Synthesis, crystal structure determination and antimicrobial studies of copper(II) picrate complexes with N,N,N′,N″-tetrakis(2-hydroxyethyl/ propyl) ethylenediamine and tris(2-hydroxyethyl)amine

Article abstract of DOI:10.1016/j.poly.2013.03.043

The present work consist of synthesis, spectroscopic and crystal structure investigations of complexes [Cu(THEEN) (H₂O)] (PIC)₂ (1), [Cu(THPEN)] (PIC)₂·C₃H₈O (2) and [Cu(TEAH₃)(PIC)] (PIC)·(H₂O) (3) and their application in antimicrobial activities. In these complexes, THEEN is N,N,N′,N″-tetrakis(2-hydroxyethyl) ethylenediamine and THPEN is N,N,N′,N″-tetrakis(2-hydroxypropyl) ethylenediamine, are tetrapodal ligands and TEAH₃ is tris(2-hydroxyethyl)amine, a tripodal ligand. Crystal structure investigations have revealed that the coordination number of Cu(II) is five with square pyramidal geometry in complex (1) and THEEN is interacting with metal ion through both of its amine nitrogens and two of the four hydroxyl oxygens in a tetradentate manner. The metal ion in complex (2) is having a distorted octahedral geometry with coordination number six and THPEN is interacting with it through all ligating sites in a hexadentate way. The picrate anions are present outside the coordination sphere in both of these complexes and are involved in hydrogen bonding interactions resulting in the formation of charge-separated complexes (1) and (2). The coordination number of Cu(II) is five with square pyramidal geometry in complex (3) where the ligand tris(2-hydroxyethyl)amine (TEAH₃) is interacting through all of its donor atoms in a tetradentate way. One of the two picrate anions is in coordination with metal ion whereas other is present outside the coordination sphere and is involved in hydrogen bonding interactions resulting in formation of partially charge-separated complex.

Full text of DOI:10.1016/j.poly.2013.03.043

Polyhedron 56 (2013) 55–61
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, crystal structure determination and antimicrobial studies
of copper(II) picrate complexes with N,N,N0,N00-tetrakis(2-hydroxyethyl/propyl)
ethylenediamine and tris(2-hydroxyethyl)amine
a
b
b
c
c
R. Kumar a, , S. Obrai , A. Kaur , G. Hundal , H. Meehnian , A.K. Jana
⇑
a Department of Chemistry, Dr. B. R. Ambedkar National Institute of Technology, Jalandhar 144011, India
b Department of Chemistry, Guru Nanak Dev University, Amritsar, India
c Department of Biotechnology, Dr. B. R. Ambedkar National Institute of Technology, Jalandhar 144011, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The present work consist of synthesis, spectroscopic and crystal structure investigations of complexes
[Cu(THEEN) (H2O)] (PIC)2 (1), [Cu(THPEN)] (PIC)2ꢀC3H8O (2) and [Cu(TEAH3)(PIC)] (PIC)ꢀ(H2O) (3) and
their application in antimicrobial activities. In these complexes, THEEN is N,N,N0,N00-tetrakis(2-hydroxy-
ethyl) ethylenediamine and THPEN is N,N,N0,N00-tetrakis(2-hydroxypropyl) ethylenediamine, are tetrapo-
dal ligands and TEAH3 is tris(2-hydroxyethyl)amine, a tripodal ligand. Crystal structure investigations
have revealed that the coordination number of Cu(II) is five with square pyramidal geometry in complex
(1) and THEEN is interacting with metal ion through both of its amine nitrogens and two of the four
hydroxyl oxygens in a tetradentate manner. The metal ion in complex (2) is having a distorted octahedral
geometry with coordination number six and THPEN is interacting with it through all ligating sites in a
hexadentate way. The picrate anions are present outside the coordination sphere in both of these com-
plexes and are involved in hydrogen bonding interactions resulting in the formation of charge-separated
complexes (1) and (2). The coordination number of Cu(II) is five with square pyramidal geometry in com-
plex (3) where the ligand tris(2-hydroxyethyl)amine (TEAH3) is interacting through all of its donor atoms
in a tetradentate way. One of the two picrate anions is in coordination with metal ion whereas other is
present outside the coordination sphere and is involved in hydrogen bonding interactions resulting in
formation of partially charge-separated complex.
Received 12 February 2013
Accepted 19 March 2013
Available online 30 March 2013
Keywords:
Copper complexes
Tetrapodal
Tripodal
Picrate anion
Antimicrobial activity
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
Here we will specify our discussion to the tripodal (TEAH3) and
tetrapodal (THEEN/THPEN) ligands having hydroxyls groups as po-
Podands are the acyclic ligands containing potential donor
atoms such as oxygen and nitrogen and may be broadly classified
as dipodal, tripodal and polypodal ligands [1–4]. They have a ten-
dency to form host- guest complexes with conformational changes
due to high degree of flexibility and exhibit rapid complexation
and decomplexation kinetics. Hence they rapidly response in sens-
ing applications but possess lower binding constants than their
cyclic analogs [5]. These compounds may bind metal ions and
other species, catalyze reactions, form novel complex structures
of biological relevance and have importance in material science.
Vögtle and Weber have examined structural variations and re-
ported a variety of podands with quinoline end groups [6]. An
enormous number of podands having a variety of end groups and
their complexes with metal ions have been reported in literature.
lar end groups. Here TEAH3 = triethanolamine, H3 indicates the
number of alcohol protons present. Recently Gulcemal and
coworkers has reported the structural characterization of complex
of Pd(II) with a tetrapodal ligand having hydroxyls as end groups
that has proved to be a good catalyst for Suzuki/Miyaura reaction
in water [7]. Cu(II) complex of tripodal ligand having hydroxyls
as end groups [Oꢁ Cu4(tea)4(BOH)4][BF4]2 [8], is also an efficient
catalyst for selective oxidation of alkylarenes to phenyl ketones
by tert-butylhydroperoxide. Like copper other transition metal
ions Mn(II), Co(II), Ni(II), Zn(II), Y(III), Cd(II), Pd(II), Hg(II) [9,10]
have also been found to get encapsulated by the pseudocyclic
cavity of triethanolamines. Not only transition metal ions but also
inner-transition metal ions La(III), Yb(III), Eu(II), Pr(III) [11] and
s-block metal ions Li(I), Na(I), Ca(II), Sr(II), Ba(II) [12–14] have been
reported to be complexed with triethanolamines under the influ-
ence of a variety of anions.
The complexes of some of s-block metal ions Na(I), Ca(II), Sr(II),
Ba(II) [15] and a few transition metal ions Cu(II), Ag(I), Ti(IV), Pd(II)
⇑
Corresponding author. Mob.: +91 9888 982369; fax: +91 181 2690320.
E-mail address: rakesh_nitj@yahoo.co.in (R. Kumar).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.03.043

56
R. Kumar et al. / Polyhedron 56 (2013) 55–61
[16,7] with tetrapodal ligands (THEEN, THPEN) have already been
reported in literature. Nature of s-block metal ion complexes was
investigated under the influence of picrate, 3,5-dinitrobenzoate,
2,4-dinitrophenolate and o-nitrobenzoate and found to be forming
and materials to be used for antimicrobial activity were sterilized
in an autoclave.
2.2. X-ray crystallographic study
charge-separated
complexes
with
the
exception
of
Ba(THPEN)(PIC)2 and Ca(THEEN)(H2O)2 (DNP)2ꢀH2O forming ion-
paired complexes whereas [Ca(THEEN)(PIC)](PIC) formed partially
charge-separated complexes [15]. Earlier crystal structure of
copper with THPEN and THEEN ligands has been investigated
under the influence of perchlorate anions [16a,b]. The present
work consists of the synthesis of copper complexes (1–3) with both
tetrapodal ligands (THEEN and THPEN) and a tripodal ligand
(TEAH3) under the influence of picrate as counter anions. The
structural characterizations are carried out by using X-ray crystal-
lography as a tool and the antimicrobial studies have been investi-
gated using microbroth dilution method.
X-ray crystallographic data was collected on ‘‘Bruker APEX-II
CCD’’ area detector diffractometer using graphite monochromated
Mo Ka radiation (k = 0.71073 Å) source. The crystal structures were
solved by direct method [17] using the program SIR-97 and refined
by full-matrix least-squares refinement methods based on F2, using
SHELXL-97 programme [18]. All the CH2 hydrogens were attached
geometrically except for those bonded to hydroxyl oxygens and
water molecules which were located from difference Fourier maps.
None of these hydrogen were refined, were made to ride on their
respective atoms. Molecular structures of the complexes were
drawn with the help of ORTEP programme [19]. Calculation of hydro-
gen bonding were performed using PARST [20].
2. Experimental
2.3. Synthesis
2.1. Materials and instrumentation
2.3.1. [Cu(THEEN)(H2O)] (PIC)2 (1)
All chemicals and solvents used in this study were of high
purity. The ligands THEEN, THPEN and TEA were supplied by Sigma
Aldrich and used without purification. Picric acid was used after
purification. The IR absorption spectra were recorded in the range
of 450–4000 cmꢂ1 by using Perkin Elemer FT-IR RX I spectrometer
with KBr pellets (Sigma Aldrich). The elemental analyses were
performed on Flash 2000 Organic Elemental Analyzer. For antimi-
crobial activity, pathogenic bacteria Serratia marcescens (MTCC-
97), Sphingobium japonicum (MTCC-6362), Stenotrophomonas
maltophilia (MTCC-2446) and Staphylococcus aureus (MTCC-3160)
were procured from Microbial Type Culture Collection (MTCC),
Institute of Microbial Technology, Chandigarh. All the glass wares
The complex (1) was synthesized by dissolving copper (II)
picrate (0.521 g, 0.001 mol) and THEEN (0.236 g, 0.001 mol) in an
aqueous solution. The mixture was stirred for 1 h at 50 °C and then
left to cool down at room temperature. Change in color of the solu-
tion indicated that the reaction has occurred. The green crystals
were obtained after 48 h at room temperature. Recrystallization
was carried out by slow evaporation in a mixture of water and
methanol. The decomposition of the product was found to be in
the range 170–195 °C. Yield: 80%. IR (KBr) cmꢂ1: 3447 (
br)), 2903 ( (C–H) br), 1632 ( (@CH) str), 1560 ( (NO2) as, str),
1335 ( (NO2) s, str), 1437 (d (@CH) w, br), 1277 ( (C–O) str),
1163 (d (–OH) s), 1078 (
m (OH,
m
m
m
m
m
m
(C–O) alcohol), 937 (d (@C–H) bend),
Table 1
Summary of the crystal structure, data collection and structure refinement parameters for complexes (1–3).
Complexes
1
2
3
Empirical formula
Formula weight
Crystal system
Crystal size
Color
C
22H30CuN8O19
C29H44CuN8O19
872.27
triclinic
C18H21CuN7O18
686.96
triclinic
774.09
triclinic
0.19 ꢃ 0.09 ꢃ 0.07
0.19 ꢃ 0.17 ꢃ 0.14
0.13 ꢃ 0.10 ꢃ 0.09
light green
needle
green
green
Shape
needle
P1
rectangular
ꢀ
ꢀ
ꢀ
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
P1
P1
7.299(5)
14.281(5)
15.814(5)
104.004(5)
91.535(5)
100.283(4)
1569.5(13)
2
1.638
0.793
12.149(5)
12.363(5)
14.667(5)
99.061(5)
110.000(5)
103.598(5)
1942.6(13)
2
8.070 (5)
12.664(5)
13.061(5)
86.605(5)
89.592(5)
72.106(5)
1267.9(11)
2
1.799
a
(°)
b (°)
c
(°)
V (Å3)
Z
qcalc. (g cmꢂ3
)
1.491
0.650
l
(cmꢂ1
)
0.966
F(000)
798.0
910.0
702.0
h Range of data collection
Limiting frequency
1.33°–24.23°
ꢂ8 < h < 9
1.53°–30.32°
ꢂ16 6 h 6 17
ꢂ17 6 k 6 17
ꢂ20 6 l 6 20
43035
1.69°–31.90°
ꢂ4 6 h 6 11,
ꢂ17 6 k 6 18
ꢂ18 6 l 6 19
8412
ꢂ18 < k < 18
ꢂ20 < l < 20
32389
Total reflections
Independent reflections
Completeness to theta = 25.00
Refinement method
7397[Rint = 0.0521]
95.4%
11456[Rint = 0.0219]
98.1%
6876 [Rint = 0.0154]
78.9%
full matrix least squares on F2
1.021
full matrix least squares on F2
1.038
full matrix least squares on F2
1.040
Goodness-of-fit (GOF) on F2
Final R indices [I > 2 (I)]
R indices (all data)
R1 = .0610 wR2 = 0.1725
R1 = .1008 wR2 = 0.1983
1.042 and ꢂ1.060
R1 = 0.0676, wR2 = 0.1920
R1 = 0.0880, wR2 = 0.2128
1.431 and ꢂ0.735
R1 = 0.0418, wR2 = 0.0956
R1 = 0.0624, wR2 = 0.1065
0.443 and ꢂ0.596
Largest diff. peak and hole (e Å3)

R. Kumar et al. / Polyhedron 56 (2013) 55–61
57
Table 2
Selected bond distances and bond angles (Å, °) for complexes (1), (2) and (3).
Table 3
Selected geometric parameters for complexes (1), (2) and (3).
Bond distances (Å)
Bond angles (°)
Hydrogen bonding geometry
Complex (1)
Cu–N1
Cu–N2
Cu–O1
Cu–O2
D–Hꢀ ꢀ ꢀA
Complex (1)
d(D–H)
d(H–A)
d(D–A)
\(DHA)
1.999 (3)
2.035 (3)
1.984 (3)
2.347 (4)
1.942 (3)
N1–Cu–N2
O1–Cu–N1
N1–Cu–O2
N2–Cu–O2
O1W–Cu–N2
O1W–Cu–N1
O1W–Cu–O1
O1W–Cu–O2
O1–Cu–N2
O1–Cu–O2
88.24 (12)
83.08 (13)
79.50 (12)
96.19 (12)
97.20 (12)
174.52(12)
91.45(13)
100.51(14)
166.64 (13)
92.21 (14)
O1–H1ꢀ ꢀ ꢀO1W
0.85
0.85
0.85
0.81
0.82
0.82
0.83
0.83
0.83
0.83
2.776
1.822
2.305
1.889
1.819
1.997
2.701
1.954
2.297
1.889
2.811 (4)
2.614 (4)
2.897 (6)
2.928 (4)
2.630 (5)
2.722 (5)
2.811 (4)
2.725 (5)
2.868 (6)
2.683 (4)
83.49
152.52
126.28
160.37
169.24
147.08
88.88
153.41
126.07
160.37
O1–H1ꢀ ꢀ ꢀO5A
O1–H1ꢀ ꢀ ꢀO11A
O2–H2ꢀ ꢀ ꢀO3C
Cu–O1W
O3–H3ꢀ ꢀ ꢀO12B
O4–H4ꢀ ꢀ ꢀO12C
O1W–H1Wꢀ ꢀ ꢀO1
O1W–H1Wꢀ ꢀ ꢀO5A
O1W–H1Wꢀ ꢀ ꢀO6A
O1W–H2Wꢀ ꢀ ꢀO4B
Complex (2)
Cu–N1
Cu–N2
Cu–O1
Cu–O2
2.019 (2)
2.013 (2)
1.994 (2)
2.324 (3)
2.413 (3)
1.960 (2)
N1–Cu–N2
N1–Cu–O2
N2–Cu–O2
O1–Cu–N1
O1–Cu–N2
O1–Cu–O2
88.82 (10)
79.26 (10)
100.87 (11)
83.08 (11)
159.76 (11)
95.81 (10)
Complex (2)
O1–H1ꢀ ꢀ ꢀO12A
O2–H15ꢀ ꢀ ꢀO19A
O3–H8ꢀ ꢀ ꢀO13A
O4–H22ꢀ ꢀ ꢀO5A
O19–H44ꢀ ꢀ ꢀO5
O19–H44ꢀ ꢀ ꢀO11
0.93
0.93
0.93
0.93
0.82
0.82
2.249
2.347
2.355
1.700
2.297
2.237
2.666 (4)
2.632 (5)
2.905 (6)
2.597 (3)‘
2.927 (5)
2.984 (1)
106.44
97.29
117.56
160.79
134.08
151.74
Cu–O3
Cu–O4
Complex (3)
Cu–N1
Cu–O1
Cu–O2
Cu–O3
1.990 (18)
2.030 (2)
2.031 (2)
2.158 (2)
1.899 (17)
N1–Cu–O1
N1–Cu–O2
N1–Cu–O3
N1–Cu–O4
O1–Cu–O2
O1–Cu–O3
O1–Cu–O4
O2–Cu–O3
O2–Cu–O4
O3–Cu–O4
82.14 (7)
84.04 (7)
82.55 (7)
177.24 (7)
151.29 (8)
97.97 (9)
100.61 (7)
105.04 (9)
93.44 (7)
97.06 (7)
Complex (3)
O1–H1ꢀ ꢀ ꢀO11
0.93
0.93
0.93
0.93
0.72
0.76
1.854
2.274
1.970
1.890
2.129
2.099
2.629 (3)
2.987 (3)
2.731 (3)
2.769 (3)
2.907 (4)
2.900 (3)
138.84
133.03
137.83
156.63
161.68
168.22
O1–H1ꢀ ꢀ ꢀO17
O2–H2ꢀ ꢀ ꢀO11A
O3–H3ꢀ ꢀ ꢀO1W
O1W–H1Wꢀ ꢀ ꢀO17
O1W–H2Wꢀ ꢀ ꢀO15B
Cu–O4
3. Antimicrobial activity
795 (d (@CH), s), 709 (d (C@C)). Elemental Analysis: Anal. Calc. for
22H30CuN8O19: C, 34.13; H, 3.90; N, 14.47. Found: C, 34.16; H,
C
In the current study, all the synthesized copper complexes were
tested against pathogenic Gram ꢂve bacteria (S. marcescens, S.
japonicum, S. maltophilia) and Gram +ve bacteria (S. aureus) using
the microbroth dilution [21] method. It is well established high
throughput screening method for antimicrobial agent used in clin-
ical laboratories. Microbroth dilution susceptibility test was car-
ried out in 96 well microtitre plate by distributing sterile media
4.03; N, 15.53%.
2.3.2. [Cu(THPEN)](PIC)2 C3H8O (2)
The synthesis of complex (2) was similar to that of (1), but with
THPEN (0.292 g, 0.001 mol) in place of THEEN. The dark green color
crystalline product obtained and was recrystallization by slow
evaporation in water–propanol mixture. Dark green color crystals
were obtained after few days. The crystals were decomposed in
240 and 30
ll of metal complexes solutions ranging from (0.197
to 500 g/ml) taking appropriate blanks and controls. Then 30 ll
l
bacterial inocula (Organism 107 cells/ml) was poured to each well
and incubated at 30 °C for 48 h at 150 rpm in incubator shaker. The
growth was observed in the form of turbidity with naked eyes
under light background by comparing clarity of blank media and
turbidity of controls. The MICs of metal complexes were recorded
as the lowest concentration where no viability of bacteria was
observed in the wells of 96-microwell plates after incubation of
48 h. The growth of the bacteria was measured by observing the
minimum inhibitory concentration. DMSO was used as a control
and ciprofloxacin as a standard drug.
the range of 175–200 °C. Yield: 76%. IR (KBr) cmꢂ1: 3293 (
m
(OH,
(NO2) as, str),
(NO2) s, str), 1435 (d (@CH) w, br), 1268( (C–O) str),
1163 (d (–OH) s), 1076 ( (C–O) alcohol), 939 (d (@C–H) bend),
788 (d (@CH), s), 709 (d (C@C)). Elemental analysis: Anal. Calc. for
29H44CuN8O19: C, 39.93; H, 5.08; N, 12.85. Found: C, 40.12; H,
br)), 2929 (
m (C–H) br), 1631 (m (@CH) str), 1564 (m
1335 (
m
m
m
C
4.94; N, 12.78%.
2.3.3. [Cu(TEAH3)(PIC)](PIC) H2O (3)
4. Results and discussion
The synthesis of complex (3) was carried out by dissolving
Cu(II) picrate (0.521 g, 0.001 mol) and TEAH3 (0.149 g, 0.001 mol)
in an aqueous medium. Change in color of the light green solution
to dark green indicated the completion of reaction. The green color
crystalline solid was separated out. Recrystallization was carried
out in a water–methanol mixture by slow evaporation. The decom-
position of the crystals was found to be in the range of 190–200 °C.
4.1. Description of crystal structures
The crystal data and refinement details of three complexes are
given in Table 1. Selected bond distances, bond angles and hydro-
gen bonding geometry are listed in Tables 2 and 3 respectively. The
X-ray crystal structure analysis reveals that the molecular struc-
ture of complex (1) consists of one Cu (II) ion, two picrate anions,
one water molecule and THEEN ligand. THEEN coordinates to Cu(II)
through two hydroxyl oxygens O1 and O2 and both amine nitrogen
atoms N1 and N2 thus behaving as a tetradentate ligand towards
the metal ion as shown in (Fig. 1a). One of the site around metal
ion is also occupied by water molecule O1W giving rise to the
Yield: 84%. IR (KBr) cmꢂ1: 3354 (
m
(OH, str)), 2931 (
(NO2) as, str), 1333 ( (NO2) s, str), 1437 (d
(C–O) str), 1162 (d (–OH) s), 1080 ( (C–O)
m (C–H) s), 1633
(
m
(@CH) str), 1560 (
m
m
m
(@CH) w, br), 1269 (
m
alcohol), 937 (d (@C–H) bend), 795 (d (@CH), s), 709 (d (C@C)). Ele-
mental analysis: Anal. Calc. for C18H21CuN7O18: C, 31.47; H, 3.08; N,
14.27. Found: C, 31.50; H, 5.03; N, 14.30%.

58
R. Kumar et al. / Polyhedron 56 (2013) 55–61
Fig. 1. (a) ORTEP diagram of the complex (1), showing the atom labeling scheme. The anions and the hydrogen atoms attached to the carbon atoms have been removed for
clarity. (b) Square pyramidal view of the complex. (c) Molecular structure of the complex with hydrogen bonding interactions.
square pyramidal geometry with coordination number five
(Fig. 1b). The atoms O1, O1W, N1 and N2 are lying in the equatorial
positions forming one plane whereas O2 occurs in axial position
above the plane. The two picrate anions do not directly interact
with the metal ion but remain outside the coordination sphere.
The complex is thus a charge- separated complex as is in previ-
ously reported complexes of calcium picrate [15]. Extensive inter-
molecular and to a less extent intramolecular hydrogen bonding
interactions involving hydroxyl oxygens, water molecule, phenolic
oxygen and oxygen of the o-nitro group of picrate anion have been
observed in the crystal structure. Solvent water is providing stabil-
ity to the entire structure by donating and accepting as well as
undergoing intermolecular and intramolecular H-bonding interac-
tions (Table 3). It is acting as donor of H-bond towards terminal
alcoholic O1 and O4 of the ligand, phenolic O5 and O6 of the nitro
group of the picrate ion of the neighboring molecule (Fig. 1c). The
terminal alcoholic groups O1, O2 O3 and O4 are donating H- bonds
to water molecule (intramolecular), hydroxyl and phenolic
oxygens (intermolecular) respectively of the neighboring molecule
in the unit cell (Fig. 1c). Besides this, the centre to centre distance
between the two phenyl rings is 4.068 Å. This indicates face to face
the metal ion and remain outside the coordination sphere resulting
in the formation of a charge-separated complex. Coordinated ligat-
ing atoms O2, O3, O4 and N1 of the ligand are present in the equa-
torial positions and form one plane whereas O1 and N2 lying on
the axial positions above and below the plane (Fig. 2b). The lattice
solvent molecule propanol is also present outside the coordination
sphere in the complex and is involved in intramolecular as well as
intermolecular hydrogen bonding interactions (Table 3). The for-
mer are displayed when propanol donates its H-bond to phenolic
oxygen and one of the oxygen of the nitro group of picrate anion
and the latter are observed when it accepts H-bond from terminal
alcoholic group O2 of the neighboring unit. All hydroxyl oxygens
O1, O2, O3 and O4 of the ligand THPEN are donating H- bonds to
phenolic oxygen and one of the oxygen of the nitro group of the
neighboring picrate anions making them acceptors of H-bonds in
an intermolecular way, thus connecting the neighboring units
together and stabilizing the molecular structure (Fig. 2c). In this
complex the two phenyl rings have centre to centre distance
3.699 Å and they are also facing each other with p–p interaction.
The final X-ray crystal structure of complex (3) is shown in
(Fig. 3a) in which all the donor sites of TEAH3 ligand O1, O2, O3,
N1 and phenolic oxygen O4 of the picrate anion is in coordination
sphere of the Cu(II) ion with square pyramidal geometry (Fig. 3b).
The other picrate anion does not directly interact with the metal
ion but remains outside the coordination sphere thus resulting in
the formation of a partially charge-separated complex. One lattice
p–p
interaction between two phenyl rings.
In complex (2), Cu(II) is six coordinated with distorted octahe-
dral geometry. THPEN is interacting with Cu(II) through all the four
hydroxyl oxygen and two amine nitrogen atoms of the ligand as
shown in (Fig. 2a). Both picrate anions interact indirectly with

R. Kumar et al. / Polyhedron 56 (2013) 55–61
59
Fig. 2. (a) ORTEP diagram of the complex (2), showing the labeling scheme. The anion and the hydrogen atoms attached to the carbon atoms have been removed for clarity.
(b) Distorted octahedral view of the complex. (c) Molecular structure of the complex with hydrogen bonding interactions.
water molecule is also present outside the coordination sphere of
the metal ion and is involved in extensive intermolecular and
intramolecular hydrogen bonding interactions by donating its H-
bonds towards O15 and O17 oxygens of the neighboring picrate
molecule respectively. It is also accepting H-bond from terminal
alcoholic oxygen O3 in an intramolecular way. O1 and O2 of TEAH3
are donating H-bonds to one of the picrate anion in an intermolec-
ular as well as intramolecular way respectively (Fig. 3c). Thus, all
the terminal hydroxyl oxygens of the ligand are acting as donors
of H-bonds. In this complex, the centre to centre distance between
adopt different modes of coordination towards the metal ion due
to their flexible behavior. Due to more steric crowding, wrapping
of tetrapodands [15] around the metal ion does not leave space
for larger anions to enter inside the coordination sphere of metal
ion resulting in the formation of charge-separated complexes (1)
and (2). Tripodand TEAH3 is having comparatively lesser steric
crowding and wraps around the metal ion in such a way that the
larger anions can enter the coordination sphere of the metal ion
resulting in the formation of partially charge-separated complex
(3) as is observed in previously reported complexes of barium
[12d,13a].
the two phenyl rings is 4.210 Å that indicates face to face
interaction between two phenyl rings.
p–p
The number of hydrogen bonds formed in the complexes (1)
and (3) are greater in comparison to the complex (2) and it may
be due to the presence of water molecule either in the inner or out-
er coordination sphere forming the intermolecular hydrogen
bonding.
5. Antimicrobial activity
In the current study, all synthesized copper complexes have
been tested on different pathogenic bacteria S. marcescens, S. japon-
icum, S. maltophilia and S. aureus using the microbroth dilution
method. All complexes showed good activity against bacterial
Both tetrapodands THEEN and THPEN have six potential donor
sites whereas tripod TEAH3 has four donor atoms. These ligands
strains with MIC value ranging from 3.2 to 50 lg/ml as shown in

60
R. Kumar et al. / Polyhedron 56 (2013) 55–61
Fig. 3. (a) ORTEP diagram of the complex (3), showing the atom labeling scheme. The anion and hydrogen atoms attached to the carbon atoms have been removed for clarity.
(b) Square pyramidal view of the complex. (c) Molecular structure of the complex with hydrogen bonding interactions.
Table 4
Minimum inhibitory concentrations for the complexes and the metal salt (
bacterial strains by microbroth dilution method.
lg/ml) on
Compounds Staphylococcus Serratia
Stenotrophomonas Sphingobium
aureus
marcescens maltophilia
japonicum
PIC
Cu(II)PIC
Complex (1) 50
Complex (2) 25
Complex (3) 6.2
Ciprofloxacin 3.2
12.5
6.2
25
12.5
6.2
12.5
6.2
3.2
25
25
12.5
6.2
3.2
3.2
6.2
6.2
6.2
6.2
12.5
1.5
Fig. 4. Antimicrobial activity of complexes with minimum inhibitory concentration
(MIC) in ( g/ml).
Table 4. The result revealed that complex (3) appeared to have
broad spectrum as it exhibits mild to moderate activity towards
most of strains and it is comparable to the standard drug ciproflox-
acin. This may be due to the enhanced penetration of complexes
into the lipid membranes, the hydrocarbon tail function as a
lipophillic group to drive the compound through the semiperme-
able membrane of the cell and blocks the metal binding sites in
the enzymes of micro-organism [22]. This study suggests that such
l
type of complexes can further be explored as specific anti bacterial
drugs due to their decent activity against studied bacterial strains.
The bacterial growth inhibition capacity of the complexes followed
the order: (3) > (1) > (2) as shown in Fig. 4.

R. Kumar et al. / Polyhedron 56 (2013) 55–61
61
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of the ligands with the metal ions also serve as useful tool for the
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6. Conclusions
Crystal structure determinations reveal that all the three
ꢀ
complexes of Cu(II) picrate have been crystallized with P1 space
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and (3) with square pyramidal geometry and six in complex (2)
with distorted octahedral geometry. The interaction of tetrapod-
ands with copper picrate results in the formation of charge-sepa-
rated complexes while interaction of tripodand (TEAH3) results in
the formation of partially charge-separated complex. Solvent
molecules are present in each of three complexes providing stabil-
ity to the entire molecules by displaying intermolecular and intra-
molecular hydrogen bonding interactions and connecting
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tendency as efficient and non-hazardous catalyst for catalyzing
some chemical reactions.
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Authors are highly thankful to MHRD, New Delhi for providing
research assistantship to Mr. Rakesh Kumar, one of the authors and
Dr. B. R. Ambedkar National Institute of Technology, Jalandhar for
providing research infrastructure.
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Appendix A. Supplementary data
CCDC 881216, 894385 and 880408 contain the supplementary
crystallographic data for complexes [Cu(THEEN) (H2O)] (PIC)2 (1),
[Cu(THPEN)] (PIC)2ꢀC3H8O (2) and [Cu(TEAH3)(PIC)] (PIC)(H2O) (3)
respectively. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.poly.2013.03.043.
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