Sodium ion assisted molecular self-assembly in a class of Schiff-base copper(II) complexes

Article abstract of DOI:10.1016/j.poly.2012.01.004

Syntheses, characterization and crystal structures of three new sodium based heterotrinuclear ionic clusters [(CuL1)₂Na(ClO ₄-O,O′)(OH₂)]·C₈H ₈O₂ (1), [(CuL2)₂Na(ClO₄-O,O′) ] (2) and [{Cu(L3)₂}₂Na]⁺·ClO ₄^- (3) derived from three different Schiff bases (L1 = 1:2 condensation of 1,2-propane diamine and o-hydroxy acetophenone, L2 = 1:2 condensation of 1,2-propane diamine and 2-hydroxy-5-methoxy acetophenone and L3 = 1:1 condensation of 2-amino pyridine and 3-ethoxy salicylaldehyde) are reported herein. The crystal structure analysis reveals that the square-planar Cu-ligand complexes act as building block for the trinuclear complex in which Na⁺ ion guides the orientation of Cu(II) Schiff-base complexes into a scissor like architecture in 1 and 2. The unique assembling feature of Na ⁺ ion is also evident in complex 3 where even in the presence of a widely different Schiff-base ligand, Na⁺ guides two Cu(II)(L3) ₂ complexes to assemble around it in a crown ether like environment. In complexes 1 and 2 the square planar metal coordination provide suitable sites for chelate ring π···π interaction and Cu···π interaction which ensures columnar assembly of trinuclear units at the supramolecular level. The present study reveals the unique nature of the self-assembly of square-planar Cu(II) Schiff-base complexes around Na⁺.

Full text of DOI:10.1016/j.poly.2012.01.004

Polyhedron 35 (2012) 108–115
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Sodium ion assisted molecular self-assembly in a class of Schiff-base copper(II)
complexes
Partha Pratim Chakrabarty a, Debabrata Biswas a, Santiago García-Granda c, Atish Dipankar Jana b,
,
⇑
Sandip Saha a,
⇑
a Department of Chemistry, Acharya Prafulla Chandra College, New Barrackpur, Kolkata 700 131, India
b Department of Physics, Behala College, Parnasree, Kolkata 700 060, India
c Departamento de Química Físicay Analítica, Universidad de Oviedo, C/Julián Clavería 8, 33006 Oviedo, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Syntheses, characterization and crystal structures of three new sodium based heterotrinuclear ionicꢁclus-
ters [(CuL1)2Na(ClO4-O,O0)(OH2)]ꢀC8H8O2 (1), [(CuL2)2Na(ClO4-O,O0)] (2) and [{Cu(L3)2}2Na]+ꢀClO4 (3)
derived from three different Schiff bases (L1 = 1:2 condensation of 1,2-propane diamine and o-hydroxy
acetophenone, L2 = 1:2 condensation of 1,2-propane diamine and 2-hydroxy-5-methoxy acetophenone
and L3 = 1:1 condensation of 2-amino pyridine and 3-ethoxy salicylaldehyde) are reported herein. The
crystal structure analysis reveals that the square-planar Cu–ligand complexes act as building block for
the trinuclear complex in which Na+ ion guides the orientation of Cu(II) Schiff-base complexes into a scis-
sor like architecture in 1 and 2. The unique assembling feature of Na+ ion is also evident in complex 3
where even in the presence of a widely different Schiff-base ligand, Na+ guides two Cu(II)(L3)2 complexes
to assemble around it in a crown ether like environment. In complexes 1 and 2 the square planar metal
Received 30 September 2011
Accepted 5 January 2012
Available online 17 January 2012
Keywords:
Sodium
Ionic clusters
Schiff base
Copper
Scissor
coordination provide suitable sites for chelate ring
p
ꢀꢀꢀ
p
interaction and Cuꢀꢀꢀ
p interaction which ensures
Crown ether
columnar assembly of trinuclear units at the supramolecular level. The present study reveals the unique
nature of the self-assembly of square-planar Cu(II) Schiff-base complexes around Na+.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
the donor atoms is an important consideration to match the shape
of the coordination sphere of the target species. In crystal
Supramolecular chemistry [1–9], the chemistry of molecular
systems beyond individual molecules is highly dependent on the
understanding of the molecular self-assembly. The controlled
organization of simple molecular building blocks is governed by
hierarchy of forces involving covalent, coordinative and various
engineering one often rely on certain robust self-assembly features
such as hydrogen bonding synthon [21], recurrent -stacking
p
motifs which are generally relied in engineering of organic crystal
structures. In the design of coordination complexes additional
information taken into account is the stereochemical information
encoded in the metal ions. In this context, with Schiff base com-
plexes we have taken the standard synthetic approach of designing
Schiff base ligands with proper sites for coordination bond as well
weak forces such as hydrogen bonding [10,11],
p
ꢀꢀꢀ
p interaction
[12–16], C–Hꢀꢀꢀ interaction [17,18], metalꢀꢀꢀ interaction [19,20],
p
p
etc. In the resultant self-assembled super structure there is often a
compromise between various strong and weak forces. The weak
forces in many cases influence the structure even in the presence
of strong forces due to simultaneous cooperative effect among
themselves.
as other weak forces such as
p
ꢀꢀꢀ
p
and CHꢀꢀꢀ
p interaction by the
condensation of amines with hydroxylated aldehydes. Metal
salicylaldimines with phenoxo groups in the 2 and 20 positions
are a fascinating group of ligands that can coordinate with not only
p- and d-block metal elements but also alkali-metal ions. These
alkali-metal complexes of metal salicylaldimines are important in
small-molecule activation [22], electron storage [23,24], and the
carrying of polar organometallics [25,26]. Moreover, they can coor-
dinate with a metal ion of suitable size and form a sandwich struc-
ture of ion complexes between two sets of Schiff base oxygen
atoms [27–29]. In a very interesting study Sui et al. have synthe-
sized and reported two novel homochiral trinuclear sodium ionic
In the design of metal–ligand complexes the choice of metal
ions and the information encoded in the ligands are intelligently
utilized. There are many factors behind the choice of the ligand
such as its dimensionality, connectivities, shape, size, conforma-
tion, chirality, etc. The degree of flexibility of the ligand bearing
⇑
Corresponding authors. Tel.: +91 33 2416 0354; fax: +91 33 2537 8797.
E-mail addresses: atishdipankarjana@yahoo.in (A.D. Jana), sandipsaha2000@
yahoo.com (S. Saha).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2012.01.004

P.P. Chakrabarty et al. / Polyhedron 35 (2012) 108–115
109
Scheme 1.
clusters with nickel salicylaldimines as host units which have
extremely rare properties like ferroelectricity [28].
purification. IR spectra were recorded as KBr pellets within the
range 4000–400 cmꢁ1 on a Perkin-Elmer Spectrum RXI FTIR Spec-
trometer. Elemental analyses were carried out using a Heraeus
CHN-O-Rapid elemental analyzer.
Here, we report three trinuclear complexes of Cu-Schiff bases
and sodium namely [(CuL1)2Na(ClO4-O,O0)(OH2)]ꢀC8H8O2 (1), [(Cu
ꢁ
L2)2Na(ClO4-O,O0)] (2) and [{Cu(L3)2}2Na]+ꢀClO4 (3). Structures of
ligands L1, L2 and L3 are shown in Scheme 1. L1 and L2 are deproto-
nated Schiff bases prepared by the 1:2 condensation of 1,2-propane
diamine and o-hydroxy acetophenone for L1, and 1,2-propane dia-
mine and 2-hydroxy-5-methoxy acetophenone for L2. Ligand L3 is
similarly prepared in a 1:1 condensation of 2-amino pyridine and
3-ethoxy salicylaldehyde. The crystal structure analysis reveals that
the square-planar Cu–ligand complexes act as building block for a
trinuclear complex in which Na+ ion guides the orientation of Cu(II)
Schiff-base complexes into a scissor like architecture in 1 and 2. The
unique assembling feature of Na+ ion is also evident in complex 3
where even in the presence of a widely different Schiff-base ligand,
Na+ guides two Cu(II)(L3)2 complexes to assemble around it in a
crown ether like environment.
2.2. Syntheses
2.2.1. Synthesis of the complexes [(CuL1)2Na(ClO4-O,O0)(OH2)]ꢀC8H8O2
(1) and [(CuL2)2Na(ClO4-O,O0)] (2)
Caution! Perchlorates complexes of metal ions in the presence
of organic ligands are potentially explosive. Only a small amount
of material should be prepared, and it should be handled with care.
To a solution of o-hydroxy acetophenone (0.272 g, 2 mmol) in
20 mL of methanol was added 1,2-propane diamine (0.741 g,
1 mmol), and the resulting mixture was heated under reflux for
3 h. A solution of Cu(AcO)2ꢀH2O (0.199 g, 1 mmol) and NaClO4
(0.366 g, 3 mmol) in 40 mL of methanol was then added, and the
mixture was refluxed for another 3 h to give a deep-red solution
and black block-shaped single crystals of 1 were obtained after 3
days. Compound 2 was obtained as black block shaped crystals
by a method similar to that of 1, except that 2-hydroxy-5-methoxy
acetophenone (0.332 g, 2 mmol) was used.
2. Experimental
2.1. Materials and physical measurements
Complex 1: Yield ca. 70%. Anal. Calc. for C46H48N4O11Cu2NaCl: C,
54.2; H, 4.7; N, 5.5. Found: C, 54.8; H, 4.8; N, 6.0%. IR (KBr pellets,
All reagents and solvents for the synthesis and analysis were
commercially available and used as received without further
cmꢁ1): (ClO4ꢁ) 1144, 1111, 1088.
mas(water) 3432; m(C@N) 1633; m
Table 1
Crystallographic data for 1–3.
Crystal data
Formula
C
38H40ClCu2N4NaO9, C8H8O2
C42H48ClCu2N4NaO12
986.38
monoclinic
P2/n (No. 13)
12.1043(6), 11.5222(6), 16.0902(10)
C56H52Cu2N8NaO8, ClO4
1214.60
Formula weight
Crystal system
Space group
a, b, c (Å)
1018.40
monoclinic
P21/c (No. 14)
14.2170(6), 22.9540(6),
16.046(1)
90, 118.456(6), 90
4603.8(5)
monoclinic
P2/c (No. 13)
8.4593(3), 15.7526(4),
20.8509(5)
90, 103.002(3), 90
2707.27(14)
2
a
, b,
c
(°)
90, 106.725(6), 90
2149.1(2)
2
1.524
2.463
V (Å3)
Z
4
Dcalc (g cmꢁ3
)
1.469
1.056
1.490
2.100
l(Mo K
a
) (mmꢁ1
)
F(000)
2104
1020
1252
Crystal size (mm)
Data collection
T (K)
0.12 ꢂ 0.18 ꢂ 0.27
0.12 ꢂ 0.19 ꢂ 0.25
0.14 ꢂ 0.19 ꢂ 0.28
293
293
293
Radiation (Å)
(Mo K
a) 0.71073
(Cu Ka
) 1.54184
(Cu Ka) 1.54184
h (°)
1.6–25.1
3.8–67.2
3.5–70.7
Dataset
Total, unique data, Rint
Observed data [I > 2.0
Refinement
Nref, Npar
ꢁ16:16; ꢁ22:27; ꢁ19:16
16746, 8244, 0.030
5894
ꢁ14:14; ꢁ13:9; ꢁ19:17
7777, 3860, 0.035
2828
ꢁ7:10; ꢁ18:19; ꢁ25:25
10047, 5211, 0.056
3303
r(I)]
8244, 593
3860, 285
4947, 364
R, wR2, S
w
0.0970, 0.3146, 1.20
1/[ns2(Fo2) + (0.2000P)2] where
P = (Fo2 + 2Fc2)/3
0.0743, 0.2158, 1.04
1/[ns2(Fo2) + (0.0984P)2 + 2.3473P]
where P = (Fo2 + 2Fc2)/3
0.00, 0.00
0.0511, 0.1450, 1.03
1/[ns2(Fo2) + (0.0493P)2] where
P = (Fo2 + 2Fc2)/3
0.00, 0.00
Maximum and average shift/error 0.00, 0.00
Minimum and maximum residual ꢁ1.54, 1.74
ꢁ0.64, 0.42
ꢁ0.26, 0.28
density (e Åꢁ3
)

110
P.P. Chakrabarty et al. / Polyhedron 35 (2012) 108–115
Table 2
Selected bond distances (Å) and bond angles (°) in 1–3.
Complex 1
Complex 2
Complex 3
Bond distances (Å)
Cu1–O1
Cu1–O2
Cu1–N1
Cu1–N2
Cu2–O3
Cu2–O4
Cu2–N3
Cu2–N4
Na1–O1
Na1–O2
Na1–O3
Na1–O4
Na1–O9
Na1–O10
Na1–O1W
1.893(5)
1.883(5)
1.931(6)
1.935(6)
1.885(4)
1.885(5)
1.941(5)
1.941(5)
2.385(5)
2.389(5)
2.379(5)
2.390(6)
2.423(9)
2.513(9)
2.600(2)
Cu1–O1
Cu1–O2
Cu1–N1
Cu1–N2
Na1–O1
Na1–O2
Na1–O1_a
Na1–O2_a
Na1–O100
Na1–O100_a
1.889(4)
1.883(4)
1.933(5)
1.939(5)
2.341(4)
2.416(3)
2.341(4)
2.416(3)
2.563(9)
2.563(9)
Cu1–O1
Cu1–O2
Cu1–N1
Cu1–N3
Na1–O2_b
Na1–O4_b
Na1–O4
Na1–O1
Na1–O2
Na1–O1_b
1.900(2)
1.906(3)
1.965(3)
1.968(3)
2.311(2)
2.666(4)
2.666(4)
2.421(3)
2.311(2)
2.421(3)
Bond angles (°)
O1–Cu1–O2
O1–Cu1–N1
O1–Cu1–N2
O2–Cu1–N1
O2–Cu1–N2
N1–Cu1–N2
O3–Cu2–O4
O3–Cu2–N3
O3–Cu2–N4
O4–Cu2–N3
O4–Cu2–N4
N3–Cu2–N4
Cu1–O1–Na1
Cu1–O2–Na1
Cu2–O3–Na1
Cu2–O4–Na1
O1–Na1–O1W
O1–Na1–O2
O1–Na1–O3
O1–Na1–O4
O1–Na1–O9
O1–Na1–O10
O2–Na1–O3
O2–Na1–O4
O2–Na1–O9
O2–Na1–O10
O3–Na1–O4
O3–Na1–O9
O3–Na1–O10
O4–Na1–O9
O4–Na1–O10
O9–Na1–O10
O1W–Na1–O2
O1W–Na1–O3
O1W–Na1–O4
O1W–Na1–O9
O1W–Na1–O10
85.6(2)
174.6(2)
93.8(2)
93.1(2)
177.0(2)
87.7(2)
87.5(2)
93.3(2)
176.0(2)
173.3(2)
92.7(2)
87.1(2)
96.1(2)
96.2(2)
100.2(2)
99.8(2)
91.0(3)
65.0(2)
148.8(2)
94.4(2)
108.0(2)
103.6(2)
91.0(2)
93.7(2)
131.3(3)
168.5(2)
66.3(2)
102.8(2)
99.1(2)
134.7(3)
85.5(2)
51.6(3)
91.0(5)
110.0(4)
174.0(4)
40.3(6)
90.5(6)
O1–Cu1–O2
O1–Cu1–N1
O1–Cu1–N2
O2–Cu1–N1
O2–Cu1–N2
N1–Cu1–N2
O1–Na1–O2
O1–Na1–O100
O1–Na1–O1_a
O1–Na1–O2_a
O1–Na1–O100_a
O2–Na1–O100
O1_a–Na1–O2
O2–Na1–O2_a
O2–Na1–O100_a
O1_a–Na1–O100
O2_a–Na1–O100
O100–Na1–O100_a
O1_a–Na1–O2_a
O1_a–Na1–O100_a
O2_a–Na1–O100_a
Cu1–O1–Na1
87.6(2)
93.0(2)
176.1(2)
176.6(2)
92.5(2)
O1–Cu1–O2
O1–Cu1–N1
O1–Cu1–N3
O2–Cu1–N1
O2–Cu1–N3
N1–Cu1–N3
O1–Na1–O4
O1–Na1–O2
O2–Na1–O4_b
O1_b–Na1–O4
O2_b–Na1–O4
O4–Na1–O4_b
O1_b–Na1–O2_b
O1_b–Na1–O4_b
O2_b–Na1–O4_b
O1–Na1–O4_b
O2–Na1–O4
O1_b–Na1–O2
O2–Na1–O2_b
O1–Na1–O1_b
O1–Na1–O2_b
Cu1–O1–Na1
b = 1 ꢁ x, y, 1/2 ꢁ z
87.4(1)
93.7(1)
151.8(1)
149.5(1)
91.6(1)
101.2(1)
129.3(8)
67.4(1)
106.4(1)
121.4(9)
106.4(1)
77.9(1)
67.4(1)
129.3(8)
62.0(1)
121.4(9)
62.0(1)
124.2(1)
166.2(2)
84.1(1)
87.2(2)
66.6(1)
111.1(2)
90.3(2)
100.3(1)
158.3(2)
92.0(2)
100.3(1)
162.1(2)
104.4(2)
158.3(2)
104.4(2)
48.1(3)
66.6(1)
111.1(2)
92.0(2)
124.2(1)
99.2(1)
100.2(2)
a = 3/2 ꢁ x, y, 1/2 ꢁ z
Complex 2: Yield ca. 60%. Anal. Calc. for C42H48N4O12Cu2NaCl: C,
2.3. Crystal structure determinations of 1–3
51.1; H, 4.86; N, 5.7. Found: C, 51.4; H, 4.9; N, 5.9%. IR (KBr pellets,
cmꢁ1):
m
(C@N) 1591;
m
(ClO4ꢁ) 1110, 1072, 1043, 1025.
Crystal data for all the three compounds are given in Table 1.
The bond distances and bond angles for all the three compounds
are given in Table 2. 8244, 3860 and 5211-independent data for
1, 2 and 3, respectively, were collected on a Bruker Smart Apex II
CCD Area Detector equipped with a graphite monochromator Mo
2.2.2. Synthesis of the complex [{Cu(L3)2}2Na]+ꢀClO4 (3)
ꢁ
To a solution of 3-ethoxy salicylaldehyde (0.332 g, 2 mmol) in
20 mL of methanol was added 2-amino pyridine (0.188 g, 2 mmol),
and the resulting mixture was heated under reflux for 3 h. A solu-
tion of Cu(AcO)2ꢀH2O (0.199 g, 1 mmol) and NaClO4 (0.366 g,
3 mmol) in 40 mL of methanol was then added, and the mixture
was refluxed for another 3 h to give a deep-red solution and black
block-shaped single crystals of 3 were obtained after 2 days.
Complex 3: Yield ca. 60%. Anal. Calc. for C56H52N8O12Cu2NaCl: C,
55.3; H, 4.3; N, 9.2. Found: C, 56.1; H, 4.9; N, 8.9%. IR (KBr pellets,
Ka radiation (k = 0.71073 Å). Data collections were carried out
using Bruker Apex2 software for all the compounds [30]. Multiscan
absorption corrections were carried out using SADABS [31] in all the
cases. The structure of the complex was solved by direct methods
with SHELXL [32] for compounds 1, 2 and 3, respectively. The struc-
ture refinements were also performed by full-matrix least squares
based on F2 with SHELXL [32] in all the cases. All non-hydrogen
atoms were refined anisotropically. The C-bound H atoms were
constrained to ideal geometry and were included in the refinement
cmꢁ1): (ClO4ꢁ) 1091.
m(C@N) 1606; m

P.P. Chakrabarty et al. / Polyhedron 35 (2012) 108–115
111
in the riding model approximation. Data for molecular geometry,
intermolecular interactions and pictures were produced using PLA-
TON-2003 [33] and ORTEP3.2 [34] programs.
3. Results and discussion
3.1. Synthesis of the complexes
All three Schiff base ligands and their complexes were synthe-
sized in a very facile and essentially identical way. The respective
diamines and the carbonyl compounds were mixed in stoichiome-
tric ratios 1:2 for L1 and L2 and 1:1 for L3, respectively, in metha-
nol and refluxed. The methanolic solution of copper acetate
monohydrate and sodium perchlorate was added to the methano-
lic solution of the Schiff base ligand prepared and refluxed for 3 h
and the desired complexes were separated after a few days.
The characteristics of the ligands as well as the substrates are
crucial in molecular recognition, because the selective bonding
between the ligand and the substrate originates from this informa-
tion. This information is literally stored in the ligand and is read out
by the substrate. This characteristic information helps to define the
stability and selectivity of the complexes. Ion–molecule complexes
are usually stronger than the molecule–molecule complexes,
because of the strong interaction between ions and the molecule.
Fig. 1. ORTEP diagram of complex
numbering scheme. There also exists one acetophenone molecule in the asymmet-
ric unit (not shown here for clarity).
1
(30% ellipsoidal probability) with atom
3.2. IR spectroscopy
ion. Na+ ion thus plays the role of a mediator to organize two
Cu(II)L1 units around it. Due to the stereo electronic disposition
of the Na+ ion, two Cu(II)L1 units are slightly rotated with respect
to each other in the outer coordination sphere of the Na+ ion. This
gives rise to the open scissor topology of the whole trinuclear sys-
tem. All the terminal methyl groups of the two Cu(II)L1 units also
facilitate the open scissor topology due to relative rotation of the
two Cu(II)L1 units with respect to each other to reduce steric con-
gestion. Due to one sided arrangement of the two Cu(II)L1 units
around the Na+ ion in which Na+ ion spends four of its coordina-
tion, the other side of the coordination sphere of the Na+ ion is rel-
atively unhindered. A perchlorate anion and a water molecule
balance the charge and saturate Na+ coordination by double coor-
dination through O9 and O10 of perchlorate anion from this unhin-
dered side. It is interesting to observe that though Cu(II)L1 neutral
complexes could be self-assembled into a hypothetical crystal
structure in the absence of Na+ ion, the presence of Na+ ion has
made the present complex to accept perchlorate ions for charge
balancing.
The first two complexes show two broad and hump bands at
3432 cmꢁ1 for complex
1 respectively. These bands can be
attributed to the mH frequency. The third complex does not
2O
show this type of band at this region as water molecule is not
present in this complex. The band corresponding to the azome-
thine (C@N) group is distinct in all the three complexes; it oc-
curs at 1633, 1591, and 1606 cmꢁꢁ1 for complexes 1, 2, and 3,
respectively. Concerning the ClO4 anions, the m3 mode occurs
at 1144, 1111, 1088 cmꢁ1 for complex 1 and 1110, 1072, 1043,
1025 cmꢁ1 for complex 2, respectively. These bands are extre-
mely broadened and divided into many parts suggesting that
these anions are coordinated to the central sodium atoms as
substantiated by the crystal structures. There is no splitting of
the band at 1091 cmꢁ1 for complex 3 is indicative for the pres-
ence of non coordinated perchlorate ion.
3.3. Description of the structures
In the Cu(II)L1 units the maximum and minimum Cu–N bond
distances are 1.931(6) and 1.941(5) Å, respectively, and the Cu–O
bond distances are in the range 1.883(5)–1.893(5) Å (Table 2).
The Na–O (hydroxyl) bond distances fall in the range
2.379(5)–2.390(6) Å [28,29]. Two Na–O (perchlorate) distances
are 2.423(9) and 2.513(9) Å, respectively. The Na–O1W distance
is 2.600(2) Å.
3.3.1. Complex 1
X-ray crystallographic analysis reveals a trinuclear complex in
the asymmetric unit containing two Cu(II) centers and a Na+ center
(Fig. 1). There is also a o-hydroxy acetophenone molecule in the
asymmetric unit. Two Cu(II) centers have square planar coordina-
tion geometry with the hepta-coordinated sodium in between. The
tetra dentate Schiff base ligand L1 binds to Cu(II) centers producing
square planar Cu(II)L1 complexes. The interesting aspect of the
complexation phenomena is that these Cu(II)L1 units act as build-
ing block for a higher level complexation in which two such
Cu(II)L1 units are organized around a Na+ ion giving a open scissor
like topology of the trinuclear complex (Fig. 1). In the Cu(II)L1
units, the ligand L1 encircles the Cu(II) center by binding it with
two adjacent N atoms of the amine group in one side and by two
hydroxyl oxygen atoms on the other side. The two long edges of
the square plane of the Cu(II) coordination environment is thus
asymmetric with three methyl groups arranged on one of the sides
making it sterically congested. On the other side of the square
plane two hydroxyl oxygen atoms are arranged and these two
oxygen atoms simultaneously act as the binding sites to the Na+
The supramolecular assembly of the trinuclear complexes is
built up by weak
phenyl rings but also, more interestingly, the Cu(II)L1 chelate rings
(shaded orange1 in Fig. 1). The
interaction
p-interaction involving not only the ligand
p
ꢀꢀꢀ
p
and C–Hꢀꢀꢀ
p
involving the ligand phenyl ring and the metal-chelate ring is
responsible for columnar assembly (Fig. 2) of the successive trinu-
clear units along the crystallographic c-axis. The square planar nat-
ure of the Cu(II) coordination environment facilitates the
interaction (for details, see Table 3) between the metal-chelate
p p
ꢀꢀꢀ
rings of adjacent trinuclear units which are centrosymmetrically
1
For interpretation of the references to color in Figs. 1 and 4, the reader is referred
to the web version of this article.

112
P.P. Chakrabarty et al. / Polyhedron 35 (2012) 108–115
Fig. 2. One dimensional supramolecular assembly of molecular complexes along the crystallographic c-axis. CHꢀꢀꢀ
p interaction is denoted by blue dotted lines and the pꢀꢀꢀp
interaction by orange dotted lines. (Color online.)
Table 3
Geometrical parameters (Å, °) for the face to face
p-stacking interactions involving metal-chelate rings and phenyl rings in compounds 1–3.
Complexes Ring(i) ? ring(j) Dihedral angle
(i,j) (°)
Slip angle
(i,j) (°)
Distance between ring-centroid(i) and ring-
centroid(j) (Å)
Perpendicular distance of ring(i) centroid and
ring(j) plane (Å)
1
R(3) ? R(6)i
R(4) ? R(5)i
R(5) ? R(8)ii
1.58
5.12
26.40
19.12
19.60
5.34
3.671(3)
3.743(3)
3.954(4)
3.497
3.601
3.658
(i) = X, 3/2 ꢁ Y, ꢁ1/2 + Z; (ii) X, Y, Z
R(3) ? Cu1–O1–C1–C6–C7–N2; R(4) ? Cu1–O2–C19–C14–C12–N1; R(5) ? Cu2–O3–C20–C25–C26–N3; R(6) ? Cu2–O4–C38–C33–C31–N4;
R(8) ? C14–C15–C16–C17–C18–C19
2
3
R(2) ? R(5)i
7.79
0.00
17.56
19.44
3.795(3)
3.721(3)
3.430
3.508
R(3) ? R(3)i
(i) = 1 ꢁ X, ꢁY, ꢁZ
R(2) ? Cu1–O1–C6–C5–C8–N1; R(3) ? Cu1–O2–C16–C15–C13–N2; R(5) ? C15–C16–C17–C18–C19–C20
R(3) ? R(4)i
R(5) ? R(5)ii
25.38
5.96
17.19
26.68
3.758(4)
3.813(3)
3.425
3.406
(i) = X, Y, Z; (ii) = 1 ꢁ X, Y, 1/2 ꢁ Z
R(3) ? N2–C1–C2–C3–C4–C5; R(4) ? N4–C17–C22–C21–C20–C19; R(5) ? C8–C9–C10–C11–C12–C13
Table 4
Geometrical parameters (Å, °) for the C–Hꢀꢀꢀ
p
interactions involving metal-chelate rings and phenyl rings in compounds 1 and 2.
Complexes
X–H ? ring(j)
X–HꢀꢀꢀR(i) angle (°)
Distance between hydrogen atom and ring-centroid(j) (Å)
Xꢀꢀꢀcentroid ring(j) distance (Å)
1
C8–H8C ? R(10)i
C13–H13C ? R(9)i
C27–H27A ? R(8)ii
C32–H31C ? R(7)ii
146
135
131
137
2.75
2.74
3.00
2.75
3.590(11)
3.483(12)
3.704(10)
3.512(13)
(i) = X, 3/2 ꢁ Y, ꢁ1/2 + Z; (ii) = X, 3/2 ꢁ Y, 1/2 + Z
R(7) ? C1–C2–C3–C4–C5–C6; R(8) ? C14–C15–C16–C17–C18–C19; R(9) ? C20–C21–C22–C23–C24–C25; R(10) ? C33–C34–C35–C36–C37–C38
2
C11–H11B ? R(4)i
141
2.95
3.749(10)
(i) = 3/2 ꢁ X, Y, 1/2 ꢁ Z
R(4) ? C1–C2–C3–C4–C5–C6
arranged. The methyl group of the acetophenone part of the ligand
between supramolecular columns of trinuclear units formed
through -interaction. The acetophenone dimers are sandwiched
among the –CH3 groups from both sides and interact by CH–
interaction with the methyl group attached to the 1,2-propane dia-
mine part of the ligand L1. The three dimensional packing arrange-
ment of the complexes inside the crystal is depicted in Fig. S1 (see
Supplementary material).
is involved in C–Hꢀꢀꢀ
p
p
interaction (Table 4) which acts in unison
interaction. The interaction involv-
p
with the chelate ring
ꢀꢀꢀ
p
p
ꢀꢀꢀ
p
p
ing metal chelate rings have been explored only in recent years
[16] and detailed nature of this type of interaction is yet to be
ascertained. The present complex is an example which shows that
square planar metal coordination may provide suitable sites for
chelate ring
pꢀꢀꢀp interaction.
An interesting side of the crystal structure is the presence of
orthohydroxy acetophenone molecules. These molecules form
hydrogen bonded dimers with R22(10) hydrogen bonded motif in
Etter’s graph [35] notation (Fig. 3). These dimers are intercalated
3.3.2. Complex 2
X-ray crystallographic analysis reveals a similar trinuclear com-
plex with two Cu(II) centers and a Na+ center in complex 2 as that
was found in 1 (Fig. 4). Unlike 1, here the Na+ ion (Na1) occupies

P.P. Chakrabarty et al. / Polyhedron 35 (2012) 108–115
113
the center of inversion and two Cu(II)L2 building blocks that are
organized into a similar scissor like topology are symmetric coun-
ter parts of each other. Two Cu(II) centers have square planar coor-
dination geometry with the tetradentate Schiff base ligand L2
encircling Cu(II) ions by two of the amine nitrogen atoms (N1,
N2) and two hydroxyl oxygen atoms (O1, O2) producing six mem-
bered chelate rings (shaded orange in Fig. 4). Instead of hepta
coordinated sodium that was observed in 1, in 2 the Na+ ion is
hexa-coordinated. Due to much more torsion (than that was found
in 1) between the scissor arms consisting of Cu(II)L2 complexes, no
Fig. 3. The hydrogen bonded acetophenone dimers are sandwiched between successive supramolecular columns of trinuclear units and are surrounded by the terminal
methyl groups of ligand L1.
Fig. 4. ORTEP diagram of complex 2 (20% ellipsoidal probability) with atom numbering scheme. Planarity of the chelate rings (shaded) facilitates p-stacking interaction in the
supramolecular assembly.

114
P.P. Chakrabarty et al. / Polyhedron 35 (2012) 108–115
Fig. 5. One dimensional supramolecular assembly of molecular complexes in the crystal of complex 2. Cuꢀꢀꢀ
p
interaction involving the metal chelate ring is the unique
(chelate ring) interaction.
supramolecular feature of the complex. ꢀꢀꢀ interaction involving phenyl ring and metal chelate ring acts in unison with the Cuꢀꢀꢀp
p
p
The Cu–N bond distances in Cu(II)L2 units are 1.933(5) and
1.939(5) Å respectively whereas the Cu–O bond distances are
1.889(4) and 1.883(4) Å (Table 2). The Na–O (hydroxyl) bond dis-
tances fall in the range 2.341(4)–2.416(3) Å [28,29]. Two Na–O
(perchlorate) distances are 2.563(9) Å each.
The supramolecular assembly of the trinuclear complexes in 2 is
also governed by similar kind of
p
interaction in which the Cu(II)L2
inter-
chelate ring plays important role. Unlike in 1, here Cu(II)ꢀꢀꢀ
p
action between adjacent units is the dominant force in organizing
successive trinuclear units into a one dimensional columnar
assembly (Fig. 5). Cu1 interacts with the 6-membered chelate ring
[Cu1–O2–C16–C15–C13–N2] with ring centroidꢀꢀꢀCua [a = 1 ꢁ x,
ꢁy, ꢁz] distance 3.721(3) Å and a slip angle of 19.44°. Along with
the Cu(II)ꢀꢀꢀ
p
forces the
p p interaction (Tables 3 and 4) between
ꢀꢀꢀ
the phenyl rings and metal-chelate rings helps this assembly. It is
to be noted that in 2, no CHꢀꢀꢀ
p
interaction involving metal-chelate
ring comes into play which is present in 1. Due to greater torsion
between the two scissor arms this interaction is prohibited in 2.
The three dimensional packing patterns of the columnar units is
depicted in Fig. S2 (see Supplementary material).
3.3.3. Complex 3
The X-ray crystallographic study reveals a trinuclear super com-
plex where Na+ ion plays analogous organizing role as that was
found in 1 and 2. Here two Cu(II)(L3)2 complexes are united into
a esthetically attractive butterfly like architecture with Na+ coordi-
nated in a crown-ether like topology (Fig. 6). The ligand L3 is the
result of condensation of 2-aminopyridine and 3-ethoxy salicylal-
dehyde, having a different nature than ligand L1 and L2. Here
two ligands bind the Cu(II) ion by the amino nitrogen and the hy-
droxyl oxygen giving rise to a distorted square planar complex
Cu(II)(L3)2. Two chelate ring planes in the complex Cu(II)(L3)2
are rotated with respect to each other due to the intra-molecular
p p interaction between the dangling pyridine rings of the two li-
ꢀꢀꢀ
gands that bind to Cu(II) ion. In the complex assembled by the Na+
ion, each of the Cu(II)(L3)2 complexes donate three coordination to
the Na+ ion making it octa coordinated. Besides the two hydroxyl
oxygens of two L3 that bind to Cu(II) the ethoxy oxygen atom also
coordinates the Na+ ion. Crown ether like topology of the Na+ ion is
Fig. 6. The ORTEP diagram (30% ellipsoidal probability) of complex 3 in which role of
Na+ ion self-organizes Cu(II)(L3)2 in a crown ether like topology.
water molecule is present in the coordination sphere of Na+. Here,
only the perchlorate ion could coordinate to Na+ ion by two of its
oxygen atoms (O100 and O100⁄, ꢃ = 3/2 ꢁ x, y, 1/2 ꢁ z).
due to intra-molecular
pꢀꢀꢀp interaction between the phenyl groups

P.P. Chakrabarty et al. / Polyhedron 35 (2012) 108–115
115
of the two Cu(II)(L3)2 complexes that are organized by Na+ ion
keeping itself at the core of the complex. It is interesting to note
that the perchlorate ion in this case cannot coordinate to the Na+
ion; instead it remains as counterion outside the coordination
sphere. Another interesting feature of complex 3 is that, in the
supramolecular assembly of the trinuclear complexes the weak
forces involving the Cu–ligand chelate rings is absent. Here a dif-
ferent supramolecular organization is mainly governed by disper-
sion forces (Fig. S3, Supplementary material) having a layered
architecture with grooves accommodating perchlorate counter
ions. This is expected as in this case the two chelate rings around
Cu(II) ion are heavily twisted with respect to each other, having
a non-planar geometry of the coordination plane.
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 doi:10.1016/j.poly.2012.01.004.
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Appendix A. Supplementary data
CCDC 826103, 826104, and 826105 contains the supplementary
crystallographic data for 1, 2, and 3, respectively. These data can be