Crystal solvates of tetrakis(3,5-di-t-butylphenyl)-porphyrinates Mn(III), Ni(II) and Zn(II) with pyridine

Article abstract of DOI:10.1007/s10973-008-9012-4

The crystal solvates of complexes MP (P is the dianion of tetrakis(3,5-di-t-butylphenyl)porphin, M=Ni(II), Zn(II)) and (Ac)MnP with pyridine have been obtained by isothermal evaporation of corresponding solutions at 35°C. The formation and the decompositi

Full text of DOI:10.1007/s10973-008-9012-4

Journal of Thermal Analysis and Calorimetry, Vol. 92 (2008) 3, 671–675
CRYSTAL SOLVATES OF TETRAKIS(3,5-DI-t-BUTYLPHENYL)-
PORPHYRINATES Mn(III), Ni(II) AND Zn(II) WITH PYRIDINE
E. V. Balantseva1*, E. V. Antina2, M. B. Berezin2 and A. I. Vyugin2
1Ivanovo State University of Chemistry and Technology, F. Engels av. 7, 153000 Ivanovo, Russia
2Institute of Solution Chemistry, Russian Academy of Sciences, Akademicheskaya Street, 1, 153045 Ivanovo, Russia
The crystal solvates of complexes MP (P is the dianion of tetrakis(3,5-di-t-butylphenyl)porphin, M=Ni(II), Zn(II)) and (Ac)MnP
with pyridine have been obtained by isothermal evaporation of corresponding solutions at 35°C. The formation and the decomposi-
tion temperatures of crystal solvates and enthalpies of evaporation pyridine molecules from those crystal solvates were received us-
ing thermogravimetric method. In addition to that, an influence of the type of metal on the compositions, the energetic and thermal
stabilities of the received complexes were analyzed.
Keywords: axial coordination, crystal solvate, molecular complexes, tetrakis(3,5-di-t-butylphenyl)porphin, TG
Introduction
t-butylphenyl)porphyrinates zinc(II), nickel(II) and
manganese(III) (Fig. 1), which have enough solubility
It is known that porphyrins are widely used for creation
of effective substitutes for blood, artificial coenzymes,
catalysts of different processes, photosensibilizers,
semiconductors, etc. The general challenge of success-
ful application of porphyrins is an understanding of the
mechanisms of intermolecular interaction processes in-
volving them. The ability of metalloporphyrins to bind
pyridine axially and form stable crystal solvate struc-
tures with it represents a special interest. Study of the
axial binding features is useful for understanding the
mechanisms of the toxic influence of pyridine and for
the creation of the new polyfunctional materials [1–6].
The crystal solvates of porphyrins were investigated
only for 30 years (the complete information about this
question has been reflected by Byrn et al. [7]). How-
ever, similar compounds were defined clathrates that
do not have strict regular structure and are unstable
even at normal conditions. For the first time the ability
of porphyrin to create crystal solvates with pyridine
was studied in [8–10], where natural porphyrins and
tetraphenylporphyrin were employed. Authors have
proved that these crystal solvates have constant
stochiometric structure and high stability. Addition-
ally, these works showed many advantages of thermo-
gravimetric method of investigation of crystal solvates
structures. In any case, a general problem with the in-
vestigation of porphyrins, conditioned by low solubil-
ity in the organic solvents (up to 10–4 mol L–1), retains
in this method. Therefore the results presented here are
the ones of the thermogravimetric investigations of the
crystal solvates of pyridine formed by tetrakis(3,5-di-
in the pyridine. That allowed to find energetically and
thermally stable molecular complexes and analyze the
influence of structural factors and a nature of a central
ion on investigated properties.
Fig. 1 The molecular structures of tetrakis(3,5-di-t- butyl-
phenyl)porphyrinates
Experimental
The synthesis, methods of purification and some H2P
and MP properties (1H NMR, EPR) were previously
published by our group [11]. The synthesis of
(Ac)Mn(III)
tetrakis(3,5-di-t-butylphenyl)porphyri-
nate were depicted in [12].
The pyridine (Py) used in experiments was a
highly purified commercial product. The water con-
tent of the solvent was determined by Karl Fischer ti-
tration [13] and did not exceed 0.02%. The crystal
solvates of metalloporphyrins were prepared by a
slow evaporating of their saturated solutions in
pyridine at 25–30°C [14].
*
Author for correspondence: Bal_lena@hotbox.ru
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2008 Akadémiai Kiadó, Budapest

BALANTSEVA et al.
Table 1 Physicochemical characteristics of MP and MTPP
crystal solvates with pyridine
Differential thermal and thermogravimetric anal-
ysis were performed on the derivatograph 1000D
(MOM, Hungary) in an air atmosphere at a heating
rate of 2.5°C min–1 at 15–250°C interval. The sample
mass was about 150–200 mg. The enthalpy change in
the process of evaporation of crystal solvate (DvapH)
was calculated from thermograms according to
method presented in [14]. There were two series of
experiments for each set of initial substances. In the
first set, the samples containing mostly crystals and a
little quantities of solution were analyzed. For the
second set the samples (crystals+saturate solution)
were being kept for not less than 24 h in the vacuum
chamber at 30–100°C up till they reached a constant
mass. The reproducibility of experiments was
achieved by five or more experiments for each set of
initial samples. Absence of decomposition processes
of porphyrin molecules was proved by spectro-
photometric experiments carried out after thermo-
gravimetric analysis.
Composition
MP–nPy
Tn
DvapH
1:2
1:1
122
140
53.5
19.2
(Ac)MnP
NiP
ZnP
1:1
1:1
115
21.2
50.4
1478
1:2
1:1
135
145
73.2
26.6
(Ac)MnTPPa
NiTPPa
ZnTPPa
does not form
190
1:1
86.4
Tn – the temperature of the decomposition start, °C;
DvapH – evaporation enthalpy of pyridine from crystal
solvates, ± 0.8–1.5 kJ mol–1; adata from the literature
perature interval [14]. Therefore the existence of this
stage depends on the extraction of residual free solvent
in steady solvate structures [15]. The mass decrease on
the second stage depends on the mass of pyridine mol-
ecules combined in a special way. That allows calcu-
lating the composition of steady MP crystal solvates,
which was determined to be 1:1 for NiP and ZnP crys-
tal solvates and 1:2 for (Ac)MnP crystal solvate. The
second stage of the mass decrease process for the sam-
ple with (Ac)MnP is also double-staged. That signifies
towards consecutive extraction of two pyridine’s mole-
cules combined non-equivalently.
Results and discussion
Typical derivatograms of samples and the results of
thermogravimetric analysis are presented on the Fig. 2,
and in Table 1 jointly with literature data for MTPP.
All samples from the first series of experiments
that contained MP exhibited two consecutive stages
that were reflected in derivatograms in the forms of en-
dothermic peaks on the DTA curve. These stages were
followed by the decrease in mass (Fig. 2a). That mass
decrease on the first low temperature stage is propor-
tional to the mass of saturated solution. Also, the
pyridine DvapH value makes a good agreement with
evaporation enthalpy of clear solvent in suitable tem-
Only one stage of decreasing mass is fixed at
heating the samples of the second set, which is ob-
served in the field of high temperatures (Fig. 2b). That
corresponds to the second stage that is experienced by
the first set of samples. It is referred to an extraction of
pyridine molecules combined in a special way. Subse-
quent heating of samples of both sets up to the temper-
ature of metalloporphyrin decomposition (200–380°C)
Fig. 2 TG, DTG, DTA and T curves of ZnP×Py crystal solvate of the a – first and b – the second groups
672
J. Therm. Anal. Cal., 92, 2008

TETRAKIS(3,5-DI-t-BUTYLPHENYL)-PORPHYRINATES Mn(III), Ni(II) AND Zn(II)
did not lead to the change in TG curve and appearance
logues (MTTP) (Table 1) allowed to define the influ-
ence of alkyl substitution on composition and ener-
getic characteristics of crystal solvates. It was found,
that introducing t-butyl substitutes in the case of
(Ac)MnTPP and ZnTPP does not influence the com-
position of crystal solvates created; although, it de-
creases their thermal and energetic stability (Table 1).
Decreasing the energetic stability of crystal solvates
due to introduction of alkyl substitutes in phenyl
groups of H2TPP can be explained by:
of the peaks on DTA and DTG curves.
According to the results shown in Table 1, NiP
has a minimal thermal and energetic stability among
investigated crystal solvates. Zinc porphyrinate is
more stable thermally; on the other hand manganese
porphyrinate is more stable energetically. The last
one forms a crystal solvate with two pyridine mole-
cules. Such composition is typical for molecular com-
plexes formed by metalloporphyrins with tri-
ple-charged metallic ions and electron-donating lig-
ands [16–20]. It is interesting that the second pyridine
molecule in (Ac)MnP-2Py crystal solvate is bound to
(Ac)MnP almost three times as stronger as the first
one. It can be explained by fact that the weaker
bounded pyridine molecule gets into 6th coordinating
site of Mn. The formation of the strong bond from this
site is difficult because metal ion is shifted out of the
plane of porphyrin macrocycle structure by acid
ligand. The addition of the second pyridine molecule
leads to the substitution of acid ligand into external
coordinating sphere of (Ac)MnP. The analogous
mechanism of (Ac)MnTPP-2Py crystal solvates for-
mation was described in earlier [21] and can be
presented by the following model below.
• electronic effects of substitutes – the displacement of
electronic density towards the macrocycle due to pos-
itive induction effect of t-butyl substitutes. This effect
leads to increase in strength of metal bonds with ni-
trogen atoms from pyrrol group and weakening the
ones with nitrogen atom from pyridine molecule
• steric effects of large substitutes, consisting of loos-
ening a crystal lattice
Some works [26–29] can serve as a confirmation
of substitutes’ steric effect. For example, it has been
shown in article [26] by the method of photoelectron
spectroscopy that distances between crystallographic
planes in H2P, CuP, NiP and ZnP crystals are close
to 7.0 , that is much larger than the ones for ligand
and tetraphenylporphyrinates [27, 28]. Steric influ-
ence of t-butyl substitutes is discussed by
Golder et al. in the investigation of nickel(II)
meso-tetrakis(3,5-di-t-butyl-4-hydrophenyl)porphyri-
nate [29]. They pointed out the decreasing density (r)
of the unit cell in solid porphyrin samples, that have
triclinic system, up to 1.01 g cm–3 and the increase of
distances between the nearest metal atoms (M×××M) up
to 10.7  (according to typical parameters for com-
plexes of tetraphenylporphyrin M×××M is about 8 
and r=1.29–1.48 g cm–3).
It is necessary to note that the high ability of
porphyrin complexes of manganese to bind elec-
tron-donor molecules axially is a typical effect. It was
described in works [19, 22, 23].
The crystal solvate of zinc porphyrinate that in-
cludes one pyridine molecule only is as energetically
stable as manganese crystal solvate. The five-coordi-
nated state of Zn that is a part of metalloporphyrin is a
fairly typical phenomenon [24]. But a six-coordinated
state has been discussed in one work only. It is inter-
esting, that in this case axial ligands contain oxy-
gen [25]. Substitution of zinc by nickel in ZnP–Py
leads to essential decrease of crystal solvate energetic
stability that, most likely, can be explained by de-
creased ionic radii of Ni2+ and Zn2+ equal to 0.78
and 0.83 , accordingly. It is necessary to explain that
the sizes of metal ions and porphyrin cavity play an
important role in formation of axial complexes. Their
relation to each other increases the stability of corre-
sponding porphyrinate and decreases the energy and
length of M–Npy axial bond.
At the same time the introduction of t-butyl substi-
tutes into NiTPP helps to form stable crystal solvates
with pyridine. But if NiTPP does not form a crystal
solvate with pyridine, then DvapH for NiP×Py is
21.2 kJ mol–1. So, introducing t-butyl substitutes makes
porphyrinate act as coordinately unsaturated complex. It
is known, that most of nickel porphyrinates are
coordinately saturate and do not have the possibility to
additionally bind electron-donating molecules. On an-
other hand, the possibility of weak binding of pyridine
by NiTPP is mentioned in work [30]. According to that
the logarithms of constants of axial binding process of
Comparative analysis of data obtained for MP
crystal solvates and their unsubstituted ana-
J. Therm. Anal. Cal., 92, 2008
673

BALANTSEVA et al.
Acknowledgements
pyridine by NiTPP in chloroform and benzene
are 2.19–3.01 and 1.85–3.15, respectively (the devia-
tions of lgK depend on the method of defining the con-
stants). The Ni(II) complexes of the natural porphyrins
form stable solvates with pyridine [10]. Formation of
bi-pyridine nickel porphyrinate NiTPP(CN)4(Py)2 was
established in work [31]. On the other hand the results
of calorimetric measurements obtained in article [32]
show the binding saturation of NiP complex. It is inter-
esting that the main reasons causing the weak binding
unsaturation of the Ni2+ ions in NiP are the effects of
alkyl substitution just like in the case of the decrease of
Mn and Zn crystal solvates stability. This seeming con-
tradiction is explained by the need to take into account a
presence of the opposite p-dative Ni®Npy bond, that is
absent in (Ac)MnP and ZnP. As a result, the opposite
p-dative interaction of nickel ion with macrocycle in
NiP–Py complex weakens due to +I-induction effect of
t-butyl substitutes. On the other hand the steric factor
leads to distortion of the plane structure causing the
metal to leave the coordinating cavity of chromophore.
Both of these factors lead to weakening of metal cation
and porphyrin anion interaction and increase of the
binding unsaturation of cation.
We would like to thank A. S. Semejkin for granting the
tetrakis(3,5-di-t-butylphenyl)porphin.
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