Synthesis, crystal structures and magnetic properties of a phenoxo-bridged dinuclear CuII complex and a dicyanamide bridged novel molecular rectangle based on it

Article abstract of DOI:10.1002/ejic.201100067

The phenoxo-bridged dinuclear Cu^II complex [Cu₂L ₂(NCNCN)₂] (1) and the dicyanamide-bridged molecular rectangle [Cu₄L₄{μ_1,5-(NCNCN)₂}] ·(ClO₄)₂(H

Full text of DOI:10.1002/ejic.201100067

FULL PAPER
DOI: 10.1002/ejic.201100067
Synthesis, Crystal Structures and Magnetic Properties of a Phenoxo-Bridged
Dinuclear CuII Complex and a Dicyanamide Bridged Novel Molecular
Rectangle Based on It
Apurba Biswas,[a] Michael G. B. Drew,[b] Joan Ribas,[c] Carmen Diaz,*[c] and
Ashutosh Ghosh*[a]
Keywords: Copper / Schiff bases / Magnetic properties
The phenoxo-bridged dinuclear CuII complex [Cu2L2-
(NCNCN)2] (1) and the dicyanamide-bridged molecular rect-
angle [Cu4L4{μ1,5-(NCNCN)2}]·(ClO4)2(H2O)2 (2) were syn-
thesized using the tridentate reduced Schiff-base ligand HL
{2-[(2-dimethylamino-ethylamino)methyl]phenol}. The com-
plexes were characterized by X-ray structural analyses and
variable-temperature magnetic susceptibility measurements.
Complex 2 was formed through the joining of the phenoxo-
bridged dinuclear Cu2O2 cores of 1 via the μ1,5-bridging
mode of dicyanamide. The structural properties of the Cu2O2
cores in two complexes are significantly different. The geom-
etry of the copper ions is distorted trigonal bipyramid in 1
but is nearly square-pyramidal in 2. These differences have a
marked effect on the magnetic properties of two compounds.
Although both are antiferromagnetically coupled, the cou-
pling constants (J = –185.2 and –500.9 cm–1 for 1 and 2,
respectively) differ considerably.
this area. However, molecular rectangles have proven diffi-
cult to make because their formation generally requires the
self-assembly of a metal precursor with two different types
of ligands, which have tended to preferentially form sepa-
rate discrete complexes.[13] Although, metallomacrocycles
offer a half-way house in that they can provide rectangular
shapes without the need for the combination of mixed li-
gands.[14] Most of the reported molecular rectangle-based
coordination compounds have been prepared with the Ru,
Rd, Ir, Pt and Pd metal ions and nitrogen donor symmetri-
cal polypyridyl ligands have been used widely with these
metal ions to prepare several 2D and 3D architectures.[15]
However, synthesis of a molecular rectangular based on 1st
transition metal ions are very rare.[15a]
Introduction
The coordination-driven self-assembly of supramolecular
entities of transition metals has received much attention
during the past decades due to their potential for porosity
and their consequent use in applications in various fields,
including host-guest chemistry,[1] gas separation and stor-
age,[2] ion recognition or ion exchange,[3] and optoelectron-
ics or photovoltaics,[4] as well as catalysis.[5] The important
aspects of this methodology are the rational design of struc-
tures of diverse shapes and sizes as well as functionalization
by incorporating suitable functional groups.[6] By employ-
ment of a rational transition metal mediated approach,
many finite and nanoscopic supramolecules have been pre-
pared.[7]
The Schiff bases derived from the condensation of di-
amines and salicylaldehyde derivatives have been employed
in the synthesis of many complexes with different transition
metals,[16] among which the most frequent ones are the
phenoxo-bridged copper(II).[17] In the field of molecular
magnetism, phenoxo-bridged complexes are an important
family of compounds. The magnetic properties of phenoxo-
bridged complexes containing the Cu2O2 core depend on
the structural properties of the core. Factors, such as the
coordination geometry of the copper ions, the Cu–O–Cu
angle, the Cu–O bond lengths, the Cu···Cu distances, Addi-
son parameter and torsion angle are the parameters that
have been postulated to influence the J values of the spin
coupling.[17]
Of the geometric shapes accessible through the direc-
tional bonding approach, tetranuclear squares have been
the most broadly reported.[8] Other high-symmetry struc-
tures, such as triangles,[9] hexagons,[10] and dodecahe-
drons,[11] have also been recognized. As lower symmetry
hosts can be expected to show enhanced guest selectivity,
especially toward planar aromatic guests,[12] rectangles rep-
resent a crucial geometrical model in the development of
[a] Department of Chemistry, University College of Science,
University of Calcutta,
92, A. P. C. Road, Kolkata 700009, India
E-mail: ghosh_59@yahoo.com
[b] School of Chemistry, The University of Reading,
P. O. Box 224, Whiteknights, Reading RG 66AD, UK
[c] Departament de Química Inorgànica, Universitat de Barcelona,
Marti i Franques 1–11, 08028 Barcelona, Spain
The pseudohalide ligand, dicyanamide, has been exten-
sively used recently to generate a wide variety of polynu-
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clear compounds of different topologies and magnetic methanol solution of 2 was treated with an aqueous solu-
properties partly due to the discovery of long-range mag- tion of sodium dicyanamide (1:2 molar ratio) and the re-
netic ordering in the M(dicyanamide)2 compounds.[18] Over sulting solution was evaporated slowly at room tempera-
the past years or so, several new binding modes have been ture.
identified although the terminal and the μ1,5-mode seem-
ingly appear on a more regular basis in the transition metal
complexes. As in the μ1,5-bridging mode, the dicyanamide
IR and Electronic Spectra
should act as a linear linker between two metal ions, it is of
our interest to utilize it in the formation of molecular rect-
angle by joining phenoxo-bridged di-copper units and study
in the changes of the magnetic coupling.
In this paper we report the syntheses, crystal structures,
and magnetic properties of a phenoxo-bridged dinuclear
CuII complex, [Cu2L2(NCNCN)2] (1) where HL is a re-
duced Schiff-base ligand, 2-[(2-dimethylamino-ethylamino)-
A moderately strong, sharp peak due to N–H stretching
vibration at 3184, and 3238 cm–1 for complexes 1 and 2,
respectively, shows that the imine group of the Schiff base
is reduced. The reduction of the imine group is also very
clearly indicated by the absence of the strong band due to
imine vibration which appears in the region 1620–1650 cm–1
for the complexes of the corresponding unreduced Schiff
bases.[19] Both the complexes exhibit several νC–N bands[20]
at 2286, 2223, 2167 cm–1 for 1 and 2293, 2221, 2161 cm–1
for 2 which are attributed to νsym + νasym (CN), νasym (CN)
and νsym (CN) modes of the bridging dicyanamide ligand,
respectively. The strong and single band at 1090 cm–1 for
complex 2 indicates the presence of anionic perchlorate
group.
The electronic spectra of these two compounds were re-
corded in acetonitrile solution. The electronic spectra show
a single absorption band at 645 and 640 nm for compounds
1 and 2, respectively. At higher energy region, the ligand to
metal charge-transfer bands were located at 420 and 455 nm
for compounds 1 and 2, respectively.
methyl]phenol and a molecular rectangle, [Cu4L4{μ1,5
-
(NCNCN)2}]·(ClO4)2(H2O)2 (2) in which the dinuclear
Cu2O2 cores of 1 are joined via the μ1,5-bridging mode of
dicyanamide.
Results and Discussion
Synthesis of the Complexes
The condensation of N,N-dimethylethylenediamine in 1:1
molar ratio with salicylaldehyde afforded the Schiff base, 2-
[(2-dimethylamino-ethylimino)methyl]phenol which on re-
duction with sodium borohydride readily produced the re-
duced Schiff base, HL (Scheme 1). HL on reaction with
copper(II) perchlorate in presence of sodium dicyanamide
in 1:1:1 and 2:2:1 molar ratios yielded compound 1 and
Crystal Structures of the Complexes
Structure of [Cu2L2(NCNCN)2] (1). The structure of
2, respectively. Compound 2 was converted into 1 when a [Cu2L2(NCNCN)2] (1) is a centrosymmetric dimer, as
Scheme 1. Formation of the complexes.
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Dinuclear CuII Complex and a Derived Molecular Rectangle Complex
shown in Figure 1 with each metal atom in a five-coordi- around CuII is considered as square pyramidal, the devia-
nate environment. Dimensions in the metal coordination tions of the coordinating atoms N(1), N(19), N(22), O(11)a
sphere are given in Table 1.
from the least-square mean plane through them are
–0.445(4), 0.501(3), –0.483(3), 0.428(2) Å, respectively. The
deviation of CuII from the same plane is 0.2974(5) Å in the
direction of chelating oxygen atom O(11) which may be
considered as axially coordinated. However, the geometry
around CuII can be described better as trigonal bipyramid
with O(11), N(1), and N(22) make up the equatorial plane
which together with CuII provide an r.m.s. deviation of
0.0413(5) Å. The Addison parameter (τ) of the pentacoordi-
nate CuII is 0.55 indicating also that the geometry is basi-
cally a distorted trigonal bipyramid with N(19) and O(11)a
occupying axial positions. The trigonal bipyramidal geome-
try also explain the apparently anomalous shorter Cu–
O(11)a bond length in this compound, as for the d9 system
the axial bonds are longer in square pyramidal or octahe-
dral geometry but are shorter in trigonal bipyramidal ar-
rangement. While there is no short contact between N(5)
and metal atoms, N(5) does act as acceptor to form an
intermolecular hydrogen bond. Thus the proton on N(19)
forms a hydrogen bond to N(5)c (c: 1 – x, 2 – y, 1 – z) with
dimensions (Table 2) N···N 2.893(5) Å, H···N 2.07 Å and
N–H···N 150° to result in a 1D supramolecular structure
(Figure 2).
Figure 1. The crystal structure of 1 (ellipsoids at 30% probability).
Table 1. Bond lengths [Å] and angles [°] for complex 1.
Table 2. Hydrogen bonding distances [Å] and angles [°] for the
complexes 1 and 2.
Cu(1)–O(11)a
1.938(3)
Cu(1)–N(19)
Cu(1)–N(1)
Cu(1)–N(22)
Cu(1)–O(11)
1.971(3)
2.032(4)
2.082(3)
2.131(2)
168.68(11)
98.61(13)
90.29(14)
93.50(11)
84.91(12)
135.47(14)
79.57(10)
90.94(11)
109.15(13)
115.16(11)
D–H···A
D–H [Å] A···H [Å] D···A [Å] Є D–H–A [°]
1
2
N(19)–H(19)···N(5)c 0.91
2.07
2.68
2.10(4)
2.23(5)
2.14
2.893(5)
3.477(4)
2.932(5)
2.972(5)
3.005(3)
150
147
160(5)
147(4)
159
N(19)–H(19)···N(5)d 0.91
O(1)–H(1)···O(74)e
O(1)–H(2)···O(73)f
0.87(4)
0.84(4)
O(11)a –Cu(1)–N(19)
O(11)a–Cu(1)–N(1)
N(19)–Cu(1)–N(1)
O(11)a–Cu(1)–N(22)
N(19)–Cu(1)–N(22)
N(1)–Cu(1)–N(22)
O(11)a–Cu(1)–O(11)
N(19)–Cu(1)–O(11)
N(1)–Cu(1)–O(11)
N(22)–Cu(1)–O(11)
N(39)–H(39)···O(72) 0.91
Symmetry operations: c: 1 – x, 2 – y, 1 – z; d: x, y – 1, z; e: 1 – x, 1 – y,
1 – z; f: x, y, 1 + z
Structure of [Cu4L4{μ1,5-(NCNCN)2}]·(ClO4)2(H2O)2 (2):
The structure of 2, contains discrete tetranuclear cations,
perchlorate anions and solvent water molecules. The cation
is a centrosymmetric tetramer containing two independent
copper atoms, both with square pyramidal geometries as
Symmetry operation: a: 1 – x, 1 – y, 2 – z
The metal atom is bonded to the mononegative triden- shown in Figure 3. Dimensions in the metal coordination
tate ligand, L via O(11) at 2.131(2), N(19) at 1.971(3) and sphere are given in Table 3.
N(22) at 2.082(3) Å, together with a bridging oxygen atom
For both copper atoms, the equatorial plane consists of
O(11)a (a: 1 – x, 1 – y, 2 – z) from a second ligand at the three donor atoms of the ligand together with one
1.938(3) Å and a terminal NCNCN ligand via N(1) at bridging oxygen atom of a second ligand. The axial site is
2.032(4) Å. The two Cu atoms are separated by 3.129 Å and occupied by nitrogen of a bridging NCNCN ligand. Bond
the Cu(1)–O(11)–Cu(1)a angle is 100.43°. If the geometry lengths in the metal coordination sphere are Cu(1)–O(11)
Figure 2. Hydrogen bonding polymeric structure of compound 1; hydrogen atoms except H19 have been excluded for clarity.
Eur. J. Inorg. Chem. 2011, 2405–2412
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Figure 3. The crystal structure of 2 with ellipsoids at 30% probability.
Table 3. Bond lengths [Å] and angles [°] for complex 2.
respectively, with the copper atoms 0.365(1), 0.365(1) Å
from the plane in the direction of the axial ligand. The over-
all geometry around copper(II) is nearly square pyramidal
with Addison parameter τ = 0.03 and 0.06 for Cu(1) and
Cu(2), respectively. In the compound the shortest Cu···Cu
distances are 3.051 and 8.054 Å corresponding to the di-
phenoxo and dicyanamide bridges, respectively. The bridg-
ing Cu(1)–O(11)–Cu(2) and Cu(1)–O(31)–Cu(2) angles are
102.56 and 100.93°, respectively.
Cu(1)–N(5)b
Cu(1)–N(19)
Cu(1)–N(22)
Cu(1)–O(11)
Cu(1)–O(31)
Cu(2)–N(1)
Cu(2)–N(39)
Cu(2)–N(42)
2.236(3)
2.014(2)
2.047(2)
1.966(2)
1.970(2)
2.165(2)
2.000(2)
2.055(2)
1.944(2)
1.986(2)
76.77(8)
91.01(8)
158.89(9)
157.19(9)
98.18(9)
86.40(9)
102.39(10)
107.05(9)
92.25(11)
100.35(10)
76.89(8)
159.89(9)
91.18(9)
98.27(9)
156.22(9)
86.09(9)
103.27(9)
100.28(10)
94.69(9)
103.48(11)
Cu(2)–O(11)
Cu(2)–O(31)
Thus by contrast with 1 in 2 the NCNCN ligand bridges
two copper atoms. The perchlorates and water molecules
are involved in intermolecular hydrogen bonding together
with the two amine hydrogen atoms. N(19)–H(19) forms a
weak hydrogen bond to N(5)d (d: x, y – 1, z) with dimen-
sions (Table 2) 3.477(4), 2.68 Å, 147° while N(39)–
H(39)···O(72) is significantly stronger with dimensions,
3.005(3), 2.14 Å, 159°. In addition the water molecule forms
hydrogen bonds to two oxygen atoms of the perchlorate,
viz. O(1)–H(1)···O(74)e (e: 1 – x, 1 – y, 1 – z) and O(1)–H(2)···
O(73)f (f: x, y, 1 + z) with dimensions 2.932(5), 2.10(4) Å,
160(5)° and 2.972(5), 2.23(5) Å, 147(4)°, respectively (Fig-
ure 4).
O(11)–Cu(1)–O(31)
O(11)–Cu(1)–N(19)
O(31)–Cu(1)–N(19)
O(11)–Cu(1)–N(22)
O(31)–Cu(1)–N(22)
N(19)–Cu(1)–N(22)
O(11)–Cu(1)–N(5)b
O(31)–Cu(1)–N(5)b
N(19)–Cu(1)–N(5)b
N(22)–Cu(1)–N(5)b
O(11)–Cu(2)–O(31)
O(11)–Cu(2)–N(39)
O(31)–Cu(2)–N(39)
O(11)–Cu(2)–N(42)
O(31)–Cu(2)–N(42)
N(39)–Cu(2)–N(42)
O(11)–Cu(2)–N(1)
O(31)–Cu(2)–N(1)
N(39)–Cu(2)–N(1)
N(42)–Cu(2)–N(1)
Symmetry operation: b: –x, –y, 1 – z
1.966(2), Cu(1)–N(19) 2.014(2) and Cu(1)–N(22) 2.047(2) Å
to the tridentate ligand L with Cu(1)–O(31) 1.970(2) and
Cu(1)–N(5)b 2.236(3) Å to the bridging NCNCN ligand
and Cu(2)–O(31) 1.986(2), Cu(2)–N(39) 2.000(2) and
Cu(2)–N(42) 2.055(2) Å to the tridentate ligand L with
Cu(2)–O(11) 1.944(2) and Cu(2)–N(1) 2.165(2) Å to the
bridging NCNCN ligand. The four donor atoms in the
Figure 4. Hydrogen bonding polymeric structure of compound 2
(hydrogen atoms except H39 and those of water molecules omitted
equatorial plane show r.m.s. deviations of 0.031, 0.051 Å, for clarity).
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Dinuclear CuII Complex and a Derived Molecular Rectangle Complex
In both the structures the geometry of the NCNCN li-
gand is similar in spite of its different binding mode. Thus
the Cu–N–C angles are 155.5(3)° in 1, and 151.9(3),
138.0(3)° in 2 while the central C–N–C angles are 121.6(4)°
in 1, and 125.6(4)° in 2.
It is to be noted that in the dinuclear structure of 1 the
two NCNCN groups are in opposite directions (trans)
whereas in 2, they orient themselves in the same direction
(cis) to form the molecular rectangle.
(1)
The best-fit parameters for reproducing satisfactorily the
experimental data, as shown in Figures 5 and 6, are J =
–185.2 cm–1 and g = 2.18 with R = 7ϫ10–5 for 1, J =
–500.9 cm–1 and g = 2.10 with R = 2ϫ10–5 for 2 [R =
Σi(χTicalc – χTiexp)2/Σi(χTiexp)2].
However, the structure of complex 2 comprises two dinu-
clear copper systems, in each of which the copper ions are
bridged by a double μ-phenoxo and additional double μ-
dicyanamide ligand bridge these dinuclear units giving the
tetranuclear compound (see description of crystal struc-
ture). The dimer model reproduces very satisfactorily the
magnetic behavior in the whole temperature range. This re-
sult is logical taking into account that the coupling though
the dicyanamide-bridge is negligible compare to the high
expected magnetic exchange through the double phenoxo-
bridged, according to the structural parameters.
Magnetic Properties
Temperature-dependence molar susceptibility measure-
ments of powdered samples 1 and 2 were carried out in an
applied field of 10000 and 500 G in the temperature range
of 2–300 K and 2–30 K, respectively. Plots of complexes 1
and 2 are shown in Figures 5 and 6, respectively, in both
cases χmT being the magnetic susceptibility per Cu2 unit.
At room temperature the χmT values are far from
0.75 cm3 mol–1 K (g = 2.00) for a non-interacting Cu2 unit
(0.66 cm3 mol–1 K for 1, and 0.22 cm3 mol–1 K for 2). When
the samples are cooled, the χmT values decreased to zero at
low temperatures. The shape of the curves indicates strong
antiferromagnetic coupling in both cases.
Magnetostructural Correlations
In Table 4 we have indicated the main structural param-
eters of complexes 1 and 2 that can influence the corre-
sponding J values.
Table 4. Selected structural parameters for complex 1 and 2 related
to their magnetic data.
1
2
J value [cm–1]
τ (Addison parameter)
–185.2
0.55
–500.9
0.03 (Cu1)
0.06 (Cu2)
1.966
Distances (Cu–O) [Å]
1.937
2.131
1.944
1.986
1.970
Angles (Cu–O–Cu) [°]
100.43
102.56
100.93
12.94
Figure 5. Plot of the χmT vs, T in the range 2–300 K for 1.
Torsion angle (Cu–O–Cu–O) [°] 0.0
12.83
According to literature data the exchange coupling in di-
nuclear complexes with Cu2O2 core depends on several fac-
tors. Magnetostructural correlations in dinuclear copper(II)
complexes bridged equatorially by pairs of hydroxide[22] or
alkoxide[23,24] groups show that the major factor controlling
spin coupling between the S = 1/2 metal centers is the Cu–
O(R)–Cu angle. Hatfield and Hodgson found a linear cor-
relation between the experimentally exchange coupling con-
stant and the Cu–O–Cu bond angle.[22] In general the larger
Cu–O–Cu angle, favors large AF J values. Thompson et
al. found strong differences in μ-hydroxo, μ-alkoxo and μ-
phenoxo.[25] It is apparent that the slopes (of J vs. Cu–O–
Cu angle) of the hydroxide and alkoxide cases are compar-
Figure 6. Plot of the χmT vs, T in the range 2–300 K for 2.
Assuming the isotropic Hamiltonian H = –JS1S2, the ex- able, but absolute values of –J are larger for the alkoxide.
perimental data were fitted to the Bleaney–Bowers expres- In general, all the alkoxo and phenoxo-bridged complexes
sion for an isotropically coupled pair of S = 1/2 ions, where show stronger antiferromagnetic coupling than the hy-
the symbols have their usual meaning;[21] see Equation (1). droxo-bridged ones (from a theoretical or experimental
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A. Biswas, M. G. B. Drew, J. Ribas, C. Diaz, A. Ghosh
FULL PAPER
point of view).[26] The slope for the phenoxide system is
smaller and absolute values of –J are inherently larger.[25]
The main conclusion for phenoxo systems is that strong
antiferromagnetic exchange will dominate in these com-
plexes.[25] However, recently three ferromagnetic bis-phen-
oxo-bridged copper(II) complexes have been reported and
theoretically studied.[17b,27]
Another important structural factor in pentacoordinate
CuII complexes is the Addison parameter (τ).[28] The in-
creasing of τ diminishes the antiferromagnetic coupling.[29]
Finally, the torsion of the Cu2O2 dihedral angle is impor-
tant: when this torsion angle is not zero the ferromagnetic
term increases.[30]
Complexes 1 and 2, have different structural parameters
(see Table 4). This feature explains their different J values
(–185.2 and –500.9 cm3 mol–1 for 1 and 2, respectively). The
parameter τ for 2 is very low, 0.03 (average), whereas is
intermediate, 0.55, for 1, indicating that for 2 the magnetic
orbital is almost exclusively dx2–y2, perfectly directed to the
Cu–O–Cu bonds, whereas for complex 1 the magnetic or-
bital is a mixture (almost 50%) of dx2–y2 and dz2, being this
mixture not so well directed to the Cu–O–Cu bonds. The
AF character is, thus, enhanced for 2. Furthermore, the
high value of the Cu–O–Cu angle of 101.74° (average) for
2 and 100.43° for 1 also favours the more AF character of
2 (see above). The torsion angle, which is equal to 0° for
complex 1 and 12.88° (average) for complex 2, does not
change this tendency.
Experimental Section
Materials: The reagents and solvents used were of commercially
available reagent quality.
Physical Measurements: Elemental analyses (C, H and N) were per-
formed using a Perkin–Elmer 240C elemental analyzer. IR spectra
in KBr pellets (4500–500 cm–1) were recorded using a Perkin–Elmer
RXI FT-IR spectrophotometer. Electronic spectra in acetonitrile
(1200–350 nm) were recorded with a Hitachi U-3501 spectropho-
tometer. The magnetic measurements were carried out in the “Un-
itat de mesures magnètiques dels SCT (Universitat de Barcelona)”
on polycrystalline samples (20 mg) with a Quantum Design
SQUID MPMSXL magnetometer in an applied field of 10000 and
500 G in the temperature ranges of 2–300 and 2–30 K, respectively.
The diamagnetic corrections were evaluated from Pascal’s con-
stants.
Synthesis of the Reduced Schiff-Base Ligand (HL) 2-[(2-Dimeth-
ylamino-ethylamino)methyl]phenol: The Schiff-base ligand was syn-
thesized by refluxing a solution of salicylaldehyde (0.52 mL,
5 mmol) and N,N-dimethylethylenediamine (0.54 mL, 5 mmol) in
methanol (30 mL) for one hour.[32] The solution was cooled to 0 °C
and solid sodium borohydride (210 mg, 6 mmol) was added slowly
to this methanolic solution with stirring. After completion of the
addition, the resulting solution was acidified with concentrated
aqueous HCl (5 mL) and then evaporated to dryness.[32,33] The re-
duced Schiff-base ligand HL was extracted from the solid mass
with methanol and this methanol solution (ca. 20 mL) was used
for preparation of complexes.
[Cu2L2(NCNCN)2] (1): An extracted methanol solution of HL as
prepared above was added to a solution of Cu(ClO4)2·6H2O
(1.850 g, 5 mmol) in methanol (20 mL) and an aqueous solution
(1 mL) of sodium dicyanamide (0.450 g, 5.00 mmol) was added to
this mixture with stirring. The mixture was stirred for 1 h and fil-
tered. The filtrate was kept undisturbed at room temperature.
Green crystals of 1 suitable for X-ray diffraction were obtained
after 2 d on slow evaporation of the solvent.
Conclusions
The tridentate reduced Schiff-base ligand HL {2-[(2-di-
methylamino-ethylamino)methyl]phenol} with CuII and di-
cyanamide anions afforded a phenoxo-bridged dinuclear
CuII complex and a novel molecular rectangle which is Complex 1: Yield 1.275 g (79%). C26H34Cu2N10O2 (645.71): calcd.
C 48.36, H 5.31, N 21.69; found C 48.31, H 5.37, N 21.62. IR
formed through the joining of the phenoxo-bridged dinu-
clear Cu2O2 cores of 1 via the μ1,5-bridging mode of dicyan-
amide. The formation of this dicyanamide-bridged molecu-
lar rectangle is unprecedented. Although a μ1,5-dicyan-
amide-bridged tetranuclear CuII complex is reported[31] but
in that compound the axial-equatorially bridged dicyan-
amide is severely bent and the tetranuclear structure is far
from a rectangular shape. In compound 2 the dicyanamide
acts as a linear linker through coordination to the axial po-
sitions of CuII and to facilitate such coordination the geom-
etry around CuII in the Cu2O2 core changes significantly
from distorted trigonal bipyramid in 1 to nearly square
pyramid in 2. The structural changes of the Cu2O2 core
have pronounced effect on the magnetic coupling that can
be explained by the well-established magneto-structural
correlations of such compounds considering the bridging
angles, Cu–O distances and Addison parameters. Thus we
have shown here that dicyanamide can acts as a linear linker
to produce molecular rectangle having Cu2O2 core and
structures of the two compounds show that although the
tridentate ligand is identical in both, the geometry around
CuII is adjusted as per requirement of the molecular struc-
ture.
(KBr): ν = 3184 (N–H), 1594 cm–1 [ν(C–N)]. UV (acetonitrile):
˜
λmax (εmax) = 645 (300), 420 nm (1970).
[Cu4L4{μ1,5-(NCNCN)2}]·(ClO4)2(H2O)2 (2): Another extracted
methanol solution of HL (20 mL) prepared using the same quan-
tity of reactants as stated above, was added to a solution of Cu-
(ClO4)2·6H2O (1.850 g, 5 mmol) in methanol (20 mL) and an aque-
ous solution (0.5 mL) of sodium dicyanamide (0.225 g, 2.5 mmol)
was added to this mixture with stirring. The mixture was stirred
for 2 h and filtered. The filtrate was kept undisturbed at room tem-
perature. Brown crystals of 2 suitable for X-ray diffraction were
obtained after 3 d on slow evaporation of the solvent.
Complex 2: Yield 1.290 g (74%). C48H72Cl2Cu4N14O14 (1394.27):
calcd. C 41.35, H 5.21, N 14.06; found C 41.28, H 5.28, N 14.01.
IR (KBr): ν = 3238 (N–H), [ν(C–N)], 1597 cm–1. UV (acetonitrile):
˜
λmax (εmax) = 640 (823), 455 nm (3858).
Crystal Data Collection and Refinement: Crystal data for the two
crystals are given in Table 5. 3971, 8382 data for 1, and 2, respec-
tively were collected with Mo-Kα radiation at 150 K using the Ox-
ford Diffraction X-Calibur CCD System. The crystals were posi-
tioned in a distance of 50 mm from the CCD. 321 frames were
measured with a counting time of 10 s. Data analyses were carried
out with the CrysAlis[34] program. The structures were solved by
direct methods with the Shelxs97[35] program. The non-hydrogen
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Eur. J. Inorg. Chem. 2011, 2405–2412

Dinuclear CuII Complex and a Derived Molecular Rectangle Complex
bonell, B. Ferrer, F. X. Llabre’s i Xamena, H. Garica, Chem.
Eur. J. 2007, 13, 5106–5112; c) H.-B. Yang, K. Ghosh, Y. Zhao,
B. H. Northrop, M. M. Lyndon, D. C. Muddiman, H. S.
White, P. J. Stang, J. Am. Chem. Soc. 2008, 130, 839–841.
a) J. S. Seo, D. Whang, H. Lee, S. I. Jun, J. Oh, Y. Jin, K. Kim,
Nature 2000, 404, 982–986; b) R. Q. Zou, H. Sakurai, Q. Xu,
Angew. Chem. Int. Ed. 2006, 45, 2542–2546; c) F. X. Llab-
re’s i Xamena, A. Abad, A. Corma, H. Garcia, J. Catal. 2007,
250, 294–298.
a) S. Ghosh, P. S. Mukherjee, Organometallics 2008, 27, 316–
319; b) S. Ghosh, P. S. Mukherjee, Inorg. Chem. 2009, 48, 549–
556; c) A. K. Bar, R. Chakrabarty, G. Mostafa, P. S. Mukh-
erjee, Angew. Chem. Int. Ed. 2008, 47, 8455–8459; d) B. P.
Dash, R. Satapathy, J. A. Maguire, N. S. Hosmane, Org. Lett.
2008, 10, 2247–2250.
a) T. Kusukawa, M. Fujita, J. Am. Chem. Soc. 1999, 121, 1397–
1398; b) F. Ibukuro, T. Kusukawa, M. Fujita, J. Am. Chem.
Soc. 1998, 120, 8561–8562.
a) S. J. Lee, W. Lin, J. Am. Chem. Soc. 2002, 124, 4554–4555;
b) X. Liu, C. L. Stern, C. A. Mirkin, Organometallics 2002, 21,
1017–1019; c) F. Karadas, E. J. Schelter, M. Shatruk, A. V.
Prosvirin, J. Bacsa, D. Smirnov, A. Ozarowski, J. Krzystek, J.
Telser, K. R. Dunbar, Inorg. Chem. 2008, 47, 2074–2082 and
references cited therein d) L. M. Toma, R. Lescouëzec, D. Can-
gussu, R. Llusar, J. Mata, S. Spey, J. A. Thomas, F. Lloret, M.
Julve, Inorg. Chem. Commun. 2005, 8, 382–385; e) D. Li, S.
Parkin, G. Wang, G. T. Yee, S. M. Holmes, Inorg. Chem. 2006,
45, 2773–2775.
a) Y. K. Kryschenko, S. R. Seidel, A. M. Arif, P. J. Stang, J.
Am. Chem. Soc. 2003, 125, 5193–5198; b) M. Schweiger, S. R.
Seidel, A. M. Arif, P. T. Stang, Inorg. Chem. 2002, 41, 2556–
2559; c) P. Mukherjee, M. G. B. Drew, M. Estrader, A. Ghosh,
Inorg. Chem. 2008, 47, 7784–7791.
atoms were refined with anisotropic thermal parameters. The hy-
drogen atoms bonded to carbon and nitrogen were included in geo-
metric positions and given thermal parameters equivalent to 1.2
times those of the atom to which they were attached. The hydrogen
atoms of the solvent water molecules in 2 were located in a differ-
ence Fourier maps and refined with distance constraints. Absorp-
tion corrections were carried out using the ABSPACK program.[36]
The structures were refined on F2 with Shelxl97[35] to R1 = 0.0565,
0.0462, wR2 = 0.1217, 0.1058 for 2242, 4759 reflections for 1, 2,
respectively, with IϾ2σ(I).
[5]
[6]
Table 5. Crystal data and structure refinement of complexes 1 and
2.
1
2
[7]
[8]
Formula
M
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C26H34Cu2N10O2
645.72
C48H72Cl2Cu4N14O14
1394.26
triclinic
triclinic
¯
¯
P1
P1
8.1856(11)
8.8309(10)
10.3860(14)
79.795(10)
73.285(12)
84.600(10)
706.93(16)
1
10.8446(5)
10.9487(5)
12.6664(6)
92.702(4)
92.016(4)
90.656(4)
1501.08(12)
1
α [°]
β [°]
γ [°]
V [Å3]
Z
Dc [g cm–3]
μ [mm–1]
F(000)
1.517
1.548
334
1.542
1.559
720
[9]
R(int)
0.048
5048
3971
2242
0.0565, 0.1217
150
0.031
10622
8382
4759
0.0462, 0.1048
150
Total reflections
Unique reflections
IϾ2σ(I)
R1, wR2
Temperature [K]
[10]
[11]
H. Abourahma, B. Moulton, V. Kravtsov, M. J. Zaworotko, J.
Am. Chem. Soc. 2002, 124, 9990–9991.
a) B. Olenyuk, M. D. Levin, J. A. Whiteford, J. E. Shield, P. J.
Stang, J. Am. Chem. Soc. 1999, 121, 10434–10435; b) M. D.
Levin, P. J. Stang, J. Am. Chem. Soc. 2000, 122, 7428–7429.
CCDC-801230 (for 1), -801231 (for 2) contain the supplementary [12]
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
C. J. Kuehl, Y. K. Kryschenko, U. Radhakrishnan, S. R. Seidel,
S. D. Huang, P. J. Stang, Proc. Natl. Acad. Sci. USA 2002, 99,
4932–4936.
a) C. J. Kuehl, S. D. Huang, P. J. Stang, J. Am. Chem. Soc.
2001, 123, 9634–9641; b) D. J. Holliday, C. A. Mirkin, Angew.
Chem. Int. Ed. 2001, 40, 2022–2043; c) D. Kim, J. H. Paek, M.-
J. Jun, J. Y. Lee, S. O. Kang, J. Ko, Inorg. Chem. 2005, 44, 7886–
7894.
[13]
via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments
[14]
a) Y. Cui, H. L. Ngo, W. Lin, Inorg. Chem. 2002, 41, 1033–
1035; b) R. Schneider, M. W. Hosseini, J.-M. Planeix, A.
De Cian, J. Fischer, Chem. Commun. 1998, 1625–1626; c) C. M.
Hartshorn, P. J. Steel, Inorg. Chem. 1996, 35, 6902–6903.
a) P. Thanasekaran, R.-T. Liao, Y.-H. Liu, T. Rajendran, S.
Rajagopal, K.-L. Lu, Coord. Chem. Rev. 2005, 249, 1085–1110;
b) Y.-F. Han, W.-G. Jia, W.-B. Yu, G.-X. Jin, Chem. Soc. Rev.
2009, 38, 3419–3434.
We thank the Government of India, Council of Scientific and In-
dustrial Research (CSIR) for a Senior Research Fellowship to
A. B., Sanction No. 09/028 (0717)/2008-EMR-I. We also thank the
British Engineering and Physical Sciences Research Council
(EPSRC) and the University of Reading for funds for the X-Cali-
[15]
bur system and the Spanish Government (grant CTQ2009-07264)
for financial support.
[16]
a) J. Costamagna, J. Vargas, R. Latorre, A. Alvarado, G. Mena,
Coord. Chem. Rev. 1992, 119, 67–88; b) S. Chattopadhyay, G.
Bocelli, A. Musatti, A. Ghosh, Inorg. Chem. Commun. 2006, 9,
1053–1057; c) P. Mukherjee, M. G. B. Drew, C. J. Gómez-
García, A. Ghosh, Inorg. Chem. 2009, 48, 4817–4827; d) S.
Naiya, M. G. B. Drew, C. Estarellas, A. Frontera, A. Ghosh,
Inorg. Chim. Acta 2010, 363, 3904–3913; e) S. Naiya, C. Biswas,
M. G. B. Drew, C. J. Gómez-García, J. M. Clemente-Juan, A.
Ghosh, Inorg. Chem. 2010, 49, 6616–6627.
[1] a) Y. Yamauchi, M. Yoshizawa, M. Fujita, J. Am. Chem. Soc.
2008, 130, 5832–5833; b) S. Takamizawa, E. Nakata, T. Akat-
suka, Angew. Chem. Int. Ed. 2006, 45, 2216–2221.
[2] a) J. L. C. Rowsell, E. C. Spencer, J. Eckert, J. A. K. Howard,
O. M. Yaghi, Science 2005, 309, 1350–1354; b) M. Eddaoudi,
J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O’Keeffe, O. M.
Yaghi, Science 2002, 295, 469–472.
[3] a) M.-L. Lehaire, R. Scopelliti, H. Piotrowski, K. Severin, An-
[17]
a) M. Stylianou, C. Drouza, Z. Viskadourakis, J. Giapintzakis,
A. D. Keramidas, Dalton Trans. 2008, 6188–6204; b) D.
Venegas-Yazigia, D. Aravena, E. Spodine, E. Ruiz, S. Alvarez,
Coord. Chem. Rev. 2010, 254, 2086–2095.
S. R. Batten, K. S. Murray, Coord. Chem. Rev. 2003, 246, 103–
130.
gew. Chem. Int. Ed. 2002, 41, 1419–1422; b) H. Piotrowski, K.
Polborn, G. Hilt, K. Severin, J. Am. Chem. Soc. 2001, 123,
2699–2700; c) Z. Grote, R. Scopelliti, K. Severin, J. Am. Chem.
Soc. 2004, 126, 16959–16972.
[18]
[4] a) G. J. Halder, C. J. Kepert, B. Moubaraki, K. S. Murray, J. D.
Cashion, Science 2002, 298, 1762–1765; b) M. Alvaro, E. Car-
Eur. J. Inorg. Chem. 2011, 2405–2412
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2411

A. Biswas, M. G. B. Drew, J. Ribas, C. Diaz, A. Ghosh
FULL PAPER
[19]
[28] A. W. Addison, T. N. Rao, J. Reedjik, J. van Rijn, C. G. Ver-
schoor, J. Chem. Soc., Dalton Trans. 1984, 1349–1356.
[29] A. Rodríguez-Fortea, P. Alemany, S. Alvarez, E. Ruiz, Inorg.
Chem. 2002, 41, 3769–3778.
a) P. Mukherjee, M. G. B. Drew, C. J. Gómez-García, A.
Ghosh, Inorg. Chem. 2009, 48, 5848–5860; b) C. Biswas,
M. G. B. Drew, E. Ruiz, M. Estrader, C. Diaz, A. Ghosh, Dal-
ton Trans. 2010, 39, 7474–7484.
[30] a) E. Ruiz, P. Alemany, S. Alvarez, J. Cano, J. Am. Chem. Soc.
1997, 119, 1297–1303; b) E. Ruiz, P. Alemany, S. Alvarez, J.
Cano, Inorg. Chem. 1997, 36, 3683–3688; c) E. Ruiz, S. Alvarez,
P. Alemany, Chem. Commun. 1998, 2767–2768.
[31] M. S. E. Fallah, F. Badyine, R. Vicente, A. Escuer, X. Solans,
M. Font-Bardia, Dalton Trans. 2006, 2934–292.
[32] A. Biswas, M. G. B. Drew, C. J. Gómez-García, A. Ghosh, In-
org. Chem. 2010, 49, 8155–8163.
[33] A. Biswas, M. G. B. Drew, A. Ghosh, Polyhedron 2010, 29,
1029–1034.
[34] CrysAlis; Oxford Diffraction Ltd., Abingdon, UK, 2006.
[35] G. M. Sheldrick, Shelxs97 and Shelxl97, Programs for Crystal-
lographic solution and refinement, Acta Crystallogr., Sect. A
2008, 64, 112–122.
[20]
[21]
[22]
S. Sen, S. Mitra, D. L. Hughes, G. Rosair, C. Desplanches, In-
org. Chim. Acta 2007, 360, 4085–4092.
B. Bleaney, K. D. Bowers, Proc. R. Soc. London, Ser. A 1952,
214, 451–465.
a) V. H. Crawford, H. W. Richardson, J. R. Wason, D. J. Hodg-
son, W. E. Hatfield, Inorg. Chem. 1976, 15, 2107–2110; b) D. J.
Hodgson, Prog. Inorg. Chem. 1975, 19, 173–241.
[23] L. Merz, W. J. Haase, J. Chem. Soc., Dalton Trans. 1980, 875–
879.
[24] M. Handa, N. Koga, S. Kida, Bull. Chem. Soc. Jpn. 1988, 61,
3853–3857.
[25] L. K. Thompson, S. K. Mandal, S. S. Tandon, J. N. Bridson,
M. K. Park, Inorg. Chem. 1996, 35, 3117–3125.
[26] H. Astheimer, W. Haase, J. Chem. Phys. 1986, 85, 1427–1432.
[27] a) P. Chaudhuri, R. Wagner, T. Weihermuller, Inorg. Chem.
2007, 46, 5134–5136; b) T. Kruse, T. Weihermüller, K. Wiegh-
ardt, Inorg. Chim. Acta 2002, 331, 81–89.
[36] ABSPACK program for absorption corrections, Oxford Diffrac-
tion, 2007, Abingdon, UK.
Received: January 20, 2011
Published Online: April 5, 2011
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Eur. J. Inorg. Chem. 2011, 2405–2412