Influence of bulky pyrrolyl substitent on the physicochemical properties of porphyrazines

Article abstract of DOI:10.1016/j.dyepig.2014.06.033

The synthesis and characterization of porphyrazines possessing 2,5-diphenylpyrrol-1-yl and dimethylamino peripheral groups and their precursors are shown. Bulky pyrrolyl substituents influenced the physicochemical properties and solid-state structure of novel porphyrazines and did not hamper the formation of the porphyrazine associates in solution and solid-state. Occurrence of centrosymmetric dimers in single crystal X-ray structure of magnesium(II) porphyrazine with Mg?Mg distance of ca. 11.2 ?, impacted by interdigitation of the phenyl substituents, was noticed. In addition, an iron(II) porphyrazine derivative was investigated. The importance of M?ssbauer spectroscopy in the assessment of valence and spin state of the iron ion inside the core of the iron(II) porphyrazine is shown.

Full text of DOI:10.1016/j.dyepig.2014.06.033

Dyes and Pigments 112 (2015) 138e144
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Influence of bulky pyrrolyl substitent on the physicochemical
properties of porphyrazines
Tomasz Koczorowski a, Wojciech Szczolko a, Kvetoslava Burda b, Magdalena Nowak a,
Malgorzata Dawidowska a, Anna Teubert c, Lukasz Sobotta d, Maria Gdaniec e,
,
, *
Jozef Korecki b, Jadwiga Mielcarek d, Ewa Tykarska a *, Tomasz Goslinski a
a Department of Chemical Technology of Drugs, Poznan University of Medical Sciences, Grunwaldzka 6, 60-780 Poznan, Poland
b AGH University of Science and Technology in Krakow, Faculty of Physics and Applied Computer Science, Al. Mickiewicza 30, 30-059 Krakow, Poland
c Institute of Bioorganic Chemistry, Polish Academy of Sciences, Z. Noskowskiego 12, 61-704 Poznan, Poland
d Department of Inorganic and Analytical Chemistry, Poznan University of Medical Sciences, Grunwaldzka 6, 60-780 Poznan, Poland
e Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznan, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and characterization of porphyrazines possessing 2,5ediphenylpyrrol-1-yl and dimethy-
lamino peripheral groups and their precursors are shown. Bulky pyrrolyl substituents influenced the
physicochemical properties and solid-state structure of novel porphyrazines and did not hamper the
formation of the porphyrazine associates in solution and solid-state. Occurrence of centrosymmetric
dimers in single crystal X-ray structure of magnesium(II) porphyrazine with Mg/Mg distance of ca.
11.2 Å, impacted by interdigitation of the phenyl substituents, was noticed. In addition, an iron(II) por-
Received 16 April 2014
Received in revised form
25 June 2014
Accepted 27 June 2014
Available online 7 July 2014
€
phyrazine derivative was investigated. The importance of Mossbauer spectroscopy in the assessment of
Keywords:
valence and spin state of the iron ion inside the core of the iron(II) porphyrazine is shown.
Macrocyclization
Porphyrazine
Crystal structure
© 2014 Elsevier Ltd. All rights reserved.
€
Mossbauer spectroscopy
Iron valence and spin states
Dimers
1. Introduction
1-yl, and 2,5-dithienylpyrrol-1-yl originate from our group [12e15].
Below we describe the synthesis of novel hybrid molecules that have
Porphyrazine (Pz) macrocycles, due to their special photo-
chemical and electrochemical properties, have proved their poten-
tial for diverse medical (photosensitizers) and technological
applications (catalysts, sensors). Pzs can be modified by the ex-
change of the metal cation inside the core or by peripheral modifi-
properties beyond the sum of the Pz macrocycles and
2,5ediphenylpyrrol-1-yl fragments. These include the formation of
centrosymmetric dimeric associates of magnesium(II) Pz molecules
by interdigitation of their bulky substituents, as observed in the
crystal. Bulky pyrrolyl substituents on the periphery of iron(II) Pz
influence its physicochemical properties, which was confirmed by
cations in their
b positions with aliphatic, aryl, sulfur, oxygen and
€
nitrogen residues [1e5]. Some Pzs have demonstrated a strong af-
Mossbauer spectroscopy.
finity towards metal ions, including Fe2þ/3þ [5,6]. Iron Pzs have been
2. Experimental section
considered
Although, Pzs possessing
a
potential catalyst in oxidation reactions [7,8].
-substituted, fused, heterocyclic rings
b,b
2.1. General procedures
have been widely studied [9,10], there has been only limited data on
those modified by peripheral 5-membered ring heteroaromatic
group attachment. One of the examples is a two-core Pz reported by
Luo et al. [11], that is substituted with trimethyl-3-thienyl groups on
its periphery. The other Pzs bearing peripheral 2,5-dimethylpyrrol-
All reactions were conducted in oven dried glassware under
argon. All solvents were rotary evaporated at or below 50 ꢀC. Re-
action temperatures reported refer to external bath temperatures.
Methanol, tetrahydrofurane and dichloromethane were distilled.
Other solvents and all reagents were obtained from commercial
suppliers and used without further purification unless otherwise
stated. Melting points were obtained on a “Stuart” Bibby apparatus
* Corresponding authors. Tel.: þ48 61 854 66 31.
E-mail addresses: etykarsk@ump.edu.pl (E. Tykarska), tomasz.goslinski@ump.
edu.pl (T. Goslinski).
http://dx.doi.org/10.1016/j.dyepig.2014.06.033
0143-7208/© 2014 Elsevier Ltd. All rights reserved.

T. Koczorowski et al. / Dyes and Pigments 112 (2015) 138e144
139
and are uncorrected. Dry flash column chromatography was carried
out on Merck silica gel 60, particle size 40e63 m. Thin layer
experimental spectra by use of Recoil software [19]. Values of iso-
mer shifts are given relative to -Fe at 295 K.
m
a
chromatography (TLC) was performed on silica gel Merck Kieselgel
60 F254 plates and visualized with UV (lmax 254 or 365 nm). UVeVis
spectra were recorded on a Hitachi UVeVis U-1900 spectrometer;
lmax (logε), nm. Elemental analysis and mass spectra (ES, MALDI
TOF) were carried out by the Advanced Chemical Equipment
and Instrumentation Facility at the Faculty of Chemistry, Adam
Mickiewicz University in Poznan. HRMS (ESI) spectra were detected
on a Thermo QExactive with the ESI source at the European Center
of Bioinformatics and Genomics in Poznan.
2.5. Synthetic procedures of 2e6
2.5.1. 2-Amino-3-(2,5-diphenyl-1H-pyrrolyl)-(2Z)-butene-1,4-
dinitrile (2)
A known compound 2 was synthesized by modifying Begland's
procedure [20]: The suspension of DAMN (462 mg, 4.28 mmol) (1),
1,2-dibenzoylethane (1.02 g, 4.82 mmol), catalytic amount of TFA
(200 mL) and methanol (50 mL) was mixed under reflux for 24 h.
After cooling to room temperature, the solvent was evaporated
using a rotavapory vacuum evaporator to dryness and purified by
column chromatography (CH2Cl2) to give small yellow crystals of
the desired compound (1.07 g, 80% yield).
2.2. Single crystal X-ray structure determination
Single, prism like yellow crystals of maleonitrile 3 and dark blue
plates of magnesium porphyrazine 4a were grown at room tem-
perature by slow evaporation method from CH2Cl2/n-hexane (1:1)
and EtOH/CHCl3/n-PrOH (1:1:0.1) solutions, respectively. The
diffraction intensity data were collected with an Oxford Diffraction
2.5.2. 2-Dimethylamino-3-(2,5-diphenyl-1H-pyrrolyl)-(2Z)-
butene-1,4-dinitrile (3)
Sodium hydride (60% dispersion in mineral oil; 45 mg,
1.13 mmol) was suspended in THF (10 mL) at (ꢁ17 ꢀC). Next 2-
amino-3-(2,5-diphenyl-1H-pyrrolyl)-(2Z)-butene-1,4-dinitrile (2)
(160 mg, 0.52 mmol) in THF (2 mL) was added and stirred 30 min at
Xcalibur Eos diffractometer using graphite-monochromated MoK
a
radiation. The structures were processed with the CrysAlis Pro
software [16], solved by direct methods with SIR2004 [17], and
refined by full matrix least-squares based on F2 by SHELXL-97 [18]
program. The hydrogen atoms attached to the C atoms were located
at geometrically calculated positions and refined in the riding mode
with isotropic temperature factors fixed at 1.2(Ueq) of the parent
atoms (1.5 for methyl groups). Non-hydrogen atoms in 3 were
refined anisotropically, except for the five atoms of the disordered
benzene ring having minor occupancy of ca. 12% (Fig. S1,
Supplementary data). Crystals of 4a were poorly diffracting and
the number of observed reflections did not allow for anisotropic
refinement of non-hydrogen atoms. The highest peaks on the
difference-Fourier map in the disordered part of the crystal were
identified as propanol and two water solvent molecules and
included in the final refinement with partial occupancy. The
hydrogen atoms of the propanol OeH groups were located in
electron density difference maps and their OeH distances stan-
dardized to 0.84 Å. In the final refinement cycles OeH group
hydrogen atoms were treated as riding on their parent atoms with
Uiso(H) ¼ 1.2 Ueq(O). In case of water molecules, hydrogen-atom
positions were not determined. A summary of the structure
determination of 3 (CCDC 986312) and 4a (CCDC 986311) is given in
Supplementary data. The asymmetric unit and atom labeling
scheme for 3 are shown in Figures S1, S2 (Supplementary data), and
for 4a e in Fig. S3 (Supplementary data).
temperature (ꢁ15 ꢀC). After that (CH3O)2SO2 (99
mL, 1.04 mmol)
was added dropwise to the reaction mixture for 30 min at (ꢁ10 ꢀC)
and stirred at room temperature for 20 h. The reaction was carefully
quenched by adding water (2 mL) and the reaction mixture was
poured into ice-water mixture (100 mL). The resulting yellow
precipitate was isolated by filtration to give 3 (160 mg, 91% yield).
The crude material was crystalized (CH2Cl2-n-hexane) to give light
yellow crystals: mp 105e107 ꢀC. Rf (CH2Cl2) 0.65. UVeVis (CH2Cl2):
lmax, nm (logε) 300 (4.39). 1H NMR (400 MHz; CDCl3): dH, ppm 2.49
(s, 6H, N(CH3)2), 6.41 (s, 2H, pyrrole-H), 7.38 (t, 3J ¼ 8 Hz, 2H, C6H5),
7.46 (t, 3J ¼ 8 Hz, 4H, C6H5), 7.52e7.55 (m, 4H, C6H5). 13C NMR
(100 MHz, CDCl3): dC, ppm 41.00 (N(CH3)2), 91.79, 111.05, 112.19,
118.61, 128.10, 128.42, 128.92, 131.91, 138.75. MS (ES neg): m/z 323
[MꢁCH3]-. MS (ES pos) 339 [MþH]þ, 361 [MþNa]þ, 378 [MþK]þ.
Anal. Calc. for C22H18N4: C, 78.08%; H, 5.36%; N, 16.56%. Found: C,
78.04%; H, 5.44%; N, 16.73%.
2.5.3. [2,7,12,17-Tetrakis(dimethylamino)-3,8,13,18-tetrakis(2,5-
diphenyl-1H-pyrrolyl)-porphyrazinato]magnesium(II) (4a) and
[2,7,12,18-tetrakis(dimethylamino)-3,8,13,17-tetrakis(2,5-diphenyl-
1H-pyrrolyl)porphyrazinato]magnesium(II) (4b)
Mg turnings (53 mg, 2.16 mmol), a crystal of I2, and 1-butanol
(25 mL) were heated under reflux for 6 h. After the mixture was
cooled to room temperature, maleonitrile derivative 3 (491 mg,
1.44 mmol) was added to the reaction mixture and heated under
reflux for 20 h. After cooling to room temperature, the dark green
mixture was filtered through Celite and evaporated. Chromatog-
raphy (CH2Cl2:CH3OH, 50:1; n-hexane:EtOAc, 7:3; n-hex-
ane:CH2Cl2:CH3OH, 7:1:1) was performed to give two products: 4a
(90 mg, 18% yield) as a dark green solid: mp > 300 ꢀC. Rf (n-hex-
ane:EtOAc 7:5) 0.83, UVeVis (CH2Cl2): lmax, nm (logε) 302 (3.74),
730 (3.48), 817 (2.96). 1H NMR (400 MHz; pyridine-d5): dH, ppm
3.26 (s, 24H, N(CH3)2), 6.73 (t, 3J ¼ 8 Hz,16H, C6H5), 6.92 (t, 3J ¼ 8 Hz,
8H, C6H5), 7.01 (s, 8H, pyrrole-H), 7.48 (dd, 3J ¼ 8 Hz, 4J ¼ 1 Hz, 16H,
C6H5); 13C NMR (100 MHz; pyridine-d5): dC, ppm 42.67 (N(CH3)2),
110.46, 113.59, 126.68, 128.50, 128.50, 135.11, 140.03, 140.03,
150.35 h, 154.70. MS (MALDI TOF): m/z 1378 [MþH]þ. HRMS (ESI)
Found: [MþH]þ 1377.6078 C88H73N16Mg requires [MþH]þ
1377.6054. 4b (4 mg, 0.8% yield): mp > 300 ꢀC. Rf (n-hexane:EtOAc
7:5) 0.83, (CH2Cl2:CH3OH 50:1) 0.11. UVeVis (CH2Cl2): lmax, nm
(logε) 292 (3.98), 342 (3.56), 522 (2.76), 691 (3.49). 1H NMR
(400 MHz; pyridine-d5): dH, ppm 3.06 (s), 3.26 (s), 3.30 (s), 3.34 (s),
6.62e6.68 (m), 6.68e6.75 (m), 6.76e6.83 (m), 6.86 (s), 6.90e6.94
2.3. NMR studies
1H NMR, 13C NMR spectra were recorded using a Bruker 400 and
500 spectrometers. Chemical shifts (d) are quoted in parts per
million (ppm) and are referred to a residual solvent peak. Coupling
constants (J) are quoted in Hertz (Hz). The abbreviations s, d, h, t,
and m refer to singlet, doublet, hidden, triplet, and multiplet,
respectively. Chemical shifts of aggregated species of Pz 6 are
signed with asterisk (*). Additional techniques (1He1H COSY, HSQC,
HMBC) and temperature spectra were used to assist allocation.
€
2.4. Mossbauer spectroscopy studies
Powder sample frozen to the temperature of liquid nitrogen was
placed in a home-built cryostat at 85 K. The temperature was sta-
bilized within 0.03 K. Mossbauer 57Fe spectra were recorded using
€
57Co(Rh)-50 mCi as a source of 14.4 keV radiation. Hyperfine pa-
rameters characterizing valence and spin states of the heme-iron in
the investigated Pzs were obtained from the theoretical analysis of

140
T. Koczorowski et al. / Dyes and Pigments 112 (2015) 138e144
(m), 6.98 (s), 7.05 (s), 7.30 (d, 3J ¼ 8 Hz) 7.38 (d, 3J ¼ 8 Hz), 7.42 (d,
3J ¼ 8 Hz), 7.53 (d, 3J ¼ 8 Hz). MS (MALDI TOF): m/z 1378 [M þ H]þ.
HRMS (ESI) Found: [M þ H]þ 1377.6063C88H73N16Mg requires
[M þ H]þ 1377.6054.
lmax, nm (logε) 296 (4.58), 381 (3.91), 440 (3.90), 691 (3.90), 911
(3.56). 1H NMR (400 MHz; pyridine-d5): dH, ppm 2.69 (s, 24H,
N(CH3)2), 2.91*-3.20* (m, 24H, N(CH3)2), 6.58 (s, 8H, pyrrole-H),
6.74* (t, 3J ¼ 6 Hz, 24H, C6H5), 7.00* (s, 8H, pyrrole-H), 7.30 (t,
3J ¼ 6 Hz 24H, C6H5), 7.50* (d, 3J ¼ 3 Hz,16H, C6H5), 7.67 (d, 3J ¼ 3 Hz,
16H, C6H5). 13C NMR (175 MHz; pyridine-d5): dC, ppm 39.98
(N(CH3)2), (42.26*-42.63*) (N(CH3)2), (110.54*), 111.73, 111.73,
(128.20*),128.44,128.44, (128.44*),128.82,134.17, (134.17*),135.20,
140.37, 140.37, (140.37*), 145.25. MS (MALDI TOF): m/z 1409
[MþH]þ. HRMS (ESI) Found: [M þ H]þ 1409.5503 C88H73N16Fe re-
quires [M þ H]þ 1409.5553.
2.5.4. 2,7,12,17-Tetrakis(dimethylamino)-3,8,13,18-tetrakis(2,5-
diphenyl-1H-pyrrol-1-yl)porphyrazine (5)
Maleonitrile 3 (338 mg, 1.0 mmol) was heated in dimethylami-
noethanol (4 mL) under reflux for 24 h. After cooling to room
temperature, the green-violet mixture was evaporated with
toluene (2 ꢂ 50 mL) to dryness and subjected to column chroma-
tography (n-hexane:CH2Cl2, 1:2) to give 5 (80 mg, 23% yield) as a
dark green solid: mp > 300 ꢀC, Rf (n-hexane:CH2Cl2, 1:2) 0.77.
UVeVis (CH2Cl2): lmax, nm (logε) 302 (4.76), 435 (4.01), 734 (4.32),
791 (4.38). 1H NMR (500 MHz; pyridine-d5): dH, ppm ꢁ0.51 (s, 2H,
NH), 3.35 (s, 24H, N(CH3)2), 6.95 (m, 16H, C6H5), 6.96 (d, 3J ¼ 9 Hz
8H, C6H5), 7.00 (s, 8H, pyrrole-H), 7.54e7.56 (m, 16H, C6H5). 13C
NMR (125 MHz; pyridine-d5): dC, ppm 42.83 (N(CH3)2), 110.91,
112.01, 125.39, 127.09, 128.55, 128.89, 129.57, 134.91, 140.13, 148.76.
MS (MALDI TOF): m/z 1356 [MþH]þ. HRMS (ESI) Found: [M þ H]þ
1355.6358 C88H75N16 requires [M þ H]þ 1355.6361.
3. Results and discussion
Maleonitrile derivative 3 was obtained in a two-step procedure
starting from diaminomaleonitrile (1) using the conditions re-
ported by Begland et al. [20] and Baum et al. [21]. Novel maleoni-
trile 3 was used in the Linstead macrocyclization with magnesium
n-butanolate in n-butanol to give porphyrazine 4a possessing an
alternate system of peripheral substituents (D4h isomer) as the
main product in 18% overall yield (Scheme 1) [5,22]. Interestingly,
only a tiny amount (0.8% of the overall yield) of the side-product 4b,
Pz possessing non-alternate system of peripheral substituents (Cs
isomer), was obtained. The macrocyclization of 3 in dimethylami-
noethanol (DMAE) led to the free base Pz 5 in 23% of the yield [23],
that was subsequently metalated, following the literature proce-
dure [24], in toluene-THF-2,6-lutidine mixture with FeBr2 to give Pz
6 in 22% yield (Scheme 1). Noteworthy, the reaction mixture was
subjected to a two-step purification procedure consisting of ex-
tractions in dichloromethane - aqueous 1 M hydrochloric acid, then
brine, and dichloromethane e aqueous saturated citric acid.
All porphyrazines were carefully purified by column chroma-
tography and further analyzed by HPLC. HPLC chromatograms of 4a
showed four separate signals, which, when analyzed by Diode
Array Detector (DAD), revealed the same absorption profiles. This
occurrence might be explained by association type interaction of
porphyrazines in solution leading to the formation of Pz aggregates
of diverse size and thus, with different retention time. This was
2.5.5. [2,7,12,17-Tetrakis(dimethylamino)-3,8,13,18-tetrakis-(2,5-
diphenyl-1H-pyrrolyl)porphyrazinato]iron(II) (6)
Porphyrazine
5 (85 mg, 0.063 mmol), FeBr2 (135 mg,
0.63 mmol), 2,6-lutidine (2 mL) were heated in toluene-THF
mixture (1:1, 10 mL) under reflux for 20 h. After cooling to room
temperature, the green mixture was evaporated to dryness. The
dark green solid dissolved in dichloromethane (10 mL) was mixed
with aqueous 1 M HCl (10 mL) for 30 min as two-phase system.
After that time, the organic layer was mixed with brine (10 mL) for
30 min as two-phase system. The organic layer was separated,
dried with anh. MgSO4 and rotavapory evaporated. The residual
iron species were removed by extraction in dichloromethane
(10 mL) e saturated citric acid solution (10 mL). The dry residue was
extensively purified by column chromatography (CH2Cl2:CH3OH,
50:1) to give the porphyrazine 6 as a dark green solid (20 mg, 22%
yield): mp > 300 ꢀC. Rf (CH2Cl2:CH3OH, 50:1) 0.17. UVeVis (CH2Cl2):
Scheme 1. Reagents and conditions: (i) 1,2-dibenzoylethane, methanol, TFA, reflux, 24 h; (ii) NaH (60% suspension in mineral oil), (CH3O)2SO2, THF, ꢁ15 ꢀC to rt, 24 h; (iii) Mg(n-
BuO)2, n-BuOH, reflux, 20 h; (iv) DMAE, reflux, 24 h; (v) FeBr2, toluene, THF, 2,6-lutidine, reflux, 24 h; TFA e trifluoroacetic acid.

T. Koczorowski et al. / Dyes and Pigments 112 (2015) 138e144
141
confirmed by the HPLC analysis of a 4a sample in the presence of
pyridine, which is known to coordinate central metal ions apically
(and in this way separates molecules) as only one signal was
registered (see Supplementary data). Noteworthy, no aggregation
was observed by HPLC for 4b, 5 and 6.
All compounds were characterized by UVeVis, MS and various
NMR techniques. Additionally, maleonitrile 3 and Pz 4a were
crystallized to provide single crystals suitable for X-ray structure
analyses. The crystal structure of 4a consists of the [Pz-Mg-
propanol] complex (Fig. 1) and disordered solvent molecules. The
Mg2þ ion is in a square-pyramidal coordination environment with
four macrocycle N atoms in the basal plane and 1-propanol O atom
in the apical position. The Mg2þ cation is displaced from the best
plane of four pyrrolyl nitrogens of Pz core toward the O atom by
surrounding the Pz core. In the crystal, the [Pz-Mg-propanol]
molecules are assembled into centrosymmetric dimers by inter-
digitation of the phenyl substituents. These are placed on the Pz
side that is free of the auxiliary n-propanol ligand (Fig. 1). In the
discussed dimer, the Mg/Mg distance of 11.2 Å is larger than found
in the other Pzs dimers reported in previous research [5].
Macrocycles 4a, 5 and 6 were characterized using one and two-
dimensional NMR techniques (HMBC, HSQC, COSY) and tempera-
ture studies (see Supplementary data). In Pzs COSY spectra, strong
cross-peaks between protons of phenyl substituents were
observed. Moreover, there appeared in magnesium and free base
NMRs explicit couplings between protons belonging to phenyl and
pyrrolyl substituents (Fig. 2). The 1H NMR spectra of 6 revealed the
presence of two forms of iron Pz: a free, non-aggregated (Pz 6) and
an aggregated (Pz 6*). Such a phenomenon was observed in earlier
studies on magnesium and zinc phthalocyanine derivatives
[25e27]. It was confirmed in the 1H NMR of 6, where a single signal
of dimethylamino substituents stands for a free form, while divided
into multiple signals indicates the formation of associated species.
The relative intensity of dimethylamino substituent proton signals
of both forms constitutes the ratio of 2:3. In the 1H NMR temper-
ature studies within the range of 273 Ke363 K simplifying of
multiplied proton signals of the dimethylamino group was
observed. Moreover, the 1H NMR measurements recorded after a
D2O addition enabled the determination of the presence of water,
coordinated to a Fe2þ ion in the core. After the addition of D2O, the
amount of non-coordinated water (water in pyridine-d5) increased
at the expense of the coordinated water.
0.538(3) Ǻ. The orientation of peripheral substituents at pyrrole b,b
positions is similar in all porphyrazine subunits. The twist of the
N(CH3)2 groups relative to the macrocycle plane is much smaller
[25.9(2) e 40.9(2)ꢀ] than of the pyrrole rings of 2,5-diphenylpyrrole
fragments [72.4(1) - 80.4(2)ꢀ]. The benzene rings from the bulky
substituents are protruding on both sides of the macrocycle
The absorption spectrum of 4a has a structure typical of por-
phyrazines and consists of two intense sharp bands: the Soret band,
at 302 nm, and the Q band at 730 nm (Fig. 3). The Q-band transition
of 4b is broad and complex, which is in accordance to the data
previously obtained for asymmetrical Pzs with peripheral 2,5-di(2-
thienyl)pyrrolyl groups that break the molecular C4 symmetry [15].
The split and broad Q-band of 5 in dichloromethane is a result of
the reduced symmetry of the macrocycle, in accordance with
Gouterman's four-orbital model. Pz complex 6 containing Fe2þ
cation with vacancies on the d
p and/or dz2 orbitals showed the
expected absorptions in the Soret and Q-band regions. The blue-
shifted Soret below 300 nm, the extra Soret band transitions at
381, 440 nm, and the single Q-band at 691 nm with additional
absorbance maxima over 900 nm presented in 6 may be due to
additional interactions [5,28,29]. It is correlated with a strong af-
finity to a Fe2þ cation to bind different moieties as a result of its
electron-acceptor property. Another characteristic that has an in-
fluence on the coordination abilities of iron is the structure of the
porphyrazine macrocycle ring. An iron Pzs central metal cation is
placed outside of a macrocycle plane due to the smaller ring size.
This is a consequence of meso-N-bridges in the Pz ring in com-
parison to meso-C-bridges in porphyrins [7]. Moreover, there is no
split in the Q band of 6 (observed in presence of a Fe3þ species),
which may indirectly suggest the presence of a Fe2þ species [30].
The absorption spectra of 4a, 5 and 6 dissolved at different
concentrations in pyridine or dichloromethane were used for ag-
gregation behavior studies. The correlations between the absor-
bance of the Q-band maximum and the concentrations of the
macrocyclic compounds were evaluated. Although these correla-
tions were linear for all compounds, the statistical analysis revealed
that the BeereLambert law was obeyed only for 6 in both solvents.
These data indicate that 5, unlike 4a, aggregates in both pyridine and
dichloromethane (Figures S4eS9, Table S8 in the Supplementary
data). Furthermore, the corresponding spectra of fluorescence
excitation and absorption spectra of 4a support its aggregation
behavior study, as they match each other in pyridine, unlike
dichloromethane (Figures S10 and S11 in the Supplementary data).
Fig. 1. (a) Molecular structure of Pz 4a showing the orientation of pyrrole b,b-sub-
stituents. Hydrogen atoms are omitted for clarity. (b) Centrosymmetric dimeric asso-
ciate formed by interdigitated complex molecules in 4a. Atoms of the encapsulated
phenyl ring of unit D are indicated as spheres of arbitrary radii.

142
T. Koczorowski et al. / Dyes and Pigments 112 (2015) 138e144
Fig. 3. Relative absorption spectra of 4a, 4b, 5 and 6 in CH2Cl2.
provides values of hyperfine parameters, an isomer shift (IS) and a
quadrupole splitting (QS). They are very sensitive to the chemical
character and arrangement of probing atom ligands (in our case
57Fe) [31,32]. At least five subcomponents were necessary to get a
good quality fit of the spectrum for Pz 6. The line widths of about
0.18 0.02 obtained for the subspectra indicate high homogeneity
of the hemeeiron binding sites. Heme-iron stabilized in a low spin
ferrous state (in a diamagnetic state, Fe2þ with S ¼ 0), charac-
terized by IS ¼ 0.18 0.01 mm/s and QS ¼ 0.24 0.02 mm/s, has
€
the highest contribution in the Mossbauer spectrum (about 35%).
This state is formed in a case of strong covalent bonds between
the iron atom and its ligands in a highly symmetric arrangement,
for 6- or 4- coordinated iron [33]. Moreover, a component with
IS ¼ 0.12 0.06 mm/s and QS ¼ 2.88 0.05 mm/s has a contri-
bution of about 25.8 3.0%. Such parameters are typical for iron
in octahedral coordination, when one of the perpendicular ligands
Fig. 2. NMR 1He13C HSQC, 1He13C-HMBC and 1He1HeCOSY connectivities of 4a, 5 and
6 with chemical shifts values (ppm). Pz 6* indicates the aggregated form of iron Pz.
€
The Mossbauer spectroscopy is a unique method, which allows
for direct detection of all valence and spin states of heme-iron in
Pz 6. In Fig. 4, the Mӧssbauer spectrum of Pz 6, measured at 85 K,
is presented. Theoretical evaluation of the experimental data
€
Fig. 4. The Mossbauer spectrum of Pz 6 at 85 K.

T. Koczorowski et al. / Dyes and Pigments 112 (2015) 138e144
143
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was in a low spin Fe2þ state [34]. A subspectrum, with IS of about
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0.00
0.10 mm/s and QS of about 3.28
0.21 mm/s, is most
probably also related to a diamagnetic state of heme-iron, but
with a stronger distortion in its first coordination sphere. For
example, a non-planar Pz ring may result in an additional increase
of an electric field gradient. The contribution of this heme-iron
state is about 15.3 3.0%. In addition, a component with hyper-
fine parameters IS ¼ 0.34 0.06 mm/s and QS ¼ 2.20 0.10 mm/s
can be ascribed to an intermediate spin state of Fe2þ. Such a state,
which is formed when the dx2-y2 orbital has higher energy than
the other orbitals, is typical for an intermediate spin state of
reduced iron [35]. The Fe2þ state with S ¼ 1 may originate from a
€
tangled Pz ring. Its content in the Mossbauer spectrum is about
13.6 3.0%. Notable, a high spin iron state is formed in Pz 6 (its
contribution is about 10.3 3.0%). A diamagnetic state of iron is
rather present in Pz associates.
4. Conclusions
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substituents did not hamper the formation of the Pz associates in
solution and solid-state. The interdigitation of the phenyl sub-
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dimer. The situation here was totally different from that reported
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Acknowledgments
[22] Linstead RP, Whalley M. 944. Conjugated macrocylces. Part XXII. Tetraza-
porphin and its metallic derivatives. J Chem Soc 1952:4839e46.
This study was supported by the National Science Centre under
Grant No. N N404 069440 and the European Fund for Regional
Development No UDA-POIG.02.01.00-30-182/09. This work was
performed within the BIONAN cooperation. T.G. thanks MSc Mar-
iusz Duda for preliminary synthetic studies.
ꢀ
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Appendix A. Supplementary data
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