Morphology dependant oxidation of aromatic alcohols by new symmetrical copper(II) metallatriangles formed by self-assembly of a shared bis-benzimidazolyl diamide ligand

Article abstract of DOI:10.1016/j.ica.2012.12.037

A new bis-benzimidazole-based diamide ligand N²,N ^2′-bis((1H-benzo[d]imidazol-2-yl)methyl)-[1,1′-biphenyl] -2,2′-dicarboxamide, L and its three Cu(II) metallatriangles of general formula [Cu₃(L)₃X₃]·3X·nH ₂O (where X = Cl, Br, NO₃) have been synthesized and one of them is structurally characterized. X-ray diffraction work reveals that the metallatriangle [Cu₃(L)₃Cl₃] ·3Cl·15H₂O crystallizes in trigonal R3? space group with two independent molecules in the asymmetric unit. The asymmetric unit contains only one-third of the molecules and the rest are generated by the crystallographic 3? axis. Each copper(II) ion adopts a highly distorted square pyramidal geometry. The copper(II) metallatriangles are used as catalyst to carry out the oxidation of substituted benzyl alcohols heterogeneously, in the presence of tert-butyl hydroperoxide. Interestingly, the ratio of product profile and the percentage conversion of the products changes with the surface morphology of the metallatriangle employed as a catalyst. A kite type morphology is found to be highly selective to the formation of acid product over the aldehyde, while a hexagonal type morphology results in a mixed acid + aldehyde product. The initial rate of formation of the aldehyde is found to be almost independent of the amount of catalyst employed.

Full text of DOI:10.1016/j.ica.2012.12.037

Inorganica Chimica Acta 399 (2013) 36–44
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Morphology dependant oxidation of aromatic alcohols by new symmetrical
copper(II) metallatriangles formed by self-assembly of a shared bis-benzimidazolyl
diamide ligand
⇑
Kuldeep Mahiya, 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
20
Article history:
A
new bis-benzimidazole-based diamide ligand N2,N -bis((1H-benzo[d]imidazol-2-yl)methyl)-[1,10-
biphenyl]-2,20-dicarboxamide, L and its three Cu(II) metallatriangles of general formula [Cu3(L)3X3]-
ꢀ3XꢀnH2O (where X = Cl, Br, NO3) have been synthesized and one of them is structurally characterized.
X-ray diffraction work reveals that the metallatriangle [Cu3(L)3Cl3]ꢀ3Clꢀ15H2O crystallizes in trigonal
Received 20 September 2012
Received in revised form 19 December 2012
Accepted 23 December 2012
Available online 3 January 2013
ꢀ
R3 space group with two independent molecules in the asymmetric unit. The asymmetric unit contains
ꢀ
only one-third of the molecules and the rest are generated by the crystallographic 3 axis. Each copper(II)
Keywords:
ion adopts a highly distorted square pyramidal geometry. The copper(II) metallatriangles are used as
catalyst to carry out the oxidation of substituted benzyl alcohols heterogeneously, in the presence of
tert-butyl hydroperoxide. Interestingly, the ratio of product profile and the percentage conversion of
the products changes with the surface morphology of the metallatriangle employed as a catalyst. A kite
type morphology is found to be highly selective to the formation of acid product over the aldehyde, while
a hexagonal type morphology results in a mixed acid + aldehyde product. The initial rate of formation of
the aldehyde is found to be almost independent of the amount of catalyst employed.
Ó 2013 Elsevier B.V. All rights reserved.
Benzimidazolyl diamide
Crystal structure
Asymmetric unit
Morphology
Catalytic oxidation
4-Methyl benzyl alcohol
1. Introduction
in DNA cleavage [6] and oxidative catalytic reactions involving a
variety of substrates [7].
Transition metal catalysts carry out a large number of chemical
reactions, where selective bond breaking and rearrangements
takes place [1]. In heterogeneous catalysis an important issue is
to probe whether metal ion sites that carry out the catalytic pro-
cesses are different from those sites, where the substrate binds
strongly leading to a low reactivity [2]. Earlier work has suggested
that both size and shape of the catalyst is important and the cata-
lyst undergo changes as catalysis proceeds [3].
With a view to probe further into the above effect, we have
synthesized a new bis-benzimidazolyl diamide ligand and its
copper(II) metallatriangles. These metallatriangles carry out the
oxidation of aromatic alcohols to corresponding acid and aldehyde
and the catalyst can be reused successfully at least three times. We
have carried out a SEM study on the catalyst after every reuse and
find that the reactivity could be attributed to the surface morphol-
ogy of the catalyst. Symmetrical trinuclear metallacycles with a
variety of metal ions and ligands have been reported in recent
years [4]. While trinuclear metallacycles involving copper(II) cen-
ters are limited in the literature [5], some of these find applications
2. Experimental
2.1. Materials
All reagents used in the experiment were of analytical grade.
2,20-Diphenic acid, 4-methyl benzyl alcohol, 2,4-dimethyl benzyl
alcohol and t-butyl hydro peroxide (TBHP) was purchased from
Sigma–Aldrich. 2-Aminomethylbenzimidazolyl dihydrochloride
was prepared following the procedure reported by Cescon and
Day [8].
2.2. Analysis and physical measurements
IR spectra were obtained in the solid state as KBr pellets using a
Perkin Elmer FTIR-2000 spectrometer. Electronic spectra were ob-
tained on a Shimadzu UV–Vis-1601 Spectrometer. Elemental anal-
yses were determined with a Gmbh VarioEL V3.00 Elemental
analyzer. Thermal gravimetric analyses (TGA) were carried out in
a nitrogen stream using a Perkin Elmer Diamond equipment at a
heating rate of 10 °C/min. The SEM micrographs were recorded
on an Environmental Scanning Electron Microscope model FEI
⇑
Corresponding author. Tel.: +91 11 27667725.
E-mail address: pavanmat@yahoo.co.in (P. Mathur).
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.12.037

K. Mahiya, P. Mathur / Inorganica Chimica Acta 399 (2013) 36–44
37
Quanta 200F with Oxford EDS system IE 250 X Max 80 at IIT Delhi,
India. GCMS analysis was done on a Shimadzu GCMS-QP2010 plus
gas chromatograph mass spectrometer with AOC-20i auto injector
and TD-20 thermal desorption system at Jawahar Lal Nehru Uni-
versity Delhi, India. Melting points were measured on BUCHI Melt-
ing Point M-560 apparatus at a heating rate of 10 °C in glass
capillaries. The powder X-ray diffraction pattern were recorded
using a high resolution D8 Discover Bruker X-ray diffractometer
equipped with a point detector (scintillation counter), employing
polarization effects. Multi-scan absorption correction was applied.
The structure was solved by direct methods using SHELXS-97 [9] and
refined by full-matrix least-squares refinement techniques on F2,
using SHELXL-97 [9]. All calculations were done with the help of
WINGX programme [10]. For the molecular graphics, the programme
DIAMOND2 [11] and MERCURY [12] were used. All non-hydrogen atoms
were refined anisotropically. All hydrogen atoms were fixed geo-
metrically with Uiso values of 1.2 times the Uiso values of their
respective carrier atoms. The hydrogen on lattice water were lo-
cated from difference fourier map. The final residual index for L
are; R 0.0651, Rw 0.1630 for the observed and R 0.0895, Rw
0.1835 for all reflections using 178 parameters. The final residual
index for LA are; R 0.0485, Rw 0.1019 for the observed and R
0.0875, Rw 0.1207 for all reflections using 396 parameters For met-
allatriangle (1), a total of 55452 reflections were measured of
which 14005 were unique and 8706 were considered observed
monochromatized Cu Ka1 radiation obtained through a globel mir-
ror with a scan rate of 1.0 s/step and step size of 0.02° at 298 K over
the range of 2h = 10–40. The single crystal diffraction data were
collected on an X’Calibur single crystal X-ray diffractor having
CCD camera at University of Delhi, Delhi, India. Magnetic measure-
ments were carried out on a vibrating sample magnetometer
microsense, Ade-Model EV9 in the field range 0–10000 G in the so-
lid state. Evan’s method was employed to obtain the solution mag-
netic susceptibility in solution state at 298 K.
(I > 2r(I)]. The final residual index are; R 0.0678, Rw 0.2197 for
the observed and R 0.1082, Rw 0.2380 for all reflections using
784 parameters. Details of the crystallographic data and structure
refinement for L, LA and (1) are given in Table 1.
2.3. X-ray data collection, structure determination and refinement
Single crystals of diamide ligands L, LA and metallatriangle (1)
suitable for X-ray diffraction studies were grown by slow evapora-
tion in methanol. The intensity data were collected at 298 K on an
X’calibur CCD diffractometer with graphite monochromatized Mo
2.4. Preparation of ligands
20
2.4.1. N2,N -bis((1H-benzo[d]imidazol-2-yl)methyl)-[1,10-biphenyl]-
2,20-dicarboxamide, L
K
a
radiation (k = 0.71073 Å). For L, a total of 8423 reflections were
measured of which 2384 were unique and 1664 were considered
observed (I > 2 (I)]. For LA, a total of 13985 reflections were mea-
sured of which 6111 were unique and 3115 were considered ob-
Ligand L was prepared by adopting a procedure reported by
Mathur and co-workers for bis-benzimidazolyl diamides [13] and
is outlined in Scheme 1. The product was analyzed for the compo-
sition C30H24N6O2, Yield (%) = 73%. M.P. 320 °C. Anal. Calc. for
r
served (I > 2r(I)].The data were corrected for Lorentz and
C30H24N6O2: C, 71.6; H, 4.5; N, 16.8. Found: C, 72.0; H, 4.8; N,
Table 1
Crystal and structure refinement data for L (1) and LA.
L
(1)
LA
Empirical formula
Formula weight
T (K)
C30H24N6O2
501
298(2)
C180H144Cl12Cu6N36O27
4050
298(2)
C30H32Cl2N6O5
628
298(2)
k (Å)
0.71073
monoclinic
C2/c
0.71073
trigonal
0.71073
monoclinic
P21/n
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
ꢀ
R3
18.406(3)
14.735(3)
9.950(3)
90
27.3168(8)
27.3168(8)
49.6611(19)
90
11.8840(7)
19.7413(7)
14.4839(8)
a
(°)
b (°)
116.08(3)
90
112.994(6)
c
(°)
90
120
32092.7(18)
6
1.257
0.803
V (Å3)
2423.8(11)
4
1.372
0.090
1048
0.22 ꢂ 0.16 ꢂ 0.12
3.33–26.00
ꢁ22 6 h 6 22,
ꢁ18 6 k 6 18,
ꢁ10 6 l 6 12
8423
3128.0(3)
4
1.333
0.256
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢁ1
F(000)
)
12420
1312
Crystal size (mm3)
h (°)
0.26 ꢂ 0.22 ꢂ 0.14
2.98–26.00
ꢁ33 6 h 6 33,
ꢁ32 6 k 6 30,
ꢁ61 6 l 6 61
55452
0.18 ꢂ 0.16 ꢂ 0.16
3.01–27.71
ꢁ11 6 h 6 14,
ꢁ24 6 k 6 24
,ꢁ15 6 l 6 18
13985
Index ranges
Reflections collected
Independent reflections (Rint
Completeness toh = 26.00°
Absorption correction
Maximum and minimum transmission
Refinement method
)
2384(0.0695)
99.8 %
14005(0.0503)
99.8 %
6111(0.0342)
99.0 %
Multi-scan
0.9893 and 0.9806
Full-matrix least-squares on F2
2384/0/172
1.039
Multi-scan
0.8959 and 0.8184
Full-matrix least-squares on F2
14005/0/784
1.039
Multi-scan
0.9620 and 0.9560
Full-matrix least-squares on F2
6111/0/396
0.935
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
r
(I)]
R1 = 0.0651,
wR2 = 0.1649
R1 = 0.0895,
wR2 = 0.1856
0.246 and ꢁ0.259
R1 = 0.0678,
wR2 = 0.2197
R1 = 0.1082,
wR2 = 0.2380
1.493 and ꢁ0.577
R1 = 0.0485,
wR2 = 0.1019
R1 = 0.0875,
wR2 = 0.1207
0.198 and ꢁ0.194
R indices (all data)
Largest difference in peak and hole (e Åꢁ3
)

38
K. Mahiya, P. Mathur / Inorganica Chimica Acta 399 (2013) 36–44
COOH
HOOC
O
O
Pyridine, 70oC
N
NH2.2HCl
NH
N
HN
N
TPP, 24 hrs
N
H
HN
NH
L
0
Scheme 1. Synthesis of N2,N2 -bis((1H-benzo[d]imidazol-2-yl)methyl)-[1,10-biphenyl]-2,20-dicarboxamide, L.
16.8%. Single crystals of L suitable for diffraction work were ob-
tained indirectly by initially allowing L to react with Cu(ClO4)2-
ꢀ6H2O. The solution upon keeping for a few days deposited
transparent crystals of L, rather than a Copper(II)–L complex.
Calc. for
12.36. Found: C, 52.29: H, 4.19: N, 12.33%.
kmax (nm), (Methanol), [log ]: 272 [4.15], 279 [4.11], 711 [1.81].
IR(KBr pellets): OH), 3204 and 3060( NH),
max/cmꢁ1: 3377(
1610( C@O), 1540( C–N), 1468( C@N–C@C), 741 (mC@C benzene).
C
180H144N36O12Cu6Cl12ꢀ15H2O: C, 52.98: H, 4.26: N,
e
m
m
m
IR (KBr pellets):
m
max/cmꢁ1: 3099 and 3021(
C–N), 1437(mC@N–C@C), 748 (mC@C benzene).
m
NH), 1623(
m
C@O),
m
m
m
1545(
m
2.5.2. Preparation of [Cu3(L)3(NO3)3].3NO3.8H2O (2)
To a suspension of ligand (100 mg, 0.2 mmol) in 20 ml metha-
nol, Cu(NO3)2.6H2O (48 mg, 0.2 mmol) dissolved in 5 ml of metha-
nol was added dropwise with constant stirring. The resulting
mixture was refluxed at 80 °C for 1 h. Thereafter the light blue col-
ored solution so obtained was transferred to a 100 ml beaker and
allowed to stand at room temperature overnight. The light blue
powder so obtained was filtered, air dried and analyzed for the
composition C90H72N24O24Cu3ꢀ8H2O, Yield (%) = 85%. M.P. 270 °C.
Anal. Calc. for C90H72N24O24Cu3ꢀ8H2O: C, 48.94; H, 4.04; N, 15.22.
Found: C, 48.54; H, 4.15; N, 15.12%.
20
2.4.2. N2,N -bis((1H-benzo[d]imidazol-2-yl)methyl)-[1,10-biphenyl]-
2,20-dicarboxamideꢀdihydrochloride, LA (Scheme 2)
The ligand L was found to be insoluble in all major organic sol-
vents, thus to characterize it in solution state, appropriate hydro-
chloride salt LA was formed by dissolving L in 4 M HCl (20 ml)
and allowing to stand for an hour. A white solid separated out. This
was filtered, washed with distilled water, air dried and analyzed
for the composition C30H24N6O2ꢀ2HClꢀ3H2O. Anal. Calc. for C30H24-
N6O2ꢀ2HClꢀ3H2O: C, 57.41; H, 5.10; N, 13.39. Found: C, 57.29; H,
5.17; N, 13.29%. M.P. 290 °C (see Scheme 2).
kmax (nm), (Methanol), [log
750 [1.66].
IR(KBr pellets):
1610( C@O), 1539(
1384 ( NO3).
e]: 272 [4.17], 279 [4.14], 364 [2.90],
max/cmꢁ1: 3376(
m
OH). 3205 and 3059(
mNH),
kmax (nm), (Methanol), [log e]: 277[4.15], 271[4.17].
m
m
1H NMR (d ppm in DMSO-d6): 4.68 (s, 4H, CH2), 7.11 (dd, 2H, 5.8
and 3.3 Hz), 7.21 (dd, 4H, 5.9 and 3.4 Hz), 7.49 (dd, 4H, 6.5 and
3.2 Hz), 7.67 (dd, 2H, 5.7 and 3.9 Hz), 7.74 (dd, 4H, 6.4 and
3.2 Hz), 9.29 (t, 2H, 5.6 Hz).
m
m
C–N), 1468( C@N–C@C), 741 (
m
mC@C benzene),
2.5.3. Preparation of [Cu3(L)3Br3]ꢀ3Brꢀ10H2O (3)
13C NMR (d ppm in DMSO-d6,): 35.48, 113.99, 125.64, 127.14,
127.75, 129.48, 129.69, 130.79, 134.53, 138.82, 150.94, 169.93.
This complex was synthesized by following the procedure used
for the preparation of the nitrate bound copper(II) complex (2) ex-
cept that copper(II) bromide was used for complexation. The
resulting mixture was refluxed at 80 °C for 1 h. Thereafter the par-
rot green colored solution so obtained was transferred to a 100 ml
beaker and allowed to stand at room temperature overnight. The
parrot green colored powder so obtained was filtered air dried
and analyzed for the composition C90H72N18O6Cu3Br6ꢀ10H2O, Yield
(%) = 82%. M.P. 205 °C. Anal. Calc. for C90H72N18O6Cu3Br6ꢀ10H2O: C,
45.59; H, 3.88; N, 10.63. Found C, 45.11; H, 3.96; N, 10.34%.
IR (KBr pellets):
3038( NH), 1649 and 1618(
and1408 ( C@N–C@C), 756 (mC@C benzene).
m
max/cmꢁ1: 3542 and 3444(
m
OH), 3197 and
m
m
C@O), 1559 and 1526( C-N), 1459
m
m
2.5. Preparation of metallatriangles
2.5.1. Preparation of {[Cu3(L)3Cl3].3Cl}2.15H2O (1)
To a suspension of ligand (100 mg, 0.2 mmol) in 20 ml metha-
nol, CuCl2.2H2O (35 mg, 0.2 mmol) dissolved in 5 ml of methanol
was added dropwise with constant stirring. The resulting mixture
was refluxed at 80 °C for 1 h. Thereafter the green colored solution
so obtained was transferred to a 100 ml beaker and allowed to
stand at room temperature overnight. The green colored crystal
obtained were filtered, air dried and analyzed for the composition
kmax (nm), (Methanol), [log
702 [1.82].
IR(KBr pellets):
1610( C@O), 1541(
The presence of water in the lattice is supported by IR and TGA
data.
e]: 272 [4.11], 279 [4.07], 360 [2.88],
m
max/cmꢁ1: 3385(
mOH), 3222 and 3060(mNH),
m
m
C–N), 1468( C@N–C@C), 742 (mC@C benzene).
m
C180H144N36O12Cu6Cl12ꢀ15H2O, Yield (%) = 80%. M.P. 215 °C. Anal.
2.6. Oxidation of aromatic alcohols by the metallatriangles (1), (2) and
(3) using tert-butyl hydroperoxide (TBHP) as an alternate source of
oxygen.
O
O
O
O
2Cl.3H2O
4 M HCl
NH
NH
NH
N
HN
HN
HN
N
OH
O
HN
NH
NH
O
OH
HN
X
X
TBHP, MeCN
2.5 hrs
X
L
LA
Y
S
Y
A
Y
B
X= H or CH3, Y= CH3
0
Scheme 2. Synthesis of N2,N2 -bis((1H-benzo[d]imidazol-2-yl)methyl)-[1,10-biphe-
nyl]-2,20-dicarboxamideꢀdihydrochloride, LA.

K. Mahiya, P. Mathur / Inorganica Chimica Acta 399 (2013) 36–44
39
Table 2(b)
2.6.1. Experimental procedure
Selected bond lengths (Å) and angles (°) for LA.
(a) Oxidation of two alcohols, 4-methyl benzyl alcohol and 2,4-
dimethyl benzyl alcohol were studied using the copper(II)
metallatriangles as catalyst, heterogeneously in acetonitrile
at 60 °C. The time duration was 2.5 h and ratio of catalyst:
substrate: oxidant was fixed as 1:60:60 for each reaction.
The progress of reaction was monitored by TLC. The catalyst
was filtered, dried and washed with acetonitrile after each
reaction and reutilized for the next reaction. The products
formed were analyzed by GCMS.
(b) The kinetics of the conversion of 4-methylbenzyl alcohol to
4-methylbenzaldehyde was studied spectrophotometrically.
0.16 mmol of 4-methylbenzyl alcohol was mixed with
0.0042 mmol of the copper(II) metallatriangle (1) in 10 ml
acetonitrile in the presence of 0.16 mmoles of tert.butyl
hydroperoxide (TBHP) at 60 °C with rapid stirring. After
C(1)–N(1)
C(1)–N(2)
C(8)–N(3)
C(9)–O(1)
C(9)–N(3)
C(15)–C(16)
C(22)–O(2)
C(22)–N(4)
C(23)–N(4)
C(24)–N(5)
C(24)–N(6)
1.328(3)
1.324(3)
1.455(3)
1.238(3)
1.315(3)
1.504(3)
1.232(3)
1.349(3)
1.441(3)
1.323(3)
1.325(3)
N(1)–C(1)–N(2)
N(1)–C(1)–C(8)
N(2)–C(1)–C(8)
109.8(2)
126.7(3)
123.4(2)
121.4(2)
120.4(2)
119.6(2)
122.8(2)
121.2(3)
122.8(2)
110.1(2)
125.1(3)
124.7(2)
O(1)–C(9)–N(3)
O(1)–C(9)–C(10)
C(10)–C(15)–C(16)
C(21)–C(16)–C(15)
O(2)–C(22)–N(4)
O(2)–C(22)–C(21)
N(5)–C(24)–N(6)
N(5)–C(24)–C(23)
N(6)–C(24)–C(23)
Table 2(c)
Selected bond lengths (Å) and angles (°) for (1).
Cu(1)–Cl(1)
Cu(1)–N(1)
2.2894(16)
1.946(4)
Cu(2)–Cl(2)
Cu(2)–N(3)
2.2924(14)
1.953(4)
every 5 min, 20 lL solution from the reaction mixture was
taken in a quartz cuvette containing 2.0 mL acetonitrile ant
the solution scanned in the UV-range for the development
of any new band. It is found that a new band immediately
starts to arise at ꢃ255 nm. This band grows in intensity for
nearly two hours and also splits into two bands viz at
ꢃ246 and 255 nm suggesting the formation of 4-methylben-
zoic acid after >1 h of reaction. This procedure was repeated
with different amount of catalyst (0.0014 and 0.0028 mmol)
keeping the amount of 4-methylbenzyl alcohol same (i.e.
0.16 mmol). The rate of formation of 4-methylbenzaldehyde
was determined by initial rate method this was obtained
from the plot of concentration of aldehyde formed versus
time.
Cu(1)–N(2)
Cu(1)–O(1)
Cu(1)–O(2)
1.945(4)
2.170(3)
2.101(3)
Cu(2)–N(4)
Cu(2)–O(3)
Cu(2)–O(4)
1.962(4)
2.093(3)
2.233(3)
N(1)–Cu(1)–N(2)
O(2)–Cu(1)–O(1)
N(1)–Cu(1)–O(2)
N(2)–Cu(1)–O(2)
N(2)–Cu(1)–O(1)
N(1)–Cu(1)–O(1)
N(1)–Cu(1)–Cl(1)
N(2)–Cu(1)–Cl(1)
O(2)–Cu(1)–Cl(1)
O(1)–Cu(1)–Cl(1)
175.06(16)
92.52(14)
83.89(15)
91.23(14)
87.02(15)
92.38(14)
91.28(12)
93.45(12)
153.23(12)
114.03(12)
N(3)–Cu(2)–N(4)
O(3)–Cu(2)–O(4)
N(4)–Cu(2)–O(3)
N(4)–Cu(2)–O(4)
N(3)–Cu(2)–O(4)
N(3)–Cu(2)–O(3)
N(3)–Cu(2)–Cl(2)
N(4)–Cu(2)–Cl(2)
O(3)–Cu(2)–Cl(2)
O(4)–Cu(2)–Cl(2)
176.46(17)
90.55(14)
85.09(15)
91.52(15)
86.91(15)
91.75(15)
92.20(12)
91.33(12)
148.93(11)
120.43(10)
Symmetry transformations used to generate equivalent atoms:
(1) ꢁy + 1, x ꢁ y ꢁ 1, z; (2) ꢁx + y + 2, ꢁx + 1, z; (3) ꢁy + 1, x ꢁ y, z; (4) ꢁx + y + 1,
ꢁx + 1, z.
3. Result and discussion
3.1. Crystal structure description
Table 3
Showing important H-bonding interactions between the cationic and anionic
moieties.
Crystal data and structure refinement parameters are given in
Table 1, selected bond lengths & angles and H-bonding parameters
for LA are given in Table 2(a–c) and Table 3 respectively. The ligand
L crystallizes in monoclinic space group C2/c with half a molecule
in the asymmetric unit. The other half of the molecule is generated
from the first one by the crystallographic two fold axis (Fig. 1). The
diamide LA crystallizes in monoclinic P21/n space group. Due to the
presence of chloride ions and water molecules in the crystal lattice,
the cationic molecule undergoes extensive intermolecular H-bond-
ing. The water molecules with oxygen atoms O1W, O2W and O3W
along with the two chloride atoms Cl1 and Cl2 are involved in very
interesting intermolecular H-bonding among themselves. The
chloride atom Cl1 forms O1W–H11W. . .Cl1i (2.359(2) Å, i = ꢁx,
ꢁy, ꢁz + 1) and O2W–H21Wꢀ ꢀ ꢀCl1ii (2.266(3) Å, ii = ꢁx, ꢁy, ꢁz)
while Cl2 is engaged in O2W–O22Wꢀ ꢀ ꢀCl2iii (2.577(3) Å,
Dꢀ ꢀ ꢀA (Å)
Hꢀ ꢀ ꢀA (Å)
D–Hꢀ ꢀ ꢀA (°)
N1–H1ꢀ ꢀ ꢀCl1
3.110(2)
3.210(2)
3.065(3)
3.190(2)
2.675(2)
3.494(3)
2.27
2.42
2.20
2.36
1.84
2.55
160
151
167
172
158
173
N4–H41ꢀ ꢀ ꢀCl1
N6–H6Aꢀ ꢀ ꢀCl2
N3–H31ꢀ ꢀ ꢀCl2a
N2–H2ꢀ ꢀ ꢀO3W
C12–H12ꢀ ꢀ ꢀO1Wb
a
ꢁx ꢁ 1/2, +y ꢁ 1/2, ꢁz + 1/2.
= x ꢁ 1/2, ꢁy ꢁ 1/2, +z ꢁ 1/2.
b
iii = ꢁx ꢁ 1,
ꢁy,
ꢁz)
and
O3W–H31Wꢀ ꢀ ꢀCl2iv(2.349(2) Å,
iv = ꢁx ꢁ 1/2, +y ꢁ 1/2, ꢁz + 1/2) hydrogen bonding interactions.
The oxygen atom O1W of one water molecule is involved in
O3W–H32Wꢀ ꢀ ꢀO1Wv (2.691(3) Å, v = x + 1/2, ꢁy ꢁ 1/2, +z ꢁ 1/2)
hydrogen bonding with the other water molecule. All these inter-
molecular hydrogen bonding interactions together lead to the for-
mation of 10 membered puckered rings constituting water and
anions. In turn these puckered rings are involved in intermolecular
hydrogen bonding with the cationic organic molecules leading to
the formation of 2D sheets, thereby holding the entire lattice to-
gether (Fig. 2).
Table 2(a)
Selected bond lengths (Å) and angles (°) for L.
C(5)–N(2)
C(6)–N(1)
C(7)–N(2)
C(7)–N(1)
C(7)–C(8)
C(8)–N(3)
C(9)–O(1)
C(9)–N(3)
C(9)–C(10)
C(11)–C(11)#1
1.389(3)
1.369(3)
1.307(3)
1.364(3)
1.487(3)
1.456(3)
1.233(2)
1.332(3)
1.497(3)
1.497(4)
N(2)–C(7)–N(1)
N(2)–C(7)–C(8)
N(1)–C(7)–C(8)
N(3)–C(8)–C(7)
O(1)–C(9)–N(3)
O(1)–C(9)–C(10)
N(3)–C(9)–C(10)
C(15)–C(10)–C(9)
C(11)–C(10)–C(9)
C(10)–C(11)–C(11)#1
112.4(2)
125.1(2)
122.5(2)
112.36(18)
122.5(2)
120.90(18)
116.6(2)
116.8(2)
124.29(19)
122.97(16)
The asymmetric unit of metallatriangle (1) has two independent
crystallographic units; each unit consists of three ligand moieties
and three copper(II) centers which occupy the three vertices of
an equilateral triangle to form a 45 membered metallacycle. Each
copper(II) ion is five coordinated with a highly distorted square
pyramidal geometry (Figs. 3 and 4). The geometry is best described
Symmetry transformations used to generate equivalent atoms:
(1) ꢁx, y, ꢁz + 1/2.
as a distorted square pyramidal with Addison parameters
s = 0.36

40
K. Mahiya, P. Mathur / Inorganica Chimica Acta 399 (2013) 36–44
Fig. 1. ORTEP Diagram of diamide ligand, L drawn in 30% thermal probability ellipsoids with asymmetric unit (left) and full molecule (right) with atomic numbering scheme.
Fig. 2. ORTEP Diagram of diamide Ligand LA drawn in 30% thermal probability ellipsoids showing atomic numbering schemes. Hydrogen, solvent water, and lattice chloride
anions are omitted for the sake of clarity (left) and packing diagram of LA with 2D sheet formed by intermolecular H-bonding between the cations and ‘water anion’ rings
(right).
Fig. 3. ORTEP Diagram of the asymmetric unit of (1) drawn in 30% thermal probability ellipsoids with atomic numbering scheme. Hydrogen and solvent water have been
removed for clarity. Only lattice chloride has been shown. Co-ordination around metal ion is distorted square pyramidal.
for the asymmetric unit I (Cu1) and
unit II (Cu2). The parameter is defined as
where and b are the largest angles; = 1 for a regular trigonal
bipyramid and = 0 for a regular square pyramid [14]. In both
the units, the basal plane of the square pyramidal is formed by
two benzimidazolyl imine nitrogen atoms (N1 and N2 for Cu1
and N3 and N4 for Cu2) and two amide carbonyl oxygen atoms
(O1 and O2 for Cu1 and O3 and O4 for Cu2) of the benzimidazolyl
diamide ligand and the apical position of the Cu(II) is occupied by
s
= 0.46 for the asymmetric
the Cl1 and Cl2 anion (Fig. 3). The dihedral angle between the phe-
nyl rings in biphenyl moiety controls the aggregation and size of
the metallacycle. A decrease in dihedral angle between the plane
of two phenyl ring in biphenyl moiety in metallatriangle (1) was
observed after binding of L with Cu(II) showing less rigidity as
compared to the free ligand. The average dihedral angle between
the plane of two phenyl ring in metallatriangle (1) was found to
be 46.04(19)° in comparison to 64.30(6)° in free ligand L. The
two units also differ in the distance between the metal centres
s
s
= ( –b)/60, ( > b),
a
a
a
s
s

K. Mahiya, P. Mathur / Inorganica Chimica Acta 399 (2013) 36–44
41
Fig. 4. ORTEP diagram of (1) drawn in 30% thermal probability ellipsoids showing two different crystallographic units in the asymmetric unit.
Fig. 5. The two units differ by distance between metal centres and distance between the centroids of the biphenyl moieties.
and distance between the centroids of the biphenyl moieties. In the
asymmetric unit 1, the distance between the metal centers is
10.4431(10) Å and in unit II, it is 10.4939(9) Å. The centroid of
the biphenyl in each unit almost bisects the arm of the triangle
(Fig. 5). Bond lengths and bond angles of metal with the coordinat-
ing atoms (i.e. N, O and Cl) were found to be slightly different in the
two units. A comparative study of bond lengths and bond angles
for (1) is given in Table 2(c). The two units lay over one another
to form hexagons with a void of 1560 Å3 in the unit cell (Fig. 6).
As suitable single crystals for the [Cu3(L)3Br3].3Br and [Cu3(L)3
(NO3)3].3NO3 could not be grown, the powder XRD pattern of both
the compound were matched with copper(II) metallatriangle re-
ported earlier [5d].
Br3].3Br.9H2O and [Cu3(L)3(NO3)3] ꢀ3(NO3) ꢀ9H2O also exist as
metallatriangles.
3.2. IR spectral properties and electronic spectroscopy
A strong band at 1623 cmꢁ1 in the free ligand L is assigned to
(m
C@O) stretching and is shifted to1610 cmꢁ1 in all the metallatrian-
gles indicating that the carbonyl oxygen of the (O@C–NH–) group
has participated in coordination with the metal ion. A strong band
at 1437 cmꢁ1 in the free ligand L is assigned to (mC@N–C@C benz-
imidazole), and is shifted to 1468 cmꢁ1 in all the metallatriangles
indicating that the imine nitrogen of the benzimidazole group
has participated in coordination with metal ion [13]. In (3) a strong
band at 1384 cmꢁ1 for nitrate stretching is observed.
The Le-Bail fit [15] of the powder X-ray diffraction pattern of
the [Cu3(L)3Br3]ꢀ3Brꢀ9H2O (Fig. 7) yielded the lattice constant
The electronic spectrum of LA and metallatriangles (1), (2) and
(3) was recorded in MeOH. For LA, two main peaks are observed
at 271 and 277 nm. In metallatriangles (1) (2) and (3), these peaks
a = 18.38818,
b = 103.25009,
b = 19.87399,
= 107.241(19); Triclinic P1.
c = 20.43810,
a = 112.69170,
ꢀ
c
The Le-Bail fit of the powder X-ray diffraction pattern of the
are observed at 272 and 279 nm due to p–
p⁄ transition in the –
[Cu3(L)3(NO3)3]ꢀ3(NO3) ꢀ9H2O (Fig. 8) yielded the lattice constant
C@N–C@C– system of the benzimidazole group [16]. A broad and
less intense d–d band was observed in the range 702–750 nm char-
acteristic of copper(II) in a distorted square pyramidal geometry.
Beside these bands a charge transfer band in the range 300–
365 nm for metallatriangles (2) and (3) is also observed [13].
a = 17.43803,
b = 82.94931,
b = 17.47857,
c = 22.16434,
a = 88.88885,
c
= 60.717(10); Triclinic P-1.
On the basis of a close fit of the a, b, c and
a, b, c parameters to
already reported metallatriangles [5d], it is proposed that [Cu3(L)3-

42
K. Mahiya, P. Mathur / Inorganica Chimica Acta 399 (2013) 36–44
Fig. 6. Unit cell packing of the title compound viewed along the crystallographic c-axis. Packing is shown in wireframe model for a better visualization.
Fig. 7. PXRD pattern of [Cu3(L)3Br3]ꢀ3Brꢀ10H2O and Le-Bail fit of the powder X-ray
diffraction pattern. Red (observed), black (calc.), blue (Obs.–Calc.), vertical line
(bragg reflection). (For interpretation of the references to colour in this figure
legend, the reader is referred to the web version of this article.)
Fig. 8. PXRD pattern of [Cu3(L)3(NO3)3]ꢀ3(NO3)ꢀ9H2O and Le-Bail fit of the powder
X-ray diffraction pattern. Red (observed), black (calculated), blue (Obs.–Calc.),
vertical line (bragg reflection). (For interpretation of the references to colour in this
figure legend, the reader is referred to the web version of this article.)
3.3. Magnetic measurements
Table 4
Solution and solid state magnetic moments of metallatriangles.
The magnetic susceptibilities for the metallatriangles were ob-
tained using the Evan’s method [17] in DMSO-d6 in solution state.
While the solid state magnetic susceptibilities were obtained by
using a vibrating sample magnetometer at room temperature.
The magnetic moment data along with appropriate diamagnetic
correction are listed in Table 4. Magnetic moment of Cu(II) metall-
atriangles at room temperature are close to theoretical value of
3.87 BM calculated for three non-interacting Cu(II) atoms with in
experimental error ( 0.2 BM) in the solution state. Earlier reports
for l3 oxo and hydroxo bridged trinuclear copper(II) complexes
find the magnetic moments at room temperature in the range
Metallatriangles Magnetic moment (leff
)
Magnetic moment (leff)
(solid state) (BM)
(solution state) (BM)
(1)
(2)
(3)
3.84
3.84
3.66
3.82
3.81
3.64
1.5–3.1 BM suggesting an antiferromagnetic coupling between
the metal centres in such complexes [5a,18,19]. While in another
case the value is reported in the range 3.33–3.56 with a weak

K. Mahiya, P. Mathur / Inorganica Chimica Acta 399 (2013) 36–44
43
ferromagnetic coupling between the metal centres in the trinuclear
copper complexes [20]. In the present case both the solid state
and solution state magnetic moment values are close to spin only
only a 9% product (acid + aldehyde) formation occurred. In the
presence of metallatriangle, the conversion of 54% (acid + alde-
hyde) to 100% was observed (Table 5).
value of three non-interacting copper(II), a result ascribed to the
0
long bridging distance of ꢃ10 ÅA between the three copper(II)
3.5. Kinetic Studies
centers.
The formation of 4-methylbenzaldehyde was studied by
continuously monitoring the growth of a band in the region
(257–254 nm) which arises due to electronic transitions involving
the aromatic ring conjugation with the carbonyl group [21]. The
initially formed band at 257–254 nm becomes broad and another
band also starts to arise at ꢃ246 nm due to the formation of
4-methylbenzoic acid along with the 4-methylbenzaldehyde. The
3.4. Metallatriangle as catalyst in the oxidation of aromatic alcohols
The oxidation of the two substituted benzyl alcohols was stud-
ied using tert-butyl hydro peroxide (TBHP) as an alternate source
of oxygen in acetonitrile in the presence of the copper(II) metall-
atriangles heterogeneously. In the absence of the metallatriangle,
Table 5
Oxidation of alcohols by metallatriangle (1) (2) and (3) using TBHP as oxidant in acetonitrile. Catalyst:substrate:oxidant ratio is 1:60:60, temperature 60 °C.
Substrate (S)
Metallatriangle (catalyst)
Reusability
(%) Yielda (A)
(%) Yielda (B)
Substrate left S (%)
(%) yield (A + B)
4-Methyl benzyl alcohol
(1)
1st use
2nd use
3rd use
24.17
28.80
37.37
56.12
37.87
19.68
16.71
28.85
40.41
80.29
66.67
57.05
4-Methyl benzyl alcohol
(2)
1st use
–
1.50
–
96.00
–
2.50
–
97.50
–
3rd use
1.61
98.39
00.00
100.00
4-Methyl benzyl alcohol
(3)
(1)
(2)
1st use
1st use
1st use
35.30
25.33
2.33
18.45
49.45
88.41
41.53
25.23
7.07
53.75
74.78
90.74
2,4-Dimethyl benzyl alcohol
2,4-Dimethyl benzyl alcohol
a
Conversions were determined using naphthalene as an internal standard.
Fig. 9. (A) Curve a: UV-spectra of 0.16 mmol solution of 4-methylbenzyl alcohol in the absence of catalyst and oxidant. Curve b–j: UV spectra 0.16 mmol solution of 4-
methylbenzyl alcohol after 5, 10, 15, 20, 35, 55, 95, 115 and 150 min, respectively in presence of TBHP (0.16 mmol) and catalyst (0.0042 mmol) at 60 °C. (B) Showing the
formation of the 4-methyl benzaldehyde(Molar) with time.
Fig. 10a. SEM micrographs showing the surface morphology of metallatriangle (1). A (pure sample), B (after 1st use), C (after 2nd use), D (3rd use).

44
K. Mahiya, P. Mathur / Inorganica Chimica Acta 399 (2013) 36–44
Fig. 10b. SEM micrographs showing the surface morphology of metallatriangle (2). A (pure sample), B (after 1st use), C (3rd use).
initial and average rate of formation is found to be in the order of
2.79 ꢂ 10ꢁ3 and 1.86 ꢂ 10ꢁ3 mol Lꢁ1 sꢁ1, respectively. The rate of
formation of product is found to be almost independent of the
amount of catalyst employed (Fig. 9A and 9B).
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Acknowledgements
The authors are grateful for financial support from University of
Delhi for a special grant. One of the authors is grateful to UGC for
providing a Senior Research Fellowship (SRF). We are thankful to
Prof. M.S. Hundal, Guru Nanak Dev University, Amritsar, India for
his help in crystal structure solution and refinement.
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Appendix A. Supplementary material
CCDC 890173, 890172 and 779116 contain the supplementary
crystallorgaphic 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
http://dx.doi.org/10.1016/j.ica.2012.12.027. Supplementary data
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.ica.2012.12.037.
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