Two isomers containing a [Cu(Me2bpzb)] unit: Molecule (0-D) and 1-D

Article abstract of DOI:10.1016/j.inoche.2010.03.039

Two isomers (molecule 1 and 1-D 2) containing [Cu(Me₂bpzb)] units have been obtained under the different reaction conditions, and their structures have been determined by X-ray crystallography. From the temperature-dependent magnetic data for 2, there was no interaction between Cu²⁺ ions through the ligand. The photoluminescence of the free H₂Me₂bpzb molecule displayed an intense emission band centered at about 482 nm, while complexes 1 and 2 exhibited no obvious emission bands.

Full text of DOI:10.1016/j.inoche.2010.03.039

Inorganic Chemistry Communications 13 (2010) 753–756
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Two isomers containing a [Cu(Me2bpzb)] unit: Molecule (0-D) and 1-D
Young Joo Song a,1, Ju Hoon Lee a,1, Hyo Geun Koo a,1, Tae Geum Lee a,1, Sung-Hyun Myoung b, Cheal Kim a,
,
⁎
c,2
Sung-Jin Kim c, , Youngmee Kim
⁎
a
Department of Fine Chemistry, Seoul National University of Technology, Seoul 139-743, Republic of Korea
Department of Life Science, Sogang University, Seoul 121-742, Republic of Korea
Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Republic of Korea
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Two isomers (molecule 1 and 1-D 2) containing [Cu(Me2bpzb)] units have been obtained under the different
reaction conditions, and their structures have been determined by X-ray crystallography. From the
temperature-dependent magnetic data for 2, there was no interaction between Cu2+ ions through the ligand.
The photoluminescence of the free H2Me2bpzb molecule displayed an intense emission band centered at
about 482 nm, while complexes 1 and 2 exhibited no obvious emission bands.
Received 12 January 2010
Accepted 23 March 2010
Available online 29 March 2010
Keywords:
© 2010 Elsevier B.V. All rights reserved.
Copper complexes
One-dimensional chain
Magnetic susceptibility
Photoluminescence
Isomers
Much attention has been paid to pyridine carboxamide ligands
containing ubiquitous carboxamide [–C(O)NH–] group in the primary
structure of proteins because they are important for construction of
metal complexes [1]. The pyridine carboxamide can be readily
obtained from the simple one-step condensation of pyridine carbox-
ylic acids and amines, and deprotonation of the carboxamide nitrogen
atom makes the ligand act as a tetradentate ligand to chelate a metal
ion. Therefore, the pyridine carboxamide ligands have been widely
used to make a variety of metal complexes. Importantly, metal
complexes containing pyridine carboxamide ligands can show
excellent characteristics in hydroxylation, epoxidation and asymmet-
ric catalysts [2], NO deliver [3], molecular receptor [4], and spin
ground state control [5] as well as magnetic interactions [6].
Vagg et al. reported the synthesis of a number of potentially
tetradentate bis-carboxamide ligands derived from picolic acid and
various diamines [7]. One such ligand, H2bpb (N,N′-bis(2′-pyridine
carboxamide)-1,2-benzene), has been shown to coordinate to
transition metal ions as a planar N4 tetradentate resulting in a
marked increase in the lability of the amide protons [2,7].
range of coordination numbers, geometries and nuclearities for
copper(II) [8].
We have also reported the structures of three Cu(II) com-
plexes with pyridine carboxamide ligands (H2Me2bpb (1,2-bis(pyri-
dine-2-carboxamido)-4,5-dimethylbenzene), H26-Me2-Mebpb (1,2-bis
(6-methylpyridine-2-carboxamido)-4-methylbenzene), and H26-Me2-
Me2bpb (1,2-bis(6-methylpyridine-2-carboxamido)-4,5-dimethylben-
zene)) [9]. 6-Methyl-substituted pyridyl bpb ligands (H26-Me2-Mebpb
and H26-Me2-Me2bpb) produced dimeric compounds with Cu(II) ions,
and weak interactions between dimers can make even polymeric
compounds, while bpb ligands without 6-methyl-substitution
(H2Me2bpb) produced monomeric Cu(II) complexes. This result
suggests that the steric effect of 6-methyl-substitution plays important
role for distortion of the structure, and 6-methyl-substitution can also
influence to make polymeric compounds with interactions between Cu
(II) ions and neighbor carbonyl oxygen atoms.
In order to produce new copper complexes having interesting
physical property and develop new catalysts, therefore, we have
reacted Cu(NO3)2 2.5H2O with a new type of carboxamide ligand 1,2-
bis(2-pyrazinecarboxamido)-4,5-dimethylbenzene (H2Me2bpzb)
(see Scheme 1). Interestingly, two kinds of complexes, a monomeric
complex (1) and a polymeric complex (2) have been obtained under
the different reaction conditions.
Copper among biologically relevant d-block metals widely inves-
tigated is a particularly fruitful element towards the behavior study of
pyridine carboxamides. Pyridine dicarboxamide ligands support a
We report here on the synthesis and characterization of two
isomers (1 and 2) containing a [Cu(Me2bpzb)] unit. Moreover,
magnetic susceptibility, thermal stability, and photoluminescence
are also discussed.
Ligand (H2Me2bpzb) was prepared in moderate yield (60%) by the
reaction between 4,5-dimethyl-1,2-phenylenediamine with 2-
⁎
Corresponding authors. C. Kim is to be contacted at Tel.: +82 2 970 6693; fax: +82
2 973 9149. S.-J. Kim, Tel.: +82 2 3277 3589; fax: +82 2 3277 2384.
E-mail addresses: chealkim@snut.ac.kr (C. Kim), sjkim@ewha.ac.kr (S.-J. Kim).
Tel.: +82 2 970 6693; fax: +82 2 973 9149.
Tel.: +82 2 3277 3589; fax: +82 2 3277 2384.
1
2
1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2010.03.039

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Y.J. Song et al. / Inorganic Chemistry Communications 13 (2010) 753–756
Scheme 1. Synthesis of two isomers 1 and 2.
pyrazinecarboxylic acid in pyridine in the presence of triphenyl
phosphite according to the literature method. The crystal structure of
H2Me2bpzb has been reported previously [10].
Me2bpzb2− ligands are coordinated to Cu(II) ions to form a
monomeric complex (1) and a polymeric compound (2) [11,12]. In
both compounds, four N atoms of the Me2bpzb2− ligand are
coordinated to the Cu(II) ion. The Cu–N(amide) distances (1.926(3)
and 1.931(3) Å for 1, and 1.914(3) and 1.930(3) Å for 2) are shorter
than the Cu–N(pyridyl) distances (2.019(3) and 2.054(3) Å for 1, and
2.019(3) and 2.039(3) Å for 2). The geometry of a Cu(II) in 1 is square
pyramid with O atom of a water molecule in the apical position
(Fig. 1A). The Cu–Owater distance is 2.313(3) Å. There are two kinds of
hydrogen bonding to form a two-dimensional polymeric compound
(Fig. 1B): (a) one between the water hydrogen atom and the carbonyl
oxygen atom of the neighboring molecule (O3–H2O···O2(1−x, −y, −z)
1.91(3) Å (165(4)°)) and (b) one between the water hydrogen atom and
the pyrazine nitrogen atom of the another neighboring molecule (O3–
H1O···N5(−x, 1−y, −z) 2.24(2) Å (146(4)°)). For 2, a pyrazine nitrogen
atom of the neighboring molecule occupies the apical position of the
square pyramid geometry to form a stair-type one-dimensional com-
pound (Fig. 2A). The Cu–Napical distance is 2.373(3) Å. There are hydrogen
H2Me2bpzb reacted with Cu(NO3)2 2.5H2O to give mononuclear and
polymeric complexes under the different reaction conditions [11]. The
1:1 reaction of Cu(NO3)2 2.5H2O with the ligand H2Me2bpzb in
methanol, in the presence of added base, gave a powdered complex
(Scheme 1), that was dissolved in pyridine and layered with ether to
produce a red crystalline solid (1). The complex 2 was obtained from the
layering method that Cu(NO3)2 2.5H2O was dissolved in DMSO and
layered with H2Me2bpzb in acetone to produce a dark-brown crystalline
solid (2). 1 and 2 are air- and moisture-stable, and soluble in DMF and
DMSO.
Two strong bands at 1618/1391 cm−1 for 1 or 1631/1387 cm−1 for
2 are assignable to the asymmetric and symmetric C O stretching
modes of the ligand, respectively. Further, the disappearance of N–H
band (3315 cm−1) of the ligand suggested the formation of these
complexes 1 and 2, which were confirmed by X-ray crystallography.
Fig. 1. (A) Crystal structure of 1. Displacement ellipsoids are shown at the 50% probability level. (B) Hydrogen bond interactions (green dotted lines) in a two-dimensional structure:
O3–H2O···O2(1−x, −y, −z) 1.91(3) Å (165(4)°) and O3–H1O···N5(−x, 1−y, −z) 2.24(2) Å (146(4)°).

Y.J. Song et al. / Inorganic Chemistry Communications 13 (2010) 753–756
755
Fig. 2. (A) One-dimensional staircase chain structure of 2. (B) Hydrogen bond interactions are shown in green dotted lines: O2S–H2A···O1 1.876(5) Å (178(5)°), O2S–H2B···O1S(x,
−1+y, −z) 1.95(2) Å (151(2)°), and C17–H17C···S1S(x, 1.5−y, −0.5+z) 2.663(2) Å (163.7(3)°).
bonding interactions between the water hydrogen atoms and the DMSO
oxygen atom and the carbonyl oxygen atom (O2S–H2A···O1 1.876(5) Å
(178(5)°) and O2S–H2B···O1S(x, −1+y, z) 1.95(2) Å (151(2)°)), and
between the methyl hydrogen atom and the DMSO sulfur atom (C17–
H17C···S1S(x, 1.5−y, −0.5+z) 2.663(2) Å (163.7(3)°)) (Fig. 2B). The
Cu···Cu distance is 4.158(2) Å.
The temperature-dependent magnetic data for 2 were examined
as shown in Fig. 3. The magnetic susceptibility data can be described
using the Curie–Weiss law, χ=χo +C/(T−θ), which has a similar
pattern to those for 1 (see Fig. S1). The effective magnetic moment at
room temperature was 1.54 μB, which was less than the spin-only
effective moment of 1.73 μB, and it can be explained by LMCT in the
amido-Cu(II) complex 2. There was no evidence of magnetic exchange
coupling between the Cu(II) units through the ligand. In addition, to
study the thermal stability of the complex 2, thermal gravimetric
analysis (TGA) of compound 2 was performed. The TGA result of 2
showed that it is stable below 370 °C, which indicates its good thermal
stability (Fig. S2).
The photoluminescence properties of free ligand H2Me2bpzb and
complexes 1 and 2 were also studied in the solid-state at room
temperature. The emission spectra of 1 and 2 and free ligand are
depicted in Fig. 4. As shown in Fig. 4, the free H2Me2bpzb molecule
displays an intense emission band centered at about 482 nm when
excited at 261 nm, while complexes 1 and 2 exhibit no obvious
emission bands (λex =261 nm). It can be presumed that the
disappearance of the emission bands for 1 and 2 is attributed to the
paramagnetic nature of Cu2+ ion and coordination of Cu2+ with the
H2Me2bpzb ligand [13].
In summary, we have shown interestingly the synthesis and
characterization of two isomers (mononuclear vs polymeric com-
plexes) containing a [Cu(Me2bpzb)] unit under the different reaction
conditions. From the temperature-dependent magnetic data for 2,
there was no interaction between Cu2+ ions through the ligand. The
photoluminescence of the free H2Me2bpzb molecule displayed an
intense emission band centered at about 482 nm, while complexes 1
and 2 exhibit no obvious emission bands, suggesting that the
paramagnetic nature of Cu2+ ion makes the emission bands for 1
Fig. 3. Magnetic susceptibility data (open circle) and reciprocal susceptibility data
(filled circle) of 2 as a function of temperature.
Fig. 4. Emission spectra of ligand, complexes 1 and 2.

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Y.J. Song et al. / Inorganic Chemistry Communications 13 (2010) 753–756
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Acknowledgments
Financial support from Korea Ministry Environment “ET-Human
resource development Project” and the Korean Science & Engineering
Foundation (R01-2008-000-20704-0 and 2009-0074066), the Converg-
ing Research Center Program through the National Research Foundation
of Korea (NRF) funded by the Ministry of Education, Science and
Technology (2009-0082832), and the SRC program of MOST/KOSEF
through the Center for Intelligent Nano-Bio Materials at Ewha Womans
University (R11-2005-008-00000-0) is gratefully acknowledged.
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Appendix A. Supplementary data
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[11] Preparation of 1: 0.16 g (0.5 mmol) of H2Me2bpzb was dissolved in 20 mL
methanol and 0.12 g (0.5 mmol) of Cu(NO3)2 2.5H2O was added while being
stirred vigorously under N2 mood. And then 140 μL (1.0 mmol) of triethylamine
was carefully dropped to the mixture and stirred for 30 min. The red solid was
precipitated and filtered and washed by 5 mL methanol three times. The red
crystal was obtained under diethyl ether/pyridine in two weeks. Yield: 0.11 g
(53%). IR(KBr): ν(cm−1)=3434(brm), 1618(s), 1578(s), 1541(w), 1485(m),
1455(w), 1391(m), 1170(m), 1045(m). 453(w), 418(w). Anal. Calc. for
CCDC 75260 and 75261 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/j.
inoche.2010.03.039.
C
18H16CuN6O3 (427.91): C, 50.52; H, 3.78; N, 19.64. Found: C, 50.43; H, 3.66; N,
19.88%. Preparation of 2: 18.6 mg (0.08 mmol) of Cu(NO3)2 2.5H2O was dissolved
in 4 mL DMSO and carefully layered by 4 mL acetone solution of H2Me2bpzb
ligand (55.7 mg, 0.16 mmol). Suitable dark brown crystals for X-ray analysis were
obtained in a week. IR(KBr): ν(cm−1)=3456(brm), 2918(w), 1631(s), 1587(s),
1483(m), 1454(w), 1415(w), 1387(m), 1277(w), 1162(m), 1013(m), 959(w),
888(w), 850(w), 774(w), 708(w), 558(w), 499(w), 454(m). Anal. Calc. for
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