Synthesis, spectral-luminescent properties, and photostability of Zn(II) complexes with dipyrrins modified by the periphery and meso-spacer

Article abstract of DOI:10.1007/s10593-014-1426-2

A comparative spectral-luminescent characterization was performed for the homoleptic zinc(II) chelates with dipyrrins containing four methyl or aryl substituents in the pyrrole rings and methine group or nitrogen atom as meso-spacer. It was shown that zinc dipyrrinates with substituted pyrrole rings and a methene spacer exhibited an intense fluorescence in nonpolar media. The phenyl-substituted complex had an order of magnitude stronger fluorescence than the methyl-substituted analog. Changing from a methene spacer to a nitrogen atom caused a substantial (up to 64 nm) red shift of the electronic absorption spectrum, and the chelate completely lost its fluorescent properties. The effects of the chelate ligand structure on the photostability of zinc(II) complexes were established.

Full text of DOI:10.1007/s10593-014-1426-2

Chemistry of Heterocyclic Compounds, Vol. 49, No. 12, March, 2014 (Russian Original Vol. 49, No. 12, December, 2013)
SYNTHESIS, SPECTRAL-LUMINESCENT PROPERTIES,
AND PHOTOSTABILITY OF Zn(II) COMPLEXES WITH
DIPYRRINS MODIFIED BY THE PERIPHERY AND meso-SPACER
1
2
1
1
1
*
N. A. Dudina , A. Yu. Nikonova , Ye. V. Antina , M. B. Berezin , and A. I. Vyugin
A comparative spectral-luminescent characterization was performed for the homoleptic zinc(II) chelates
with dipyrrins containing four methyl or aryl substituents in the pyrrole rings and methine group or
nitrogen atom as meso-spacer. It was shown that zinc dipyrrinates with substituted pyrrole rings and a
methene spacer exhibited an intense fluorescence in nonpolar media. The phenyl-substituted complex
had an order of magnitude stronger fluorescence than the methyl-substituted analog. Changing from a
methene spacer to a nitrogen atom caused a substantial (up to 64 nm) red shift of the electronic
absorption spectrum, and the chelate completely lost its fluorescent properties. The effects of the chelate
ligand structure on the photostability of zinc(II) complexes were established.
Keywords: azadipyrrin, complex, dipyrrin, zinc, photostability, spectral-luminescent properties.
Dipyrrins (dipyrrolylmethenes) are the simplest representatives of chromophores with an open-chain
oligopyrrole structure. The stable covalent complexes of these compounds with cations of p-, d-, and f-elements
are effective visible-light chromophores (ε > 105 l·mol-1·cm–1, λmax ≥ 450 nm) [1-5]. The intensity of d-element
dipyrrinates fluorescence is often comparable to that of boron dipyrrinates (BODIPY), which are the most
promising luminophores among those with such ligands. In comparison to BODIPY, the dipyrrin complexes of
d-elements offer the advantages of easy self-assembly with the complex-forming metal ions under mild
conditions both in solutions and in biological systems, and a high sensitivity of the spectral-luminescent
properties even to the slightest changes of the chromophore structure and the medium (polarity, viscosity, pH,
etc.), which enables the use of these compounds as fluorescent probes.
While the spectral-luminescent properties of BODIPY have been relatively well investigated [6, 7], the
effects of dipyrrin metal complex structure on the chromophore characteristics and luminescent
properties remain little known and without practical applications. A possible reason for this is the low
fluorescence of most dipyrrinates that have been previously synthesized and tested, and which typically
_______
*To whom correspondence should be addressed, e-mail: nad@isc-ras.ru.
1G.A. Krestov Institute of Solution Chemistry, the Russian Academy of Sciences, 1 Akademicheskaya St.,
Ivanovo 153045, Russia.
2Ivanovo State University of Chemistry and Technology, 7 Sheremetevsky Ave., Ivanovo 153000, Russia;
rediska93@inbox.ru.
_________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1878-1886, December, 2013.
Original article submitted September 23, 2013.
1740
0009-3122/14/4912-1740©2014 Springer Science+Business Media New York

contained a phenyl group in the meso-spacer. The rotation of this phenyl group was found to quench
fluorescence [8-10]. A subsequent modification of the ligand structure enabled the preparation of the first
effective fluorophores among zinc(II) dipyrrinates.
An important current task in this field is the search for methods of influencing the spectral-luminescent
properties and photostability of dipyrrinate through the modification of peripheral substituents and the meso-
spacer structure. Our work was focused on establishing the spectral-luminescent and photostability effects
caused by periferal methyl and phenyl substituents, as well as resulting from changing the methene spacer of the
dipyrrin ligand to an aza spacer. The investigated zinc(II) complexes [ZnL2] had the following ligands: 2-[(3,5-
dimethyl-2Н-pyrrol-2-ylidene)methyl]-3,5-dimethyl-1Н-pyrrole (1), 2-[(3,5-diphenyl-2Н-pyrrol-2-yl-idene)-
methyl]-3,5-diphenyl-1Н-pyrrole (2) and N-(3,5-diphenyl-2Н-pyrrol-2-ylidene)-3,5-diphenyl-1Н-pyrrol-2-
amine (3).
R
R
X
N
N
N
R
R
Zn
R
R
N
X
R
R
1–3
1 X = CH, R = Me; 2 X = CH, R = Ph; 3 X = N, R = Ph
The electronic absorption spectra (EAS) of the complexes 1-3 were quite different from each other, both
in the number of bands caused by electronic transitions SoSn, as well as the absorption wavelengths (Fig. 1,
Table 1). The complex 2 with a phenyl-substituted dipyrrin was obtained for the first time, while the electronic
absorption spectra of the chelates 1 and 3 were previously described only in one solvent [11, 12], and no
detailed testing of luminescent properties was performed. We should note that the value and direction of the
auxochromic effect was determined by the wavelength change of the strongest absorption band of dipyrrin and its
complex, and it was highly structure-dependent.
In the case of the zinc(II) complex with 3,3',5,5'-tetramethyl-2,2'-dipyrrolylmethene, similarly to most
of the other alkyl-substituted dipyrrolylmethenes [13], the auxochromic effect was manifested in the spectrum
of the complex as a bathochromic shift (~20 nm) of the intense absorption band compared to the ligand
spectrum. The opposite direction of the auxochromic effect was observed for the complexes formed with the
phenyl-substituted dipyrrin and azadipyrrin, which gave a clearly different EAS from those of the alkyl-
substituted dipyrrinates. The solutions of all three complexes 1, 2, and 3 gave EAS exhibiting one high-intensity
abs
band with the maximum (
) in the range of 485-490, 525-532, and 586-595 nm, as well as a broad low-
max
intensity band at 350-367, 391-414, and 470-500 nm, respectively. Unlike the complex 1, the phenyl-
substituted dipyrrinate 2 and the azadipyrrinate 3 had EAS (Fig. 1, Table 1) with an additional shoulder at the
long wavelength side of the intense absorption band (at 572-575 and 650-652 nm, respectively) and distinct
intense UV absorption bands at 286-293 and 301-306 nm, respectively.
The examination of spectral changes during the formation of the tetraphenyl-substituted azadipyrrin
zinc(II) complex 3 in tetrahydrofuran showed that the characteristic ligand absorption band with the maximum
at 596 nm (log ε = 4.66) underwent a slight hypsochromic shift to 591 nm, while the intensity was doubled to
abs
log ε = 4.93. At the same time, a shoulder appeared on its long wavelength side (
= 640 nm, log ε = 4.76),
max
caused by the corresponding transition SоSn [12]. A similar spectral change was observed also
1741

Fig. 1. The electronic absorption spectra of zinc(II) complexes 1-3 in cyclohexane, where А is absorbance in
arbitrary units.
during the formation of the phenyl-substituted dipyrrin analog, the chelate 2. It must be noted that a change from
methyl groups (complex 1) to phenyl groups (complex 2) resulted in a considerable red shift in the EAS: depending
on the organic solvent type, the maximum of the intense band was shifted by 39-45 nm, while the extinction
coefficient was significanty decreased (1.5-2 times) (Fig. 1, Table 1). The dipyrrin having an aza group in the
meso-spacer exhibited an even greater bathochromic shift of the chelate 3 absorption maximum (by 59-64 nm),
compared to the EAS of the complex 2 with a similar peripheral substitution pattern (Fig. 1, Table 1).
Fig. 2. Fluorescence spectra of zinc(II) complexes 1, 2 in cyclohexane,
where I is fluorescence intensity in arbitrary units.
The EAS of the complexes 1 and 3 exhibited significant solvatochromic effects upon changing from
polar to nonpolar solvents. While the general character of the spectrum did not change (Table 1), in nonpolar
media the absorption maximum in the spectrum of the complex 1 was redshifted by up to 4 nm, but that of the
complex 3 was blueshifted by up to 8 nm. There was no solvatochromic effect found for the complex 2 with the
solvents used in the study.
The complexes 1 and 2, when dissolved in organic solvents, each exhibited one fluorescence band with
the maximum at 497-503 nm or 607-614 nm, respectively (Fig. 2, Table 2), which mirrored the most intense
absorption bands of these compounds.
1742

TABLE 1. The EAS of Zinc(II) Complexes 1-3 in Organic Solvents
abs
max

, nm (log ε)
Solvent
1
2
3
С6Н12
С6Н14
PhH
488 (5.18), 465 (4.90) sh,
352–358 (3.97)
487 (5.05), 464 (4.78) sh,
353–361 (3.95)
490 (5.11), 465 (4.82) sh,
351–367 (3.88)
490 (5.09), 465 (4.78) sh,
358–365 (3.90)
574 (4.74) sh, 528 (4.94),
394-410 (3.93), 289 (4.77)
573 sh, 526, 398-410, 288
652 (4.66) sh, 587 (4.90),
470-495 (4.01), 302 (4.81)
―
575 (4.71) sh, 532 (4.88),
396-410 (3.83), 293 (4.67)
575 (4.73) sh, 532 (4.91),
394-410 (3.90), 293 (4.72)
574 (4.70) sh, 529 (4.88),
391-409 (3.79), 293 (4.66)
573 sh, 526, 388-410, 288
652 (4.76) sh, 591 (4.95),
486-500 (4.11), 305 (4.82)
651 (4.71) sh, 590 (4.92),
478-494 (4.04), 306 (4.79)
650 (4.71) sh, 590 (4.91),
480-495 (4.02), 306 (4.81)
651 sh, 588, 475-495, 302
PhMe
CHCl3
488 (5.08), 464 (4.80) sh,
354–367 (3.81)
1-PrOH 487 (5.05), 464 (4.77) sh,
355–365 (3.92)
EtOH
DMF
485, 464 sh, 350–367
486 (5.05), 464 (4.77) sh,
354-366 (3.84)
572 sh, 525, 398-414, 286
574 (4.73) sh, 531 (4.91),
385-408 (3.94), 291 (4.73)
651 sh, 586, 480-498, 301
652 (4.74) sh, 595 (4.91),
480-494 (3.81), 303 (4.80)
TABLE 2. The Fluorescence Characteristics of Zinc(II) Complexes 1, 2 in
Organic Solvents*
fl
max
Δλst, nm Δνst, cm-1 fl (λex, nm)
k
rad ·10-8, s-1
τ, ns

Complex
Solvent
, nm
С6Н12
С6Н14
PhH
PhMe
CHCl3
1-PrOH
EtOH
DMF
С6H12
С6H14
PhH
PhMe
CHCl3
1-PrOH
EtOH
DMF
501
13
14
13
13
13
12
12
―
34
34
40
39
36
34
35
36
532
574
527
527
532
494
498
―
0.024 (475)
0.018 (475)
0.028 (475)
0.031 (475)
0.001 (475)
0.001 (475)
0.001 (475)
―
2.47
2.00
2.10
1.97
2.18
2.29
―
0.097
0.090
0.134
0.157
0.005
0.004
―
1
501
503
503
501
499
497
―
―
―
608
607
615
614
610
607
607
610
975
977
1131
1104
1029
977
1008
1029
0.331 (510)
0.115 (505)
0.157 (510)
0.138 (510)
0.043 (510)
0.011 (505)
0.007 (510)
0.003 (510)
1.64
―
2.025
―
2
1.50
1.60
1.49
―
1.047
0.864
0.289
―
―
―
1.52
0.020
_______
fl
*
– the wavelength of the maximum in the fluorescence spectra; Δλst
max
and Δνst – Stokes shift; λex – excitation wavelength; krad – radiative rate
constant (the rate constant of the radiative process).
The Stokes shift value (Δλst) in the solvents used was found to be 12-14 nm for the complex 1 and nearly 3
times higher (Δλst = 34-40 nm) for the phenyl-substituted dipyrrinate 2, which had a higher fluorescence
intensity than the complexes 1 and 3. The highest fluorescence quantum yield for the dipyrrinate 2 (fl = 0.33)
was observed in cyclohexane. The fl value was 14 times lower in the same medium for the methyl-substituted
complex 1. The azadipyrrinate 3 completely lacked fluorescence regardless of the nature of the solvent. The
fluorescent excited state half-life (τ) depended on the solvent, and in the case of the complexes 1 and 2 it was in
1743

the range of 0.004-0.157 and 0.020-2.025 ns, respectively (Table 2). In general, the fluorescent properties,
Stokes shift values, quantum yields, and excited state half-lives increased in the series 3 < 1 < 2.
Fig. 3. The dependence of fluorescence quantum yield (fl) of the complexes 1 and 2
on the function of the universal intermolecular interactions (Δf). Solvents: 1 – cyclohexane,
2 – benzene, 3 – toluene, 4 – hexane, 5 – chloroform, 6 – 1-propanol, 7 – ethanol, 8 – DMF.
The Stokes shift value (Δλst) in the solvents used was found to be 12-14 nm for the complex 1 and nearly 3
times higher (Δλst = 34-40 nm) for the phenyl-substituted dipyrrinate 2, which had a higher fluorescence
intensity than the complexes 1 and 3. The highest fluorescence quantum yield for the dipyrrinate 2 (fl = 0.33)
was observed in cyclohexane. The fl value was 14 times lower in the same medium for the methyl-substituted
complex 1. The azadipyrrinate 3 completely lacked fluorescence regardless of the nature of the solvent. The
fluorescent excited state half-life (τ) depended on the solvent, and in the case of the complexes 1 and 2 it was in
the range of 0.004-0.157 and 0.020-2.025 ns, respectively (Table 2). In general, the fluorescent properties,
Stokes shift values, quantum yields, and excited state half-lives increased in the series 3 < 1 < 2.
A comparative analysis of the fluorescence data for the chelates 1 and 2 in various solvents showed that
a higher polarity of the medium resulted in significantly lower values of fl (Fig. 3, Table 2).
In the case of the methyl-substituted dipyrrinate 1, the highest values of fl = 0.018–0.031 were obtained
in nonpolar saturated or aromatic solvents, while in polar or even weakly polar solvents (e.g., chloroform) the
fluorescence was almost completely quenched (fl = 0–0.001). The complex 2 produced a better correlation of
the fl values with function of the universal intermolecular interactions (Δf). The weak fluorescence in polar
electron- or proton-donating media was caused by the high probability of non-radiative deactivation of the
excited state, due to specific interactions in the solvation shell. The specific nature of these interactions was
confirmed by the non-linear dependence of the Stokes shift values on the function of the universal intermolecular
interactions as the solvent polarizability parameter (Fig. 4) [14, p. 211].
As demonstrated before, the thermal analysis of stable solvates of dipyrrin zinc(II) complexes indicated
that the specific solvation in electron-donating solvents (DMF, pyridine, etc.) was caused by zinc coordination
with additional solvent molecules, involving a change in the coordination geometry from a deformed
tetrahedron to a deformed octahedron [15]. The additional coordination in alcohols could be mediated by donor-
acceptor interactions between the hydroxyl oxygen and metal, as well as the hydroxyl hydrogen and nitrogen.
The fluorescence in chloroform may have been quenched through interactions between the solvent hydrogen
atoms and the nitrogen atoms of the ligand pyrrole rings. Besides, the fluorescence of the phenyl-substituted
complex 2 was quenched by more than a half in aromatic solvents: in benzene fl = 0.157 and in toluene
fl = 0.138, compared to a saturated hydrocarbon solvent, cyclohexane (Table 2), due to the enhanced π–π
stacking interactions with the aromatic rings in the excited chromophore.
1744

Fig. 4. The dependence of the Stokes shift (Δνst) on the function of the universal intermolecular interactions (Δf)
for the complexes а) 1 and b) 2. Solvents: 1 – cyclohexane, 2 – benzene, 3 – toluene, 4 – hexane, 5 – chloroform,
6 – 1-propanol, 7 – ethanol, 8 – DMF.
Photostability is one of the most important properties of chromophores. The effects of UV irradiation on
the EAS of the phenyl-substituted dipyrrinate 2 in cyclohexane are presented in Fig. 5.
The photodegradation of the complexes 1-3 was accompanied by a decreased absorption at the
characteristic visible and near-UV ranges (230-720 nm), and an increased absorption at the shorter UV
wavelengths (210-230 nm), characteristic of the photodegradation products – oligopyrroles and their phenyl-
substituted photoproducts: aromatic pyrrole derivatives, dipyrrolylmethane, and benzene [16]. The photo-
degradation half-life, as calculated by the loss of optical density at the characteristic EAS band maximum,
significantly increased in the series of complexes 3, 1, and 2 (τ1/2 = 6, 76, and 475 min, respectively), i.e., the
photostability of the zinc (II) complex with tetraphenyl-substituted dipyrrinate (compound 2) was more than 6
times higher than the photostability of its methyl-substituted analog 1, and 80 times higher than the
photostability of the aza analog 3.
Fig. 5. The changes in а) electronic spectra and b) relative absorbance of the complex
2 (с = 1 · 10-5 mol/l) in cyclohexane under UV irradiation.
The obtained results provided a preliminary roadmap to the design of zinc(II) dipyrrinates with the
spectral-luminescent properties required of chromophore and luminophore tags, laser dyes, sensors, etc. Thus,
changing the pyrrole ring substituents in the dipyrrin ligand from alkyl groups to aryl groups resulted in a
substantial (6-fold) increase of photostability, a significant red shift (by up to 45 nm) of the electronic
absorption and emission spectra, 10-40-fold improvement of quantum yields, 5-10 times longer half-life and
sensitivity of chelate fluorescence to the nature of solvating environment. Switching from the tetraphenyl-
substituted dipyrrin structure to the analogous azadipyrrin structure gave a substantial (up to 64 nm) red shift of
EAS towards the spectral window suitable for phototherapy, but completely quenched the fluorescence and
sharply decreased the photostability of zinc(II) azadipyrrinate.
1745

EXPERIMENTAL
Electronic absorption and fluorescence spectra for solutions of the complexes 1-3 were recorded on an
Akvilon SF 103 spectrophotometer (Russia) and a SOLAR SM 2203 spectrofluorimeter (Belarus) in the UV-Vis
range of 200-750 nm. Quartz cuvettes with the absorbing layer optical path length (l) of 1 and 10 mm were used
with ~10-7-10-5 mol/l concentrations of the investigated complexes in organic solvents. The standard for
determination of fl was an ethanol solution of Rhodamine 6G (fl 0.94) [17]. The fluorescence spectra were all
recorded under the same conditions when the optical density at the excitation wavelength did not exceed 0.1 [14,
p. 143]. The fluorescence half-life () was estimated, based on the spectral and luminescence characteristics [18, 19].
According to  = krad/(krad + kd) and  = 1/(krad + kd), the fluorescence half-life () was determined as  =  / krad,
where kd – the rate of non-radiative processes, krad – radiative rate constant (the rate of radiative processes),
which was estimated according to [14, p. 19; 18] from the characteristics of EAS by the formula krad = 2.9·10-9
[(9nD )/(nD +2)2]·max2·max·1/2, where nD – the solvent refractive index,  – wavenumber (cm-1), 1/2 – half-
width of the absorption band (cm-1),  – extinction coefficient at the absorption band. The value of  was
determined with a 10-15% accuracy.
2
2
The Stokes shift was determined as the difference between the wavelengths of maxima in the
fluorescence and absorption spectra:
fl
max
abs
max
fl
max
abs
max
and st (cm-1) =
-
.




Δλ (nm) =
-
The function of the universal intermolecular interactions (Δf) was calculated according to the Lippert–
Mataga equation [14, p. 211]:
 1
2 1
nD2 1


,
f 





2nD2 1
where ε – dielectric permittivity and nD – refractive index of the medium.
The photostability of the complexes was investigated by irradiation with an OUFK-01 quartz UV lamp
(230-400 nm wavelength). The ~1·10-5 mol/l cyclohexane solutions of the complexes 1-3 were irradiated in
10 mm quartz cuvettes at a 3 cm distance from the UV source with the power density of 1.0 W/m2.
1Н NMR spectra were acquired on a Bruker 500 instrument (500 MHz) in CDCl3 solutions, and TMS
was used as internal standard. Elemental analysis was performed on a Flash EA 1112 apparatus. The organic
solvents (benzene, toluene, hexane, chloroform, ethanol, DMF) were purified to the "chemically pure" grade
according to standard methods. The water content in these solvents was determined by Karl Fischer titration and
did not exceed 0.02%. Cyclohexane (Panreac) and 1-propanol (UV-IR-HPLC-HPLC preparative, PAI) were used
without additional purification.
The 2-[(3,5-dimethyl-2Н-pyrrol-2-ylidene)methyl]-3,5-dimethyl-1Н-pyrrole hydrobromide was
prepared by an updated method [20].
Zinc(II) Complex with 2-[(3,5-Dimethyl-2Н-pyrrol-2-ylidene)methyl]-3,5-dimethyl-1Н-pyrrole (1).
2-[(3,5-Dimethyl-2Н-pyrrol-2-ylidene)methyl]-3,5-dimethyl-1Н-pyrrole hydrobromide (0.115 g, 0.407 mmol)
was dissolved in methanol (5 ml) with heating and stirring. Triethylamine (0.041 g, 0.405 mmol) was added,
followed by a solution of Zn(OAc)2·2Н2О (0.178 g, 0.814 mmol) in methanol (3 ml). The solution was refluxed
for 1 h. Then the mixture was cooled, the precipitated complex was filtered off, washed with hot water,
1
methanol, ether, and air-dried. Yield 0.090 g (69%). H NMR spectrum, δ, ppm: 1.96 (12H, s, 4CH3); 2.34
(12H, s, 4CH3); 6.01 (4H, s, pyrrole CH); 7.04 (2H, s, –CH=). Found, %: С 67.05; Н 6.48; N 12.02.
C26H30N4Zn. Calculated, %: С 67.32; Н 6.52; N 12.08.
Zinc(II) Complex with 2-[(3,5-Diphenyl-2Н-pyrrol-2-ylidene)methyl]-3,5-diphenyl-1Н-pyrrole (2).
2-[(3,5-Diphenyl-2Н-pyrrol-2-ylidene)methyl]-3,5-diphenyl-1Н-pyrrole (0.144 g, 0.321 mmol) was dissolved in
1-butanol (10 ml) and mixed with a solution of Zn(OAc)2·2H2O (0.06 g, 0.273 mmol) in 1-butanol (6 ml), and
the mixture was refluxed for 1 hour. The mixture was then cooled, the precipitate was filtered off, washed with
hot water, and air-dried. The crude product was dissolved in dichloromethane and purified by silica gel
chromatography with CH2Cl2 as the eluent. The eluate was concentrated by evaporation, and the product was
1746

1
precipitated with methanol at low temperature. Yield 0.150 g (95%). H NMR spectrum, δ, ppm : 6.45 (4H, s,
pyrrole CH); 7.10 (2H, s, –CH=); 7.46-7.50 (40H, m, H Ph). Found, %: С 82.17; Н 4.48; N 5.65. C66H46N4Zn.
Calculated, %: С 82.53; Н 4.83; N 5.83.
Zinc(II) Complex with N-(3,5-Diphenyl-2Н-pyrrol-2-ylidene)-3,5-diphenyl-1Н-pyrrol-2-amine (3).
A solution of Zn(OAc)2·2H2O (0.1 g, 0.460 mmol) in THF (10 ml) was added to a solution of N-(3,5-di-phenyl-
2Н-pyrrol-2-ylidene)-3,5-diphenyl-1Н-pyrrol-2-amine (0.3 g, 0.667 mmol) in THF (10 ml) and stirred for 24 h
at room temperature. The solvent was evaporated to dryness, the residue was dissolved in dichloromethane and
purified by silica gel chromatography, with CH2Cl2 as the eluent. The eluate was concentrated by evaporation,
and the product was precipitated with methanol. Yield 0.234 g (73%). 1H NMR spectrum, δ, ppm : 6.73 (4H, s,
pyrrole CH); 7.51-7.52 (20H, m, Н Ph); 7.87-7.89 (20H, m, Н Ph). Found, %: С 79.54; Н 4.27; N 8.53.
C64H44N6Zn. Calculated, %: С 79.87; Н 4.61; N 8.73.
The authors are grateful to Professor, Dr. A. S. Semeikin (Ivanovo State University of Chemistry and
Technology) for the contribution of ligands: 2-[(3,5-diphenyl-2Н-pyrrol-2-ylidene)methyl]-3,5-diphenyl-
1Н-pyrrole and N-(3,5-diphenyl-2Н-pyrrol-2-ylidene)-3,5-diphenyl-1Н-pyrrol-2-amine, the synthesis of which will
be published separately.
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