Properties and structures of porphyrexides

Article abstract of DOI:10.1007/s11172-006-0278-z

The molecular and crystal structures of porphyrexides, viz., 4-amino-2-imino-(1) and (Z)-2-amino-4-bromoimino-5,5-dimethyl-4,5-dihydro-1H- imidazole 1-oxyls (7), and their diamagnetic precursors were determined. Compound 1 is kinetically unstable because it is oxidized with atmospheric oxygen to form (E)-1,2-bis[1-amino-1-(cyanoimino)-2-methyl-propan-2-yl]diazene 1,2-dioxide.

Full text of DOI:10.1007/s11172-006-0278-z

Russian Chemical Bulletin, International Edition, Vol. 55, No. 3, pp. 457—463, March, 2006
457
Properties and structures of porphyrexides
E. V. Tretyakov,a A. S. Bogomyakov,b E. Yu. Fursova,a G. V. Romanenko,a V. N. Ikorskii,a and V. I. Ovcharenkoa,b
ꢀ
aInternational Tomography Center, Siberian Branch of the Russian Academy of Sciences,
3a ul. Institutskaya, 630090 Novosibirsk, Russian Federation
Fax: +7 (383) 333 1399. Eꢀmail: Victor.Ovcharenko@tomo.nsc.ru
bNovosibirsk State University,
2 ul. Pirogova, 630090 Novosibirsk, Russian Federation
The molecular and crystal structures of porphyrexides, viz., 4ꢀaminoꢀ2ꢀiminoꢀ (1) and
(Z )ꢀ2ꢀaminoꢀ4ꢀbromoiminoꢀ5,5ꢀdimethylꢀ4,5ꢀdihydroꢀ1Hꢀimidazole 1ꢀoxyls (7), and their
diamagnetic precursors were determined. Compound 1 is kinetically unstable because it is
oxidized with atmospheric oxygen to form (E)ꢀ1,2ꢀbis[1ꢀaminoꢀ1ꢀ(cyanoimino)ꢀ2ꢀmethylꢀ
propanꢀ2ꢀyl]diazene 1,2ꢀdioxide.
Key words: nitroxides, porphyrexide, Xꢀray diffraction study.
The synthesis of new types of magnetically active comꢀ
pounds is based on the development of methods for the
construction of highly efficient exchangeꢀcoupled enꢀ
sembles. The use of complexes of paramagnetic transition
metal ions with paramagnetic organic ligands is one of
approaches that have gained wide acceptance in the deꢀ
sign of such ensembles.1—5 Nowadays, at the early stage
of investigation, i.e., at the molecular level, researchers
try to endow the structure of a paramagnetic ligand with
parameters, which would be expected to be favorable for
the desired physical characteristics at the macrolevel. First,
a paramagnetic ligand should be polyfunctional to induce
selfꢀassembly of polymeric structures, i.e., the ligand
should serve as a bridge. Second, the ligand should proꢀ
vide efficient exchange interactions between the unpaired
electrons of the paramagnetic centers, between which this
ligand is located, and, what is extremely important, the
occurrence of cooperative magnetic interactions at the
macrolevel. Third, the ligand should possess high kinetic
stability, which is necessary for growing single crystals
required for the subsequent structure solution and conꢀ
struction of reliable magneticꢀstructure relationships. In
addition, kinetic stability of ligands allows one to perform
desired transformations without the introduction and reꢀ
moval of protective groups.
tions for the formation of an efficient exchange interacꢀ
tion channel between the unpaired electrons of paramagꢀ
netic metal ions.
Classical porphyrexide (1) has atꢀ
tracted our attention because it satisꢀ
fies all the aboveꢀmentioned requireꢀ
ments. A procedure for the synthesis
of this compound has been described
many years ago.6 Much more reꢀ
cently, radiospectroscopic studies of solutions of isotopiꢀ
cally labelled porphyrexide derivatives by ESR have deꢀ
monstrated that porphyrexide 1 exists in dioxane as a
mixture of tautomeric forms 1A and 1B (Scheme 1),
form 1B being the major one.7 The representation of the
porphyrexide molecule as tautomer 1B is commonly acꢀ
cepted and was cited in reviews and monographs for more
than three decades.8,9
Scheme 1
These requirements can be simultaneously satisfied
only by introducing a particular combination of funcꢀ
tional fragments. Nitroxide bound to
the α,βꢀunsaturated heteroatomic
fragment or its vinylog can serve as
such a construction, which allows
also bridging coordination.
Spin density delocalization in the
bridging fragment provides condiꢀ
Porphyrexide has attracted our attention as a potent
paramagnetic ligand. This has stimulated the need for a
more detailed analysis of its structural characteristics.
Since the data on its structure were absent in the Camꢀ
bridge Structural Database,10 we studied the structure of
this compound by Xꢀray diffraction. It was unexpectedly
Y = N, O
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 441—447, March, 2006.
1066ꢀ5285/06/5503ꢀ0457 © 2006 Springer Science+Business Media, Inc.

458
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 3, March, 2006
Tretyakov et al.
H(42)
found that, in the solid state, 1 exists in the form different
from 1B. Since the molecular structure of the diamagꢀ
netic precursor of porphyrexide in the solid state also
differs from the commonly accepted structure, we report
here the Xꢀray diffraction data for compound 1 and its
diamagnetic precursors.
For each compound (Scheme 2), it was necessary to
find a procedure for the growth of single crystals suitable
for Xꢀray diffraction. For example, we succeeded in growꢀ
ing wellꢀfaceted crystals of hydroxylamine 2 only from
the mother liquor obtained after a twofold dilution of a
methanolic solution of 2 with a diethyl ether—hexane
mixture (1 : 1, v/v).
O(4)
H(41)
N(5)
H(91)
C(9)
H(92)
H(31)
C(8)
Cl(1)
H(72)
N(3)
C(6)
N(2)
H(93)
H(71)
C(7)
H(32)
H(73)
H(22)
Fig. 1. Molecular structure 2.
H(21)
Scheme 2
H(31)
C(3)
H(32)
C(1)
H(21)
H(12)
H(11)
Cl
N(1)
H(33)
C(2)
N(3)
N(2)
H(22)
H(41)
C(4)
H(42)
Fig. 2. Molecular structure of dimer 3.
O(1)
H(43)
amidine 3, like compound 2, is protonated at both amidine
groups, all atoms of the latter being located virtually in
a single plane. The dication is centrosymmetric with reꢀ
spect to the midpoint of the N—N bond (Fig. 2). The
bond lengths in this fragment are as follows: C(1)—N(1),
1.288(2) Å; C(1)—N(2), 1.301(2) Å; N(3)—O(1),
1.265(2) Å; and N(3)—N(3´), 1.310(3) Å. As a whole, the
structure of 3 consists of layers in which all organic
dications and chloride anions are linked to each other by
numerous hydrogen bonds.
In the solid state, the C(6)—N(3) and C(6)—N(2)
bonds involving both N atoms of the protonated amidine
fragment in compound 2 have similar lengths (1.313(3)
and 1.305(3) Å, respectively), which are intermediate beꢀ
tween single and double bond lengths (Fig. 1). The
pꢀπ conjugation in the amidine fragment of molecule 2 is
also evidenced by the arrangement of the N(2), C(6),
N(3), H(21), H(22), H(31), and H(32) atoms in a single
plane. The C—C (1.524(4)—1.531(4) Å), O(4)—N(5)
(1.452(3) Å), and N(5)—C(8) (1.477(3) Å) distances are
typical of single bonds. It should also be noted that the
organic cations and chloride anions in the solid state of 2
are linked to each other by a hydrogen bond network to
form a threeꢀdimensional framework.
Polar aqueousꢀalcoholic media proved to be solutions
of choice for the crystal growth of 4 (see Scheme 2).
Crystallization of the reaction product of nitroso derivaꢀ
tive 3 with NaCN from a MeOH—water mixture afforded
crystals of dihydrate 4•2H2O, whereas crystallization
from water gave crystals of the corresponding trihydrate
4•3H2O. Xꢀray diffraction study demonstrated that molꢀ
ecules 4 in both hydrates exist in the aminoꢀnitronic form,
i.e., as 2,5ꢀdiaminoꢀ4,4ꢀdimethylꢀ4Hꢀimidazole 3ꢀoxide
(Fig. 3, a).
Earlier,13 the structure of hydroxyꢀ
aminoꢀimine tautomer 4´ has been asꢀ
Single crystals of (E)ꢀ1,2ꢀbis(1ꢀaminoꢀ1ꢀiminioꢀ2ꢀ
methylpropanꢀ2ꢀyl)diazene 1,2ꢀdioxide dichloride (3, see
Scheme 2) suitable for Xꢀray diffraction were isolated
directly from the reaction mixture upon oxidation of an
aqueous solution of 2 with chlorine. Dimeric nitrosoꢀ
signed to the cyclic product formed by
the reaction of 3 with NaCN, whereas
the results of investigation of the strucꢀ
tures of 4•2H2O and 4•3H2O correꢀ
spond to the structure of nitrone 4 (see

Properties and structures of porphyrexides
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 3, March, 2006
459
H(311)
H(312)
O(1)
N(1)
a
N(1)
H(22)
H(31)
C(3)
C(1)
C(1)
C(2)
H(313)
N(3)
N(2)
H(31)
H(53)
H(211)
H(21)
N(2)
C(4)
C(4)
N(3)
C(5)
C(2)
H(212)
N(4)
H(52)
H(51)
C(5)
N(4)
H(42)
H(213)
H(41)
H(61)
H(62)
O(1)
C(6)
H(63)
H(42)
H(32)
H(41)
b
H(33)
C(3)
H(31)
Fig. 4. Structure of dimer 6.
N(4)
C(5)
C(1)
K3[Fe(CN)6]. As a result, we prepared porphyrexide 1 in
~40% yield as a finely dispersed crystalline red precipiꢀ
tate. Attempts to grow larger single crystals of 1 from
acetone, MeOH, THF, or water gave similar results. Upon
storage in an open vessel for several hours either at room
or low temperature, the color of the mother liquor changed
from red to orange, and compound 1 was absent from the
resulting precipitate (IR spectroscopic data). Hence, we
attempted to grow crystals of 1 directly from the reaction
mixture formed in the course of the synthesis of porphyrꢀ
exide. Slow cooling and storage of the reaction mixture at
5—6 °C for 14 h afforded three types of rather large parꢀ
tially intergrown crystals. Xꢀray diffraction study demonꢀ
strated that red prisms were porphyrexide 1, paleꢀbrown
prisms were (E)ꢀ1,2ꢀbis[1ꢀaminoꢀ1ꢀ(cyanoimino)ꢀ2ꢀ
methylpropanꢀ2ꢀyl]diazene 1,2ꢀdioxide (6), and paleꢀyelꢀ
low plates were K4[Fe(CN)6]. In dimer 6, whose structure
is shown in Fig. 4, the C(2)—N(2) and C(2)—N(3) disꢀ
tances are 1.306(2) and 1.307(2) Å, respectively, the
N(4)—O(1) distance is 1.265(1) Å, the N(4)—N(4´) disꢀ
tance is 1.310(2) Å, and the N(1)—C(1) distance is
1.153(2) Å, which correspond to the structural formula
of 6 presented in Scheme 3.
H(23)
C(2)
N(3)
C(4)
H(21)
O(12)
O(11)
H(22)
H(212)
N(1)
O(1)
N(2)
N(11)
O(13)
H(211)
c
d
O
N
H
C
Fig. 3. Structure and geometry of 2,4ꢀdiaminoꢀ5,5ꢀdimethylꢀ
5Hꢀimidazole 1ꢀoxide 4 (a, c); the molecular structure of 5 (b)
and the geometry of the cation in molecule 5 (d).
Scheme 2). The nitrone form is also evidenced by the fact
that all atoms of molecule 4, except for the atoms of the
gemꢀmethyl groups, are in a single plane. Their maximum
deviation from the mean plane is at most 0.054 Å (see
Fig. 3, c). This is a fundamental difference between the
structure of nitrone 4 and the structure of hydroxyamine
derivative 5 (Fig. 3, b), in which the O atom substantially
deviates from the plane of the heterocycle (Fig. 3, d). The
rearrangement of the nitrone fragment into the hydroxyꢀ
amine group is also evidenced by the fact that the
N(1)—C(4), C(4)—N(2), and C(4)—N(3) bond lengths
in hydrates 4•2H2O and 4•3H2O differ from those in
compound 5 (Table 1).
Scheme 3
Using the classical procedure6,13 for the preparaꢀ
tion of porphyrexide, we oxidized compound 4 with

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Tretyakov et al.
Table 1. Selected bond lengths in the structures of 1, 4•2H2O, 4•3H2O, 5, and 7
Bond
d/Å
4•3H2O
4•2H2O
5
7
1
A
B
C
D
C(5)—N(4)
N(3)—C(5)
C(4)—N(3)
C(4)—N(2)
N(1)—C(4)
N(1)—O(1)
C(1)—N(1)
C(1)—C(2)
C(1)—C(3)
C(1)—C(5)
N(4)—Br
1.311(3)
1.317(3)
1.382(2)
1.318(3)
1.302(2)
1.364(2)
1.466(2)
1.521(3)
1.520(3)
1.512(3)
1.310(2)
1.324(2)
1.386(2)
1.317(2)
1.310(2)
1.374(2)
1.463(2)
1.521(2)
1.527(3)
1.518(2)
1.303(2)
1.318(2)
1.365(2)
1.298(2)
1.330(2)
1.388(2)
1.475(2)
1.508(3)
1.518(3)
1.511(3)
1.284(4)
1.381(3)
1.315(4)
1.310(4)
1.401(4)
1.260(3)
1.483(3)
1.514(4)
1.515(4)
1.528(4)
1.895(2)
1.364(7)
1.369(7)
1.361(8)
1.278(6)
1.449(6)
1.267(6)
1.483(6)
1.514(6)
1.573(8)
1.447(7)
1.331(7)
1.420(6)
1.341(7)
1.266(6)
1.446(6)
1.279(6)
1.481(6)
1.570(7)
1.574(8)
1.447(8)
1.307(7)
1.274(7)
1.416(8)
1.296(6)
1.443(6)
1.249(6)
1.483(6)
1.553(7)
1.579(7)
1.468(8)
1.303(8)
1.279(7)
1.405(7)
1.300(6)
1.419(6)
1.258(6)
1.490(7)
1.507(8)
1.566(7)
1.486(6)
An increase in the time of storage of the reaction
C(5)—N(3) double bond is clearly seen also in the
amidine group of molecules 1C and 1D. On the conꢀ
trary, the N(3)—C(4)—N(2) amidine fragment and the
C(5)—N(4) bromoimine group are clearly distinguished
in the structure of molecules 7 based on Xꢀray diffracꢀ
tion data (Table 1). According to these data, the amidine
fragment in 7 involves the N(3)—C(4)—N(2) atoms,
whereas the amidine fragment in molecule 1 is formed
by the N(3)—C(5)—N(4) atoms. This is confirmed
by the fact that pairs of molecules A—D and B—C are
present in the structure of 1 (see Fig. 5). These pairs
are formed by two H bonds between the aboveꢀmenꢀ
tioned amidine fragments. It was unambiguously estabꢀ
lished that the amidine fragments in the structure of 7
are linked to each other through hydrogen bonds in the
same fashion. In addition, there are hydrogen bonds beꢀ
tween the Br atoms and the O atoms of the adjacent
nitroxides and the hydrogen atoms of the amino groups in
the structure of 7, resulting in the formation of ribbons
(Fig. 6, b).
In the ribbons, pairs of nitroxide fragments face
each other. Hence, the structure of 7 is formed by exꢀ
changeꢀcoupled pairs of paramagnetic centers, within
which the O...O distances are short (3.485 Å). In comꢀ
plete agreement with these data, the experimental temꢀ
perature dependences of the effective magnetic moment
µeff and the magnetic susceptibility χ (Fig. 7) for 7 are
well processed according to the model of exchangeꢀ
coupled dimers11 with the exchange interaction energy
J/k = –19.7 K.
mixture to several days led to the complete disappearance
of crystals of 1, and the precipitate contained only crystals
of 6 and K4[Fe(CN)6]. Therefore, not only recrystallizaꢀ
tion of 1 but also the synthesis of porphyrexide is accomꢀ
panied by its gradual decomposition.
Hence, we decided to synthesize porphyrexide under
argon with the use of preꢀdeaerated solutions of the reꢀ
agents. Under these conditions, the reaction afforded
only porphyrexide 1 in the solid state. The magnetic moꢀ
ment of 1 (µeff = 1.71 µB at 293 K) is virtually equal to
the theoretical value for the monoradical (1.73 µB), which
is indicative of high purity of the resulting sample. Unꢀ
fortunately, porphyrexide crystallized from the reacꢀ
tion mixture as crystal intergrowths. However, we sucꢀ
ceeded in separating rather homogeneous crystalline
fragments from these intergrowths and studied them by
Xꢀray diffraction. The quality of crystals of 1 was lower
than that of the other compounds under study (Table 2).
We failed to locate hydrogen atoms, and their positions
were calculated geometrically and then refined using a
riding model. The satisfactory R factor for compound 1
was obtained only taking into account a twin model
(1 0 0 / 0 1 0 / 0 0 –1; BASF = 0.4168). For the correꢀ
sponding brominated derivative 7, whose solid phase conꢀ
sisted only of the tautomeric form, the quality of the
crystals appeared to be much higher. Hence, it was reaꢀ
sonable to consider the structure of 1 in comparison with
the structure of bromoporphyrexide 7, which we also synꢀ
thesized.
In four crystallographically independent molecules
comprising the structure of 1 (Fig. 5), like in molecules 4,
all atoms are in a single plane, except for the gemꢀmethyl
groups. The bond lengths (see Table 1) allowed us
to unambiguously distinguish the double bond in the
C(4)—N(2) fragments in molecules 1A—D. The
To summarize, we established the earlier unknown
structures of porphyrexide, its bromo derivative, and diaꢀ
magnetic precursors of porphyrexide. The results of our
study confirmed the assignment of the structural formulas
presented in Schemes 2 and 3 to compounds 1 and 7,
respectively.

Properties and structures of porphyrexides
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 3, March, 2006
461
Table 2. Principal crystallographic data and details of Xꢀray diffraction study
Parameter
1
2
3
4•3H2O
4•2H2O
5
6
7
Molecular
formula
T/K
FW
Space group
a/Å
C5H9N4O C4H12ClN3O C8H20Cl2N6O2 C5H16N4O4 C5H14N4O3 C5H11N5O4 C10H16N8O2 C5H8BrN4O
240
141.16
P21
240
153.62
P212121
240
303.20
P21/c
240
196.22
P21/c
295
178.20
P21/n
295
205.19
P21/c
295
280.30
C2/c
240
220.06
P21/c
5.946(2)
18.471(7)
13.204(5)
90.123(6)
1450.1(10)
8
5.9701(9)
7.7732(12)
16.904(3)
6.5586(14)
10.264(2)
10.658(2)
102.472(4)
700.5(3)
2
11.246(4)
7.125(2)
13.563(4)
109.525(6) 106.923(3) 95.852(3)
1024.2(6)
4
11.603(3) 6.1563(10)
6.5529(14) 9.4328(15) 10.4588(16)
13.932(2)
8.411(4)
7.932(4)
13.316(6)
106.753(6)
850.6(7)
4
b/Å
c/Å
13.321(3)
16.439(3)
11.0347(17)
120.990(2)
1378.3(4)
4
β/deg
V/Å3
784.5(2)
4
968.9(4)
4
949.6(3)
4
Z
Dc/g cm–3
µ(MoꢀKα)
/mm–1
θ/deg
1.293
0.096
1.301
0.420
1.437
0.469
1.273
0.108
1.222
0.100
1.435
0.123
1.351
0.101
1.718
4.784
1.10—29.05
12513/6558
0.0632
2.41—23.32
3291/1117
0.0248
2.79—23.28
2919/1007
0.0194
1.92—23.27 2.05—23.34 2.49—23.32 3.41—23.26 2.53—23.24
4227/1467 6776/1401 7098/1373
0.0540
182
Inkl
*
5095/981
0.0213
124
5985/1215
0.0433
133
Rint
N
0.0376
170
0.0632
172
495
131
123
GOOF
R1
wR2
0.969
0.0579
0.1081
0.481
0.0300
0.0866
0.823
0.0281
0.0926
0.965
0.0350
0.0813
0.496
0.0370
0.1167
0.905
0.0386
0.1109
1.053
0.0325
0.0957
1.047
0.0266
0.0726
(I > 2σ )
I
R1
wR2
0.0990
0.1336
0.0322
0.0918
0.0305
0.0954
0.0440
0.0855
0.0420
0.1253
0.0451
0.1170
0.0348
0.0981
0.0293
0.0745
* Number of reflections, measured/independent.
O(1d)
C(3d)
C(3c)
C(2d)
N(1d)
C(5d)
O(1c)
N(4d)
C(1c)
C(2c)
C(1d)
N(1c)
C(4c)
C(4d)
N(2d)
N(4c)
C(5c)
N(3d)
N(3c)
D
N(2c)
C
N(2b)
N(3b)
C(5b)
N(4b)
C(3b)
N(3a)
N(4a)
N(2a)
C(4b)
N(1b)
C(5a)
C(1a)
C(1b)
B
O(1b)
C(4a)
C(2a)
N(1a)
O(1a)
C(2b)
C(3a)
A
Fig. 5. Dimerization of molecules 1.

462
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 3, March, 2006
Tretyakov et al.
a
O(1)
H(21)
H(312)
H(311)
C(3)
N(1)
N(2)
C(4)
H(313)
H(213)
H(22)
C(1)
b
N(3)
C(2)
H(211)
C(5)
N(4)
H(212)
3.485 Å
3.485 Å
Br
O
Br
N
Fig. 6. Molecular structure of bromoporphyrexide 7 (a) and an Hꢀbond system giving rise to polymeric ribbons (b) (hydrogen atoms of
the methyl groups are omitted).
µ
eff(β)
Crystals of 2 suitable for Xꢀray diffraction study were grown as
follows. Finely crystalline hydroxyamine 2 was dissolved in
MeOH. The solution was diluted with a diethyl ether—hexane
mixture (1 : 1, v/v). After 10 h, the growth of colorless wellꢀ
faceted prismatic crystals started. IR, ν/cm–1: 451, 568, 654,
740, 845, 916, 970, 1031, 1071, 1113, 1193, 1250, 1373, 1429,
1511, 1658, 1689, 2789, 3062, 3269 br.
(E)ꢀ1,2ꢀBis(1ꢀaminoꢀ1ꢀiminioꢀ2ꢀmethylpropanꢀ2ꢀyl)diazene
1,2ꢀdioxide dichloride (3) was synthesized according to a proceꢀ
dure described earlier.13 Nitrosoamidine 3 was crystallized diꢀ
rectly from a mixture as wellꢀfaceted colorless crystals. IR,
ν/cm–1: 420, 456, 565, 688, 757, 859, 960, 1071, 1152, 1189,
1213, 1301, 1372, 1468, 1516, 1685, 3051, 3370 br.
a
b
1.6
1.2
0.8
0.4
χ/cm3 mol–1
0.006
0.004
0.002
2,4ꢀDiaminoꢀ5,5ꢀdimethylꢀ5Hꢀimidazole 1ꢀoxide (4) was preꢀ
pared by the reaction of 3 with NaCN in 80—90% yields.13
Crystallization of 4 from a MeOH—water mixture afforded highꢀ
quality crystals of its dihydrate, 4•2H2O, whereas crystallizaꢀ
tion from water gave colorless crystals of trihydrate 4•3H2O.
IR, ν/cm–1: 498, 580, 706, 787, 944, 1047, 1110, 1154, 1176,
1216, 1251, 1367, 1381, 1448, 1590, 1686, 3245, 3441 br.
2ꢀAminoꢀ1ꢀhydroxyꢀ5,5ꢀdimethylꢀ1Hꢀimidazoleꢀ4(5H )ꢀ
iminium nitrate (5). A solution of 4•3H2O (140 mg, 0.07 mmol)
in water (1 mL) was added to a solution of Cu(NO3)2•3H2O
(85 mg, 0.35 mmol) in water (1 mL). The reaction mixture was
stored for 3 days in an open flask. Colorless crystals of the same
shape appeared on the bottom. One crystal was taken and used
for Xꢀray diffraction study.
4ꢀAminoꢀ2ꢀiminoꢀ5,5ꢀdimethylꢀ2,5ꢀdihydroꢀ1Hꢀimidazole 1ꢀ
oxyl (1).6 A solution of 4•3H2O (0.1 g, 0.51 mmol) in water
(0.1 mL) was added to a solution of K3[Fe(CN)6] (0.17 g,
0.52 mmol) in water (0.3 mL). An aqueous KOH solution (30 mg
in 50 µL) was added to the resulting red solution, which was
accompanied by a sharp intensification of the color and the
appearance of the brown tint. Then the reaction mixture was
cooled.
100
200
250
T/K
T/K
0
50
100
150
200
Fig. 7. Plots µeff(T ) (a) and χ(T ) (b) for compound 7 (experiꢀ
mental data are indicated by dotted lines and the calculated data
are shown by a solid line).
Experimental
The IR spectra were recorded on a Bruker VECTORꢀ22
spectrophotometer (KBr pellets) in the 400—4000 cm–1 region.
The melting points were determined on a Boetius hotꢀstage apꢀ
paratus. Microanalyses were carried out on a Carlo Erba 1106
analyzer at the Vorozhtsov Novosibirsk Institute of Organic
Chemistry of the Siberian Branch of the Russian Academy of
Sciences. The mass spectra were obtained on a Finnigan
MATꢀ8200 instrument (electron impact, 70 eV). The magnetic
measurements were performed on a SQUID MPMSꢀ5S (Quanꢀ
tum Desing) magnetometer in the temperature range of 2—300 K
in magnetic field of 5 kOe.
1ꢀAminoꢀ2ꢀ(hydroxyamino)ꢀ2ꢀmethylpropylideneimidinium
chloride (2) was prepared according to a known procedure.12
A. After fast cooling of the reaction mixture to ~0 °C, a finely
crystalline red precipitate was obtained. The precipitate was

Properties and structures of porphyrexides
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 3, March, 2006
463
filtered off and dried in air. Study by IR spectroscopy and
magetochemical measurements demonstrated that the precipiꢀ
tate was an individual phase of nitroxide 1. The yield was
41 mg (57%).
For compound 1, R1 was 0.0579, which was due to poor
quality of the crystals. Individual crystals of 1 were visually
transparent. However, internal cracks were observed under a
light transmission microscope. These cracks decreased the qualꢀ
ity of the crystals and, consequently, Xꢀray diffraction data sets
gave the higher R factors for the calculated structure. The crysꢀ
tal, from which Xꢀray data were collected, was obtained by
cleaving from an intergrowth, which, apparently, gave rise to
internal stresses, although visible defects were unobservable even
under a microscope. In addition, all crystals of 1 were twins, and
the structure was solved taking into account the twin model
(1 0 0 / 0 1 0 / 0 0 –1; BASF = 0.4168), which made it possible
to reduce the R factor by more than half.
B. Slow cooling and storage of the reaction mixture at 5—6 °C
for 14 h afforded rather large individual crystals and three types
of crystal intergrowths. The total weight was 42 mg. Xꢀray difꢀ
fraction study demonstrated that nitroxide 1 was obtained as red
prisms, (E)ꢀ1,2ꢀbis[1ꢀaminoꢀ1ꢀ(cyanoimino)ꢀ2ꢀmethylpropanꢀ
2ꢀyl]diazene 1,2ꢀdioxide (6) was obtained as paleꢀbrown prisms,
and K4[Fe(CN)6] was obtained as paleꢀyellow plates. After storꢀ
age of the reaction mixture at 5—6 °C for one week, the initially
formed crystals of nitroxide 1 completely disappeared. The preꢀ
cipitate contained only crystals of 6 and K4[Fe(CN)6].
This study was financially supported by the Russian
Science Support Foundation, the Russian Academy of
Sciences, the Siberian Branch of the Russian Academy of
Sciences, the Russian Foundation for Basic Research
(Project No. 05ꢀ03ꢀ32305), and the US Civilian Reꢀ
search and Development Foundation (CRDF, Grant
Y2ꢀCꢀ08ꢀ01).
C. Before the synthesis, argon was bubbled through the soluꢀ
tions of the reagents. The synthesis and subsequent storage of
the reaction mixture at 5—6 °C for 14 h were also performed
under argon. The large red crystals of nitroxide 1 that formed
were filtered off, washed with ice water (2×1 mL), and dried
in air. The yield was 30 mg (42%). IR, ν/cm–1: 409, 570, 649,
760, 815, 841, 1067, 1105, 1181, 1242, 1338, 1366, 1480,
1554, 1662, 3022, 3222, 3270. Highꢀresolution MS. Found:
m/z 141.0762 [M+]. C5H9N4O. Calculated: M = 141.0776. MS,
m/z (Irel (%)): 141 (19), 125 (7), 111 (31), 83 (39), 74 (42), 69
(100), 68 (52). µ = 1.71 µB (293 K).
References
(Z )ꢀ2ꢀAminoꢀ4ꢀ(bromoimino)ꢀ5,5ꢀdimethylꢀ4,5ꢀdihydroꢀ1Hꢀ
imidazole 1ꢀoxyl (7). Compound 1 (100 mg, 0.7 mmol) was
added to a stirred solution of NaBrO (0.68 g, 0.7 mmol), which
was prepared by the addition of Br2 (0.67 g, 4.2 mmol) to a
solution of NaOH (0.5 g, 12.5 mmol) in water (3 mL). Argon
was bubbled through the resulting darkꢀbrown solution for
15 min. Then the reaction mixture was neutralized with a 25%
aqueous AcOH solution (340 mg, 1.4 mmol). The darkꢀbrown
precipitate that formed was filtered off and dried in air. The
yield was 125 mg (80%). Crystals suitable for Xꢀray diffraction
study were grown from ethyl acetate. IR, ν/cm–1: 554, 607, 693,
718, 757, 853, 933, 1096, 1155, 1191, 1277, 1375, 1475, 1549,
1. K. Inoue, T. Hayamizu, H. Iwamura, D. Hashizumi, and
Y. Ohashi, J. Am. Chem. Soc., 1996, 118, 1803.
2. K. Fegy, D. Luneau, T. Ohm, C. Paulsen, and P. Rey,
Angew. Chem., Int. Ed. Engl., 1998, 37, 1270.
3. K. Fegy, N. Sanz, D. Luneau, E. Belorizky, and P. Rey,
Inorg. Chem., 1998, 37, 4518.
4. V. I. Ovcharenko and R. Z. Sagdeev, Usp. Khim., 1999, 68,
381 [Russ. Chem. Rev., 1999, 68, 345].
5. S. J. Blundell and F. L. Pratt, J. Phys.: Condens. Matter.,
2004, 16, R771.
6. O. Piloty and B. Graf Schwerin, Ber. Deutsch. Chem. Ges.,
1901, 34, 1870.
1611, 1699, 3107, 3379. µ = 1.73 µ (293 K). Found (%):
B
7. H. G. Aurich and J. Trösken, Tetrahedron, 1974, 30, 2515.
8. J. F. W. Keana, Chem. Rev., 1978, 78, 37.
9. L. B. Volodarsky, V. A. Reznikov, and V. I. Ovcharenko,
Synthetic Chemistry of Stable Nitroxides, CRC Press,
Florida, 1994.
10. Cambridge Structural Database, Version 5.26, November
2004 (Updates August 2005).
11. V. T. Kalinnikov and Yu. V. Rakitin, Vvedenie v magnetoꢀ
khimiyu [Introduction to Magnetochemistry], Nauka, Moscow,
1980, 302 pp. (in Russian).
C, 26.8; H, 3.6; N, 24.8. C5H8BrN4O. Calculated (%): C, 27.3;
H, 3.7; N, 25.5.
Xꢀray diffraction study. Xꢀray diffraction data sets were colꢀ
lected on a Smart Apex diffractometer (λMoꢀKα, graphite monoꢀ
chromator, SMART V5.625, SAINT+ V6.0, SADABS, and
Bruker AXS programs). The structures were solved by direct
methods and refined by the fullꢀmatrix leastꢀsquares method
using the SHELXTL program package.* The positions of the
H atoms in the structures of 2—7 were located from difference
electron density maps and refined isotropically along with the
nonhydrogen atoms. The positions of the H atoms in the strucꢀ
ture of 1 were calculated geometrically and refined using a riding
model. The principal crystallographic characteristics and details
of Xꢀray data study are given in Table 2.
12. O. Piloty and B. Graf Schwerin, Ber. Deutsch. Chem. Ges.,
1901, 34, 1863.
13. H. A. Lillevik and R. L. Hossfeld, J. Org. Chem., 1942, 7, 164.
* SHELXTL, V6.14, August 10, 2003.
Received February 22, 2006