Synthesis, electrochemical, magnetic, catalytic and antimicrobial studies of N-functionalized cyclam based trinuclear copper(II) and nickel(II) complexes

Article abstract of DOI:10.1007/s10847-009-9621-y

Trinuclear copper(II) and nickel(II) complexes have been prepared by using Schiff base ligands derived from 1,8-[bis(3-formyl-2-hydroxy-5-methyl) benzyl]-4,11-dimethyl-l,4,8,11-tetraazacyclotetradecane, and 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-4,11

Full text of DOI:10.1007/s10847-009-9621-y

J Incl Phenom Macrocycl Chem (2010) 66:297–306
DOI 10.1007/s10847-009-9621-y
ORIGINAL ARTICLE
Synthesis, electrochemical, magnetic, catalytic and antimicrobial
studies of N-functionalized cyclam based trinuclear copper(II)
and nickel(II) complexes
S. Sreedaran Æ K. Shanmuga Bharathi Æ
A. Kalilur Rahiman Æ L. Jagadish Æ V. Kaviyarasan Æ
V. Narayanan
Received: 30 December 2008 / Accepted: 22 June 2009 / Published online: 18 July 2009
Ó Springer Science+Business Media B.V. 2009
Abstract Trinuclear copper(II) and nickel(II) complexes
have been prepared by using Schiff base ligands derived
from 1,8-[bis(3-formyl-2-hydroxy-5-methyl) benzyl]-4,11-
dimethyl-l,4,8,11-tetraazacyclotetradecane, and 1,8-[bis(3-
formyl-2-hydroxy-5-bromo)benzyl]-4,11-dimethyl-l,4,8,
11-tetraazacyclotetradecane with aliphatic and aromatic
diamines. All the complexes were characterized by ele-
mental and spectroscopic analysis. Electrochemical studies
of the copper(II) complexes in DMF solution show three
Keywords Tricompartmental ligand ꢀ Cyclam ꢀ
Copper(II) complexes ꢀ Catecholase ꢀ Cyclicvoltammetry ꢀ
Antifungal activity
Introduction
Polyamine macrocyclic ligands with one or more pendant
arms containing a potentially coordinating group such as
carboxylate, pyridine, amine, etc. have been prepared but
they generally have been found not to bind a second metal
ion [1]. N-functionalized derivatives of these ligands con-
tinue to be explored in a variety of contexts such as
molecular recognition of DNA and RNA [2] depending
upon their coordination properties of the pendant donor
groups. In recent years, there has been a considerable
interest in the synthesis of polyamine ligands able to bind
two or more metal ions in close proximity. Special atten-
tion has been devoted to macrocyclic ligands, because of
their ability to enforce a high degree of reorganization on
metal coordination [3–5]. In particular, polyamine macro-
cyclic ligands with a large number of donors, appropriate
cavity size, shape and dimension may be able to hold two
or more metal centers at short distances, mimicking the
multinuclear metal arrays at the active sites of several
metalloenzymes. Asymmetric nature of a number of
homotrinuclear transition metal-derived metallobiosite and
the ability of the individual metal ions to have quite distinct
roles in functioning of metalloenzymes has led to a search
for newly designed unsymmetrical ligands which will give
trinuclear complexes capable of acting as models for the
metallobiosite [6]. The presence of multinuclear copper
centers at the active sites of copper oxidases and oxygen-
transport proteins continues to stimulate interest in model
irreversible one electron reduction process around Ep1c
=
=
-0.59 to -0.80 V, E2pc = -0.89 to -1.14 V and E3pc
-1.17 to -1.29 V, and for nickel(II) complexes it is
around E1pc = -0.63 to -0.77 V, Ep2c = -1.20 to -1.35 V
and E3pc = -1.60 to -1.74 V. ESR spectra and magnetic
moments of the trinuclear Cu(II) complexes show the
presence of antiferromagnetic coupling. Cryomagnetic
investigation of the trinuclear copper(II) complexes show
that the observed -2J values are in the range of 116–
178 cm-1. The rate constants for hydrolysis of 4-nitro-
phenylphosphate by the complexes are in the range of
2.68 9 10-2 to 9.81 9 10-2 min-1. The rate constants
values for the catecholase activity of the copper(II) com-
plexes fall in the range of 3.03 9 10-2 to 9.32 9
10-2 min-1. All the complexes.
S. Sreedaran ꢀ K. S. Bharathi ꢀ A. K. Rahiman ꢀ
V. Narayanan (&)
Department of Inorganic Chemistry, School of Chemical
Sciences, University of Madras, Guindy Campus,
Chennai 600 025, India
e-mail: vnnara@yahoo.co.in
L. Jagadish ꢀ V. Kaviyarasan
Centre for Advanced Studies in Botany, University of Madras,
Guindy Campus, Chennai 600 025, India
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J Incl Phenom Macrocycl Chem (2010) 66:297–306
Synthesis of macrocyclic tricompartmental ligands
(Scheme 1)
compounds which closely mimic the structure, properties
and function of these biosites [7, 8].
The present work describes the synthesis and charac-
terization of trinuclear copper(II) and nickel(II) complexes
derived from N-functionalized cyclam based tricompart-
mental ligands. These ligands are capable of binding upto
three metal centers in close proximity.
Synthesis of ligand L1
A solution of 1,8-[bis(3-formyl-2-hydroxy-5-methyl) ben-
zyl]-4,11-dimethyl-l,4,8,11 tetraazacyclotetradecane (PC
1) (1.05 g, 0.002) in methanol (60 mL) was refluxed with 2
equivalents of N,N-dimethyl-1,3-propanediamine (0.02 g,
0.002 mol) for 8 h at 70 °C. Then the solvent was evapo-
rated under reduced pressure. The crude compound was
purified by column chromatography using chloroform:
methanol (98:2) as eluent. Yield: 0.96 g (69%); M.p.:
292 °C (dec); Selected IR (KBr) (m/cm-1): 3397 m(OH),
Experimental
Materials and methods
5-methyl salicylaldehyde [9], 3-chloromethyl-5-bromo
salicylaldehyde [10], 1,4,8,11-tetraazatricyclo[9.3.1.14,8
1
1625 [s, m(C=N)]; H NMR d (ppm in CDCl3): 1.70–1.74
]
(m, 8H, b-CH2), 2.28 (s, 6H Ar–CH3) 2.41–2.49 (m, 20H,
N–CH2), 2.65 (m, 18H, N–CH3), 3.65 (m, 4H), 4.13 (s, 4H,
N–CH2–Ar), 7.13 (d, 4H, Ar–H), 8.45 (s, 2H, Ar–CH=N),
13.76 (s, Ar–OH); 13CNMR: d (ppm in DMSO-D6): 20.3,
20.6, 28.4, 29.0, 32.1, 35.3, 46.9, 49.1, 50.1, 51.6, 52.0, 53,
hexadecane [11], 1,8-[bis(3-formyl-2-hydroxy-5-methyl)
benzyl]-4,11 diazaniatricyclo[9.3.1.14,8]hexadecane dichlo-
ride [12], 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-
4,11diazaniatricyclo[9.3.1.14,8] hexadecane dichloride were
prepared by the literature method [12] using 5-bromo sali-
cylaldehyde instead 5-methyl salicylaldehyde. Analytical
grade methanol, acetonitrile and dimethylformamide were
purchased from Qualigens and used as such. TBAP used as
supporting electrolyte in electrochemical measurement
was purchased from Fluka and recrystallised from hot
methanol. (Caution! TBAP is potentially explosive; hence
care should be taken in handling the compound). All other
chemicals and solvents were of analytical grade and were
used as received.
57.4, 118.5, 124.6, 127.0, 131.3, 135.7, 158.1, 163.0; kmax
nm (e, M-1 cm-1) in DMF: 274 (20,220).
,
Synthesis of ligand L2
H2L2 was prepared following the previous method using 1,8-
[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-4,11-dimethyl-
l,4,8,11-tetraazacyclotetradecane (PC-2) (1.31 g, 0.002)
and N,N-dimethyl-1,3-propanediamine (0.02 g, 0.002 mol)
Scheme 1 Synthesis of
tricompartmental ligands
X
H3C
CH3
H3C
N
N
N
N
N
N
N
X
OH
H3C
OH
N
CH3
CH3
i
H3C
N
N
N
N
OH
O
X
O
X
OH
CH3
ii
H3C
N
N
N
N
N
N
N
X
OH
OH
X
N
CH3
X=CH3 or Br
(i) N,N-dimethyl-1,3-propanediamine, CH3OH ( ii) 2-(aminomethyl)pyridine, CH3OH
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J Incl Phenom Macrocycl Chem (2010) 66:297–306
299
instead of (PC-1). Yield: 1.1 g (67%); M.p.: 290 °C (dec);
Selected IR (KBr) (m/cm-1): 3407 m(OH), 1630 [s, m(C=N)];
1H NMR d (ppm in CDCl3): 1.50–1.57 (m, 8H, b-CH2),
2.53–2.58 (m, 20H, N–CH2), 2.73 (m, 18H, N–CH3), 3.60
(m, 4H), 4.1 (s, 4H, N–CH2–Ar), 7.43 (d, 4H, Ar–H), 8.29 (s,
2H, Ar–CH=N), 12.78 (s, Ar–OH); 13CNMR:d (ppm in
DMSO-D6): 27, 30.1, 49.7, 54.7, 55.2, 55.8, 60.2, 124.1,
124.8, 126.5, 133.0, 136.4, 157.9, 160.0; kmax, nm (e,
M-1 cm-1) in DMF: 278 (21,340).
(dec); Selected IR (KBr) (m/cm-1): 3398 m(OH), 1618
[s, m(C=N)]; H NMR d (ppm in CDCl3): 1.65–1.70 (m,
1
4H, b-CH2), 2.38–2.41 (m, 16H, N–CH2), 3.31(s, 4H), 3.39
(s, 6H, N–CH3) 3.61 (s, 4H, N–CH2–Ar), 6.95 6.98 (m, 8H
Ar–H), 7.23 (d, 4H, Ar–H), 8.67 (s, 2H, Ar–CH=N), 12.35
(s, Ar–OH); 13CNMR: d (ppm in DMSO-D6): 21.7, 24.6,
34.0, 38.3, 45.0, 46.7, 53.2, 58.5, 117.4, 118.3, 122.8,
123.8, 124.7, 125.2, 128.0, 130.5, 157.0, 157.8, 165.1;
k
max, nm (e, M-1 cm-1) in DMF: 278 (21,340).
Synthesis of ligand L3
Synthesis of trinuclear copper(II) and nickel(II)
complexes (Scheme 2)
H2L3 was prepared by following the above method, using
the (PC-1) (1.05 g, 0.002) and 2-(aminomethyl)pyridine
(0.22 g, 0.002 mol). Yield: 0.95 g (67%); M.p.: 289 °C
(dec); Selected IR (KBr) (m/cm-1): 3405 m(OH), 1610 [s,
General procedure:
A solution of copper(II) perchlorate hexahydrate or nick-
el(II) perchlorate hexahydrate (0.002 mol) in methanol
(50 mL) was added to a hot solution of the ligand
(0.0015 mol) in methanol (50 mL). The mixture was
refluxed for 1 h. After 1 h, another 2 equivalents of cor-
responding metal(II) perchlorate (0.002 mol) in methanol
and triethylamine (0.003 mol) in methanol (50 mL) was
added and the solution was refluxed for 24 h. The resulting
solution was filtered whilst hot and allowed to stand at
room temperature. After slow evaporation of the solvent at
25 °C, dark green compound was collected by filtration,
which was recrystallised from acetonitrile, and dried in
vacuum.
1
m(C=N)]; H NMR d (ppm in CDCl3): 1.87–1.95 (m, 4H,
b-CH2), 2.41 (s, 6H Ar–CH3) 2.45–2.53 (m, 16H, N–CH2),
3.31 (s, 4H), 3.37 (s, 6H, N–CH3), 3.57 (s, 4H, N–CH2–
Ar), 6.79–6.85 (m, 8H Ar–H), 7.13 (d, 4H, Ar–H), 8.65 (s,
2H, Ar–CH=N), 11.49 (s, Ar–OH); 13CNMR: d (ppm in
DMSO-D6): 24.2, 24.2, 34.3, 38.1, 46.7, 53.3, 58.5, 118.6,
119.2, 122.8, 123.3, 124.7, 125.2, 126.4, 130.0, 157.1,
159.2, 161.5; kmax, nm (e, M-1 cm-1) in DMF: 270
(21,340).
Synthesis of ligand L4
H2L4 was prepared by following the above method using
(PC-2) (1.31 g, 0.002) and 2-(aminomethyl)pyridine
(0.22 g, 0.002 mol). Yield: 0.91 g (55%); M.p.: 292 °C
[Cu3L1(ClO4)2](ClO4)2: Dark green compound; Yield:
0.89 g (50%); FAB mass (m/z) (%): [Cu3L1(ClO4)]ClO4
?
1180. Selected IR data (KBr) (m/cm-1): 1628 [s, m(C=N)],
Scheme 2 Synthesis of
trinuclear copper(II) and
nickel(II) complexes
X
X
H3C
CH3
H3C
ClO4
N
H3C
CH3
N
N
N
N
N
H3C
M
N
i
N
N
N
N
O
M
O
M
N
N
N
N
OH
O4Cl
OH
N
CH
H3C
CH3
3
CH3
CH
3
H3C
X
X
X
X
H3C
N
N
ClO4
N
N
N
N
M
H3C
M
O
ii
N
O
M
N
N
N
N
N
N
OH
O4Cl
N
N
OH
CH3
N
CH3
X
X=CH3 or Br
M = Cu or Ni
X
i,ii) 1. M(ClO4)2.6H2O, CH3OH, Et3N. 2. M(ClO4)2.6H2O
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-
1093, 1087 (w) [m(ClO4
)
coordinated], 1103 (w)
electrode, a saturated Ag/AgCl electrode was the reference
electrode and a Pt wire was used as the auxiliary electrode.
The ferrocene/ferrocenium (1?) couple was used as an
internal standard with E1/2 couple under the experimental
conditions of 470 mV. Tetra(n-butyl)ammonium perchlo-
rate (TBAP) was used as the supporting electrolyte. Room
temperature magnetic moments were measured on a PAR
vibrating sample magnetometer Model-155. Variable-
temperature magnetic studies were performed on a PAR
model 155 vibrating sample magnetometer in the temper-
ature range 77–300 K, and the instrument was calibrated
using metallic Ni as supplied with the instrument. X-band
ESR spectra were recorded using DMF as a solvent at
liquid nitrogen temperature on a Varian EPR-E 112 spec-
trometer with diphenylpicrylhydrazine (DPPH) as the ref-
erence. The catalytic oxidation of catechol to o-quinone
and the hydrolysis of 4-nitrophenylphosphate by the cop-
per(II) complexes were studied in a 10-3 M dimethyl-
formamide solution. The reaction was followed
spectrophotometrically by choosing the strongest absorp-
tion band of o-quinone at 390 nm and monitoring the
increase in the absorbance and the hydrolysis of 4-nitro-
phenylphosphate was monitored by following the UV
absorbance change at 420 nm (assigned to the 4-nitro-
phenolate anion) as a function of time. A plot of log (Aa/
Aa - At) versus time was made for each complex and the
rate constants for the catalytic oxidation and the hydrolysis
of 4-nitrophenylphosphate were calculated.
[m(ClO4-) uncoordinated], 632 (s); g = 2.10, leff: 1.47.
[Ni3L1(ClO4)2](ClO4)2: Dark green compound; Yield:
0.93 g (53%); Selected IR data (KBr) (m/cm-1): 1633 [s,
m(C=N)], 1093, 1085 (w) [m(ClO4-) coordinated], 1105 (w)
[m(ClO4-) uncoordinated], 630 (s).
[Cu3L2(ClO4)2](ClO4)2: Dark green compound; Yield:
0.93 g (55%); Selected IR data (KBr) (m/cm-1): 1623 [s,
m(C=N)], 1093, 1085 (w) [m(ClO4-) coordinated], 1100 (w)
[m(ClO4-) uncoordinated], 624 (s); g = 2.11, leff: 1.51.
[Ni3L2(ClO4)2](ClO4)2: Dark green compound; Yield:
0.97 g (58%); FAB mass (m/z) (%): [Ni3L2(ClO4)]? 1195.
Selected IR data (KBr) (m/cm-1): 1610 [s, m(C=N)], 1105,
1091 (w) [m(ClO4-) coordinated], 1107 (w) [m(ClO4
uncoordinated], 634 (s).
)
-
[Cu3L3(ClO4)2](ClO4)2: Dark green compound; Yield:
0.95 g (53%); FAB mass (m/z) (%): [Cu3L3(ClO4)]? 1092.
Selected IR data (KBr) (m/cm-1): 1643 [s, m(C=N)], 1092,
1098 (w) [m(ClO4-) coordinated], 1105 (w) [m(ClO4
uncoordinated], 630 (s); g = 2.10, leff: 1.49.
)
-
[Ni3L3(ClO4)2](ClO4)2: Dark green compound; Yield:
1.00 g (56%); Selected IR data (KBr) (m/cm-1): 1628 [s,
m(C=N)], 1097, 1085 (w) [m(ClO4-) uncoordinated], 1103
(w) [m(ClO4-) coordinated], 629 (s).
[Cu3L4(ClO4)2](ClO4)2: Dark green compound; Yield:
0.95 g (56%); Selected IR data (KBr) (m/cm-1): 3290
-
m(NH), 1632 [s, m(C=N)], 1093, 1087 (w) [m(ClO4
)
coordinated], 1101 (w) [m(ClO4-) uncoordinated], 625 (s);
g = 2.10, leff: 1.47.
[Ni3L4(ClO4)2](ClO4)2: Dark green compound; Yield:
0.98 g (58%); Selected IR data (KBr) (m/cm-1): 1627 [s,
m(C=N)], 1090, 1084 (w) [m(ClO4-) coordinated], 1100 (w)
[m(ClO4-) uncoordinated], 626 (s).
Results and discussion
The analytical data of the ligands and the complexes are
given in Table 1. The coordination geometries of the
complexes were deduced from their spectra. Conductivity
measurements of (Km, 87–97 S cm2 mol-1) all the com-
plexes show that they are 1:2 electrolytes in DMF solution.
A broad spectrum with no hyperfine splitting was obtained
for the trinuclear copper(II) complexes with g = 2.05–2.11
indicating the presence of an antiferromagnetic interaction
[2.8] between the three copper ions.
Analytical and physical measurements
Elemental analysis of the complexes was obtained using a
Haereus CHN rapid analyzer. 1H NMR spectra were
recorded using a JEOL GSX 400 MHZ NMR spectrometer.
Electronic spectra studies were obtained on a Hitachi 320
spectrophotometer in the range 200–1,100 nm. IR spectra
were recorded on a Shimadzu FTIR 8300 series spectro-
photometer on KBr disks in the range 4,000–400 cm-1
.
FTIR spectral studies
Molar conductivities were measured using an Elico digital
conductivity bridge model CM-88 using freshly prepared
solutions of the complex in DMF. Atomic absorption
spectra were recorded using a Varian spectra AA-200
model atomic absorption spectrophotometer. Mass spectra
were obtained on a JEOL SX-102 (FAB) mass spectrom-
eter. Cyclic voltammograms were obtained on a CHI-600A
electrochemical analyzer. The measurements were carried
out under oxygen free conditions using a three-electrode
cell in which a glassy carbon electrode was the working
The FTIR spectra of free macrocycles show a band in the
region 3,395–3,407 cm-1, assigned to the phenolic m(OH)
group. The absence of a peak around 3,400 cm-1 in all the
complexes indicates the absence of phenolic m(OH) due to
deprotonation followed by complexation [13]. The FTIR
spectra of the ligands H2L1–H2L4 show a sharp band in the
region 1,610–1,643 cm-1 due to the presence of m(C=N)
group [14–16]. All the complexes showed two sharp peaks
near 1,100 cm-1, perchlorate ions [14–16]. Only one
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301
Table 1 Analytical and conductance data of the ligands and the complexes
Cald (found) %
No.
Compound
M
C
H
N
(Km/X-1 cm2 mol-1
)
1
L1
L2
L3
L4
69.3 (69.3)
55.5 (55.4)
71.6 (71.5)
57.6 (57.5)
37.5 (37.5)
32.4 (32.4)
39.1 (39.0)
33.8 (33.8)
37.9 (37.9)
32.7 (32.7)
39.5 (39.4)
34.2 (34.1)
9.9 (9.8)
7.6 (7.6)
8.0 (7.9)
6.0 (6.0)
5.2 (5.1)
4.3 (4.2)
4.2 (4.2)
3.4 (3.3)
5.3 (5.2)
4.4 (4.4)
4.3 (4.2)
3.4 (3.4)
16.2 (16.1)
13.6 (13.5)
15.9 (15.9)
13.4 (13.4)
8.8 (8.8)
7.9 (7.9)
8.7 (8.6)
7.9 (7.9)
8.9 (8.9)
8.0 (8.0)
8.8 (8.7)
8.0 (7.9)
2
3
4
5
[Cu3L1(ClO4)2](ClO4)2
[Cu3L2(ClO4)2](ClO4)2
[Cu3L3(ClO4)2](ClO4)2
[Cu3L4(ClO4)2](ClO4)2
[Ni3L1(ClO4)2](ClO4)2
[Ni3L2(ClO4)2](ClO4)2
[Ni3L3(ClO4)2](ClO4)2
Ni3L4(ClO4)2](ClO4)2
14.9 (14.8)
13.5 (13.5)
14.8 (14.7)
13.4 (13.4)
13.9 (13.9)
12.6 (12.6)
13.8 (13.7)
12.5 (12.5)
95
77
98
89
93
89
87
93
6
7
8
9
10
11
12
Table 2 Electronic spectral
data of the trinuclear copper(II)
and nickel(II) complexes
Complexes
k )
max, nm (e, M-1 cm-1
d–d
Charge transfer
[Cu3L1(ClO4)2](ClO4)2
[Cu3L2(ClO4)2](ClO4)2
[Cu3L3(ClO4)2](ClO4)2
[Cu3L4(ClO4)2](ClO4)2
[Ni3L1(ClO4)2](ClO4)2
[Ni3L2(ClO4)2](ClO4)2
[Ni3L3(ClO4)2](ClO4)2
[Ni3L4(ClO4)2](ClO4)2
779 (96)
395 (12,200), 273 (21,000)
397 (11,240), 301 (18,200)
391 (12,200), 276 (20,100)
403 (11,300) 278 (20,800)
398 (12,300), 340 (19,700)
397 (12,100), 338 (18,700)
415 (10,600), 324 (19,700)
410 (12,300), 312 (18,600)
817 (102)
848 (110)
875 (130)
1,075 (28), 884 (56), 628 (135)
1,084 (28), 870 (76), 604 (153)
1,015 (42), 718 (68), 654 (127)
1,058 (30), 721 (76), 660 (167)
among these two peaks shows splitting consistent with the
presence of both coordinate and uncoordinated perchlorate
[14–17]. Apart from this an additional peak is observed in
the range of 624–630 cm-1 is assigned to a perchlorate
bending vibration. The appearance of bands in the region
of 1,530–1,545 cm-1 in all the complexes suggests phen-
oxide bridging with the metal ions [14–16].
copper atoms in the complexes with the molecular ion peak
at m/z = 1180, 1195 and 1092 respectively, which
are assigned to the {[Cu3L1(ClO4)2]ClO4}?, {[Ni3L2
(ClO4)2]}?and {[Cu3L3(ClO4)2]}? ions.
Electronic spectral analysis
The electronic spectra data of the complexes were given in
Table 2. Electronic spectra of the complexes were obtained
in DMF. The electronic spectra of all the complexes exhibit
three main features. One or two peaks in the range of 250–
320 nm is assigned to the intra ligand transition (p–p*). An
intense peak in the range of 350–412 nm is due to ligand-
to-metal charge transfer. All the copper(II) complexes
show the d–d transition in the range of 779–875 nm, which
are characteristic of Cu2? in the 6/4 coordination envi-
ronment [18]. Even though the metal ions are present in
two different compartments (N4O2 and N2O), we observed
a broad d–d band that could not be further resolved. The
d–d transition for the nickel(II) complexes show three main
bands in the region of 604–1,084 nm, which is character-
istic of Ni2? in the 6/4 coordination environment [19]. The
1H NMR spectral analysis
1
The H NMR spectra of all the free macrocycles show a
singlet at d 11.49–13.76 assigned to phenolic OH protons.
A singlet in the region of d 8.29–8.67 due-CH=N– (imine)
protons. A peak in the region of d 3.57–4.13 for all the
macrocycle is assigned to the benzylic proton (Ar–CH2) in
addition to other aliphatic and aromatic protons.
Mass spectral analysis
The FAB mass spectra were obtained for the complexes
[Cu3L1(ClO4)2](ClO4)2, [Ni3L2(ClO4)2](ClO4)2 and [Cu3L3
(ClO4)2](ClO4)2. The spectra show the presence of three
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10
8
2.0
appearance of the spectra bear similarities with those for
octahedrally coordinated Ni(II) ions, with the assignment
3
3
3
of the three most intense bands A2g ? T2g(P), A2g
?
1.5
1.0
0.5
0.0
3T1g(F), A2g ? T1g(P) to the spin allowed transitions
from the ground state of an octahedrally coordinated d8 ion.
The charge transfer and the visible absorption spectra of
the present complexes (tetra N-substituted cyclam) falls
into higher wavelength region than the complexes derived
from 1,8-disubstituted cyclam ligands [14c].
3
3
6
4
2
Magnetic studies
0
100
150
200
250
300
All the copper(II) complexes show magnetic moments in
the range of 1.51 to 1.54 B.M., which are less than the total
spin-only values. The lowering of these magnetic moments
is due to antiferromagnetic coupling by superexchange
through the phenolic oxygen atoms [20]. To evaluate the
singlet–triplet energy separation(-2J), variable tempera-
ture magnetic studies for the trinuclear copper(II) com-
plexes were performed in the temperature range 78–298 K,
and the experimental magnetic susceptibility values were
fitted to the modified Bleaney–Bowers equation [21, 22].
Fig. 2 Temperature-dependent magnetic properties for [Cu3L3
(ClO4)2](ClO4)2 where filled circle is leff/lB and open square is vM
geometry around the copper atom of the [Cu3L1(ClO4)2]
(ClO4)2 complex is perhaps more distorted due to more
flexible nature [21–24] of the N,N-dimethyl-1,3-propanedi-
amine side arm, when compared with the 2-(amino-
methyl)pyridine side arm. This distortion in geometry
around the metal ion increases the dihedral angle between the
copper magnetic orbitals, which results lower -2J values.
The most probable reason for the strong antiferromagnetic
exchange interaction in the complex of L3 may be the greater
planarity induced by the aromatic 2-(aminomethyl) pyridine
group.
The lower -2J value for the copper(II) complexes of L2
(-2J = 96 cm-1) compared to L1 complex may be due to
the electron withdrawing group (Br). The electron with-
drawing group (Br) in the para position of the phenolic ring
in the complex of L2 decreases the electron density on the
copper centers and weakens the Cu–O bond and reduces
the spin exchange interaction [23, 24].
È
É
vm ¼ Ng2b2=3kT ½3 þ expðꢁ2J=kTÞꢂꢁ1ð1 ꢁ PÞ
þ ð0:45P=TÞ þ Na;
The temperature dependence of magnetic properties for
the copper(II) complexes of L1 and L3 are shown in Figs. 1
and 2.
Since, the nature of the donor atoms and phenoxide
bridging groups in all the complexes are same, a comparison
of the magnetic properties based on the side arm of the imine
compartment would be useful in discovering the possible
effects on spin exchange interactions in the complexes. The
antiferromagnetic exchange interaction (-2J) for the trinu-
clear copper(II) complexes of L1 (-2J = 116 cm-1) is
lower than that of L3 (-2J = 178 cm-1). The coordination
Electrochemical properties
1.6
1.4
1.2
1.0
0.8
0.6
0.4
14
12
10
8
Electrochemical behavior of the complexes was studied by
cyclic voltammetry in DMF containing 10-1 M tetra(n-
butyl)ammonium perchlorate over the range of 0 to
-1.4 V. Cyclic voltammograms for copper(II) complexes
are shown in Figs. 3 and 4. The electrochemical data of the
complexes were given in Table 3.
6
Reduction process at negative potential
4
All the copper(II) complexes show three irreversible
reduction waves in the cathodic potential region in the
range of -0.59 to -0.80 V, -0.89 to -1.14 and -1.17 to
-1.29 V. Controlled potential electrolysis was also carried
out at 100 mV more negative to the cathodic peak, and the
100
150
200
250
300
Fig. 1 Temperature-dependent magnetic properties for [Cu3L1
(ClO4)2](ClO4)2 where filled circle is leff/lB and open square is vM
123

J Incl Phenom Macrocycl Chem (2010) 66:297–306
303
due to the presence of two trans nitrogen’s in the cyclam
ring, causing more distortion of the geometry of the
complexes which ease reduction.
Further, the complexes of the ligands L2&4 undergo
reduction at less negative potential compared to the com-
plexes of L1&3. The easy reduction of the complexes of
L2&4 may be due to the presence of electron-withdrawing
substituent (Br) at the para position to the phenoxide
oxygen [29, 30]. Literature reports, [29, 30] also suggest
that the complexes containing electron withdrawing groups
get reduced at less negative potential than complexes,
which contain electron donating substituent.
Oxidation process at anodic potential
All the trinuclear nickel(II) complexes show three irre-
versible one electron oxidation processes in the range of 0
to ?1.6 V. The cyclic voltammogram of the trinuclear
nickel(II) complexes in the anodic potential region are
shown in Fig. 5. The electrochemical data were given in
Table 3 The three oxidation processes for nickel(II) com-
plexes as follows,
Fig. 3 Cyclic voltammogram of the copper(II) complexes: (reduction
process) (a) [Cu3L1(ClO4)2](ClO4)2 (b) [Cu3L2(ClO4)2](ClO4)2
NiIINiIINiII ! NiIIINiIINiII ! NiIIINiIIINiII
! NiIIINiIIINiIII
From the results it is observed that the para substitution
and the side arm influence the oxidation potential to less
extend only.
Kinetic studies
Hydrolysis of 4-nitrophenylphosphate
Fig. 4 Cyclic voltammogram of the nickel(II) complexes: (reduction
process) (a) [Ni3L3(ClO4)2](ClO4)2 (b) [Ni3L4(ClO4)2](ClO4)2
The catalytic activity of the trinuclear copper(II) and
nickel(II) complexes with respect to hydrolysis of 4-ni-
trophenylphosphate was determined spectrophotometri-
cally as described previously [14–16]. A linear relationship
for all the complexes shows a first-order dependence on the
complex concentration. Figure 6 shows the results hydro-
lysis of 4-nitrophenylphosphate by and [Ni3l1&2(ClO4)2]
ClO4. The observed initial rate constant values for the
complexes are given in Table 3.
results show that each wave corresponds to one-electron
transfer process, as follows:
MIIMIIMII ! MIIMIIMI ! MIIMIMI ! MIMIMI
The first and second reduction potential in the range of
(E1pc ꢁ 0:59 to ꢁ 0:80; and Ep2c ꢁ 0:89 to ꢁ 1:14 V) are
attributed to the reduction of copper(II) in the imine
compartment. The third reduction wave in the range of
-1.17 to -1.29 V, is attributed to the reduction of
copper(II) in the amine (cyclam) compartment. From the
results it is observed that the complex of the ligand L3 and
L4 get reduced at high negative potential due to greater
planarity [25, 26] of the complexes induced by the
2-(aminomethyl)pyridine group and conjugation [27, 28].
The reduction potential of the complexes is less negative
(-0.59 to -0.89 V) when compared to the di-N-substituted
cyclam complexes (-0.73 to -0.98 V) [14c]. This may be
Oxidation of pyrocatechol (catecholase activity)
The catecholase activity of the copper(II) complexes was
studied using pyrocatechol as model substrate by following
our previous reports [31]. The observed kinetics shows a
first-order dependence on the complex concentration. Fig-
ure 7 shows the plots of log(Aa/Aa - At) versus time for
catecholase activity of the [Cu3L1&2(ClO4)2](ClO4)2. The
initial rate constant values for the copper(II) complexes are
given in Table 3. It is remarkable that the reactivity of the
123

304
J Incl Phenom Macrocycl Chem (2010) 66:297–306
Table 3 Electrochemicala (reduction at cathodic potential), hydrolysis of 4-nitrophenylphosphateb and catecholaseb activity data of the trinu-
clear copper(II) complexes
No.
Complexes
E1pc ðVÞ
E2pc ðVÞ
E3pc ðVÞ
Rate constant (k) (910-2) min-1
NPP
Catecholase
1
2
3
4
5
6
7
8
a
[Cu3L1(ClO4)2](ClO4)2
[Cu3L2(ClO4)2](ClO4)2
[Cu3L3(ClO4)2](ClO4)2
[Cu3L4(ClO4)2](ClO4)2
[Ni3L1(ClO4)2](ClO4)2
[Ni3L2(ClO4)2](ClO4)2
[Ni3L3(ClO4)2](ClO4)2
[Ni3L4(ClO4)2](ClO4)2
-0.69
-0.59
-0.80
-0.59
-0.89
-0.77
-0.77
-0.63
-0.92
-0.89
-1.14
-0.93
-1.26
-1.20
-1.35
-1.22
-1.20
-1.17
-1.29
-1.23
-1.72
-1.60
-1.74
-1.63
7.58
9.81
3.98
4.23
7.44
8.47
2.68
3.12
8.15
9.32
3.03
3.43
–
–
–
–
Measured by CV at 50 mV/s. V versus Ag/AgCl conditions: GC working and Ag/AgCl reference electrodes; supporting electrolyte TBAP;
M
concentration of complex 1 9 10-3 M, concentration of TBAP 1 9 10-1
b
Measured spectrophotometrically in DMF
Concentration of the complexes: 1 9 10-3
Concentration of 4-nitrophenylphosphate: 1 9 10-1
Concentration of catechol: 1 9 10-1
M
M
M
1.2
b
1
0.8
0.6
0.4
0.2
a
0
0
10
20
30
40
50
Time (min)
Fig. 7 Catecholase activity of trinuclear copper(II) complexes: (a)
[Cu3L1(ClO4)2](ClO4)2 (b) [Cu3L2(ClO4)2](ClO4)2
Fig. 5 Cyclic voltammogram of the nickel(II) complexes: (oxidation
process) (a) [Ni3L1(ClO4)2](ClO4)2 (b) [Ni3L2(ClO4)2](ClO4)2
of L3&4 are lower than the complexes of L1&2 presence of
2-(aminomethyl)pyridine group [25–28].
Further, the rate constant values of the complexes are
also higher 2.68 to 9.81 x 10-1 min-1 than the trinuclear
complexes derived from the di-N-substituted cyclam
ligands (2.67 to 7.58 x 10-1 min-1). This shows, the rate of
oxidation of catechol to o-quinone and the hydrolysis of 4-
nitrophenyl phosphate is increases due to the increase of
macrocyclic N-alkylation. The structural features and
electrochemical properties are important factors in deter-
mining the catalytic activity of the complexes. The cata-
lytic activity of the complexes of L2 is higher than that of
the complexes of L1. This may be due to the para-sub-
stituent of the phenoxide of the phenyl ring. The complexes
containing electron-withdrawing substituent (Br) at the
para-position to the phenyl ring L2 are reduced at less
negative potential show higher catalytic activity than
complexes with electron-donating substituent (CH3) [29,
1.9
b
a
1.4
0.9
0.4
-0.1
0
20
Time (min)
40
60
Fig. 6 Hydrolysis of 4-nitrophenylphosphate by trinuclear nickel(II)
complexes: (a) [Ni3L1(ClO4)2](ClO4)2 (b) [Ni3L2(ClO4)2](ClO4)2
complexes differs significantly by varying side arm of the
imine compartment and by the Para substituent of the
phenyl ring. The rate constants of the copper(II) complexes
123

J Incl Phenom Macrocycl Chem (2010) 66:297–306
305
Table 4 Antibacterial and antifungal screening data of complexes
No.
Compound
Representation zone of inhibition (100 lg/mL)
Antibacterial
Antifungal
S. a
B. c
K. p
P. a
E. c
C. a
1
Cu(ClO4)2ꢀ6H2O
H2L1
H2L2
H2L3
H2L4
[Cu3L1(ClO4)2](ClO4)2
[Cu3L2(ClO4)2](ClO4)2
[Cu3L3(ClO4)2](ClO4)2
[Cu3L4(ClO4)2](ClO4)2
[Ni3L1(ClO4)2](ClO4)2
[Ni3L2(ClO4)2](ClO4)2
[Ni3L3(ClO4)2](ClO4)2
[Ni3L4(ClO4)2](ClO4)2
1.5
10
12
13
12
17
21
19
18
27
20
23
17
–
11
10
10
13
16
19
18
20
16
19
21
19
2
10
12
12
11
19
12
16
22
20
20
19
18
2.5
12
11
12
13
16
14
16
18
14
17
23
18
–
9
3
13
9
2
3
11
9
4
10
9
5
11
15
18
19
12
17
17
16
14
6
19
20
16
22
23
26
21
22
7
8
9
10
11
12
13
S. a—Staphylococcus aureus
B. a—Bacillus subtilis
K. p—Klebsiella pneumonia
P. a—Pseudomonas aeruginosa
E. c—Escherichia coli
C. a—Candida albicans
30]. The same trend was also observed for the complexes
of L3&4
complexes show moderate activity against gram (-)
Escherichia coli. But trinuclear nickel(II) complexes show
no inhibition against gram (-) Escherichia coli. All the
complexes show superior activity than the ligands and the
metal salts. The complexes are all highly potent against
P. aeruginosa, B. subtilis, K. pneumonia and S. aureus,
with moderate activity against E. coli. It is of interest to
compare the electronic spectra results with antimicrobial
activity. The trinuclear complexes which have maximum
charge transfer show slightly higher antimicrobial activity
than the other complexes. From the results it is observed
that the copper(II) complexes of the ligands L2 have higher
charge transfer value and show higher antibacterial activ-
ity. The same is also true for the nickel(II) complexes.
.
Antimicrobial activities
Antifungal and antibacterial activities of the complexes
were tested by following our earlier literature reports [31].
We have evaluated the antifungal activity of all the cop-
per(II) and nickel(II) complexes against the human patho-
genic fungus Candida albicans. The screening data were
reported in the Table 4. All the tested complexes show
some antifungal activity. The activity reported by the
present complexes was comparable with the N-substituted
tetraazamacrocycles [32].
The complexes have also been screened for their in vitro
antimicrobial activity against the human pathogenic bac-
teria gram (-) Escherichia coli (ATCC 11775), Pseudo-
monas aeruginosa (ATCC 10145), Bacillus subtilis (ATCC
6633) Klebsiella pneumonia (ATCC 13883) and gram (?)
Staphylococcus aureus (ATCC 12600) were using the agar
dilution method. The screening results are given in
Table 4.
Conclusion
In conclusion, it has been observed that the small variation
in the side arm of the imine compartment and the para
substituent of the phenoxide to the phenyl ring influences
on electrochemical, magnetic and catalytic properties of
the copper(II) and nickel(II) complexes.
All the trinuclear copper(II) and nickel(II) complexes
are highly potent against Pseudomonas aeruginosa,
Bacillus subtilis, Klebsiella pneumonia and gram (?)
Staphylococcus aureus. All the tested trinuclear copper(II)
Acknowledgments Financial support from University Grants
Commission (RGN-JRF), New Delhi, is gratefully acknowledged. We
123

306
J Incl Phenom Macrocycl Chem (2010) 66:297–306
are thankful to CDRI-Lucknow for providing FAB Mass spectral
analysis.
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dicopper(II) complexes with variable Cu-OH(phenol) moieties.
Inorg. Chem. 41, 1788 (2002)
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123