.3. Crystallography
Single crystals suitable for X-ray diffraction studies were
grown by the vapour diffusion of diethyl ether to a DMF
solution of complex 1 and slow evaporation of a saturated
MeOH solution of 2. The suitable crystals of 1 and 2 were
mounted lengthways with the largest dimension in a sealed
capillary. The intensity data for 1 were collected at 295 K
on a Siemens P4 X-ray diffractometer by using scanning
mode with graphite monochromatized Mo Ka radiation.
A total of 15503 reflections were measured of which
10999 reflections (I > 2r(I)) were used in the structure
refinement. The data were corrected for Lorentz and polar-
ization effects and a psi-scan absorption correction was
also applied. The structure was solved by direct methods
and refined by full-matrix least-squares refinement tech-
niques on F2. There are two crystallographically indepen-
dent molecules of the complex and the solvent DMF in
the unit cell. All calculations were performed using
SHELXTL-PC. One of the DMF molecules showed rotational
disorder which has been treated by refining all five non-
hydrogen atoms of this molecule (C60, C61, C62, N20,
O12) being split at two sites with total site occupancy of
1.00 for each one of them. This DMF molecule was refined
isotropically with similar Uiso values assigned to two atoms
of the pair. The molecule was refined with restraints on the
bond distances of this disordered molecule being C(sp3)–N
2. Experimental
2.1. Materials
All reagents were obtained from the commercial sources
and used as received. N,N-dimethyl formamide (DMF) was
˚
dried and distilled from 4 A molecular sieves and was
stored over sieves. Acetonitrile (MeCN) was dried by distil-
lation from anhydrous CaH2. Diethyl ether and petroleum
ether (boiling range 60–80 ꢁC) were dried by refluxing over
sodium metal under inert atmosphere. Tetrahydrofuran
(THF) was dried by refluxing and distilling from sodium
metal and benzophenone. Ethyl alcohol (C2H5OH) and
methyl alcohol (CH3OH) were distilled from magnesium
ethoxide and magnesium methoxide, respectively. Chloro-
form (CHCl3) and dichloromethane (CH2Cl2) were purified
by washing with 5% sodium carbonate solution followed
by water and finally dried over anhydrous CaCl2, before
a final reflux and distillation. N,N0-bis(chloroacetyl)ethy-
lenediamine and N,N0-bis(chloroacetyl)-o-phenylenedi-
2
˚
1.440(3), C(sp )–N 1.350(3), C@O 1.226(3) A and non-
˚
bonding distances being 2.20(3) A. All non-hydrogen
atoms except for one DMF molecule were refined aniso-
tropically. All hydrogen atoms were attached geometrically
except for those belonging to the water molecules which
were determined from the difference Fourier map. For 2,
the intensity data were collected on a BRUKER AXS
SMART-APEX CCD diffractometer equipped with a
amine were synthesized according to
procedure [33,34].
a
reported
˚
2.2. Physical measurements
molybdenum sealed tube (Mo Ka = 0.71073 A) and a
highly orientated graphite monochromator [35]. Frames
were collected at T = 293 K by x, / and 2h-rotation at
10 s per frame with SMART [35]. The measured intensities
were reduced to F2 and corrected for absorption with
The conductivity measurements were done in organic
solvents using the digital conductivity bridge from Popular
Traders, India (model number: PT-825). The elemental

J. Singh et al. / Polyhedron 26 (2007) 3893–3903
3895
SADABS [36]. The structure of 2 was solved by SIR 92
expanded by Fourier difference syntheses and refined with
the SHELXL 97 package incorporated in WINGX 1.64 crystal-
lographic collective package [37–39]. The positions of the
hydrogen atoms were calculated by assuming ideal geome-
tries but not refined. All non-hydrogen atoms were refined
with anisotropic thermal parameters by full-matrix least-
squares procedures on F2. Details of the crystallographic
data are given in Table 1.
added and the mixture was refluxed for 24 h. The mixture
was cooled, filtered and the solvent was removed under
reduced pressure to afford an off-white solid. The crude
product was recrystallized by layering the CHCl3 solution
with the petroleum ether (boiling range 60–80 ꢁC). Yield:
2.24 g, 83%. Microanal. Calc. for H2L1, C14H30N4O2: C,
58.74; H, 10.57; N, 19.58. Found: C, 58.28; H, 10.96; N,
19.52%. M.p. 80 ꢁC. Selected IR bands (FT-IR, KBr) m
(cmꢀ1): 3301s (NH), 2965m, 2933m, 2873w, 2814w (CH),
1649s (C@O). 1H NMR spectrum (CDCl3): d 1.023 (t,
J = 6.8 Hz, 12H, ethyl CH3), 2.54 (quartet, J = 6.7 Hz,
8H, ethyl CH2), 3.01 (s, 4H, CH2CO), 3.42 (s, 4H, ethylene
CH2), 7.65 (br s, 2H, amidic NH). ESI mass spectrum
(CH3CN): m/z = 287.24 [M+H+].
2.4. Magnetic measurements
Magnetic susceptibility measurements for crushed crys-
talline samples of 1 and 2 were carried out at the Servei
de Magnetoquimica of the Universitat de Barcelona with
a Quantum Design SQUID MPMS-XL susceptometer.
The magnetic susceptibility data were recorded in the
2–300 K temperature range under magnetic fields of
500 G (2–30 K) and 10000 G (2–300 K). Diamagnetic
corrections were estimated from Pascal Tables. The fits
were performed minimizing the function R =
R(vMTexp ꢀ vMTcal)2/R(vMTexp)2. Magnetic fields ranging
from 0 to 50000 G were used for magnetization measure-
ments at 2 K.
2.5.2. Synthesis of H2L2
To a solution of N,N0-bis(chloroacetyl)-o-phenylenedi-
amine (2 g, 7.6 mmol) in ethanol (25 cm3), 40% aqueous
solution of dimethylamine (5.2 g, 46 mmol) was added
and the mixture was refluxed for 24 h. The mixture was
cooled and the solvent was removed under reduced pres-
sure. The resultant oil was washed with a saturated solu-
tion of NaHCO3 (10 cm3) and the ligand was then
extracted with dichloromethane (3 · 10 cm3). The com-
bined extracts were dried over Na2SO4 and evaporated
under reduced pressure to leave a pale yellow solid. The
crude product was then recrystallized by layering the
CHCl3 solution with the petroleum ether (boiling range
60–80 ꢁC). Yield: 1.8 g, 85%. Microanal. Calc. for H2L2,
C14H22N4O2: C, 60.31; H, 7.8; N, 20.10. Found: C, 59.59;
H, 7.6; N, 19.86%. M.p. 82 ꢁC. Selected IR bands (FT-
IR, KBr) m (cmꢀ1): 3231m (NH), 2952w, 2826m, 2780m
2.5. Ligand Syntheses
2.5.1. Synthesis of H2L1
To a solution of diethylamine (1.37 g, 18.76 mmol) in
MeCN (30 cm3), K2CO3 (39 g, 282 mmol) and N,N0-
bis(chloroacetyl)ethylenediamine (2 g, 9.38 mmol) were
1
(CH), 1693s (C@O), 1601m (C@C). H NMR spectrum
(CDCl3): d 2.30 (s, 12H, methyl CH3), 3.03 (s, 4H,
CH2CO), 7.10 (m, 2H, benzyl CH) 7.56 (m, 2H, benzyl
CH), 9.17 (br s, 2H, amidic NH). ESI mass spectrum
(CH3CN): m/z = 279.4 [M+H+].
Table 1
Crystallographic data for complexes, [Cu3(L1)2(Cl)2(H2O)] Æ DMF (1) and
[Cu(L2)]n (2)
1 Æ DMF
31H65N9O6Cl2Cu3
2
Formula
Mr
C
C14H20N4O2Cu
339.88
921.47
2.6. Syntheses of the copper complexes
Crystal system
Space group
triclinic
orthorhombic
Pn21a (#33)
16.560(5)
8.427(5)
11.203(5)
90.0
90.0
90.0
1563.4(13)
4
293(2)
blue, block
0.3 · 0.2 · 0.2
1.444
708
0.0450
0.1171
0.831
0.351, ꢀ0.560
ꢀ
P1 (#2)
2.6.1. [Cu3(L1)2(Cl)2(H2O)] Æ 2H2O (1)
˚
a (A)
13.078(5)
17.696(5)
21.210(5)
102.420(5)
93.680(5)
110.500(5)
4438(2)
To a stirred solution of H2L1 (0.200 g, 0.699 mmol) in
DMF (10 cm3), solid NaH (0.033 g, 1.398 mmol) was
added under dinitrogen atmosphere. The resulting mixture
was stirred until H2 evolution ceased. To this CuCl2
(0.141 g, 1.048 mmol) was added as solid followed by the
addition of few drops of water. The resulting green-blue
solution was stirred at room temperature for 2 h. During
this time the colour changed to dark blue. The solution
was passed through a celite pad in a medium porosity frit.
The resultant solution was layered with diethyl ether and
stored at 4 ꢁC. This afforded dark blue microcrystalline
product within a day. Yield: 0.18 g, 61%. Microanal. Calc.
for 1, C28H58N8O5Cl2Cu3 Æ 2H2O: C, 38.03; H, 7.01; N,
12.68. Found: C, 38.36; H, 7.20; N, 12.56%. Selected IR
bands (FT-IR, KBr) m (cmꢀ1): 3367m br. (OH), 2967m,
2930m, 2874m (CH), 1610s, 1572s (C@O). UV–Vis
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
4
T (K)
Colour, shape
Crystal size (mm)
295(2)
blue, prism
0.18 · 0.15 · 0.13
1.379
1932
0.0598
0.1683
1.031
0.710, ꢀ1.184
Dcalc (g cmꢀ3
F(000)
Ra
)
wRb
Goodness of fit on F2
ꢀ3
˚
Dqmax,min (e A
)
P
P
a
R ¼ jjF oj ꢀ jF cjj= jF oj.
P
2
2
2
1=2
b
wR ¼ f½ ðjF oj jF cj Þ ꢁg
.

3896
J. Singh et al. / Polyhedron 26 (2007) 3893–3903
spectrum (MeCN: kmax (nm) [emax] (Mꢀ1 cmꢀ1)): 625 [390],
515sh [280], 350sh [4230], 317sh [7700], 264 [14050]. UV–
Vis spectrum (MeOH: kmax (nm) [emax] (Mꢀ1 cmꢀ1)): 625
[370], 260 [15200], 215 [27800]. Conductivity (CH3CN,
ꢂ1 mM solution, 298 K): KM = 12 Xꢀ1 cm2 molꢀ1. ESI
mass spectrum (CH3OH) m/z = 852.5 ([Cu3(L1)2(CH3OH)-
(OCH3)2]+H+).
diamine is converted to the respective bis(chloroamide)
by treating with 2 equiv. of chloroacetyl chloride [33,34].
In the second step, the bis(chloroamide) was subsequently
treated with diethyl- or dimethyl-amine to afford the
ligands, H2L1 and H2L2, respectively. Excess Me2NH
(6 equiv.) was used for the synthesis of H2L2, where it also
functioned as a base in the reaction. Both ligands were
characterized thoroughly and gave satisfactory microanal-
yses results.
2.6.2. [Cu(L2)]n (2)
To a stirred solution of H2L2 (0.200 g, 0.719 mmol) in
DMF (10 cm3), solid NaH (0.034 g, 1.438 mmol) was
added under dinitrogen atmosphere. The resulting solution
was stirred until H2 evolution ceased. Solid CuCl2 (0.097 g,
0.719 mmol) was added to the above mixture. The resulting
indigo-blue solution was stirred at room temperature for
2 h. The DMF was then removed under reduced pressure
and the residue was redissolved in CH3OH (50 cm3). The
solution was passed through the celite pad in a medium
porosity frit and allowed to evaporate for a day to afford
dark blue microcrystalline product. The product was fil-
tered and dried under vacuum. Yield: 0.20 g, 82%. Micro-
anal. Calc. for 2, C14H20N4O2Cu: C, 49.33; H, 5.89; N,
16.49. Found: C, 49.33; H, 6.03; N, 16.33%. Selected IR
bands (FT-IR, KBr) m (cmꢀ1): 3060w, 2893w, 2793w
(CH), 1616s, 1598s (C@O), 1564s, 1478m, 1454w (C@C).
UV–Vis spectrum (MeOH: kmax (nm) [emax] (Mꢀ1 cmꢀ1)):
550 [410], 413sh [180], 311sh [12270], 302sh [18600], 270
[47050], 250sh [52500], 240 [62050]. UV–Vis spectrum
(MeCN: kmax (nm) [emax] (Mꢀ1 cmꢀ1)): 530 [360], 405sh
[175], 311sh [11050], 280 [31000], 242 [50400], 214
[28000]. conductivity (CH3OH, ꢂ1 mM solution, 298 K):
3.2. Synthesis and characterization of copper complexes
Complex 1 was synthesized by the initial reaction of
2 equiv. of deprotonated ligands with 3 equiv. of CuCl2.
The reaction mixture was then treated with few drops of
water to afford the final compound (Scheme 1). The com-
plex 2 was also synthesized in an analogous fashion by
treating deprotonated ligand, [L2]2ꢀ, with CuCl2 (Scheme
2). In the FTIR spectra, the absence of m(N–H) stretching
frequency confirms the deprotonated nature of the amide
ligands. Moreover, a red shift was observed for the amidate
C@O group compared to the free ligand, thus indicating
coordination through anionic amidate-N center. The com-
plex 1 also shows the m(OH) stretches in the region of
ꢂ3370 cmꢀ1 for the coordinated as well as lattice water
[40]. Solution conductivity data [41] confirms the non-elec-
trolytic nature of both copper complexes, whereas elemen-
tal analyses results authenticate the purity of the bulk
samples. In the electrospray mass spectrum for complex 1
in CH3CN, the molecular ion peak was observed at
887.35 that matches well with the following composition,
[Cu3(L1)2(Cl)2(H2O)] + H2O + Na+ (calculated m/z =
887.64). This is to be noted, however, when recorded in
CH3OH, a new molecular ion peak was observed at 852.5
which fits well with the following composition,
K
M = 16 Xꢀ1 cm2 molꢀ1. ESI mass spectrum (CH3OH)
m/z = 362.18 ([Cu(L2)]+Na+).
3. Results and discussion
3.1. Ligand design and synthesis
The ligands H2L1 and H2L2 are designed to simulta-
neously provide two amide and two amine coordinations
to the metal centre while maintaining an identical primary
coordination environment around it. While the ligand
H2L1 has a flexible ethylenediamine backbone, the ligand
H2L2 incorporates a rigid o-phenylenediamine backbone.
These ligands are synthesized in two steps starting from
the corresponding primary diamines. In the first step, the
O
NH HN
O
O
N
N
N
N
O
O
1. 2 NaH, DMF, N2
2. CuCl2
Cu
N
N
H2L2
[Cu(L2)]n 2
Scheme 2. Synthesis of complex 2.
H
O
H
N
N
Cl
O
NH HN
O
N
O
N
N
N
O
N
Cu
1. 4NaH, DMF, N2
2. 3 CuCl2
Cu
Cu
2
O
N
O
N
N
Cl
3. 1 H2O
[Cu3(L1)3(Cl)2(H2O)] 1
Scheme 1. Synthesis of complex 1.
H2L1

J. Singh et al. / Polyhedron 26 (2007) 3893–3903
3897
[Cu3(L1)2(OCH3)2(CH3OH)] + H+
(calculated
m/z =
amine-N centres, two amidate-O centres, and an apical
water molecule. The geometry around the central cop-
per(II) ion is distorted square-pyramidal. The s value
[42], which is an indication of the distortion of the 5-coor-
dinate geometry towards square-pyramidal (s = 0) or trigo-
nal bipyramidal (s = 1), is 0.14 and 0.04, for central copper
ion in molecules A and B, respectively. It is clear from the
value of s that the central Cu(II) ion has much more dis-
torted geometry in molecule A. The displacement from
the basal plane (defined by two amide-N, one amine-N,
and a Clꢀ) for the terminal copper centres (Cu1, Cu3,
852.3). Interestingly, while recording the spectrum in
CH3OH, two chloride ions were replaced by methoxide
ions while the coordinated water got exchanged with meth-
anol. Complex 2, on the other hand, shows the molecular
ion peak at 362.18 that matches well with [Cu(L2)] + Na+
(calculated m/z = 362.25).
3.3. Solid state structures
3.3.1. Structure of complex 1
˚
The molecular structure of 1 contains two slightly differ-
ent independent trinuclear motifs of [Cu3(L1)2(Cl)2(H2O)],
hereafter referred as molecule A and molecule B. The ther-
mal ellipsoidal representation of molecules A and B are
shown in Fig. 1 while important structural parameters
are presented in Table 2. Each trinuclear assembly is com-
posed of two [L1]2ꢀ ligands, three copper ions, two chloride
ions, and a water molecule. The terminal copper ions (Cu1
and Cu3 in molecule A; and Cu4 and Cu6 in molecule B)
are coordinated by two amidate-N centres, one amine-N
centre, and a chloride ion completing a distorted square-
planar geometry. The central copper ion (Cu2 and Cu5
in molecules A and B, respectively) is coordinated by two
Cu4, and Cu6) is quite small, 0.028–0.087 A. On the other
hand, the central coppers are significantly displaced out of
basal plane (defined by two amide-Os and two amine-Ns)
towards the apical water molecule; displacement for Cu2
˚
and Cu5 is 0.210 and 0.171 A, respectively. These values
again indicate that the copper ion in molecule A has much
more distorted geometry than in B. The bond length differ-
ence for the coordination of two amidate-N centres to the
terminal Cu(II) ions (for example, between Cu1–N2 and
˚
Cu1–N3 for molecule A) is quite significant, ꢂ0.1 A. This
difference may be attributed due to the presence of a delo-
calized structure of one of the amide group which is
involved in the bonding with the central Cu(II) ion. This
Cl(2)
N(5)
N(2)
N(8)
O(2)
N(3)
Cu(3)
O(3)
Cu(2)
Cu(1)
N(1)
N(6)
O(4)
N(4)
N(7)
Cl(1)
N(10)
Cl(4)
N(13)
N(16)
O(8)
N(11)
O(7)
Cu(6)
N(9)
Cu(4)
Cu(5)
N(14)
O(9)
N(12)
N(15)
Cl(3)
Fig. 1. Thermal ellipsoidal representation (30% probability level with partial numbering) of complex 1 (molecule A (top) and molecule B (bottom)
Hydrogen atoms and solvent molecules are omitted for clarity.

3898
J. Singh et al. / Polyhedron 26 (2007) 3893–3903
˚
Table 2
neighbouring copper centres is ꢂ5.74(3) A, while the termi-
˚
Selected bond distances (A) and angles (ꢁ) for molecules A and B in
complex [Cu3(L1)2(Cl)2(H2O)] (1)
˚
nal copper ions are separated by ꢂ11.5(3) A. The coordi-
nated water molecule forms hydrogen bonds with the
carbonyl oxygen atoms from the neighbouring complexes,
Molecule A
Molecule B
˚
Bond distances
Cu1–N1
Cu1–N2
Cu1–N3
Cu1–Cl1
Cu2–N4
Cu2–N5
Cu2–O2
Cu2–O3
Cu2–O4
Cu3–N6
Cu3–N7
Cu3–N8
Cu3–Cl2
the distance are within the range of ꢂ2.62(3)–2.68(4) A.
2.105(4)
1.898(4)
2.007(4)
2.2226(19)
2.051(4)
2.045(4)
1.938(3)
2.192(4)
1.942(3)
1.981(4)
1.894(4)
2.109(4)
2.2332(19)
Cu4–N9
Cu4–N10
Cu4–N11
Cu4–Cl3
Cu5–N12
Cu5–N13
Cu5–O7
Cu5–O8
Cu5–O9
Cu6–N14
Cu6–N15
Cu6–N16
Cu6–Cl4
2.083(4)
1.891(4)
1.993(4)
2.2393(17)
2.057(4)
2.043(4)
1.938(3)
2.271(4)
1.923(3)
2.001(4)
1.894(4)
2.117(4)
2.2251(18)
There are strong H-bonding interactions involving the
amide oxygens, water molecules and the DMF molecule
resulting in an interesting crystal structure of the molecule.
The water molecule O3 of molecule A shows strong inter-
molecular Oꢃ ꢃ ꢃO bonding with amide oxygens O1 and O5
of its centrosymmetrically related molecules (Table S1).
This gives rise to polymeric, pleated ribbon like chains run-
ning along the c axis in the bc plane (Fig. S1) constituting
lattice I. The DMF molecule close to this is not involved in
any Oꢃ ꢃ ꢃO bonding but is merely being held in space by
weak Cꢃ ꢃ ꢃO H-bonding interactions. On the other hand
second DMF molecule is acting as H-bond acceptor to
water molecule O8 of molecule B, which is also behaving
as a H-bond donor to amide oxygen O10. These interac-
tions give rise to a H-bonded 2B:2DMF tetrameric synthon
as shown in Fig. S2, constituting lattice II. There are only
some weak Cꢃ ꢃ ꢃO H-bonding interactions between these
synthons. Thus involvement of DMF in H-bonding inter-
actions with the trinuclear coordination compound
destroys the polymeric nature of molecule B. Taken
together the crystal structure may be looked at as two
interpenetrating lattices I and II (Fig. S3).
Bond angles
N2–Cu1–N3
N2–Cu1–N1
N3–Cu1–N1
N2–Cu1–Cl1
N3–Cu1–Cl1
N1–Cu1–Cl1
O4–Cu2–O2
O4–Cu2–N5
O2–Cu2–N5
O4–Cu2–N4
O2–Cu2–N4
N5–Cu2–N4
O4–Cu2–O3
O2–Cu2–O3
N5–Cu2–O3
N4–Cu2–O3
N7–Cu3–N6
N7–Cu3–N8
N6–Cu3–N8
N7–Cu3–Cl2
N6–Cu3–Cl2
N8–Cu3–Cl2
Cu1–Cu2–Cu3
83.04(17)
81.98(18)
164.89(18)
171.24(15)
102.56(14)
92.10(14)
172.18(17)
83.30(15)
96.03(15)
95.42(15)
83.07(15)
164.00(18)
94.08(16)
93.73(16)
97.54(19)
98.5(2)
82.35(18)
82.55(18)
164.07(19)
166.77(16)
100.61(14)
95.24(14)
176.61(11)
N10–Cu4–N11
N10–Cu4–N9
N11–Cu4–N9
N10–Cu4–Cl3
N11–Cu4–Cl3
N9–Cu4–Cl3
O9–Cu5–O7
O9–Cu5–N13
O7–Cu5–N13
O9–Cu5–N12
O7–Cu5–N12
N13–Cu5–N12
O9–Cu5–O8
83.00(19)
83.4(2)
161.3(2)
166.18(17)
102.02(13)
94.16(15)
168.71(17)
84.75(16)
95.75(16)
94.02(15)
83.69(15)
170.85(19)
93.97(16)
97.26(16)
93.18(18)
95.95(17)
82.76(19)
81.80(18)
162.59(19)
167.67(16)
100.66(14)
96.12(14)
170.139(12)
The alignment of the basal plane containing metal cen-
ters plays a very important role in the magnetic exchange
interactions in any multimetallic system [51,52]. If these
planes are coplanar with each other, a strong antiferromag-
netism results and deviation from this planarity results in
the alteration of the extent of orbital overlapping. The
angle between the basal planes containing copper ion is
within the range of 20–40ꢁ. For example, in molecule B,
the angle between the planes containing Cu(4) and Cu(5)
is 39.61ꢁ. These numbers suggest a moderate to weak anti-
ferromagnetic interaction between the magnetic orbitals
emerging from the planes containing copper ions (cf. mag-
netic properties).
O7–Cu5–O8
N13–Cu5–O8
N12–Cu5–O8
N15–Cu6–N14
N15–Cu6–N16
N14–Cu6–N16
N15–Cu6–Cl4
N14–Cu6–Cl4
N16–Cu6–Cl4
Cu4–Cu5–Cu6
delocalization of the electron density has contributed in
inducing a partial negative charge on the amidate-O atom
that eventually coordinate to the central copper ion to
afford the linear trinuclear complex. The implication of this
delocalized resonance structure is the lengthening of the
C@O bond involved in the bonding than the un-coordi-
nated one. The C@O bond length increased from a average
3.3.2. Structure of complex 2
The molecular structure of this complex is shown in
Fig. 2 and the selected bonding parameters are presented
in Table 3. The complex 2 exists as a one-dimensional
(1D) chain of infinite length. The copper(II) ion is coordi-
nated by the ligand [L1]2ꢀ, in a tetradentate fashion via two
deprotonated amidate-N and two amine-N centers. The
5th coordination comes from the oxygen atom of the amide
group of the neighbouring complex, with the distance of
˚
˚
value of ꢂ1.23(2) A (uncoordinated one) to ꢂ1.28(2) A
(coordinated one). This lengthening is lower for molecule
˚
˚
B (0.03–0.04 A) than for molecule A (0.05–0.06 A). The
Cu–Oamide distances for the central metal ion, are in the
range of 1.923(3)–1.942(3) A for molecules A and B. These
distances are on the lower side than the examples reported
in the literature and indicate a stronger bond to the copper
ion [31,32]. The Cu–OH2 bond distances are also on the
lower side compared to the similar distance in other struc-
turally characterized complexes [43–47]. The Cu–Cl dis-
tances are comparable to other structurally characterized
complexes [48–50]. The average distance between the
˚
˚
2.354(2) A. This additional interaction leads to the
generation of an infinite length chain in the solid state.
The geometry around the Cu(II) ion is almost perfect
square – pyramidal with a very small s value [42] of 0.01.
The average Cu–Namide distance at 1.935(2) A is shorter
by 0.14 A than the average Cu–Namine bond lengths of
˚
˚
˚
2.075(3) A, thus indicating a tight chelation from the

J. Singh et al. / Polyhedron 26 (2007) 3893–3903
3899
orthogonal to each other and gave us a clue about their
expected magnetic behaviour (cf. magnetic properties).
Vagg and co-workers [53] have reported a copper(II)
complex with a pyridine-amide based ligand (N,N0-bis-
(60-methylpyridine-20-carboxamide)-1,2-benzene)
where
O(2)
oxygen atoms of the neighbouring molecules coordinate
to form a chain. However, this is to be noted that here
two O-atoms from two neighbouring molecules coordinate
to complete an octahedral geometry around the copper ion.
The two Cu–Oamide bond distances are 2.693(6) and
O(1)
N(1)
N(2)
Cu
˚
2.798(6) A, respectively, and are quite longer than that of
N(4)
N(3)
2. The average Cu–Namide and Cu–Npyridine distances are
˚
1.934(7) and 2.079(7) A, respectively, and are quite similar
O(2')
to that of complex 2. Interestingly, when the authors used
the un-substituted pyridine-amide ligand (N,N0-bis(20-pyri-
dinecarboxamide)-1,2-benzene), only one water molecule
coordinate axially to afford a square-pyramidal copper
complex [54]. The authors have reasoned that the presence
of methyl substituents on the pyridine ring in the former
case caused the distortion around the metal centre and
resulted in the twisting of the basal plane. The implication
of this twisting is the availability of the coordination sites
both from top and bottom of the basal plane, thus Oamide
coordinate to the copper ion affording the octahedral
geometry in the former case. Despite an interesting chain
structure of the Cu(II) complex of Vagg and co-workers,
magnetic properties have not been carried out.
Cu
Cu
O(2')
Cu
O(2')
O(2')
O(2')
Cu
O(2')
Cu
Fig. 2. Thermal ellipsoidal representation (30% probability level with
partial numbering, hydrogen atoms are omitted for clarity) of complex 2.
Top: monomeric unit; bottom: zig-zag chain formation (methyl substit-
uents are removed for clarity).
3.4. Magnetic properties
The magnetic properties of 1 and 2 in the form of vMT
versus T plot are shown in Figs. 3 and 4. For 1, the value of
vMT, at room temperature is 1.13 cm3 molꢀ1 K, close to
the expected value for three uncoupled Cu(II) ions. The
vMT product decreases upon cooling, reaching a plateau
at 23 K, with vMT value equal to 0.4 cm3 molꢀ1. This value
is close to the expected value for a spin state S = 1/2. This
behaviour is characteristic of an antiferromagnetic
Table 3
2
˚
Selected bond distances (A) and angles (ꢁ) for complex [Cu(L )]n (2)
Bond distances
Cu–N1
Cu–N2
Cu–N3
Cu–N4
Cu–O20
1.930(2)
1.939(2)
2.060(3)
2.090(3)
2.354(2)
C14–O1
C7–O2
N1–C14
N2–C7
1.232(4)
1.238(4)
1.321(4)
1.316(4)
Bond angles
N1–Cu–N2
N1–Cu–N3
N2–Cu–N3
N1–Cu–N4
N2–Cu–N4
N3–Cu–N4
82.47(10)
162.19(11)
82.61(11)
82.29(11)
161.50(10)
110.27(10)
N1–Cu–O20
N2–Cu–O20
N3–Cu–O20
N4–Cu–O20
101.98(11)
104.48(10)
91.14(10)
88.91(11)
1.2
1.0
0.8
anionic amidate donors. The lateral 5-membered chelate
rings are making an angle of ꢂ13ꢁ with each other, while
they make an angle of 8–10ꢁ with the central 5-membered
χ
0.6
0.4
˚
chelate ring. The copper(II) ion is 0.202 A out of the least
square basal plane (defined by N1, N2, N3, and N4)
towards the apical amide oxygen atom from the neighbour-
ing molecule. Any of the two copper ions in the chain are
˚
0
50
100
150
200
250
300
separated by ꢂ6 A. The two neighbouring molecular
T (K)
planes containing copper ions make an angle of ꢂ74(1)ꢁ
with each other. This significant number suggests that
any of the two monomeric units in the 1D chain are almost
Fig. 3. vMT vs. T plot for compound 1. The solid line was calculated with
the parameters reported in the text.

3900
J. Singh et al. / Polyhedron 26 (2007) 3893–3903
0.9
0.8
0.7
0.6
0.5
0.4
Compounds 1 and 2 show the same bridging motif,
1.2
1.0
0.8
0.6
0.4
0.2
0.0
NCO, between the Cu(II) ions, nevertheless the magnetic
behaviour is very different. For the trinuclear complex
(compound 1) strong antiferromagnetic coupling is
observed, while the one-dimensional system (compound
2) shows a ferromagnetic interaction.
β
In the trinuclear compound, the coordination around
the two terminal ions is square planar, while for the central
ion is a square pyramidal, and its basal plane is quite copla-
nar with the coordination planes of the terminal ions. For
the three copper(II) ions, the single electron is in the
x2 ꢀ y2 orbital, and taking into consideration that these
orbitals are almost coplanars, a good overlap through the
bridging motif NCO could be attended (Fig. 5). In the
one-dimensional system, the coordination polyhedra of
the Cu(II) ion is a square pyramidal, but, in this case, the
basal planes between neighbours ions are almost perpen-
dicular (in the crystal structure, two planes make an angle
of 74ꢁ with each other), and as a result of this, the x2 ꢀ y2
orbital are orthogonal, and a very small overlap through
the bridge must be attended (Fig. 6). So, the different mag-
netic behaviour observed for compounds 1 and 2, could be
explained by the different disposition of the magnetic
orbitals.
χ
0
10000
20000
30000
H (G)
40000
50000
0
50
100
150
200
250
300
T (K)
Fig. 4. vMT vs. T plot for compound 2. The solid line was calculated with
the parameters reported in the text. In the inset, experimental M/Nb vs. H
plot (¤) and calculated from the brillouin equation for a S = 1/2 (solid
line).
coupling. Below 4 K, vMT product decreases again, indi-
cating that an intermolecular antiferromagnetic interaction
also occur in this compound.
The experimental data were fitted using the theoretical
expression deduced from the following Heisenberg Hamil-
tonian H = ꢀJ(S1 Æ S2 + S2 Æ S3) ꢀ J0(S1 Æ S3). Taking into
account the geometry of this compound (the terminal cop-
per centres are separated by the distance in the range of
Several trinuclear compounds with oxamide bridging
ligands have been reported in the literature [24–30]. These
trinuclear compounds show significant antiferromagnetic
coupling with the J value ranging between ꢀ80 and
˚
11.4–11.5 A), the interaction between the two terminal
Cu(II) ions was assumed to be nil (J0 = 0). The best fit
was obtained for J = ꢀ110.34 cmꢀ1 and g = 2.06 (R =
1.8 · 10ꢀ4).
O
N
Cl
For 2, the vMT value at room temperature is
0.45 cm3 molꢀ1 K, which is as expected for one magneti-
cally quasi-isolated Cu(II) ion (g > 2.0). On cooling, the
vMT values smoothly increases up to 0.84 cm3 molꢀ1 K at
2 K. The shape of this curve clearly indicates weak ferro-
magnetic coupling among the Cu(II) ions. The mathemat-
ical formula derived by Baker et al. [55] for ferromagnetic
1D systems with S = 1/2 is valid only at relatively high
temperatures. Thus, when the ferromagnetic coupling is
weak, this formula is not very accurate. For this reason,
the fit of the experimental data was performed in the
numerical form from a full-matrix diagonalization of the
Hamiltonian corresponding to a ring of 12 local S = 1/2
centers with the adequate J coupling parameter using the
CLUMAG program [56]. With this program, the use of 12
cycled centers give a good approximation for the system,
which is actually infinite. The best fit parameters of the
data are J = +3.08 cmꢀ1 and g = 2.15 cmꢀ1 (R =
8.6 · 10ꢀ5). The reduced molar magnetization (M/Nb)
per Cu entity tends to be 1 Nb (electron) (Fig. 4 inset)
but the shape of the experimental curve is clearly above
the theoretical ones for the Brillouin law. These features
agree with the global ferromagnetic coupling between the
copper(II) ions.
N
N
N
Cl
N
N
O
Fig. 5. Schematic drawing of the disposition of the x2 ꢀ y2 orbital in the
trinuclear compound 1.
O
N
N
N
N
O
N
N
O
N
O
N
Fig. 6. Schematic drawing of the disposition of the x2 ꢀ y2 orbital in the
one-dimensional system 2.

J. Singh et al. / Polyhedron 26 (2007) 3893–3903
3901
ꢀ600 cmꢀ1 [51,52]. The extent of coupling (J value) has
been found to be very sensitive to the geometry around
the terminal Cu(II) ions with respect to the central cop-
per(II) ion. For the square-planar, 4-coordinate, or
square-based geometries (such as (4 + 1)- or (4 + 2)-coor-
dinate), the magnetic orbitals are predominantly dx2ꢀy2 in
nature. These terminal metal-based magnetic orbitals are
approximately coplanar with that of the central ion and
have x2 ꢀ y2 symmetry. Thus, the magnetic coupling is well
described by the antibonding combination of the dx2ꢀy2
metallic orbitals with the symmetry-adapted molecular
orbitals of the oxamido bridge. However, in case of trigo-
nal bipyramidal geometry for the terminal copper ions,
the magnetic orbitals are predominantly dz2 in character;
this reduces the effective overlap and the magnitude of
the interaction is smaller (lower value of ꢀJ) [25–27]. Basi-
cally, when the magnetic orbitals of the three Cu(II) ions
are not coplanar with respect to each other, the J value
decreases. The oxamido ligand provides two coplanars
NCO bridging motifs, while for compound 1, only one
NCO group bridge the two Cu(II) ions. Therefore, in com-
pound 1, with only one way for the magnetic exchange, the
antiferromagnetic coupling must be smaller than in the
oxamide complexes. This agrees nicely with the smaller J
value found for 1 (ꢀ110 cmꢀ1) compared to the oxamido
bridged complexes.
The solution state magnetic moment were also deter-
mined for both complexes using Evans’ method [57]. The
room temperature magnetic moment (leff) for complex 2
in (CH3)2SO, was found to be 1.85 lB which matches very
well with the solid state value of 1.90 lB. The similarity
between the results from the solid and the solution state
indicate a similar structure. However, taking into account
that at room temperature if the magnetic coupling is small,
the values are close to the uncoupled ions; it is, therefore,
not possible to be sure if the 1D structure is maintained
or if it is a mononuclear structure in the solution. For tri-
nuclear complex 1, however, a value of 2.68 lB/trimer was
obtained at room temperature in (CH3)2SO or DMF. This
value is lower by ꢂ0.3 lB/trimer than the solid state value.
The difference in the magnetic moment is indicative of
some changes in the geometry of the trinuclear complex
and indicate that the copper centres are better antiferro-
magnetically coupled in the solution state at room temper-
ature. This could happen due to a more relaxed geometry
around the copper ions allowing better overlap of the metal
based magnetic orbitals through ligand based magnetic
orbitals.
1
2
2800
3000
3200
3400
3600
3800
H (G)
Fig. 7. Powder EPR spectra for compounds 1 and 2 at 4 K.
the EPR spectrum at 4 K. The experimentally observed g
value of 2.08 in EPR measurement matches very well with
the g value (=2.06) obtained after fitting the magnetic data.
For one-dimensional compound, 2, the EPR spectrum at
4 K, shows two superimposed bands at 2.11 and 2.06, with
a DHp–p = 145 G (Fig. 7). The two different g values clearly
indicate the anisotropy [58] around the copper centre
caused due to the coordination of the O-atom of the neigh-
bour molecule, as observed structurally (cf. crystal struc-
ture of 2). The effect of the temperature in the peak-to-
peak gap is opposite in both compounds. For compound
1, a narrowing of the band was observed on cooling, from
190 to 62 G. However, for 2, a little broadening of the band
was observed, from 130 to 145 G. The observed tempera-
ture-dependent behaviour for both complexes clearly indi-
cates that they significantly differ with each other and
support their opposite magnetic properties (cf. magnetic
measurements).
The EPR spectra were also recorded in the solution state
to understand the solution-based geometry and the effect of
solvent (CH3OH and pyridine). For 1, a broad feature,
with the giso at 2.107 and 2.097 was observed in methanol
and pyridine, respectively. In solution, at room tempera-
ture there is only one isotropic g value. For complex 2, a
four lines signal was observed in methanol or pyridine at
room temperature. This feature is characteristic of the
hyperfine coupling with the nuclear spin of the Cu (I = 3/
2) and typically observed for a tetragonal copper ion in
solution [58]. The giso was observed at ꢂ2.12 with the
A(Cu)iso value of 106 G.
3.5. EPR spectra
Powder electron paramagnetic resonance spectra (EPR)
were recorded at 298, 77 and 4 K for compounds 1 and 2
(Figs. 7, S4 and S5). The trinuclear complex 1, with an
appreciable antiferromagnetic coupling (J = ꢀ110.34
cmꢀ1), shows a ground state of S = 1/2, and a narrow sig-
nal (DHp–p = 62 G) centered at g = 2.08 was observed in
3.6. Absorption spectra
The electronic spectra of both complexes were recorded
in the solid state (dispersed in mineral oil) as well as in solu-
tions (CH3OH, CH3CN, and pyridine) to gain insight into
the coordination geometry around the copper ion (Figs. S6

3902
J. Singh et al. / Polyhedron 26 (2007) 3893–3903
and S7). The solid state spectrum of 1 displays a broad
band in the visible region at 655 with a low energy shoulder
at ꢂ850 nm, suggestive of a square-pyramidal geometry
[59,60]. A less clear feature was also observed at
ꢂ515 nm which we assign due to the square-planar Cu(II)
ion. This corroborate the findings from the crystal struc-
ture of 1 that clearly show that terminal copper ions are
square-planar while the central ion is square-pyramidal.
In CH3OH or CH3CN, a main peak was observed at
625 nm while a less intense peak at ꢂ515 nm was also
noticed. We tentatively assign the former from the
square-pyramidal ion (central copper) while the later due
to the square-planar ion (terminal coppers). For 2, a broad
band at 590 nm with a weak shoulder at ꢂ760 nm was dis-
played in the solid state spectrum. These features clearly
support a 5-coordinate geometry around the Cu(II) ion
[59,60] as seen in the crystal structure of 2. However, a shift
in the kmax was noticed when the spectra were recorded in
various solvents; the kmax changed from 530 in CH3CN to
548 in MeOH to 555 nm in pyridine. This experiment
strongly suggests that the axial position(s) occupied by
the Oamide in the solid state (as seen in the crystal structure)
are displaced by the solvent molecule(s) when the spectrum
is recorded in the solution state.
New Delhi for the generous financial support, and DST
funded single crystal facility at IIT – Delhi for the data col-
lection of complex 2. M.C. thanks Ministerio de Educacion
y Ciencia for financial support (CTQ2006 – 01759/BQU).
J.S. thanks CSIR – UGC for the JRF fellowship.
Appendix A. Supplementary material
CCDC 634199 and 634200 contain the supplementary
crystallographic data for 1 and 2. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@
ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at
doi:10.1016/j.poly.2007.04.021.
References
[1] P.V. Rao, R.H. Holm, Chem. Rev. 104 (2004) 527.
[2] E.I. Solomon, R.K. Szilagyi, S.D. George, L. Basumallick, Chem.
Rev. 104 (2004) 419.
[3] M.L. Alvarez, J.Y. Ai, W. Zumft, J. Sanders-Loehr, D.M. Dooley, J.
Am. Chem. Soc. 123 (2001) 576.
[4] S. Suzuki, K. Kataoka, K. Yamaguchi, Acc. Chem. Res. 33 (2000)
728.
4. Conclusions
[5] R.L. Lieberman, D.B. Shrestha, P.E. Doan, B.M. Hoffman, T.L.
Stammler, A.C. Rosenzweig, Proc. Natl. Acad. Sci. USA 100 (2003)
3820.
[6] K. Brown, K. Djinovic-Carugo, T. Haltia, I. Cabrito, M. Saraste,
J.J.G. Moura, I. Moura, M. Tegoni, C. Cambillau, J. Biol. Chem. 275
(2000) 41133.
[7] K. Brown, M. Tegoni, M. Prudencio, A.S. Pereira, S. Besson, J.J.G.
Moura, I. Moura, C. Cambillau, Nat. Struct. Biol. 7 (2000) 191.
[8] B.T. Rasmussen, B.C. Berks, J. Sanders-Loehr, D.M. Dooley, W.G.
Zumft, A.J. Thomson, Biochemistry 39 (2000) 12753.
[9] P. Chen, I. Cabrito, J.J.G. Moura, I. Moura, E.I. Solomon, J. Am.
Chem. Soc. 124 (2002) 10497.
[10] R.L. Lieberman, A.C. Rosenzweig, Nature 434 (2005) 177.
[11] R.L. Lieberman, K.C. Kondapalli, D.P. Shrestha, A.S. Hakemian,
S.M. Smith, J. Telser, J. Kuzelka, R. Gupta, A.S. Borovik, S.J.
Lippard, B.M. Hoffman, A.C. Rosenzweig, T.L. Stemmler, Inorg.
Chem. 45 (2006) 8372.
[12] M. Melnik, Coord. Chem. Rev. 42 (1982) 259.
[13] D.J. Hodgson, in: S.J. Lippard (Ed.), Progress in Inorganic Chem-
istry, vol. 19, Wiley, New York, 1975, p. 173.
[14] M. Kato, Y. Muto, Coord. Chem. Rev. 92 (1988) 45.
[15] L. Merz, W. Haase, J. Chem. Soc., Dalton Trans. (1980) 875.
[16] M. Handa, N. Koga, S. Kida, Bull. Chem. Soc. Jpn. 61 (1988) 3853.
[17] R. Gupta, R. Hotchandani, R. Mukherjee, Polyhedron 19 (2000)
1429.
[18] R. Gupta, S. Mukherjee, R. Mukherjee, J. Chem. Soc., Dalton Trans.
(1999) 4025.
[19] L.K. Thompson, S.K. Mandal, S.S. Tandon, J.N. Bridson, M.K.
Park, Inorg. Chem. 35 (1996) 3117.
The present work show interesting coordination behav-
iour of the amide-based ligands towards copper(II) ion.
The backbone flexibility of the ligand [L1]2ꢀ, resulted in
the flipping of one of the arm to accommodate the second
copper ion; this generates the trinuclear complex,
[Cu3(L1)2(Cl)2(H2O)] 1. This trinuclear complex belongs
to a rare group of complexes where both amidate-N and
amidate-O participate in the coordination [31,32]. The
ligand [L2]2ꢀ, incorporating the rigid o-phenylene backbone
affords a simple mononuclear complex. The substituted
methyl groups restricted the coordination of any additional
axial ligand. However, the molecular basal plane tilt in a
unique way to allow the coordination of the neighbouring
amidate-O to the Cu(II) centre [53,54]. This generates a
zig-zag one-dimensional chain, [Cu(L2)]n 2. Both com-
plexes, 1 and 2 have NCO bridge between the copper ions
and show interesting but contrast magnetic properties.
The 1 shows moderately strong antiferromagnetic coupling
(J = ꢂꢀ110 cmꢀ1). The moderate nature of antiferromag-
netic coupling in 1 is due to the availability of only one mag-
netic exchange pathway (NCO bridge) between the copper
ions compared to two in the oxamido-bridged systems.
Whereas 2 shows a weak ferromagnetic interaction
(J = ꢂ+3 cmꢀ1) due to the accidental orthogonality of the
magnetic orbitals from two copper containing basal planes.
[20] S.S. Tandon, L.K. Thompson, J.N. Bridson, V. McKee, A.J.
Downard, Inorg. Chem. 31 (1992) 4635.
[21] K. Nonoyama, H. Ojima, K. Ohki, N. Nonoyama, Inorg. Chim. Acta
41 (1980) 155.
[22] N.F. Curtis, I.R.N. McCormick, T.N. Waters, J. Chem. Soc., Dalton
Trans. (1973) 1537.
Acknowledgements
R.G. thanks University Grant Commission (UGC),
Delhi, and Department of Science & Technology (DST),
[23] D.M. Duggan, D.N. Hendrickson, Inorg. Chem. 12 (1973) 2422.
[24] Y. Journaux, J. Sletten, O. Kahn, Inorg. Chem. 25 (1986) 439.

J. Singh et al. / Polyhedron 26 (2007) 3893–3903
3903
[25] A. Garcia, R. Costa, J. Ribas, Inorg. Chim. Acta 168 (1990) 249.
[26] R. Costa, A. Garcia, J. Ribas, T. Mallah, Y. Journaux, J. Sletten, X.
Solans, V. Rodriguez, Inorg. Chem. 32 (1993) 3733.
[27] R. Costa, A. Garcia, R. Sanchez, J. Ribas, X. Solans, V. Rodriguez,
Polyhedron 12 (1993) 2697.
[28] R. Veit, J.-J. Girerd, O. Kahn, F. Robert, Y. Jeannin, Inorg. Chem.
25 (1986) 4175.
[29] J.-J. Girerd, S. Jeannin, Y. Jeannin, O. Kahn, Inorg. Chem. 17 (1978)
3034.
[30] R. Veit, J.-J. Girerd, O. Kahn, F. Robert, Y. Jeannin, N. El Murr,
Inorg. Chem. 23 (1984) 4448.
[31] U.P. Chaudhuri, L.R. Whiteaker, L. Yang, R.P. Houser, Dalton
Trans. (2006) 1902.
[32] A. Mondal, Y. Li, M.A. Khan, J.H. Ross Jr., R.P. Houser, Inorg.
Chem. 43 (2004) 7075.
[33] A. Davison, A.G. Jones, C. Orvig, M. Sohn, Inorg. Chem. 20 (1981)
1629.
[42] A.W. Addition, T.N. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor, J.
Chem. Soc., Dalton Trans. (1984) 1349.
[43] F.S. Stephens, R.S. Vagg, Inorg. Chim. Acta 88 (1984) 7.
[44] F.S. Stephens, R.S. Vagg, Inorg. Chim. Acta 57 (1982) 43.
[45] M. Mulqi, F.S. Stephens, R.S. Vagg, Inorg. Chim. Acta 52 (1981)
177.
[46] F.S. Stephens, R.S. Vagg, Inorg. Chim. Acta 51 (1981) 149.
[47] M. Mulqi, F.S. Stephens, R.S. Vagg, Inorg. Chim. Acta 51 (1981) 9.
[48] J.M. Rowland, M.M. Olmstead, P.K. Mascharak, Inorg. Chem. 39
(2000) 5326.
[49] A. Mondal, E.L. Klein, M.A. Khan, R.P. Houser, Inorg. Chem. 42
(2003) 5462.
[50] M.C.B. de Oliveira, M. Scarpellini, A. Neves, H. Terenzi, A.J.
Bortoluzzi, B. Szpoganics, A. Greatti, A.S. Mangrich, E.M. de Souza,
P.M. Fernandez, M.R. Soares, Inorg. Chem. 44 (2005) 921.
[51] O. Kahn, Angew. Chem., Int. Ed. Engl. 24 (1985) 834, and references
therein.
[34] H.-J. Krugar, G. Peng, R.H. Holm, Inorg. Chem. 30 (1991) 734.
[35] Bruker Analytical X-ray System, SMART: Bruker Molecular Analysis
Research Tool, Version 5.0 618, 2000.
[52] O. Kahn, Inorg. Chim. Acta 62 (1982) 3, and references therein.
[53] R.L. Chapman, F.S. Stephens, R.S. Vagg, Inorg. Chim. Acta 52
(1981) 169.
[36] Bruker Analytical X-ray System, SAINT-NT, Version 6.10, 2000.
[37] G. Cascarano, L. Favia, C. Giacovazzo, J. Appl. Crystallogr. 25
(1992) 310.
[38] G.M. Sheldrick, SHELXL-97: Program for Crystal Structure Refine-
ment, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[39] L.J. Farrugia, WINGX Version 1.64, An Integrated System of Windows
Programs for the Solution, Refinement and Analysis of Single-Crystal
X-ray Diffraction Data, Department of Chemistry, University of
Glasgow, Glasgow, UK, 2003.
[54] R.L. Chapman, F.S. Stephens, R.S. Vagg, Inorg. Chim. Acta 43
(1980) 29.
[55] G.A. Baker, G.S. Rushbreoke, H.E. Gilbert, Phys. Rev. A. 135 (1964)
1272.
[56] D. Gatteschi, L. Pardi, Gazz. Chim. Ital. 123 (1993) 231.
[57] D.F. Evans, J. Chem. Soc. (1959) 2003.
[58] B.J. Hathaway, in: G. Wilkinson, R.D. Gillard, J.A. McCleverty
(Eds.), Comprehensive Coordination Chemistry, vol. 5, Pergamon
Press, Oxford, 1987, p. 533.
[40] K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, Wiley, 1986.
[59] T.K. Lal, R. Gupta, S. Mahapatra, R. Mukherjee, Polyhedron 18
(1999) 1743.
[41] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[60] R. Gupta, R. Mukherjee, Polyhedron 19 (2000) 719.