Synthesis and spectral studies of copper complexes using a N-octylated bis benzimidazole diamide ligand

Article abstract of DOI:10.1016/j.saa.2010.11.033

Monomeric Cu(II) and Cu(I) complexes bound to a tetradentate bis-benzimidazole diamide ligand N,N′-bis(N-octyl benzimidazolyl-2yl) (methyl)pentane diamide (O-GBGA) have been isolated and characterized. X-Band EPR spectra of the copper(II) complexes in CH<

Full text of DOI:10.1016/j.saa.2010.11.033

Spectrochimica Acta Part A 78 (2011) 612–616
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis and spectral studies of copper complexes using a N-octylated bis
benzimidazole diamide ligand
∗
Subash Chandra Mohapatra, 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:
Monomeric Cu(II) and Cu(I) complexes bound to a tetradentate bis-benzimidazole diamide ligand
N,N -bis(N-octyl benzimidazolyl-2yl)(methyl)pentane diamide (O-GBGA) have been isolated and char-
acterized. X-Band EPR spectra of the copper(II) complexes in CH2Cl2 were recorded in a frozen solution
Received 22 January 2010
Received in revised form 19 March 2010
Accepted 29 November 2010
ꢀ
as solvent at liquid nitrogen temperature. Solution spectra typically indicate a dx
2−y2
ground state
(g|| > g⊥ > 2.0023) and show less than four nuclear hyperfine lines with broadening of g⊥ line in some
Keywords:
cases, thus indicating distorted tetragonal geometry. One of the copper(II) complexes shows a five line
Bis benzimidazole diamide
Copper(II) complexes
Fluorescence quenching
2
N-SHF structure (16 ± 1 G) implying the binding of imine nitrogen of the benzimidazole to copper ion. ˛
ranges from 0.57–0.97 indicating considerable amount of covalent character in Cu–L bond. Anodic shifts
in E1/2 values indicate the retention of anion in the coordination sphere of Cu(II), E1/2 values becoming
−
−
−
anodic in the order C6H5COO < SCN < Cl . The fluorescence quantum yield of complexes was found
to be lower than that of the ligand O-GBGA (˚ = 0.029) and the relative fluorescence data reveals that
fluorescence of such compounds could distinguish between small and large anions.
©
2010 Elsevier B.V. All rights reserved.
1
. Introduction
2. Experimental
Copper in metalloproteins acquires various coordination
2.1. Physical measurements
numbers and geometries [1,2]. Their redox properties are
greatly affected by the nature of donor atoms, geometry
and flexibility of the chelating ligands. Protein constraints
are known to confer distorted geometries upon copper(II).
Thus it is of interest to investigate model compound struc-
tures with imidazole and benzimidazole bound ligands, since
the incorporation of bulky benzimidazole moieties, apart
from mimicking the imidazole function in proteins, causes
steric crowding and induces unusual coordination geometries
Elemental analyses were obtained from USIC, Delhi University,
Delhi, INDIA.
Electronic spectra were recorded on a Shimadzu 1601 spec-
trophotometer.
IR spectra were recorded in solid state as KBr Pellets on a Perkin-
−
1
Elmer FTIR-2000 spectrometer the range of 400–4000 cm
.
Cyclic-voltametric measurements were carried out using a BAS
CV 50W electrochemical analyzing system. Cyclic-voltamograms
of all the complexes were recorded in (2:8) DMSO:Acetonitrile
solutions with 0.1 M tert-butyl ammonium perchlorate (TBAP) as
supporting electrolyte. A three-electrode configuration composed
of Pt-disk working electrode (3.1 mm2 area), a Pt-wire counter
electrode, and a Ag/AgCl reference electrode was used for the mea-
[
3].
Imidazole, pyrazole and benzimidazole amide ligands
have been reported to afford peptidic Cu(II) complexes
4–12]. The present study reports the synthesis and spec-
[
tral studies of copper(II) complexes with
N,N -bis(N-octyl benzimidazolyl-2 methyl)pentane diamide
a new ligand
ꢀ
+
surements. The reversible one-electron Fc /Fc couple in the above
(
O-GBGA).
solvent system has an E1 of 0.487 versus Ag/AgCl electrode.
/2
1
H NMR spectra were recorded on a 300 MHz BRUKER-spin
instrument, at the Department of Chemistry, University of Delhi,
India. AAS studies were carried out on Perkin-Elmer aanalyst-200
spectrophotometer at the Department of Chemistry, University of
Delhi, India. Mass spectral studies were carried out on LCT Micro
mass at the Department of Chemistry, University of Delhi, India.
X-Band EPR spectra were recorded on a BRUKER-Spectrospin with
∗ Corresponding author. Tel.: +91 1127667725 1381; fax: +91 1127666605.
E-mail addresses: subashcm@gmail.com (S.C. Mohapatra),
pavanmat@yahoo.co.in (P. Mathur).
1
386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.11.033

S.C. Mohapatra, P. Mathur / Spectrochimica Acta Part A 78 (2011) 612–616
613
H2
C
CH2
H C
2
C
O
NH
N
HN
C
O
CH2
CH2
(
CH )
2 7
(
H C)
-
2
7
N
X
N
N
Cu2+
CH3
H C
3
X-
Fig. 1. Tentative structures of the [Cu(O-GBGA)Cl2].
a variable temperature liquid Nitrogen cryostat at 120 K at IIT, Kan-
pur, India.
Fluorescence studies were carried out on FL3-11, Fluorolog-3
spectro fluorometer at IIT, New Delhi.
ing in warm methanol and allowed to cool slowly. The recrystallised
product was analyzed for the composition CuC37H54N O ·Cl .
6
2
2
Yield: (50%).
CHN analysis: found (calcd): C: 58.1 (59.1); H: 8.0 (7.2); N: 11.0
11.2); Cu: 8.12 (8.49).
(
2.2. Synthesis of ligand and complexes
UV–vis [ꢁmax (nm, log ε) in 2:8 DMSO:Acetonitrile]: 274 (4.09),
81 (4.06), 750 (2.40). E1/2 versus Ag/AgCl: +0.53 (V).
2
2
2
.2.1. Synthesis of the ligands
.2.1.1. N,N -bis(benzimidazolyl-2yl)(methyl)pentane
We have earlier reported single crystal structures for a num-
ꢀ
ber of Cu(II) complexes with similar bis-benzimidazole diamide
ligands that show clear evidence of the binding of this class of lig-
ands through the amide carbonyl rather than amide NH [11–14].
Further in the synthetic procedure no base was employed so as to
deprotonate the amide NH as has been reported for amides that
bind through amide NH rather than amide carbonyl [15]. A tenta-
tive structure of complex is given in Fig. 1. The mass spectrum is
shown in Fig. 1.1 (Supplementary data). m/z = 749.3.
diamide
(
GBGA). This ligand was synthesized using a procedure reported
1
earlier [13]. The product was characterized by H NMR spectra.
1
H NMR (ı ppm, d -DMSO): 1.84–1.80 (q, 2H), 2.25–2.20 (t, 4H),
6
4
.5 (d, 4H), 7.1–7.4 (m, 8H), 9.11 (t, 2H), 12.30 (s, 2H).
ꢀ
2.2.1.2. N,
N -bis(N-octyl
benzimidazolyl-2-yl)(methyl)pentane
diamide (O-GBGA). N-octylation of GBGA to prepare O-GBGA was
carried out as earlier [13]. GBGA (500 mg) was suspended in 20 ml
of dry DMF and was stirred with dry K CO3 (350 mg) for 4–5 h
2.2.1.4. Synthesis of the complex [Cu(O-GBGA)(CH3COO)2]. A dilute
methanolic solution of aqueous NaOH was added drop wise to a
5 ml methanolic solution of CuCl2·2H2O (0.48 mmol) till the for-
mation of a light-green precipitate was completed. This solution
was centrifuged and the filtrate was discarded. The precipitate was
washed 4 times with methanol. To this slurry, a very dilute solu-
tion of acetic acid (CH3COOH, in methanol) was added drop wise
till all precipitate dissolves. This was centrifuged and the filtrate
was added immediately to a methanolic solution of the ligand (O-
GBGA) (0.48 mmol). This solution was stirred for 2 h on a water bath
2
◦
on a water bath at a temperature of 70–75 C. Octyl bromide
0.44 ml) was added to the turbid solution and was allowed to
(
◦
stir for next 72 h on a water bath at a temperature of 70–75 C.
Subsequently the solvent was stripped off on a rotary evaporator
and the residue was extracted with chloroform. The insoluble part
was discarded. A white precipitate deposited along the sides of
the beaker on the addition of hexane to the above chloroform
filtrate. This was filtered and dried on anhydrous CaCl . This was
2
recrystalized with hot methanol and analyzed for the composition
◦
(
C37H54N O )
Yield: 250 mg, mp, 130 C.
at 40 C. Reduction in its volume by evaporation and leaving it in
6
2
◦
the freezer for 30 min resulted in a bluish-green product which was
dried in air. This product was recrystallised as before by dissolving
in minimum amount of hot methanol, and cooling. A pure dark blue
product was obtained which was air dried and analyzed for the
composition of CuC37H54N6O2·(CH3COO)2. A direct reaction with
the copper(II) acetate salt with the ligand gave an identical prod-
uct, however the yield was lower in comparison to the modified
procedure adopted in the present case.
CHN analysis: found (calcd): C: 71.5 (72.3%); H: 9.0 (8.8%); N:
3.6 (13.7%).
1
IR data (ꢀ/cm−1): 3284 (ꢀNH amide), 1642 amide I (ꢀC O), 1550
amide II (ꢀC N amide), 1473 (ꢀC
benzimidazole stretching).
N–C
C
NMR data (ı ppm) (CDCl ): 11.26 (t, 2H), 7.59–7.25 (m, 8H),
3
4
1
.78–4.76 (d, 4H), 4.12–4.10 (t, 4H), 2.43 (t, 4H), 2.08 (quin, 2H),
.80 (quin, 4H), 1.32–1.24 (s, 20H), 0.86 (t, 6H).
UV data [ꢁmax (nm), (log ε) in CH Cl ]: 284 (3.9), 276 (3.8), 252
Yield: (55%).
2
2
(
3.5).
CHN analysis: found (calcd): C: 61.6 (61.8); H: 8.3 (7.5); N: 11.0
(10.5); Cu: 8.01 (7.98).
UV data: [ꢁmax (nm, log ε) in 2:8 DMSO:Acetonitrile]: 274 (3.22),
81 (4.04), 650 (2.33).
2
.2.1.3. Synthesis of the complex [Cu(O-GBGA)Cl ]. To a methanolic
2
2
solution of CuCl ·2H O (0.48 mmol) (5 ml) was added a methanolic
2
2
solution of the ligand O-GBGA (0.48 mmol) (10 ml) The resulting
green coloured solution was stirred for 30 min, after which the
volume was reduced on a water bath. The parrot-green product
obtained was washed with small amount of methanol (4–5 ml) and
air dried. The powdered compound was recrystallised by dissolv-
2.2.1.5. Synthesis of the complex Cu[(O-GBGA)(C H5COO) ]. This
6
2
complex was synthesized by the method as described for the
acetato complex, except that in this case benzoic acid was taken
in place of acetic acid. This was done as no analogous copper(II)

6
14
S.C. Mohapatra, P. Mathur / Spectrochimica Acta Part A 78 (2011) 612–616
benzoate salt was available. The pale green product obtained was
analyzed for the composition CuC37H54N O ·(C H5COO) ·2H O.
6
2
6
2
2
Yield: (59%).
CHN analysis: found (calcd): C: 63.4 (64.0); H: 7.9 (7.1); N: 8.0
8.8); Cu: 6.26 (6.65).
(
UV data: [ꢁmax (nm, log ε) in 2:8 DMSO:Acetonitrile]: 274 (3.75),
2
82 (4.02), 755 (2.58).
E1/2 versus Ag/AgCl: +0.46 (V). m/z = 919.6.
I
2
.2.1.6. Synthesis of the complex [Cu (O-GBGA)(SCN)]. For the prepa-
ration of this complex, CuCl ·2H O was first converted to Cu(SCN) .
2
2
2
This was done since a copper(II) salt with thiocyanate was unavail-
able. A solution of KSCN in MeOH was added dropwise to the
solution of CuCl ·2H O (0.48 mmol) in 5 ml MeOH, till there was
2
2
no further precipitation. After centrifugation, the centrifugate, a
brown solution, was added immediately to the solution of ligand
O-GBGA (0.48 mmol) in 15 ml methanol. A green precipitate was
obtained after 1/2 h of slow stirring of solution-mixture in a sep-
tum sealed three neck flask. A solution of quinol (0.48 mmol) in
methanol (10 ml) was then transferred under nitrogen, via a double
end needle, to the copper(II) complex solution. Immediate colour
change from peacock green to pale yellow was observed. Stirring
for 10 min resulted in a white solid that was filtered off, washed
with methanol and air-dried. This compound was analyzed for the
composition CuC37H54N O ·SCN·2H O.
6
2
2
Yield: (46%).
CHN analysis: found (calcd): C: 58.0 (59.1); H: 8.0 (7.5); N: 12.5
12.7); S: 4.0 (4.1); Cu: 8.32 (8.23).
(
UV–vis [ꢁmax (nm, log ε) in 2:8 DMSO:Acetonitrile]: 272 (4.35),
2
82 (4.30), 293 (3.80).
E1/2 versus Ag/AgCl: +0.50 (V). The oxidation state of copper was
1
confirmed by H NMR spectra.
3
. Results and discussion
3.1. Electronic spectroscopy
Fig. 2. X-Band EPR spectra of [Cu(O-GBGA)Cl2] (1), [Cu(O-GBGA)(C6H5COO)2] (2)
and [Cu(O-GBGA)(CH3COO)2] (3) in CH2Cl2 at microwave frequency 9.448 GHz and
receiver gain 10 .
The electronic spectra of the copper(II) complexes were
3
recorded in mixed DMSO/Acetonitrile and DMF/Acetonitrile (2:8),
solvent system. Two peaks in the range 270–285 nm are observed
for all the complexes which have been assigned to intraligand ␲–␲*
transition of benzimidazole moiety in their respective ligands [16].
The bands show enhanced absorptions as indicated by their extinc-
tion coefficients. A band around 293 nm is assigned to the charge
transfer band from ligand to metal for the Cu(O-GBGA)(SCN) com-
plex.
Table 1
X-Band EPR data of copper(II) complexes of the ligand (O-GBGA), at 120 K.
˛2
(g||/A||)/10
−4
Complex
Cu(O-GBGA)(NO3)2] [13]
g||
g(
A||
[
2.31
2.30
2.29
2.42
2.10
2.10
2.05
2.13
130
143
166
181
0.62
0.59
0.57
0.90
177
160
137
133
[Cu(O-GBGA)Cl2]
[Cu(O-GBGA)(C6H5OO)2]
[
Cu(O-GBGA)(CH3COO)2]
The copper(II) complexes exhibit a broad d–d band in the
region 600–800 nm, characteristic of tetragonal geometry. This
broad band is obtained due to the overlapping transitions and
dxy → dx2−y . The difference in absorption band position is often
complexes do not lie on the Peisach Blumberg Plots of A|| versus g||
for two nitrogen and two oxygen in structural plane and suggests a
distortion of the equatorial plane. The values of hyperfine coupling
constant A|| are quite low in comparison to the normal range found
for other copper(II) complexes, implying a marked tetrahedral dis-
tortion of the tetragonal site [17]. The factor g||/A|| also reflects the
distortion of coordination geometry. Higher the value of this fac-
tor, greater is the distortion. This is because when the geometry is
no longer planar, repulsion between the unpaired electron in the
2
attributed to the ligand field splitting of the coordinated lig-
and. The decrease in energy of the absorption maxima on going
−
−
−
from CH COO > Cl ∼ C H5COO in O-GBGA complexes can be
3
6
attributed to a decrease of the in-plane LFS, which reflects different
degrees of distortions of copper(II) ion bound to the ligand.
3.2. EPR spectra
X-Band EPR spectra of the copper(II) complexes were recorded
dx
2
2
orbital and ligand electron pair decreases. As a result, this
−y
in a frozen solution in CH Cl2 as solvent at liquid nitrogen tem-
unpaired electron can now be delocalized on the ligand framework
to a greater extent thus reducing coupling with the copper nucleus
and lowering the A|| value.
Further no nitrogen super hyperfine splitting could be observed,
implying non-planarity of the complexes, except in case of [Cu(O-
GBGA)(C H5OO) ] complex, where blow up of g⊥ peak shows very
weak, five line structure of 16 ± 1 G (Fig. 2), indicating the N-
2
perature (Fig. 2 and Table 1). Solution spectra typically indicate a
dx
2
2
ground state (g|| > g⊥ > 2.0023). Solution state spectra in the
−y
complexes show less than four lines and a broadening of g⊥ line in
some cases, thus indicating severely distorted tetragonal geometry.
Broadening of g⊥ indicates lowering in symmetry that manifest
itself through rhombic splitting [11,12]. The A|| and g|| values for the
6
2

S.C. Mohapatra, P. Mathur / Spectrochimica Acta Part A 78 (2011) 612–616
615
Table 2
ꢀ
IR spectral studies of the Cu(II) and Cu(I) complexes with ligand N,N -bis(2-benzimidazolylethyl)hexanediamide (O-GBGA).
Assignments (KBr Pellets)
NH amide
[Cu(O-GBGA)Cl2]
[Cu(O-GBGA)(SCN)]
[Cu(O-GBGA)(C6H5OO)2]
[Cu(O-GBGA)(CH3COO)2]
ꢀ
3171
1623
1550
1455
3205
1656
1541
1445
2077
3265
1631
1550
1455
1600
3183
1640
1545
1450
1330
gꢀC O amide I
ꢀ
ꢀ
ꢀ
C–N amide II
C–N C– gp.
special for anions
C
KBr Pellets (cm 1).
−
super hyperfine structure, due to two equivalent benzimidazole
N-atoms coordinated to the copper(II) nucleus, such N-super hyper
line structure has been reported by us for copper(II) complexes
with similar benzimidazole based ligands [13,17]. g||/A|| follows
nate through the amide NH. Loss of splitting, downfield shifting and
slight broadening confirms that copper in this complex exists in the
+1 oxidation state.
−
−
−
the order CH COO ∼ C H5COO < Cl for O-GBGA series indicat-
3
6
3.5. IR spectral studies
ing that distortion in coordination geometry is least for acetate and
greatest in the chloro complex. The covalency factor ˛2 has been
calculated (Table 1) using the relationship.
In all the complexes, IR bands due to benzimidazole NH and
amide NH are shifted considerably indicating the involvement
of these groups in hydrogen bonding either with the solvent
molecules or with the exogenous anionic ligand in the complexes
8
ꢂXY
ꢁ˛2
g|| = 2.0023 −
[
11].
Shift in amide I band, due to C O group and increase/decrease
where ꢁ is the spin orbit coupling constant for copper(II) and ꢂXY
−1
is the d–d band energy in cm for the respective copper(II) com-
in amide II band, due to C–N group, in the amide are indicative
of the coordination of the ligand through carbonyl oxygen in the
complexes (Table 2) [11–13,17].
2
plex [18]. ˛ is a function whose numerical value depends on the
nature of copper–ligand bond and decreases with increasing cova-
2
lency of Cu–L bond. The minimum theoretical value of ˛ is 0.5 and
−
1
A broad band in the region 3300–3500 cm
in all the com-
maximum is 1.0.
plexes indicates the presence of water molecule or O–H stretching
due to H-bonding with the solvent. The presence of anions in the
respective complex is justified by the presence of strong IR bands
at 2077 cm (ꢀSCN stretch), 846 cm (ꢀC–N stretch). This shows
coordination group through N atom of thiocynate group. Bands at
For the series of complexes obtained from O-GBGA ligand, ˛2
ranges from 0.59–0.90 indicating considerable amount of covalent
character in Cu–L bond. It is interesting to note that the chloro com-
plex in this series is relatively more covalent, while the acetato
complex is more ionic for this series.
−
1
−1
−
), 1330 cm (ꢀCH3COO ) are assigned to unidentate
−
6H5COO–
1
1
600 (ꢀC
mode of binding of the respective anions [19].
3.3. Cyclic voltammetry
All the complexes display a quasi reversible redox wave due
3.5.1. Fluorescence studies
to Cu(II)/Cu(I) process. Anodic shifts in E1/2 values indicate the
retention of anion in the coordination sphere of Cu(II). E values
The fluorescence spectra of the O-GBGA and its copper(II/I)
complexes are shown in Fig. 3. Quantum yields ϕ (Table 3) were
calculated by comparison of the spectra with that of anthracene
(ϕ = 0.292) taking the area under the total emission.
1/2
−
−
−
becoming anodic in the order C H5COO < SCN < Cl for the O-
6
−
GBGA series. The CH COO bound complex shows an irreversible
3
anodic wave at 0.57 V versus Ag/AgCl.
.4. 1H NMR study of [Cu (O-GBGA)(SCN)]
I
3
1
The 1H NMR spectrum of the free ligand O-GBGA shows sig-
nals for aliphatic and aromatic protons with theoretically predicted
splittings. A signal is observed between 11.26 ppm corresponding
to N–H amide proton; while multiplets in the range 7.2–7.5 ppm
1
1
50000
00000
50000
0
2
arise due to the benzimidazole ring protons. The linker –CH –
2
protons are found at 2.0 and 4.1 ppm for the ligand. The –CH –
2
group adjacent to the benzimidazole ring gives rise to a doublet
between 4.7 ppm due to coupling with the adjacent amide NH pro-
tons. The methylene –CH – and the methyl –CH of the octyl chain
2
3
3
are observed at 2.4, 1.8, 1.2, and 0.8 ppm, respectively [13].
1
4
In the H NMR spectrum of the complex synthesized using
−
SCN as the anion, shifted signals were observed with the loss of
5
splitting. The central linker –CH2 protons and those of the octyl
chain show a very slight shifting. While some of the 1H signals
were found to be downfield shifted as compared to the free lig-
and O-GBGA, these include the benzimidazole ring protons which
appear at 7.9 ppm instead of 7.5 ppm and the methylene protons
that appear at 4.3 ppm instead of 4.1 ppm. The amide NH proton
3
00
350
400
450
500
550
wavelength(nm.)
is upfield shifted at 9.2 ppm instead of 11.2 ppm. The –CH – group
2
adjacent to the benzimidazole ring gives rise to a doublet at 4.7 ppm
due to coupling with the adjacent amide NH protons. The presence
of amide NH protons proves that the copper ion does not coordi-
Fig. 3. Fluorescence spectra of ligand (5) and [Cu(O-GBGA)Cl2] (1), [Cu(O-
GBGA)(NO3)2] (2), [Cu(O-GBGA)(C6H5COO)2] (3), [Cu(O-GBGA)(C6H5COO)2] (4) in
−
6
concentration of 7 × 10 M in HPLC grade CH2Cl2.

6
16
S.C. Mohapatra, P. Mathur / Spectrochimica Acta Part A 78 (2011) 612–616
Table 3
study confirms the binding of amide carbonyl rather than amide-
NH a result supported by crystal data on similar bis-benzimidazolyl
diamide ligands. EPR work suggests a highly distorted copper(II)
geometry in solution state as evidenced by low A|| values, further
N-SHF structure on one of the complexes, implicates the binding
Fluorescence spectra of copper(II) complexes with O-GBGA in concentration of
.0 × 10− M in HPLC grade CH2Cl2.
6
7
Complexes
Quantum yield (photon)
O-GBGA
0.029
0.010
0.022
0.021
0.012
[
[
[
[
Cu(O-GBGA)(CH3COO)2]
Cu(O-GBGA)Cl2]
Cu(O-GBGA)(NO3)2]
Cu(O-GBGA)(C6H5COO)2]
of imine N-atoms of the benzimidazole, giving a N O2 donor envi-
2
ronment on copper(II). The ligand and its copper(II) complexes give
fluorescence quantum yield which is higher than for some nitrogen
containing fluorophores implying that the lone pair of the benz-
imidazole N-atom is only weakly involved in PET to the aromatic
fluorophore. The relative fluorescence intensity change reveals that
The fluorescence spectrum of 7 ␮M solution in dichloromethane
for O-GBGA shows two groups of bands, one group (F1) arising
between 350 and 385 nm, while the other arising between 400 and
− −
3 6
5
it is larger for larger anions like CH COO and C H COO while
−
−
smaller for anions like Cl and NO3 . Thus, fluorescence of these
copper(II) compounds can distinguish between small and large
anions.
4
65 nm (F2). The short wave length fluorescence bands within (F1)
are found to be red shifted with respect to simple benzimidazole
and bis benzimidazole type ligands [20,21]. The fluorescence quan-
tum yield of the present ligating system is similar to that reported
for bis benzimidazole type ligand but quite higher than for some of
the nitrogen containing fluorophores [22], implying that the lone
pair of the benzimidazole nitrogen is only weakly involved in photo
induced electron transfer (PET) to the aromatic fluorophore. The
fluorescence spectra of the copper(II) complexes of O-GBGA show
only very slight shift in the ꢁmax of the bands in 350–465 nm region,
as compared to the ligand. However, the total area under the curve
between these wavelength regions does change. This change is
reflected in the quantum yields as reported in Table 3. The quantum
yields have been calculated by utilizing the formula:
Acknowledgement
Authors are grateful to the University of Delhi, Delhi, for a special
grant.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2010.11.033.
References
areacomp εanth
˚
= 0.292
areaanth εcomp
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[
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where ε = extinction coefficient of the compound, while anth:
anthracene.
(
Chapter 3).
The fluorescence quantum yields of complexes were found to
be lower than that of the ligand O-GBGA. This indicates that all
complexes quench the fluorescence of the parent ligand. However,
some changes are observed which are assigned to the effect of the
anion bound to the copper(II) complexes. Much larger quenching
is observed for the acetate and benzoate bound complexes rather
than the chloride complexes.
[
[
4] P.S. Subramanian, D. Srinivas, Polyhedron 15 (1996) 985–989.
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[
(
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323–1328.
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[
[
[
The relative fluorescence intensity change (ꢃ) is given by:
1
F − F
0
ꢃ =
[12] M. Gupta, S.K. Das, P. Mathur, A.W. Cordes, Inorg. Chim. Acta 353 (2003)
197–204.
F
0
[
13] S.C. Mohapatra, S. Tehlan, M.S. Hundal, P. Mathur, Inorg. Chim. Acta 361 (2008)
1897–1907.
where F , fluorescence intensity of free ligand; F, fluorescence
0
intensity of the complex.
The relative fluorescence intensity data reveals that for the
larger anions like acetate and benzoate, value of ꢃ is also larger
[14] S. Tehlan, M.S. Hundal, P. Mathur, Inorg Chem. 43 (2004) 6589.
[
[
15] A.K. Patra, R.N. Mukerjee, Inorg. Chem. 38 (1999) 1388.
16] 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.
(
0.65, 0.58) while for smaller anions like chloride and nitrate ꢃ rel-
[17] G. Batra, P. Mathur, Inorg. Chem. 31 (1992) 1575–1580.
[
[
[
[
18] R.S. Himmelwright, N.C. Eickman, C.D. LuiBien, E.I. Solomon, J. Am. Chem. Soc.
ative is smaller (0.24, 0.27). This suggests that fluorescence of such
compounds could distinguish between small and large anions.
102 (1980) 5378–5388.
19] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Com-
pounds, 5th edition, Wiley, New York, 1997.
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4
. Conclusion
152–157.
21] A. Kumar, H.K. Sinha, S.K. Dogra, Can. J. Chem. 67 (1989) 1200–1205.
New copper(II) complexes with a N-octylated bis benzimida-
zolyl ligand have been synthesized and characterized. IR spectral
[22] P. Ghosh, P.K. Bhardawaj, J. Roy, S. Ghosh, J. Am. Chem. Soc 119 (1997)
11903–11909.