Ligand mediated structural diversity and role of different weak interactions in molecular self-assembly of a series of copper(II)-sodium(I) Schiff-base heterometallic complexes

Article abstract of DOI:10.1016/j.ica.2013.09.011

We report three new Cu-Na heterometallic complexes namely [Cu(L1 ^2-)Na(NO₃)(CH₃OH)] (1), [Cu(L2 ^2-)Na(NO₃) (CH₃OH)] (2) and [Cu Na (L3 ^3-)]_n (3) where the topology of

Full text of DOI:10.1016/j.ica.2013.09.011

Inorganica Chimica Acta 408 (2013) 172–180
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Ligand mediated structural diversity and role of different weak
interactions in molecular self-assembly of a series of
copper(II)–sodium(I) Schiff-base heterometallic complexes
b,
Debabrata Biswas a, Partha Pratim Chakrabarty a, Sandip Saha a, , Atish Dipankar Jana
⇑
⇑
,
Dieter Schollmeyer c, Santiago García-Granda d
a Department of Chemistry, AcharyaPrafulla Chandra College, New Barrackpur, Kolkata 700 131, India
b Department of Physics, Behala College, Parnasree, Kolkata 700 060, India
c Institut fur OrganischeChemie, Universit at Mainz, Duesbergweg 10-14, 55099 Mainz, Germany
d Departamento de QuímicaFísicayAnalítica, Universidad de Oviedo, C/JuliánClavería 8, 33006 Oviedo, Spain
a r t i c l e i n f o
a b s t r a c t
We report three new Cu–Na heterometallic complexes namely [Cu(L12ꢀ)Na(NO3)(CH3OH)] (1), [Cu(L22ꢀ)-
Na(NO3) (CH3OH)] (2) and [Cu Na (L33ꢀ)]n (3) where the topology of the synthon is directly governed by
Article history:
Received 15 June 2013
Received in revised form 3 September 2013
Accepted 4 September 2013
Available online 13 September 2013
the
how the systematic variation in the ligand framework influences the supramolecular assembly and the
mutual cooperation of different -forces and the hydrogen bonding forces in the supramolecular assem-
bly. The -forces are more important than the hydrogen bonding forces in such compounds is evident
from the supramolecular assembly of compound 3. Most interesting revelation of the studies are the
presence of relatively uncommon interactions
p–p interaction involving the Cu-Schiff base chelate rings. The crystal structure analysis also reveals
p
p
Keywords:
Heterometallic
Schiff bases
Weak interactions
Supramolecular assembly
Tape motif
p
-forces such as chelate ringꢁ ꢁ ꢁchelate ring and metal–
p
in the supramolecular architecture of the complexes. The analysis of the supramolecular assembly of
the complexes 1–3 reveals that metal-chelate rings play prominent role in the organization of the molec-
ular complexes and should seriously consider along with other
p
-stacking forces.
Self-organization
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
encoded in the metal ions which is revealed in the preferred coor-
dination geometry of metal ions in the presence of a particular or a
set of organic ligands. In this case ligand induced weak forces oper-
ate in a particular manner so that it can cooperate with coordina-
tive forces but at times the weak forces can also compete with
coordinative forces [51]. Prediction of the self-assembled structure
is beset with the problem of accuracy due to the weak nature of
directing forces. A slight perturbation in the physicochemical con-
dition or a slight modification of the ligand framework generally
leads to widely diverse self-assembled super structures. Designing
a robust supramolecular motif is the key step in the reliable predic-
tion of superstructure. Such robust recurring motifs are termed as
‘‘synthon’’ by G.R. Desiraju [52]. Usually the relatively strong
hydrogen bonding forces are employed to design a robust supra-
Molecular self-assembly is the nature inspired methodology
widely adopted in diverse areas of science and technology like
supramolecular chemistry[1–7], crystal engineering [8–10], liquid
crystal engineering [11–12], molecular electronics [13–15], bio-
technology [16–17], host–guest chemistry[18–20], etc. Wide
spread utilization of self-assembly has provided enough maturity
to the field of crystal engineering which is the area where scientists
aim the designed synthesis of crystalline materials where the
molecular organization in the solid state can be reliably predicted
from the knowledge of molecular tectons. In the endeavor of con-
trolled organization of molecular building blocks generally various
weak forces such as hydrogen bonding [21–29],
[30–45], C–Hꢁ ꢁ ꢁ interaction [46–50], metal-
have mostly been relied upon. Often particular hydrogen bonding
synthon or a stable -stacking motif has been employed to direct
molecular units. In the design of molecular materials involving me-
tal ions, additional consideration is the stereochemical information
p p interaction
interaction [47]
ꢁ ꢁ ꢁ
p
p
molecular motifs, but other weak forces such as p-p and CH-p
interactions are also suitable for designing such motifs. In the
supramolecular assembly of the discrete metal–organic complexes
the supramolecular assembly of discrete units are controlled by
suitably designing the ligand. This involves tuning the coordination
sites as well as organizing appropriate groups for hydrogen bond-
p
ing or
ligand centric
emerged recently in square planar Cu, Ni and Pt complexes which
p
-stacking on the ligand framework. Beyond the completely
⇑
Corresponding authors. Fax: +91 33 2537 8797.
E-mail addresses: sandipsaha2000@yahoo.com (S. Saha), atishdipankarjana@ya-
p-stacking groups another stacking capable unit has
hoo.in (A.D. Jana).
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.09.011

D. Biswas et al. / Inorganica Chimica Acta 408 (2013) 172–180
173
is the metal–ligand chelate ring [53–55]. It is intriguing that, even
in the presence of ligand centric -stacking moieties which are
-stacking sties, metal–ligand chelate
-stacking capability. The structures
Elemental analyses were carried out using a Heraeus CHN-O-Rapid
elemental analyzer.
p
supposed to provide strong
rings in many cases exhibit
p
p
2.3. Syntheses
presented in the present paper are designed with an intention to
explore the detailed nature of the competition between these
two type of p-stacking sites. Recently we have shown that square
2.3.1. Synthesis of the ligands
The Schiff base ligands H2L1, H2L2 and H2L4 were synthesized
by refluxing1,2-propane diamine (0.074 ml, 1 mmol), 1,3-propane
diamine (0.074 ml, 1 mmol) and ethylenediamine (0.06 ml,
1 mmol) with 3-methoxy salicylaldehyde (0.332 g, 2 mmol) in
methanol (10 mL) for two hrs, respectively. The H3L3 was pro-
duced in the same procedure by using 1,3 diamino-2-propanol
(0.09 ml, 1 mmol) and 3-ethoxy salicylaldehyde (0.332 g, 2 mmol).
The ligands were not isolated; instead the resulting yellow metha-
nolic solutions were subsequently used for complex formation in
every case.
planar Cu complexes can reliably be designed with Schiff bases
resulting from the condensation of amines with hydroxylated alde-
hydes and saturating its remaining coordination sites by simulta-
neous use of auxiliary Na metal ions [56]. In the present paper
we report a set of closely related Cu–Na hetero bimetallic com-
plexes with suitably designed Schiff-base ligand bearing aromatic
p
p
-rings. The six coordination sites and two possible ligand centric
–interaction sites on Salicylaldimines with phenoxo groups in
the 2 and 20 positions render it suitable for coordinating various
p- and d-block metal elements and also various alkali-metal ions
[57–62] and subsequent intra complex supramolecular interaction.
In the present study we have chosen Cu and Na along with a set of
three closely related ligands H2L1, H2L2, H3L3 and along with re-
ported earlier [57] H2L4 (Scheme 1) which differs from each other
systematically.
2.3.2. Synthesis of complexes [Cu(L12ꢀ)Na(NO3)(CH3OH)] (1) and
[Cu(L22ꢀ)Na (NO3) (CH3OH)] (2), [Cu(L42-)Na(NO3)(CH3OH)] (4)
A clear solution of Cu(CH3COOH)2ꢁH2O (0.199 g, 1 mmol) in
methanol (10 ml) was added to a 10 mL methanolic solution of
the H2L1, and the mixed solution was stirred for 0.5 h. Aqueous
solution of Sodium Nitrate(0.34 g, 4 mmol) dissolved in minimum
volume of water was added drop wise to the resulting solution
with constant stirring for 2 h. The reddish solution was filtered.
On slow evaporation of the resulting reddish colored solution the
dark red block shaped single crystal of the complex 1 was sepa-
rated out in a few days. The crystals were filtered and washed with
methanol and dried in air. The crystals of complex 2 and 4 were ob-
tained in the same manner described above using yellow methano-
lic solution of H2L2 and H2L4 for complex 1. Complex 4 was
reported earlier by Cunningham et. al. [57] but our synthetic pro-
cedure is different and we have considered it for our weak interac-
tions discussion section.
We report three new Cu–Na heterometallic complexes namely
[Cu(L12ꢀ)Na(NO3)(CH3OH)] (1), [Cu(L22ꢀ)Na(NO3)(CH3OH)] (2),
and [Cu Na (L33ꢀ)]n (3) where the topology of the supramolecular
assembly is decisively influenced by the stacking interaction
involving the Cu-Schiff base chelate rings.H2L1, H2L2 were synthe-
sized in 1:2 condensation of 1,2-propane diamine and 1,3-propane
diamine with 3-methoxy salicylaldehyde, respectively. The H3L3
was produced in the same procedure by using 1, 3 diamino-2-pro-
panol and 3-ethoxy salicylaldehyde. The analysis of the supramo-
lecular assembly of the complexes 1–3 reveal that metal-chelate
rings play prominent role in the organization of the molecular
complexes and should seriously consider along with other p-stack-
ing forces. We also compare our complexes with a similar set of
three complexes reported by Bhowmick et al. [60] recently where
they have highlighted the hydrogen bonding forces in the self-
organization.
Complex 1: Yield 65%. Anal. Cacl. for (complex 2) C20H24CuN3-
NaO8: C, 46.06; H, 4.60; N, 8.06. Found: C, 46.07; H, 4.56; N,
8.1%. IR (KBr pellets, cmꢀ1):
m(CH3OH) 3412, m(C@N) 1638,
m
(NO3) 1384.
Complex 2: Yield 70%. Anal. Cacl. for (complex 3) C20H24CuN3-
NaO8: C, 46.06; H, 4.6; N, 8.06. Found: C, 46.1; H, 4.58; N, 8.04%.
IR (KBr pellets, cmꢀ1):
(CH3OH) 3434, (C@N) 1628, (NO3) 1384.
2. Experimental
m
m
m
Complex 4 (reported): Yield 60%. Anal. Cacl. for (complex 1) C19-
2.1. Materials
H22CuN3NaO8: C, 44.97; H, 4.33; N, 8.28. Found: C, 44.98 H, 4.3; N,
8.3%. IR (KBr pellets, cmꢀ1):
1384.
m(CH3OH) 3435; m(C@N) 1630; m(NO3)
All reagents and solvents were purchased from Sigma–Aldrich
and were used as received. All other chemicals used were of ana-
lytical grade.
2.3.3. Synthesis of complex 3: [Cu Na (L43ꢀ)]n
A clear solution of Cu(CH3COOH)2ꢁH2O (0.199 g, 1 mmol) in
methanol (10 ml) was added to a 5 ml methanolic solution of the
H3L3, and the mixed solution was stirred for 0.5 h. Aqueous solu-
tion of Sodium Nitrate dissolved in minimum amount of water
(0.34 g, 4 mmol) was added dropwise to the resulting solution with
2.2. Physical measurements
IR spectra were recorded as KBr pellets within the range 4000–
400 cmꢀ1on
a Perkin-Elmer Spectrum 65 FTIR Spectrometer.
OH
N
H
H
N
H
N
N
H H
N
N
N
H H
N
H
OH
O
HO
O
HO
OH
OHHO
OHHO
O
O
O
O
O
O
H2L4
H2L1
H3L3
H2L2
Scheme 1. Schematic presentation of the Schiff base ligands.

174
D. Biswas et al. / Inorganica Chimica Acta 408 (2013) 172–180
constant stirring for 2 h. The reddish solution was filtered. On slow
evaporation of the resulting reddish colored solution the dark red
block shaped single crystals of the complex 3 were separated out
in a few days. The crystals were filtered and washed with methanol
and dried in air.
light uniformly) were attached to the end of a MiTeGen mount
using paratone oil. X-ray diffraction intensity data of the title com-
pounds were collected at 173(2) K using a Bruker APEX-II CCD dif-
fractometer equipped with graphite monochromated MoK
a
radiation (k = 0.71073 Å). Data reduction was carried out using
the program Bruker SAINT [63]. Because of very small values of the
absorption coefficient, no absorption correction was applied. The
structure of the title compounds were solved by direct method
and refined by the full-matrix least-square technique on F2 with
anisotropic thermal parameters to describe the thermal motions
of all non hydrogen atoms using the programs SHELXS97 and SHEL-
XL97 [64,65] respectively. All the calculations were carried out
using PLATON [66] and WinGX system Ver-1.64 [67]. All hydrogen
atoms of the substituent groups were located from difference Fou-
rier map and refined isotropically whereas all the hydrogen atoms
attached to the ring carbons were placed at their geometrically ide-
alized positions. The aromatic H-atoms were assigned isotropic
temperature factors equal to 1.2 times the equivalent temperature
factor of the parent atom whereas the displacement parameters for
the hydrogen atoms were taken as Uiso(H) = 1.5 Ueqv (C) for –CH3
groups. A summary of crystal data and relevant refinement param-
eters are given in Table 1. Selected bond distances and bond angles
are given in Table 2 for compounds 1–3 and all the relevant H-
bonding parameters are given in Table 3. All the relevant other
Complex 3: Yield 67%. Anal. Cacl. for (complex 3) C21H23CuN2-
NaO5: C, 53.73; H, 4.9; N, 5.97. Found: C, 53.65; H: 4.86; N:
5.96%. IR (KBr pellets, cmꢀ1):
3489.
m(C@N) 1628, m(Na–O) 3248, 3444,
3. Results and discussion
3.1. Synthesis
Compounds 1–2 were synthesized in a facile and identical man-
ner. The Schiff base ligands produced by the 1:2 condensations of
diamines with hydroxylated aldehydes in methanol solution were
not isolated. Instead the yellow methanolicsolution produced were
subsequently used for further preparation of the heterometallic
complexes. When Na(I) is incorporated in the system the geometry
of the Copper(II) ion is changed from square pyramidal to square
planar. A slight modification in the ligand framework systems
can play an important role for the designing of these types of het-
erometallic complexes which is evident from the single crystal
structure analysis of Compounds 1 and 2. Compounds 1 and 2
are Cu(II)–Na(I) dimeric compound as they possess similar kind
of ligands set H2L1, H2L2 compared to compound 3 which is one
dimensional Cu(II)–Na(I) polymer as it contains H3L3 which is
something different from the other ligands. Thus we can conclude
that ligand mediated structural diversity can also be obtained.
weak interaction parameters for Cuꢁ ꢁ ꢁ
p
, chelate-ringꢁ ꢁ ꢁchelate-
ring, chelate-ringꢁ ꢁ ꢁ
p
and
p p stacking interactions are given in
ꢁ ꢁ ꢁ
Tables 4a–e.
3.3. Crystal structure description
3.3.1. Complex 1
3.2. X-ray crystal structure determinations
Single crystal X-ray structural analysis reveals that complex 1 is
a discrete dinuclear system of Cu(II) and Na(I) simultaneously
coordinated by the hexadentate ligand H2L1 (Fig. 1). Cu1 possess
square planar coordination geometry and Na1 has a distorted
octahedral coordination with seven coordination bonds to O
atoms. The dihedral angle between Cu1–L2 six member chelate
Single crystals of the title compounds (1–3) were harvested di-
rectly from the slow evaporation preparations and all cases suit-
able single crystals (i.e. those found by inspection to have
well-defined morphology and that extinguished plane polarized
Table 1
Crystal data and structure refinement parameters for compounds (1)–(3).
Crystal data (1)
Crystal data (2)
Crystal data (3)
Formula
CuC20H24N3NaO8
520.96
triclinic
CuC20H24N3NaO8
520.95
triclinic
CuC21H23N2NaO5
469.95
triclinic
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
ꢀ
ꢀ
ꢀ
P1
P1
P1
7.1416(7)
11.6143(11)
14.1186(14)
77.095(2)
76.034(2)
77.487(2)
1091.22(18)
2
7.2395(10)
11.3007(15)
13.4789(19)
96.090(3)
99.796(3)
97.852(3)
1067.0(3)
2
1.622
8.3165(9)
10.5403(8)
13.2830(13)
111.567(8)
105.814(9)
95.450(7)
1016.78(19)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g/cm3)
1.586
1.535
Mu(Mo K
a
) (mm)
1.074
1.098
2.042
F(000)
538
538
486
Crystal size (mm)
T (K)
.20 ꢂ .30 ꢂ .30
.10 ꢂ .27 ꢂ .27
.20 ꢂ .28 ꢂ .30
173
173
293
Radiation (Å)
h Min–Max [°]
Dataset
Tot., Uniq. Data, Rint
Observed data [I > 2.0
Nref, Npar
0.71073
2.6, 26.2
0.71073
1.8, 28.0
1.54184
3.8, 70.6
ꢀ8: 9; ꢀ15: 15; ꢀ18: 17
5285, 3976, 0.0328
3250
5285, 320
0.0465, 0.1244, 1.025
0.001, 0.00
ꢀ0.529, 1.314
ꢀ9: 9; ꢀ12: 14; ꢀ17: 16
12717, 5110, 0.025
4460
5110, 301
0.0288, 0.0755, 1.03
0.00, 0.00
ꢀ9: 10; ꢀ12: 10; ꢀ16: 15
6351, 3717, 0.044
2710
3717, 274
0.0697, 0.2085, 0.99
0.00, 0.00
ꢀ0.72, 2.06
r
(I)]
R, wR2, S
Max. and Av. Shift/error
Min. and Max. Resd. Dens. (e/Å3)
ꢀ0.53, 0.81–0.33, 0.34

D. Biswas et al. / Inorganica Chimica Acta 408 (2013) 172–180
175
Table 2
Slecected bond distances and angles for compounds 1–3.
Compound 1
Compound 2
Compound 3
Cu1–O19
Cu1–O23
Cu1–N8
Cu1–N11
Na2–O1L
Na2–O2
Na2–O3
Na2–O19
Na2–O20
Na2–O23
Na2–O24
O1L–H1L
O1L–C2L
N1–O2
1.884(2)
1.893(2)
1.97(1)
Cu1–O20
Cu1–O23
Cu1–N8
Cu1–N12
Na1–O1L
Na1–O1
Na1–O3
Na1–O21
Na1–O20
Na1–O23
Na1–O24
O1L–H1L
O1L–C2L
N1–O1
1.923(1)
1.938(1)
1.988(1)
1.998(2)
2.422(2)
2.626(2)
2.491(2)
2.419(1)
2.349(1)
2.375(2)
2.454(1)
0.962(1)
1.418(3)
1.257(2)
1.238(2)
1.246(2)
C2–O1
C3–O1
C8–O3
C9–N2
C10–N2
C11–O5
C12–N1
C13–N1
C18–O2
C19–O4
N1– Cu1
N2–Cu1
O2–Na1
O3 –Cu1
O3–Na1
O4–Cu1
1.445(5)
1.376(8)
1.309(6)
1.273(7)
1.466(6)
1.34(1)
1.925(2)
2.386(3)
2.511(3)
2.474(2)
2.337(2)
2.584(3)
2.368(3)
2.660(3)
0.902(3)
1.417(4)
1.257(3)
1.244(4)
1.244(4)
1.471(8)
1.285(8)
1.365(6)
1.300(6)
1.958(4)
1.952(6)
3.039(5)
1.914(3)
2.963(6)
1.901(4)
2.901(5)
2.771(9)
118.1(5)
117.0(4)
124.1(4)
124.2(4)
115.7(4)
115.5(3)
118.8(4)
123.2(3)
129.2(3)
103.8(2)
126.9(3)
119.8(3)
106.4(2)
111.6(5)
89.8(2)
N1–O3
N1–O4
N1–O2
N1–O3
O4–Na1
O5–Na1
N8–Cu1–N11
N8–Cu1–O19
N8–Cu1–O23
N11–Cu1–O19
N11–Cu1–O23
O19–Cu1–O23
O1L–Na2–O2
O1L–Na2–O3
O1L–Na2–O19
O1L–Na2–O20
O1L–Na2–O23
O1L–Na2–O24
O2–Na2–O3
O2–Na2–O19
O2–Na2–O20
O2–Na2–O23
O2–Na2–O24
O3–Na2–O19
O3–Na2–O20
O3–Na2–O23
O3–Na2–O24
O19–Na2–O20
O19–Na2–O23
O19–Na2–O24
O20–Na2–O23
O20–Na2–O24
O23–Na2–O24
84.4(3)
171.5(3)
95.3(3)
N8–Cu1–N12
N8–Cu1–O20
N8–Cu1–O23
N12–Cu1–O20
N12–Cu1–O23
O20–Cu1–O23
O1–Na1–O3
97.05(6)
91.94(6)
171.89(6)
170.35(6)
91.05(6)
79.95(5)
49.62(5)
106.89(5)
108.25(5)
94.79(5)
79.07(5)
143.10(6)
136.71(6)
85.94(5)
139.56(6)
86.29(5)
99.25(6)
66.31(5)
63.35(5)
129.09(5)
109.95(5)
128.77(5)
161.34(5)
84.88(5)
65.78(5)
103.45(5)
79.66(5)
C12–N1–C13
C12–N1–Cu1
C13–N1–Cu1
C9–N2–Cu1
C10–N2–Cu1
C18–O2–Na1
C21–O2–Na1
C8–O3–Cu1
C8–O3–Na1
Cu1–O3–Na1
C19–O4–Cu1
C19–O4–Na1
Cu1–O4–Na1
C11–O5–Na1
N1–Cu1–N2
N1–Cu1–O3
N1–Cu1–O4
N2–Cu1–O3
N2–Cu1–O4
O3–Cu1–O4
O2–Na1–O3
O2–Na1–O4
O2-Na1–O5
O3–Na1–O4
94.7(1)
179.6(1)
85.56(9)
155.0(1)
105.9(1)
105.76(9)
87.53(9)
98.93(9)
80.86(9)
50.94(9)
98.54(9)
98.67(9)
96.18(9)
89.08(9)
133.6(1)
85.92(9)
138.8(1)
90.34(9)
62.64(8)
66.09(8)
127.55(9)
128.09(9)
166.33(9)
61.50(8)
O1–Na1–O20
O1–Na1–O21
O1–Na1–O23
O1–Na1–O24
O1–Na1–O1L
O3–Na1–O20
O3–Na1–O21
O3–Na1–O23
O3–Na1–O24
O3–Na1–O1L
O20–Na1–O21
O20–Na1–O23
O20–Na1–O24
O20–Na1–O1L
O21–Na1–O23
O21–Na1–O24
O21–Na1–O1L
O23–Na1–O24
O23–Na1–O1L
O24–Na1–O1L
159.6(2)
94.0(2)
92.0(2)
157.0(2)
92.3(2)
105.7(2)
51.9(1)
101.7(2)
55.9(1)
Table 3
Relevant hydrogen bonding parameters (Å, °).
D–Hꢁ ꢁ ꢁA
D–H
Hꢁ ꢁ ꢁA
Dꢁ ꢁ ꢁA
D–Hꢁ ꢁ ꢁA
Symmetry
Compound 4 (reported)
O1L–H1Lꢁ ꢁ ꢁO2
O1L–H1Lꢁ ꢁ ꢁO3
O1L–H3ꢁ ꢁ ꢁO2
O1L–H1Lꢁ ꢁ ꢁO2
O1L–H1Lꢁ ꢁ ꢁO3
C7–H7ꢁ ꢁ ꢁO1
0.82
0.82
0.90
0.96
0.96
0.95
2.50
2.14
2.01
2.02
2.46
2.56
3.177(2)
2.939(2)
2.874(2)
2.930(2)
3.280(2)
3.476(2)
140
163
162
157
162
112
ꢀ1 + x, y, z
ꢀ1 + x, y, z
1655
ꢀ1 + x, y, z
ꢀ1 + x, y, z
2665
Compound 1
Compound 2
ring planes (Cu1–N11–C12–C13–C14–O19) and (Cu1–N8–C7–C6–
C1–O23) is 6.11(5)° which reflects that Cu1 posses square planar
coordination geometry. Cu–N8, Cu–N11 bond distances are
1.97(1) Å and 1.925(2) Å while Cu1–O19 and Cu1–O23 bond dis-
tances are 1.884(2) and 1.893(2) Å, respectively. Na1 is coordi-
nated by four O atoms donated by the ligand L2, two O atoms
donated by a nitrate anion and a solvent methanol O (O1l) atom.
Na2–O distances vary in the range 2.337(2)–2.660(3) Å.
and the methanol molecule to the Na(I) ion which act as self-com-
plementary donor acceptor set between adjacent dinuclear units.
The
p forces arise from the aromatic as well as chelate rings involv-
ing the ligand L1 and the Cu(II) ion. Uncoordinated nitrate O atom
act as acceptor for the methanol O–H donor group. The hydrogen
bonded chains run along the crystallographic a-axis. Multiple
stacking interactions operate in unison with the hydrogen bonding
forces. It is also notable that Cuꢁ ꢁ ꢁ interaction operates between
Cu(II) ion and the aromatic ring .. along with this chelate-
ringꢁ ꢁ ꢁchelate-ring and chelate-ringꢁ ꢁ ꢁ interactions form a di-
meric subunit. These subunits are organized along the a-axis by
chelate-ringꢁ ꢁ ꢁ and ꢁ ꢁ ꢁ interactions in cooperation with the
p
p
Discrete dinuclear units are organized by cooperative hydrogen
bonding and
p
ꢁ ꢁ ꢁ
p
forces in the (101) plane with a distinct 1D tape
p
motif along the crystallographic a-axis (Fig. 2). Hydrogen bonding
sites are provided by the trans axially coordinated nitrate anion
p
p p

176
D. Biswas et al. / Inorganica Chimica Acta 408 (2013) 172–180
Table 4a
Geometrical parameters (Å, °) for the chelate-ringꢁ ꢁ ꢁ
p
stacking interactions in compouns(1–4).
Rings i–j
Rca
R1vb
ad
be
Symmetry
Compound 4 (reported)
R3ꢁ ꢁ ꢁR4
3.8320(8)
3.5015(8)
3.7699()
ꢀ3.3915(5)
3.4906(8)
ꢀ3.3316(5)
2.88(6)
2.88(6)
3.28(6)
27.61
18.65
27.32
ꢀx, ꢀy, ꢀz
R3ꢁ ꢁ ꢁR4
1 ꢀ x, ꢀy, ꢀz
1 ꢀ x, ꢀy, 1 ꢀ z
R2ꢁ ꢁ ꢁR5 (Inter tape)
R2 = C1–C2–C3–C4–C5–C6; R3 = C1–C2–C3–C4–C5–C6; R5 = C1–C2–C3–C4–C5–C6
Compound 1
R3ꢁ ꢁ ꢁR7
3.5753(19)
3.6734(19)
4.3710()
ꢀ3.2540(12)
3.3440(12)
3.714
5.01(14)
5.01(14)
4.10
19.55
20.83
31.83
1 ꢀ x, ꢀy, 1 ꢀ z
2 ꢀ x, ꢀy, 1 ꢀ z
2 ꢀ x, ꢀy, 1 ꢀ z
R3ꢁ ꢁ ꢁR7
R6ꢁ ꢁ ꢁR4(Inter tape)
R3 = C1–C2–C3–C4–C5–C6; R4 = C1–C2–C3–C4–C5–C6; R6 = C1–C2–C3–C4–C5–C6; R7 = C1–C2–C3–C4–C5–C6
Compound 2
R1ꢁ ꢁ ꢁR4
3.7303(10)
3.5667(10)
ꢀ3.4374(5)
2.21(7)
2.21(7)
22.32
22.42
ꢀx, 1 ꢀ y, ꢀz
R1ꢁ ꢁ ꢁR4
3.2544(5)
1 ꢀ x, 1 ꢀ y, 1 ꢀ z
R1 = C1–C2–C3–C4–C5–C6; R4 = C1–C2–C3–C4–C5–C6
Compound 3
R2ꢁ ꢁ ꢁR5
3.556(3)
3.219(2)
4.6(3)
20.70
1 ꢀ x, 1 ꢀ y, ꢀz
R2 = C1–C2–C3–C4–C5–C6; R4 = C1–C2–C3–C4–C5–C6
(Same references apply to Tables 4b–d).
a
Centroid distance between ring i and ring j.
Vertical distance from ring centroid i to ring j.
Dihedral angle between the first ring mean plane and the second ring mean plane of the partner molecule.
Angle between centroids of first ring and second ring mean planes.
b
d
e
Table 4b
Table 4e
Geometrical parameters (Å, °) for the chelate-ringꢁ ꢁ ꢁchelate-ring stacking interactions
Geometrical parameters (Å, °) for the CHꢁ ꢁ ꢁ
p
interactions in compounds 4 (reported)
in compouns(1–4).
and 3.
Rings i–j
Rca
R1vb
ad
0.0
0
be
Symmetry
Rings i–j
Rca
R1vb
ad
be
Symmetry
1 + x, y, z
Compound 4 (reported)
R3ꢁ ꢁ ꢁR3
Compound 1
R3ꢁ ꢁ ꢁR3
Compound 2
R1ꢁ ꢁ ꢁR1
Compound 4 (reported)
C2L–H2LBꢁ ꢁ ꢁR5
Compound 3
C21–H21Aꢁ ꢁ ꢁR2
3.7796(7)
3.6249(16)
3.5215(9)
3.569(3)
3.7796(7)
ꢀ3.2519(12)
3.2727(5)
3.246(2)
28.98
26.22
21.66
24.55
1 ꢀ x, ꢀy, ꢀz
2.96
2.67
23.38
23.38
138
150
68
55
1 ꢀ x, ꢀy, 1 ꢀ z
1 ꢀ x, 1 ꢀ y, 1 ꢀ z
1 ꢀ x, 1 ꢀ y, ꢀz
ꢀx, 1 ꢀ y, ꢀz
0
Compound 3
R2ꢁ ꢁ ꢁR2
0
Table 4c
Geometrical parameters (Å, °) for the Cuꢁ ꢁ ꢁ
p
interactions in compounds (1–4).
Rings i–j
Rca
R1vb
ad
be
Symmetry
Compound 4 (reported)
R4ꢁ ꢁ ꢁCu1
Compound 1
R7ꢁ ꢁ ꢁCu1
Compound 2
R4ꢁ ꢁ ꢁCu1
Compound 3
R5ꢁ ꢁ ꢁCu1
3.746
3.765
3.573
3.656
3.196
3.372
3.240
3.247
31.42
26.43
24.95
27.36
1 ꢀ x, ꢀy, ꢀz
1 ꢀ x, ꢀy, 1 ꢀ z
1 ꢀ x, 1 ꢀ y, ꢀz
1 ꢀ x, 1ꢀy, ꢀz
Table 4d
Geometrical parameters (Å, °) for the
pꢁ ꢁ ꢁp interactions in compounds 1 and 2.
Rings i–j
Rca
R1vb
ad
be
Symmetry
Compound 1
R7ꢁ ꢁ ꢁR7
Compound 2
R4ꢁ ꢁ ꢁR4
3.617(2)
3.6506(11)
3.4293(14)
0
18.54
18.46
2 ꢀ x, ꢀy, 1 ꢀ z
ꢀx, 1 ꢀ y, ꢀz
Fig. 1. ORTEP diagram (30% ellipsoidal probability) of 1. (Rings R3, R4, R6 and R7
are involved in -stacking interactions).
p
ꢀ3.4626(7)
0
of 4 (reported complex), the inter tape chelateꢁ ꢁ ꢁ
considerably weakened here (R6–R4 = 4.371 Å) compared to the
chelateꢁ ꢁ ꢁ interaction in 4. The packing of (101) layers are also
p interaction is
hydrogen bonding forces to produce the tape motif. Though
these tapes are organized in the (101) plane in a similar fashion
p

D. Biswas et al. / Inorganica Chimica Acta 408 (2013) 172–180
177
Fig. 2. The slef-assembled tape motif through Cuꢁ ꢁ ꢁ
p, chelate-ringꢁ ꢁ ꢁchelate-ring
Fig. 4. The slef-assembled tape motif through Cuꢁ ꢁ ꢁ
p
, chelate-ringꢁ ꢁ ꢁchelate-ring
and chelate-ringꢁ ꢁ ꢁ
p
interaction in 1. Cu is shown in Magenta and Na in Yellow. (For
and chelate-ringꢁ ꢁ ꢁ
p interaction in 2. Cu is shown in Magenta and Na in Yellow. (For
interpretation of the references to colour in this figure legend, the reader is referred
to the web version of this article.)
interpretation of the references to colour in this figure legend, the reader is referred
to the web version of this article.)
Fig. 5. ORTEP diagram (30% ellipsoidal probability) with atom numbering scheme
of 3 (Rings R1, R2, R4 and R5 are involved in
p-stacking interactions in the self-
assembly of the depicted unit) [⁄ = x, 1 + y, z].
Fig. 3. ORTEP diagram (30% ellipsoidal probability) with atom numbering scheme
of 2 (Rings R1, R2, R4 and R5 are involved in
assembly of the depicted unit.)
p-stacking interactions in the self-
and a solvent methanol O (O1l) atom. Na1–O distances vary in
the range 2.349(1)–2.626(2) Å.
The nature of self-organization of dinuclear units in 2 is very
close to that of 1. Dinuclear units are arranged into 1D supramolec-
ular tapes running along crystallographic a-axis (Fig. 4) by the sim-
of similar nature to 4 which are arranged side by side along the b-
axis and the inter layer separation is governed by van der Waals
forces (Fig. S1).
ilar set of Cuꢁ
p
, chelate-ringꢁchetalte-ring, chelate-ringꢁ
p
and
pꢁp
interactions. These are further organized side by side running par-
allel to each other in the ac plane (Fig. S2) by apparently weaker
chelateꢁ
p interactions. At the next level of hierarchy these layers
are stacked along the crystallographic b-axis like 1 and 2 by Van-
3.3.2. Complex 2
der-Waals forces.
Single crystal X-ray structural analysis reveals that complex 2 is
a discrete dinuclear system of Cu(II) and Na(I) simultaneously
coordinated by the hexadentate ligand H2L2. While Cu1 posses
square planar coordination geometry, Na1 is hepta coordinated
with distorted octahedral coordination environment (Fig. 3). The
dihedral angle between Cu1–L2 six member chelate ring planes
(Cu1–N8–C7–C6–C1–O20) and (Cu1–N12–C13–C14–C15–O23) is
5.11(5)° which reflects that Cu1 posses square planar coordination
geometry.
3.3.3. Complex 3
Single crystal X-ray structural analysis reveals that complex 3 is
a 1D coordination chain of dinuclear units consisting of Cu(II) and
Na(I) that are simultaneously coordinated by the hexadentate li-
gand H3L3 (Fig. 5). Cu1–Na1 distance within a dinuclear unit is
3.893 Å. Cu1 possesses heavily distorted square planar coordina-
tion geometry. The angle between the two chelate ring planes
Cu1–N8, Cu1–N12 bond distances are 1.988(1) and 1.998(2) Å
while Cu1–O20 and Cu1–O23 bond distances are 1.923(1) and
1.938(1) Å, respectively. Na1 is coordinated by four O atoms do-
nated by the ligand L1, two O atoms donated by a nitrate anion
Cu1–N1–C13–C14–C19–O4
and
Cu1–O3–C8–C7–C9–N2
is
36.5(2)°. The Cu-N distances are slightly longer than the Cu–O dis-
tances. Whereas Cu1–O3 distance is 1.915(4) Å the Cu1–O4 dis-
tance is 1.902(4) Å. The Cu1–N1 and Cu1–N2 distances are

178
D. Biswas et al. / Inorganica Chimica Acta 408 (2013) 172–180
ture was reported recently with the similar kind of Schiff base [61]
but no deprotonation occurred in that case.
1D coordination chains in complex 3 are further self-assembled
into 1D tape motif in which two oppositely running self-comple-
mentary chains are recognized by each other through the con-
certed Cuꢁ ꢁ ꢁ
p
,
chelate ringꢁ ꢁ ꢁ
p
and chelate-ringꢁ ꢁ ꢁchelate-ring
interaction (Fig. 6).
3.3.4. Weak interactions present in reported complex 4
Discrete dinuclear units are organized by weak force namely
hydrogen bonding and
p p forces in the ac plane and forms a
ꢁ ꢁ ꢁ
2D supramolecular sheet (Fig. 7) with an embedded 1D tape motif
running along the crystallographic a-axis. Whereas the hydrogen
bonding sites are provided by coordinated NO3 anion and the
methanol molecule, the
p forces involved are due to the aromatic
phenyl rings on the H2L4 ligand and the chelate rings formed
due to coordination of ligand H2L4 with Cu. The phenyl rings on
H2L4 are marked R4 and R5 whereas the six member chelate rings
relevant for the stacking interactions are marked R2 and R3 in
(Fig. S6). In the hydrogen bonding interaction the uncoordinated
nitrate O atom act as acceptor for the methanol O–H donor group.
The hydrogen bonded chains run along the crystallographic a-axis.
Fig. 6. Self-assembly of 1D coordination chains into 1D supramolecular tapes by
Cuꢁ ꢁ ꢁp, chelate ringꢁ ꢁ ꢁp and chelate-ringꢁ ꢁ ꢁchelate-ring interaction in complex 3.
1.958(5) and 1.951(5) Å respectively. The O3–Cu1–N2 angle is
92.03(18)° and the O4–Cu1–N1 angle is 93.99(18)°. Few other
selective bond distances and angles are given in Table 2.
Multiple
p stacking interactions that operate in unison with the
hydrogen bonding forces further stabilizes the hydrogen bonded
Na1 is unusually penta coordinated in the complex. It is coordi-
nated by five O atoms present in the ligand. Four O atoms surround
Na1 from one side in each unit and the translational symmetry re-
lated alcoholic oxygen atom (O5⁄, ⁄ = x, 1 + y, z) from an adjacent
unit coordinate to Na1 from the opposite side. This coordination
gives rise to one dimensional coordination polymeric chain of the
dinuclear units. The coordination chains are aligned along the crys-
tallographic b-axis. Among the four coordination from one side,
Na1–O3 and Na1–O4 bond distances are relatively shorter
(2.946(6) and 2.902(6) Å respectively) than the Na1–O1 and
Na1–O2 distances (3.061(6) and 3.038(6) Å respectively). Na1–
O5⁄ distance is the shortest 2.770(8) Å among all the coordination
bond lengths. The beauty of this structure lies in the deprotonation
of the alkoxo hydroxyl group present in the middle position of the
Schiff base ligand H2L3. It is coordinated to the sodium ion after
deprotonation and thus this unique one dimensional structure is
obtained. It is to be noted that another Cu(II)–Na(I) dinuclear struc-
chain and augments the dimensionality of the system into 2D
through inter chain interaction. Besides these
tions, Cuꢁ ꢁ ꢁ interactions also come into effect. Detailed bonding
paramets of the -stacking interaction is given in Table 3. These
p stacking interac-
p
p
supramolecular sheets are further organized side by side along
the crystallographic b-axis (Fig. 8). Intra layer separation is equal
to the length of the unit cell dimension along the b-axis and this
is determined by the interlayer Van-der-Waals forces originating
from the interactions between abundant –CH3 groups present on
adjacent stacking faces of successive layers.
3.3.5. Comparative discussions of the pattern of self-assembly
Three Cu(II) complexes reported here are closely related with
identical coordination environment for Cu(II) and Na(I) except in
3 where a different coordination mode of Na(I) appeared. In each
case Cu(II) assumes square planar coordination environment. In
1–2, Na(I) assumes distorted octahedral coordination environment
with the Schiff-bases binding in the equatorial plane and the trans
axial sites occupied by a nitrate ion and a methanol molecule
respectively. In 3 no methanol molecule or nitrate ion take part
in the complexation, Na(I) is coordinated only by the O and N
atoms on the Schiff-base which are five in number. The robust fea-
ture in the supramolecular self-assembly of complexes 1, 2 and 4 is
the appearance of a tape motif in each complex. The novel feature
of this organization is the involvement of the Cu(II)-Schiff base
chelate ring in the
been described in the structural part, in each case chelate ring–
chelate ring, chelate ring– (aromatic), Cu– (aromatic) interac-
p-interaction between successive units. As has
p
p
tions come into play in structuring the tape motif. Hydrogen bond-
ing between Na centered nitrate ion and methanol molecule
cooperate with these
by chelate ring– (aromatic) interactions into a two dimensional
supramolecular sheet in the ac plane. In 1 and 2 this inter tape che-
late ring– (aromatic) interactions do not come into play. This is
p forces. In 4, these tapes are further united
p
p
due to the presence of an additional –CH3 group in H2L1 and the
additional central carbon atom in H2L2 which rotates successive
tapes in such a way that the inter tape chelate ring–
interactions in 1 and 2 become considerably weaker with long cen-
troid to centroid distances (R3–R4 = 4.3710 Å in and R2–
R5 = 4.1102 Å in 3). The presence of the central O atom (O5) in
H3L3 widely changes the mode of self-assembly in 3. Here coordi-
nation of this O atom to an adjacent unit give rise to a 1D
p(aromatic)
Fig. 7. The self-assembled tape motif through Cuꢁ ꢁ ꢁ
and chelate-ringꢁ ꢁ ꢁ interaction and the 2D sheet the tapes joined by chelate-
ringꢁ ꢁ ꢁ interaction in 4. Cu is shown in Magenta and Na in Yellow. (For
p, chelate-ringꢁ ꢁ ꢁchelate-ring
2
p
p
interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)

D. Biswas et al. / Inorganica Chimica Acta 408 (2013) 172–180
179
pattern of assembly due to small variations in the ligand frame
work. The present study establishes that the recurrent tape motif
in the self-assembly of the complexes is due to the
p-stacking
interaction involving the chelate ring of Cu and the Schiff-bases.
That the hydrogen bonding forces merely cooperates with these
p-forces is revealed in the self-assembly of compound 3 where
hydrogen binding forces is absent but the tape motif recurs. In
summary, in supramolecular design of Cu complexes the stacking
interaction of Cu-ligand chelate ring should be paid more attention
and can be utilized in the design of molecular materials.
Acknowledgements
Financial support from DST [Sanction no. SR/FT/CS-060/2009]
and UGC [Sanction no.F.38-5/2009 (SR)], New Delhi to S. S. are
gratefully acknowledged.
Appendix A. Supplementary material
Fig. 8. Packing of successive (101) layers in 4 along b-axis.
CCDC 902506–902508 contains the supplementary crystallo-
graphic data for 1–3. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2013.09.011.
coordination chain along the crystallographic b-axis (Fig. 5). Inter-
estingly the inter-chain supramolecular association is again estab-
lished through chelate ring–chelate ring, chelate ring–
p (aromatic),
Cu– (aromatic) interactions giving rise to a tape motif along the
p
b-axis. This motif is solely organized by
p forces and no hydrogen
bonding forces come into play.
Recently a similar set of three complexes were reported by
Bhowmick et al. [60]where they have ignored the importance of
References
[1] B. Moulton, M.J. Zaworotko, Chem. Rev. 101 (2001) 1629.
[2] J.A. Thomas, J.L. Atwood, J.W. Steed (Eds.), Encyclopedia of Supramolecular
Chemistry, CRC Press, Boca Raton, FL, 2004. p. 1248.
[3] D. Braga, L. Maini, M. Polito, L. Scaccianoce, G. Cojazzi, F. Grepioni, Coord.
Chem. Rev. 225 (2001) 216.
[4] J.P. Sauvage (Ed.), Transition Metals in Supramolecular Chemistry:
Perspectives in Supramolecular Chemistry, vol. 5, Wiley, London, 1999.
[5] G.R. Desiraju (Ed.), The Crystal as a Supramolecular Entity: Perspectives in
Supramolecular Chemistry, vol. 2, Wiley, London, 1996.
[6] I.G. Dance, in: G.R. Desiraju (Ed.), The Crystals as a Supramolecular Entity, John
Wiley, New York, 1996.
[7] A.D. Jana, S.C. Manna, G.M. Rosair, M.G.B. Drew, G. Mostafa, N.R. Chaudhuri,
Cryst. Growth Des. 7 (2007) 1365.
[8] R.K. Seddon, M.J. Zaworotko, Crystal Engineering: The Design and Application
of Functional Solids (NATO Science Series), 1999.
[9] G.R. Desiraju, Crystal Engineering: The Design of Organic Solids, Elsevier,
Amsterdam, 1989.
p
-forces in these complexes and have only stressed on the hydro-
gen bonding forces in the self-organization. When relooked and see
that similar chelate ring–chelate ring, chelate ring– (aromatic),
Cu– (aromatic) interactions are also present in these complexes
(Figs. S3–S5 and Tables S1, S2a, S2b, S3a, S3b and S4). interac-
p
p
p
tions involving metal-chelate rings is a relatively new area in the
self-assembly of molecular complexes and the present study shows
that this interaction can play important role vis a vis other interac-
tions and should be paid more attention in the design of molecular
complexes. This study shows that Cu-ligand chelate ring possibly
posses some kind of aromaticity.
[10] G.R. Desiraju, Angew. Chem., Int. Ed. 34 (1995) 2311.
[11] I.C. Khoo, Liquid Crystsl, Wiley-Interscience, A John Wiley and Sons, Inc.
Publications, 2007.
4. Conclusion
[12] D.K. Yang, S.T. Wu, Fundamentals of Liquid Crystal Devices John Wiley & Sons,
Ltd., 2006.
[13] C.D. Dimitrakopoulos, P.R.L. Malenfant, Adv. Mater. 14 (2002) 99.
[14] S.R. Forrest, Nature 428 (2004) 911.
[15] H. Meng, F. Sun, M.B. Goldfinger, F. Gao, D.J. Londono, W.J. Marshal, G.S.
Blackman, K.D. Dobbs, E. Dalen, D.E. Keys, J. Am. Chem. Soc. 128 (2006) 9304.
[16] D.S. Godsell, Bionanotechnology lessons from nature, Wiley-Liss, A John Wiley
& sons, Inc. publication, 2004.
[17] M.D. Cuyper, J.W.M. Bulte, Physics and Chemistry Basis of Biotechnology,
Kulwar Academic Publishers 2002.
Understanding the mutual role of multiple weak forces in the
molecular self-assembly is emerging to be crucial in formulating
the design principles in various areas of science and technology.
Recently the metal–ligand chelate rings have been seen to take
part in stacking interactions and in the present study we employ
this interaction in the design of a set of three complexes. We see
that instead of the ligand centric
p–p
interaction the chelate ring
stacking interaction aided by Cuꢁ ꢁ ꢁ
p
interaction governs the self-
[18] T. Niu, A.J. Jacobson, Inorg. Chem. 38 (1999) 5346.
[19] K.K. Klausmeyer, T.B. Rauchfuss, S.R. Wilson, Angew. Chem., Int. Ed. 37 (1998)
1694.
[20] A.M.A. Ibrahim, Polyhedron 18 (1999) 2711.
[21] G.R. Desiraju, T. Steiner, The Weak Hydrogen Bond in Structural Chemistry and
Biology, Oxford University Press, Oxford, 1999.
[22] G.A. Jeffrey, W. Saenger, Hydrogen Bonding in Biological Structures, Springer,
Berlin, 1991.
[23] W.C. Hamilton, J.A. Ibers, Hydrogen Bonding in Solids, Benjamin, New York,
1968.
[24] S. Scheiner, Hydrogen Bonding: A Theoretical Perspective, Oxford University
Press, Oxford, 1997.
[25] G.A. Jeffrey, An Introduction to Hydrogen Bonding, Oxford University Press,
Oxford, 1997.
assembly of the molecular complexes. The solvent induced hydro-
gen bonding forces cooperate with these forces. With the design
Schiff base ligands targeted square-planar Cu-Schiff base units
can be achieved and the secondary alkali metal ion Na(I) provides
the self-complementary hydrogen bonding sites through trans-ax-
ial coordination of the NO3ꢀ counter ion and CH3OH solvent mole-
cule. The primary Cu(II)-Schiff-base square plane motif is
particularly amenable for stacking interactions involving the Cu-li-
gand chelate ring. Chelate ring of one unit interacts with both the
phenyl ring and the chelate ring of adjacent unit. Chelate
[26] T. Steiner, Angew. Chem., Int. Ed. 41 (2002) 48.
[27] Y. Zhang, Z. Yang, F. Yuan, H. Gu, P. Gao, B. Xu, J. Am. Chem. Soc. 126 (2004)
15028.
ringꢁ ꢁ ꢁchelate ring, chelate ringꢁ ꢁ ꢁ
p
, Cuꢁ ꢁ ꢁ
p cooperate in the com-
plexes. That the mutual interactions of these weak forces are quite
subtle is revealed by the small but recognizable differences in the
[28] S.I. Noro, T. Akutagawa, T. Nakamura, Cryst. Growth Des. 7 (2007) 1205.

180
D. Biswas et al. / Inorganica Chimica Acta 408 (2013) 172–180
[29] A.K. Ghosh, A.D. Jana, D. Ghoshal, G. Mostafa, N.R. Chaudhuri, Cryst. Growth
Des. 6 (2006) 701.
[49] D. Braga, S.L. Giaffreda, F. Grepioni, L. Maini, M. Polito, Coord. Chem. Rev. 250
(2006) 1267.
[30] C.J. Janiak, Chem. Soc. Dalton Trans. (2000) 3885.
[31] O. Yamauchi, A. Odani, S. Hirota, Bull. Chem. Soc. Jpn. 74 (2001) 1525.
[32] M.J. Packer, M.P. Dauncey, C.A. Hunter, J. Mol. Biol. 295 (2000) 71.
[33] M.J. Packer, M.P. Dauncey, C.A. Hunter, J. Mol. Biol. 295 (2000) 85.
[34] K. Müller-Dethlefs, P. Hobza, Chem. Rev. 100 (2000) 143.
[35] R. Ghosh, A.D. Jana, S. Pal, G. Mostafa, H.K. Fun, B.K. Ghosh, Cryst. Eng.
Commun. 9 (2007) 353.
[36] B.L. Schottel, H.T. Chifotides, M. Shatruk, A. Chouai, L.M. Perez, J. Bacsa, K.R.
Dunbar, J. Am. Chem. Soc. 128 (2006) 5895.
[37] A.D. Jana, A.K. Ghosh, D. Ghoshal, G. Mostafa, N.R. Chaudhuri, Cryst. Eng.
Commun. 9 (2007) 304.
[50] H.J. Schneider, Angew. Chem., Int. Ed. 48 (2009) 3924.
[51] J.J. Jiang, Y.R. Liu, R. Yang, M. Pan, R. Cao, C.Y. Su, Cryst. Eng. Commun. 10
(2008) 1147.
[52] G.R. Desiraju, Angew. Chem., Int. Ed. Engl. 34 (1995) 2311.
[53] A. Michaelides, S. Skoulika, V. Kiritsis, C. Raptopoulou, A. Terzis, J. Chem. Res.
(S) (1997) 204.
´
´
´
[54] MilosꢁK. Milcꢁic, Vesna B. Medakovic, Snezꢁana D. Zaric, Inorg. Chimi. Acta 359
(2006) 4427.
[55] R.T. Edward, Chem. Commun. 47 (2011) 6623.
[56] P.P. Chakrabarty, D. Biswas, S. García-Granda, A.D. Jana, S. Saha, Polyhedron 35
(2012) 108.
[38] A.D. Jana, S.C. Manna, G.M. Rosair, M.G.B. Drew, G. Mostafa, N.R. Chaudhuri,
Cryst. Growth Des. 7 (2007) 1365.
[57] D. Cunningham, P. McArdle, M. Mitchell, N.N. Chonchubhair, M.O. Gara, Inorg.
Chem. 39 (2000) 1639.
[39] P. Hobza, H.L. Selzle, E.W. Schlag, Chem. Rev. 94 (1994) 1767.
[40] K.S. Kim, P. Tarakeshwar, J.Y. Lee, Chem. Rev. 100 (2000) 4145.
[41] M.O. Sinnokrot, C.D. Sherrill, J. Phys. Chem. A 110 (2006) 10656.
[42] E.C. Lee, D. Kim, P. Jurecka, P. Tarakeshwar, P. Hobza, K.S. Kim, J. Phys. Chem. A
111 (2007) 3446.
[58] Y. Sui, D.P. Li, C.H. Li, X.H. Zhou, T. Wu, X.Z. You, Inorg. Chem. 49 (2010) 1286.
[59] M. Das, S. Chatterjee, S. Chattopadhyay, Inorg. Chem. Commun. 14 (2011)
1337.
[60] P. Bhowmik, S. Jana, P.P. Jana, K. Harms, S. Chattopadhyay, Inorg. Chim. Acta
390 (2012) 53.
[43] M. Pitonak, P. Neogrady, J. Rezac, P. Jurecka, M. Urban, P. Hobza, J. Chem.
Theory Comput. 4 (2008) 1829.
[44] N.J. Singh, S.K. Min, D.Y. Kim, K.S. Kim, J. Chem. Theory Comput. 5 (2009) 515.
[45] E.A. Mayer, R.K. Castellano, F. Diederich, Angew. Chem., Int. Ed. 42 (2003)
1210.
[61] M. Dolai, M. Mistri, A. Panja, M. Ali, Inorg. Chim. Acta 399 (2013) 95.
[62] S. Biswas, S. Naiya, M.G.B. Drew, C. Estarellas, A. Frontera, A. Ghosh, Inorg.
Chim. Acta 266 (2011) 219.
[63] SMART, and SADABS, Bruker AXS Inc. Madison, Wisconsin, USA.
[64] G.M. Sheldrick, SHELXS-97 and SHELXL-97, University of Göttingen, Germany,
1997.
[46] M. Nishio, M. Hirota, Y. Umezawa, The C–Hꢁ ꢁ ꢁ
p Interaction: Evidence, Nature
and Consequences, Wiley–VCH, New York, 1998.
[47] M. Nishio, Cryst. Eng. Commun. 6 (2004) 130.
[65] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
[66] A.L. Spek, J. Appl. Crystallogr. 36 (2003) 7.
[48] M.d.C. Fernandez-Alonso, F.J. Canada, J. Jimenez-Barbero, G. Cuevas, J. Am.
Chem. Soc. 127 (2005) 7379.
[67] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.