Unusual formation of a stable 2D copper porphyrin network

Article abstract of DOI:10.1021/ic302257g

Copper(II) 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin was obtained and characterized by means of cyclic voltammetry, electron paramagnetic resonance, Fourier transform infrared, and UV-visible spectroscopy. Three crystalline forms were grown and studied by means of X-ray diffraction methods (single crystal and powder). The highly electron-withdrawing effect of phosphoryl groups attached directly to the porphyrin macrocycle results in a self-assembling process, with formation of a stable 2D coordination network, which is unusual for copper(II) porphyrins. The resulting 2D structure is a rare example of an assembly based on copper(II) porphyrins where the copper(II) central metal ion is six-coordinated because of a weak interaction with two phosphoryl groups of adjacent porphyrins. The other polymorph of copper(II) 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin contains individual (isolated) porphyrin molecules with four-coordinated copper(II) in a distorted porphyrin core. This polymorph can be obtained only by slow diffusion of a copper acetate/methanol solution into solutions of free base 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin in chloroform. It converts to the 2D structure after dissolution in chloroform followed by consecutive crystallizations, using slow diffusion of hexane. A six-coordinated copper(II) porphyrin containing two axially coordinated dioxane molecules was also obtained and characterized by X-ray diffraction crystallography. The association of copper(II) 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin in solution was also studied.

Full text of DOI:10.1021/ic302257g

Article
pubs.acs.org/IC
Unusual Formation of a Stable 2D Copper Porphyrin Network
Anna A. Sinelshchikova,† Sergey E. Nefedov,‡ Yulia Yu. Enakieva,† Yulia G. Gorbunova,*,†,‡
Aslan Yu. Tsivadze,†,‡ Karl M. Kadish,§ Ping Chen,§ Alla Bessmertnykh-Lemeune,⊥ Christine Stern,⊥
and Roger Guilard*,⊥
†Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Pr. 31, Moscow 119071,
Russia
‡Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninsky Pr. 31, Moscow 119991, Russia
§Department of Chemistry, University of Houston, Houston, Texas 77204-5003, United States
⊥Universite
́
de Bourgogne, ICMUB (UMR CNRS 6302), 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex, France
S
* Supporting Information
ABSTRACT: Copper(II) 5,15-bis(diethoxyphosphoryl)-
10,20-diphenylporphyrin was obtained and characterized by
means of cyclic voltammetry, electron paramagnetic resonance,
Fourier transform infrared, and UV−visible spectroscopy.
Three crystalline forms were grown and studied by means of
X-ray diffraction methods (single crystal and powder). The
highly electron-withdrawing effect of phosphoryl groups
attached directly to the porphyrin macrocycle results in a
self-assembling process, with formation of a stable 2D
coordination network, which is unusual for copper(II)
porphyrins. The resulting 2D structure is a rare example of an assembly based on copper(II) porphyrins where the copper(II)
central metal ion is six-coordinated because of a weak interaction with two phosphoryl groups of adjacent porphyrins. The other
polymorph of copper(II) 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin contains individual (isolated) porphyrin
molecules with four-coordinated copper(II) in a distorted porphyrin core. This polymorph can be obtained only by slow
diffusion of a copper acetate/methanol solution into solutions of free base 5,15-bis(diethoxyphosphoryl)-10,20-
diphenylporphyrin in chloroform. It converts to the 2D structure after dissolution in chloroform followed by consecutive
crystallizations, using slow diffusion of hexane. A six-coordinated copper(II) porphyrin containing two axially coordinated
dioxane molecules was also obtained and characterized by X-ray diffraction crystallography. The association of copper(II) 5,15-
bis(diethoxyphosphoryl)-10,20-diphenylporphyrin in solution was also studied.
to coordinate one or two additional axial ligands, generating
networks of different topologies.16−24
INTRODUCTION
■
Mimicking biological processes, which occur in living systems, is
of great current interest. In this regard, synthetic metal-
loporphyrin assemblies have been widely studied because they
are key functional systems for many biochemical processes.1−9
Porphyrins and their metal complexes are important building
blocks for self-organization of highly ordered assemblies that
have different dimensionality and topology (1D, 2D, and 3D
structures) because of their unique structural and coordination
properties, thermal and chemical robustness, and rich
physicochemical properties.10−15 It is not easy to predict how
exactly molecular building blocks will assemble in the solid state,
but some tuning can be made by changing the peripheral
functional groups, the ligand topology, and the nature of the
metal center. The majority of known porphyrin self-assemblies
have been formed from zinc porphyrins possessing nitrogen/
oxygen-donor functional groups at the meso- or β-pyrrole
positions of the macrocycle. The exceptional role of zinc ions
in porphyrin assemblies relies on the simple metalation of
functionalized porphyrins by zinc salts and the ability of zinc ions
Copper porphyrins are easy to prepare under mild conditions.
However, there are only a few examples of coordination
polymers formed by copper(II) porphyrins. Indeed, copper(II)
porphyrins are almost always composed of individual molecules
in the solid state because of the preferred four-coordinated
environment of copper(II) ions in these receptors.25−31 External
metal cations are often needed for assembling functionalized
copper(II) porphyrins using coordinating groups at the
porphyrin core. Thus, coordination polymers have been
obtained by the reaction of copper(II) porphyrins with different
metal salts, for example, Cd(NO3)2, CuBr2, or Cu(BF4)2.32−38
The self-assembly of copper(II) porphyrins via internal metal
centers is even more rare. To our knowledge, there is only one
example in the literature for a 1D coordination polymer formed
by the self-assembly of a copper porphyrin in which the
Received: October 15, 2012
© XXXX American Chemical Society
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copper(II) center adopts a distorted octahedral coordination
environment.39 Axial coordination of adjacent porphyrin
molecules via the formation of Cu···N bonds for copper(II)
meso-tetrakis(o-isonicotinoylamidophenyl)porphyrin in the solid
state results in formation of the coordination polymer. Moreover,
studies of copper porphyrin assemblies are of key importance for
the modeling of biochemical processes because copper(II) is an
essential metal cation found in enzymes, structural proteins,
assimilation pigments, and different biological processes.40−42 It
was shown, for example, that the formation of a complex
containing three metal copper(II) centers bound to a central
phosphate unit bridging oxygen atoms and to a tripodal N(CH2-
o-C6H4CH2N(CH2py)2)3 ligand structurally mimics trimetallic
active sites of proteins involved in phosphate metabolism.43
Our recent synthetic efforts have led to the development of
porphyrins bearing diethoxyphosphoryl groups at two meso
positions of the macrocycle (see, for example, compound 1 in
Chart 1).44,45
Table 1. Crystal Growth Conditions for Polymorphs 3a and
3b and Solvate 3c
a
solvent
XRD structure of
the porphyrin
precursor
single-
crystal
structure
entry
A
B
additive
b
1
2
3
4
1
CHCl3
CHCl3
CHCl3
3a
3b
3b
3b
3b
3b
3b
hexane
MeOH
hexane
CHCl3/
MeOH
5
6
7
8
3b
3b
3a
3b
CHCl3
CHCl3
CHCl3
dioxane
MeOH
MeOH
hexane
AcOH
3b
3b
3b
3c
Cu(OAc)2
a
The porphyrin precursor was dissolved in solvent A, and solvent B
b
was used as a second phase in slow diffusion experiments. A solution
of Cu(OAc)2 in MeOH was used as a second phase.
Chart 1
The electron-withdrawing nature of the diethoxyphosphoryl
groups favors the self-assembly of a related zinc porphyrinate, 2,
both in the solid state and in solution.
In a continuation of our earlier studies of porphyrin 1 as a new
building block,44,45 we report here on the peculiarities of the
coordination chemistry of copper(II) 5,15-bis-
(diethoxyphosphoryl)-10,20-diphenylporphyrin (3) and provide
the first example of a 2D coordination polymer formed by the
self-assembly of copper porphyrin molecules (Chart 1).
Figure 1. Molecular structure of complex 3a. Displacement ellipsoids
are drawn at the 50% probability level. Hydrogen atoms are omitted for
clarity.
RESULTS AND DISCUSSION
within 0.100 Å. The porphyrin macrocycle is significantly
saddled, and the four pyrrole rings are considerably distorted in
an alternant fashion, either upward or downward with respect to
the mean N4 plane. The displacement of carbon atoms from the
macrocycle varies from −0.742 to +0.575 Å [maximum for
C(17/17A)], values that are significantly larger than those in
several structurally characterized meso-tetraaryl-substituted
copper porphyrins.25,30,31,47−51
Copper atoms of the two closest molecules of 3a in the crystal
cell are located at a distance of 5.490 Å from each other (Figure
S1 in the Supporting Information) and have relatively short
atomic interactions with carbon atoms of the pyrrole fragment in
the adjacent porphyrin molecule [Cu(1A/1B)−C(16B/16A) =
3.351 Å; Cu(1A/1B)−C(17B/17A) = 3.131 Å]. The atom
C(16A/16B) is located 3.393 Å from the atom N(2D/2C),
which probably influences distortion of the molecule. All other
intermolecular contacts between the two closest molecules are
much longer than 3.5 Å [the shortest ones are N(2A/2B)−
C(18B)/(18A) = 3.562 Å, N(2A)−N(2B) = 3.611 Å, and
CporphA−CporphB = 3.886−3.911 Å].
■
Synthesis and X-ray Study. Paddle-wheel dinuclear
carboxylates of transition metals are well-known deprotonating
agents,46 and copper(II) carboxylate could be used as a metal
source to obtain the copper(II) porphyrin 3 under mild
conditions in the absence of additional base. Thus, slow diffusion
of a Cu(OAc)2·H2O/methanol solution (c = 5.08 × 10−3 M) into
a stoichiometric amount, or a 4-fold excess, of the free base 5,15-
bis(diethoxyphosphoryl)-10,20-diphenylporphyrin (1; 1.27 ×
10−3 M) in CHCl3 at room temperature over 2 days resulted in
deprotonation of 1 and the formation of violet single crystals of 3
(Table 1, entry 1).
According to the X-ray data (Figure 1 and Tables S1 and S2 in
the Supporting Information), the copper(II) ion in the crystals
(3a) is located in the center of symmetry and adopts a distorted
square-planar environment formed by four nitrogen atoms of the
porphyrin macrocycle [Cu(1)−N(1/1A) = 2.005(3) Å; Cu(1)−
N(2/2A) = 1.993(3) Å]. The angle between the Cu−N(1)−
N(2) and Cu−N(1A)−N(2A) planes is 8.2°, and a displacement
of the four pyrrole N4 atoms from the mean porphyrin plane is
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The phenyl substituents at the meso positions of the
macrocycle [C(2A)−C(3A) = 1.502(3) Å; C(19A)−C(20A) =
1.499(3) Å] have different twist angles toward the porphyrin
plane [C(1A)−C(2A)−C(1C)/C(3A)−C(4A)−C(4C) =
88.1°; C(18A)−C(19A)−C(18C)/C(20A)−C(21A)−C(22C)
= 54.9°]. This fact can be explained by steric contacts in the
crystal packing between one of the phenyl rings and a pyrrole
fragment of the adjacent porphyrin. The shortest distances are
3.440 and 3.520 Å from C(21A) or C(21B) to C(8B) or C(8A)
and C(9B) or C(9A), respectively (Figure S1 in the Supporting
Information).
plane is 0.286 Å, and the P(1)−C(10) distance is 1.806(3) Å.
The P(1)−O(1) distance is 1.470(2) Å, P(1)−O(2) is 1.568(3)
Å, and P(1)−O(3) is 1.585(3) Å. The dihedral angle between the
C(9)−C(10)−C(15) and C(10)−P(1)−O(1) planes is 14.6°.
In contrast to the distorted porphyrin macrocycle in 3a, the
molecule of porphyrin 1 is almost planar, with displacement of
the nitrogen atoms from the N4 plane being 0.012 Å (Figure 3).
The dihedral angles of the phosphoryl substituents are 5.4° and
7.9° between the CCC−CPO planes [the P−C distances are
1.808(2) and 1.813(2) Å, and the displacement values of the
phosphorus atoms from the N4 plane are −0.1496 and +0.5582
Å). With respect to the N4 plane, which represents the mean
plane of the porphyrin core, the twist angles of the aryl rings are
77.7° and 74.4°. The displacement of the meso-carbon and
phenyl carbon atoms from the N4 plane ranges from −0.108 to
+0.089 Å, and the meso-C−CPh distance is 1.501 Å. In the crystal
packing of the free base porphyrin 1, there are no remarkable
intermolecular contacts; this is because of the presence of two
chloroform solvate molecules, which form hydrogen bonds with
oxygen atoms of the phosphoryl substituents (PO distance
The oxygen atoms of the two diethoxyphosphoryl substituents
have no major interactions with other atoms of the molecule
(Figure 2). Displacement of the phosphorus atom from the N4
=1.467 Å; P−O distance = 1.565−1.584 Å; PO···HCHCl
3
contacts are 2.143−2.150 Å).45
The preparative synthesis of 3 was monitored by UV−visible
absorption spectroscopy and showed complete consumption of
free base 1 after 30 min in a reaction with copper acetate
monohydrate (ratio 1:3.5) in a CHCl3/methanol solution (10:1,
v/v) at room temperature. This led to the formation of a violet
complex, which was isolated after purification by column
chromatography (SiO2 and eluent CHCl3) in 91% yield. This
complex was characterized by means of matrix-assisted laser
Figure 2. Crystal packing of 3a. The hydrogen atoms and meso-aryl
group are omitted for clarity except for the ipso-carbon atoms.
Figure 3. Crystal packing of porphyrin 1. The hydrogen atoms and solvate molecules of chloroform are omitted for clarity.
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desorption ionization time-of-flight mass spectrometry
(MALDI-TOF MS) and high-resolution electrospray ionization
mass spectroscopy (ESI-MS) as well as Fourier transform
infrared (FT-IR) spectroscopy (see the Supporting Informa-
tion).
Surprisingly, the powder X-ray diffraction (XRD) pattern of
this polycrystalline sample 3 did not correspond to a simulated
pattern for the single-crystal data of 3a. Dissolving the
polycrystalline solid 3 in CHCl3, followed by the addition of
hexane and slow evaporation of the solvents, led to the formation
of crystals suitable for single-crystal XRD.
O(1) = 22.0°].44 The dihedral angles between the planes of the
phosphoryl substituents (CPO) and the porphyrin anion
(CCC) change little upon formation of the polymer [C(4)−
C(5)−C(10)/C(5)−P(1)−O(1) angle = 4.6° in 3b and 4.0° in
2]. The twist angles of the meso-phenyl substituents toward the
porphyrin plane decrease to 64.3° in 3b (63.0° in 2) compared to
the free-base porphyrin 1 and the distorted complex 3a (Figure
4).
The observed interactions between the oxygen atoms of the
phosphoryl groups and the metal centers in 3b and 2 allow us to
conclude that, in these structures, the metals have a distorted
tetragonal-bipyramidal environment and the porphyrin building
blocks form a 2D coordination polymer. Apart from the 1D
According to XRD, the obtained crystals are another
polymorphic modification of complex 3 (3b; Figure 4 and
coordination polymer mentioned in the Introduction,39
a
tetrahydrofuran (THF) solvate of copper(II) tetra(4-pyridyl)-
porphyrinate was reported, where the copper ions are formally
six-coordinated and ligated by four nitrogen atoms of the
porphyrin core and two oxygen atoms of axially coordinated
THF molecules [Cu−OTHF = 2.81(3) Å].52
Thus, copper(II) porphyrin 3 exists in two polymorphic forms,
labeled as a and b. In order to control the formation of a desirable
polymorph, the experimental conditions for crystallization of
each polymorph were studied (Table 1).
The polycrystalline sample 3b was dissolved in chloroform,
and single crystals suitable for X-ray analysis were grown by the
slow diffusion of hexane or methanol, which have opposite
polarity and different coordinating properties (Table 1, entries 2
and 3). In both cases, the same single crystals of 3b were
obtained. Slow diffusion of hexane into a chloroform/methanol
(1:1) solution of polycrystalline 3b also led to single crystals of
3b (Table 1, entry 4).
In an attempt to find the best experimental conditions for
obtaining single crystals of 3a from the polycrystalline sample 3b,
we checked the influence of different parameters on the crystal
growth process. In the experiments where polymorph 3a was
obtained, copper(II) acetate was used in excess and acetic acid
was formed as a byproduct of the metalation reaction. We tried to
simulate these conditions by adding trace amounts of acetic acid
or a copper(II) acetate/methanol solution during crystallization.
The single crystals were grown by slow diffusion of these
solutions into a chloroform solution of copper complex 3 (Table
1, entries 5 and 6). However, the 2D network 3b was obtained in
both cases.
Single crystals of polymorph 3a could be easily transformed
into single crystals of the coordination polymer 3b by dissolving
3a in chloroform, followed by consecutive crystallizations, using,
for example, slow diffusion of hexane (Table 1, entry 7).
Thus, polymorph 3a was formed only during slow diffusion of
a methanol solution containing copper acetate into a porphyrin 1
solution in chloroform, followed by a simultaneous evaporation
of the solvents. It is possible to assume that the growth of crystals
3a under these conditions is favored because of the low solubility
of porphyrin 1 in methanol. The metalation reaction could
proceed simultaneously with nucleation and crystal growth
under these conditions. These processes lead to formation of the
crystals of polymorph 3a, where the porphyrin backbones are not
assembled in the framework similar to the crystals of the free base
porphyrin 1.
Figure 4. Molecular structure of complex 3b. Displacement ellipsoids
are drawn at the 50% probability level. The hydrogen atoms are omitted
for clarity.
Tables S1 and S3 in the Supporting Information). In this case, the
simulated pattern from the single-crystal data was found to be in
good agreement with the powder XRD patterns of polycrystal-
line sample 3 (Figure S2 in the Supporting Information).
According to the single-crystal X-ray data of 3b, the copper
atom has a square-planar environment with the four nitrogen
atoms of the porphyrin macrocycle; the dihedral angle between
the Cu−N(1)−N(2) and Cu−N(1A)−N(2A) planes is equal to
0°; the metal−nitrogen distances Cu(1)−N(1/1A) and Cu(1)−
N(2/2A) are 2.0146(16) and 2.0220(15) Å, respectively. These
bonds are longer than those of 3a. The phosphorus atoms of the
phosphoryl substituents are almost in the same plane (the
displacement of the phosphorus atoms from the CuN4 plane is
0.0681 Å). Such a geometry of the copper porphyrin 3b is
probably due to the presence of weak atomic interactions
between the oxygen atoms of the phosphoryl group and the
copper atom of adjacent porphyrinate [Cu(1/1A)−O(1/1A) =
2.649(3) Å; angle Cu(1A)−P(1)−O(1) = 24.6°]. These
interactions lead to the formation of a 2D coordination polymer
that is unexpected for copper porphyrins (Figure 5). Similar
interactions have been observed in the isostructural zinc
porphyrin 2, but these contacts are much shorter in the zinc
complex [Zn(1)−O(1/1A) = 2.487(4) Å; angle Zn(1A)−P(1)−
The unusual ease of formation of the 2D copper porphyrin
network can originate from two factors. One involves the known
high affinity of the phosphoryl groups to a metal atom, which
could be the driving force of self-assembly. In this case, polymer
formation should only be the feature of phosphoryl-substituted
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Figure 5. Fragment of crystal packing 3b. The hydrogen atoms and meso-aryl group are omitted for clarity except for the ipso-carbon atoms.
Figure 6. Molecular structure of the dioxane solvate of copper porphyrin complex 3c. Displacement ellipsoids are drawn at the 50% probability level.
The hydrogen atoms are omitted for clarity.
porphyrins. On the other hand, the axial coordination of different
coordinating groups could arise from the substantially reduced
metal-centered electron density, which is affected by the
macrocycle’s non-π-conjugating, σ-electron-withdrawing meso-
phosphoryl substituents. In this case, the self-assembly could be
the feature of all electron-deficient porphyrins bearing
appropriate coordinating groups. In order to further investigate
the influence of these two factors, the interaction of 3 with small
coordinating (donor) molecules was studied. Indeed, recrystal-
lization of compound 3 in the presence of dioxane leads to the
formation of single crystals of dioxane solvate 3c (Figure 6, Table
1, entry 8, and Tables S1 and S4 in the Supporting Information).
According to XRD, the copper atom in adduct 3c has a square-
planar environment of four nitrogen atoms [Cu(1)−N(1/1A) =
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Figure 7. Fragment of the crystal packing of 3c. The hydrogen atoms are omitted for clarity.
2.017(4) Å; Cu(1)−N(2/2A) = 2.010(3) Å], like in 3b. Copper
has relatively long contacts with the oxygen atoms of the two
solvate molecules of dioxane [Cu−O = 2.731(4) Å]. Each of the
dioxane molecules is located at an angle of 133.4° [the line
O(4)−O(5) with respect to the CuN4 porphyrin plane].
The porphyrin core is flat [angle Cu−N(1)−N(2)/Cu−
N(1A)−N(2A) = 0°], with the phosphorus atoms located above
and below the CuN4 plane and displaced from the plane by
0.0623 Å. The dihedral angles between the planes of the phenyl
substituents and the porphyrin anion are 83.6°. The C(8)−
C(11) distance is 1.504(6) Å; the displacements of atoms C(8)
and C(11) from the N4 plane are 0.057 and 0.052 Å,
respectively. The phosphoryl fragments CPO are almost in the
plane of the porphyrin macrocycle [angle CCC−CPO = 2.5°,
P(1)−C(3) = 1.818(5) Å, P−O(1) = 1.461(4) Å, P−O(2) =
1.564(4) Å, and P−O(3) = 1.593(4) Å]. This strong tendency of
the PO group to be almost in the plane of the porphyrin
macrocycle may result from the steric interactions of the ethyl
groups as well as the formation of hydrogen bonds between the
oxygen atom and the nearest β-hydrogen atom. It should be
noted that, in the studied structures (3a−3c), the distance
between the oxygen atom in the PO group and the nearest β-
carbon atom is 2.842−2.863 Å away.
Self-Assembly of 3 in Solution. The association of
porphyrins in a solution can be studied by different spectral
techniques, such as, for example, NMR, luminescent, and
absorption spectroscopy. The association can also be studied
by electrochemical methods. The best choice of spectral
instrumentations is dependent on the aggregate nature and
stability of the aggregates. Unfortunately, NMR and luminescent
spectroscopy are not informative in the case of copper(II)
complexes; thus, electron spin resonance (ESR), UV−visible
spectroscopy, and cyclic voltammetry were used for this
investigation.
The ESR spectrum of 3 in toluene (c = 6 × 10−3 M) at 107.2 K
shows a well-defined signal with both copper hyperfine and
nitrogen superhyperfine structures (Figure S3 in the Supporting
Information). These parameters are typical for copper(II)
complexes coordinated by four nitrogen atoms:53 gII = 2.203,
g⊥ N= 2.060, AIICu = 220 × 10−4 cm−1, A⊥N = 17 × 10−4 cm−1, and
AII = 16 × 10−4cm−1. Unfortunately, the sensitivity of ESR
spectroscopy to axial aggregate formation in copper(II)
complexes is low.54
The UV−visible absorption spectra of 1 and 3 in chloroform
were also investigated. An intense Soret band is located at 415
nm (S0 → S2 transition) in both compounds. Four less intense Q
bands (519, 558, 596, and 650 nm; S0 → S1 transitions) are
observed in the spectrum of 1 in chloroform, and these are
transformed into two Q bands (553 and 595 nm) after
metalation by copper (Figure 8). The shapes and positions of
the bands are in good correspondence with previously obtained
data for other tetraphenylporphyrins.55,56 It was earlier shown
that UV−visible absorption spectroscopy could be used to
estimate the ability of polyphosphorylporphyrin toward self-
In crystal 3c, the molecules are bound only by van der Waals
interactions (Figure 7) and the donor atoms O(5) in the dioxane
solvate molecules do not have any major interactions.
Thus, the presence of strong electron-withdrawing groups
directly attached to the porphyrin backbone seems to be the key
factor for self-assembly of the investigated copper porphyrin into
coordination polymer 3b.
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Figure 8. UV−visible absorption spectra of 1 and 3 in chloroform.
assembly in solution.44,45,57,58 We have investigated the
concentration-dependent behavior of copper(II) 5,15-bis-
(diethoxyphosphoryl)-10,20-diphenylporphyrinate in toluene
and chloroform. Unfortunately, we were unable to see any
association of the copper complex in these solvents by means of
UV−visible spectroscopy. No evolution of the UV−visible
spectrum was observed in toluene over a compound
concentration range of 10−6−10−3 M or in chloroform over a
concentration range of 10−5−10−3 M. There is no deviation from
Lambert-Beer’s law (concentration) in this concentration range
in these solvents (Figures S4−S6 in the Supporting Informa-
tion).
The self-association of 3 was also investigated in solution by
means of cyclic voltammetry. The electrochemical properties of
complex 3 (c = 10−3 M) in PhCN, CDCl3, and CH2Cl2 was
studied and compared with the properties of complexes 1 and 2
(Table 2 and Figures 9 and 10).
Figure 9. Cyclic voltammograms of porphyrins 1−3 and the related
tetraphenylporphyrins TPPH2, (TPP)Zn, and (TPP)Cu in PhCN
containing 0.1 M TBAP.
As shown in Table 2 and Figure 9, neutral phosphorylpor-
phyrins 1−3 are easier to reduce and harder to oxidize than the
corresponding tetraphenylporphyrins with the same central
metal ions.59 These values differ from what has been reported for
copper octaethylpophyrins or copper porphyrins substituted
with other electron-donating groups.30,60−62 This is consistent
with the effect of the highly electron-withdrawing P(O)(OEt)2
groups on the π-ring systems of 1−3. However, this magnitude of
the substituent effect on redox potentials differs as a function of
the reaction. For example, when two meso-phenyl groups of the
tetraphenylporphyrin macrocycles are replaced by two P(O)-
(OEt)2 groups to form compounds 1−3, the potentials for the
first oxidation are positively shifted by 230 mV for all three
compounds, while the first reduction potentials are shifted by
larger amounts of 360−420 mV (Figure 9). Because a smaller
potential shift is seen for the first oxidation, the electrochemical
highest occupied molecular orbital (HOMO)−lowest unoccu-
pied molecular orbital (LUMO) gap of the phosphorylporphyr-
ins 1−3 in PhCN is less than that of the tetraphenylporphyrin
compounds, i.e., 2.03−2.08 V for 1−3 compared to 2.16−2.27 V
for the related derivatives.
Table 2. Half-Wave Potentials (V vs SCE) of the Investigated Phosphorylporphyrins and Related Tetraphenylporphyrins
oxidation
2nd ox
1.28
reduction
2nd red
−1.28
compd
M
solvent
Δox 2-1
1st ox
1st red
3rd red
HOMO−LUMO gap
a
1
2H
Zn
Cu
2H
Zn
PhCN
0
1.28
1.06
1.22
1.05
0.83
0.99
1.25
1.00
1.26
−0.77
−0.97
−0.86
−1.15
−1.33
−1.28
−0.81
−0.99
−0.90
−1.70
c
2.05
2.03
2.08
2.20
2.16
2.27
2.06
1.99
2.16
b
b
2
0.26
0.14
0.28
0.35
0.34
0
1.32
−1.42
−1.43
b
3
1.36
1.33
1.18
1.33
1.25
1.18
1.36
−1.73
TPP
−1.54
−1.72
−1.74
−1.40
d
Cu
2H
e
1
2
3
CDCl3
f
Zn
Cu
0.18
0.10
a
b
c
d
Containing 0.1 M TBAP. Peak potential at a scan rate of 0.1 V/s. Not observed due to the poor solubility in PhCN. Data taken from ref 59.
e
f
Containing 0.2 M TBAP. Data taken from ref 45.
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Figure 11. Cyclic voltammograms of copper complex 3 (c = 10−3 M) in
CH2Cl2 containing 0.1 M TBAP with/without PPh3O.
Figure 10. Cyclic voltammograms of 3 (c = 10−3 M) in PhCN, CH2Cl2,
and CDCl3 containing 0.1/0.2 M TBAP.
The Δ|ox2 − ox1| value of 3 is also a function of the solvent
binding ability. As shown in Figure 10, the first two reversible
oxidations of 3 (at E1/2 = 1.26 and 1.36 V) are closely spaced in
the nonbinding solvent CDCl3 but are further apart in the
bonding solvent PhCN. The value of Δ|ox2 − ox1| for 3 ranges
from 140 mV in PhCN to 100 mV in CDCl3, suggesting that the
first two oxidations of 3 are affected by the solvent binding, axial
coordination in the case of PPh3O, and aggregation in the
nonpolar solvents CH2Cl2 and CDCl3. The Δ|ox2 − ox1| value of
3 is also a function of the temperature (Figure S7 in the
Supporting Information).
The introduction of the P(O)(OEt)2 groups onto the
porphyrins also leads to a large substituent effect on the second
reduction potentials of 1−3 (260−310 mV positive shift), while a
small effect is seen for the second oxidation (only a 30 mV
positive shift occurs in the case of 3). As a result, the potential
difference between the first and second oxidations (Δ|ox2 − ox1|)
of 1−3 is substantially smaller than the corresponding separation
for the tetraphenylporphyrins.
CONCLUSION
■
The introduction of the P(O)(OEt)2 groups onto porphyrin 1
leads to overlapping of the first and second oxidations (Table 2
and Figure 9). There are many documented examples where the
two one-electron oxidations of a porphyrin to give a porphyrin π-
cation radical and a dication become overlapped into a single
two-electron transfer.59 This is best known for nickel(II)
porphyrins, but it also occurs for some free-base porphyrins. In
the current study, the first oxidation is shifted positively by 230
mV from E1/2 for oxidation of H2TPP and the second oxidation is
shifted negatively by about 50 mV from the same process of
H2TPP so that both processes overlap, as shown in Figure 9. The
fact that the oxidation peak current of 1 at 1.28 V is double that of
the reduction at −0.77 V implies an EE mechanism (two one-
electron transfers occurring at the same potential) rather than a
single two-electron transfer, where the current would increase by
In summary, we have described the first example of copper(II)
meso-phosphorylated porphyrins that exists in the solid state in
two polymorphic states: one consists of isolated molecules, and
another is the 2D coordination polymer. The unexpected
formation of the 2D coordination polymer can be understood if
one takes into account the electronic effect of the diethox-
yphosphoryl substituents directly attached to the porphyrin core,
which modify its coordination properties. Thus, for example, the
interaction of copper(II) 5,15-bis(diethoxyphosphoryl)-10,20-
diphenylporphyrinate with dioxane molecules also leads to a
formally six-coordinated copper(II) ligated by four nitrogen
atoms from the porphyrin core and two oxygen atoms of weakly
coordinated dioxane molecules. The self-assembly of complex 3
in solution is weak but could be observed by cyclic voltammetry.
This process could be prevented or minimized by the use of
coordinating solvents, by the addition of coordinating molecules
to solution, or by an increase of the temperature of the solution.
Taking into account these results, it is possible to assume that
copper−organic frameworks based on porphyrin derivatives
should be readily obtained if electron-deficient porphyrins are
used as molecular building blocks. The electron-withdrawing
nature of the macrocycle peripheral substituents is the key factor
of this process, whereas the nature of the axial ligand seems to be
less important. Work is now in progress to obtain new examples
of copper porphyrin frameworks to prove our conclusion.
n3/2
.
The separation between the two ring oxidations of 3 is closely
related to the self-assembly, as shown previously for related
zinc(II) derivatives.45 In the nonbinding CHCl3 solvent,
compound 3 is able to aggregate by the binding of a P(O)(OEt)2
group from one porphyrin molecule to the copper(II) center of
another molecule (see Figure 5), while in coordinating solvents,
the self-assembly of 3 would be weakened (or blocked) upon
axial coordination of the solvent molecules (see Figure 7). Our
previous studies of similar zinc porphyrins45 indicated that the
two one-electron oxidations of the self-assembled zinc
compounds are always partially overlapped, but these processes
were well-separated upon binding with a strong coordinated axial
ligand like PPh3O. This also seems to be the case for compound 3
in CH2Cl2 containing added PPh3O, where the first oxidation
shifts negatively by 90 mV from the E1/2 value in CH2Cl2
containing 0.1 M tetra-n-butylammonium perchlorate (TBAP)
and the ΔE1/2 between the two oxidation peaks increases from
130 to 190 mV. This is illustrated by the cyclic voltammograms in
Figure 11.
EXPERIMENTAL SECTION
■
Measurements. UV−visible absorption spectra were recorded with
a Cary-100 spectrophotometer in quartz cells (1−10 mm). MALDI-
TOF MS spectra were recorded on an Ultraflex mass spectrometer
(Bruker Daltonics) without a matrix. Accurate mass measurements
(high-resolution mass spectrometry) were obtained by ESI on an
Orbitrap spectrometer. The measurements were made at the Po
̂
le
Chimie Moleculaire, the technological platform for chemical analysis
́
and molecular synthesis (http://www.wpcm.fr), which relies on the
H
dx.doi.org/10.1021/ic302257g | Inorg. Chem. XXXX, XXX, XXX−XXX

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Article
Institute of the Molecular Chemistry of University of Burgundy and
Welience, a Burgundy University private subsidiary.
IR spectra were registered on a FT-IR Nexus (Nicolet) spectrometer
The tube with the lid was left in the refrigerator (T = 4 °C) for 5 days,
and then the tube was left at room temperature without the lid for 9 days.
Single crystals of 3b suitable for X-ray analysis were obtained by the slow
evaporation of solvents.
with a micro-ATR accessory (Pike).
(c) A solution of 3b in a mixture of chloroform and methanol (2 mL,
3 × 10−3 M, solvent ratio 1:1) was put in the glass tube, and the same
volume of hexane was added to the tube as an upper layer. The tube with
the lid was left in the refrigerator (T = 4 °C) for 9 days, after which single
crystals of 3b suitable for X-ray analysis were obtained by slow diffusion.
(d) A solution of 3b in chloroform (1 mL, 3 × 10−3 M) was put in a
glass tube, and methanol with a trace of CH3COOH (1 drop of
CH3COOH in 500 μL of methanol) was added to the tube as an upper
layer. The tube with the lid was left in the refrigerator (T = 4 °C) for 5
days, after which the lid was removed and the tube was left at room
temperature for 9 days. Single crystals of 3b suitable for X-ray analysis
were obtained by the slow evaporation of solvents.
ESR spectra were recorded with an ELEXSYS E-680X microwave
spectrometer (Bruker). The powder XRD patterns were measured in
Bragg−Brentano mode using an EMPYREAN (PANalytical) diffrac-
tometer (Cu Kα1 radiation; λ = 1.54059 Å; tube voltage/current 45 kV/
40 mA) with a linear X’celerator detector at ambient conditions [T =
295(2) K]. The data collection region was 2θ = 3−30° with a step of
0.008° and 50 s/step in continuous mode. Samples suspended in hexane
were dropped onto a zero-background-oriented plate (silicon, single
crystal), and after evaporation of the solvent, the powder XRD pattern
was measured.
XRD data collection was carried out on a Bruker SMART APEX II
́
CCD detector with λ(Mo Kα) = 0.71073 Å, a graphite monochromator,
(e) A solution of 3b in chloroform (1 mL, 3 × 10−3 M) was put in the
glass tube, and the copper(II) acetate hydrate solution in MeOH (1 mL,
c = 5.08 × 10−3 M) was added to the tube as an upper layer. The tube was
left at room temperature without a lid for 2 weeks. Single crystals of 3b
suitable for X-ray analysis were obtained by the slow evaporation of
solvents.
ω scanning, and 2θmax = 56°. Diffraction data sets were corrected for
absorption using SADABS.63 Structures were solved by direct methods
and refined by a full-matrix least-squares method for F2 with anisotropic
parameters for all non-hydrogen atoms. All calculations were performed
by means of the SAINT64 and SHELXTL-9765 program packages.
CCDC reference numbers are 902785−902787. The data can be
obtained free of charge from the Cambridge Crystallographic Data
Centre at www.ccdc.cam.ac.uk/data_request/cif.
Synthesis. All chemicals used were of analytical grade and were
purchased from Acros and Sigma-Aldrich Co. Chloroform was dried
over anhydrous CaCl2, followed by distillation over CaH2. Methanol was
dried over 4 Å molecular sieves. Silica gel (0.04−0.063 mm; 230−400
mesh; ASTM, Merck) was used for column chromatography. The free
base 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin was syn-
thesized according to previously published methods.44,45
(f) Single crystals of 3a were dissolved in chloroform (1 mL). Hexane
(1 mL) was added to the tube as an upper layer, and the tube then was
left at room temperature without a lid for 3 days. Single crystals of 3b
suitable for X-ray analysis were obtained by the slow evaporation of
solvents.
Electrochemical Measurements. Cyclic voltammetry was carried
out with an EG&G model 173 potentiostat/galvanostat. A homemade
three-electrode cell was used and consisted of a platinum button or
glassy carbon working electrode, a platinum wire counter electrode, and
a saturated calomel reference electrode (SCE). The SCE was separated
from the bulk of the solution by a fritted-glass bridge of low porosity,
which contained the solvent/supporting electrolyte mixture. All
potentials are referenced to the SCE (+0.2444 V vs NHE at 25 °C).
TBAP (≥99%) was purchased from Fluka Chemical Co., recrystal-
lized from ethyl alcohol, and dried under vacuum at 40 °C for at least 1
week prior to use. Absolute dichloromethane (CH2Cl2; 99.8%, EMD
Chemical Inc.) and chloroform-d (CDCl3; 99.8+% isotopic, Alfa. Aesar
Co.) were used as received. Benzonitrile (PhCN; 99%, Aldrich Co.) was
distilled over phosphorus pentoxide (P2O5) under vacuum prior to use.
Synthesis of Copper(II) 5,15-Bis(diethoxyphosphoryl)-10,20-
diphenylporphyrinate (3). Copper(II) acetate hydrate (14.6 mg,
0.07 mmol) in 0.25 mL of CH3OH was added to a solution of 5,15-
bis(diethoxyphosphoryl)-10,20-diphenylporphyrin (15.2 mg, 0.02
mmol) in a 3 mL mixture of CHCl3 and CH3OH (10:1). The mixture
was stirred at room temperature for 30 min and the solvent removed
under reduced pressure. The violet precipitate was dissolved in CHCl3
and chromatographed on silica gel. The compound was eluted with
CHCl3. Slow evaporation of this solution in air yielded crystalline
compound 3 (15 mg, 91%). UV−visible [toluene; λmax, nm (ε, dm3
mol−1 cm−1)]: 413 (3.75 × 105), 543 (1.44 × 104), 585 (3.14 × 104).
UV−visible [chloroform; λmax, nm (ε, dm3 mol−1 cm−1)]: 415 (2.59 ×
105), 553 (1.05 × 104), 595 (2.61 × 104). MALDI-TOF MS: m/z 796.9
(exptl); m/z 796.3 (theor). HRMS: m/z 818.14383 (exptl, [M + Na]+);
m/z 818.14548 (theor, [M + Na]+). EPR spectrum (toluene, c = 6 ×
10−3 mol/L, 107.2 K): gII = 2.203, g⊥ = 2.060, AIICu = 220 × 10−4 cm−1,
AN = 17 × 10−4 cm−1, and AIIN = 16 × 10−4 cm−1.
ASSOCIATED CONTENT
■
S
* Supporting Information
X-ray crystallographic files in CIF format for 3a, 3b, and 3c,
powder XRD experiment, spectral and electrochemical data. This
material is available free of charge via the Internet at http://pubs.
acs.org.
́
Powder XRD analysis of the solid: monoclinic, a = 12.314(2) Å, b =
11.808(1) Å, c = 12.449(1) Å, and β = 91.814 (9)°.
́
́
Crystal Growth. Single crystals of 3a suitable for X-ray analysis were
obtained by slow diffusion of a 1 mL of copper(II) acetate hydrate
solution in MeOH (c = 5.08 × 10−3 M) into a solution (1 mL) of the
free-base porphyrin 1 in CHCl3 (c = 1.27 × 10−3 M) in reagent ratio 1:1
or 4:1. The experiment was performed at room temperature in tubes
without lids. Violet single crystals of 3a suitable for X-ray analysis were
obtained in both cases.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: yulia@igic.ras.ru (Y.G.G.), Roger.Guilard@u-
bourgogne.fr (R.G.).
Notes
Single crystals of 3b suitable for X-ray analysis were obtained at room
temperature by the slow diffusion of hexane (1 mL) to a chloroform
solution of polycrystalline compound 3 (1 mL, 3 × 10−3 M).
Single crystals of 3c suitable for X-ray analysis were obtained by slow
evaporation of a solution of 3b in dioxane (2 mL, 3 × 10−3 M).
Crystallization of 3b in Different Conditions. (a) A solution of
3b in chloroform (1 mL, 3 × 10−3 M) was placed in a glass tube. Hexane
(1 mL) was added to the tube as an upper layer, and the tube was left at
room temperature without the lid for 3 days. Single crystals of 3b
suitable for X-ray analysis were obtained by the slow evaporation of
solvents.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was performed in the frame of the French−Russian
Associated Laboratory “LAMREM” supported by the CNRS and
Russian Academy of Sciences, Russian Foundation for Basic
Research (Grant 12-03-93110). The authors thank Prof. V. V.
Minin and Dr. N. N. Efimov for EPR experiments and Dr. A. A.
Shiryaev with Prof. V. V. Chernyshov for help with powder XRD
experiments. Support from the Robert A. Welch Foundation (to
K.M.K.; Grant E-680) is also gratefully acknowledged.
(b) A solution of 3b in chloroform (1 mL, 3 × 10−3 M) was put in the
glass tube, and methanol (1 mL) was added to the tube as an upper layer.
I
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Article
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