Complex formation of β-brominated tetraphenylporphyrins and metal exchange of their cadmium complexes with d-metal salts in dimethylformamide

Article abstract of DOI:10.1134/S1070363216010187

Complex formation of zinc and copper(II) acetates with tetraphenylporphyrin, 2-bromo-5,10,15,20-tetraphenylporphyrin, 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin, and 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrin in N,N-dimethylformamide has been studied. The rate constants determined in the study of the complex formation and the metal exchange reactions have been compared.

Full text of DOI:10.1134/S1070363216010187

ISSN 1070-3632, Russian Journal of General Chemistry, 2016, Vol. 86, No. 1, pp. 102–109. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © O.V. Maltseva, S.V. Zvezdina, N.V. Chizhova, N.Zh. Mamardashvili, 2016, published in Zhurnal Obshchei Khimii, 2016, Vol. 86,
No. 1, pp. 110–117.
Complex Formation of β-Brominated Tetraphenylporphyrins
and Metal Exchange of Their Cadmium Complexes
with d-Metal Salts in Dimethylformamide
O. V. Maltseva, S. V. Zvezdina, N. V. Chizhova, and N. Zh. Mamardashvili
Krestov Institute of Solutions Chemistry, Russian Academy of Sciences, ul. Akademicheskaya 1, Ivanovo, 153045 Russia
e-mail: ovt@isc-ras.ru
Received April 2, 2015
Abstract—Complex formation of zinc and copper(II) acetates with tetraphenylporphyrin, 2-bromo-5,10,15,20-
tetraphenylporphyrin, 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin, and 2,3,7,8,12,13,17,18-octa-
bromo-5,10,15,20-tetraphenylporphyrin in N,N-dimethylformamide has been studied. The rate constants
determined in the study of the complex formation and the metal exchange reactions have been compared.
Keywords: brominated derivative, porphyrin, complex formation, metal exchange
DOI: 10.1134/S1070363216010187
R1
NH
R2
R2
Processes of formation and decomposition of metal
porphyrinates have been studied over the recent
decades [1–3] in view of the importance of the
porphyrinates existence in the biological systems and
application as technical catalysts, dyes, and stabilizers.
The doubly charged cations with the size cor-
responding to that of the macrocycle cavity readily
interact with porphyrins; however, even in these cases
the interaction may be slow or incomplete without
heating. This is primarily due to the metal ion
desolvation in the course of the porphyrinates forma-
tion, increasing the process activation energy. On top
of that, the process is hindered by the extraordinal
rigidity of the aromatic macrocyclic porphyrin
molecule.
Ph
Ph
N
N
R3
R3
R3
R3
HN
Ph
Ph
R2
R1 = R2 = R3 = H (Н2TPP); R1 = Br, R2 = R3 = H
(Н2TPPBr); R1 = R2 = Br, R3 = H (Н2TPPBr4); R1 = R2 =
R3 = Br (Н2TPPBr8).
The reactivity of the substituted porphyrins is
mainly determined by the effect of the substituent on
the state of the conjugated π-electronic system as well
as the spatial distortion of the macrocycle and steric
hindrance of the reactive site with the substituents.
According to the earlier reported data [1–3], π-
electronic system of the macrocycle is more sensitive
to the β-substitution that to the meso-substitution.
The structure of H2TPPBr4 has been studied in
comparison with that of H2TPP in [4]. It has been
found that the β-bromination practically does not
distort the macrocycle planarity (the deviation of the
brominated pyrrole rings from the macrocycle plane
N4H2 is 4.8°). In the both cases, the phenyl rings are
perpendicular to the N4H2 plane. The bromination has
resulted in certain shortening of the Cβ–Cβ bonds and
shrinkage of the coordination cavity.
This work was aimed to elucidate the effect of
bromination of tetraphenylporphyrin at the β-pyrrole
positions on the spectral properties and complex
formation of the macrocycle.
102

COMPLEX FORMATION OF β-BROMINATED TETRAPHENYLPORPHYRINS
Table 1. Electron absorption spectra [λmax, nm (log ε)] of the studied tetraphenylporphyrinsa
103
Compound
H2TPP
Solvent
Band I
Band II
Band III
Band IV
Soret band
References
Toluene
DMF
652(3.81)
645(3.86)
592(3.79)
591(3.83)
591(3.96)
596(3.70)
597(3.74)
595(3.75)
–
549(3.95)
548(3.97)
549(4.08)
552(3.64)
553(3.67)
552(3.68)
–
515(4.28)
415(5.35)
416(5.31)
417(5.61)
424(5.41)
424(5.40)
420(5.31)
452(3.75)
421(5.58)
439(5.36)
442(5.34)
432(5.26)
432(5.10)
436(5.52)
470(5.25)
367(4.41)
477(5.10)
371(4.38)
469(5.31)
[7]
This work
This work
[7]
513(4.28)
Dichloromethane 647(3.89)
514(4.40)
H2TPPBr Toluene
Pyridine
653(3.71)
653(3.75)
651(3.76)
678(4.06)
519(4.23)
519(4.23)
[7]
DMF
519(4.10)
This work
This work
[8]
CH3COOH
–
Dichloromethane 649(3.79)
594(3.81)
614(3.79)
613(3.79)
612(3.63)
–
551(3.78)
568(3.97)
568(3.97)
536(3.90)
–
518(4.33)
H2TPPBr4 Toluene
680(3.86)
680(3.85)
696(3.53)
711(4.31)
–
–
–
–
–
–
–
–
–
–
[7]
Pyridine
DMF
[7]
This work
[7]
CH3COOH
Dichloromethane 685(4.02)
612(3.58)
622(4.10)
646(4.08)
627(3.44)
–
533(4.30)
568(3.95)
–
[9]
H2TPPBr8 Toluene
738(3.85)
760(3.89)
783(3.63)
745(4.17)
[7]
Pyridine
DMF
[7]
–
This work
[7]
CH3COOH
–
Dichloromethane 743(3.87)
626(4.12)
569(3.96)
[10]
a (–) the band is absent.
Crystal structure of the octabroninated derivative
[Н4TPPBr8](CF3COO)2·0.5CHCl3 has been studied in
[5]. It has been demonstrated that all the phenyl
fragments are practically coplanar, and the signi-
ficantly distorted macrocycle is saddle-shaped. The
bromine atoms in the two adjacent pyrrole rings are
located above the corresponding ring planes, and these
in the other two pyrrole rings are found below the ring
planes. Noteworthily, all the four bromine atoms of the
Н2TPPBr4 molecule are located in the same plane [4].
dently, these two factors lead to the red shift of the
bands in the electron absorption spectrum.
Table 1 lists parameters of electron absorption
spectra of solutions of the studied tetraphenylpor-
phyrins in various organic solvents. Noteworthily, the
successive β-bromination resulted in the regular shift
of band I and Soret band towards longer wavelength.
The long-wave absorption bands simultaneously
became weaker, especially in the electron-donor sol-
vents. The described spectral changes were mainly
caused by the intramolecular polarization of the
chromophore because of the non-equivalence of the β-
and meso-substituents as well as by the molecule
distortion due to the steric interaction of the peripheral
substituents [8, 10]. The non-planar structure of the
studied molecules was confirmed by quantum-
chemical simulation with full optimization of geometry
parameters in a vacuum applying the DFT/B3LYP
The position and the intensity of the bands in
electron absorption spectra of porphyrins are signif-
icantly affected by the spatial structure of the mole-
cule. For example, dodeca-substitution of porphin
molecule distorts its planar structure, simultaneously
giving rise to the push-pull effect resulting in the
synchronous intramolecular polarization of the
chromophore with β- and meso-substituents [6]. Evi-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 1 2016

104
MALTSEVA et al.
H2TPP
H2TPPBr
H2TPPBr4
H2TPPBr8
Fig. 1. Structure of the studied porphyrins in a vacuum simulated using the DFT/B3LYP method (6-31G** basis).
method (the 6-31G** basis) implemented in GAUSSIAN
98 software package [11] (Fig. 1). The simulation
showed that successive β-bromination led to the
distortion of the H2TPP planar structure. Full β- and
meso-substitution in the Н2TPPBr8 molecule can be
regarded as a special case of the H2P molecule dodeca-
substitutiin, when all β- and meso-atoms of hydrogen
are substituted. The dodeca-substitution has been
recognized among the most efficient ways to distort
the planar structure of H2P molecule [3].
Substitution of hydrogen atoms with bromine
resulted in positive conjugation (+С) and negative
inductive (–I) effects. The highest occupied molecular
orbital of porphyrin is localized at the pyrrole (а2u) and
meso (а1u) carbon atoms. A strong absorption band
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 1 2016

COMPLEX FORMATION OF β-BROMINATED TETRAPHENYLPORPHYRINS
105
Table 2. Electron absorption spectra (λmax, nm) of the
appearing in the spectrum of H2TPPBr8 solution in
dichloromethane (λmax = 626 nm, log ε = 4.12) origin-
nated likely from overlapping of the Qy and Qx
transition bands; a similar behavior has been earlier
marked in the case of H2TPPBr8 solution in toluene
[12].
studied Cd(II), Zn(II), and Cu(II) porphyrinates in DMFa
Complex
CdTPP
Band I
621
Band II
577
Soret band
437
ZnTPP
CuTPP
598
539
627
601
544
646
613
598
731
680
642
558
–
420
412
441
427
419
448
435
430
490
472
472
The formation of complexes of β-brominated tetra-
phenylporphyrins with 3d-metal salts was accom-
panied by the changes of the electron absorption
spectra; the complexes spectra contained the Soret
band and two bands in the visible spectral range (Table 2
and Fig. 2) assigned to purely electronic transitions.
The decrease in the number of the bands upon the
complexes formation was due to the increased
symmetry of the molecule and suppression of the
vibrational transitions.
CdTPPBr
582
562
–
ZnTPPBr
CuTPPBr
CdTPPBr4
ZnTPPBr4
CuTPPBr4
CdTPPBr8
ZnTPPBr8
CuTPPBr8
a (–) the band is absent.
589
569
557
661
624
592
The position of the bands in the electron absorption
spectra of the porphyrinates is determined by the
character and the strength of the M–N bonds. It has
been noticed that the higher thermodynamic stability
of the metal complexes in a series of similar metal
porphyrinates corresponds to the more prominent blue
shift of the absorption band I of the complex (МP) as
compared to that of the free ligand (Н2P) [13].
the polarity of the N–H bond, thus affecting the kinetic
features of the complex formation [7]. For instance,
reaction (1) with the weak NH-acids (like H2TPP) was
the fastest in anhydrous acetic acid medium and the
slowest in pyridine medium. In the cases of strong NH-
acids as ligand (like Н2TPPBr8), the situation was the
opposite: Reaction (1) occurred instantly in pyridine,
being much slower in anhydrous acetic acid medium.
The comparative analysis of the spectral and kinetic
data obtained in this work confirmed that the
mentioned spectral criterion of the complex stability
was applicable to all the studied tetraphenylporphyrins.
For instance, the shift of band I upon formation of
complexes with Cu(II) (these complexes were relati-
vely stable and contained covalent Cu–N bonds) was
more prominent than in the cases of the less stable cor-
responding complexes with Cd(II) and Zn(II) (where
the M–N bonds were noticeably ionic) (Tables 1 and 2).
A
The effects of β-bromination of H2TPP on its coor-
dination properties in the complex formation reac-
tion (1) with Zn(OAc)2 in toluene, pyridine, and acetic
acid has been studied in [7, 12] (below a simplified
scheme is given neglecting the possible coordination
of the free porphyrin H2TPP and the evolving acid
AcOH with the solvent; М standing for the metal ion,
MTPP being the corresponding porphyrinate, and Solv
designating the solvent).
H2TPP + М(OAc)2(Solv)n–2
→ MTPP + 2AcOH + (n – 2)Solv.
λ, nm
(1)
Fig. 2. Evolution of electron absorption spectrum in the
course of the complex formation reaction between
Н2TPPBr and Zn(ОAc)2 in DMF. csalt = 2.5 × 10–3 mol/L,
It has been demonstrated that β-bromination of
tetraphenylporphyrin leads to the redistribution of π-
electron density on nitrogen atoms and to increasing
c
ligand = 2.5 × 10–5 mol/L, Т = 328 K.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 1 2016

106
MALTSEVA et al.
Table 3. Kinetic parameters of the complex formation reactions of the studied tetraphenylporphyrins with Cu(II) and Zn(II)
acetates in DMF (csalt = 2.5 × 10–3 mol/L, cligand = 2.5 × 10–5 mol/L)
298
Porphyrin
H2TPPBr
Salt
k
× 103, s–1
kv298, L mol–1 s–1
Еа, kJ/mol
ΔS≠, J mol–1 K–1
eff
Zn(OAc)2
Cu(OAc)2
Zn(OAc)2
Cu(OAc)2
Zn(OAc)2
Cu(OAc)2
0.265а
0.106
0.495
0.892
3.9
75±5
70±1
69±4
67±4
–20±19
–24±3
1.24±0.06
2.23±0.09
9.8±0.5
H2TPPBr4
H2TPPBr8
–22±15
–20±12
b
b
a Calculated according to the Arrhenius equation. b Not be determined because the reaction rate is too high.
In the case of H2TPPBr4 the rate constants in pyridine
and acetic acid were of the same order of magnitude,
evidencing the partial polarization of the N–H bonds
by the introduced bromine atoms.
ing salts (however, in certain cases, the metal exchange
can be slower than the complex formation) [15–17].
We investigated the metal exchange reaction (2)
between the cadmium porphyrinates (CdTPP,
CdTPPBr, CdTPPBr4, and CdTPPBr8) and copper(II)
or zinc acetates in DMF.
The kinetics of the Н2TPPBr8 complex formation
with cobalt, copper, and zinc salts in the 1 : 1 chloro-
form–methanol mixture has been studied in [14] by the
stop-flow spectrophotometric method. The reaction
rate constants have been 2–3 orders of magnitude
higher than these in the case of Н2TPP. The effect has
been attributed to the distortion of the macrocycle
planarity due to bromination rather than by the in-
creased basicity of tertiary nitrogen atoms (bromine-
tion of tetraphenylporphyrin reduces the protonation
constants [7]).
CdTPP + М(OAc)2(DMF)n
→ MTPP + Cd(OAc)2(DMF)n.
(2)
Figure 3 shows the spectral changes in the course of
the metal exchange reaction of CdTPPBr with
Zn(OAc)2. Quantitative kinetic parameters of the metal
exchange for all studied systems are summarized in
Table 4.
Comparison of the data in Tables 3 and 4 revealed
that the complex formation of Н2TPPBr with cop-
per(II) acetate was 66 times slower (in the case of zinc
acetate, 11 times slower) than the metal exchange
between СdTPPBr and the same salts. That was
evidently caused by the absence of the stage of N–H
bonds cleavage in the metal exchange mechanism;
combined with the lability of the cadmium complex
that facilitated formation of the copper(II) and zinc
porphyrinates. Hence, the preparative synthesis of
copper and zinc tetraphenylporphyrinates should be
carried out via the metal exchange rather than the
direct complex formation.
In this work we investigated the kinetics of
complexes formation of β-brominated tetraphenylpor-
phyrins with Zn(II) and Cu(II) acetates. DMF (having
the occupied non-bonding φN orbitals and possessing
σ-donor properties) was used as the organic solvent.
It was found that successive β-bromination ac-
celerated the complex formation of the corresponding
porphyrins as compared to H2TPP, the activation
energy (Ea) and entropy (ΔS≠) of the reaction
remaining practically unchanged (Table 3). The
complex formation reactions of Н2TPPBr8 with the
metal salts in DMF occurred during the components
mixing. That was evidently caused by the change of
the macrocycle electronic structure (the enhanced
polarization of the N–H bond not suppressed in DMF).
Monobromination of the ligand (the CdTPPBr case)
noticeably accelerated the studied metal exchange
reactions (Table 4), likely due to the weakening of the
Cd–N σ-bond (the –I effect of bromine). However, the
effective rate constants of the metal exchange de-
creased in the case of the octabromination
(CdTPPBr8). We believe that the effect resulted from
the significant distortion of the macrocycle and
The metal exchange reaction between the metal
porphyrinate and another metal salt is generally 1–
3 orders of magnitude faster that the complex forma-
tion reaction of the free porphyrin with the correspond-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 1 2016

COMPLEX FORMATION OF β-BROMINATED TETRAPHENYLPORPHYRINS
strengthening of the Cd–N σ-bond owing to the
107
A
positive inductive effect of bromine.
To summarize, we elucidated the effect of β-bromina-
tion on the spectral properties of tetraphenylporphyrin
and its complexes with copper(II), cadmium, and zinc,
as well as on kinetics of the complexes formation with
copper(II) and zinc acetates and metal exchange
involving the corresponding cadmium complexes. The
obtained data are of interest in view of development of
macroheterocyclic compounds capable of selective
binding various metal cations.
λ, nm
Fig. 3. Evolution of electron absorption spectrum in the
course of the metal exchange reaction between CdTPPBr
and Zn(ОAc)2 in DMF. The final spectrum is shown in
bold. csalt = 2.5 × 10–3 mol/L, cCdTPPBr = 2.5 × 10–5 mol/L,
Т = 328 K.
EXPERIMENTAL
Tetraphenylporphyrin Н2TPP (97%, Aldrich), DMF
(99%, Merck), CdCl2 (chemically pure grade) as well
as Cu(CH3COO)2 and Zn(CH3COO)2 (both from
Acros, 99%) were used. The brominated porphyrins
were prepared using the procedures adopted from the
earlier studies: Н2TPPBr [8], Н2TPPBr4 [9], and
Н2TPPBr8 [10]. Electron absorption (Table 2) and Н
NMR spectra of the prepared products fully coincided
with the reference data [8–10].
hexane–dichloromethane 1 : 1). Yield 0.034 g (75%,
0.0495 mmol).
2,3,12,13-Tetrabromo-5,10,15,20-tetraphenyl-
porphyrin (H2TPPBr4). 0.017 g (0.0955 mmol) of N-
bromosuccinimide was added in four portions to a
solution of 0.04 g (0.0649 mmol) of Н2ТРР in 10 mL
of СНСl3. The mixture was then refluxed during 30–
40 min, and DMF and water were added after cooling
to ambient. The organic layer was separated, washed
with water three times, and dried over Na2SO4. The
solvent was eliminated, and the residue was purified
by chromatography (silica gel, eluent chloroform–
hexane 1 : 2, then pure chloroform) and recrystallized
from ethanol. Yield 0.039 g (65%, 0.0419 mmol).
1
NMR spectrum was registered using a Bruker AV
III-500 spectrometer.
2-Bromo-5,10,15,20-tetraphenylporphyrin
(H2TPPBr). 0.02 g (0.112 mmol) of N-bromosuccin-
imide was added to a solution of 0.04 g (0.0649 mmol)
of Н2ТРР in 10 mL of СНСl3. The reaction mixture
was refluxed at stirring during 45–60 min. 0.16 mL of
pyridine was added after cooling, and the solvent was
evaporated. The residue was washed with ethanol,
dried, dissolved in a minimal amount of chloroform,
and purified by chromatography on silica gel (eluent
Copper(II) 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-
tetraphenylporphyrinate. 0.118 g (0.65 mmol) of
Cu(OAc)2 was added to a solution of 0.04 g (0.065 mmol)
of Н2ТРР in 50 mL of DMF. The reaction mixture was
refluxed during 2 min and cooled to ambient; five-fold
Table 4. The rates of exchange Cd(II) for Zn(II) and Cu(II) in complexes with DMF studied porphyrins (csalt = 2.5 ×
10–3 mol/L, ccomplex = 2.5 × 10–5 mol/L)
k2e9f8f × 103, s–1
3.50±0.09
8а
kv298, L mol–1 s–1
Еа, kJ/mol
56±27
54±2
ΔS≠, J mol–1 K–1
–120±90
–112±8
Complex
CdTPP
Salt
Zn(OAc)2
1.4
Cu(OAc)2
Zn(OAc)2
Cu(OAc)2
Zn(OAc)2
Cu(OAc)2
3.2
CdTPPBr
CdTPPBr8
17.5±0.1
14.00±0.05
0.22±0.01
7.0
49±8
–123±27
–94±8
5.60
0.09
58±2
22±1
–249±3
4.6±0.3
1.8
44±4
–149±13
a Calculated according to the Arrhenius equation.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 1 2016

108
MALTSEVA et al.
excess of water and NaCl was added. The precipitate
was filtered off, washed with water, and dried. Yield
0.04 g (0.059 mmol) of CuTPP.
temperature-controlled cell, and the absorbance at the
wavelength corresponding to the absorbance maximum
of the formed copper(II) or zinc tetraphenylpor-
phyrinate was monitored. The reactions of Н2TPPBr
with Cu(OAc)2 and of Н2TPPBr4 with Zn(OAc)2 were
studied at 298–318 K, the reaction of Н2TPPBr with
Zn(OAc)2 was studied at 308–238 K, the reaction of
Н2TPPBr4 with Cu(OAc)2 was studied at 288–298 K,
the reactions of CdTPP and CdTPPBr with Cu(OAc)2
and Zn(OAc)2 and of CdTPPBr8 with Cu(OAc)2 were
studied at 288–298 K, and the reaction of CdTPPBr8
with Zn(OAc)2 was studied at 298–318 K. Tempera-
ture was maintained with an accuracy of ±0.1°С
throughout the experiment.
0.0157 g (0.088 mmol) of N-bromosuccinimide was
added to a solution of 0.04 g (0.059 mmol) of CuТРР
in 20 mL of СНСl3, and the mixture was refluxed
during 30 min. The operation was repeated three times,
total amount of the added N-bromosuccinimide being
0.047 g (0.26 mmol). After addition of the last portion
of the reactant, the mixture was refluxed during 2 h
and cooled to ambient; a solution of 0.07 g (0.44 mmol)
of bromine in 5 mL of CHCl3 was then added at
stirring. The resulting mixture was kept at 20°С during
about 24 h. Excess of bromine was removed by
washing the reaction mixture with 15 mL of 20%
aqueous solution of Na2S2O3. The organic layer was
washed with water and dried over Na2SO4. The solvent
was removed, and the residue was purified by chro-
matography on alumina eluting with chloroform,
followed by recrystallization from ethanol. Yield 0.055 g
(72%, 0.0421 mmol).
The current concentration of the substrate (tetra-
phenylporphyrin or cadmium tetraphenylporphyrinate)
was calculated using Eq. (3)
с = с0(А∞ – Аτ)/(А∞ – А0),
(3)
with А0, Аτ, and А∞ being the solution absorbance at
time zero, at time τ, and after the reaction was com-
plete, correspondingly; с0 being the initial concentra-
tion of the substrate.
2,3,7,8,12,13,17,18-Octabromo-5,10,15,20-tetra-
phenylporphyrin (Н2TPPBr8). 7 mL of 70% aqueous
perchloric acid was added to a solution of 0.05 g of
CuTPPBr8 in 25 mL of chloroform. The mixture was
stirred during 1 day. The organic layer was separated,
neutralized with 20% of aqueous solution of sodium
carbonate, and dried over Na2SO4. The solvent was
then removed, and the residue was purified by
chromatography on alumina eluting with chloroform.
Yield 0.036 g (75%, 0.0289 mmol).
The effective rate constant keff (related to the true
rate constant kv as keff = kvcsalt) was determined using
the pseudo first-order kinetic equation (4).
keff = (1/τ)ln (c0/c).
(4)
The activation energy (Еа) of the reactions was
calculated from the temperature dependence of the rate
constant of the complexes formation using the Arrhenius
equation. The activation entropy (ΔS≠) was calculated
using the fundamental equation of the transition state
theory [Eq. (5)].
Cadmium tetraphenylporphyrinate (CdTPP). A
mixture of 0.06 g (0.325 mmol) of CdCl2 and 0.02 g
(0.0325 mmol) of TPP in 30 mL of DMF was heated
in air to boiling (158°С), cooled down, and poured into
water. The formed precipitate was filtered off, washed
with water, and dried. Yield 0.019 g (81%, 0.0262 mmol).
1Н NMR spectrum (C6D6, 500 MHz), δ, ppm: 9.07 s
(8H, β-pyrrole), 8.36 d (8H, o-Ph, J = 7.7 Hz), 7.59 m
(12H, m,p-Ph).
κkBT
kv = –—— exp ————— ,
ΔH≠ – TΔS≠
(5)
h
R
with ΔH≠, enthalpy of activation (ΔH≠ = Ea – RT); κ,
transport factor (taken equal to unity); kB, the
Boltzmann’s constant; and h, the Planck’s constant.
Cadmium complexes with β-brominated ligands
ACKNOWLEDGMENTS
were prepared similarly, the yields being 80–87%.
Spectral studies were carried out applying the
Upper Volga Regional Center of Physicochemical
Studies.
Reactions of complex formation and metal ex-
change were studied by monitoring electron absorp-
tion spectra of the solutions using a Cary 100 (Varian)
spectrophotometer. To do so, a solution of the studied
tetraphenylporphyrin (or its cadmium salt) (с = 2.5 ×
10–5 mol/L) and the studied salt [copper(II) or zinc
acetate, с = 2.5 × 10–3 mol/L] in DMF was put into a
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