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K. Mahiya et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 663–668
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Preparation of N2,N2 -bis[(1-butyl-benzimidazol-2yl)methyl]biphenyl-
2,20-dicarboxamide (L)
Introduction
The assembly of metallacycles is an area of current interest due
to applications as functional materials in areas of gas storage, catal-
ysis and magnetism [1]. Amongst the multinuclear complexes, the
trinuclear copper clusters have gained attention as structural mim-
ics for multicopper oxidases. A trinuclear copper center has been
elucidated for ascorbate oxidase and laccase, which carries out a
four electron reduction of dioxygen at the trinuclear center [2].
Earlier studies on trinuclear copper(II) complexes have revealed
that they can exists as equilateral triangular [3], isosceles-
triangular [4] or linear arrays [5]. The trinuclear complexes that
have large bridging groups offer an opportunity to study long range
superexchange interactions between metal ions [6]. With the
above facts in mind, we report the synthesis and structural charac-
terization of a series of copper(II) trinuclear clusters formed
through the sharing of benzimidazolyl arm of a bis-benzimidazolyl
diamide ligand.
This ligand was prepared by following the procedure as
reported by Mathur et al. [7] and outlined in scheme 1. The struc-
ture was confirmed by 1H and 13C NMR spectroscopy, (see support-
ing information Figs. S1 and S2).
Yield: (50%); m.p. 150 °C. Anal. Calcd. for C38H40N6O2ꢁH2O: C,
68.46; H, 6.90; N, 12.6. Found: C, 68.21; H, 6.53; N, 12.40. 1H-
NMR(DMSO-d6, dppm): 9.54 (t, J = 5.8 Hz, 2H), 7.05 (dd, J = 7.6 Hz,
2H), 7.21 (m, 8H), 7.45 (m, 4H), 7.57 (dd, J = 7.5 Hz, 1.6 Hz, 2H),
4.52 (s, 4H), 4.01 (t, J = 7.4 Hz, 4H), 1.51 (m, 4H), 1.14 (m, 4H),
0.81 (t, J = 7.2 Hz, 6H). 13C-NMR(DMSO-d6, dppm): 13.54, 19.43,
35.54, 42.86, 31.41, 110.44, 118.33, 121.81, 122.34, 135.93,
138.27, 150.84, 126.94, 127.61, 128.96, 129.54, 134.81, 140.93,
169.11. UV–vis (Methanol, kmax, nm, loge
Mꢂ1 cmꢂ1): 276(4.11),
284(4.02). IR (KBr pellets, cmꢂ1): 3440 (m), 3228 (m), 2958 (m),
1654 (vs), 1545 (vs), 1458 (vs), 743 (vs).
Preparation of copper(II) metallatriangles
Experimental section
Preparation of 1, 2 and 3
To a methanolic solution of L, (0.163 mmol, 5.0 ml), CuX2ꢁ2H2O,
X = Cl, Br and NO3 (0.163 mmol), predissolved in 5.0 ml methanol
was added dropwise at room temperature. The desired product
formed immediately as a solid. It was filtered, washed with meth-
anol and dried in vacuum over P2O5.
Materials and method
All the reagents and solvents were purchased from commercial
sources. 2,20-Diphenic acid was purchased from Sigma–Aldrich and
all other chemicals were of analytical grade and used as received.
2,4,6-tri-tert-butyl phenol, 2-amino-5-methyl phenol, 2-amino-4-
tert-butyl phenol were purchased from Sigma Aldrich. 2-Aminom-
ethylbenzimidazolyl dihydrochloride was prepared following the
procedure reported by Cescon and Day. HPLC grade solvents were
used for spectral work. IR spectra were obtained in the solid state
[Cu3(L)3Cl3]ꢁ3Clꢁ3H2O, 1. Yield 80%, m.p.: 207 °C. Anal. Calcd. for
C
114H120N18O6Cl6Cu3ꢁ3H2O: C, 59.64; H, 5.49; N, 10.98. Found: C,
59.88: H, 5.12; N, 11.07. IR (KBr pellets, cmꢂ1): 3448 (m) 3253
(m), 2958 (m), 2871(m), 1608 (vs), 1541 (s), 1471 (s), 742 (s).
UV–vis (Acetonitrile, kmax
,
nm, loge
Mꢂ1 cmꢂ1): 275(4.76),
as KBr pellets on
a Perkin Elmer FTIR-2000 spectrometer.
282(4.68), 740(2.86).
Electronic spectra were obtained on a Shimadzu UV–vis-1601
Spectrometer. Melting points were measured on BUCHI Melting
point M-560 apparatus at a heating rate of 10 °C in glass capillaries.
[Cu3(L)3Br3]ꢁ3Brꢁ3H2O, 2. Yield 90%; m.p.: 197 °C Anal. Calcd. for
C
114H120N18O6Br6Cu3.3H2O: C, 53.42; H, 4.92; N, 9.84. Found: C,
53.65; H, 4.70; N, 9.75. IR (KBr pellets, cmꢂ1): 3447 (m) 3153
(m), 2959 (m), 2871 (m), 1608 (vs), 1542 (s), 1465 (s), 741 (s).
Instrumentations
UV–vis (Acetonitrile, kmax
,
nm, loge
Mꢂ1 cmꢂ1): 275(4.80),
283(4.73), 306(4.26), 742(2.95).
The micro analytical data were obtained from the Elemental
Analyzer System GmbH Vario EL-III instrument. 1H (400 MHz)
and 13C (100 MHz) NMR spectra were recorded on
a JEOL
[Cu3(L)3(NO3)3]ꢁ3NO3ꢁ9H2O, 3. Yield 84%; m.p.: 230 °C. Anal. Calcd.
for C114H120N24O24Cu3.9H2O: C, 53.05; H, 5.42; N, 13.03. Found:
C, 52.17; H, 4.96; N, 12.87. IR (KBr pellets, cmꢂ1): 3433 (m) 3185
(m), 2960 (m), 2932 (m), 1602 (vs), 1543 (s), 1466 (s), 743 (s),
1384 (vs), 1296 (s), 1497 (s). UV–vis (Acetonitrile, kmax, nm,
ECX-400P NMR spectrometer using tetramethylsilane (TMS) as
an internal reference. The single crystal diffraction data were col-
lected on an X’Calibur single crystal X-ray diffractor having CCD
camera [Mo/Ka radiation (k = 0.71073 Å)] at Department of chem-
loge
Mꢂ1 cmꢂ1): 276(4.65), 283(4.56), 732(2.18).
istry, University of Delhi, India. Magnetic measurements were per-
formed on polycrystalline samples with a Quantum Design SQUID
magnetometer equipped with a 5 T magnet, at Instituto de Ciencia
Molecular (ICMol), Universidad de Valencia, Spain. The magnetic
data of 1–4 were corrected for the diamagnetic contribution of
the constituent atoms as well as for the sample holder. A value
of 60 ꢄ 10ꢂ6 cm3 molꢂ1 was used for the temperature-independent
paramagnetism of the copper(II) ion.
Preparation of 4
Cu(II) benzoate (0.163 mmol) was prepared by adding KOH to a
solution of cupric chloride in water, centrifuging the precipitated
copper hydroxide and suspending in 5 ml of MeOH, addition of
benzoic acid causes dissolution to give a solution of Copper(II) ben-
zoate in desired molarity. This solution was added dropwise at
Scheme 1. Reagents and conditions: (i) pyridine, triphenyl phosphite; (ii) KOH, dry DMF, n-butyl bromide.