Synthesis, characterization and complexation studies of some novel cyclophane amides and sulfonamides

Article abstract of DOI:10.1016/j.tetlet.2009.12.077

A series of tricyclic tetraamides have been synthesized and were characterized from spectral and XRD studies. XRD studies revealed that the pyridine-based tricyclic cyclophane amide exists with twisted phenyl rings. All the cyclophane compounds form charge-transfer (CT) complexes with TCNQ. Metal ion complexation studies show that the cyclophane amides are more selective towards Cu(II) ions rather than Ni(II) and Cd(II) ions.

Full text of DOI:10.1016/j.tetlet.2009.12.077

Tetrahedron Letters 51 (2010) 1059–1063
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Tetrahedron Letters
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Synthesis, characterization and complexation studies of some novel
cyclophane amides and sulfonamides
b
Perumal Rajakumar a, , Ramar Padmanabhan
*
a Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, India
b Research and Development Centre, Orchid Chemicals and Pharmaceuticals Ltd, Sholinganallure, Chennai 600 119, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of tricyclic tetraamides have been synthesized and were characterized from spectral and XRD
studies. XRD studies revealed that the pyridine-based tricyclic cyclophane amide exists with twisted phe-
nyl rings. All the cyclophane compounds form charge-transfer (CT) complexes with TCNQ. Metal ion com-
plexation studies show that the cyclophane amides are more selective towards Cu(II) ions rather than
Ni(II) and Cd(II) ions.
Received 13 September 2009
Revised 11 December 2009
Accepted 15 December 2009
Available online 21 December 2009
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Tricyclic amides
Cyclophane tetraamides
Charge transfer
The enhanced applications of aza crown ethers in supramolecu-
lar chemistry1–5 have influenced the synthetic chemist to modify
the molecular structure. The most important aspect of supramolec-
ular chemistry is the host–guest complexation process. Hence the
basic crown ether structures were modified significantly to in-
crease the selectivity and specificity of guest molecules for com-
plexation. One of the key modifications is the replacement of
oxygen donor atoms by sulfur and/or by nitrogen atoms.6 The
other significant modification is the insertion of functional groups,
viz., amides and esters in the macrocyclic ring system.7–10 Synthe-
sis of amide-based supramolecular systems have been reported in
the literature.11–15 Neutral macrocyclic amides display anion-bind-
ing properties.16 In fact peptides exhibit molecular shuttling
through anion recognition.17 Interactions between electron donors
and complementary electron acceptor groups in cyclophanes can
form intramolecular charge-transfer (CT) complexes and can exhi-
Five different cyclophane amide derivatives 1–5 shown in
Figure 1 were synthesized from m-xylylenediamine (Schemes 1
and 2). Reaction of 1 equiv of m-xylylenediamine 6 and 1 equiv of
isophthalaldehyde 7 in ethanol under high-dilution conditions24
at room temperature resulted in the formation of cyclophane tetrai-
mine 8 in 95% yield. The product was slowly precipitated from the
reaction mixture during the course of the reaction and used without
further purification. Reduction of cyclophane imine 8 with sodium
borohydride in toluene–THF–MeOH mixture at 0–5 °C afforded sec-
ondary tetraamine cyclophane 9 in about 80% yield25 and the prod-
uct was purified from cold acetonitrile (Scheme 1). The tetraamine
cyclophane 9 was recrystallized from chloroform. The structure of
tetraamine cyclophane 9 was confirmed from the spectroscopic
and XRD data. The 1H NMR spectrum of tetraamine cyclophane 9
displayed the N-methylene protons as a singlet at d 3.79. The rest
of the aromatic protons appeared in the region ranging from d
7.20–7.29. In the 13C NMR spectrum of 9, the N-methylene carbons
appeared at d 53.8. The structure of 9 was also confirmed by XRD.
The crystal parameters for cyclophane amine 9 are given in Table
1 and ORTEP diagram is shown in Figure 2.
In order to test the synthetic utility of secondary tetraamine
cyclophane 9 for the synthesis of tricyclic amide, 1.0 equiv of cyclo-
phane amine 9 was coupled with 2.0 equiv of isophthaloyl chloride
10, pyridine-2,6-dicarboxylic acid chloride 11, benzene-1,3-dis-
ulfonyl chloride 12 in the presence of triethylamine in dry DCM
at room temperature under high dilution conditions.26 The reac-
tion afforded the tricyclic cyclophane amides 1,27 228 and 329 in
65%, 70% and 75% yields, respectively, after purification by column
chromatography (Scheme 1). The amide 2 was recrystallized from
chloroform/acetonitrile mixture. The structure of cyclophane
bit self complementary properties in addition to
p–p interac-
tions.18–20 Furthermore such cyclic amides can form complexes
with metal ions like Cd(II),21 Fe(III)22 and Cu(II)23 and hence they
can be used for selective metal ion complexation. Hence it is of
interest to synthesize and study the CT, metal complexation prop-
erties of novel cyclophane amides. Herein, we report the synthesis
of tricyclic cyclophane amides 1 and 2, cyclophane sulfonamide 3
and monocyclic cyclophane amides 4 and 5 along with charge
transfer complex studies with TCNQ and also metal complexation
studies with Cu(II), Ni(II) and Cd(II) ions.
* Corresponding author. Tel.: +91 4422351269; fax: +91 4422352494.
E-mail address: perumalrajakumar@hotmail.com (P. Rajakumar).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.12.077

1060
P. Rajakumar, R. Padmanabhan / Tetrahedron Letters 51 (2010) 1059–1063
O
O
O
O
O
O
N
S
N
S
N
O
O
N
N
N
N
N
N
N
N
N
N
O
O
S
N
S
O
O
O
O
O
O
1
2
3
O
O
O
O
N
NH
NH
HN
HN
NH
NH
HN
HN
N
O
O
O
O
5
4
Figure 1. Structures of cyclophane amides 1–5.
amides 1–3 was confirmed from the spectroscopic and XRD data.
The 1H NMR spectrum of cyclophane amide 2 displayed four sets
of doublets for the N-methylene protons at d 3.80, d 5.00, d 5.10
and d 5.41. The rest of the aromatic protons appeared between d
6.95 and 7.94. In the 13C NMR spectrum of cyclophane amide 2,
the N-methylene carbons appeared at d 50.8 and d 55.0 and car-
bonyl carbon at d 169.2. FT-IR spectrum shows the carbonyl
stretching frequency at 1631 cmÀ1 for the cyclophane amide 2.
XRD analysis of compound 2 shows that out of four benzene rings,
two of them are parallel to each other. Moreover, the pyridine moi-
eties are parallel to each other. XRD studies indicate that intermo-
lecular hydrogen bonding exists between cyclophane amide 2 and
water. The crystal parameters for cyclophane amide 2 are given in
Table 2 and ORTEP diagram is shown in Figure 3.
TCNQ shows an absorption maximum at 395.0 nm. Cyclophanes
1, 2, 3, 4 and 5 form a charge transfer complex with TCNQ as evi-
denced by the appearance of absorption maxima at 843.5, 842.0,
842.5, 843.0 and 842.5 nm, respectively. (Table 3, Figs. 4 and 5)
The plot of (concentration of cyclophane)/absorbance (Y/A) versus
1/concentration of guest (1/X) was linear. Benesi–Hildebrand
equation was employed to calculate Ka values.34 From the slope
and the intercept values, Ka (Ka = intercept  slopeÀ1) and
e (e
= interceptÀ1) were evaluated. The plot was linear suggesting that
the predominate species in solution as a 1:1 complex (Fig. 6). Nhe
Ka,
e and r values of the CT complexes formed from 1, 2, 3, 4 and 5
with TCNQ are shown in Tables 4 and 5.
Complexation studies were carried out with cyclophane amides,
1, 2, 3, 4 and 5 with Cu(II) acetate in a mixture of CHCl3 and etha-
nol.35 The complex formation was studied using an absorption
spectrophotometer by following the maximum absorption of the
ligands. Further studies show that the shift of the maximum
absorption towards the higher wavelength was observed with
Cu(II) complexes (Table 6). However, the complexation studies
with Ni(II) acetate and Cd(II) acetate did not show any shift in
the maximum absorption of the ligand band. Thus the cyclophane
amides 1, 2, 3, 4 and 5 are more selective towards the Cu(II) rather
than Ni(II) or Cd(II) ions. This selectivity is due to the cavity size
(0.73–0.85 Å) which matches with the size of Cu(II) ion (0.73 Å)
rather than Ni(II) (0.69 Å) and Cd(II) (0.95 Å) ions. Thus cyclophane
amides 1, 2, 3, 4 and 5 form complexes with Cu(II) rather than
Ni(II) and Cd(II) ions. Further the presence of Ni(II) ions or Cd(II)
ions did not interfere with the formation of a complex by the
receptor molecules with Cu(II).
However, the reaction between m-xylylenediamine
6 and
isophthaloyl chloride 10, pyridine-2,6-dicarboxylic acid chloride
11 in the presence of triethylamine in dry DCM at room tempera-
ture under high dilution conditions30 afforded the cyclophane
amides, 431 and 532 each in about 80% yield (Scheme 2). The 1H
NMR spectrum of cyclophane amide 4 displayed the N-methylene
protons as a doublet at d 4.44 and NH protons as a triplet at d 9.08.
The rest of the aromatic protons appeared in the region ranging
from d 7.19–8.38. In the 13C NMR spectrum of 4, the N-methylene
carbons appeared at d 42.69 and the carbonyl carbon at d 165.3 and
d 165.8. FT-IR spectrum shows the carbonyl stretching frequency at
1638 cmÀ1 for compound 4. The structure of the cyclophane amide
4 has been confirmed from the spectral data. Similarly the struc-
ture of the cyclophane amide 5 was also confirmed from spectral
and analytical data.
Cyclophane amides 1, 2, 3, 4 and 5 exhibited charge transfer
complexes with TCNQ.33 Complexation studies of compounds 1,
2, 3, 4 and 5 with TCNE and PQT were not successful. Cyclophanes
1, 2, 3, 4 and 5 show UV–Vis absorption maxima at 225.5, 261.0,
262.0, 255.0 and 258.0 nm, respectively. However, the acceptor
In summary we have synthesized various cyclophane amides
which show strong CT interactions selectively with TCNQ rather
than TCNE and PQT. Complexation studies of all the five cyclo-
phane amides show that they are more selective towards the Cu(II)
rather than Ni(II) and Cd(II) ions. The biological activity and de-

P. Rajakumar, R. Padmanabhan / Tetrahedron Letters 51 (2010) 1059–1063
1061
N
N
i
7
NH2
NH2
N
N
6
8
ii
NH
NH
HN
HN
9
iii
12
10
v
iv
11
O
O
O
O
O
O
N
S
S
N
O
O
N
N
N
N
N
N
N
N
N
N
N
O
O
S
N
S
O
O
O
O
O
O
2
3
1
Scheme 1. Reagents and conditions: (i) isophthalaldehyde 7, ethanol, rt, 48 h, 8 (95%); (ii) NaBH4, toluene–THF–MeOH, 0–5 °C, 1 h, 9 (80%); (iii) isophthaloyl chloride 10, TEA,
DCM, rt, 24 h, 1 (65%); (iv) pyridine-2,6-dicarboxylic acid chloride 11, TEA, DCM, rt, 24 h, 2 (70%) and (v) benzene-1,3-disulfonylchloride 12, TEA, DCM, rt, 24 h, 3 (75%).
O
O
O
O
N
NH
NH
HN
HN
NH
NH
HN
HN
11
ii
10
i
NH2
NH2
N
O
O
O
O
5
4
Scheme 2. Reagents and conditions; (i) isophthaloyl chloride 10, TEA, DCM, rt, 24 h, 4 (80%) and (ii) pyridine-2,6-dicarboxylic acid chloride 11, TEA, DCM, rt, 24 h, 5 (80%).

1062
P. Rajakumar, R. Padmanabhan / Tetrahedron Letters 51 (2010) 1059–1063
Table 4
Benesi–Hildebrand treatment data of the CT complex formed between the cyclophane
amide, 1 and TCNQ
Concd of guest, [X] (M)
Absorbance (Å)
[Y]/A(M)
1/[X] (MÀ1
)
4.9 Â 10À6
9.8 Â 10À6
14.7 Â 10À6
19.6 Â 10À6
24.5 Â 10À6
29.4 Â 10À6
0.066
0.113
0.155
0.171
0.202
0.230
0.0003540
0.0002080
0.0001506
0.0001360
0.0001160
0.0001018
204,081
102,040
68,027
51,020
40,816
34,013
kmax = 843.5 nm; concentration of cyclophane amide, 1 = 2.34 Â 10À5 M.
Ka = 3.79 Â 104 MÀ1
;
e
= 1.80 Â 104 [MÀ1 cmÀ1] and r = 0.9991.
Table 5
Complexation of TCNQ with cyclophane amides 1, 2, 3, 4 and 5
Cyclophane amide
Ka (molÀ1 dm3)
e
(MÀ1 cmÀ1
)
r
1
2
3
4
5
3.79 Â 104
1.57 Â 104
1.11 Â 104
6.34 Â 103
1.22 Â 104
1.80 Â 104
2.03 Â 104
2.34 Â 104
2.48 Â 104
1.68 Â 104
0.9991
0.9996
0.9999
0.9997
0.9981
Figure 2. ORTEP diagram of cyclophane tetraamine 9.
Table 6
Complexation of Cu (II) acetate with cyclophane amides 1, 2, 3, 4 and 5
Cyclophane amide
k
(nm) of the
k
(nm) of
max
max
cyclophane amide
Cu(II) complex
1
2
3
4
5
225.5
261.0
262.0
255.0
258.0
697.0
785.5
694.0
710.0
670.5
kmax for Cu(II) acetate is 427.0 nm.
Acknowledgements
The authors thank DST, New Delhi, for financial assistance, UGC
SAP for facility provided for XRD data, RSIC, CDRI, Lucknow, for FAB
MS, and DST-FIST for providing NMR facility for the Department.
R.P. thanks Orchid Chemicals & Pharmaceuticals Ltd. for providing
the laboratory and analytical facility.
Figure 3. ORTEP diagram of cyclophane amide 2.
Supplementary data
X-ray crystal data for cyclophane tetraamine 9 (Table 1) and
cyclophane amide 2 (Table 2) are available. Crystallographic data
for the structures in this paper have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary publication
numbers CCDC 743880 and CCDC 743881. Copies of the data can
be obtained, free of charge, on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [e-mail: deposit@ccdc.cam.ac.uk]. kmax for
cyclophane amides and TCNQ complex of cyclophane amides 1, 2,
3, 4 and 5 (Table 3), CT spectra of cyclophane amides (Figs. 4 and 5)
are also available. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.tetlet.2009.
12.077.
Cyclophane amide 1
0.0004
0.00035
0.0003
0.00025
0.0002
0.00015
0.0001
0.00005
0
0
50000
100000
150000
200000
250000
1/X
References and notes
Figure 6. Plot between 1/X and Y/A for cyclophane amide 2.
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1063
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(KBr, cmÀ1): 1631, 1421; 1H NMR (400 MHz, CDCl3) d 3.80 (d, 4H, J = 14.2 Hz),
5.00 (d, 4H, J = 15.7 Hz), 5.10 (d, 4H, J = 15.5 Hz), 5.41 (d, 4H, J = 14.1 Hz), 6.96
(t, 4H, J = 7.5 Hz), 7.06 (d, 4H, J = 6.8 Hz), 7.23–7.25 (m, 2H), 7.37 (s, 2H,), 7.94
(t, 8H, J = 12.8 Hz); 13C NMR (100 MHz, CDCl3) d 50.8, 55.0, 125.7, 126.2, 127.0,
127.5, 128.1, 128.5, 129.1, 137.1, 138.3, 138.6, 152.4, 169.2; MS (ES) m/z: 739.3
(M+1), Elemental Anal. Calcd for C46H38N6O4: C, 74.78; H, 5.18; N, 11.37.
Found: C, 74.92; H, 5.41; N, 11.87.
29. Spectral data for cyclophane amide 3: Yield 75%; mp 370 °C (decomposed); IR
(KBr, cmÀ1): 1624, 1449, 1334; 1H NMR (400 MHz, DMSO-d6) d 3.65 (s, 4H),
4.17 (s, 4H), 4.37 (s, 8H), 7.15–7.18 (m, 5H), 7.24–7.29 (m, 8H), 7.53 (d, 1H,
J = 7.8 Hz), 7.60 (d, 2H, J = 7.5 Hz), 7.66 (t, 2H, J = 7.7 Hz), 7.83 (s, 1H), 7.94 (t,
3H, J = 8.8 Hz), 9.13 (bs, 2H); 13C NMR (100 MHz, DMSO-d6) d 45.6, 48.9, 49.3,
51.8, 124.0, 127.3, 128.3, 128.7, 128.9, 129.1, 129.2, 129.3, 129.5, 129.6, 130.1,
130.4, 130.8, 131.3, 132.0, 132.3, 136.8, 138.5, 149.4; MS (ES) m/z: 881.1 (M+1),
Elemental Anal. Calcd for C44H40N4O8S4: C, 59.98; H, 4.58; N, 6.36. Found: C,
60.23; H, 4.65; N, 6.42.
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Chem. 2006, 14, 7458; (b) Rajkumar, P.; Abdul Rasheed, A. M.; Rabia, A. I.;
Chamundeeswari, D. Bioorg. Med. Chem. Lett. 2006, 16, 6019.
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17. Claire, M. K.; David, A. L. Angew. Chem., Int. Ed. 2004, 43, 1222.
18. (a) Bauer, H.; Stier, F.; Petry, C.; Stadler, C.; Staab, H. A. Eur. J. Org. Chem. 2001,
3255–3279; (b) Sorenson, A. P.; Nielsen, M. B.; Becher, J. Tetrahedron Lett. 2003,
44, 2979.
30. General procedure for the synthesis of cyclophane amides 4 and 5: A solution of
m-xylylenediamine
6 (7.3 mmol) in dry dichloromethane (400 mL) and a
19. Srinivasan, K.; Rajakumar, P. Supramol. Chem. 2005, 17, 215.
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21. Didier, C.; Pierre, R. C. J. Chem. Soc., Perkin Trans. 2 1994, 891.
22. Bruce, H. R.; Andrew, D. H. J. Chem. Soc., Chem. Commun. 1987, 171.
23. (a) Inoue, M. B.; Medrano, F.; Inoue, M.; Raitsimring, A.; Fernando, Q.
Inorg. Chem. 1997, 36, 2335; (b) Inoue, M. B.; Velazquez, E. F.; Medrano,
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37, 4070.
solution of the corresponding diacidchloride (7.3 mmol) in dichloromethane
(400 mL) were simultaneously added dropwise to a well-stirred solution of
triethylamine (23.7 mmol) in dry dichloromethane (1000 mL) for 8 h. After the
addition was completed the reaction mixture was stirred for another 24 h. The
solvent was removed at reduced pressure and the solid obtained was washed
with water (2 Â 200 mL) to remove triethylammonium chloride and then
washed with dichloromethane (25 mL), which was purified by column
chromatography (SiO2).
24. Shinubu, H.; Shinya, C.; Hitoshi, O.; Masahiko, Y. Heterocycles 2002, 57, 1091.
31. Spectral data for cyclophane amide 4: Yield 80%; mp >370 °C; IR (KBr, cmÀ1):
1638, 1542, 1303; 1H NMR (400 MHz, DMSO-d6) d 4.44 (d, 8H, J = 5.9 Hz), 7.19–
7.30 (m, 8H), 7.48 (t, 2H, J = 7.7 Hz), 7.95–7.99 (m, 4H), 8.28 (s, 2H), 9.08 (t, 4H,
J = 5.8 Hz); 13C NMR (100 MHz, DMSO-d6) d 42.7, 125.2, 126.1, 126.6, 128.0,
128.3, 129.8, 134.1, 134.5, 139.6, 139.8, 165.3, 165.8; MS (ES) m/z: 533 (M+1),
Elemental Anal. Calcd for C32H28N4O4: C, 72.16; H, 5.30; N, 10.52. Found: C,
72.46; H, 5.38; N, 10.61.
25. Procedure for the synthesis of cyclophane imine 8:
A
solution of m-
solution of
xylylenediamine (15.2 mmol) in ethanol (400 mL) and
6
a
isophthalaldehyde 7 (15.2 mmol) in ethanol (400 mL) were simultaneously
added dropwise to a well-stirred solution of ethanol (800 mL) for 6 h. After the
addition was completed the reaction mixture was stirred for another 48 h. The
precipitated solid was filtered, washed with ethanol and dried.
26. General procedure for the synthesis of tricyclic cyclophane amides 1–3: A solution
of tetraamine 9 (1.05 mmol) in dry dichloromethane (250 mL) and a solution of
the corresponding diacid chloride (2.10 mmol) in dichloromethane (250 mL)
32. Spectral data for cyclophane amide 5: Yield 80%; mp 259 °C; IR (KBr, cmÀ1):
1658, 1534, 1445; 1H NMR (400 MHz, DMSO-d6) d: 4.48 (br s, 8H), 7.11–7.21
(m, 8H), 8.06–8.18 (m, 6H), 9.80 (br s, 4H); 13C NMR (100 MHz, DMSO-d6) d:
42.1, 124.3, 125.5, 128.4, 139.3, 139.5, 148.5, 163.3; MS (FAB+) m/z: 534 (M),
Elemental Anal. Calcd for C30H26N6O4: C, 67.40; H, 4.90; N, 15.72. Found: C,
67.56; H, 4.98; N, 15.93.
33. CT complexation studies of cyclophane amides 1, 2, 3, 4 and 5 with TCNQ: A
solution of TCNQ (4.9 Â 10À6 M) in a 1:1 mixture of CHCl3/CH3CN at various
dilutions (1 mL, 2 mL, 3 mL, 4 mL, 5 mL and 6 mL) were prepared and added to
the solution of the cyclophane amide 1, 2, 3, 4 and 5 (2.34 Â 10À5 M) in a 1:1
mixture of CHCl3/CH3CN (3 mL) in a quartz cuvette of path length 1 cm. The
UV–Vis spectrum was also obtained for each of the sample separately and the
changes in the absorbance of CT bands were recorded.
were simultaneously added dropwise to
a
well-stirred solution of
triethylamine (4.2 mmol) in dry dichloromethane (500 mL) for 6 h. After the
addition was completed the reaction mixture was stirred for another 24 h. The
solvent was removed at reduced pressure and the residue obtained was then
dissolved in chloroform (250 mL), washed with water (2 Â 200 mL) to remove
triethylammonium chloride and then dried over anhydrous sodium sulfate.
Removal of the chloroform under reduced pressure gave the corresponding
cyclophane amide as
chromatography (SiO2).
a crude material, which was purified by column
Similar procedure was adopted for the synthesis of compound, 3 by using the
corresponding 1,3-benzenedisulfonylchloride.
34. Benesi, H. A.; Hildebrand, J. H. J. Am. Soc. 1949, 71, 2703.
27. Spectral data for cyclophane amide 1: Yield 65%; mp 176 °C; IR (KBr, cmÀ1):
1639, 1406; 1H NMR (400 MHz, CDCl3) d 4.10 (d, 8H, J = 14.7 Hz), 4.81 (d, 8H,
J = 14.7 Hz), 7.15(d, 8H, J = 7.5 Hz), 7.23 (d, 4H, J = 7.5 Hz), 7.63 (ABq, 12H,
J = 7.6 Hz); 13C NMR (100 MHz, CDCl3) d 45.2, 49.4, 51.0, 53.6, 57.1, 124.8,
125.5, 127.1, 127.1, 127.2, 127.8, 128.0, 128.4, 128.9, 129.0, 129.2, 130.0, 130.7,
131.2, 136.3, 137.4, 137.5, 140.3, 160.7, 170.1, 172.7, 174.3; MS (ES) m/z: 737.2
(M+1), Elemental Anal. Calcd for C48H40N4O4: C, 78.24; H, 5.47; N, 7.60. Found:
C, 78.63; H, 5.31; N, 7.92.
35. Complexation studies of cyclophane amides 1, 2, 3, 4 and 5 with Cu(II), Ni(II) and
Cd(II) acetates: A solution of copper(II) acetate monohydrate (0.054 mmol) in
ethanol (10 mL) was added to a solution of cyclophane amides 1, 2, 3, 4 and 5
(0.054 mmol) in 10 mL chloroform. The mixture was kept at room temperature
for 1 h and UV–Vis spectrum was recorded. The absorbance maxima were
observed at 697.0, 785.5, 694.0, 710.0 and 670.5 nm, respectively, indicate the
formation of Cu(II) complex with the amides. Similarly experiments were
carried out with Ni(II) and Cd(II) acetates also.