Insights into the new cadmium(II) metalloporphyrin: Synthesis, X-ray crystal structure, Hirshfeld surface analysis, photophysical and cyclic voltammetry characterization of the (morpholine){(meso-tetra(para-chloro-phenyl)porphyrinato}cadmium(II)

Article abstract of DOI:10.1016/j.poly.2019.06.055

In this work we report the synthesis of the cadmium(II)-meso-tetra(para-chloro-phenyl)porphyrin with the morpholine O-donor axial ligand with formula [Cd(TClPP)(morph)] (I). This coordination compound adopts a distorted five-coordinate square pyramidal ge

Full text of DOI:10.1016/j.poly.2019.06.055

Accepted Manuscript
Insights into the New Cadmium(II) Metalloporphyrin: Synthesis, X-ray Crystal
Structure, Hirshfeld surface analysis, Photophysical and Cyclic voltammetry
Characterization of the (Morpholine){(meso-tetra(para-chloro-phenyl)por-
phyrinato}cadmium(II)
Chadlia Mchiri, Selma Dhifaoui, khaireddine Ezzayani, Mouhieddinne
Guergueb, Thierry Roisnel, Fredérique Loiseau, Habib Nasri
PII:
S0277-5387(19)30466-8
https://doi.org/10.1016/j.poly.2019.06.055
POLY 14046
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
16 April 2019
26 June 2019
28 June 2019
Please cite this article as: C. Mchiri, S. Dhifaoui, k. Ezzayani, M. Guergueb, T. Roisnel, F. Loiseau, H. Nasri, Insights
into the New Cadmium(II) Metalloporphyrin: Synthesis, X-ray Crystal Structure, Hirshfeld surface analysis,
Photophysical and Cyclic voltammetry Characterization of the (Morpholine){(meso-tetra(para-chloro-
phenyl)porphyrinato}cadmium(II), Polyhedron (2019), doi: https://doi.org/10.1016/j.poly.2019.06.055
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Insights into the New Cadmium(II) Metalloporphyrin: Synthesis, X-ray
Crystal Structure, Hirshfeld surface analysis, Photophysical and Cyclic
voltammetry Characterization of the (Morpholine){(meso-tetra(para-
chloro-phenyl)porphyrinato}cadmium(II)
Chadlia Mchiri a, Selma Dhifaoui a khaireddine Ezzayani a, Mouhieddinne Guergueb a, Thierry
Roisnel b Fredérique Loiseauc and Habib Nasri a
a
Laboratoire de Physico-chimie des Matériaux, Faculté des Sciences de Monastir, Avenue de l'environnement, 5019
Monastir, University of Monastir, Tunisia.
b
Centre de Diffractométrie X, Institut des Sciences Chimiques de Rennes, UMR 6226, CNRS–Université de Rennes,1,
Campus de Beaulieu, 35042 Rennes Cedex, France.
cDépartement de Chimie Moléculaire, Université Grenoble-Alpes, CNRS UMR 5250, BP53 38041 Grenoble, France.
Absract
In this work we report the synthesis of the cadmium(II)-meso-tetra(para-chloro-
phenyl)porphyrin with the morpholine O-donor axial ligand with formula
[Cd(TClPP)(morph)] (I). This coordination compound adopts a distorted five-coordinate
square pyramidal geometry indicated by a major doming, a moderate ruffling and saddle
distortions of the porphyrinato core. The supramolecular architecture is dominated by
intermolecular N−H···Cl and C−H···Cl interactions formed between the morpholine and the
chlorine atom of the adjacent meso-phenylporphyrin of complex (I). Hirshfeld surface
analysis was carried out to understand the nature of intermolecular contacts, where the
fingerprint plot provides the information about the percentage contribution. UV-visible
spectroscopy study highlighted the red-shift of the absorption bands after the insertion of
Cd(II) metal ion into TClPP moiety and after coordination of the morpholine axial ligand.
Fluorescence emission spectroscopy study showed a remarkable blue-shift effect of the Q
bands followed by a dramatical diminution of the fluorescence intensity, quantum yield (φf)
and lifetime (τf) as consequence of the high quenching effect of the cadmium heavy metal
and the distortion of the porphyrin core, which promotes the loss of the “motion energy” by
other non-radiative energy dissipation processes than light emission. An increase of the
singlet oxygen quantum yield () is also observed due to the heavy atom effect of
cadmium(II) cation. The cyclic voltammetry investigation of the free base H2TClPP, the
starting material [Cd(TClPP)] and the Cd(II)-morpholine porphyrin species (I) is also
reported.
Keywords: Cadmium(II) porphyrin coordination compound, X-ray crystal structure,
Hirshfeld surfaces, Fluorescence, Singlet Oxygen, .

1. Introduction
The chemistry of porphyrins and related compounds dates back to the late nineteen century.
The porphyrin species and metalloporphyrins complexes are currently used in a variety of
applications such as photodynamic therapy, [1-3] optoelectronics, [4-5] chemical sensors,
[6] catalysis, [7] and photovoltaic systems [8]. Much of the excitement in porphyrin research
lies in their modular and relatively facile synthesis, large size, ready dissolution in organic
solvents, characteristic colors, rigidity, thermal stability, and affinity for metallation [9].
Since the middle of the last century, cadmium porphyrins have been studied and the physical
and chemical properties of Cd-porphyrin derivatives have been of general interest.
Cadmium(II) ion is too big to fit co-planarly into the cavity of porphyrin, it is located out of
the ligand plane and distorts it. Therefore the structure deformation of cadmium(II)
metalloporphyrins results in kinetic lability as well as peculiar photophysical and
photochemical behavior [10-11]. By the other hand, both cadmium and porphyrin exhibit
rich coordination chemistry. In fact, the Cd2+ site shows equally diverse coordination modes
and exists in five different coordination environments [12]. However, it has been noticed
that for porphyrins, cadmium(II) can coordinated only one axial ligand to form five-
coordinated complexes [13]. This makes cadmium metalloporphyrins simple systems to
evaluate the effect of the type of the axial ligands on the electronic and structural properties
of porphyrin coordination compounds.
It is noteworthy that cadmium porphyrin derivatives exhibit several biological applications. In
this context, we can mention the investigations in 2001 of Nyarko et al.,[14] which reported the
interactions of cadmium(II), mercury(II), and lead(II) metalloporphyrins with DNA and their
effects on this enzyme. Due to the fact that Cd(II), Hg(II) and Pb(II) are large divalent cations,
which are known to dissociate from their metalloporphyrin complexes in the presence of DNA
and ethylenediamine tetraacetic acid (EDTA). This is not the case of d transition center metals
such as Mn3+, Fe3+ and Co3+, the characteristic effects of the already mentioned heavy divalent
cations are expected to influence the DNA cleavage reaction. More recently, in 2012, Lee et al;
[15] noticed that hydrolysis of carbon dioxide is an important reaction for CO2 collection by
using accurate first-principles electronic structure calculations. These authors, predict how the
catalytic hydrolysis reaction in carbonic anhydrase (CA) can be mimicked in a zinc(II) and
cadmium(II) metalloporphyrins - carbon nanotube system.

Notably, morpholine is widely used as a solvent and it possesses two sites for coordination
to the metal ions. In the literature, are reported the spectroscopic properties of the
morpholine with divalent metallo-tetraphenyl porphyrins type [M(TPP)] (M = Co(II),
Cu(II), Ni(II) and Zn(II)), which elucidate the nature of ligation and the binding site of the
morpholine [16].
Nevertheless, up to date no reported investigation on the effect of the coordination of
morpholine axial ligand to the structural, spectroscopic, photophysical and electrochemical
properties of metalloporphyrins. In this work, we report the first example of the reaction of a
Cd(II)-porphyrin complex with the morpholine leading to the (morpholine)[(meso-tetrakis(4-
chlorophenyl)porphyrinato]cadmium(II) complex with the formula [Cd(TClPP)(morph)] (I)
(Scheme 1) where the morpholine axial ligand is bonded to the cadmium through the oxygen
atom.
Scheme 1. Structure of [Cd(TClPP)(morph)] (I).
2. Experimental Section
2.1. Syntheses
The synthesis of the meso-tetrakis(para-chlorophenyl)porphyrin (H2TClPP) and the [meso-
tetrakis(para-chlorophenyl)porphyrinato)]cadmium(II)
starting
material
complex
[Cd(TClPP)] were performed according to the methods described in the literature [17-18].
Scheme S1 gives the main steps of the preparation method.
1
H2TClPP porphyrin was obtained as purple crystals with 21% yield. H NMR (300 MHz,
DMSO-d6): δ (ppm.) -2.84 (s, 2H, N-H), 7.77 (d, 8H, Hm-Ph), 8.15 (d, 8H, Ho-Ph), 8.86 (s,
8H, β-pyr). UV-vis [max (nm) in CH2Cl2, (ε x 10-3, mol-1.L.cm-1)] 420(309), 517(15.8),
553(11), 589(5.6), 645(2). FTR-IR cm-1: 3316 ν[(NH) porphyrin], 2960 ν[(CH) porphyrin],
967 [(δCCH) porphyrin], 780 ν(C-Cl).

1
[Cd(TClPP)] was obtained as a dark green solid with 85% yield. H NMR (300 MHz,
DMSO-d6) (ppm), 8.11 (d, 8H, Ho-Ph), 7.97 (d, 8H, Hm-Ph), 8.75 (s, 8H, β-pyr). UV/vis
(CH2Cl2), [max (nm) in CH2Cl2, (ε x 10-3, mol-1 x L x cm-1)]: 433 (117), 568(2.3), 609(2.6).
FTR-IR cm-1: 2926 ν[(CH) porphyrin], 1086 [(δCCH) porphyrin], 720 ν(C-Cl).
[Cd(TClPP)(morph)] (I) [Cd(TClPP)] (20 mg, 0.020 mmol) and morpholine (0.5 mL,
0.125 mmol) were dissolved in 3 mL of chloroform. The solution was stirred overnight
before to be filtrated. Crystals of complex (I) were obtained by slow diffusion of hexane into
the chloroform solution with 80% yield (Scheme S1). Elemental analysis (%) calcd for
C48H33Cl4CdN5O (950.04). C, 60.68, H, 3.51, N, 7.37; found : C, 60.81, H, 3.59, N, 7.49.
1H NMR (300 MHz, DMSO-d6) (ppm), 2.64 (t, 4Hb, morph), 3.47 (t, 4Ha, morph); 5.75
(s, Hc, NH morph), 7.97 (d , 8H, Hm-Ph), 8.21 (d, 8H ,Ho-Ph), 8.74 (s, 8H, β-pyr). UV/vis
(CH2Cl2), [max (nm) in CH2Cl2, (ε x 10-3, mol-1 L cm-1)]: 436 (126), 575(4.4) , 620(2.6).
FTR-IR (cm-1): 2849 ν[(CH) porphyrin], 1089 [(δCCH) porphyrin], 3293 ν(N-H)morph, 1387
ν(CO)morph, 719 ν (C-Cl).
2.2 Spectroscopic and photophysical measurements:
1H spectra were recorded using Brucker Advance 300 spectrometer. The spectra were
recorded in DMSO-d6 solutions at room temperature (T = 298 K) using DMSO residual
peaks (δ = 2.50 ppm) as internal references. Chemical shifts (δ) and coupling constants (J)
are given in parts per million (ppm) and Hertz (Hz), respectively. Multiplicities are reported
as follow: s = singlet, d = doublet, t= triplet, m-Ph and o-Ph = meta and ortho protons on the
phenyl rings, and β-pyr = β-pyr protons on the pyrrole rings. Infrared spectra were recorded
from 4000 to 400 cm-1 FT-IR Nexus (Nicolet) spectrometer. Absorbance spectra were
recorded on a UV-3600 Shimadzu spectrophotometer and the concentrations of porphyrin
derivatives were controlled to be ca. 10-5 M in CH2Cl2. Fluorescence spectra were recorded
on a Fluorolog-3 spectrofluorimeter FL3-222 with a thermostated cell compartment (25 °C)
using a 450 W Xenon lamp and the concentrations of porphyrin derivatives were controlled
to be ca. 10-6 M in CH2Cl2. The singlet oxygen production 30 was measured by the IR
detector through a SPEX double grating monochromator (600 grooves/mm blazed at 1 µm).
All spectra were recorded using four optical faces quartz cells. Fluorescence quantum yield
(φf) were determined using tetraphenyl porphyrin (H2TPP) solution in toluene as
fluorescence standard (φf = 0.11) [19]. H2TPP in toluene was used as standard (Φ∆ = 0.63)
[20]. The absorbance value at the excitation wavelength of the reference and the sample

solutions were set to around 0.2. The fluorescence decays were recorded using the single
photon counting method. Data were collected up to 1000 counts accumulated in the
maximum channel and analyzed using Time Correlated Single Photon Counting (TCSPC)
software Fluofit (PicoQuant GmbH, BERLIN, Germany) based on iterative reconvolution
using a Levensberg-Marquandt algoritm, enabling the obtention of multi-exponential
profiles (mainly one or two exponentials in our cases).
2.3 cyclic voltammetry
Cyclic voltammetry (CV) experiments were performed with a CH-660B potentiostat (CH
Instruments). The analytical experiment is conducted at room temperature under an argon
atmosphere in a standard one-compartment, three-electrode electrochemical cell. Tetra-n-
butylammonium perchlorate (TBAP) was used as the supporting electrolyte (0.2 m) in
dichloromethane. An automatic Ohmic drop compensation procedure was systematically
implemented before the CV data were recorded with electrolytic solutions containing the
studied compounds at concentrations of ca. 10-3 M. CH Instruments vitreous carbon (f = 3
mm) working electrodes were polished with 1 µm diamond paste before each recording. The
Ag/AgNO3 (TBAP 0.2 m in CH2Cl2) redox couple was used as the reference electrode and a
platinum wire as an auxiliary electrode. For comparison with previously published data, all
potentials given in the text have been converted to values relative to the saturated calomel
electrode (SCE) by using the following relationship: E(SCE) = E(Ag/AgNO3) + 298 mV.
2.4 X-ray Crystallography
Single crystals of [Cd(TClPP)(morph)] (I) were grown at room temperature from CHCl3-
hexane mixture and carefully selected under a microscope and mounted on a Mitegen
micromesh with the help of a trace of mineral oil. on a D8 VENTURE Bruker AXS
diffractometer equipped with a graphite monochromatic Mo-K radiation source (λ = 0.71073
Å). The unit-cell parameters were calculated and refined from the full data and the data
collection was performed with a Bruker D8 VENTURE diffractometer at 150 K. The
reflections were scaled and corrected for absorption effects by using Multi-Scan method
[21]. The structure was solved by direct method by using SIR-2004 program [22] and
refined by full-matrix least-squares techniques on F2 by using the SHELXL-97 program

[23]. The drawings were made with Mercury [24]. Crystal data and experimental parameters
used for the intensity data collection are available free of charge from the Cambridge
Crystallographic Data Centre
(CCDC 1908921).
2.5 Hirshfeld surface analysis
Hirshfeld surfaces and their two-dimensional fingerprint [25-26] have been used to gaining
additional insight into the intermolecular interactions in the title compound, based on results
of single crystal X-ray diffraction studies. The Hirshfeld surface enveloping a molecule is
defined by points where the molecule of interest and all the other molecules that surround it
have the same contribution to the electronic density. For each point on that isosurface one
has two distances: “di” the distance to the nearest nucleus internal to the surface, and “de”
the distance from the point to the nearest nucleus external to the surface. The normalized
contact distance (dnorm) based on both di and de, and the vdW radii of the atom [27]. The
value of the dnorm is positive or negative when intermolecular contacts are longer or shorter
than vdW separations, respectively. Because of the symmetry between de and di in the
expression for dnorm, where two Hirshfeld surfaces touch, both will display a red spot
identical in color intensity as well as size and shape. The Hirshfeld surfaces are mapped with
di, and 2D fingerprint plots presented in this paper were generated using CrystalExplorer
3.1. Graphical plots of the molecular Hirshfeld surfaces mapped with dnorm (Eq. I) using a
red-white-blue color scheme, where red highlights shorter contacts, white is used for
contacts around the vdW separation, and blue is for longer contacts.
di ‒ rivdW de ‒ revdW
dnorm
=
+
Eq. (I)
rivdW
revdW
3. Results and discussion
3.1 Crystal structure description
The complex (I) crystallizes in the triclinic system, space group P-1 with a = 10.987(8) Ȧ, b
= 12.096(8) Ȧ, c = 16.586(9) Å, α = 88.24(2)°, β = 72.54(2)°, γ = 82.35(2)°, V = 2084(2) Å3
and Z=2. Crystallographic data and structure refinement are reported in Table S1. The
asymmetric unit of our cadmium(II) derivative consists of one [Cd(TClPP)(morph)]
molecule. The atom numbering and thermal ellipsoids are shown in Figure 1. Selected bond
distances and angles are given in Table 1. The Cd2+ ion is positioned above the porphyrin

core and coordinated to the four nitrogens of the porphyrin and axially by the oxygen atom
of the morpholine axial ligand leady to a pentacoordinate Cd(II) porphyrin complex with a
square pyramidal geometry.
Figure 1. ORTEP diagram of [Cd(TClPP)morph] (I) with atomic numbering. Thermal ellipsoids
shown at 50 % probability level and the hydrogen atoms are omitted for clarity.
Table 1. Selected bond lengths (A˚) and angles (deg) of [Cd(TClPP)morph] (I).
Cadmium(II) coordination polyhedron
Cd–N1
Cd–N2
Cd–N3
Cd–N4
Cd–O
2.205(5)
2.206(5)
2.215(6)
2.191(5)
2.337(7)
N1–Cd–N2
N1–Cd–N3
N1–Cd–N4
N1–Cd–O
N2–Cd–O
N3–Cd–O
148.30(17)
143.04(19)
84.77(19)
99.3(2)
104.1(3)
107.2(2)
Morpholine Ligand

O1–C62
N5–C65
1.490(13)
1.399(14)
C62–O–Cd
C66–O–Cd
115.3(7)
113.9(6)
The coordination environment around the Cd(II) center in (I) is presented in Figure 2 where
we can see that the morpholine ligand adopts the usual chair conformation. The fact that the
morpholine is coordinated to Cd(II) via the oxygen atom and not the nitrogen atom needs to
be discussed. Cadmium(II) cation is known to be a soft Lewis acid and oxygen donor
ligands are known to be generally hard Lewis bases while, nitrogen donor ligand are in the
borderline between hard and soft base. Therefore, since the morpholine ligand is O-bonded
to the Cd(II) central ion (soft base – soft acid), the crystallographic data confirms the
Pearson “HSAB” concept [28]. The Cd—O(morph) bond length [2.337(7) Å] is
considerably close to those of related non-porphyrinic cadmium–morpholine distances
which are in the range [2.323-2.371 Å] (Table 2) [29]. The Cd__O bond length is close to
those of reported Cd(II) porphyrin complexes with oxygen atom-coordinated axial ligands
(such as H2O and 2-dioxane) [30-32]. The average equatorial (Cd—Np) distance is in
normal range of pentacoordinate Cd(II) metalloporphyrins with a value of 2.204(5) Å. It is
noteworthy that the central Cd(II) ion is, as expected, very displaced from the the N4 plane
towards the axial ligand (0.60 Ȧ), leading to a domed structure of the porphyrin core of (I)
(Figures 2 and 3) . By the other hand, the distance between the cadmium atom and the mean
plane made by the 24-atom core of the porphyrin (Cd__PC) for (I) (0.741 Å) is similar to
those of the related five-coordinated cadmium metalloporphyrin (Table 2).

Figure 2. The coordination environment of Cd2+ ion.
Figure 3. Formal diagrams of the porphyrinato core of [Cd(TClPP)morph] complex.
Table 2. Selected bond lengths [Å] and angles [°] for complex (I) and several related Cd(II)
porphyrintic and non-porphyrintic complexes.
a
b
c
Complex
Cd__Np
Porphyrinic complexes
Cd__Oax
Cd__PC
Ref.
[Cd(TClPP)(morph)]
[Cd(TPP)(H2O)].(18-C-6)d,e
2.204(5)
2.230(2)
2.338(7)
2.237(2)
0.741
0.803
This work
[30]
[Cd(TClPP)(DMF)]
[Cd(TPP)(2-dioxane)]d
[Cd(TClPP)(py)]
2.197
2.140
2.280
2.650-2.80
0.824

[31]
[32]
[31]
[33]
[34]
[35]
[36]
2.203(4)
2.204
0.729
0.729
0.751
0.744
0.739
0.796
[Cd(TPP)(pip)]d,f




[Cd(TPP)(4-picoline)]d
[Cd(TPP)(2-NH2-py)]d
[Cd(TPP)(N3)]d
2.195
2.204(3)
2.215(1)
Non-porphyrinic complexes
{[Cd2Cl6(morph)2]}n
{[Me2Cd]3[NH2N(CH2)4O]}n
a: Cd__Np =average equatorial distance between the cadmium and the nitrogen atoms of the porphyrin ring,
2.323-2.371
2.655
[29]
[37]



b: Cd__Oax= cadmium- oxygen axial ligand distance, c: Cd__PC is the distance between the cadmium atom and the mean
plane made by the 24-atom core of the porphyrin (PC), d: TPP = meso-tetraphenylporphyrinato d : 18-C-6 =
1,4,7,10,13,16-hexaoxacyclooctadécane (18-crown-6), f: tetraphenylporphinato-bis(dioxane)cadmium(II), f: pip = the
piperidine.
In porphyrins, the π-conjugation favor the planar structure, however, geometrical distortion
can be imposed on the macrocycle by several factors: (1) packing constraints in the crystal,
(2) steric crowding caused by peripheral substituents of the porphyrin ligand, (3) the effects
of intramolecular interactions between atoms of the axial ligands and the porphyrinate core,
(4) intermolecular interactions, typically between two porphyrins ligands, i.e., dimeric
interactions, and (5) the coordination requirements of the central metal ion itself [38]. The
most characteristic types of distortions of the porphyrin core are the saddle, the dome, the
ruffling and the wave distortion. Thus, the doming distortion (dom) is often observed in five-
coordinate complexes when the axial ligand causes a displacement of the metal center out of
the mean plane, and the nitrogen atoms are also displaced toward the axial ligand, the
ruffling distortion (ruff) is indicated by the values of the meso-carbon atoms above and
below the porphyrin mean plane, the saddle distortion (sad) involves the displacement of the
pyrrole rings alternately above and below the mean porphyrin macrocycle so that the pyrrole
nitrogen atoms are out of the mean plane and in the waving distortions (wav), the four
fragments “(β-carbon)-(α-carbon)(meso-carbon)-(α-carbon)-(β-carbon)” are alternatively
above and below the 24-atoms of the C20N4 least squares plane (PC plane). For the
[Cd(TClPP)(morph)] complex, the formal diagrams of the porphyrinato cores showing the
displacements of each atom from the mean plane of the 24-atom porphyrin macrocycle in
units of 0.01 Å is illustrated in Figure 3 where we can see that the porphyrinic core exhibits
an important doming distortion and moderate ruffling and saddle deformations.
The supramolecular assemblies for the [Cd(TClPP)morph] complex is depicted in Figure 4.
The molecules of this complex are connected by several weak non-conventional hydrogen
bonds, such as N−H···Cl involving the NH group of the coordinated morpholine and the Cl2
atom of the meso-phenylporphyrin with N5−H5A···Cl2 distance of 2.905(5) Ȧ. The crystal
packing is also stabilized by weak C−H···Cl interactions between a pyrrolic proton of one
porphyrin and a chlorine atom of an adjacent porphyrin such as the C65-H65···Cl3
interaction with a distance of 2.953 (7) Å (Table 3 and Figure 4). Additionally, we notice the
presence of several C−H···π contacts, for example, the C43-H43···Cg3 interaction
involving the carbon C43 of a phenyl group and the centroid Cg3 of a pyrrole ring of an
adjacent [Cd(TClPP)morph] complex with a distance of 3,761(10) Å (Figure S1).The

C−H···π interaction is observed also between the carbon C65 of the morpholine ring and the
centroid Cg3 with C65-H65···Cg3 distance of 3.935(14) Å.
Figure 4. Schematic representation of the N−H···Cl and the C−H···Cl hydrogen bonds between the
morpholine axial ligand and the chlorine atom of the adjacent meso-phenylporphyrin complex.
Table 3. Inter-and intramolecular interactions in (I).
Da__H …Ab
Symmetry of A
-1+x, 1+y, z
1-x, -y, 2-z
1+x,-1+y, z
x, y,-1+z
D-H…A [Å]
147
D…A [°]
2.905 (5)
2.953 (7)
3.676(8)
3.526(9)
3.761(10)
3.935(14)
N5-H5A…Cl2
C65-H65…Cl3
C14-H14…Cl2
C20-H20…Cl3
C43-H43…Cg3
C63-H63A…Cg3
152
155
145
151
174
1-x, 1-y, 2-z
x, y, z
a : D is the donor atom, b : A is the acceptor atom, Cg3 is the centroid of the N3/C8–C9–C10–C11
five membered ring.
3.2 Hirshfeld Surface
For a given crystal structure, the Hirshfeld surface is unique and it suggests the possibility of
obtaining additional insight into the crystal [39]. Figure 5 illustrates the Hirshfeld surfaces
of the title complex, showing surfaces that have been mapped over dnorm. The surfaces are
shown transparent for the purpose of visualizing the molecular fragment. The fingerprint
plot is illustrated is given in the Figure 6 and the Hirshfeld surface, which have been mapped
over a dnorm range of -0.6 to 2.8 Å, are shown in Figure 5. The red spots on the Hirshfeld
surface indicate the presence of close contacts, whereas areas without close contacts are
shown as blue spots. The crystal packing in porphyrin is mainly controlled by the close

contacts involving chlorine; Cl···H__C, which are observed as intense red spots on the
Hirshfeld surface. In the crystal, 42 % of the intermolecular contacts are associated with
H···H contacts, 27% for the contacts between chlorine and hydrogen Cl···H and for the
C···H contacts appear by the percentage contributions are 17.9%. Further, the Hirshfeld
surface, shows intense red spot on thes (de) surface near the pyrrole ring which is due to
close (Porph/pyr) C-H...Cl and (ph) Cl....H-C (Porph/pyr) contacts. In addition to this,
(morph) H-H(ph) contacts are also seen as intense red spots.
Figure 5. (a): Hirschfeld surfaces mapped over dnorm for the title compound and (b) : Tow-
dimensional fingerprint plot with a dnorm of the title compound.

Figure 6. Two-dimensional fingerprint plots with a dnorm view of the H…H (42%), H…Cl/Cl…H (27%)
and C…H/H…C (17.9%) contacts in the title compound.
3.3. 1H NMR spectroscopy
1
The H NMR spectrum of the free-base H2TClPP presents the expected profile for meso-
tetra-substituted porphyrins molecules. For instance, the signals at δ = 8.86 ppm correspond
to the resonances of the β-pyrrolic protons. The phenyl protons (Ho, Ho'/Hm, Hm') present
chemical shift values at 8.15/7.77 ppm and the NH pyrrole protons are very shielded and
appears at -2.84 ppm in the form of a low-intensity singlet. The disappearance of the
1
resonance of the peak corresponding to the pyrrole N-H protons was observed in the H
NMR spectrum of the metallated porphyrin [Cd(TClPP)] starting material. This spectrum of
the later species is very similar to that of the free-base meso-porphyrin due to the
diamagnetic nature of cadmium ion which is at the oxidation state (+II). For (I), the NMR
spectrum (Figure S2) reveals also the characteristic signals of the axial morpholine ligand,
where the Ha and Hb protons of the morpholine resonate at 3.47 and 2.64 ppm respectively
in the form of triplet and the NH proton of the same ligand resonates as a broad singlet
around 5 ppm. These values are slightly different from those of the free morpholine
molecule.

3.4 IR spectroscopy
-1
The [Cd(TClPP)(morph)] IR spectrum has been recorded in the 4000-400 cm domain
(Figure S3) and is characteristic of a meso-porphyrin complex with the morpholine as axial
ligand. Thus, the C-H stretching frequency of TClPP moiety is located in the 2850 cm-1
spectral region. The metalled meso-porphyrin exhibits also absorption bands attributed to the
δ(CCH) vibration mode at 1089 cm -1. The (C-Cl) vibration of the meso-substituted
porphyrin is identified as a strong absorption band at 719 cm-1 which is in the [800–600]
cm−1 domain [40-41].
The IR spectrum of the title compound exhebits also a very weak absorption band at 3293
cm-1 corresponding to (NH) vibration of the morpholine ligand and a band at 1387 cm-1
attributed to the carbonyl stretching ν(CO) of the axial ligand.
3.5 Photophysical properties
The photophysical properties such as the optical absorption, the steady state emission, the
fluorescence quantum yield, the fluorescence decay and the singlet oxygen profile were
studied for the porphyrin free-base H2TClPP, and the [Cd(TClPP)] and [Cd(TClPP)(morph)]
complexes in dichloromethane solvent.
3.5.1 UV–vis spectroscopy
Metalloporphyrins display usually two types of absorption bands, i.e., intensive B band
(known as the Soret band) locating at about 400 nm corresponds to S0 → S2 transition with
the value of ε (namely, molar absorption coefficient) being about 105.M−1.cm−1 and four
weak Q bands residing at about 500− 650 corresponds to S0 → S1 transition with the ε
values being about 103−104 M−1.cm−1. The normalized absorption spectra of the free base
porphyrin H2TClPP, [Cd(TClPP)] and [Cd(TClPP)(morph)] complexes are presented in
Figure 7. The value of the max of the Soret absorption band of the free base H2TClPP
appears at 420 nm while, the four Q bands are found at 517, 553,589, and 645 nm. The λmax
value of the Soret band is 433 nm for [Cd(TClPP)] which is red-shifted by 13 nm while the
number of Q-band is reduced to two which are located at 568 and 609 nm (Table S2). The
difference of the Q-band number between [Cd(TClPP)] and the free base H2TClPP is
attributed to the increase of the molecular symmetry originated from the metalation of the
porphyrinic macrocycle center of the free base H2TClPP. Whereas for (I) the λmax values of

the Soret and Q bands are 436 nm for the first band and 575, and 620 nm for the latter band,
which are slightly red-shifted compared with those of [Cd(TClPP)] indicating the
complexation of the morpholine axial ligand. This is also the case for others related five-
coordinated metalloporphyrins [MII(TPP)(Morph)] (M = Co, Cu, Ni and Zn) (Table S2). It is
noteworthy that the higher redshift of the absorption bands is related mainly to the important
distortion of the porphyrin core [10-11]. The higher atomic radius of Cd(II) metal ion
compared to the other metals (M = Zn, Cu, Ni, Co) (Table S2) implies that Cd(II) is too
large to fit into the central hole of the TClPP which generates significant the deformations of
the TClPP core and the complexation of the morpholine O-donor axial ligand tends to
increase the doming distortion by pulling out the Cd(II) metal ion from of the porphyrinato
plane. The optical band gap energy (Eg) refers to the energy difference between the HOMO
and the LUMO orbitales of the porphyrin species can be calculated from the UV-visible
spectrum using the Tauc plot method [42]. The Eg values in CH2Cl2 solution are 1.960 and
1.903 eV for [Cd(TClPP)] and [Cd(TClPP)(morph)] respectively, indicating that the gap
energy of the metallized species are higher than that obtained for H2TClPP free base (1.820
eV) (Table S2) suggesting that the Cd-meso-porphyrin display interesting organic
semiconducting properties [43].
Figure 7. UV-visible absorption spectra in CH2Cl2 (c = 10-5 M) of H2TClPP, [CdII(TClPP)], and
[CdII(TClPP)(morph)] (I).
3.5.2 Steady-State fluorescence and Singlet oxygen
The steady-state fluorescence of porphyrins was performed in order to study their electronic
properties in excited state. The fluorescence emission spectra of the free base porphyrin

(H2TClPP), [Cd(TClPP)] and [Cd(TClPP)(morph)] coordination compounds at room
temperature were recorded in CH2Cl2 (c = 10-6 M) under the excitation wavelength of 433
nm (Figure-8a). Table 5 summarizes the maxima of the fluorescence of the Q(0,0) and
Q(0,1) bands, the fluorescence quantum yields (ɸf) and the fluorescence lifetimes (τf) of our
derivatives (I) as well as a selected species. The emission spectrum of the free base
porphyrin H2TClPP in CH2Cl2 exhibits two well-defined emission bands near 605 nm
(Q(0,0)) and 657 nm (Q(0,1)) displays two emission Q bands at 650 and 717 nm (Q(0,0) and
Q(0,1), respectively), the emission spectrum of [Cd(TClPP)] shows a 31 nm (from 650 to
619 nm) and a 67 nm (from 717 to 650 nm) blue shifts of the Q(0,0) and Q(0,1) bands,
respectively, accompanied by a decline of fluorescence intensity, ɸf and τf (Fig. 8a). Thus,
after the insertion of cadmium ions into the porphyrin cavity, the emission band became
blue-shifted and less intense compared to those of free-base porphyrin (Table 6), indicating
that the structure of the originally flat porphyrin (free base porphyrin H2TClPP) is distorted
in out-of-plane [Cd(TClPP)] causing a dome distortion in the structure, consequently the ɸf
decrease. The decrease of the fluorescence quantum yield can be also explained by the high
molar mass of Cd(II) which leads to a quenching effect, resulting in the very low ɸf values.
Which may be due to other non–radiative energy dissipation processes such as enhanced
internal conversion, intersystem crossing [44-45]. The emission spectrum of complex (I) is
quite similar to that of [Cd(TClPP)] and shows that the coordination of the morpholine O-
donor axial ligand to Cd(II) metal ion have a minor effect. This result suggests that the out-
of-plane distortion of porphyrin rings in [Cd(TClPP)] and [Cd(TClPP)(morph)] complex are
relatively similar.
The Fluorescence lifetimes (f) were measured by time-correlated single photon counting
technique. The representative fluorescence decays for the free base H2TClPP, [Cd(TClPP)]
and [Cd(TClPP)(morph)] are shown in Figure. S4. The f values of the free base H2TClPP (~
8.9 ns) is as expected much higher than those of [Cd(TClPP)] and [Cd(TClPP)(morph)]
which are 1.6 and 1.5 ns respectively (Table 6). We notice that the τf of the cadmium
porphyrins is not influenced by the axial ligand. Whereas the lifetimes of the fluorescences
decrease consequence of the macrocycle distortion [46] and mainly to the large Cd atom.

Figure 8. (a) : Fluorescence emission spectra and (b) : Singlet oxygen production spectra performed
at λex = 433 nm of H2TClPP, [CdII(TClPP)] and [CdII(TClPP)(morph)], in CH2Cl2 (c 10-6 M) at
room temperature.
Table 5. Photophysical data of our synthetic species and a selection of cadmium porphyrins
complexes recorded in CH2Cl2.
Fluorescence a max (nm)
τf (ns) c
Ref.
b
d
Compound
f

Q(0,1)
652.9
Q(0,0)
678.8
H2TClPP e
0.063
0.075
0.065
0.018
0.06
8.2
8.9
-
0.69
0.49
0.69
0.73
0.41
0.53
[47]
H2TClPP
650
620
624
619
715
655
668
650
652
This work
[48]
[Cd(TPP)] f
[Cd(TMPP)] g
[Cd(TClPP)]
-
[49]
1.6
This work
This work
[Cd(TClPP)(morph)] 619
0.046
1.5
a: Fluorescence spectra of porphyrins were obtained as a function of λex = 433 nm.
b: Fluorescence quantum yield, c: Fluorescence lifetime (ns), d: Singlet oxygen production quantum yield. e: in toluene
solvent, f: in ethanol solvent, g: in THF solvent.
Singlet oxygen production was detected in the infrared region, following excitation of the
porphyrin at 433 nm. Figure 8b illustrates the singlet oxygen production spectra of the our
synthetic compounds with the maximum emission at 1270 nm. As seen in Table 5, the
[CdII(TClPP)(morph)] presents the highest singlet oxygen quantum yield ( = 0.53 )
compared to [CdII(TClPP)] ( = 0.41) and H2TClPP ( = 0.49). The singlet oxygen
quantum yield depends generally on the intersystem crossing rate. Thus, the increase of Φ∆
for the [CdII(TClPP)(morph)] can be attributed to the structure distortion caused by the
insertion of the cadmium heavy metal as well as the coordination of morpholine axial ligand.
These factors are thought to promote the intersystem crossing rate through the enhanced
spin-orbit coupling, consequently, increase the triplet quantum yield [50-51].

3.6 Cyclic Voltammetry
The electrochemical behavior of the free base H2TClPP, the staring material [Cd(TClPP)]
and the [Cd(TClPP)(morph)] complex (I) were studied by cyclic voltammetry (CV) with the
tetra-n-butylammonium hexafluorophosphate (TBAPF6) as the supporting electrolyte (0.2
M) in the non-coordinating solvent CH2Cl2 under an argon atmosphere. In Figure 9 is
illustrated the voltamogramm of (I) while in Table 6 is summarized the CV data our the free
base, the starting material, complex (I) and a selection of some meso-porphyrins and zinc(II)
metalloporphyrins. cadmium(II) as well as zinc(II) cations for which the correspondent
metal belong to the same 12 group exhibit the 4d10 and 3d10 ground state electronic
configurations respectively. Therefore, these cations are diamagnetic and only the oxidation
and reduction waves of the porphyrin ring are observed in the voltammograms. Indeed, the
CV of the H2TClPP, the [Cd(TClPP)] and the [Cd(TClPP)(morph)] present each one a two
one-electron reduction waves and three one-electron oxidation waves (Table 6). We notice
that the values of the half potentials (E1/2) for the metallated porphyrin are shifted toward
more negative values compared to the H2TCLPP species. This is also the case of zinc(II)
metalloporphyrins. Unfortunately, up to date, there are no reported CV data of Cd(II)
metalloporphyrins,nevertheless, the E1/2 values of complex (I) are quite smaller than those of
the related zinc(II) pent-coordinated [Zn(TPP)(Him)] [52] and [Zn(TPBP)(4,4′-mda)] [53]
complexes.
The cadmium-porphyrin HOMO-LUMO gap can be expressed as the potential difference of
the first oxidation and the first reduction. is given by the empirical rule of Fuhrhop et al.,
[54]. This energy gap is known as the electrochemical gap (Eg-el). The electrochemical Gap
values are 2.20, 2.00 and 1.94 eV pour our three species H2TClPP, [Cd(TClPP)] and
[Cd(TClPP)(morph)] respectively are as expected higher than those of the optical gap (see
UV-visible section). We notice that the tetra-coordinated and the penta-coordinated zinc(II)
complexes reported in Table 6 present Eg-el values close to those of our [Cd(TClPP)] and
[Cd(TClPP)(morph)].

Table 6. Electrochemical data a for H2TClPP, [Cd(TClPP)], complex (I) and a selection of metalloporphyrins.
_______________________________________________________________________________________________________________________________________
Oxidations
Reductions
Eg-el (eV)
Ref..
1st oxidation (O1,R1) 2nd oxidation (O2,R2) 3rd oxidation (O3,R3) 1st reduction (R4,O4) 2nd reduction (R5,O5)
-------------------------- ------------------------- ------------------------- ------------------------- ---------------------------
b
E1/2
E1/2
E1/2
E1/2
E1/2
_________________________________________________________________________________________________________________________________________
H2TPP
H2TPBP
H2TClPP
[Zn(TPP]
1.02
0.95
1.00
0.89*
0.81
0.87
0.65*
1.26
1.36
1.23
1.18*
1.11
1.09
1.35*
1.28*
1.06
-
-1.20
-1.12
-1.09
-1.26*
-1.48
-1.19
-1.35*
-1.38
-1.17
-1.55
-1.53
-1.41
-1.70*
-1.67
-1.47
-1.70*
-1.69
-1.41
-
[55]
1.48
1.53
-
1.40
1.39
-
2.26 [53]
2.20 this work
-
2.28 [53]
2.00 this work
-
[52]
[Zn(TPBP)]c
[Cd(TClPP)]
[Zn(TPP)(Him)]d
[52]
[Zn(TPBP)(4,4′-mda)]e 0.81
-
2.31 [53]
1.94 this work
[Cd(TClPP)(morph)] 0.77
1.35
____________________________________________________________________________________________________________________________________
*: irreversible wave, a : The potentials are reported versus SCE, b : E1/2 = half wave potential, c: TPBP = meso-{tetrakis-4-(benzoyloxy)phenyl]porphyrinato,
d: Him = imidazole, e: 4,4’-mda = 4,4′-diaminodiphenylmethane.

Figure 9. Cyclic voltammogram of [Cd(TClPP)(morph)] (I). The solvent is CH2Cl2, and the
concentration is ca. 10-3 M in 0.2 M (TBAP), 100 mVs-1, vitreous carbon working electrode (Ø = 3
mm).
4. Conclusion
In summary, we have synthesized and characterized the five-coordinate cadmium(II) meso-
tetrachlorophenylporphyrin complex with the oxygen coordinated morpholine to the central
metal. The structure of [Cd(TClPP)morph] (I) complex was determined by single-crystal X-
ray crystallographic analysis. The molecules of this complex are connected by hydrogen
bonds type N−H···Cl, C−H···Cl, and C−H···π. By the other hand, based on Hirshfeld
topology analyses all possible intermolecular interactions occurring in the crystal structure
have been quantified. The displacement of the Cd(II) metal atom out of the porphyrinato
mean plane is 0.74 Å. This high value induces a significant porphyrinato core doming,
moderate ruffling and saddle distortion. Absorption spectra reveal that the insertion of Cd(II)
metal ion into TClPP and the addition of the morpholine axial ligand are accompanied by a
redshift of the Soret and Q bands of the [Cd(TClPP)] starting material and the
[Cd(TClPP)(morph)] complex. While the Q bands of fluorescence emission spectra are blue-
shifted with a decrease of the fluorescence intensity, quantum yield (φf) and lifetime (τf). The
important singlet oxygen quantum yield () makes this complex a good candidate to develop
antibacterial and antiviral treatments. The cyclic voltammetry investigation on the H2TClPP, the

starting material [Cd(TClPP)] and complex (I) are also reported and the electrochemical gap values of
these porphyrinic species were determined from the CV voltammogram which are slightly higher than
those of the optical gap.
.

Supporting information
CCDC 1908921 contain the supplementary crystallographic data of complex (I). These data can be
obtained
free
of
charge
from
the
Cambridge
Crystallographic
Data
Centre
viawww.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements
The authors gratefully acknowledge financial support from the Ministry of Higher Education and
Scientific Research of Tunisia.
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The five-coordinate cadmium(II) meso-tetrachlorophenylporphyrin complex, containing
morpholine O-donor as axial ligand was prepared. Their Structural and Photophysical
properties have been studied.