Mutual influence of ligands and reactivity of Gd and Dy acidophthalocyaninate complexes

Article abstract of DOI:10.1023/B:RUCO.0000040727.21739.44

The results of the kinetic study of dissociation of Gd(III) and Dy(III) complexes with phthalocyanine of the composition (X)LnPc (X is single-charged acido ligand) with isolation of macrocyclic ligand depending on the temperature, composition of mixed eth

Full text of DOI:10.1023/B:RUCO.0000040727.21739.44

Russian Journal of Coordination Chemistry, Vol. 30, No. 9, 2004, pp. 660–664. Translated from Koordinatsionnaya Khimiya, Vol. 30, No. 9, 2004, pp. 700–705.
Original Russian Text Copyright © 2004 by Lomova, Andrianova.
Mutual Influence of Ligands and Reactivity of Gd and Dy
Acidophthalocyaninate Complexes
T. N. Lomova and L. G. Andrianova
Institute of Solution Chemistry, Russian Academy of Sciences, ul. Akademicheskaya 1, Ivanovo, 153045 Russia
Received July 27, 2003
Abstract—The results of the kinetic study of dissociation of Gd(III) and Dy(III) complexes with phthalocya-
nine of the composition (X)LnPc (X is single-charged acido ligand) with isolation of macrocyclic ligand
depending on the temperature, composition of mixed ethanol–acetic acid solvent, and the nature of acido ligand
are presented. The total kinetic equations, the rate constants, and activation parameters of dissociation reaction
are determined. The stoichiomeric mechanism is suggested for the complex dissociation involving the limiting
elementary reaction between acetic acid molecule and the complex that occurs as the chelate salt (X)LnPc or
the outer-sphere complex [(HOAc)LnPÒ]+X–. The state of metal phthalocyaninate at the reaction slow stage is
shown to be determined by the electronic structure of the metal cation, the strength of binding of the axial
ligand, and by its cis-effect on the metal bonds with macrocycle.
The study of the properties of acidophthalocyaninate
complexes of analogous Ln metal cations with composi-
tion (X)LnPc (Ln is lanthanide from Sm to Lu, Pc is phtha-
locyanine dianion (H2Pc), X is Cl–, Br–, and AcO–)
showed that correlations can be derived between the
parameter of a complex and the physicochemical param-
eter of a central ion and used further to determine the
nature of the donor–acceptor bonds and their contribution
to the complex stability [1]. However, these studies were
performed with the same acido ligand X, and the data on
the bond between the axially coordinated ligands and the
Ln cation are absent. Using complexes of meso-tetraphen-
ylporphine (H2TPP) as an example, it was shown [2] that
the rate of dissociation of macrocyclic complexes
(X)MTPP (M is d metal) in solutions changes with the
change of acido ligand in the complex composition.
EXPERIMENTAL
The (X)LnPc complexes were obtained from Li2Pc
and the corresponding Ln salt using the procedure
described in [3]. The mixture of Li2Pc (1.95 g,
3.7 mmol) and LnX3 (11 mmol) in 50 ml of DMSO was
heated and thermostatted at boiling temperature for
80 min and then cooled. Water (8 ml) was added to the
reaction mixture. The precipitated H2Pc was filtered
off. The filtrate was diluted with water in the volume
ratio 1 : 2. The obtained precipitate of the (X)LnPc
complex was filtered off, washed with water, and dried
in air. The yield of the complexes was ~90%.
The rates of reactions of (X)GdPc and (X)DyPc
with AcOH in ethanol were determined by spectropho-
tometric method. The electronic absorption spectra of
the solutions were recorded on Specord M400 and
SF-26 spectrophotometers in thermostatted cell. An
accuracy of the temperature maintenance was 0.1 K.
The change in the optical density of solutions of the
complexes in mixed proton-donor solvent was recorded
at the operating wavelength (λ = 668–672 nm depend-
ing on the complex type) near the maximum of band I
(Q band (0,0)).
This paper reports for the first time how the nature
of acido ligand in the complexes (X)GdPc and (X)DyPc
affects the kinetics and mechanism of their dissociation
with isolation of a free macrocycle in the mixed ethan-
ol–AcOH solvent at 313–353 K.
The axial ligands used in this study were Cl–, Br–,
and AcO–:
The reagent grade acetic acid was dehydrated using
thawing by stages, while ethanol was dehydrated
according to the standard procedure [4]. The water con-
tent (titration with the Fisher reagent) in the dried sol-
vents did not exceed 0.03%.
X
N
Ln
N
N
N
N
N
N
The effective rate constants (keff), the true rate con-
stants (k), and the reaction order in the concentration of
the proton-donor species (n) were determined using the
Microsoft Excel program of optimization of depen-
dences ln(c0(X)LnPc/cτ(X)LnPc) –τ and keff–c0AcOH, respec-
tively, the activation energies (Ea) were found by opti-
N
Ln(III) acidophthalocyaninate complexes
Ln = Gd, Dy; X = Cl–, Br–, AcO–.
1070-3284/04/3009-0660 © 2004 åÄIä “Nauka /Interperiodica”

MUTUAL INFLUENCE OF LIGANDS
Table 1. Absorption bands in electronic absorption spectra of (X)LnPc in ethanol
Absorption band, λmax, nm
661
Absorption band, λmax, nm
Complex
Complex
Q(0,0)
Q(0,1)
Soret
Q(0,0)
Q(0,1)
Soret
(Cl)GdPc
(Br)GdPc
(AcO)GdPc
671
671
670
606
606
605
344
344
343
(Cl)DyPc
(Br)DyPc
(AcO)DyPc
671
669
670
604
604
604
344
342
342
mization of the dependences in the Arrhenius equation second orders, as well as the activation parameters are
coordinates. The rate constants of dissociation at a stan- given in Table 3.
dard temperature (298 K) were obtained by extrapola-
With account of the above data, the dissociation
tion of logkeff –1/T and logk–1/T. The activation
reactions for the complexes can be written as
entropy (∆S#) was calculated from the fundamental
(X)LnPc + 2HOAc = [(X)Ln]2+ + H2Pc + 2OAc– (3)
equation of transient state theory that was transformed
as follows [5]
while the experimentally found rate equations for the
Gd and Dy complexes, respectively, as
∆S# = 19.1logkT + E/T – 19.1logT – 205.
(1)
The average ∆S# value was found as the arithmetic
mean of the ∆S# values calculated for all temperatures
of the kinetic experiment.
–dc(X)GdPc/dτ = kc(X)GdPc(c0AcOH)2,
(4)
673.1
A
RESULTS AND DISCUSSION
The electronic absorption spectra of (X)LnPc (Ln is
Gd and Dy) in the visible region (Table 1) are similar to
those of Ln(III) phthalocyaninates in organic solvents
reported in [6]. The spectra of complexes remain
unchanged with time and on heating, while the optical
density is proportional to their concentration (1–10) ×
10–5 mol/l, which indicates that Ln(III) phthalocyani-
nates do not undergo dissociation or association in eth-
anol.
The dissociation of the complexes begins when a
100% AcOH is added to the ethanol solutions to bring
about the formation of H2Pc that remains in dissolved
state under experimental conditions (Fig. 1, 2). For all
metal phthalocyaninates under study, the first order of
dissociation in the complex concentration was deter-
mined. The corresponding effective dissociation rate
constants are presented in Table 2. The dissociation rate
for all complexes was found to increase with AcOH
concentration. However, Gd and Dy complexes show
different dependences of the reaction rate on the initial
AcOH concentration, which can be explained by differ-
ent reaction mechanisms.
1
0.7
0.6
0.5
0.4
0.3
709.4
0.2
0.1
2
The plot of the dependence
n
kTeff = kT(c0AcOH
)
(2)
350
450
550
650
750
λ, nm
in the logarithmic coordinates (Figs. 2 and 3) gives the
linear correlation (reliability of approximation R2 =
0.957–0.999) with a slope close to two for the (X)GdPc
complexes and to unity for the (X)DyPc complexes.
The true rate constants of the respective total third and
Fig. 1. Electronic absorption spectra of (1) (AcO)DyPc and
(2) product of its dissociation in ethanol–AcOH mixture
(c0AcOH = 3.55 mol/l) at 333.2 K.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 9 2004

662
LOMOVA, ANDRIANOVA
Table 2. Rate constants of dissociation of Gd(III) and Dy(III) complexes with phthalocyanine in ethanol–acetic acid mixture
keff × 103, s–1
c0HOAc , mol/l
298.2 K
313.2 K
323.2 K
333.2 K
(Cl)GdPc
1.244 0.008
1.63 0.01
3.19 0.03
4.68 0.03
(Br)GdPc
1.42
2.13
2.84
3.55
0.761 0.002
0.85 0.01
1.67 0.02
2.73 0.025
1.69 0.03
2.45 0.05
4.79 0.07
6.6 0.1
2.31 0.09
3.71 0.09
7.2 0.1
9.2 0.2
1.42
2.13
2.84
3.55
0.472 0.001
0.507 0.001
1.101 0.002
1.63 0.02
1.232 0.004
1.318 0.009
2.38 0.07
3.28 0.08
(AcO)GdPc
2.23 0.04
2.39 0.045
3.84 0.06
5.1 0.1
4.10 0.07
4.3 0.1
6.2 0.1
7.7 0.1
1.42
2.13
2.84
3.55
4.26
0.0407 0.0001
0.10 0.08
0.24 0.03
0.44 0.04
0.61 0.02
0.325 0.004
0.538 0.009
0.99 0.02
0.64 0.02
0.97 0.02
1.55 0.08
1.35 0.03
1.76 0.02
2.63 0.08
(Cl)DyPc
0.370 0.009*
0.508 0.008*
0.618 + 0.007*
(Br)DyPc
2.13
2.84
3.55
0.0656 0.0007
0.102 0.004
0.246 0.006
0.514 0.005**
0.73 0.01**
0.74 0.01**
0.262 0.006
0.384 0.005
0.516 0.009
2.13
2.84
3.55
0.057 0.0055
0.097 0.002
0.211 0.09
0.302 0.007*
0.508 0.009*
0.61 0.01*
(AcO)DyPc
0.423 0.007**
0.69 0.01**
0.73 + 0.01**
0.214 0.003
0.363 0.006
0.49 0.02
2.13
2.84
3.55
0.039 0.004
0.064 0.005
0.186 0.008
0.29 0.03*
0.39 0.02*
0.56 0.02*
0.41 0.02**
0.55 0.01**
0.69 0.04**
0.188 0.004
0.270 0.009
0.450 0.008
343.2 K
353.2 K
* k
** k
.
.
–dc(X)DyPc/dτ = kc(X)DyPccA0 cOH
.
(5)
where K1 is the equilibrium constant of acido ligand X
ionization.
Taking into consideration the spectrophotometric
data, i.e., the electronic absorption spectra at the begin-
ning and at the end of the reaction (Fig. 1), one can
assume the following stepwise mechanism of transforma-
tions that adequately reflects the summary kinetic Eq. (4):
[(AcOH)GdPc]+X– + AcOH
(AcOH)Gd3+ + H2Pc + AcO– + X–,
(7)
k1
where k1 is the rate constant of an elementary limiting
K1
(X)GdPc + HOAc
[(AcOH)GdPc]+X–,
(6) state of the complex dissociation. The kinetic equation
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 9 2004

MUTUAL INFLUENCE OF LIGANDS
663
logcÄ0 Òéç
logcÄ0 Òéç
0.30
–2.0
0.35
0.40
0.45
0.50
0.55
0.60
0.30
–3.1
0.35
0.40
0.45
0.50
0.55
0.60
–2.2
–2.4
–2.6
–2.8
–3.0
–3.2
3
–3.2
–3.3
–3.4
–3.5
–3.6
3
2
2
1
1
–3.4
–3.6
logkeff
–3.7
logkeff
Fig. 3. The plot of logk vs. logc0
for (X)DyPc com-
Fig. 2. The plot of logk vs. logc0
for (X)GdPc com-
eff
eff
AcOH
AcOH
plexes at (1) 333, (2, 3) 343 K; X = (1) Cl, (2) AcO, (3) Br.
plexes at 313 K: X = (1) AcO, (2) Br, and (3) Cl.
dently, both reaction courses are realized to different
extent, depending on the structure of coordination
sphere of the complex participating in the limiting stage
and temperature.
The kinetic stability of the complexes of both cat-
ions with macrocyclic ligand is sensitive to the nature
of the axial acido ligand X (Table 3). The k298 value
decreases in the series
for the low stage (7) has the form
–dc[(AcOH)GdPc]+X–/dτ = k1c
cAcOH
.
(8)
[(AcOH)GdPc]+X–
With account of equilibrium (6), Eq. (8) can be written
as follows:
–dc[(AcOH)GdPc]+X–/dτ = –dc(X)GdPc/dτ
(9)
= k1K1c(X)GdPc(cAcOH)2.
(Cl)LnPc > (Br)LnPc > (OAc)LnPc,
(11)
Equation (9) corresponds to the experimental Eq. (4),
and k = k1K1. The elementary reaction for the Dy com-
plexes has the form
i.e., in agreement with the electronegativity of the
donor atom X.
However, the halogen–Ln or O–Ln (for the acetate
complexes) π-dative bonds smooth out the above-men-
tioned sensitivity toward ligand X in the case of the Dy
complexes: in series (11), the largest value of the disso-
ciation rate constant is 24.4 and 2.4 times as high as the
k
(X)DyPc + AcOH
[(X)Dy]2+ + H2Pc + OAc–.(10)
The kinetic equation for the elementary reaction (10)
coincides with the experimental Eq. (5).
Thus, in the course of the (X)GdPc dissociation, the smallest dissociation rate constant for the Gd and Dy
outer-sphere complex [(AcOH)GdPc]+X– reacts at the complexes, respectively. The kinetic stability of the
limiting stage, while the (X)DyPc complexes enter the (X)DyPc complexes (k298) is 4.30 and 44 times as high
elementary slow dissociation reaction at the Dy–N as that for the (X)GdPc complexes, where X is AcO–,
bond in the initial state with the X ligand in composi- Br–, and Cl–, respectively (Table 3). This is likely to
tion of the first coordination sphere. This means that in occur due to the Dy–N π-dative bonds and to more
the Dy complexes, the acido ligand X is bound more closer arrangement of the Dy cation with respect to the
strongly than in the Gd complexes. The reason for this macrocyclic plane as the result of the “lanthanide con-
is likely to lie in the nonsymmetric occupation of the f 9 traction” effect.
shell in the (X)DyPc complexes, which stimulates the
π-dative properties in acido ligands Cl–, Br–, and AcO–.
The f shell in the (X)GdPc complexes is stable (f 7 elec-
tronic configuration) and therefore, acido ligands are
bonded to the Gd cation through a single σ bond.
It should be stressed that the stability of the complex
with phthalocianine ligand increases from Gd to Dy
simultaneously with the sharp decrease in the activation
energy of dissociation reaction (Table 3) in the case of
(Br)LnPc and (AcO)LnPc (Br– and AcO– are more
The stoichiometric mechanisms of dissociation of stronger π-donors than Cl [7]). With account of the dif-
the complexes described above are based on the ferent mechanisms of dissociation of the Gd and Dy
assumption that the reaction orders in the AcOH con- complexes, one can conclude that this is associated
centration are integers (the first order for the Dy com- with the steric hindrances for the reagent attack at the
plex and the second order for the Gd complex). How- limiting stage (7) with the participation of the outer-
ever, as seen from Table 3, the experimental reaction sphere complex [(AcOH)GdPc]+X–, whose coordinated
orders noticeably differ from the whole numbers and AcOH molecule lies on one side of the macrocyclic
decrease on heating. This fact suggests more compli- plane and the X– anion electrostatically bound in the
cated real mechanism of the dissociation reaction. Evi- second coordination sphere lies on the other side of this
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 9 2004

664
LOMOVA, ANDRIANOVA
Table 3. Kinetic parameters of dissociation of Gd(III) and
Dy(III) complexes with phthalocyanine in ethanol–AcOH
mixture
Thus, the mutual effect (the Chernyaev cis-effect) of
ligands in lanthanide acidophthalocyaninate complexes
and its manifestation in the kinetic stability of the com-
plexes significantly depends on the lanthanide elec-
tronic structure.
The rate of dissociation of the previously studied [8,
9] and less stable Ln complexes with tetraphenylpor-
phine is either insensitive to the X nature (for the Tm
complex) or only slightly changes (for the Dy complex)
upon the replacement of Cl– by Br– and AcO– in com-
position of the coordination sphere. In turn, when the
stable d-metal phthalocyaninate complexes are dis-
solved in concentrated H2SO4 (that has the high content
of the solvated protons and the high acidity), they lose
their acido ligands and occur in solutions as the
[MPc](n – 2)+ cations [10]. Thus, the replacement of
acido ligands in complexes with moderate stability in
solutions can be used, on the one hand, as the way to
change their stability, and on the other hand, as an indi-
rect method to study the strength and the nature of the
axial ligand binding in the metal phthalocyaninates.
k × 104,
–∆S≠,
*
Ea ,
Complex T, K
n
s–1 mol–2 l2
J/mol K
kJ/mol
(Cl)GdPc
(Br)GdPc
298
313
323
333
298
313
323
333
3.91
3.45
56.1 140.2 0.6
2.08
1.95
1.81
5.80
12.69
2.41
71.3
90.4
91.3 0.2
44.7 0.3
3.46
1.80
1.48
1.17
7.91
17.95
0.160
0.612
1.70
(AcO)GdPc 298
313
323
333
2.16
1.72
1.29
4.94
ACKNOWLEDGMENTS
(Cl)DyPc
(Br)DyPc
298
333
343
353
298
333
343
353
0.0885
0.961
1.73
56.4 160.8 0.2
55.15 168.1 0.2
60.0 154.5 0.2
This work was supported by the RAS Integrated
Program “Target Synthesis of Compounds with Speci-
fied Properties and Production of Functional Materials
on Their Basis”, 2003–2004.
1.33
1.01
0.74
3.05
0.0788
0.627
1.105
1.94
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1.64
1.38
1.11
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(AcO)DyPc 298
0.0362
0.547
1.077
333
343
353
1.69
1.28
1.03
4. Non-aqueous Solvents, Waddington, T.C., Ed., Nelson,
1.868
1969.
2
* Reliability of approximation R = 0.982–0.999.
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plane. It is obvious that the same reason underlies a
substantial difference in the activation energies and
kinetic stabilities of the Gd complexes with different X.
8. Lomova, T.N., Andrianova, L.G., and Berezin, B.D., Zh.
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i ftalotsianina (Coordination Compounds of Porphyrins
and Phthalocyanine), Moscow: Nauka, 1978.
This conclusion agrees well with the more negative
entropies of activation of the (X)DyPc dissociation as
compared to the Gd complexes (Table 3). As compared
to the Gd complexes, the transition states for the Dy
complexes are more solvated than those of the initial
reagents.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 9 2004