Complex formation between zinc(II) tetraphenylporphyrinate and alkylamines

Article abstract of DOI:10.1134/S1070363214020303

Zinc(II) tetraphenylporphyrinate in chloroform forms complexes with primary amines containing up to 18 carbon atoms; the complex with n-octylamine is the most stable. Zinc(II) tetraphenylporphyrinate complex with octanol-1 is more stable than those with o

Full text of DOI:10.1134/S1070363214020303

ISSN 1070-3632, Russian Journal of General Chemistry, 2014, Vol. 84, No. 2, pp. 320–325. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © V.P. Andreev, P.S. Sobolev, D.O. Zaitsev, V.A. Tafeenko, 2014, published in Zhurnal Obshchei Khimii, 2014, Vol. 84, No. 2,
pp. 335–340.
Complex Formation between Zinc(II) Tetraphenylporphyrinate
and Alkylamines
V. P. Andreeva, P. S. Soboleva, D. O. Zaitseva, and V. A. Tafeenkob
a Petrozavodsk State University, pr. Lenina 33, Petrozavodsk, 185910 Russia
e-mail: andreev@petrsu.karelia.ru
b Moscow State University, Moscow, Russia
Received April 10, 2013
Abstract―Zinc(II) tetraphenylporphyrinate in chloroform forms complexes with primary amines containing
up to 18 carbon atoms; the complex with n-octylamine is the most stable. Zinc(II) tetraphenylporphyrinate
complex with octanol-1 is more stable than those with other alcohols. Reasons for this highest complex
stability have been discussed basing on X-ray diffraction data for the n-octylamine complex.
DOI: 10.1134/S1070363214020303
Previously in the study on complex formation
between Zn(II) tetraphenylporphyrinate (Zn-ТРР) and
n-alkylamines in chloroform [1] we demonstrated that
the complex stability constant K was an intricate
function of RNH2 alkyl chain length. The most stable
complex was formed by n-octylamine.
cases of Zn-TPP coordination with amines and al-
cohols. However, due to low basicity and weak nucleo-
philicity of alcohols the complete complex formation
of Zn-TPP could only be achieved at a significant
excess of the ligand (Table 1). Therefore, the deter-
mination of K, ΔH0, and ΔS0 in the case of alcohols
was questionable: with such excess of alcohol the
solvent composition was substantially altered. For
example, in the case of 30000-fold excess of alcohol
the extinction coefficient ε of the Zn-TPP complex
deviated evidently from that in pure chloroform,
hence, the determination of K in chloroform from
absorbance in chloroform-alcoholic medium could be
inaccurate. Nevertheless, the determined Zn-TPP–
alcohols stability constants (chloroform, 25°С, Table 1)
coincided with those measured in benzene at 24°С [5].
Moreover, the published alcohols basicity values [6–9]
are contradictory due to insufficient reliability of
quantitative methods of measuring acid-base properties
of alcohols in liquid state.
In order to explain the unusual trend in the
complexes stability of primary amines, in this work we
determined the stability constants of Zn-TPP com-
plexes with series of amines and alcohols at 283–308 K
and calculated thermodynamic functions of formation
of Zn-TPP complexes with amines (Table 1).
The ΔH0 values were negative in all cases whereas
ΔS0 were positive for many of complexes (except for
those of ammonia and alcohols). Thus, formation of
the Zn-TPP complexes with amine was favored by
both entropy and enthalpy factors. Analysis of kinetic
and thermodynamic parameters of Zn-TPP coordina-
tion with n-alkylamines (Table 1) revealed that the
complexes stability constant K as well as ΔH0 and ΔS0
increased in the series from ammonia to n-butylamine;
in the case of n-pentylamine all three parameters they
decreased but then were increasing again in going from
n-pentylamine to n-octylamine. Further the observed
parameters somewhat decreased; in the cases of C12–
C18 n-alkylamines, the stability constants were close to
those of ethylamine and n-propylamine.
Despite the possible inaccuracy of the data, we
previously found a linear correlation between log K
and ∆λII of alcohols and amines containing the same
substituents (for instance, logKalcohol = 0.685, logKamine
=
–1.78, r = 0.98; ∆λII,alcohol = 1.39∆λII,amine –13.5, r =
0.985) [1].
The observed trends in the changes of K, ΔH0, and
ΔS0 values (Table 1) in the case of Zn-TPP
coordination with amines along with the ligands
Note that the changes of K, ΔH0, and ΔS0 with
increasing alkyl length were somewhat similar in the
320

COMPLEX FORMATION BETWEEN ZINC(II) TETRAPHENYLPORPHYRINATE
321
Table 1. Physicochemical parameters of selected primary alcohol and amine ligands and their complexes with Zn(II)
tetraphenylporphyrinate (chloroform, 25°C)
Ligandа
Ammonia
K, L/mol
1550±25
∆GB, kcal/mol [2] logP [3]
Ip [4]
10.15
8.97
8.86
8.78
8.71
–
∆λII, nm
16.2
16.5
16.8
16.8
16.8
16.8
16.9
16.9
16.9
16.8
16.8
16.7
∆H0, kJ/mol
–21.41±0.23
–19.82±0.22
–13.18±0.31
–12.68±0.28
–11.85±0.51
–13.48±0.37
–13.07±0.13
–12.67±0.41
–8.32±0.28
–12.76±0.34
–12.85±0.6
–18.20±0.03
∆S0, J mol–1 K–1
–11.32±0.83
8.80±0.69
31.1±1.6
0.0
9.1
11.8
13.0
13.5
13.4
13.5
13.6
–
–
Methylamine
Ethylamine
9174±139
10142±142
11125±260
15213±302
13087±369
13335±400
15152±423
21738±808
17200±506
14958±57
10150±150
–0.57
–0.13
0.48
0.86
1.49
2.06
2.57
3.09
3.60
4.1
n-Propylamine
n-Butylamine
n-Pentylamine
n-Hexylamine
n-Heptylamine
n-Octylamine
n-Nonylamine
n-Decylamine
n-Dodecylamine
34.60±1.5
40.00±1.7
33.4±1.6
–
35.0±0.7
–
37.4±1.2
–
54.8±2.4
–
–
38.0±1.2
–
–
36.7±1.9
–
–
–
15.5±0.01
n-Pentadecylamine
n-Octadecylamine
Ethylenediamine
2-Aminoethanol
Methanol
10847±391
11150±235
19750±232
6340±152
7.32±0.21
10.11±0.30
9.14±0.16
10.20±0.23
9.50±0.20
11.7±0.9
–
–
–
–
–
16.7
16.6
17.3
16.3
9.3
–17.95±0.54
–18.34±0.15
–11.52±0.16
–17.3±0.32
–15.14±0.24
–13.54±0.26
–13.63±0.27
–11.79±0.24
–9.14±0.22
–10.3±0.24
–9.51±0.34
15.5±0.7
15.9±0.64
43.5±1.6
15.2±1.0
–35.0±1.4
–26.7±1.2
–27.6±1.4
–20.5±1
–
–
19.0
–
–
–
–0.74
–0.30
0.25
0.84
2.62
3.07
4.02
10.85
10.50
10.15
10.1
–
Ethanol
9.8
Propanol-1
9.8
Butanol-1
9.8
Heptanol-1
9.8
–11.9±0.8
–15.5±1
Octanol-1
–
10.2
9.8
Nonanol-1
9.71±0.20
–
–13.00±2
a
Zn(II) porphyrinate was completely transformed into the complex at 1 : 30000 ratio with alcohols and 1 : 1000 ratio with amines.
Zn–ТPP = 2×10–5 mol/L; stability constants were determined at (600–5000)-fold excess of alcohols and (0.5–10)-fold excess of amines.
c
properties (ionization potential Ip and octanol-water
partition coefficient log P) suggested that at alkyl
substituent shorter than pentyl the inductive effect was
the major factor governing the strength of the N→Zn
donor-acceptor bond. As the σ* constant is almost the
same for the unbranched alkyl groups longer than C3,
further complicated behavior of K, ΔH0, and ΔS0
should be due to additional action of other factors (for
example, solvation effects). The logP values increased
monotonously with the alkyl length (Table 1),
therefore, hydrophobicity could not account for the
observed trends.
The non-uniform change in kinetic and
thermodynamic parameters allowed classification of
the ligands into 4 groups (Fig. 1). The lowest point
corresponded to ammonia (highest Ip, ΔS0 < 0); the
second group consisted of C1, C12, C15, and C18
n-alkylamines; the most numerous group includes C2–7
,
C9, and C10 n-alkylamines; the highest point
(n-octylamine) forms another single-compound group.
The reasons for such distribution are not clear for us,
but the maximum values of K, ΔH0, and ΔS0 in the
case of Zn-TPP complex with n-octylamine are
remarkable.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 2 2014

322
∆S, J mol–1 K–1
ANDREEV et al.
With increasing alkyl length from C4 to C5 another
abnormal change of ΔH0 (from –11.85 to –13.48 kJ/mol)
and of ΔS0 (from 40.0 to 33.4 J mol–1 K–1) were ob-
served; those changes were larger that the experi-
mental error but were less significant that in the case of
n-octylamine. Probably, at that point (C5 alkyl chain)
the increase in n-alkylamine chain length allows close
contact of Zn-TPP π-system with the farther part of the
ligand and the formation of the chelate composition.
Due to some reason (likely, of steric origin) the
increase of the alkyl chain length to C9 or more
destabilized such conformation.
–∆H, kJ/mol
The K, Δλ, ΔH0, ΔS0, and ΔG0 values of Zn-TPP
with ethanol were higher than those in the case of
methanol. With C2–C9 primary alcohols as ligands, no
definite trends in the parameters change were found,
nevertheless, the complex with n-octanol was the most
stable.
Fig. 1. ΔS0 as function of ΔH0 (1) and of log K (2) in the
case of primary amines complex formation with Zn(II)
tetraphenylporphyrinate (chloroform, 25°С).
Spacial structure of Zn-TPP complexes with amines
was studied using that with n-octylamine; results of the
X-ray diffraction studies are collected in Figs. 2 and 3
and in Table 2.
Possibly, in contrast to the micelles and membranes
formed in water by carboxylic acids and lipids, in the
cases of molecular complexes of Zn-TPP with amines
in low-polar aprotic chloroform medium the cyclic
structures can exist with one (polar) donor-acceptor
bond being formed between Zn and the ligand nitrogen
atom whereas the second (non-polar) one is due to
interaction of the Zn-TPP macrocycle aromatic system
and the amine hydrocarbon fragment. The attractive
interactions with alkylamine ligand are possible via the
CH3 group as well as via the (CH2)n part, similarly to
the cases of salts of aromatic and aliphatic acids at the
interphase boundary [10].
As seen in Figs. 2 and 3, the ligand is bound to zinc
atom of Zn-TPP via nitrogen atom; the alkyl part was
located between phenyl rings thus being brought close
to the central part of porphyrin macrocycle of the
neighboring Zn-TPP molecule.
The distances from Zn atom to the porphyrin plane
and to nitrogen of n-octylamine were 0.352 and
2.165 Å, respectively. In the Zn-TPP complexes with
2-phenylethylamine (pKa = 9.83 [1]) and (S)-α-methyl-
benzylamine (pKa = 9.08 [1]) the corresponding
distances were 0.356 and 2.193; 0.211 and 2.256 Å,
respectively (Table 3).
Probability of such cyclic structures is enhanced in
aprotic low-polar solvents and in the gas phase [11].
Aprotic solvent may facilitate formation of cyclic
structures involving the interactions with partially
positively charged acceptor complexes other than
protons, for example, with Zn-TPP. Generally, the
most stable structures are five- and six-membered
cycles. In the studied case. the chelate structure
containing more atoms was likely to form due to
attractive interactions between macrocyclic Zn-TPP π-
system and the suitable part of the alkyl group.
Possibly, in CHCl3 medium without other Zn-TPP
molecules in the close neighborhood the octyl group
could enhance the complex stability due to interaction
with the macrocycle, or even facilitate the favorable
ligand orientation (for example, in reaction with
Pheophorbide A).
To conclude, studies of complex formation between
Zn-TPP and amines or alcohols supported by X-ray
diffraction studies of Zn-TPP complex with n-octyl-
amine have demonstrated that n-octyl group bears some
unique structural features resulting in formation of ex-
tremely stable chelate and/or intermolecular complexes
with porphyrin-containing compounds As compared
with other unbranched primary amines, the n-octyl-
CH2
CH2
CH2
(CH2)3CH3
N
H
ZnТPP
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 2 2014

COMPLEX FORMATION BETWEEN ZINC(II) TETRAPHENYLPORPHYRINATE
323
Fig. 2. Spacial structure of Zn(II) tetraphenylporphyrinate complex with n-octylamine.
Fig. 3. Fragment of crystal packing of Zn(II) porphyrinate complex with n-octylamine. The short intermolecular distance is shown
[С7–H75···C14i (1 + x, 1 + y, 1 + z), 2.82 Å], reflecting the C–H···π interaction between octyl group hydrogen and π-system of Zn(II)
tetraphenylporphyrinate.
amine complex formed with Zn-TPP in chloroform pos-
sessed unusually high ΔS0 value (54.8 J mol–1 K–1) along
with relatively low ΔH0 value (–8.32 kJ/mol) (Table 1).
As future direction of this work, we plan the
investigation of structure of various metal porphy-
rinates complexes with octyl-containing primary,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 2 2014

324
ANDREEV et al.
Table 2. X-ray diffraction data on Zn(II) porphyrinate com-
plex with n-octylamine
Table 3. Bond lengths and bond angles in Zn(II) porphyrinate
complex with n-octylamine
Parameter
Empirical formula
Value
C52H47N5Zn1
807.34
Bond
Zn1–N1
d
Угол
H60N1H61
φ
2.165(8)
105.9
М
Zn1–N2
Zn1–N3
Zn1–N4
Zn1–N5
N1–C1
2.063 (8)
2.070 (6)
2.092 (6)
2.086 (7)
1.46 (2)
Zn1N1C1
Zn1N1H60
Zn1N1H61
H60N1C1
H61N1C1
N1C1C2
128(1)
105.4
105.5
105
Crystal size, mm,
0.15×0.12×0.12
296
Т, K
Crystal system
Triclinic
P1
Space group
105
a, Å
10.6305(2)
10.8344(2)
11.0428(2)
117.2320(10)
103.638(2)
90.870(2)
1087.79(3)
1
b, Å
108(2)
c, Å
α, deg
Gaseous ammonia, methylamine, or ethylamine
(produced by heating of their hydrochlorides with
calcium hydroxide and passed through anhydrous
NaOH and CaCl2) were bubbled through chloroform.
The ligand concentration was determined by back
titration: excess of HCl (0.01 mol/L) was added to
aliquot of the chloroform solution, and the sample was
titrated with NaOH (0.01 mol/L) in the presence of
phenolphthalein. The stability constants of the formed
complexes were determined in mixtures of Zn-TPP
and the ligand solutions corresponding to the
calculated molar ratio of the components.
β, deg
γ, deg
V, Å3
Z
dcalc, g/cm3
1.232
μ
θmax, deg
68
h, k, l ranges
–12.12; –13.10; –8.13
Number of independent reflections
5408
4571
Thermodynamic parameters of the complex
formation were calculated by graphic method
assuming that the ΔH and ΔS values were constant at
288–308 K (283–298 K in the cas of gaseous ligands)
[12]: lnKT = –ΔH0298/RT + ΔS0298/R.
Number of reflections with [I > 2σ(I)]
Number of refined parameters
R(F2)
Rw(F2)
551
0.067
0.17
X-ray diffraction studies were performed using
StadiVari Pilatus 100K STOE diffractometer (CuKα,
equipped with multilayer thin-film ellipsoidal FOX3D
HF Xenocs monochromator). Data collection, deter-
mination and refining of the crystal cell parameters
were performed using STOE X-Area software
package. The main X-ray diffraction parameters are
collected in Table 2. The structural data were
deposited in Cambridge Crystallographic Data Center
(CCDC 912709).
Quality
Δρmax, Δρmin, e/Å3
1.03
0.58, –0.66
secondary, and tertiary amines as well as ethylene-
diamine derivatives in solution and in solid phase by
spectroscopy methods.
EXPERIMENTAL
The amines were distilled over alkali, the alcohols
were dried and distilled over barium oxide. Physical
constants of the purified substances coincided with the
corresponding published data. Electron absorption
spectra were registered using SF-2000-02 spectro-
photometer. Stability constants of Zn(II) tetraphenyl-
porphyrinate complexes were determined as described
in [1].
The structure was solved by the direct method
(SHELXS-97 software [13]). Positions and thermal
parameters of non-hydrogen atoms were refined under
full-matrix approximation. Positions of hydrogen
atoms were calculated and refined under isotropic
approximation applying the rider model. Molecular
structures were prepared using DIAMOND software
[14].
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 2 2014

COMPLEX FORMATION BETWEEN ZINC(II) TETRAPHENYLPORPHYRINATE
325
3. Sangster, J., J. Phys. Chem. Reference Data, 1989,
Zn(II) tetraphenylporphyrinate complex with n-
octylamine. Saturated hot solution of Zn(II) tetra-
phenylporphyrinate in 10 mL of acetone (containing
10 mg, 1.47×10–5 mol of Zn-TPP) was mixed with n-
octylamine (2 mg, 1.55×10–5 mol) solution in chloro-
form. The mixture was left in air in dark place at room
temperature. The precipitated crystals were washed
with acetone (3×2 mL) and dried in air.
vol. 18, no. 3, p. 1111.
4. Vilesov, F.I., Usp. Fiz. Nauk, 1963, vol. 81, no. 4,
p. 669.
5. Nardo, J.V. and Dawson, J.H., Inorganica Chimica
Acta, 1986, vol. 123, p. 9.
6. Lee, D.G. and Demchuc, K.J., Canad. J. Chem., 1987,
vol. 65, no. 8, p. 1769.
ACKNOWLEDGMENTS
7. Bordwell, F.G., Acc. Chem. Res., 1988, vol. 21, p. 456.
8. Bohumir, V., Chemicke Lysty, 1986, vol. 80, no. 9,
X-ray diffraction studies were performed at
Moscow State University in the frame of Agreement
on Collaboration between Chemistry Department of
Moscow State University and Department of Ecology
and Biology of Petrozavodsk State University.
p. 918.
9. Butin, K.P., Ross. Khim. Zh., 2001, vol. 45, no. 2, p. 21.
10. Fridrikhsberg, D.A., Kurs kolloidnoi khimii (Course of
Colloid Chemistry), Leningrad: Khimiya, 1984.
11. Kabachnik, M.I., Russ. Chem. Rev., 1979, vol. 48, no. 9,
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