Syntheses, crystal structures and density functional theory investigations of copper(II) complexes bearing tridentate Schiff base ligands derived from 8-aminoquinoline

Article abstract of DOI:10.1039/c5ce00809c

Three copper(ii) complexes, [Cu(L¹)(H₂O)(OClO₃)]_n (1), [Cu(L¹)(N₃)] (2) and [Cu(L²)(Cl)(H₂O)] (3) [HL¹ = 4-chloro-2-((quinolin-8-ylimino)methyl)phenol and H

Full text of DOI:10.1039/c5ce00809c

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Graphical Abstract
Syntheses, crystal structures and density functional
theoretical investigations of copper(II) complexes bearing
tridentate Schiff base ligands derived from 8-
aminoquinoline
Prasanta Kumar Bhaumik, Antonio Bauzá, Antonio Frontera, Shouvik
Chattopadhyay
Three copper(II) Schiff base complexes have been synthesized and
characterized. The theoretical study, carried out using density functional theory
calculations, is devoted to the analysis of the interesting supramolecular assemblies in
the solid state of the structures, paying special attention to lp−π and π−π interactions.

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Journal Name
RSCPublishing
ARTICLE
Syntheses, crystal structures and density functional
theoretical investigations of copper(II) complexes
bearing tridentate Schiff base ligands derived from 8-
aminoquinoline
Cite this: DOI: 10.1039/x0xx00000x
Prasanta Kumar Bhaumik,a Antonio Bauzá,b Antonio Frontera,*,bShouvik
Chattopadhyay*,a
Three copper(II) complexes, [Cu(L1)(H2O)(OClO3)]n
(
1
), [Cu(L1)(N3)]
(
2
)
and
[Cu(L2)(Cl)(H2O)] HL1 = 4ꢀchloroꢀ2ꢀ((quinolinꢀ8ꢀylimino)methyl)phenol and HL2 = 2ꢀ
(3)
ethoxyꢀ6ꢀ((quinolinꢀ8ꢀylimino)methyl)phenol, have been synthesized and characterized by
elemental analyses, IR and UV–Vis spectroscopy and singleꢀcrystal Xꢀray diffraction
studies. The theoretical study, carried out using density functional theory (DFT)
calculations, is devoted to the analysis of the interesting supramolecular assemblies in the
solid state of the structures, paying especial attention to lp−πandπ−π interactions involving
the quinolinꢀ8ꢀylimino moiety.
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
www.rsc.org/
Consequently, the relevance of these nonꢀcovalent interactions
is broadly analysed by a large number of researchers using
1.Introduction
The nonꢀcovalent interactions, popularly known as
“supramolecular interactions”, have shown to play an important
role in structural biology and supramolecular chemistry.1ꢀ6The
synchronization of many chemical and biological processes is
often executed by combinations of different nonꢀcovalent
interactions.7 The correct description of these nonꢀcovalent
interactions is needed for the understanding and development of
supramolecular chemistry. A number of wellꢀrecognized strong,
directional nonꢀcovalent interactions such as hydrogen bonding
and halogen bonding, and less directional forces like ion pairing
have been used to govern the organization of multiꢀcomponent
supramolecular assemblies.8ꢀ11 In addition, nonꢀcovalent
interactions involving aromatic rings {πꢀπ stacking, cationꢀπ,
C–H/π, lpꢀπ and anionꢀπ interactions}12ꢀ16are enormously
significant in this field. They could play a key role in chemistry
and biology, in particular, drug–receptor interactions, crystal
engineering, enzyme inhibition and protein folding.17 They
could also manage the structures of bioꢀmolecules e.g. proteins
and DNA, several host–guest systems, enzyme–substrate
binding etc.18ꢀ19 They have also shown to have the ability to
regulate antigen–antibody recognition.20ꢀ21 Because of their
ubiquitous role in diverse fields, the investigation and
understanding of these weak nonꢀcovalent interactions have
become one of the major objectives of contemporary chemistry.
combined theoretical and experimental investigations22ꢀ28 and
currently it is an interesting topic of research.
In the present work, we have used two Schiff bases, HL1
=
4ꢀchloroꢀ2ꢀ((quinolinꢀ8ꢀylimino)methyl)phenol and HL2 = 2ꢀ
ethoxyꢀ6ꢀ((quinolinꢀ8ꢀylimino)methyl)phenol to prepare three
copper(II) complexes, [Cu(L1)(H2O)(OClO3)]n ), [Cu(L1)(N3)]
(1
(2 (3). The structures of all three
) and [Cu(L2)(Cl)(H2O)]
complexes have been characterized by single crystal Xꢀray
crystallography. Three complexes presented interesting
supramolecular assemblies in the solid state dominated by Hꢀ
bonding, πꢀπ and lpꢀπ interactions that are analyzed in detail by
means of DFT calculations allowing the calculation of the
different contributions to the molecular recognition.
2. Experimental
2.1. Materials
All chemicals were of AR grade and were used as
purchased from SigmaꢀAldrich without further purification.
Caution!!
Complexes containing azide and perchlorate are potentially
explosive. Only small amount of those materials should be
prepared and handled with care.
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2.2. Preparations
2.2.1. Preparation of ligands, HL1 and HL2
× 102), 452 (5.6 × 103), 320 (1.0 × 104). Magnetic moment:
1.72 BM.
The tridentate Schiff bases, HL1 {4ꢀchloroꢀ2ꢀ((quinolinꢀ8ꢀ
ylimino)methyl)phenol} and HL2 {2ꢀethoxyꢀ6ꢀ((quinolinꢀ8ꢀ
ylimino)methyl)phenol} were synthesized by refluxing
quinolinꢀ8ꢀamine (144 mg, 1 mmol), respectively with 5ꢀ
chloroꢀ2ꢀhydroxybenzaldehyde (156.5 mg, 1 mmol) and 3ꢀ
ethoxyꢀ2ꢀhydroxybenzaldehyde (166 mg, 1 mmol) in methanol
(20 ml) for 1 h. The ligands were not isolated and used directly
for the preparation of complexes. Structures of ligands are
given in Scheme1.
2.2.4. Synthesis of [Cu(L2)(Cl)(H2O)] (3)
A methanol solution (25 ml) of copper(II) chloride
dihydrate (170 mg, 1 mmol) was added to the methanol
solution of HL2and the resulting solution was refluxed for 1 h to
give a deep brown solution. It was cooled and kept for a few
days to get brown precipitate. The precipitate was collected by
filtration and dissolved in water and refluxed. It was then
cooled to room temperature Single crystals, suitable for Xꢀray
diffraction, were obtained after ten days by slow evaporation of
the filtrate in open atmosphere.
Yield: 310 mg (76%). Anal.Calcd.for C18H16ClCuN2O3
(FW 407.33): C, 53.08; H, 3.96; N, 6.88%. Found: C, 52.8; H,
4.1; N, 7.2%. IR (KBr, cmꢀ1):1607 (νC=N), 3443 (νOH), UV–Vis,
λmax (nm) (εmax, (L molꢀ1 cmꢀ1)) (acetonitrile): 603 (1.3 × 102),
456 (2.4 × 103), 350 (6.4 × 103). Magnetic moment: 1.73 BM.
2.3. Physical measurements
Elemental analyses (carbon, hydrogen and nitrogen) were
performed using a Perkin–Elmer 240C elemental analyzer.
Infrared spectra in KBr (4500–500 cmꢀ1) were recorded using a
PerkinElmer FTꢀIR spectrum two spectrometer. Electronic
Scheme 1: Schematic representation of ligands used in the present work.
2.2.2. Synthesis of [Cu(L1)(H2O)(OClO3)]n (1)
spectra of complexes
200 nm were recorded on
spectrophotometer at room temperature (32°C). The magnetic
susceptibility measurements were done for complexes with
1
ꢀ
3
(in acetonitrile) in the range of 900ꢀ
A methanol solution (25 ml) of copper(II) perchlorate
hexahydrate (370 mg, 1 mmol) was added to the methanol
solution of HL1 and the resulting solution was refluxed for 1 h
to give a brown solution. It was cooled and kept for a few days
to get greenish brown crystalline precipitate. The precipitate
was collected by filtration and dissolved in acetonitrile. Single
crystals, suitable for Xꢀray diffraction, were obtained after five
days on slow evaporation of the acetonitrile solution in open
atmosphere.
Yield: 320 mg (69%). Anal. Calc. for C16H12Cl2CuN2O6
(FW 462.73): C, 41.53; H, 2.61; N, 6.05%. Found: C, 41.2; H,
2.3; N, 6.3%. IR (KBr, cmꢀ1): 1612 (νC=N), 1120 (νClO4), 3422
(νOH), UV–Vis, λmax (nm) (εmax, (L molꢀ1 cmꢀ1)) (acetonitrile):
619 (1.1 ×102), 452 (1.1 × 104), 317 (1.4 × 104). Magnetic
moment: 1.70 BM.
a
Jasco Vꢀ630 UV–Vis
1ꢀ3
an EG and PAR vibrating sample magnetometer, model 155 at
room temperature (300 K) in 5000 G magnetic field and
diamagnetic corrections were done using Pascal’s constants.29
Effective magnetic moments were calculated using the formula
ꢁeff
susceptibility.
= , where χM is the corrected molar
2.828(χMT)1/2
2.4. X-ray Crystallography
Single crystal of complex
1 was used for data collection
using an ‘Oxford Diffraction XꢀCalibur System’ diffractometer
equipped with graphiteꢀmonochromated Mo Kα radiation (λ =
0.71073 Å) at 150 K. Single crystals of complexes
2 and 3
2.2.3. Synthesis of [Cu(L1)(N3)] (2)
having suitable dimensions, were used for data collection using
a ‘Bruker SMART APEX II’ diffractometer equipped with
graphiteꢀmonochromated Mo Kα radiation (λ = 0.71073 Å) at
A methanol solution (25 ml) of copper(II) perchlorate
hexahydrate (370 mg, 1 mmol) was added to the methanol
solution of HL1 and the resulting solution was refluxed for 1 h
to give a brown solution. An aqueous methanol solution of
sodium azide (65 mg, 1 mmol) was added to it and refluxed
again for an additional hour to obtain a brown solution.
Thereafter it was cooled to room temperature and an immediate
separation of a small amount of side product was filtered off.
Single crystals, suitable for Xꢀray diffraction, were obtained
after three days by slow evaporation of the filtrate in open
atmosphere.
293 K. The R value of
quality of the crystals. The poor quality of crystals of
1
was rather high because of the poor
gave
1
rise to misshapen large spots in the diffraction pattern which in
turn led to several warning signs flagged up by checkcif.
For all three complexes molecular structures were solved by
direct methods and refinement by fullꢀmatrix least squares on
F2 using the SHELXꢀ97 package.30 Nonꢀhydrogen atoms were
refined with anisotropic thermal parameters. H atoms, attached
with O atom, were located by different Fourier maps and were
kept fixed. All other H atoms were placed in their geometrically
idealized positions and constrained to ride on their parent
Yield: 265 mg (68%). Anal. Calc. for C16H10ClCuN5O (FW
387.29): C, 49.62; H, 2.60; N, 18.08%. Found: C, 49.2; H, 2.8;
N, 18.2%. IR (KBr, cmꢀ1):1611 (νC=N), 2049 (νN3), 3445 (νOH),
UV–Vis, λmax (nm) (εmax, (L molꢀ1 cmꢀ1)) (acetonitrile): 613 (1.1
atoms. Empirical absorption corrections were applied to
1 using
the ABSPACK program.30 Multiꢀscan empirical absorption
2 | J. Name., 2012, 00, 1-3
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corrections were applied to
SADABS.31
2
and
3
using the program information). Selected bond lengths and bond angles are
gathered in Table S2 (Supplementary information).
2.5. Theoretical methods
The geometries of the complexes included in this study
were computed at the BP86ꢀD3/def2ꢀTZVP level of theory
using
the
crystallographic
coordinates
within
the
TURBOMOLE program.32This level of theory that includes the
latest available dispersion correction (D3) is adequate for
studying non covalent interactions dominated by dispersion
effects like πꢀstacking. The basis set superposition error for the
calculation of interaction energies has been corrected using the
counterpoise method.33 The “atomsꢀinꢀmolecules” (AIM)34 Fig. 1 Perspective view of complex
1
with the selective atom numbering scheme.
The hydrogen atoms (except water hydrogen atoms) are not shown for clarity.
Symmetry transformation * = 1+x, y, z.
analysis of the electron density has been performed at the same
level of theory using the AIMAll program.35
3. Results and discussion
3.3.1. [Cu(L1)(H2O)(OClO3)]n(1)
ꢀ
The complex
1 crystallizes in the triclinic space group P1 .
3.1. Syntheses
The structure consists of a 1D infinite chain with the repeating
unit [Cu(L1)(H2O)(OClO3)]+ bridged by perchlorate groups
(Fig. 1). Within the asymmetric unit, the copper(II) center is
sixꢀcoordinated, being bonded to nitrogen atoms, N(19), N(28)
and a phenoxo oxygen atom, O(11) of the tridentate Schiff base
ligand (L1)ꢀ and an oxygen atom, O(1), of a water molecule in
the basal plane. A perchlorate oxygen atom, O(21) and a
symmetry related perchlorate oxygen atom, O(22)* (symmetry
The Schiff base ligands, HL1 and HL2 are produced by the
1:1 condensation of quinolinꢀ8ꢀamine respectively with 5ꢀ
chloroꢀ2ꢀhydroxybenzaldehyde
and
3ꢀethoxyꢀ2ꢀ
hydroxybenzaldehyde in methanol following the literature
method.36 A methanol solution of HL1 was made to react with
copper(II) perchlorate hexahydrate to prepare the complex
[Cu(L1)(H2O)(OClO3)]n, which on refluxing with sodium azide
produced complex
[Cu(L1)(N3)]. Similarly on reaction of a
methanol of HL2 with copper(II) chloride dihydrate produced
complex
1,
2
,
*
transformation = 1+x, y, z) coordinate axially at rather long
distances {Cu(1)–O(21) = 2.595(6), Cu(1)–O(22)* = 2.539(6)
Å} to form a tetragonally distorted octahedron. The angles and
equatorial Cu−N and Cu−O bond lengths of the asymmetric
unit, [Cu(L1)(H2O)(OClO3)]+, are in the expected range for
typical Jahn−Teller distorted octahedral copper(II) complexes.41
The shortest copper⋅⋅⋅copper distance in the polymer is 7.159(2)
Å.
3
.
3.2. IR, electronic spectra and magnetic moments
The IR bands corresponding to the C=N stretching
vibrations for complexes
cmꢀ1.37 A broad band at around 1120 cmꢀ1 in the IR spectrum of
complex
indicates the presence of perchlorate anion.38 The IR
spectrum of complex exhibits characteristic νN3 band at 2049
cmꢀ1.39 In IR spectra of complexes
and , broad bands at 3422
1ꢀ3 appear in the range 1607–1650
1
2
1
3
and 3443 cmꢀ1 respectively were observed, which may be
assigned to the OH stretching vibration of coordinated water
molecules.
The electronic spectra in acetonitrile are recorded in the
range 200–1000 nm. The intense absorption bands at short
wavelengths, around 360 nm, may be assigned to ligand to
metal ion charge transfer bands (LMCT). The absorptions
around 600 nm may be assigned to d–d transitions.
Room temperature magnetic susceptibility measurements
for the complexes show that they have magnetic moment values
in the range 1.70–1.73 BM, as expected for discrete
magnetically nonꢀcoupled spin only value for copper(II) ion, as
also observed in similar systems.40
Fig. 2: Perspective view of complex
2
with the selective atom numbering scheme.
3.3.2. [Cu(L1)(N3)] (2)
ꢀ
.
The complex
2
crystallizes in the triclinic space group
P
1
A perspective view of the complex together with the atomꢀ
numbering scheme is shown in Fig. 2. The structure consists of
discrete mononuclear units. The tridentate ligand coordinates to
the copper(II) center via the phenolate oxygen atom, O(11), the
imine nitrogen atom, N(19), and the pyridinium nitrogen atom,
N(28), forming one five member and one six member chelate
rings. The azide nitrogen atom, N(1), occupies the fourth
3.3. Description of the structures
The structures of complexes were confirmed by single
crystal Xꢀray diffraction analysis. The crystallographic and
refinement details are summarized in Table S1 (Supplementary
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coordination site and completes an ON3 square plane around plane).42 The basal plane of the said geometrical structure is
the metal center. Sum of the different angles around the formed by two nitrogen donor sites {N(19), N(28)} and one
copper(II) center is 360.23˚ indicating almost undistorted oxygen donor, O(11), from tridentate Schiff base ligand, one
square planar geometry around copper(II) center. The trans chlorine atom, Cl(1) and the apical position is occupied by the
angles are found to be 175.85(7) {O(11)–Cu(1)–N(28)} and oxygen donor, O(1), of a water molecule. Deviations of the
171.53(8) {N(1)–Cu(1)–N(19)}. Deviations of the coordinating coordinating atoms, O(11), N(19), N(28) and Cl(1) from the
atoms, O(11), N(1), N(19) and N(28), from the leastꢀsquare leastꢀsquare basal plane are 0.2963(15), ꢀ0.3542(17),
mean planes through them are ꢀ0.0709(16), 0.070(2), 0.3218(19) and ꢀ0.2638(6) Å, respectively and that of copper
0.0750(17) and ꢀ0.0743(17) Å respectively and that of copper atom from the same plane is 0.2847(3) Å. Sum of the different
atom from the same plane is ꢀ0.0394(2) Å.
angles around the metal center in the equatorial plane is
360.93˚.
3.4. Supramolecular interactions: Theoretical Study
In the polymeric complex
1 we have evaluated energetically
the nonꢀcovalent interactions that are relevant to rationalize the
crystal packing. In particular, the polymeric chains selfꢀ
assemble by means of πꢀπ stacking and Hꢀbonding interactions
involving the extended πꢀsystem of the tridentate Schiff base
ligand as shown in Fig. 4A. We have used a repeating structural
unit of the polymeric chain of complex
1 for the calculations.
Fig. 3 Perspective view of complex
3 with the selective atom numbering scheme.
The theoretical model used to analyze the πꢀπ interaction is
shown in Fig. 4B. In the theoretical model we have used only
one perchlorate coꢀligand to keep the charge of the model
neutral (using two perchlorate coꢀligands, each monomeric unit
would be negatively charged and the interaction repulsive). In
addition, the perchlorate ligand of one monomer is located in
such a way that does not interact with the organic ligand of the
other complex and viceꢀversa in the theoretical selfꢀassembled
dimer (see Fig. 4B). In the Xꢀray structure, the perchlorate
ligands of one polymeric chain interact with the aromatic
hydrogen atoms of the organic ligands of the other chain and
viceꢀversa (see dashed lines in Fig. 4A). However, we have
used the theoretical dimer shown in Fig. 4B in order to evaluate
only the contribution of the weak πꢀπ interaction. Moreover, a
close inspection of the πꢀπ complex shows that the chlorine
3.3.3. [Cu(L2)(Cl)(H2O)] (3)
The complex crystallizes in the monoclinic space group
. A perspective view of the complex with the atomꢀ
3
C2/c
numbering scheme is shown in Fig. 3. The tridentate Schiff
base ligand, HL2, coordinates the copper(II) center via the
phenolate oxygen atom, O(11), the imine nitrogen atom, N(19)
and the pyridinium nitrogen atom, N(28), forming one five
member and one six member chelate rings. One water molecule
and a chlorine atom coordinate with the copper(II) center
forming a square pyramidal structure which is confirmed by the
Addison structural index, τ = 0.015 (τ = (α ꢀ β)/60˚, where a and
b are the bond angles of the trans donor atoms in the basal
Fig. 5 (A) X-ray fragment of complex
complex . Distances are in Å.
2
. (B, C and E) Theoretical models used to evaluate the non-covalent interactions. (D) Molecular electrostatic surface of
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atom is close to a C=C bond of the quinoline ring establishing
In complex
2 we have evaluated energetically the nonꢀ
an lpꢀπ interaction. The interaction energy of the selfꢀassembled covalent interactions that are significant to explain the
dimer is large in absolute value (ꢂE1 = –17.9 kcal/mol) and assemblies observed in the solid state. In particular, it forms
corresponds to two πꢀπ interactions and two lpꢀπ interactions. In infinite 1D ladders that are dominated by two types of πꢀπ
order to estimate both contributions separately, we have also stacking interactions involving the extended πꢀsystem of the
computed the interaction energy [denoted as ꢂE1’(Cl→H)] tridentate Schiff base ligand (see Fig. 5A). This ladder interacts
using a theoretical model where only the chlorine atoms have with the adjacent one by means of C–H/π interactions involving
been replaced by hydrogen atoms and consequently only the the aromatic hydrogen atoms and the πꢀsystem of the azide
stacking interaction is evaluated. As a result the interaction (central N atom). Several nonꢀcovalent interactions involving
energy is reduced to ꢂE1’(Cl→H) = –14.0 kcal/mol indicating the πꢀsystem of coordinated pseudohalides has been analyzed
that each πꢀπ interaction contributes in 7.0 kcal/mol. The both theoretically and exploring the Cambridge structural
difference between both interaction energies correspond to the database.43ꢀ44We have used several theoretical models to
double lpꢀπ interaction that is weaker than the stacking analyze the πꢀπ and C–H/π interactions that are shown in Fig. 5.
interaction, i.e. ꢂE1–ꢂE1’(Cl→H) = –3.9 kcal/mol.
Two different πꢀπ stacking modes are observed in the formation
of the ladder. The first one (denoted as πꢀπ1) is highlighted in
the theoretical dimer shown in Fig. 5B. A close inspection of
the πꢀπ complex reveals that the chlorine atoms of the ligands
establish ancillary interactions with the copper metal centers.
The interaction energy of the dimer that represents the πꢀπ1
complexation mode (ꢂE2 = –17.9 kcal/mol) is stronger than
expected for a πꢀπ stacking due to the presence of both Cu⋅⋅⋅Cl
ancillary interactions. In order to evaluate these ancillary
interactions, we have also computed the dimer shown in Fig.
5B where the Cl atoms have been replaced by hydrogen atoms
[denoted as ꢂE2’(Cl→H)]and consequently only the stacking
interaction is evaluated. The difference between ꢂE2 and
ꢂE2’(Cl→H) is the contribution of both Cu⋅⋅⋅Cl ancillary
interactions to the dimer formation, which is –3.2 kcal/mol. The
second stacking mode (denoted as πꢀπ2), which is also involved
in the ladder formation, is highlighted in the dimer shown in
Fig. 5C. A close examination shows an intricate combination of
interactions in this dimer that include Hꢀbonding, cationꢀπ and
πꢀπ interactions. This explains the very large interaction energy
computed for this dimer (ꢂE3 = –45.6 kcal/mol), likely due to
the electrostatically favoured Hꢀbonding (involving the terminal
N atom of azide) and cationꢀπ interactions. To corroborate this,
we have computed the molecular electrostatic potential surface
(MEPS) of the monomer (see Fig. 5D). It can be clearly
Fig. 4: (A) X-ray fragment of complex 1. (B) Theoretical model used to evaluate
the lp-π and π-π non-covalent interactions. Distances in Å.
Fig. 6 (A) X-ray fragment of complex 3. (B and C) Theoretical models used to evaluate the non-covalent interactions. Distances in Å.
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observed a region of positive potential over the copper ion (22 Hirshfeld surface indicative of O⋅⋅⋅H, Cl⋅⋅⋅H, N⋅⋅⋅H contacts.
kcal/mol) and a region of negative potential (–5 kcal/mol) over Other visible spots in the Hirshfeld surfaces correspond to
the phenolic ring where the cationꢀπ interaction is formed. The
H⋅⋅⋅H contacts. The dominant interactions are seen in dnorm
8ꢀaminoquinoline part of the ligand presents a positive potential surface plots as the bright red areas in Fig. 7. The curvedness
over the ring and therefore it is not suitable to establish cationꢀπ surface indicates the electron density surface curves around the
interactions. The most negative part of the molecule is the molecular interactions. The 2D fingerprint plots of complexes
ending nitrogen atom of the coordinated azide ligand and the illustrate the significant differences between the intermolecular
most positive part comprise the aromatic hydrogen atoms thus interaction patterns. In fingerprint plots (Fig. 8, 9 and 10),
favouring the Hꢀbonding interaction, explaining the large
O⋅⋅⋅H, Cl⋅⋅⋅H and N⋅⋅⋅H interactions are represented by a spike
interaction energy observed in this πꢀπ2 interaction mode and in the bottom area whereas the H⋅⋅⋅O, H⋅⋅⋅Cl, H⋅⋅⋅N interactions
contributing to the stabilization of the 1D ladder observed in the are represented by a spike in the top left regions.
solid state. Finally, we have also computed the interaction
energy of both symmetrically related C–H/π(azide) contacts
that are responsible for the interꢀladder interaction using the
model represented in Fig. 5E. As a result, the interaction energy
is ꢂE4 = –10.0 kcal/mol, thus each C–H/π interaction is ½×ꢂE4
= –5.0 kcal/mol, comparable to conventional Hꢀbonding
interactions.
In complex
3 we have also analyzed theoretically the nonꢀ
covalent interactions that are responsible for the formation of
the infinite 1D ladder in the solid state that is dominated by two
types of πꢀπ stacking interactions (see Fig. 6A). The first one is
shown in Fig. 6B and, additionally to the πꢀπ stacking
interaction between the electron rich and electron poor rings of
the ligand (phenol and quinoline respectively), two strong Hꢀ
bonds (electrostatically favoured) contribute to the large
binding energy computed for this dimer (ꢂE5 = –45.4
kcal/mol). The second one is shown in Fig. 6B and it is
characterized by an antiparallel stacking of the coordinated
quinoline moieties and two Hꢀbonds involving the coordinated
water molecules. The interaction energy of this dimer is ꢂE6 =
Fig. 7: Hirshfeld surfaces mapped over dnorm for complexes
(right).
1 (left), 2 (middle) and
3
–15.5 kcal/mol that correspond to both the πꢀπ stacking and Hꢀ Fig. 8 Fingerprint plots of
1: full (left) and resolved into H⋅⋅⋅O/O⋅⋅⋅H (bottom)
contacts showing the percentage of contact contributed to the total Hirshfeld
surface area of the molecule.
bonding interactions. We have also computed the interaction
energy (denoted as ꢂE6’, see Fig. 6B) of an additional
theoretical model where the copperꢀcoordinated water
molecules have been eliminated and, consequently, the Hꢀ
bonds are not established. As a result the interaction energy is
reduced to ꢂE6’ = –12.8 kcal/mol, that is the contribution of the
antiparallel stacking interaction.
The proportions of H⋅⋅⋅O/O⋅⋅⋅H interactions comprise 32%,
3.5% and 9.6% of the Hirshfeld surfaces for each molecule of
1
,
2
and
a spike (di = 1.067, de = 0.667 Å in
and di = 1.233, de = 0.898 Å in
area of the fingerprint plot (Fig. 8ꢀ10). The H⋅⋅⋅O interaction is
also represented by another spike (de = 1.067, di = 0.667 Å in
de = 1.41, di = 1.07 Å in and de = 1.233, di = 0.898 Å in ) in
3
, respectively. The O⋅⋅⋅H interaction is represented by
, di = 1.41, de = 1.07 Å in
) in the bottom left (donor)
1
2
3
3.5. Hirshfeld surface analysis
1
,
The Hirshfeld surface45 surrounded a molecule is defined by
points where the attempt to the electron density from the
molecule of interest is equal to the contribution from all the
other molecules. For each point on that isosurface two distances
are determined: one is de represents the distance from the point
to the nearest nucleus external to the surface and second one is
di represents the distance to the nearest nucleus internal to the
surface. The normalized contact distance (dnorm) is based on
both de and di. The Hirshfeld surfaces mapped over dnorm (range
of ꢀ0.1–1.5 Å) are displayed in Fig. 7. The Hirshfeld surfaces
mapped over shape index and curvedness (range of ꢀ0.1–1.5 Å)
are shown in Fig. S1ꢀS2 (Supplementary information). The
surfaces are shown as transparent to allow visualization of
molecules, around which they were calculated. The surface
represents the circular depressions (deep red) visible on the
2
3
the bottom right (acceptor) region of the fingerprint plot. The
proportions of H⋅⋅⋅Cl/Cl⋅⋅⋅H interactions comprise 11.6% and
13.6% of the Hirshfeld surfaces for each molecule of
complexes
represented by a spike (di = 1.813, de = 1.167 Å in
1.367, de = 0.767 Å in ) in the bottom left (donor) area of the
fingerprint plot (Fig. 9ꢀ10). The H⋅⋅⋅Cl interaction is also
represented by another spike (de = 1.813, di = 1.167 Å in and
de = 1.367, di = 0.767 Å in ) in the bottom right (acceptor)
region of the fingerprint plot. The proportion of H⋅⋅⋅N/N⋅⋅⋅
interaction comprises 26.4% of the Hirshfeld surfaces for
complex . The N⋅⋅⋅H interaction is represented by a spike (di =
1.433, de = 1.0 Å in ) in the bottom left (donor) area of the
2
and
3
, respectively. The Cl⋅⋅⋅H interaction is
2
and di =
3
2
3
H
2
2
fingerprint plot (Fig. 9). The H⋅⋅⋅N interaction is represented by
6 | J. Name., 2012, 00, 1-3
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another spike (de = 1.433, di = 1.0 Å in
(acceptor) region of the fingerprint plot.
2
) in the bottom right Diffractometer Facility at the Department of Chemistry,
Jadavpur University.
Notes and references
aDepartment of Chemistry, Inorganic Section, Jadavpur University,
Kolkata ꢀ700 032, India. eꢀmail: shouvik.chem@gmail.com
Tel:+(91)33ꢀ24572941.
bDepartament de Química, Universitat de les IllesBalears, Crta.
deValldemossa km 7.5, 07122 Palma (Baleares), Spain. Eꢀmail:
toni.frontera@uib.es.
† CCDC 1053588ꢀ1053590 for 1–3 respectively.
1
2
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Fig. 9 Fingerprint plots of 2: full (top left) and resolved into H⋅⋅⋅Cl/Cl⋅⋅⋅H (top
right), H⋅⋅⋅N/N⋅⋅⋅H (bottom left) and H⋅⋅⋅O/O⋅⋅⋅H (bottom right) contacts showing
the percentage of contact contributed to the total Hirshfeld surface area of the
molecule.
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Fig. 10 Fingerprint plots of
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H⋅⋅⋅O/O⋅⋅⋅H (right) contacts showing the percentage of contact contributed to the
total Hirshfeld surface area of the molecule.
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We have synthesized and Xꢀray characterized three new
copper(II) complexes that present interesting supramolecular
assemblies in the solid state, which are dominated by Hꢀ
bonding, πꢀπ and lpꢀπ interactions. Hirshfeld surface analysis
was used for visually analyzing intermolecular interactions in
the crystal structures. Surfaces mapped with dnorm help to
envisage hydrogen bonding interactions. Fingerprint plots
reveal the percentage of intermolecular contacts (H⋅⋅⋅H O⋅⋅⋅H,
Cl⋅⋅⋅H and N⋅⋅⋅H) in the complexes. On the other hand, we have
evaluated energetically, by means of DFT calculations, the
contribution of each interaction to the formation of the
supramolecular assemblies. The energetic analysis confirms the
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