Bis-benzimidazolyl diamide copper (II) complexes: Synthesis, crystal structure and oxidation of substituted amino phenols

Article abstract of DOI:10.1016/j.inoche.2011.12.011

A new tetradentate ligand N,N′-Bis (1-butyl-benzimidazol-2-yl-methyl) -hexane-1,6-dicarboxamide (b-GBSA) has been utilized to synthesize mononuclear copper (II) complexes with inner sphere anionic ligands like NO₃ ^-, Br^- and Cl^-. Two of the complexes [Cu(L)NO₃]NO₃ (1) and [Cu(L)Br]Br (2) have been structurally characterized. The geometry of copper (II) in (1) is a distorted octahedral with NO₃^- anion acting as a bidentate ligand, while for (2) the geometry is found to be a near square pyramidal. The complexes carry out the oxidation of substituted amino phenols in the presence of molecular oxygen. The oxidation gets blocked at the dihydrophenoxazinone stage for 2-amino-5-methyl phenol, and to o-quinone for 2-amino-4-tertiary butyl phenol, quite like the enzyme phenoxazinone synthase.

Full text of DOI:10.1016/j.inoche.2011.12.011

Inorganic Chemistry Communications 17 (2012) 42–48
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Bis-benzimidazolyl diamide copper (II) complexes: Synthesis, crystal structure and
oxidation of substituted amino phenols
⁎
Gauri Ahuja, Pavan Mathur
Department of Chemistry, University of Delhi, Delhi-110007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 July 2011
Accepted 16 December 2011
Available online 24 December 2011
A new tetradentate ligand N,N′-Bis (1-butyl-benzimidazol-2-yl-methyl)-hexane-1,6-dicarboxamide (b-GBSA)
has been utilized to synthesize mononuclear copper (II) complexes with inner sphere anionic ligands like NO3−
,
Br− and Cl−. Two of the complexes [Cu(L)NO3]NO3 (1) and [Cu(L)Br]Br (2) have been structurally characterized.
The geometry of copper (II) in (1) is a distorted octahedral with NO3− anion acting as a bidentate ligand, while for
(2) the geometry is found to be a near square pyramidal. The complexes carry out the oxidation of substituted
amino phenols in the presence of molecular oxygen. The oxidation gets blocked at the dihydrophenoxazinone
stage for 2-amino-5-methyl phenol, and to o-quinone for 2-amino-4-tertiary butyl phenol, quite like the enzyme
phenoxazinone synthase.
Keywords:
Benzimidazole diamides
Copper (II) complexes
Substituted amino phenols
Phenoxazinone synthase
© 2011 Elsevier B.V. All rights reserved.
Copper metalloproteins with copper ion at the active site and
histidine as one of the ligands are involved in a number of important
biological functions, such as electron transfer, oxygen transport and
substrate oxidation [1–4]. Phenoxazinone synthase is naturally found in
the bacterium Streptomyces and catalyzes the oxidative coupling of two
molecules of aminophenol to form the phenoxazinone chromophore
[5]. The enzyme is a type II copper-containing protein and catalyzes
the oxidation of a wide variety of aminophenols to phenoxazinones
[6]. Later work has shown that the enzyme catalyzed oxidation of
substituted amino phenols blocks the formation of phenoxazinone at
various intermediate stages [7].
In the present study, a tetradentate bis-benzimidazole di amide ligand
N,N′-Bis(1-butyl-benzimidazol-2-yl-methyl)-hexane-1,6-dicarboxamide
(L = b-GBSA) (Scheme 1) has been synthesized and characterized
[8]. Copper (II) complexes with cupric salts such as Cu(NO3)2.3H2O,
CuBr2 and CuCl2.2H2O with the ligand (L) have been prepared [9].
Two of the copper complexes (1 and 2) are characterized by single-
crystal X-ray crystallographic measurement [10–13]. The complexes
carry out the oxidation of substituted amino phenols to various stages
in the presence of molecular oxygen and mimic the phenoxazinone
synthase activity.
The electronic spectra of the copper (II) complexes were recorded
in DMF solution. Two peaks in the range 273–287 nm were observed
⁎
for all the complexes which have been assigned to intra ligand π–π
transition in \C_N\C_C\ system of the benzimidazole moiety.
The bands show decreased absorption values in comparison to parent
ligand [15]. The copper (II) complexes exhibit a single symmetrical
but broad d–d band in the region 690–750 nm, characteristic of copper
(II) in a tetragonal geometry [16]. The ligand and its copper (II) com-
plexes have characteristic IR bands in the range 1618–1643 cm−1
,
1542–1560 cm−1, and 1451–1465 cm−1. These are assigned to amide
I (νC_O stretching), amide II (νC\N stretching) and benzimidazole
ring (νC_C\N_C stretching). Shifts in the amide band I, due to C_O
group and in amide II band due to C\N group, is indicative of the coor-
dination of the ligand through the carbonyl oxygen in the complexes
[17–19]. The benzene ring gives a peak in the range of 735–745 cm−1
.
Strong peaks for the nitrate ion is observed at 1384 cm−1 (vs) and
823 cm−1 (w) in the nitrate complex and are assigned to νO\N\O
symmetric and antisymmetic stretching frequency [20]. A broad band at
3431 cm−1 in the complex (3) is assigned to νO\H stretching, indicating
the presence of water of crystallization.
Cyclic voltammograms of the copper (II) complexes were obtained
in DMSO: Acetonitrile (8:2) mixed solvent system [Fig. 1.1(a)–(c)
Supplementary data] 0.1 M TBAP; Pt vs. Ag/AgNO3 reference elec-
trode. E1/2 values are in the range of −108 mV to −160 mV and are
dependent on the coordinated anion. The E1/2 follows the order of
NO3−bCl−bBr−. For the present series of copper (II) complexes, E1/2
values are not as positive as have been reported for similar benz-
imidazole diamide complexes [21]. Conductivity measurements
were carried out in methanol and molar conductance values were
Spectroscopic grade solvents were used for the spectral and elec-
trochemical studies and the rest were freshly distilled off before use.
All other chemicals were obtained from commercial sources and were
used as such. Glycine benzimidazole dihydrochloride was prepared
following the procedure reported by Cescon and Day [14].
found to be 99.6∗10−4
Ω Ω
−1 cm2 mol−1, 90.0∗10−4 −1 cm2 mol−1
⁎
Corresponding author. Tel.: +91 1127667725x1381; fax: +91 1127666605.
E-mail address: pavanmat@yahoo.co.in (P. Mathur).
and 79.2∗10−4 −1 cm2 mol−1 for complexes (1), (2) and (3)
Ω
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.12.011

G. Ahuja, P. Mathur / Inorganic Chemistry Communications 17 (2012) 42–48
43
O
C
H
N
H
C
H
H
C
H
H
N
O
C
N
N
H2
C
H2
C
H2
C
H2
C
H2
C
H2
C
N
H
N
H
H2
C
H2
C
H2
C
CH3
Br
DM F, K 2CO3
70oC, 72 hrs
e
d
H
d
H
e
H
g
g
3
N
4
O
C
H
C
H
9
a
b
c
b
a
O
C
c
H2
C
N
h
h
5
6
H2
C
H2
C
H2
C
H2
C
H2
C
C
H
N
N
2
N
N
8
i
1
7
i
CH2
CH2
CH2
CH2
CH3
j
CH2
CH2
CH3
j
k
L
k
L
Scheme 1. Synthesis of N,N'-Bis(1-butyl-benzimidazol-2-yl-methyl)-hexane-1,6-dicarboxamide (L=b-GBSA).
respectively. Data shows that they can be regarded as 1:1 electrolytes
[22]. EPR spectra of the copper (II) complexes were recorded in
The copper center in (1) has a tetragonally distorted octahedral
environment. The six coordinations comprise of two imine nitrogens
of the two benzimidazole rings, two amide carbonyl oxygen atoms
and two oxygens of one of the nitrate anions. The carbonyl oxygen
atom O2, nitrate oxygen atom O3 and the two benzimidazole nitrogen
atoms N1, N6 occupy the equatorial positions of the plane while the
axial position is occupied by another amide carbonyl oxygen atom O1
and nitrate oxygen atom O4 to generate distorted octahedral geometry.
Bond length shows that nitrate behaves as unsymmetrical bidentate
chelating ligand, with Cu1\O4 bond length of 2.375 Å being much lon-
ger than Cu1\O3 bond length of 2.140 Å. The bond angle between
O3\Cu1\O4 of 56.84°(19) is in the range for weakly coordinating
bidentate ligands [20,25] (Fig. 1).
DMF at liquid nitrogen temperature [Fig. 2.1(a)–(c) Supplementary
2 2
data]. The g >g >2.0023 values indicate a d
ground state. For
x − y
(1) g =2.33, g =2.08, A =140, g /A ∗104 =166, (2) g =2.28, g =
2.07, A =140, g /A ∗104 =162 (3) g =2.35, g =2.06, A =146, g /
A ∗104 =160. The value of hyperfine splitting constant A is low in
comparison to the normal range found for the copper (II) complexes,
implying a marked tetrahedral distortion of the equatorial plane
[23]. Further no nitrogen super hyperfine splitting could be observed
implying non planarity of the complexes .The covalency factor α2
was found to be in the range of 0.56–0.70 indicating covalent nature
of Cu\L bond [24].
The structure of the above complex is similar in some respects to
that found earlier for a copper nitrate complex of a related benzimid-
azole diamide ligand [20]. The bond distances of 1.985(5) Å Cu\N6
and 1.971(5) Å Cu\N1 are found to be typically similar with other
imidazole/benzimidazole \N-atoms reported in the equatorial plane
[26]. The bond lengths Cu1\O1 2.142(5) Å and Cu1\O2 2.056(5) Å
for the N-butylated complex are considerably longer than those reported
in the literature for amide carbonyl coordination [27]. The bond angles in
the present complexes are quite close to the values expected for an
octahedral structure except the bond angles O2\Cu1\O3
163.6(2)° and O4\Cu1\O3 56.84(19)°. The distortion may be due
to the combined results of Jahn teller effects and the fixed bite size
of the nitrate anion. The crystal structure shows intermolecular
N\H….O hydrogen bonding through amide \NH and oxygen of the
lattice nitrate (Fig. 2).
The copper center in 2 is pentacoordinate consisting of two imine
nitrogens of the two benzimidazole rings, two amide carbonyl oxygen
atoms of the ligand and a bromide ion. The structure has the appearance
of a distorted square pyramidal in which axial position is occupied
by a Br atom and equatorial positions are occupied by amide carbon-
yl oxygen atoms O1 and O1′, benzimidazole imine nitrogen atoms
N2 and N2′. Cu\N bond distances of 1.966 Å for (Cu\N2 and
Cu\N2′) and are in the range found for similar benzimidazole and
imidazole-ligated compounds [21,28,29]. Cu\O bond distances of
2.156 Å for Cu\O1 and Cu\O1′ are considerably longer than those
reported in the literature for amide carbonyl coordination [27]
(Fig. 3).
Fig. 1. Ortep diagram of 1 drawn in 30% thermal probability level; hydrogen atoms
were omitted for clarity. Selected bond lengths (Å) and bond angles (°): Cu1\O1
2.142(5), Cu1\O2 2.056(5), Cu1\O3 2.140(6), Cu1\O4 2.375(7), Cu1\N1 1.985(5),
Cu1\N6 1.971(5). N6\Cu1\N1 178.5(2), N6\Cu1\O2 85.7(2), N1\Cu1\O2
94.9(2), N6\Cu1\O1 95.2(2), N1\Cu1\O1 86.2(2), O2\Cu1\O1 92.7(3),
N6\Cu1\O3 88.4(2), N1\Cu1\O3 90.7(2), O2\Cu1\O3 163.6(2), O1\Cu1\O3
103.1(2), N6\Cu1\O4 92.9(2), N1\Cu1\O4 85.6(2), O2\Cu1\O4 108.2(2),
O1\Cu1\O4 158.1(2), O3\Cu1\O4 56.84(19).

44
G. Ahuja, P. Mathur / Inorganic Chemistry Communications 17 (2012) 42–48
Fig. 2. The intermolecular hydrogen-bonding interactions in the crystal structure of 1. Hydrogen atoms are omitted for clarity (red O; blue N; gray C; light blue Cu). The light green dotted
bond shows the intermolecular hydrogen bonding interactions between N3\H3A…O6=2.891(9)Å, N3\H3A…O8=3.065(9)Å, N4 H4A…O8=3.043(9)Å, and N4H4A…O7=2.992(8)Å.
Fig. 3. Ortep diagram of compound 2 drawn in 30% thermal probability level; hydrogen atoms were omitted for clarity. Selected bond lengths (Å) and bond angles(°) :Cu1\Br1
2.3772(19), Cu1\N2 1.966(5), Cu1\N2i 1.967(5), Cu1\O1i
1
2.156(5), Cu(1)\O(1) 2.156(5), N2\Cu1\N2i 176.3(3), N2\Cu1\O1i 93.6(2), N2i\Cu1\O1i 83.7(2),
N2\Cu1\O1 83.7(2), N2i\Cu1\O1 93.6(2), O1i\Cu1\O1 90.6(3), N2\Cu1\Br1 91.85(16), N2i\Cu1\Br1 91.85(16).
Fig. 4. The intermolecular hydrogen interactions in the crystal structure of 2. Hydrogen atoms are omitted for clarity. Red O; blue N; white C; green Br; LIGHT Blue Cu. The dotted red
line shows the intermolecular hydrogen bonding interactions between N3\H3A…Br2=3.284(6) Å.

G. Ahuja, P. Mathur / Inorganic Chemistry Communications 17 (2012) 42–48
45
The uncoordinated Br anion is hydrogen bonded to the amide of
the neighboring complex molecule as shown in (Fig. 4).
Our earlier work on structures of copper (II) compounds with bis-
benzimidazole di-amide ligands shows the formation of mononuclear
complexes when the linker spacer is four methylene carbon chain.
The coordination environment around copper (II) atom is found to
vary between a pentacoordinate [21] and hexacoordinate [20,30]
Some changes do occur when the benzimidazole \NH is replaced
by an octyl chain which results in the conformation of the chain link-
ing two benzimidazole rings as gaagagaag. It also results in the kink at
the linker spacer C3–C4–C5–C6 giving a spiral turn to the ligand
which then wraps around the metal ion in the form of half helix
[20]. Further, if the benzimidazole \NH is substituted by aromatic
linker like 2-picolyl resulting in a center of inversion in the crystal
structure and allows the ligand to extend its arm and bind with a
symmetry related copper atom, the complex forms a one dimensional
polymer of the type \Cu\L\Cu\L\. In case the chain length between
the benzimidazole amide groups is made smaller (from four methylene
groups to three methylene groups) the result of this small chain length
is lowered flexibility. This ligand then adopts an extended conformation
and a di-nuclear complex results [19]. In the present case, we have
increased the spacer between the benzimidazole amide groups to
six methylenes, thus creating greater flexibility and substituted
benzimidazole \NH with a smaller butyl chain. However, this does
not lead to any major departure in the coordination geometry which
Fig. 5 (continued).
is still found to be either pentacoordinate or hexacoordinate and
there is no resultant formation of 1D polymer or a dinuclear complex.
However, there appears to be a change in the electrode potentials of
copper (II) complexes, which in the present case with a more flexible
linker are more cathodic in comparison to mononuclear copper (II)
complexes where the linker chain is smaller (four methylene groups)
[20,21].
The oxidation of substituted amino phenols using these copper (II)
complexes was observed spectrophotometrically. A 1.0 ml (0.2 mM)
methanolic solution of copper complex was added to 2.0 ml (4 mM)
methanolic solution of substituted amino phenol and was placed in
a 1 cm path length optical cell in a spectrophotometer. Product for-
mation due to oxidation reaction was observed by the increase of
Fig. 5. (A) [Curve a] UV–visible spectra of 2-amino-4-tertiary butyl phenol (4 mM,
methanolic solution). [Curve b] New peak generated in the presence of [Cu(L)Cl2]
(0.2 mM) solution at 2 min and [Curve c] at 80 min. Inset marked as B shows a
peak at 382 nm in the region between 300 nm and 600 nm and inset marked as C
shows peaks at 750 nm and 860 nm in the region of 500 nm to 1100 nm. (B) [Curve a]
UV–visible spectra of 2-amino-4-tertiary butyl phenol (4 mM, methanolic solu-
tion). [Curve b] A new peak generated in the presence of [Cu(L)(NO3)2] (0.2 mM)
solution at 2 min and [Curve c] at 100 min. (C) A new peak generated in the pres-
ence of [Cu(L)Br2] (0.2 mM) solution with 2A4TBP [Curve a] at 2 min, [Curve b] at
58 min.

46
G. Ahuja, P. Mathur / Inorganic Chemistry Communications 17 (2012) 42–48
the formation of o-quinone of 2amino-4-tertiary butyl phenol [31],
whereas the presence of two bands found at 760 nm and 860 nm for
[Cu(L)NO3]NO3 suggests the formation of a new intermediate copper
(II) species. This is different from the original copper (II) complexes
which possess a single broad band at 760 nm. While for the [Cu(L)
NO3]NO3 complex, new bands are generated at 380 nm,760 nm and
860 nm. However in this case, as the reaction progresses, the band
at 860 nm slowly shifts to a broad feature at 900 nm, suggesting
the formation of a secondary intermediate. A similar behavior was
observed for the [Cu(L)Br]Br complex. For the complex [Cu(L)Cl]Cl,
the new bands associated with the intermediate species at 760 and
860 nm slowly increase in intensity as the reaction progresses and
remain intact, as no shift in λmax is observed for both the bands
(Fig. 5A–C).
There appears to be a correlation between the average rate of
reaction for the formation of the o-quinone species and the rate of
formation of the intermediate copper (II) species. The average rate of
reaction was obtained from the slope of the plot between concentration
of the product formed and time, which gives a near linear correlation
(Fig. 6A–B).
A plot of absorbance at 860 nm vs time (min) shows a steady rise
for the catalyst [Cu(L)Cl]Cl, while for the corresponding [Cu(L)NO3]
NO3, the rate of formation of the intermediate species is found to be
lower than for the chloride bound complex (Fig. 6C).
This change is reflected in the average rate for the formation of the
o-quinone which is found to be highest i.e. 50.0∗10−4 m ML−1 min−1
for [Cu(L)Cl]Cl complex and lower i.e.34.0∗10−4 m ML−1 min−1
for [Cu(L)NO3]NO3 complex. A similar explanation can be given for
the lower average rate of o-quinone formed for the [Cu(L)Br]Br
complex .
It has been reported earlier that enzyme catalyzed oxidation of
3,5-ditertiary butyl-2-aminophenol results in the formation of the in-
termediate o-quinoneimine, which is hydrolyzed to corresponding o-
quinone rather than phenoxazinone [7]. Similarly in our case, the ox-
idation of 2-amino-4-tertiary butyl phenol does not result in the for-
mation of p-quinoneimine [32]. This is confirmed from the λmax of the
product formed in the present case, which is found at 380 nm, rather
than 566 nm as reported for p-quinoneimine. In this case, the tertiary
butyl group at the 4th position blocks the conjugate addition of the
second molecule of 2-mino-4-tertiary butyl phenol. Thus the product
formed in the present case is o-quinone (B) generated as result of the
hydrolysis of the oxidized o-quinone imine (A) (Scheme 2).
The oxidation reaction of the 2-amino-5-methyl phenol is found
to be quite fast in comparison to 2-amino-4-tertiary butyl phenol
(Fig. 3.1(a–c) Supplementary data). Thus in this case the concentra-
tion of the catalyst had to be lowered by 5 times so that appropriate
spectral readings could be taken. Under such low concentrations,
the intermediate copper (II) species that might form is not observed.
In this case, the present series of copper (II) complexes catalyze the
oxidation of 2 amino-5-methyl phenol to the stage of dihydrophenox-
azinone (C) (Scheme 3). This is confirmed from the λmax of the optical
band generated during the oxidation cycle which in all cases is at
around 400 nm. Had the oxidation reaction proceeded beyond the
Fig. 6. Plot of concentration of product formed (∗10−4 M) vs time (min). (A) Complex
(0.2 mM): 2A4TBP (4 mM), (B) complex (0.03 mM): 2A5MP (5 mM). (C) Plot of absorbance
at 860 nm vs time (min) for all the complexes (0.2 mM) with 2A4TBP (4 mM).
stage of dihydrophenoxazinone to phenoxazinone the λ
would
max
have shifted to 435 nm [7,32]. The average rate of reactions is
23.4∗10−4 m ML−1 min−1
,
22.5∗10−4 m ML−1 min−1
and
12.4∗10−4 m ML−1 min−1 for [Cu(L)NO3]NO3 and [Cu(L)Br]Br and
relatively lower for the [Cu(L)Cl]Cl complex respectively. The order
of the average rate of reaction is different since the final product
formed in this case is also different from the reaction with 2-amino-
4-tertiary butyl phenol.
characteristic absorption band in the region of 380–400 nm. Blank
run for substituted amino phenol was also performed in the same
manner by adding 1.0 ml of oxygen saturated methanol to 2.0 ml of
amino phenol solution (4 mM) in the absence of the copper complex,
no new band is generated in the blank implying the role of copper (II)
complexes in the oxidation reaction.
When the copper (II) complex [Cu(L)Cl]Cl is mixed with 2-amino-
4-tertiary butyl phenol, new bands are generated in the region of
380 nm and 700–860 nm. The presence of a band at 380 nm suggests
In summary, we find that like the enzyme catalyzed oxidation,
present copper (II) complexes do not oxidize 2-amino-5-methyl phe-
nol beyond the dihyrophenoxazinone stage and 2-amino-4-tertiary
butyl phenol only to o-quinone stage (B). This is reminiscent of the
functioning of the phenoxazinone synthase enzyme.

G. Ahuja, P. Mathur / Inorganic Chemistry Communications 17 (2012) 42–48
47
OH
O
O
NH2
O
NH
H2O
-2e-
H3C
CH3
H3C
CH3
H3C
CH3
CH3
CH3
CH3
Scheme 2. Hydrolysis of intermediate orthoquinone-imine to form the final oxidized product 4-tert-butyl quinone.
A
B
O
NH2
OH
N
NH2
OH
NH
O
-2e-
O
O
C
Scheme 3. Condensation of intermediate othroquinone-imine with substituted aminophenol to form the dihydrophenoxazinone.
1.34–1.43 (br,4H), 1.21 (br, m, 4H), 0.92–0.96 (6H, t); 13C NMR (d6-DMSO): (C4,
C7) 118, (C8, C9) 135, (C5, C6) 122, (C2) 152, e 32, C_O 32, C 36, b 25, a 28, i 43, j
32, K 19, L 13; Anal Calcd for C32H44N6O2 C 70.5, H 8.0, N 15.4, Found: C 69.1, H
7.5, N 15.3.λmax (nm) [logε] in DMF=281[4.81], 274 [4.83].
Acknowledgment
Financial support from the University of Delhi is gratefully acknowl-
edged. The authors also thank Mr. Kuldeep Mahiya for helping in X-ray
Crystallography.
[9] Synthesis of complexes (1), (2), and (3): A solution of [Cu(NO3)2.3H2O, CuBr2 and
CuCl2.2H2O] (1 mmol) in 5 ml of methanol was added to a solution of L (1 mmol)
in 5 ml of methanol. The mixture was stirred for 3–4 h. The precipitated green
products were filtered off, washed with small amounts of acetonitrile and dried
over P2O5. Suitable single green crystals for 1 and 2 were obtained on slow evap-
oration. 1: Yield: (73%). C32H44CuN8O8 (732.29): Calcd (%). C 52.5, H 6.0, N 15.3;
Found C 51.3, H 6.8, N 14.6; IR (KBr, cm−1): 3235(νNH amide), 1617 (νC_O amide
I), 1560 (νC\N amide II); UV (DMF): λmax (nm) (log ε): 273(3.95), 281(3.90),
743(1.83). 2: Yield: (70%). C32H44Br2CuN6O2 (768.09): Calcd (%) C 47.3, H 6.0,
Appendix A. Supplementary material
CCDC numbers 829607 and 829608 contain the supplementary
crystallographic data for 1 and 2 of this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the
Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge
CB2 1EZ, UK); fax: (44) 1223-336-033; or e-mail: deposit@ccdc.com.a-
c.uk. Supplementary data associated with this article has also been
included.
N
10.3; found
C 46.5, H 5.7, N
9.6; IR (KBr, cm−1): 3280(νNH amide),
1618(νC_O amide I), 1542 (νC\N amide II); UV (DMF) λmax (nm) (log ε):
277(4.12), 287(4.05), 747(2.38). 3: Yield: (68%).
C32H44Cl2CuN6O2 (714.5):
Calcd (%) C 53.7, H 6.7, N 11.7; found C 53.3, H 7.3, N 11.6; IR (KBr, cm−1):
3231(νNH amide), 1618 (νC_O amide I),1560 (νC\N amide II); UV (DMF):
λmax (nm) (log ε): 274(4.55), 281(4.49), 750(2.20).
[10] Single crystals suitable for X-ray diffraction studies were grown by slow evapora-
tion in methanol. The intensity data were collected at 295 K on Xcalibur CCD dif-
fractometer with graphite monochromatized Mo Kα radiation. The intensity data
were corrected for Lorentz and polarization effects. No absorption correction was
applied. The structure was solved by direct methods using SIR-92 [11] and re-
fined by full-matrix least-squares refinement techniques on F2, using SHELXL-
97 [12]. All calculations were done with the help of WINGX programme [13].
The weighted R factor, wR2 and goodness of fit S are based on F2, the convention-
al R factor is based on F with F set to zero for negative F2. All non-hydrogen atoms
were refined anisotropically. Hydrogens of the water molecule were located from
the difference Fourier and were refined isotropically initially for a few cycles.
Crystal data for compound 1: C32H44CuN8O8, Mr =732.29 T=120(2) K, triclinic,
P-1, a=11.9194(17) Å, b=11.9616(17) Å, c=12.2773(11) Å, α=86.360(10)°,
β=83.617(10)°, γ=89.869(12)°, V=1736.1(4) A3, Z=2, d=1.401 mg/m3, F
(000)=770, 0.20×0.14×0.10 mm3, 2θ=26.00°, −14≤h≤14, −10≤k≤14,
References
[1] (a) Bioinorganic Catalysis, in: J. Reedijk, E. Bouwman (Eds.), Marcel Dekker, 1999;
(b) K.D. Karlin, Z. Tyeklar, Bioinorganic Chemistry of Copper, Chapman & Hall,
New York, 1993;
(c) L. Casella, Eur. J. Inorg. Chem. (2006) 3545–3546;
(d) J. Reedijk, Science 308 (2005) 1876–1877.
[2] L.M. Mirica, M. Vance, D.J. Rudd, B. Hedman, K.O. Hodgson, E.I. Solomon, T.D.P.
Stack, Science 308 (2005) 1890–1892.
[3] (a) D. Maiti, A.A. Narducci Sarjeant, K.D. Karlin, J. Am. Chem. Soc. 129 (2007)
6720–6721;
(b) H.C. Liang, M.J. Henson, L.Q. Hatcher, M.A. Vance, C.X. Zhang, D. Lahti, S.
Kaderli, R.D. Sommer, A.L. Rheingold, A.D. Zuberbuhler, E.I. Solomon, K.D.
Karlin, Inorg. Chem. 43 (2004) 4115–4117.
−15≤l≤14, 13,102 reflections were collected and 6690 are unique, Rint
=
0.0515, GOF=1.080, R1 =0.0946, WR2 =0.2593. Crystal data for compound 2: C-
32H44Br2CuN6O2, Mr =768.09, T=298(2) K, monoclinic, C2/c, a=17.881(2) Å,
b=16.5552(17) Å, c=11.8886(12)Å, α=90°, β=101.04(11)°, γ=90°, V=
3454.1(6) Å3, Z=4, d=1.477 mg/m3, F(000)=1572, 0.22×0.20×0.16 mm3,
2θ=68.00°, −21≤h≤21, −19≤k≤19, −11≤l≤14, 6492 reflections were
collected and 2989 are unique, Rint=0.0788, GOF=0.905, R1=0.0604, WR2 =
0.1040.
[4] M.J. Colaneri, J. Peisach, J. Am. Chem. Soc. 117 (1995) 6308–6315.
[5] E. Katz, H. Weissbach, J. Biol. Chem. 237 (1962) 882–886.
[6] J.A. Connor, E.M. Jones, J. Chem. Soc. Dalton Trans. (1973) 2119–2124.
[7] C.E. Barry, P.G. Nayar, T.P. Begley, J. Am. Chem. Soc. 110 (1988) 3334–3335.
[8] Preparation of N,N′-Bis(1-butyl-benzimidazol-2-yl-methyl)-hexane-1,6-
dicarboxamide (L = b-GBSA): A solution of GBSA (500 mg, 1.1567 mmol) was
suspended in 20 ml of dry DMF taken in a round bottom flask (100 ml) and stir-
red for 4–5 h with dry K2CO3 (479 mg, 3.470 mmol) on a water bath at 70–75 °C
temperature. When turbidity appeared n-butyl bromide (0.37 ml, 3.470 mmol)
was added and the solution was left for stirring for the next 72 h on a water bath
at 70–75 °C. Subsequently, the solvent was stripped off on a heating mantle and
the residue was extracted with chloroform (insoluble part was rejected). Upon
adding hexane to this filtrate, a white precipitate was deposited, which was
washed with hexane, dried and recrystallized using methanol. The product
was filtered off and dried. Yield: (300 mg) 60%. 1H NMR (400 MHz, CDCl3):
δ(ppm)=9.83–9.86 (2H, t), 7.61–7.64 (4H, m), 7.22–7.35 (4H, m), 4.64–4.65
(4H, d), 2.38–2.41 (4H, t), 1.75–1.82 (4H, m), 1.66 (br,4H, m), 4.22–4.26 (4H, t),
[11] A. Altomare, M.C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, A. Gaugliardi,
A.G.G. Moliterni, G. Polidori, R. Spagna, SIR-92, A New Programme for Solving
and Refining Structures, , 1997.
[12] G.M. Sheldrick, SHELXL-97, Programme for Crystal Structure Refinement, University
of Gottingen, Germany, 1997.
[13] L.J. Farugia, WINGX, an integrated system of Windows programs for the solution,
Refinement and Analysis of Single Crystal X-ray Diffraction Data, University of
Glasgow, Glasgow, 2006.
[14] L.A. Cescon, A.R. Day, J. Org. Chem. 27 (1962) 581–586.
[15] R. Bakshi, P. Mathur, Inorg. Chim. Acta 363 (2010) 3477–3488.
[16] F. Afreen, P. Mathur, A. Rheingold, Inorg. Chim. Acta 358 (2005) 1125–1134.

48
G. Ahuja, P. Mathur / Inorganic Chemistry Communications 17 (2012) 42–48
[17] M. Gupta, S.K. Das, P. Mathur, A.W. Cordes, Inorg. Chim. Acta 353 (2003) 197–205.
[18] S.K. Upadhyay, S. Tehlan, P. Mathur, Spectrochim. Acta, Part A 66 (2007) 347–352.
[19] S.C. Mohapatra, S. Tehlan, M.S. Hundal, P. Mathur, Inorg. Chim. Acta 361 (2008)
1897–1907.
[20] S. Menage, L. Que Jr., Inorg. Chem. 29 (1990) 4293–4297;
b) S. Tehlan, M.S. Hundal, P. Mathur, Inorg. Chem. 43 (2004) 6589–6595.
[21] M. Gupta, P. Mathur, R.J. Butcher, Inorg. Chem. 40 (2001) 878–885.
[22] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81–122.
[23] G. Batra, P. Mathur, Inorg. Chem. 31 (1992) 1575–1580.
[24] Rajesh, P. Mathur, Polyhedron 17 (1998) 2607–2615.
[25] H.M.J. Hendriks, P.J.M.W.L. Birker, J.V. Rijn, G.C. Verschoor, J. Reedijk, J. Am. Chem.
Soc. 104 (1982) 3607–3617.
[26] M. Gupta, S.K. Upadhyay, M.A. Sridhar, P. Mathur, Inorg. Chim. Acta 359 (2006)
4360–4366.
(b) V. Jeffery, V.M. Dagdigian, C.A. Reed, Inorg. Chem. 21 (1982) 1332–1342.
[28] N.R. Sangeetha, K. Baradi, R. Gupta, C.K. Pal, V. Manivannan, S. Pal, Polyhedron 18
(1999) 1425–1429.
[29] (a) S.S. Tandon, L.K. Thompson, J.N. Bridson, J.C. Dewan, Inorg. Chem. 33 (1994)
54–61;
(b) A.W. Addison, P.J. Burke, K. Henrick, T.N. Rao, E. Sinn, Inorg. Chem 22 (1983)
3645–3653;
(c) E. Monzani, L. Quinti, A. Perotti, L. Casella, M. Gulloti, L. Randaccio, S. Geremia,
G. Nardin, P. Faleschini, G. Tabbi, Inorg. Chem. 37 (1998) 553–562.
[30] R. Bakshi, M. Rossi, F. Caruso, P. Mathur, Inorg. Chim. Acta 376 (2011) 175–188.
[31] S.P. Harmalker, D.T. Sawyer, J. Org. Chem. 49 (1984) 3579–3583.
[32] M. Giurg, K. Piekielska, M.G. bala, B. Ditkowski, M. Wolanski, W.P. Czoch, J.
Mlochowski, Synth.Commun. 37 (2007) 1779–1789.
[27] (a) H.J. Prochaska, W.F. Shwindinger, M. Schwartz, M.J. Burk, E. Bernarducci, R.A.
Lalancette, J.A. Potenza, H.J. Schugar, J. Am. Chem. Soc. 103 (1981) 3446–3455;