Supramolecular assembly of hydrogen bonding, ESR studies and theoretical calculations of Cu(II) complexes

Article abstract of DOI:10.1002/aoc.4504

A series of copper(II) complexes were synthesized by the reaction of copper(II) chlorid with 1-phenyl-3methyl-(3-dervitives phenylhydrazo)-5-pyrazolone (HL_n) yields 1:1 and 1:2 (M:L) complexes depending on the reaction conditions. The elemental analysis, spectral (IR, ¹H NMR, UV-Vis and ESR), conductance and magnetic measurements were used to characterize the isolated complexes. The IR spectral data indicate that the metal ions are coordinated through the oxygen of the keto and nitrogen of hydrazone groups. The UV-Vis spectra, magnetic moments and ESR studies indicate square planar geometry for Cu(II) complexes (1–3) by NO monobasic bidentate and the two monobasic trans bidentate in octahedral geometry for Cu(II) complexes (4–6). It is found that the change of substituent affects the theoretical calculations of Cu(II) complexes. Molecular docking was used to predict the binding between the ligands (HL_n) and the receptors of prostate cancer mutant (2Q7K), breast cancer mutant (3HB5), crystal structure of E. coli (3T88) and crystal structure of S. aureus (3Q8U). The molecular and electronic structures of Cu(II) complexes and quantum chemical calculations were studied. According to intramolecular hydrogen bond leads to increasing of the complexes stability.

Full text of DOI:10.1002/aoc.4504

Received: 13 March 2018
DOI: 10.1002/aoc.4504
Revised: 26 May 2018
Accepted: 13 June 2018
F U L L P A P E R
Supramolecular assembly of hydrogen bonding, ESR studies
and theoretical calculations of Cu(II) complexes
Sh.M. Morgan1
| M.A. Diab2
| A.Z. El‐Sonbati2
1 Environmental Monitoring Laboratory,
Ministry of Health, Port Said, Egypt
2 Chemistry Department, Faculty of
Science, Damietta University, Damietta,
Egypt
A series of copper(II) complexes were synthesized by the reaction of copper(II)
chlorid with 1‐phenyl‐3methyl‐(3‐dervitives phenylhydrazo)‐5‐pyrazolone
(HLn) yields 1:1 and 1:2 (M:L) complexes depending on the reaction condi-
tions. The elemental analysis, spectral (IR, 1H NMR, UV‐Vis and ESR), conduc-
tance and magnetic measurements were used to characterize the isolated
complexes. The IR spectral data indicate that the metal ions are coordinated
through the oxygen of the keto and nitrogen of hydrazone groups. The
UV‐Vis spectra, magnetic moments and ESR studies indicate square planar
geometry for Cu(II) complexes (1–3) by NO monobasic bidentate and the two
monobasic trans bidentate in octahedral geometry for Cu(II) complexes (4–6).
It is found that the change of substituent affects the theoretical calculations of
Cu(II) complexes. Molecular docking was used to predict the binding between
the ligands (HLn) and the receptors of prostate cancer mutant (2Q7K), breast
cancer mutant (3HB5), crystal structure of E. coli (3T88) and crystal structure
of S. aureus (3Q8U). The molecular and electronic structures of Cu(II) com-
plexes and quantum chemical calculations were studied. According to intramo-
lecular hydrogen bond leads to increasing of the complexes stability.
Correspondence
M. A. Diab, Chemistry Department,
Faculty of Science, Damietta University,
Damietta, Egypt.
Email: m.adiab@yahoo.com
KEYWORDS
Cu(II) supramolecular structure, ESR study, molecular docking, molecular structures, pyrazolone
derivatives
1 | INTRODUCTION
the phenol and imine groups in ground and/or excited
state.[10] The presence of azo/hydrazone tautomerism in
Aromatic azo dyes are the most widely used class of
coloring materials due to their massive application in
various fields of science and technology.[1–3] The photo‐
physical and photo‐chemical properties of this class of
dyes make them suitable as optical sensors and advanced
materials. Furthermore, azo compounds are known to be
involved in a number of biological reactions such as inhi-
bition of DNA, and biological activity against bacteria
and fungi.[4–9] The azo/hydrazone tautomerism in azo
compounds is very attractive from theoretical and practi-
cal viewpoints and has been of particular interest.[4–6] It is
described by the intramolecular proton transfer between
these compounds may influence considerably in their
unique photo‐physical and photo‐chemical properties,
which is turn strongly influenced by several factors
including temperature, the substituent structure and sol-
vent polarity.[11]
Cu(II) complexes have received much attention
because of their rich electrochemical and photophysical
properties as well as their potential applications in various
supramolecular structures.[12–14] Multinuclear systems of
this kind can be developed by covalent linking of building
blocks with spacers which, therefore, is the key compo-
nent because the size, shape and electronic nature of the
Appl Organometal Chem. 2018;e4504.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4504

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MORGAN ET AL.
bridge controls the electronic communication between
the chromophores and thereby the molecule as a whole.
The present study describes the chelation behavior of
Cu(II) complexes (1–6) of 1‐phenyl‐3‐methyl‐(3‐deriva-
tives phenylazo)‐5‐pyrazolone (HLn) (where n = 1;
COOH (HL1), n = 2; OH (HL2) and n = 3; OCH3
(HL3)). R = COOH (HL1); R = OH (HL2) and
R = OCH3 (HL3). The structure of the Cu(II) complexes
(1–6) is elucidated using elemental analysis, IR, electron
spin resonance (ESR), UV–Vis spectra, magnetic moment
and molar conductance. Molecular docking was used to
predict the binding between HLn and the receptors of
prostate cancer mutant (2Q7K), breast cancer mutant
(3HB5), crystal structure of E. coli (3T88) and crystal
structure of S. aureus (3Q8U). Theoretical study of Cu(II)
complexes (1–6) were optimized theoretically and the
quantum chemical parameters were calculated.
acid and ethanol were used without any further
purification.
2.2 | Preparation of 1‐phenyl‐3‐methyl‐(3‐
derivatives phenylazo)‐5‐pyrazolone (HLn)
In a typical preparation, 25 ml of distilled water contain-
ing 0.01 mol hydrochloric acid were added to m‐deriva-
tives aniline (0.01 mol).[15] To the resulting mixture
stirred and cooled to 0 °C, a solution of 0.01 mole sodium
nitrite in 20 ml of water was added dropwise. The formed
diazonium chloride was consecutively coupled with an
alkaline solution of 0.01 mol 3‐methyl‐1‐phenyl‐1H‐
pyrazol‐5(4H)‐one as shown in Figure 1. The colored pre-
cipitate, which formed immediately, was filtered through
sintered glass crucible, washed several times with water.
Table S1 shows the details of elemental analysis of the
ligands.
2 | EXPERIMENTAL
2.3 | Preparation of complexes
2.1 | Material and reagents
For the synthesis of copper complexes; a solution of
CuCl2.2H2O in approximately 50 ml of absolute alcohol
was mixed with an appropriate amount of HLn ligands
to give a molar ratio of 1:1/1:2(M:Ln). Reflux was
The standard chemicals, 3‐methyl‐1‐phenyl‐1H‐pyrazol‐
5(4H)‐one and 3‐alkyl anilines (alkyl: OCH3, COOH and
OH; Aldrich Chemical Co.), sodium nitrite, hydrochloric
FIGURE 1 The formation mechanism
and tautomeric forms of ligands (HLn)

MORGAN ET AL.
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continued for ~ 2 hrs, followed by removal of the excess
solvent under reduced pressure. The complexes were
filtered and washed with Et2O.
All precipitates were dried in a vacuum oven at 40 °C
for several days. Table 1 shows the details of elemental
analysis of the isolated complexes.
atoms, Kollman united atom type charges, and solvation
parameters were added with the aid of AutoDock
tools.[19,20] Auto Dock parameter set‐ and distance‐depen-
dent dielectric functions were used in the calculation of
the van der Waals and the electrostatic terms, respectively.
The molecular structures of the compounds were
optimized by HF method with 3‐21G basis set. The mole-
cules were built with the Perkin Elmer ChemBio Draw
and optimized using Perkin Elmer ChemBio3D soft-
ware.[21–24] Quantum chemical parameters such as the
highest occupied molecular orbital energy (EHOMO), the
2.4 | Measurements
Elemental microanalyses of the separated ligands and
solid chelates for C, H and N were performed in the
Microanalytical Center, Cairo University, Egypt. The
analyses were repeated twice to check the accuracy of
the analyzed data. The metal content in the complexes
was estimated by standard methods.[16] The 1H NMR
spectrum was obtained with a JEOL FX90 Fourier trans-
form spectrometer with DMSO‐d6 as the solvent and
TMS as an internal reference. The infrared spectra were
recorded as KBr discs using a Perkin‐Elmer 1340 spec-
trophotometer. Ultraviolet–Visible (UV–Vis) spectra of
the compounds were recorded in Nuzol solution using
a Unicom SP 8800 spectrophotometer. The magnetic
moment of the prepared solid complexes was deter-
mined at room temperature using the Gouy's method.
Mercury(II) (tetrathiocyanato cobalt(II)), [Hg {Co
(SCN)4}], was used for the calibration of the Gouy's
tubes. Magnetic moments were calculated using the
lowest unoccupied molecular orbital energy (ELUMO
)
and HOMO–LUMO energy gap (ΔE) for the investigated
molecules were calculated.
3 | RESULTS AND DISCUSSION
3.1 | The solid state structures
In general, most of the azo compounds give spectral local-
ized bands in the wavelength range 46620–34480 and
31250–270370 cm−1. The first region is due to the absorp-
1
1
tion of the aromatic ring compared to Bb and Lb of
mono substituted benzene while the second region is
due to the conjugation between the azo group and the
aromatic nuclei, with intermolecular charge transfer
resulting from π‐electron migration to the diazo group
from electron donating substituents. The position of the
π‐π* transition of the azo groups remains is one of the
most interesting unresolved questions of molecular
spectroscopy.[25]
equation, μeff. = 2.84 [T χM ]
coor. 1/2. Electron spin reso-
nance (ESR) measurements of powdered samples were
recorded at room temperature using an X‐band spec-
trometer utilizing a 100 kHz magnetic field modulation
with 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) as a refer-
ence material.
Docking process in which the ligand–protein interac-
tion energies are calculated using a Docking Server.[17,18]
Docking calculations were carried out on prostate cancer
mutant (2Q7K), breast cancer mutant (3HB5), crystal
structure of E. coli (3T88) and crystal structure of S.
aureus (3Q8U) protein models. Essential hydrogen
The principal ligands (HLn) were synthesized by cou-
pling of 3‐methyl‐1‐phenyl‐1H‐pyrazol‐5(4H)‐one with
diazonium salts. The elemental analysis is in good agree-
ments with the proposed structure, 1‐phenyl‐3‐methyl‐(3‐
derivatives phenylazo)‐5‐pyrazolone (HLn) can exist
either as the keto or enol form or as an equilibrium mix-
ture of the two since it has a hydrazone function. How-
ever, the IR and NMR spectra of HLn indicate that in
TABLE 1 Elemental analysis data for Cu(II) complexes
Exp. (calcd.)%
Compound
μeff. (B.M.)
C
H
N
M
[CuL1 (Cl)(OH2)](1)
[CuL2 (Cl)(OH2)](2)
[CuL3 (Cl)(OH2)](3)
[Cu (L1)2(OH2)2](4)
[Cu (L2)2(OH2)2](5)
[Cu (L3)2(OH2)2](6)
1.89
1.90
1.91
2.05
1.93
2.15
46.47 (46.57)
46.57 (46.82)
48.05 (48.11)
55.07 (55.02)
56.07 (56.01)
56.97 (57.18)
3.29 (3.42)
3.52 (3.66)
3.95 (4.01)
3.92 (4.05)
4.28 (4.38)
4.57 (4.77)
12.58 (12.78)
13.38 (13.66)
12.88 (13.21)
14.78 (15.10)
16.18 (16.34)
15.58 (15.70)
14.31 (14.51)
15.35 (15.50)
14.56 (14.99)
8.31 (8.57)
9.01 (9.27)
8.51 (8.91)

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MORGAN ET AL.
solid state it remains in the keto form. This indicates that
in solution and presence of metal, it converts to enol/
hydrazone form and coordinates to the metal in the
hydrazone‐keto form.[26]
The elemental analysis corresponds to the general
formulae [Cu (Ln)(Cl)(OH2)] (1–3) and [Cu (Ln)2(OH2)2]
(4–6) for all complexes. The principal ligands (HLn)
undergoes mono deprotonation to form Ln in copper
complexes and act as a bidentate ligand thus occupying
one/two positions of a square planar/octahedral geome-
try. The chloride and aqua/two aqua groups occupy the
four/sixth position. All complexes exhibited non‐
conducting properties in DMF solution.
3.4 | Infrared spectra and nature of
coordination
The bonding of the metal ion to the ligands can be clari-
fied by comparing the IR spectra of the complexes with
those of the ligands. Microanalytical data as well as
metal, and cholride estimations are in good agreement
with stoichiometry proposed for complexes (Figure 2 and
Table 1). The following conclusions can be drowning:
1 The infrared spectra of ligands exhibit a strong band
at 1645–1625 cm−1 due to υ (C=O) (pyrazolone
ring).[27] The discussed infrared features beside the
band appeared at ~1595–1575 cm−1, can guide to
assume the presence of υ (C=N‐) (hydrazone group)
structure through resonating phenomena.[9] In gen-
eral, the presence of electron attracting group mini-
mizes the charge transfer from the phenyl ring and
this leads to increase the C=O band modes. The βC‐
H, δC‐H and γC‐H modes of vibrations are identified
by the presence of strong bands in the 1180–1110,
1030–930 and 840–780 cm−1 region, respectively.
The C–C vibrations also are identified by the presence
3.2 | Stoichiometries of the copper(II)
complexes
The stoichiometries of the complexes have been deduced
from their elemental analyses. HLn is mononucleating
and hence requires one metal ion for coordination. All
the products were partially soluble in common organic
solvents. On the basis of elemental analysis (Table 1),
the compositions of the complexes agree well with their
structural formulae.
of several bands at frequencies lower than 755 cm−1
.
Generally, the electron donor methoxy group
enhances the change transfer from the phenyl ring
to the heterocyclic moiety.[28,29] This leads to increase
both polarizability of the carbonyl group. Such class of
compounds as illustrated in (Figure 1) has different
types of hydrogen bonding according to El‐Sonbati
et al.,[30,31] as follows:
i. H‐bonding of the type O–H····N between the –OH
group and –N=N– group (Figure 1. (B)).
ii. H‐bonding of the type N–H····O between the –NH
group and C=O group (Figure 1. (C)).
Copper chloride reacts with the HLn in 1:1/1:2 (metal:
ligand) mole ratios in anhydrous alcohol, giving partially
soluble products as indicated below.
The formation of the complexes may be represented
by the following reactions.
1 Complexes with half equivalent anions.
The ligands behave as a monobasic and one contain
one anion (chloride ion).
HLn þ CuCl2:2H2O
→ ½CuLnðClÞðOH2Þꢀ
2 Intermolecular hydrogen bonding of the O–H….N
(Figure 1. (D)) or N–H….O (Figure 1. (E)) shows type
of one molecule to another as given in Figure 1.
2 Complexes deprived of the anions.
In this case the anions of the copper salt are elimi-
nated in the reaction medium as the corresponding
acid on the following the Cu2+ salt to react with the
ligands.
3 The case (2) is more favored than case (1). This is due to
the presence of broad band located at 875–975 cm−1
,
Â
Ã
2HLn þ CuCl2:2H2O
→
Cu ðLnÞ2ðOH2Þ2
3.3 | Molar conductance of the copper(II)
complexes
The conductance measurements, of solutions of
copper(II) complexes (10−3 M in DMSO) show the value
in the range of 7–11 Ω−1 cm2 mol−1. These values sug-
gest that all copper(II) complexes are non‐electrolyte in
nature.[12]
FIGURE 2 The structures of Cu(II) complexes

MORGAN ET AL.
5 of 15
which could be taken as a good evidence for the intra-
Karabatoses et al.[32] where the hydrazone formed is
more than the azo structure for similar compounds.
• The carbonyl absorption band υ (CO) (of the
pyrazolone ring) was shifted to frequencies higher by
25–10 cm−1 for all complexes. The change in the car-
bonyl band position in the IR spectra of the metal
complexes indicates that the carbonyl group in the
hydrazone pyrazolone compounds is coordinated to
the metal ions (Figure 2).
• The disappearance of the υ (NH) stretching frequency
for ligands on chelate formation may be caused by
coordination of the hydrazo‐nitrogen to the metal
ion upon complexation (Figure 1).
• Introduction of a hydrazone group instead of N=N
leads to a change in the coordination mode of the
azo group from the azo‐nitrogen to the amine nitro-
gen (NH) (Figure 1).
• Coordination of the carbonyl oxygen and the nitrogen
of hydrazone in the chelate ring is supported by the
appearance of new bands which are assigned to υ
(Cu–N) and υ (Cu–O).
molecular hydrogen bonding.[5,9]
1
In the H NMR spectrum of the HL3 measured in
DMSO‐d6 (Table S2), the hydrogen proton appear as a
singlet at 11.32 ppm, which corresponds to NH proton
resonance of the hydrazone form.[5] The above results
suggest that the ligand exists in the keto hydrazone form.
By comparing the infrared spectra of free ligands to
that of the prepared complexes the following points are
observed.
1 The infrared spectra of the free ligands show no char-
acteristic absorption assignable to NH2 function. This
confirms the formation of the azo compounds.
2 In all complexes bands at 3480–3150 cm−1 are
observed. Such region is attributed to different proba-
bilities: (a) it is due to either free OH or NH; (b)
bonded –OH group or –NH group; or (c) due to pres-
ence of water molecules.
3 The absence of any peak attributed to the ‐N=N‐
moiety, implies that the ligands exist predominantly
in solution as the form shown in Figure 1. However,
in solution and in the presence of Cu(II) ion these
compounds exist in a tautomeric equilibrium 1B↔1C.
The main change is observed in the azo stretching
vibration, thus suggesting that the form shown in
Figure 1. Prevails this tautomeric form losses
hydrazone proton when complexed with Cu(II) ion as
mononegative chelating agents produces the C=N‐
NH mode of the free ligands. New bands assigned to
υ (NH) in the free ligands is absent, suggesting the
cleavage of intramolecular hydrogen bonding of υNH
group and coordination of nitrogen to the metal ion.
• The ligand orbitals of hydrazone pyrazolones are
group theoretically, energetically and occupationally
suitable for participation in both donor (Cu → L)
and acceptor (L → Cu) π‐interactions with the copper
ion.[12] Convincing evidence has been adduced that
Cu → L π‐bonding makes a significant contribution
to the bonding in copper complexes.
• The spectra of copper(II) complexes reveal the pres-
ence of band at ~ 3460 cm−1 due to the vibrational fre-
quency of O‐H of coordinated water. The presence of
coordinated water is further confirmed by the rocking
band at ~ 840 cm−1 and twisting band at ~ 730 cm−1
.
According to the structure shown in Figure 1, the HLn
ligands take its usual anionic (Ln) to chelate Cu(II)
through N‐of hydrazone group and oxygen atom of car-
bonyl group (Figures 1 and 2) as the potential binding
sites, whereas the chloride/aqua anion just fit the remain-
ing free coordination position.
3.5 | Molecular geometry optimization of
Cu(II) complexes
The optimized structures of Cu(II) complexes are given in
Figure 3. The selected geometrical structures of Cu(II)
complexes were calculated by optimizing their bond
lengths and bond angles (Tables S3‐S8). Quantum chem-
ical parameters such as the highest occupied molecular
orbital energy (EHOMO), the lowest unoccupied molecular
orbital energy (ELUMO) and HOMO–LUMO energy gap
(ΔE) for the investigated molecules were calculated.
In Figure 4 the HOMO–LUMO energy gap, ΔE,
which is an important stability index, is applied to
develop theoretical models for explaining the structure
and conformation barriers in many molecular sys-
tems.[27] The complexes (1) and (4) are more reactive
than other complexes as reflected from energy gap
values. The calculated quantum chemical parameters
• The sharp, medium intensity band of (C=N‐)
(hydrazone) appears at 1595–1575 cm−1 for ligands.
• The strong band observed at 1124–1140 cm−1, which
may be assigned to υ (N‐N) vibration modes[5,9] is
affected on complexation. It is blue shifted and
appeared as a weak band.
• The spectra exhibits a strong band at ~ 1650 cm−1
,
which is indicative to υ (C=O). However, the broad
band located at 3430 cm−1 leads to characterize the
υNH rather than hydrogen bonded –OH with N=N.
This is rather confirmed from the observation of

6 of 15
MORGAN ET AL.
FIGURE 3 Optimized structures of Cu(II) complexes
are given in Table 2. Additional parameters such as ΔE,
absolute electronegativities, χ, chemical potentials, Pi,
absolute hardness, η, absolute softness, σ, global
softness, S, and additional electronic charge, ΔNmax,
have been calculated according to the following equa-
tions:[21]

MORGAN ET AL.
7 of 15
FIGURE 4 The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of Cu(II) complexes (1–6)
In this context, we used molecular docking between
ligands (HLn) and receptors of prostate cancer mutant
ΔE ¼ ELUMO−EHOMO
−ðEHOMO þ ELUMO
Þ
(2Q7K), breast cancer mutant (3HB5), crystal structure of
E. coli (3T88) and crystal structure of S. aureus (3Q8U).
The results showed a possible arrangement between the
ligands (HLn) and the receptors (2Q7K, 3HB5, 3T88 and
3Q8U). The docking study showed a favorable interaction
between the ligands (HLn) and the receptors (2Q7K, 3HB5,
3T88 and 3Q8U) as shown in Figures 5–8 and the calculated
energy is listed in Table 3. According to the results obtained
in this study, HB plot curve indicates that the ligands (HLn))
binds to the proteins with hydrogen bond interactions and
decomposed interaction energies in kcal/mol were exist
between ligands (HLn) with receptors of prostate cancer
mutant (2Q7K), breast cancer mutant (3HB5), crystal
structure of E. coli (3T88) and crystal structure of S. aureus
(3Q8U) as shown in Figures S1‐S4. 2D plot curves of
docking with ligands (HLn) are shown in Figures S5‐S8.
The ligand (HL1) shows best interaction with the receptors
(3HB5, 3T88 and 3Q8U) than other ligands (HL2 and
HL3). Also, the ligand (HL1) shows best interaction with
receptor of breast cancer mutant (3HB5) than other
receptors.
χ ¼
2
E
LUMO−EHOMO
η ¼
2
1
σ ¼ ;
η
Pi ¼ −χ
1
2η
S ¼
;
Pi
ΔNmax ¼ −
η
3.6 | Molecular docking
The molecular docking is a key tool in computer drug
design.[5,9] Molecular docking aims to achieve an opti-
mized conformation for both the protein and drug with
relative orientation between them such that the free
energy of the overall system is minimized.[17]

8 of 15
MORGAN ET AL.
FIGURE 4 Continued.
TABLE 2 The calculated quantum chemical parameters of Cu(II) complexes
Complexa
EHOMO (eV)
ELUMO (eV)
ΔE (eV)
χ (eV)
η (eV)
σ (eV)−1
Pi (eV)
S (eV)−1
ω (eV)
ΔNmax
(1)
(2)
(3)
(4)
(5)
(6)
−4.167
−4.491
−4.509
−2.975
−6.240
−2.177
−3.909
−2.184
−2.159
−2.717
−2.569
−1.079
0.258
2.307
2.350
0.258
3.671
1.098
4.038
3.338
3.334
2.846
4.405
1.628
0.129
1.154
1.175
0.129
1.836
0.549
7.752
0.867
0.851
7.752
0.545
1.822
−4.038
−3.338
−3.334
−2.846
−4.405
−1.628
3.876
0.433
0.426
3.876
0.272
0.911
2.019
1.669
1.667
1.423
2.202
0.814
31.302
2.893
2.838
22.062
2.399
2.965
aNumbers as given in Table 1.
copper(II) complexes as shown in Table 1, are charac-
teristic of magnetically diluted copper(II) complexes.
The higher magnetic moment values than the spin only
(1.73 B.M.) imply the presence of a low lying excited
term which is able to mix some of its orbital angular
3.7 | Magnetic moment and electronic
spectra studies
The room temperature magnetic moment values for the
complexes are characteristic magnetically diluted

MORGAN ET AL.
9 of 15
FIGURE 5 Ligands (HLn) (green in (a) and gray in (b)) in interaction with receptor of prostate cancer mutant (2Q7K). (For interpretation
of the references to color in this figure legend, the reader is referred to the web version of this article)
momentum with the spin angular momentum of the
ground state.[33]
The electronic spectra of the free ligands display bands
at ~ 45400–45700, 42120–43320 and 31100–32340 cm−1

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MORGAN ET AL.
FIGURE 6 Ligands (HLn) (green in (a) and gray in (b)) in interaction with receptor of breast cancer mutant (3HB5). (For interpretation of
the references to color in this figure legend, the reader is referred to the web version of this article)
regions are assigned to Ph‐Ph*, π‐π* (phenyl) and n‐π*,
respectively. In all complexes, the first band is replaced
by a new intense one at 36000–36800 cm−1 assignable
to σ(N) → Cu2+ charge transfer transition. The new
band appeared at 25350–26300 cm−1 in the spectra of
complexes is assigned to π (O) → Cu2+ CT transition.
The band due to n → π* transition is merged into a
broad band in all complexes centered at 29850 cm−1 that
can be assigned as composite of the remaining n → π*
and σ(O) → Cu2+ and other LMCT transitions. The
spectra of all complexes exhibit a broad band at 14230–
18400 cm−1 which consists of at least three overlapping

MORGAN ET AL.
11 of 15
FIGURE 7 Ligands (HLn) (green in (a) and gray in (b)) in interaction with receptor of crystal structure of E. coli (3T88). (For
interpretation of the references to color in this figure legend, the reader is referred to the web version of this article)

12 of 15
MORGAN ET AL.
FIGURE 8 Ligands (HLn) (green in (a) and gray in (b)) in interaction with receptor of crystal structure of S. aureus (3Q8U). (For
interpretation of the references to color in this figure legend, the reader is referred to the web version of this article)

MORGAN ET AL.
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TABLE 3 Values obtained in docking calculations of ligands (HLn) with receptors of prostate cancer mutant (2Q7K), breast cancer mutant
(3HB5), crystal structure of E. coli (3T88) and crystal structure of S. aureus (3Q8U)
Electrostatic
Est. inhibition
constant (Ki)
(μM)
vdW+ bond+
desolve energy
(kcal/mol)
Energy
(kcal/mol)
Total intercooled
Energy (kcal/mol)
Code of
receptor
Est. free energy of
binding (kcal/mol)
Interact
surface
Ligand
2Q7K
3HB5
3T88
HL1
HL2
HL3
−5.24
−6.05
−6.38
144.95
36.65
21.11
−7.10
−7.40
−7.88
+0.06
−0.03
−0.02
−7.04
−7.43
−7.90
568.175
559.443
574.800
HL1
HL2
HL3
−7.48
−6.72
−7.03
3.31
11.79
7.09
−8.44
−8.48
−7.95
+0.01
−0.08
+0.02
−8.43
−8.56
−7.93
873.633
823.621
868.268
HL1
HL2
HL3
−6.13
−5.27
−5.55
32.38
136.84
85.65
−7.49
−6.14
−6.26
−0.02
+0.01
−0.08
−7.51
−6.13
−6.35
728.344
715.059
654.252
3Q8U
HL1
HL2
HL3
−6.22
−5.40
−6.02
27.68
109.32
38.92
−7.20
−6.39
−6.83
+0.06
+0.00
−0.16
−7.14
−6.38
−6.99
719.779
687.423
805.877
bands. The absorption in this region can be assigned to
ligand field transition characteristic of square planar
and/or tetrahedrally distorted octahedral copper(II)
complexes.[34] The spectral bands are assigned to
TABLE 4 ESR spectral assignments of Cu(II) complexes (1–3)
Complexa
gll
g⊥
gav
G
(1)
(2)
(3)
2.392
2.350
2.239
2.055
2.100
2.060
2.154
2.183
2.120
> 4
> 4
> 4
2
2
2
2
2
2B1g → Eg, B1g → B2g and B1g → A1g transitions.
aNumbers as given in Table 1.
3.8 | Electronic spin resonance spectral
(ESR) studies
estimated for each species. The α2 value of 0.5 indicates
complete covalent bonding, while that of 1.0 suggests
complete ionic bonding. Since α2‐values obtained lies
above 0.5 and below 1.0, which is expected for 100% ionic
character of the bonds and become smaller with increas-
ing covalent bonding, it is inferred that the complexes
have some covalent character in the ligand environment.
The value β2, which is observed less than unity for the
present complexes, also indicates the presence of in‐plane
π–bonding in the complexes. These findings support that
there is significant in‐plane σ‐bonding and in‐plane π‐
bonding in the complexes[36] the larger the covalency of
the bonding.
It has been suggested that the smaller value of All
arises from a distortion of a copper site away from planar-
ity.[37] The value of All < 140 x 10−4 cm−1 rules out the
possibility of square planar nature (Table S9). The empir-
ical factor f is an index of tetrahedral distortion and its
value vary from 105 to 135 for small to extreme distortion
in square planar complexes, and that depends on the
nature of the coordinated atom.[38] Hence the f values of
the complexes are indicating significant distortion from
planarity. The value of f can increases markedly on the
introduction of tetrahedral distortion to the chromo-
phore. The tetrahedral distortion of a square planar
ESR spectra studies of paramagnetic Cu(II) complexes
gives information about the distribution of the unpaired
electrons and hence about the nature of the bonding
between the metal ion and its ligands.
3.8.1 | ESR spectra of copper(II) com-
plexes (1–3)
ESR spectra of the present Cu(II) complexes (1–3)
were recorded at room temperature. The ESR spectra
of Cu(II) complexes. The g‐values are in the order
gll > g⊥> 2.0023, indicates the unpaired electron that is
corresponding to dx2‐y2 orbital as ground state with 3d9
configuration. The geometric parameter G, which is a
measure of the exchange interaction between copper cen-
ters in a polycrystalline compound, is calculated using the
equation G = gll‐2.0023/g⊥‐2.0023 for axial spectra. If
G > 4, exchange interaction is negligible and if it is less
than 4, considerable exchange interaction is indicated in
the solid complex.[35] The calculated G values for these
complexes indicate that there are no interactions between
the copper centers (Table 4). The value of in‐plane
σ‐bonding parameter α2 is related to gll and g⊥and

14 of 15
MORGAN ET AL.
TABLE 5 ESR spectral assignments of Cu(II) complexes (4–6)
associated with tetragonally distorted octahedral ligand
field around the copper(II) centers.
Complexa
gll
g⊥
gav
G
The bonding parameters (α2, β2 and γ2) of the com-
plexes have been calculated and summerised (Tables S9
and S10). The bonding parameters α2, β2 and γ2 which
may be regarded as measure of the covalency of in‐plane
σ‐bonds, in‐plane π‐bonds and out‐of plane π‐bonds,
have also been calculated. α2, β2 and γ2 parameters are
calculated according to the following equations:[42]
(4)
(5)
(6)
2.245
2.243
2.241
2.052
2.060
2.064
2.116
2.121
2.123
> 4
> 4
3.9
aNumbers as given in Table 1.
chroimophore with any of the biomimetic (N,O or S)
donors reduces All and increases gll, shifting the f
values.[39]
α2 ¼ ðAll=0:036Þ þ ðgll–2:0023Þ þ 3=7ðg⊥–2:0023Þ þ 0:04
β2 ¼ ðgll–2:0023ÞE=−8 λ α2
3.8.2 | ESR spectra of copper(II) com-
plexes (4–6)
γ2 ¼ ðg⊥–2:0023ÞE=−2 λ α2
The ESR spectra of all the complexes (4–6) (Table 5) are
of axial shape with gll > g⊥characteristic of complexes
with 2B1 (dx2‐y2) ground state. In the axial spectra, the
g‐values are related with exchange interaction coupling
constant (G) by the expression G = gll‐2.0023/g⊥‐2.0023.
According to Hathaway and Tomlinson,[40] if G > 4, the
local tetragonal axes are aligned parallel or only slightly
misaligned. If G < 4.0, significant exchange coupling is
present and the misalignment is appreciable. The calcu-
lated G values for these complexes indicate that there
are no interactions between the copper interaction
between the copper centers (see Table 5). All for com-
plexes exhibit gll < 2.3, suggesting covalent characters of
the copper‐ligand bonding in the present complexes.
The ESR parameters gll, g⊥, All and the energy of the
d‐d transition were used to evaluate the bonding parame-
ters α2, β2 and γ2, which may be regarded as measures of
the covalency of the in‐plane σ‐bonds, in‐plane π‐bonds
and out‐of‐plane π‐bonds.[12,41] The orbital reduction fac-
tors Kll = α2β2 and K⊥ = α2γ2 were calculated. Significant
information about the nature of bonding in the Cu(II)
complex can be derived from the relative magnitudes of
The λ value is calculated according to Tharmaraj et al.[42]
The observed λ value for complexes (1–6) (Tables S9 and
S10), which is less than that for the free Cu(II) ion
(828 cm−1). This reduction in λ from the free ion value
is an evidence of covalence in M‐L bond.[43] The lower
value of λ indicates that there is a considerable mixing
of ground and excited state terms.
The ESR data showed that: (i) the value of α2 of Cu(II)
complexes (4–6) increases with increasing gav. and
All × 10−4 (Figure S9) and (ii) the value of g⊥of Cu(II)
complexes (4–6) increases with increasing K2⊥as shown
in Figure S10.
4 | CONCLUSIONS
HLn ligands behave as a chelating bidentate monobasic
ligands, bonding through NH/CO group and nitrogen
atom of the hydrazone group. The electrical conductiv-
ities reveal that the complexes are non electrolytes
where the anions are bended to the metal ions as indi-
cated by IR.
Kll and K⊥. In the case of pure σ‐bonding, Kll ≈ K⊥
=
The data above indicate the possibilities of the signif-
icant variation of the structure and, therefore, properties
of metal chelate complexes caused by diverse structural
modifications of the ligands. Studied in this respect is
dominated by problems arise from the influence of strong
electron‐withdrawing and electron‐releasing substituents
in the aryl rings of the aromatic and heterocyclic azo
compounds, which is essential for defining basicity and
ligating abilities of the nitrogen centers in the azo groups.
It is expected that the investigation into these problems
may be promoted by further extended studies of the series
containing relevant azo ligands and gaining deeper
insight into the mechanism and preparative application
of the azo coupling reactions under the phase transfer
catalysis conditions.
0.77, whereas Kll < K⊥= 0.77 implies considerable in‐
plane π‐bonding while for out‐of‐plane π‐bonding
Kll > K⊥= 0.77. For the present complexes, the observed
order Kll > K⊥for complexes (4) and (5), while complex
(6), K⊥> Kll implies a greater contribution from in‐plane
π‐bonding than for out‐of‐plane. The empirical factor f
cm−1 is taken as an indication for the stereochemistry
of the copper(II) complexes. Addison has suggested that
this ratio may be an empirical indication of the tetrahe-
dral distortion of the square planar geometry. The values
lower than 135 cm−1 are observed for square planar struc-
tures and those higher than 150 cm−1 for tetrahedrally
distorted complexes. The values for the complexes under
investigation, Table 5, showed that all complexes

MORGAN ET AL.
15 of 15
[24] A. Z. El‐Sonbati, M. A. Diab, Sh. M. Morgan, A. M. Eldesoky,
M. Z. Balboula, Appl. Organometal. Chem. 2018, 32, e4207.
ORCID
Sh.M. Morgan http://orcid.org/0000-0002-8921-4894
M.A. Diab http://orcid.org/0000-0002-9042-1356
A.Z. El‐Sonbati http://orcid.org/0000-0001-7059-966X
[25] M. A. Diab, A. Z. El‐Sonbati, A. A. El‐Bindary, Sh. M. Morgan,
Res. Chem. Intermed. 2015, 41, 9029.
[26] Sh. M. Morgan, N. A. El‐Ghamaz, M. A. Diab, J. Mol. Struct.
2018, 1160, 227.
[27] A. Z. El‐Sonbati, M. A. Diab, A. A. El‐Bindary, A. M. Eldesoky,
Sh. M. Morgan, Spectrochim. Acta A 2015, 135, 774.
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SUPPORTING INFORMATION
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How to cite this article: Morgan ShM, Diab MA,
El‐Sonbati AZ. Supramolecular assembly of
hydrogen bonding, ESR studies and theoretical
calculations of Cu(II) complexes. Appl Organometal
Chem. 2018;e4504. https://doi.org/10.1002/aoc.4504
[22] H. M. Refaat, H. A. El‐Badway, Sh. M. Morgan, J. Mol. Liq.
2016, 220, 802.
[23] G. G. Mohamed, A. A. El‐Sherif, M. A. Saad, S. E. A. El‐Sawy,
Sh. M. Morgan, J. Mol. Liq. 2016, 223, 1311.