Mono-and Di-chloro-bridged discrete dimers and trimers and mono-chloro-bridged 1d-coordination polymer of copper(II). Magneto-structural studies

Article abstract of DOI:10.1002/zaac.201400005

The synthesis, structural characterization, and magnetic properties of three copper(II) complexes, a mono-chloro-bridged [Cu₂ ^II(L⁶)₂(μ-Cl)(Cl)(Cu^IICl ₄)] (1) and a dichloro-bridged [Cu^II₂(L ⁷)₂(μ-Cl)₂][ClO₄]₂ (3) discrete trimers and dimers, and a mono-chloro-bridged 1D-coordination polymer [Cu^II(L⁶)(μ-Cl)][ClO₄]·CH ₃CN (2), are reported. Molecular structures were authenticated by X-ray crystallography. Temperature-dependent magnetic measurements carried out on powdered samples of 1-3 indicated a very weak antiferromagnetic exchange-coupling within the {Cu^II(μ-Cl)Cu^II(μ-Cl) Cu^IICl₃}⁺ units in 1 [Curie-Weiss plot: θ =-0.19(1) K and g = 2.07(1)], a ferromagnetic behavior within {Cu ^II(μ-Cl)₂Cu^II}²⁺ units in 3 [H =-JS₁·S₂: J = +6.0(1) cm^-1, D (zero-field splitting parameter) = 4.5(2) cm^-1, and g = 2.11], and a weak intrachain antiferromagnetic behavior due to {Cu^II(μ-Cl) Cu^II}³⁺ units in 2 [single-chain polymer: J =-0.20(1) cm^-1 and g = 2.11]. The square-pyramidal stereochemistry of the central copper(II) atoms in 1-3 was identified by their absorption spectral properties in acetontrile. An attempt was made to rationalize the observed magneto-structural behavior. Copyright

Full text of DOI:10.1002/zaac.201400005

ARTICLE
DOI: 10.1002/zaac.201400005
Mono- and Di-chloro-bridged Discrete Dimers and Trimers and Mono-
Chloro-Bridged 1D-Coordination Polymer of Copper(II). Magneto-structural
Studies
Ravindra Singh,[a] Francesc Lloret,[b] and Rabindranath Mukherjee*[a,c]
Dedicated to Professor C. N. R. Rao on the Occasion of His 80th Birthday
Keywords: Mono-chloro-bridges; Copper(II) complexes; Discrete trimer and 1D polymeric chain; Cu2Cl2 dimer; Crystal
structures; Magnetic properties
Abstract. The synthesis, structural characterization, and magnetic 1 [Curie-Weiss plot: θ = –0.19(1) K and g = 2.07(1)], a ferromagnetic
properties of three copper(II) complexes, a mono-chloro-bridged behavior within {CuII(μ-Cl)2CuII}2+ units in 3 [H = –JS1·S2: J =
ˆ
[Cu2II(L6)2(μ-Cl)(Cl)(CuIICl4)] (1) and a dichloro-bridged [CuII2(L7)2- +6.0(1) cm–1, D (zero-field splitting parameter) = 4.5(2) cm–1, and g
(μ-Cl)2][ClO4]2 (3) discrete trimers and dimers, and a mono-chloro- = 2.11], and a weak intrachain antiferromagnetic behavior due to
bridged 1D-coordination polymer [CuII(L6)(μ-Cl)][ClO4]·CH3CN (2),
are reported. Molecular structures were authenticated by X-ray crystal-
lography. Temperature-dependent magnetic measurements carried out
{CuII(μ-Cl)CuII}3+ units in 2 [single-chain polymer: J = –0.20(1) cm–1
and g = 2.11]. The square-pyramidal stereochemistry of the central
copper(II) atoms in 1–3 was identified by their absorption spectral
on powdered samples of 1–3 indicated a very weak antiferromagnetic properties in acetontrile. An attempt was made to rationalize the ob-
exchange-coupling within the {CuII(μ-Cl)CuII(μ-Cl)CuIICl3}+ units in served magneto-structural behavior.
magnetic properties, expressed as exchange coupling constant
J (ferromagnetic coupling: J Ͼ 0; antiferromagnetic coupling:
J Ͻ 0). The study of magnetic interaction between the central
metal atoms in dinuclear ligand-bridged copper(II) complexes
Introduction
The magnetic properties of transition metal complexes are
of great importance both from the point of view of basic re-
search and also because of their potential applications.[1–3]
remains the center of magneto-structural investigations.
From this perspective the magnetic studies of dinuclear dis-
This report is concerned with both discrete and coordination
crete complexes containing paramagnetic centers connected
polymeric mono-[18] and discrete di-chloro-bridged[14,16,18i,19]
through various types of bridges (e.g. oxo, hydroxo, alkoxo,
copper(II) complexes. The magnitude of the coupling between
phenoxo, acetato, azido, chloro, pyrazolato etc.)[4–20] continue
magnetic orbitals of two central copper(II) atoms in singly
to attract widespread attention. Investigation and understand-
chloro-bridged systems is mainly related to the Cu–Cl–Cu
ing of the nature and extent of magnetic-exchange coupling
bridge angle, Cu–Cl distance, and nature of the terminal li-
between the paramagnetic centers from the standpoint of mag-
gand.[18] For doubly chloro-bridged square-pyramidal dimeric
neto-structural aspects are very important for designing new
copper(II) complexes, Hatfield[16] provided a correlation be-
molecular magnetic materials.[21] Emphasis is always directed
tween the J (singlet-triplet energy gap) and the structural pa-
to look for meaningful correlations between the structural and
rameter φ/R in deg·Å–1, where φ is the bridging Cu–Cl–Cu
angle and R is the long Cu–Cl bond length. Antiferromagnetic
coupling is observed for values of φ/R below 32.6 or above
34.8, while ferromagnetic exchange is found for the values of
* Prof. Dr. R. Mukherjee
Fax: +91 512 2597437
E-Mail: rnm@iitk.ac.in
[a] Department of Chemistry
φ/R between these limits.
Indian Institute of Technology Kanpur
Kanpur 208 016, India
Using two tridentate N-donor ligands L1 and L2 we
reported[22a] structural properties of two discrete dimeric
CuII(μ-Cl)2CuII complexes [{(L1)CuII(μ-Cl)(OClO3)}2] and
[{(L2)CuII(μ-Cl)(OClO3)}2]. Using a m-xylyl-based dinucleat-
ing ligand L3 we reported[22b] a complex of composition
“CuII(L3)Cl2”; magneto-structural studies revealed it to be a
3D-coordination polymer with {CuII(μ-Cl)2CuII}2+ repeating
units and the central copper(II) atoms are antiferromagnetically
coupled (J = –10 cm–1). We extended our investigation with
[b] Departament de Química
Inorgànica/Instituto de Ciencia Molecular (ICMOL)
Universitat de València, Polígono de la Coma, s/n
46980-Paterna (València), Spain
[c] Present address:
Indian Institute of Science Education and Research Kolkata
Mohanpur Campus
Mohanpur 741 252, India
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201400005 or from the au-
thor.
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© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2014, 640, (6), 1086–1094

Chloro-bridged Discrete Dimers and Trimers, and Polymer of Copper(II)
the use of two more m-xylyl-based ligands L4 and L5 and
reported[22c] magneto-structural studies of 1D-cordination
polymeric complexes [CuII2(L4)Cl2][ClO4]2·CH3CN·THF and
[CuII2(L5)Cl2][ClO4]2·CH3CN, respectively. In discrete di-
meric and 1D coordination polymeric complexes of L1/L2 and
L4/L5, respectively, each central CuII atom assumes square-
pyramidal arrangement, encompassing base-to-apex edge-shar-
Physical Measurements: Elemental analyses were obtained with a
Thermo Quest EA 1110 CHNS-O, Italy. Spectroscopic measurements
were made using the following instruments: IR (KBr, 4000–600 cm–
1), Bruker Vector 22. UV/Vis, Perkin-Elmer Lambda 2 and Agilent
1
8453 diode-array spectrophotometers. H NMR spectra were obtained
with a JEOL JNM LA (500 MHz) spectrophotometer. Chemical shifts
are reported in ppm referenced to TMS.
ing with parallel basal planes. The magnetic properties of N-{(Pyrazol-1-yl)methyl}-N-methyl-2-(pyridin-2-yl)ethanamine
(L6): N-methyl-(2-aminoethyl-2-pyridine) (1.01 g, 7.45 mmol) and
pyrazole-1-carbinol (0.730 g, 7.45 mmol) were dissolved in dry aceto-
nitrile (60 mL). The resulting solution was purged with nitrogen and
stirred for 4 d at room temperature. The reaction mixture was dried
with anhydrous Na2SO4 and after filtration the solvent was evaporated
under reduced pressure. The desired ligand was obtained as thick
brownish yellow oil. Yield: 1.4 g, 87%. C12H16N4 (Mr = 216.28 g·mol–1):
calcd. C 66.58, H 7.40, N 26.89%; found C 66.12, H 6.96, N 26.80%.
1H NMR (500 MHz, CDCl3/TMS): δ = 2.40 (s, 3 H, –NCH3), 2.91 (t,
2 H, –CH2–), 2.98 (t, 2 H, –CH2–), 4.97 (s, 2 H, –CH2– of pyrazole).
6.26 (t, 1 H, pyrazole H4Ј), 7.12 (t, 1 H, pyridine H5), 7.17 (d, 1 H,
pyridine H3),) 7.43 (d, 1 H, pyrazole H3Ј), 7.52 (d, 1 H, pyrazole H5),),
7.59 (t, 1 H, pyridine -H4), 8.51 (d, 1 H, pyridine H6) ppm.
[{(L2)CuII(μ-Cl)(OClO3)}2], [CuII2(L4)Cl2][ClO4]2·CH3CN·
THF, and [CuII2(L5)Cl2][ClO4]2·CH3CN revealed the presence
of weakly antiferromagnetic J = –3.89 cm–1 and –1.84 cm–1,
and ferromagnetic J = +6.27 cm–1, respectively.[22c] The li-
gands of pertinence of this investigation are in Figure 1.
N-{(Pyrazol-1-yl)methyl}-N-benzyl-2-(pyridin-2-yl)ethanamine
(L7): The synthetic strategy comprises the following two steps.
N-Benzyl-2-(pyridin-2-yl)ethanamine:
Benzaldehyde
(1.33 g,
12.59 mmol) was dissolved in dry ethanol (40 mL) and a solution of
2-(2-aminoethyl)pyridine (1.53 g, 12.59 mmol) in dry ethanol (10 mL)
was added dropwise. After completion of the addition, the resulting
solution was refluxed for 3 h. The solution was cooled to room tem-
perature, the solvent was removed under reduced pressure, and the
thick brown oil that obtained was dissolved in dry methanol (15 mL)
and heated on a steam bath. To it excess NaBH4 (1.9 g, 50.35 mmol)
was added in small portions. After each addition, the mixture was
thoroughly shaken. After cooling, to the resulting mixture 25 mL of a
saturated brine solution was added and the ligand was extracted with
diethyl ether (50 mL). The organic layer was collected and kept with
anhydrous K2CO3. After filtration, the solvent was evaporated under
reduced pressure. The desired amine was obtained as thick yellow oil.
Yield: 2.3 g, 90%. C14H16N2 (Mr = 212.29 g·mol–1): calcd. C 79.14,
H 7.54, N 13.19%; found C 79.10, H 7.58, N 13.31%. 1H NMR
(500 MHz, CDCl3/TMS): δ = 2.05 (s (br), 1 H, –NH–), 3.05 (m, 4
H, –CH2CH2– of pyridine), 3.84 (s, 2 H, –CH2– of benzene), 7.31–
7.10 (m, 7 H, arom. proton), 7.59 (t, 1 H, pyridine H4), 8.53 (d, 1 H,
pyridine H6) ppm.
Figure 1. Ligands of pertinence to this work.
In this work, we have considered two new tridentate N-do-
nor ligands L6 and L7 to synthesize chloro-bridged complexes
[Cu2II(L6)2(μ-Cl)(Cl)(CuIICl4)] (1) and [CuII2(L7)2(μ-Cl)2]-
[ClO4]2 (3), and 1D coordination polymer [CuII(L6)(μ-Cl)]-
[ClO4]·CH3CN (2). The structures of all the three complexes
were elucidated by single-crystal X-ray crystallography. The
magnetic properties of 1–3 were analyzed and the observed
results compared with similar kind of complexes reported in
the literature.
N-{(Pyrazol-1-yl)methyl}-N-benzyl-2-(pyridin-2-yl)ethanamine: N-
Benzyl-2-(pyridin-2-yl)ethanamine (0.44 g, 2.07 mmol) and pyrazole-
1-carbinol (0.098 g, 2.07 mmol) were dissolved in dry acetonitrile
(25 mL). The resulting solution was purged with nitrogen and stirred
for 4 d at 298 K. The solution was dried with anhydrous Na2SO4 and
after filtration the solvent was evaporated under reduced pressure. The
desired ligand was obtained as thick brownish yellow oil. Yield: 0.5 g,
82%. C18H20N4 (Mr = 292.38 g·mol–1): calcd. C 73.88, H 6.84, N
19.15%; found C 74.12, H 6.96, N 19.24%. 1H NMR (500 MHz,
CDCl3/TMS): δ = 3.02 (m, 4 H, –CH2CH2– of pyridine), 3.73 (s, 2
H, –CH2– of benzene), 4.98 (s, 2 H, –CH2– of pyrazole),. 6.26 (s, 1
H, pyrazole H4), 7.58–7.09 (m, 10 H, arom. proton), 8.50 (d, 1 H,
pyridine H6) ppm.
Experimental Section
Materials and Reagents: All reagents were obtained from commercial
sources and used without further purification, unless otherwise stated.
Pyrazole-1-carbinol was prepared as reported in the literature.[23] The [Cu2II(L6)2(μ-Cl)(Cl)(CuIICl4)] (1): To a solution of L6 (0.048 g,
ligands L6 and L7 were prepared by following a reported pro-
cedure.[10d]
0.22 mmol) in acetonitrile (4 mL), solid CuIICl2·2H2O (0.057 g,
0.33 mmol) was added portion-wise. The color of the solution changed
Z. Anorg. Allg. Chem. 2014, 1086–1094
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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R. Singh, F. Lloret, R. Mukherjee
ARTICLE
from light yellow to green. The solution was stirred for 2 h at 298 K.
The green solid that formed was filtered and washed with acetonitrile/
diethyl ether (1:3; v/v) mixture. The resulting green solid was recrys-
tion factor of 0.5. Selected bond lengths and angles are listed in
Table 1. Pertinent crystallographic parameters for complexes 1–3 are
summarizes in Table 2. Figure 3b was generated using the DIAMOND
tallized by diffusion of diethyl ether into a solution of the complex in package.[26]
methanol and dried in vacuo. Yield: 0.055 g, 60%. Dark green single-
Table 1. Selected bond lengths (Å) and angles (°) for [CuII2(L6)2(μ-
crystals suitable for X-ray diffraction studies were obtained by slow
diffusion of diethyl ether into a solution of the complex in methanol.
C24H32Cl6Cu3N8 (Mr: 835.9 g·mol–1): calcd. C 34.45, H 3.83, N,
13.40%; found C 34.44, H 4.16, N 13.62%. UV/Vis [λmax, nm
(ε, m–1·cm–1)] (in methanol): 690 (320), 285 (8960), 245 (16 600).
Cl)(Cl)(CuIICl4)] (1), [CuII(L6)(μ-Cl)][ClO4]·CH3CN (2) and
[CuII2(L7)2(μ-Cl)2][ClO4]2 (3).
[Cu2II(L6)2(μ-Cl)(Cl)(CuIICl4)] (1)
Cu1–N1
Cu1–N2
Cu1–N4
Cu1–Cl1
Cu1–Cl2
Cu2–N5
Cu2–N6
Cu2–N7
Cu2–Cl2
Cu2–Cl3
Cu3–Cl3
Cu3–Cl4
Cu3–Cl5
Cu3–Cl6
Cu1···Cu2
Cu2···Cu3
2.129(4)
1.987(4)
1.958(4)
2.2795(13)
2.6448(13)
2.130(4)
1.966(4)
1.959(4)
2.3348(12)
2.6482(13)
2.2957(13)
2.2512(13)
2.2134(13)
2.2603(13)
4.0169(10)
4.3394(12)
N1–Cu1–N2
N1–Cu1–N4
N2–Cu1–N4
N1–Cu1–Cl1
N1–Cu1–Cl2
N2–Cu1–Cl1
N2–Cu1–Cl2
N4–Cu1–Cl1
N4–Cu1–Cl2
Cl1–Cu1–Cl2
N5–Cu2–N6
N5–Cu2–N7
N6–Cu2–N7
N5–Cu2–Cl2
N5–Cu2–Cl3
N6–Cu2–Cl2
N6–Cu2–Cl3
N7–Cu2–Cl2
N7–Cu2–Cl3
Cl2–Cu2–Cl3
Cl3–Cu3–Cl4
Cl3–Cu3–Cl5
Cl3–Cu3–Cl6
Cl4–Cu3–Cl5
Cl4–Cu3–Cl6
Cl5–Cu3–Cl6
Cu1–Cl2–Cu2
Cu2–Cl3–Cu3
90.99(16)
81.31(17)
167.34(18)
163.40(12)
100.56(11)
92.85(12)
94.68(12)
91.84(13)
96.60(13)
95.22(5)
92.03(16)
80.81(16)
169.85(16)
166.66(12)
100.09(11)
93.87(12)
96.79(12)
91.70(12)
91.57(12)
91.09(4)
[CuII(L6)(μ-Cl)][ClO4]·CH3CN (2): To a magnetically stirred solution
of L6 (0.050 g, 0.231 mmol) in ethanol (3 mL) was added dropwise an
ethanol solution (2 mL) of CuIICl2·2H2O (0.04 g, 0.231 mmol). The
resulting blue solution was stirred for 1 h at 298 K. Afterwards, 1 mL
of
a concentrated aqueous solution of NaClO4·H2O (0.130 g,
0.924 mmol) was added to it. After 15 min of stirring, the solution was
filtered, and the filtrate was kept for slow evaporation. A blue solid
that formed was recrystallized by diffusion of diethyl ether into a solu-
tion of the complex in acetonitrile and dried in vacuo. Yield: 0.053 g,
50%. Single-crystals suitable for X-ray diffraction were obtained by
slow diffusion of diethyl ether into a solution of the complex in aceto-
nitrile. C14H19Cl2CuN5O4 (Mr = 455.78 g·mol–1): calcd. C 36.86, H
4.17, N 15.36%; found C 37.26, H 4.96, N 15.92%. Conductivity
(acetonitrile, 1 mM solution at 298 K): ΛM = 130 Ω–1 cm2 mol–1
(expected range[24] for 1:1 electrolyte: 100–160 Ω–1·cm2·mol–1). IR
–
(KBr, selected peaks): ν˜ = 1116, 628 [ClO4 ] cm–1. UV/Vis [λmax, nm
(ε, m–1·cm–1)] (in acetonitrile): 650 (130), 290 (3920), 260 (6500).
98.89(5)
101.88(5)
122.93(5)
129.27(5)
101.94(5)
104.39(5)
107.38(5)
122.58(5)
[CuII2(L7)2(μ-Cl)2][ClO4]2 (3): CuIICl2·2H2O (0.031 g, 0.184 mmol)
was added to a solution of L7 (0.054 g, 0.184 mmol) in ethanol (4 mL).
Green reaction mixture thus obtained was stirred for 1 h at 298 K.
Afterwards, 1 mL of a saturated aqueous solution of NaClO4·H2O
(0.104 g, 0.739 mmol) was added to it. The color of the solution
changed from green to blue. After 1 h of stirring, a blue compound
precipitated out. It was collected by filtration and dried in vacuo. The
product was recrystallized by diffusion of diethyl ether into a solution
of the complex in acetonitrile. Yield: 0.058 g, 64%. Single-crystals
suitable for X-ray diffraction studies were obtained by diffusion of
[CuII(L6)(μ-Cl)][ClO4]·CH3CN (2)
Cu1–N1
Cu1–N2
Cu1–N3
Cu1–Cl1Aeq
Cu1–Cl1Beq
Cu1–Cl1A#ax
Cu1–Cl1B#ax
Cu1···Cu1#
2.057(7)
2.027(5)
1.985(7)
2.255(7)
2.278(8)
2.823(14)
2.822(14)
3.984(4)
N1–Cu1–N2
N1–Cu1–N3
N2–Cu1–N3
N1–Cu1–Cl1A
N1–Cu1–Cl1B
N2–Cu1–Cl1A
N2–Cu1–Cl1B
N3–Cu1–Cl1A
N3–Cu1–Cl1B
96.2(2)
80.0(2)
176.1(3)
164.3(5)
162.2(5)
96.3(3)
95.9(3)
87.3(3)
88.1(3)
diethyl ether into
a solution of the complex in acetonitrile.
C36H40Cl4Cu2N6O8 (Mr = 981.64 g·mol–1): calcd. C 44.01, H 4.08, N
8.56%; found C 44.58, H 4.54, N 8.42%. Conductivity (acetonitrile,
1 mM solution at 298 K): ΛM = 240 Ω–1·cm2·mol–1 (expected range[24]
for 1:2 electrolyte: 220–300 Ω–1 cm2 mol–1). IR (KBr, selected peaks):
–
ν˜ = 1094, 622 [ClO4 ] cm–1. UV/Vis [λmax, nm (ε, m–1·cm–1)] (in aceto-
Cu1–Cl1A–Cu1# 102.8(3)
Cu1–Cl1B–Cu1# 102.2(4)
nitrile): 660 (280), 290 (11 700), 264 (18 300).
Caution. Perchlorate salts are potentially explosive. Caution is advised
and handling of only small quantities is recommended.
[CuII2(L7)2(μ-Cl)2][ClO4]2 (3)
Cu1–N1
Cu1–N3
Cu1–N4
Cu1–Cl1
Cu1–Cl1#
Cu1···Cu1#
1.977(4)
2.085(4)
1.993(4)
2.286(1)
2.732(1)
3.503(3)
N1–Cu1–N3
N1–Cu1–N4
N3–Cu1–N4
N1–Cu1–Cl1
N3–Cu1–Cl1
N4–Cu1–Cl1
N1–Cu1–Cl1#
N3–Cu1–Cl1#
N4–Cu1–Cl1#
Cu1–Cl1–Cu1#
79.3(2)
172.7(2)
93.4(2)
90.9(1)
162.7(1)
96.4(1)
89.3(1)
102.1(1)
91.13(1)
88.09(4)
Single Crystal Structure Analysis: Single-crystals of suitable dimen-
sions were used for data collection. Diffraction intensities were col-
lected with a Bruker SMART APEX CCD diffractometer, with graph-
ite-monochromated Mo-Kα (λ = 0.71073 Å) radiation at 100(2) K. The
data were corrected for absorption. The structures were solved by SIR-
97 expanded by Fourier-difference syntheses, and refined with the
SHELXL-97 package incorporated in WinGX 1.64 crystallographic
package.[25] The position of the hydrogen atoms were calculated by
assuming ideal geometries, but not refined. All non-hydrogen atoms
were refined with anisotropic thermal parameters by full-matrix least-
#
Symmetry transformations used to generate equivalent atoms: 2:
1.5+x, 1–y, 1–z. 3: 1 –x, –y, 2–z.
squares procedures on F2. The convergence was measured by the fac-
2
tors R1 and R2, where R1 = Σ(||Fo| – |Fc||)/Σ|Fo| and R2 = {Σ[w(Fo
–
Fc ) ]/Σ[w(Fo ) ]}1/2. For complex 2, the Cl1 atom is disordered over
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
2 2
2 2
two positions (Cl1A and Cl1B), which was refined with a site occupa-
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© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2014, 1086–1094

Chloro-bridged Discrete Dimers and Trimers, and Polymer of Copper(II)
Table 2. Data collection and structure refinement parameters for [Cu2II(L6)2(μ-Cl)(Cl)(CuIICl4)] (1), [CuII(L6)(μ-Cl)][ClO4]·CH3CN (2),
[CuII2(L7)2(μ-Cl)2][ClO4]2 (3).
1
2
3
Formula
C24H32Cl6Cu3N8
835.90
C14H19Cl2CuN5O4
455.78
C36H40Cl4Cu2N8O10
981.64
MW /g·mol–1
Crystal color, habit
T /K
green, block
100(2)
blue, block
100(2)
blue, block
100(2)
λ /Å
Crystal system
Space group
a /Å
b /Å
c /Å
α /°
β /°
Mo-Kα (0.71073)
triclinic
P1(no. 2)
Mo-Kα (0.71073)
orthorhombic
P21cn (no. 33)
6.5723(18)
11.185(3)
25.092(7)
90.0
90.0
90.0
1844.6(9)
4
1.641
Mo-Kα (0.71073)
monoclinic
P21/n (no. 14)
11.7516(16)
13.1571(18)
14.1066(19)
90.0
113.031(2)
90.0
2007.3(5)
2
¯
9.1576(14)
13.360(2)
15.001(2)
65.383(2)
78.100(2)
71.173(2)
1573.7(4)
2
γ /°
V /Å3
Z
Dcalcd. /g·cm–3
1.764
2.5490
1.624
1.388
μ /mm–1
2.504
Reflections measured
Unique reflections (Rint
8398
5709 (0.0237)
8944
3363
12831
4952
)
(0.0764)
2402
(0.0491)
3678
Reflections used
[I Ͼ 2σ(I)]
4729
R1, wR2
[I Ͼ 2σ(I)]
R1, wR2 (all data)
R1 = 0.0464
wR2 = 0.1272
R1 = 0.0592
wR2 = 0.1643
R1 = 0.0759
wR2 = 0.1999
R1 = 0.1053
wR2 = 0.2389
R1 = 0.0663
wR2 = 0.1840
R1 = 0.0999
wR2 = 0.2858
ramidal arrangement.[21] Higher energy transitions in the range
260–285 nm are due to metal-perturbed intraligand transitions.
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK.
Copies of the data can be obtained free of charge on quoting
the depository numbers CCDC-978949 for 1, CCDC-978950
for 2, and CCDC-978951 for 3 (Fax: +44-1223-336-033; E-Mail:
deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk)
Structural Analysis. Structure of [Cu2II(L6)2(μ-Cl)(Cl)
(CuIICl4)] (1)
Supporting Information (see footnote on the first page of this article):
1H NMR spectra of L6 and L7, UV/Vis spectra of 1–3.
To confirm the structure of the complexes and mode of coor-
dination of the terminal ligands L6 and L7 and the bridging
ligands, single-crystal X-ray structure determination of 1–3
was carried out. Selected bond lengths and bond angles are
listed in Table 1.
Results and Analysis
Syntheses of Ligands and Complexes
A perspective view of the crystal structure of [Cu2II(L6)2-
Two new ligands L6 and L7 were synthesized by condensa- (μ-Cl)(Cl)(CuIICl4)] is shown in Figure 2. The tridentate ligand
tion of pyrazole-1-carbinol with N-methyl-2-aminoethyl-2-pyr- L6 is coordinated to the CuII in a meridional mode. The ar-
idine and N-benzyl-2-(pyridin-2-yl)ethanamine, respectively, rangement around copper(II) is distorted square-pyramidal for
in the presence of anhydrous Na2CO3 in dry acetonitrile. Li- Cu1 and Cu2 and distorted tetrahedral for Cu3. The τ values
1
gands were characterized by their H NMR spectra, displayed are 0.06 and 0.05 for Cu1 and Cu2, respectively, indicating
in Figures S1 and S2 (Supporting Information), respectively. that the environment around these two central copper(II) atoms
The complex [CuII2(L6)2(μ-Cl)(Cl)(CuIICl4)] (1) was synthe- is nearly perfect square-pyramidal.[27] The equatorial plane
sized from the reaction between L6 and CuIICl2·2H2O (2:3 mo- around Cu1 consists of a tertiary amine nitrogen N1, a pyridyl
lar ratio) in acetonitrile. The coordination polymer [CuII(L6) nitrogen N2, pyrazole nitrogen N4, and a terminal chloride
(μ-Cl)][ClO4]·CH3CN (2) and the discrete dimer [CuII2(L7)2- Cl1. The apical site is occupied by a bridging chloride Cl2,
(μ-Cl)2][ClO4]2 (3) were prepared by the reaction of CuIICl2· which is in the equatorial plane of the neighboring Cu2 ion.
2H2O in stoichiometric ratio with L6 and L7, respectively, in Three basal sites for Cu2 are occupied by three donor atoms
the presence of excess sodium perchlorate.
N5, N6, and N7 of L6. The axial site of Cu2 is occupied by
Complexes 2 and 3 display characteristic IR spectral absorp- another bridging chloride ion, provided by a [CuIICl4]2– unit.
–
tions at ca. 1100 cm–1 and 600 cm–1, due to ν(ClO4 ) stretching It is observed that the average Cu–Clax (ax = axial) distance is
vibration. The electronic spectra of 1–3 recorded in acetonitrile larger than the Cu–Cleq (eq = equatorial) distance, which is
are displayed in Figures S3–S5 (Supporting Information), typical for copper(II) square-pyramidal complexes due to Jahn-
respectively. Crystal-field transitions for these complexes were Teller distortion of the copper(II) ion [Cu–Cl2ax 2.6448(13) Å,
observed in the range 620–700 nm, attesting their square-py- Cu–Cl1eq 2.2795(13) Å for Cu1 and Cu–Cl3ax 2.6482(13) Å,
Z. Anorg. Allg. Chem. 2014, 1086–1094
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1089

R. Singh, F. Lloret, R. Mukherjee
ARTICLE
Cu–Cl1eq 2.3348(12) Å for Cu2]. The average Cu–Npz (pz = ure 3b). The Cu1–Cl1A#ax distance is greater than Cu1–
pyrazole) distance is shorter than that of Cu–Npy (py = pyr- Cl1Aeq distance [Cu1–Cl1A#ax 2.823(14) Å, Cu1–Cl1eq
idine) [Cu–Npz 1.958(4) Å, Cu–Npy 1.987(4) Å]. The Cu–Nam 2.255(7) Å]. The Cu1–Npz distance is shorter than that of Cu1–
(am = amine) bond lengths [2.129(4) Å for Cu1 and Npy [Cu1–Npz 1.985(7), Cu1–Npy 2.027(5) Å]. The Cu–Nam
2.130(4) Å for Cu2] are appreciably longer than Cu–Npz and bond length 2.057(7) Å is appreciably longer than Cu1–Npz
Cu–Npy distances. The Cu1 and Cu2 ions are positioned out of and Cu1–Npy bond lengths. The central copper(II) atom is po-
equatorial plane towards Cl2 by 0.244 Å and Cl3 by 0.183 Å, sitioned out of the equatorial plane towards Cl1A# by 0.188 Å.
respectively. The tetrahedral site around the central Cu3 atom The separation between Cu1···Cu1# along the chain is
is occupied by three terminal chloride ions Cl4, Cl5, and Cl6 3.984(4) Å. The Cu1–Cl1A#–Cu1# bridging angle is
and a bridging chloride ion Cl3. The angles around the Cu3 102.8(3)°.
atom are varying from 98.89(5)° to 129.27(5)°. The Cu1···Cu2
and Cu2···Cu3 distances are 4.0169(10) Å and 4.3394(12) Å,
respectively. The Cu1–Cl2–Cu2 and Cu2–Cl3–Cu3 bridging
angles are 107.38(5)° and 122.58(5)°, respectively.
Figure 2. Perspective view of the cationic part of [Cu2II(L6)2(μ-Cl)(Cl)
(CuIICl4)] (1). All hydrogen atoms are omitted for clarity.
Structure of [CuII(L6)(μ-Cl)][ClO4]·CH3CN (2)
The asymmetric unit contains the mononuclear unit
“CuII(L6)(Cl)”, one perchlorate anion, and an acetonitrile mo-
lecule as solvent of crystallization. Notably, the Cl1 atom is
disordered over two positions Cl1A and Cl1B. A perspective
view of the cationic part of the crystal of [CuII(L6)(μ-Cl)]-
Figure 3. (a) Perspective view of the cationic part of [CuII(L6)-
(μ-Cl)][ClO4]·CH3CN (2). All hydrogen atoms are omitted for clarity.
(b) 1D polymeric chain of [CuII(L6)(μ-Cl)][ClO4]·CH3CN (2). All hy-
drogen atoms are omitted for clarity.
[ClO4]·CH3CN is shown in Figure 3, with the presence of only
Cl1A. In the subsequent discussion only Cl1A is considered, as
metric parameters associated with Cl1A and Cl1B are closely
similar. The tridentate ligand L6 coordinates to CuII in a merid-
Structure of [CuII2(L7)2(μ-Cl)2][ClO4]2 (3)
ional mode, as in complex 1. Axial coordination is provided
A perspective view of the cationic part of the complex is
by a chloride ion from a neighboring molecule. In the mononu- displayed in Figure 4. The complex consists of a discrete
clear unit, the coordination polyhedron around the copper(II) [CuII2(L7)2(μ-Cl)2]2+ unit. The two mononuclear units are re-
ion can be best described as distorted square-pyramidal (τ = lated by a crystallographic center of symmetry. Each CuII atom
0.17).[27] The basal plane is completed by the tertiary amine is in distorted square-pyramidal coordination environment with
nitrogen N1, pyridyl nitrogen N2, pyrazole nitrogen N3, and trigonality index parameter τ = 0.16.[27] A bridging chloride
the chloride ion Cl1A. The chloride ion Cl1A# acts as a bridge ion Cl1, pyrazole nitrogen N1, a tertiary amine N3, and pyridyl
and is occupied at the apical position of the symmetry-related nitrogen N4 comprise the basal plane. The apical site is occu-
central copper(II) atoms (Figure 3a). This coordination eventu- pied by bridging chloride Cl1#, which is in the equatorial plane
ally leads to the formation of a 1D polymeric chain (Fig- of a neighboring Cu1# atom. The ligand L7 coordinates to CuII
1090
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Chloro-bridged Discrete Dimers and Trimers, and Polymer of Copper(II)
Figure 4. Perspective view of the cationic part of [CuII2(L7)2(μ-Cl)
2][ClO4]2 (3). All hydrogen atoms are omitted for clarity.
Figure 5. Plot of χMT vs. T for a powdered sample of [Cu2II(L6)2(μ-
in the meridional mode, as that L6 in complexes 1 and 2. The
Cu1–Clax distance is appreciably longer than Cu1–Cleq dis-
tance [Cu1–Cl1#ax 2.732(1), Cu1–Cl1eq 2.286(1) Å]. The
Cu1–Npz distance is shorter than that of Cu1–Npy [Cu1–Npz
1.977(4), Cu1–Npy 1.993(4) Å]. The Cu–Nam bond length
[Cu1–Nam 2.085(4) Å] is appreciably longer than Cu1–Npz and
Cu1–Npy. The central copper(II) atom is displaced by 0.133 Å
from the least-squares plane defined by the N3Cl basal plane
towards the bridging chloride Cl1#. The Cu1–Cl1–Cu1# bridg-
ing angle is 88.09(4)o. The Cu1···Cu1# distance 3.503(3) Å.
Cl)(Cl)(CuIICl4)] (1).
Magnetic Properties of [Cu2II(L6)2(μ-Cl)(Cl)(CuIICl4)] (1),
[CuII(L6)(μ-Cl)][ClO4]·CH3CN (2), and [CuII2(L7)2(μ-Cl)2]-
[ClO4]2 (3)
Magnetic susceptibility measurements of the powdered sam-
ples of 1–3 were carried out in the temperature range 2–300 K.
For complex 1, the χMT value at 300 K is 1.30 cm3·K·mol–1
(μeff/Cu = 1.86 μB). The χMT values are almost constant over
the temperature range 50–300 K. The χMT values decrease
very slightly with decreasing temperature to reach
1.19 cm3·K·mol–1 at 2 K, indicating the presence of very weak
antiferromagnetic interaction between the CuII ions
(Figure 5). The variation of the χMT values is so small that any
model [both intramolecular (dimer or trimer) as intermo-
lecular] can reproduce the experimental data, precluding an
unambiguous knowledge of the pathway responsible of this
weak magnetic interaction. In this sense, the experimental data
were fit by using the Curie-Weiss law. The best-fit parameters
are θ = –0.19(1) K and g = 2.07(1), where θ is the parameter,
which takes into account antiferromagnetic interactions be-
tween the paramagnetic CuII ions. The small negative Weiss
constant indicates the very weak antiferromagnetic interaction
which, in principle, can be attributed to Cu(1)–Cl(2)–Cu(2)
and/or Cu(2)–Cl(3)–Cu(3) and/or intermolecular pathways (see
Figure 2).
Figure 6. Plot of χMT vs. T for a powdered sample of [CuII(L6)-
(μ-Cl)][ClO4]·CH3CN (2).
K·mol–1 at 2 K. This indicates that there exists antiferromag-
netic coupling between the CuII atoms. The experimentally ob-
served χM values were fitted using the numerical expression
[Equation (1)] for a regular antiferromagnteic single-chain
polymer.[18g,28] The best-fit parameters obtained are J =
–0.20(1) cm–1 and g = 2.11.
χM = (Nβ2g2/kT) A/B
(1)
A = 0.25 + 0.074975x + 0.075235x2
B = 1 + 0.9931x + 0.172135x2 + 0.757825x3
x = |J|/kT
The magnetic behavior of 2 is illustrated in Figure 6. The
For complex 3 the value of χMT at 300 K is 0.82 cm3·K·mol–1
value of χMT is 0.42 cm3·K·mol–1 at 300 K (μeff/Cu = 1.83 μB) (μeff/Cu = 1.81 μB) and upon cooling the value increases and
and the values are almost constant over the temperature range reaches a maximum of 0.95 cm3·K·mol–1 at T = 6 K. This be-
50–300 K. Then the values decrease rapidly to 0.36 cm3· havior is due to ferromagnetic coupling between the CuII
Z. Anorg. Allg. Chem. 2014, 1086–1094
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1091

R. Singh, F. Lloret, R. Mukherjee
ARTICLE
Figure 8. Schematic presentation of HOMO and LUMO for parallel-
planar CuII(μ-Cl)2CuII dimers.
By now the structure of a large variety of mono-chloro- and
di-chloro-bridged copper(II) complexes has been determined,
aiming at correlating their structures and magnetic properties.
Various structural parameters have been considered in the pur-
suit of identifying systematic magneto-structural variations.
For five-coordinate di-chloro-bridged copper(II) complexes
with the bridging ligands occupying apical and equatorial sites
of each CuII ion, Hatfield[16b] provided a correlation between
the J (singlet-triplet energy gap) and the structural parameter
φ/R (deg·Å–1), where φ is the Cu–Cl–Cu bridge angle and R
is the Cu–Cl long bond length. Antiferromagnetic coupling is
observed for values of φ/R below 32.6 (deg·Å–1) or above 34.8
(deg·Å–1), while ferromagnetic exchange is found for the val-
ues of φ/R falling between these limits. In [(L7)2CuII2(μ-Cl)2]-
[ClO4]2 (3) two square-pyramids (τ = 0.16) share one base-to-
apex edge with parallel basal plane and the value of φ/R is
32.2 (deg·Å–1) (Table 1), which is very close to the reported
range predicted to exhibit ferromagnetic exchange. Thus
for complex 3 the observed ferromagnetic coupling J =
+6.0(1) cm–1 is consistent with this correlation.
Figure 7. Plot of χMT vs. T for a powdered sample of [(L7)2CuII2(μ-Cl)2]-
[ClO4]2 (3).
atoms. A plot of χMT vs. T is presented in Figure 7. Below
6 K, the χMT value decreases, indicating the presence of anti-
ferromagnetic intermolecular interactions and/or zero-field
splitting. The experimental data were fitted by using the modi-
fied expression [Equation (2)] for two interacting S = 1/2 cen-
ters,[1] developed under the usual isotropic (Heisenberg) ex-
ˆ
change Hamiltonian H = –JS1.S2. The best-fitting for experi-
mental data leads to the parameters: J = +6.0(1) cm–1, D (zero-
field splitting parameter) = 4.5(2) cm–1 and g = 2.11. The solid
line in Figure 7 corresponds to the best theoretical fit.
χM = (2Nβ2g2/kT)exp(–D/3kT)[exp(–2D/3kT)
+2exp(–D/3kT)+exp(–J/kT)]–1
(2)
The positive value of J reveals a ferromagnetic interaction
between the CuII ions. The observed result is due to the bridg-
ing mode present in 3: a chloride ion that occupies a basal
coordination site in one CuII atom occupies an apical position
in the coordination sphere of the neighboring CuII atom (see
Figure 4).
Some correlations have been obtained between the magnetic
and structural parameters for mono-μ-chloro–copper
chains.[18e,18h] The magnetic and structural data are consistent
with the reduced number of exchange pathways but the authors
of these two reports caution that more data are required before
the apparent magneto-structural correlation can be established.
However, following these correlations, overall ferromagnetic
Discussion
The five-coordinate chloro-bridged dinuclear copper(II) behavior can be expected for values of the quotient φ/R lower
complexes with square-pyramids sharing a base-to-apex edge than approximately 40 and higher than 57, whereas antiferro-
with parallel basal planes usually show small ferromagnetic or magnetic character appears when this quotient φ/R is between
antiferromagnetic coupling constants J.[16,18c,18d] Theoretical these two values.[18h] Complex 2 is a mono-chloro-bridged sin-
calculations show that the dx2–y2 orbital of Cu is used for a gle-chain 1D coordination polymer, in which the bridging Cl–
σ* interaction with the pN and pCl orbitals of the basal plane ion occupies an equatorial position for one CuII atom and an
ligands.[18c,18d] The HOMO is an antisymmetric combination axial position for symmetry-generated CuII atoms. The central
of dCu–dCu orbitals, whereas the LUMO is the symmetric one copper(II) atom assumes closer to a square-pyramidal arrange-
(Figure 8). The superexchange pathway will take place mainly ment (τ = 0.16). For complex 2 the value of φ/R is 36.4 deg·Å–1
through a π* type of interaction between the Cu dx2–y2 and the and it shows antiferromagnetic coupling with J = –0.20(1) cm–1.
apical pCl orbitals. For an ideal square CuII(μ-Cl)2CuII core the According to literature prediction,[18h] complex 2 should exhi-
overlap integral for such an interaction would be zero. Hence, bit ferromagnetic interaction. However, a qualitative relation
there would be no magnetic coupling between the central cop- between the ferro- or antiferro-magnetic behavior and θ (Cl–
per(II) atoms. Deviation from orthogonality facilitates the Cu–L angle, L = ligand trans to Cl) has also been propo-
overlap of magnetic orbitals and thereby increases antiferro- sed.[18c,18d,18f,18i] It has been observed that θ angles close to
magnetic interaction.
180° favor the ferromagnetic behavior, whereas an antiferro-
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Chloro-bridged Discrete Dimers and Trimers, and Polymer of Copper(II)
[5] a) P. J. Hay, J. C. Thibeault, R. Hoffmann, J. Am. Chem. Soc.
magnetic behavior is observed for θ angles smaller than
167°.[18f] For complex 2 the θ value is 164° (Table 1). The
observed antiferromagnetic behavior is thus justified.
1975, 97, 4884–4899; b) O. Kahn, Inorg. Chim. Acta 1982, 62,
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Complex 1 is a trimer, which presents two different mono-
chloro-bridges (Cu1–Cl2–Cu2 and Cu2–Cl3–Cu3), similar to
2 and 3. In 1 the Cu1 and Cu2 atoms present a nearly perfect
square-pyramidal arrangement (τ values are 0.06 and 0.05,
respectively) and its value of φ/R is 40.5 deg·Å–1, whereas Cu3
presents a distorted tetrahedral environment and its φ/R value
is 46.3 deg Å–1. For both pathways an antiferromagnetic inter-
action is expected, although for the last one no predictions can
be made due to the tetrahedral arrangement of Cu3. So, given
the weak antiferromagnetic interaction observed for 1, we may
attribute it to the Cu1–Cl2–Cu2 pathway.
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Summary and Conclusions
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The chloro-bridged CuII complexes [Cu2II(L6)2(μ-Cl)(Cl)
(CuIICl4)] (1) [CuII(L6)(μ-Cl)][ClO4]·CH3CN (2), and
[CuII2(L7)2(μ-Cl)2][ClO4]2 (3) were synthesized by using pyr-
idine- and pyrazole-based tridentate ligands L6 and L7. Com-
plex 2 presents a chain structure via equatorial-apical chloride
bridges, whereas complex 3 is a di-chloro-bridged dinuclear
complex, where each bridging chloride simultaneously occu-
pies an in-plane coordination site on one CuII ion and an apical
site on the other CuII ion. Using a common tridentate ligand L6
but differing in the synthetic procedure afforded two copper(II)
complexes with different structure types 1 (mono-chloro-
bridged copper(II) dimer with terminally coordinationg CuI-
2–
ICl4 ion) and 2 (1D copper(II) chain). While the complexes
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1 and 2 show weak antiferromagnetic coupling, complex 3 ex-
hibits ferromagnetic coupling between the central CuII atoms.
The magnetic properties of complexes 2 and 3 are structurally
correlated with reported complexes in the literature.
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1982, 21, 2679–2684; b) W. E. Marsh, K. C. Patel, W. E. Hatfield,
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Acknowledgements
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This work is supported by the Department of Science & Technology,
Government of India. RM sincerely thanks DST for J. C. Bose fellow-
ship. RS gratefully acknowledge the award of SRF by Council of Sci-
entific & Industrial Research, Government of India.
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Received: January 3, 2014
Published Online: March 7, 2014
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