Coordination Properties of Ga, In, and Tl Tetraphenylporphine Complexes in Reactions with Nitrogen-containing Extra Ligands

Article abstract of DOI:10.1023/A:1023455325461

The formation of Ga³⁺, In³⁺, and T1³⁺ tetraphenylporphine mixed-ligand complexes (X)MTPP + L = (X)M(L)TPP (X = Cl ^-, AcO^-, acac^-; L = N-methylimidazole, imidazole, pyridine, 3,5-dimethylpyr

Full text of DOI:10.1023/A:1023455325461

Russian Journal of General Chemistry, Vol. 73, No. 1, 2003, pp. 145 150. Translated from Zhurnal Obshchei Khimii, Vol. 73, No. 1, 2003,
pp. 153 158.
Original Russian Text Copyright
2003 by Zaitzeva, Zdanovich, Ageeva, Golubchikov.
Coordination Properties of Ga, In, and Tl Tetraphenylporphine
Complexes in Reactions with Nitrogen-containing Extra Ligands
S. V. Zaitzeva, S. A. Zdanovich, T. A. Ageeva, and O. A. Golubchikov
Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russia
Ivanovo State University of Chemical Engineering, Ivanovo, Russia
Received December 29, 2000
Abstract The formation of Ga3+, In3+, and Tl3+ tetraphenylporphine mixed-ligand complexes (X)MTPP +
L = (X)M(L)TPP (X = Cl , AcO , acac ; L = N-methylimidazole, imidazole, pyridine, 3,5-dimethylpyrazole,
dimethylformamide) in chloroform was studied by spectrophotometric titration and quantum-chemical calcula-
tions. The stability of the Ga, In, and Tl porphyrin extra complexes was found to depend on the nature of the
acido and nitrogen-containing ligands. The geometric and energetic characteristics of the complexes of six-
coordinate gallium and indium porphyrins were calculated. Correlations between calculated and experimental
energies of formation and Gibbs energies were found. The cis- and trans-effects of ligands in the extra com-
plexes of metal porphyrins were explained.
Thermodynamic stability characteristics of metal
porphyrin extra complexes are very important for
interpretation of the physicochemical properties of
these systems and for technological design. The
interest in high-valent metal porphyrins is first of all
connected with search for effective catalysts for redox
processes [1 4]. The catalytic activity of such com-
pounds is enhanced by their incorporation into extra
complexes [3, 4]. This work is a continuation of a
systematic study of the coordination properties of
porphyrin complexes of aluminum-group metals and
deals with special features of formation of mixed-
ligand compounds of Ga, In, and Tl tetraphenylpor-
phines in chloroform with various acido and extra
ligands. Aluminum porphyrins were described earlier
in [5, 6]. In the study we used spectrophotometric
This fact enables us to use the spectral method for
studying the extra coordination which is described by
the following equation.
(X)MTPP + nL
(X)M(L)nTPP.
Metal porphyrin extra ligand equilibrium is
achieved almost immediately, which is experimentally
proved by the corresponding electronic spectra
(Fig. 1). Chloroform is a weak solvating agent for the
central metal atoms of metal porphyrins, and, there-
fore, the effect of specific metal CHCl3 interactions
on the equilibrium of extra coordination can be
neglected.
The calculated stability constants (Kst) of the
aluminum, gallium, and indium extra complexes
titration and computer simulation. The use of quantum- (Table 1) show that the ability of metal porphyrin to
chemical calculations for optimization of chemical
processes and structures of various compounds was
described in [7 9]. The dependence of the stability of
extra complexes (X)M(L)TPP on the basicity of the
molecular extra ligand L and the nature of the central
metal atom and acido ligand X was characterized on
the basis of calculated and experimental data. The
geometric and energetic parameters of gallium,
indium, and thallium porphyrins and of their extra
complexes were calculated using the PM3 method.
coordinate extra ligand decreases from aluminum to
thallium. First of all, this is attributable to the increas-
ing ionic radius and ionization potential of the central
atom [10]. The formation of the mixed-ligand com-
pounds is also affected by the cis effect of ligands in
the complex. In contrast to aluminum tetraphenyl-
porphyn, M X bonds in indium and thallium por-
phyrins seem to be stronger due to the fact that the
latter metals have larger covalent radii and thus
deviate significantly from the N4 plane. The geometric
factor, too, contributes much into the ability of metal
porphyrin to coordinate extra ligand. For instance, a
Like with aluminum porphyrins, the formation of
extra complexes with the compounds under produces
significant changes in the positions and intensities of
bands in the electronic absorption spectra (Fig. 1).
much smaller size of gallium (rcov 1.19
[10]) can
give rise to radial deformation of the macroring in
(X)GaTPP and thus decrease the covalent contribution
1070-3632/03/7301-0145$25.00 2003 MAIK Nauka/Interperiodica

146
ZAITZEVA et al.
0.13
A
595 nm
0.11
0.09
A
1
0
50
100
cL 104, M
2
11
10
550
580
, nm
Fig. 1. Electronic absorption spectra of the mixed-ligand (Cl)GaTPP complex with imidazole (Im): (1) pure (Cl)GaTPP
6
6
4
(c
9
10 M); (2) (10) (Cl)GaTPP with various imidazole concentrations (c
9
10 , c
6 10
Im
(Cl)GaTPP
(Cl)GaTPP
3
9.4 10 M); and (11) (Cl)GaTPP with an excess of imidazole in chloroform.
into the Ga NP bond strength. Therewith, the Ga X
bond strengthens (Table 2). The deformation in the
indium and thallium complexes {rcov(In) 1.36 and
significant. This is probably responsible for the
absence of correlation between stability and metal
extra ligand (M NL) bond length in the series of
indium and gallium porphyrin extra complexes
(Table 2). Thus, the data in Tables 1 and 2 suggest
that the structural features of the compounds under
study affect their coordination properties.
rcov(Tl) 1.45
[10]} and the resulting electron
density redistribution of the macroring are not so
Table 1. Thermodynamic characteristics of imidazole
extra coordination to Al, Ga, and In porphyrins in chloro-
form
Compounds (X)AlTPP form complexes with
N-methylimidazole (MeIm), imidazole (Im) pyridine
(Py), 3,5-dimethylpyrazole (DMP), and dimethylform-
amide (DMF) [5, 6]. For (X)GaTPP and (Cl)InTPP
only extra coordination with imidazole is typical,
because this ligand is highly basic and produces no
steric hindrances to M NL bond formation. Using the
Benth French method [11], we found that gallium and
indium tetraphenylporphine complexes coordinate one
Im molecule each (Fig. 2).
3
Kst 10 ,
l/mol
(298 K)
G,
kJ/mol
Eb(M NL),
kJ/mol
,
Complex
nm
(Cl)AlTPP
4.0 0.3a
12.0 1.0a
1.88 0.07
2.9 0.2
(AcO)AlTPP
(Cl)GaTPP
(AcO)GaTPP
(Cl)InTPP
18.1
19.3
5.8
145.56
156.46
47.90
38.86
20.91
25.01
12.0
13.0
2.5
0.135 0.001
Though MeIm is the strongest base among all the
nitrogen-containing extra ligands under study, its
coordination by gallium and indium porphyrins is
almost impossible, which seems to be caused by the
fact that the desolvation energy of N-methylimidazole
in the case of chloroform, as calculated by the PM3
method [12], is double that of imidazole [5]. There-
(Cl)GaTPPb
(AcO)GaTPPb
(Cl)InTPPb
a
b
Data of [5, 6]; metal porphyrins with imidazole in the cis
position.
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COORDINATION PROPERTIES OF Ga, In, AND Tl TETRAPHENYLPORPHINE COMPLEXES
147
tan 1.1
1
1.5
2
1.0
0.5
tan 1.1
0
4.7
log cL
3.7
2.7
1.7
3
0.5
tan 1.3
1.0
1.5
2.0
Fig. 2. Dependences of log [(A
A )/(A
A )] on log c for extra coordination of (1) (Cl)GaTPP, (2) (AcO)GaTPP, and
0 L
e
0
(3) (Cl)InTPP with Im in chloroform.
fore, the formation of the (X)Ga(MeIm)TPP and
(Cl)In(MeIm)TPP extra complexes becomes energe-
tically unprofitable and the formation of M MeIm
bonds finds difficulties because of the energy con-
sumption for desolvation. Steric distortions and spatial
restrictions involved also prevent MeIm extra co-
ordination. The complex (AcO)TlTPP is not prone to
extra cooordination with MeIm under the experi-
mental conditions, since the increased ionic radius of
the metal and the possibility of bidentate binding of
AcO result in a stronger deviation of thallium from
the macroring plane [13] and prevent trans addition
of the molecular ligand to the acido ligand.
quantum-chemical calculations (Tables 1 and 2), too,
establish that extra ligands are most probably arranged
on a side opposite to the acetate ion.
It should be noted that the ability of metal por-
phyrins to coordinate an extra ligand is strongly
affected by the nature of the covalently bonded acido
ligand X. Replacement of AcO by Cl in gallium
tetraphenylporphyn complexes results in reduced
stability of (Cl)Ga(Im)TPP, on account of the en-
hanced covalent nature of the Ga Cl bond. Therefore,
the reduction of the effective positive charge on the
gallium atom results in destabilization of the extra
complex. The strongest interaction between the metal
and chlorine weakens the Ga Im bond. Thus, in the
systems under study the mutual trans effect of ligands
in the extra complexes is very strong. The low sta-
bility of (AcO)M(Im)TPP complexes (M = Ga3+, In3+)
results from both the steric strain in the porphyrin and
the high polarizability of the elecronic shell of AcO ,
The ability of (AcO)M(L)TPP complexes to co-
ordinate an extra molecule in the cis position is very
weak, which is associated with steric hindrances
arising from the neighborhood of two bulky ligands.
The formation energies of the mixed-ligand com-
pounds and the M NL bond strengths, obtained by
Table 2. Bond lengths ( ) in Ga and In porphyrin extra complexes
Complex
(Cl)GaTPP
(AcO)GaTPP
(Cl)InTPP
L
M N1
M N2
M N3
M N4
M X
M NL
M Ct
2.495
2.406
1.802
1.800
2.089
2.088
1.789
2.486
2.076
1.802
1.803
1.793
1.794
2.091
2.090
2.403
1.794
2.094
1.816
1.795
2.361
2.335
2.088
2.085
2.406
1.794
2.077
2.448
2.399
2.399
2.352
2.077
2.075
1.788
2.458
2.093
1.865
1.813
2.218
2.283
2.528
2.651
2.284
1.809
2.592
0.608
0.436
0.478
0.287
0.329
0.066
0.557
0.710
0.329
Im
Im
Im
2.487
2.380
2.124
4.143
3.482
3.978
(AcO)GaTPPa Im
(Cl)GaTPPa
(Cl)InTPPa
Im
Im
a
Metal porphyrin with imidazole in the cis position.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 1 2003

148
ZAITZEVA et al.
Fig. 3. Structure of (Cl)In(Im)TPP calculated by the PM3 quantum-chemical method.
which substantially reduce the effective positive
charge on the metal atom and the M NL bond strength
(Table 2).
ligands (Fig. 2). Since the macroring deformations are
different in nature, no correlation between the stability
of gallium and indium porphyrins and the deviation
of the metal from the M Ct plane is observed (Table
2). This type of deformation is preserved in extra
complexes, but M Ct distances decrease significantly.
We have found no correlation between the macroring
deformation (i.e. the size of the coordination cavity),
Ct M, M X and M Im, for the compounds under
study. However, we found a dependence between
M NL bond strengths and Kst values for complexes of
gallium porphyrins: As the M NL bond length in-
creases, the stability of the complexes decreases
(Table 2). According to Table 2, when imidazole is
coordinated by a metal porphyrin, the M NP bond is
slightly strengthened but the M X bond becomes
longer. Thus, the trans effect is accompanied by the
cis effect, which suggests the presence of a fairly strong
mutual influence of ligands in the extra complexes.
As compared to porphyrin complexes of double-
charged metal ions [14 16], gallium and indium
porphyrins form less stable extra complexes, even
though their formal charge is higher. Obviously, there
are several reasons for that. First, the X M bond is
covalent rather than ionic [17 20]. Second, the metal
cation deviates from the N4 plane of the porphyrin to
acido ligand X, which is proved by quantum-chemical
calculations (Table 2). This deviation is also preserved
in the extra complexes (Fig. 3).
Computer simulation based on quantum-chemical
calculations allows us to predict the extra coordination
process and to explain the trends in variation in the
stability of the tetraphenylporphyrin extra complexes
with acido and extra ligands. According to Table 1,
the energy of M NL bond formation (Eb) in the extra
complexes changes in parallel with their stability.
EXPERIMENTAL
The calculated changes in the geometry of metal
porphyrins, produced by extra coordination, allow us
to explain the specificity of this process for
aluminum-subgroup metal complexes (Table 2). The
mixed-ligand compounds have a square-pyramidal
structure of the coordination centers, with the metal
atoms deviating from the N4 plane to the acido
Spectrophotometric titration and computer simula-
tion were used as investigation techniques. The ex-
perimental and calculation procedures were similar to
those described in [6, 21]. Quantum-chemical calcula-
tions were carried out using the MOPAC 6.0 program.
The geometry of aluminum porphyrins was optimized
using a combination of conjugate gradient methods
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 1 2003

COORDINATION PROPERTIES OF Ga, In, AND Tl TETRAPHENYLPORPHINE COMPLEXES
149
1
Table 3. Metal nitrogen [ (M N), cm ] and metal acido
spectra was beyond the scope of this work, and the
spectral assignment was based on published data
[23 25].
1
ligand [ (M X), cm ] stretching vibrations frequencies in
the IR spectra of (AcO)GaTPP, (Cl)InTPP, and
(AcO)TlTPP.
REFERENCES
Complex
(M N)
450
433
430 [23]
(M X)
1. Scheidt, W.R. and Lee, Y.J., Struct. Bonding (Berlin),
(AcO)GaTPP
(Cl)InTPP
(AcO)TlTPP
573, 615 (Ga O)
525, 566 (In Cl)
562, 615 (Tl O) [23]
1987, vol. 1, no. 1, p. 64.
2. Kurori, M. and Inoue, S., J. Synth. Org. Chem. Jpn.,
1989, vol. 47, no. 11, p. 1017.
3. Wonwoo, N. and Selverston, V.J., J. Am. Chem. Soc.,
1990, vol. 112, no. 12, p. 4977.
of Fletcher Reeves and Pollack Ribiere [22]. The
1
1
value 0.04 kJ mol
for the gradient was accepted
4. Arai, T. and Sato Y., Chem. Lett., 1990, no. 4, p. 551.
as a criterion for calculation termination. The experi-
mental and calculated characteristics of the extra co-
ordination process are shown in Tables 1 and 2.
5. Zaitzeva, S.V., Cand. Sci. (Chem.) Dissertation,
Ivanovo, 1999.
6. Lomova, T.N., Zaitzeva, S.V. , Molodkina, O.V., and
Ageeva, T.A., Koord. Khim., 1999, vol. 25, no. 6,
p. 424.
Complexes (X)MTPP were obtained by reacting
metal salts with tetraphenylporphine in a high-boiling
solvent and isolated by liquid chromatography and
recrystallization.
7. Stewart, J.J.P., J. Comput. Chem., 1989, vol. 10, no. 2,
p. 209.
(AcO)GaTPP was obtained by the known proce-
dure [7] by reacting H2TPP and (AcO)Ga(OH) at a
1:2 molar ratio in boiling PhOH for 10 min. The re-
action mixture was dissolved in chloroform and
washed with warm water many times. The resulting
solution of the complex in chloroform was dried by
CaCl2, concentrated, and subjected to chromatography
on AlaO3 with chloroform as eluent. After repeated
chromatography, the chloroform was distilled off in a
vacuum. Yield 92%. Electronic absorption spectrum
(CHCl3), max, nm (log ): 627.2 (3.04), 587.5 (3.55),
547.0 (4.32), 512.0 sh, 418.2 (5.76).
8. Anderson, W.P., Edwards, W.D., and Zerner, M.C.,
Inorg. Chem., 1986, vol. 25, no. 16, p. 2728.
9. Stewart, J.J.P., J. Computer-Aided Molecular Design,
1990, vol. 4, no. 1, p. 1.
10. Batzanov, S.S., Eksperimental’nye osnovy strukturnoi
khimii (Experimental Foundations of Structural
Chemistry), Moscow: Izd. Standartov, 1986.
11. Bulatov, M.I. and Kalinkin, I.P., Prakticheskoe ru-
kovodstvo po fotokolorimericheskim i spektrofoto-
metricheskim metodam analiza (Manual on Photo-
colorimetric and Spectrophotometric Analytical
Methods), Leningrad: Khimiya, 1968.
(Cl)GaTPP was obtained by boiling (AcO)GaTPP
in 33% HCl for 3 h. The acid was removed in a
vacuum, the dry residue was dissolved in a small
amount of CHCl3, washed with water, dried with
CaCl2, subjected to chromatography on Al2O3 with
chloroform as eluent. After repeated chromatography,
the chloroform was distilled off in a vacuum. Yield
12. Stewart, J.J.P., J. Comput. Chem., 1991, vol. 12, no. 3,
p. 320.
13. Collins, D.V. and Hoard, J.L., J. Am. Chem. Soc.,
1970, vol. 92, no. 2, p. 3761.
14. Karmanova, T.V., Koifman, O.I., and Berezin, B.D.,
90%. Electronic absorption spectrum (CHCl3),
,
max
Koord. Khim., 1983, vol. 9, no. 6, p. 772.
nm (log ): 620.0 (3.36), 581.0 (3.58), 545.0 (4.30),
510.0 sh, 416.4 (5.73).
15. Koroleva, T.A., Koifman, O.I., and Berezin, B.D.,
Koord. Khim., 1983, vol. 7, no. 8, p. 2007.
(Cl)InTPP and (AcO)TlTPP were synthesized by
the procedure in [18, 19]. Electronic absorption spec-
trum for (Cl)InTPP (CHCl3), max, nm (log ): 634.0
(3.19), 598.0 (3.83), 559.0 (4.39), 526.4 (3.55), 425.0
(5.85).
16. Berezin, B.D., Uspekhi khimii porfirinov (Progress in
Porphyrin Chemistry), St. Petersburg: NII Khimii St.-
Peterb. Gos. Univ., 1997.
17. Lomova, T.N., Mozhzhukhina E.G., and Berezin, B.D.,
Zh. Neorg. Khim., 1993, vol. 38, no. 9, p. 1552.
The metal porphyrins were identified by the charac-
teristic vibration frequencies in the IR spectra re-
corded on an IKS-29 spectrophotometer in KBr pellets
(Table 3). However, detailed interpretation of the
18. Lomova, T.N., Mozhzhukhina E.G., and Shormano-
va, L.P., Zh. Obshch. Khim., 1989, vol. 59, no. 10,
p. 2317.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 1 2003

150
ZAITZEVA et al.
19. Lomova, T.N. and Mozhzhukhina, E.G., Zh. Neorg.
Khim., 1997, vol. 42, no. 10, p. 1691.
Wiley, 1980.
23. Cullen D.L., Meyer E.F., and Smith K.M., Inorg.
Chem., 1977, vol. 16, no. 5, p. 1179.
20. Senge, M.O., Ruhlandt-Senge, K., and Kevin, J.,
J. Chem. Soc., Dalton Trans., 1993, no. 23, p. 3619.
24. Henrick K., Matthews R., and Tasker P., Inorg. Chem.,
21. Tipugina, M.Yu., Lomova, T.N., and Ageeva, T.A.,
1977, vol. 16, no. 12, p. 3293.
Zh. Obshch. Khim., 1999, vol. 69, no. 3, p. 459.
25. Brady, F., Henrick, K., and Matthews, R., J. Organo-
met. Chem., 1981, vol. 210, no. 2, p. 281.
22. Fletcher R., Methods of Optimization, New York:
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 1 2003