Oxidation of 3-(3-or 4-pyridyl)-1,5-diphenylformazans in tetrazolium trichlorometallates: Structural and electrochemical investigation

Article abstract of DOI:10.1007/s10593-006-0261-5

On interacting pyridine-containing formazans with cobalt(II) and copper(II) chlorides the richlorometallates of the corresponding cations are isolated, the structures of which were established by X-ray structural analysis. Using data of cyclic voltamperometry a scheme is proposed for the oxidation-reduction process of converting formazans into tetrazolium cations.

Full text of DOI:10.1007/s10593-006-0261-5

Chemistry of Heterocyclic Compounds, Vol. 42, No. 11, 2006
OXIDATION OF 3-(3- or 4-PYRIDYL)-1,5-DIPHENYL-
FORMAZANS IN TETRAZOLIUM TRICHLORO-
METALLATES: STRUCTURAL AND ELECTRO-
CHEMICAL INVESTIGATION
N. A. Frolova, S. Z. Vatsadze, A. I. Stasha, R. D. Rakhimov, and N. V. Zyk
On interacting pyridine-containing formazans with cobalt(II) and copper(II) chlorides the
richlorometallates of the corresponding cations are isolated, the structures of which were established by
X-ray structural analysis. Using data of cyclic voltamperometry a scheme is proposed for the oxidation–
reduction process of converting formazans into tetrazolium cations.
Keywords: cation radicals, tetrazolium cations, trichlorometallates, formazans, complexes, reduction,
oxidation, X-ray structural analysis, cyclic voltamperometry.
One of the most vigorously growing directions of supramolecular chemistry is the chemistry of
coordination polymers, which are promising materials possessing semiconductor, optical, and magnetic
properties [1, 2]. The process of forming coordination polymers 2 may consist of the preliminary preparation of
a complex ligand 1 (with metal M1) with another metal M2. The complex ligands 1 (metalloligands or metal-
organic building blocks/tectones) must possess as a minimum, two exodentate groups capable of forming
additional coordination bonds [3-6].
R1
M2
M1
N
R1
H
L M1 L
L
M1 M2
L
L
N
n
n
R2
N
N
N
N
R2
2
1
N
H
N
R3
R3
A
B
Formazans are convenient substrates for building such metalloligands thanks to the presence
of potentially chelate chromophoric groupings and the possibility of varying the substituents in positions 1, 3,
and 5. It is known that formazans may exist in two forms, chelate A (E,Z) and linear B (E,E) (the Z-form of the
azo group is usually not considered) [7].
_______
* Dedicated to deeply respected Academician M. G. Voronkov in connection with his birthday and as a mark of
gratitude for his contribution to heterocyclic chemistry
__________________________________________________________________________________________
Moscow M. V. Lomonosov State University, Moscow 119992, Russia e-mail:szv@org.chem.msu.ru
aKarpov Institute of Physical Chemistry, Moscow 105064, Russia e-mail: adam@cc.nifhi.ac.ru. Translated from
Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1682-1696, November, 2006. Original article submitted May
10, 2006.
1444
0009-3122/06/4211-1414©2006 Springer Science+Business Media, Inc.

On forming complexes with metal salts the deprotonated form A of the formazan, in which the negative
charge is delocalized along all the conjugated chain, usually reacts. As a result six-membered metallochelates are
formed in which a hydrogen atom is replaced by metal [8].
R1
R3
N
N
N
N
N
N
N
R2
R2
M1
N
R3 R1
1, 1a
1 R1 = R3 = Ar, R2 = Ar, Alk; 1a R1 = R3 = Ar, Het; R2 = Ar, Het;
M1 = Co2+, Ni2+, Cu2+, Cd2+, Pd2+, Zn2+
Formazans coordinate the transition metals Co(II), Ni(II), Cu(II), Cd(II), Pd(II), and Zn(II) with the
formation of neutral complexes with coordination unit MN4 [9-18] (type 1, 1a). Formazans are known with
heterocyclic substituents (benzazoles [19-24], azoles [25], pyridines [26-29], and quinolines [28-35]), however
their use for obtaining metalloligands has not been considered in the literature.
Results are given in the present paper of an investigation of the process of forming metalloligands from
formazans with pyridine substituents in position 3. The chlorides of copper(II) and cobalt(II) were chosen as
sources of metal ions. Model 3-(3-pyridyl)- and 3-(4-pyridyl)-1,5-diphenylformazans (4a,b) were obtained by
azocoupling the phenylhydrazones of the appropriate pyridinecarbaldehydes 3 with benzenediazonium chloride
at 0°C by methods analogous to those described in [7, 29].
Ph
Ph
N
N
N
+
–
N
N
1. PhN2 Cl
Py
O
H
Py
H
H
Py
H2N
N
Ph
Py
+
H
2. NaOH
H2O
N
5 oC, 2 h
H
Ph
3a, b
4a,b
3,4 a Py = 3-Py, b Py = 4-Py
The synthesis of formazan 4a is not described in the literature although it is used as a starting material
for obtaining the 6-(3-pyridyl)-2,4-diphenylverdazyl radical [37]. Formazan 4b was obtained in [26]. For
compounds 4a,b, as also for the initial phenylhydrazones of pyridinecarbaldehydes 3, only melting points and
data of elemental analysis are given in the literature. In our work compounds 3 and 4 were characterized for the
1
first time by H NMR spectroscopy. Characteristic signals were observed in the 1H NMR spectra of hydrazones
3a,b for the ortho, meta, para protons of the benzene rings, the protons of the pyridine rings of the aldehyde
component, the proton of the amino group, and the proton at the double bond (see EXPERIMENTAL). In
1
comparison with the spectra of the hydrazones the signal of the amino group proton in the H NMR spectra of
formazans 4 was displaced towards high field by more than 7 ppm, the ortho, meta, and para protons of both
phenyl rings have the same chemical shifts respectively, and together with the signals of the pyridine ring
protons were displaced towards high field by 0.4 ppm. These changes in the spectra are explained by the fact that
as a result of rapid exchange of proton between the N(1) and N(5) atoms the phenyl rings in the formazans become
equivalent in the NMR time scale.
1445

To obtain metallochelates of type 1 solutions of ligand and acetates [9, 12, 38, 39] or chlorides [19, 40]
of copper and cobalt are usually mixed at room temperature or on heating. To obtain complexes of type 1a we
used alcoholic solutions of cobalt and copper chlorides. On mixing a solution of formazans 4 in acetonitrile and
a solution of salt in alcohol at room temperature only the complex of formazan 4a with cobalt chloride was
successfully isolated and characterized. Complex-forming reactions of formazans 4a,b with copper(II) chloride
dihydrate and 4b with cobalt(II) chloride hexahydrate were carried out by the method of slow diffusion [5] of an
alcoholic solution of salt into a solution of the ligand in methylene chloride. In the reactions of formazans 4 with
cobalt chloride the color of the mixed solutions on standing changed from claret to dark blue, which serves as a
sign of complex formation. The reaction of formazans 4 with copper chloride proceeded analogously. At the
border separating the two phases pink needle-shaped crystals grew and the mixed solution became yellow from
red.
Ph
Cl
Cl
N
N
–
+
Py
Cl
M
MCl2
4a, b
N
+
N
Ph
5,6
5 a Py = 3-Py, M = Co; b Py = 4-Py, M = Co; 6 a Py = 3-Py, M = Cu;
b Py = 4-Py, M = Cu
TABLE 1. Experimental X-Ray Structural Parameters
Compound
5a
6b
Formula
C20H17Cl3CoN6
506.68
C18H14Cl3CuN5
470.23
Molecular weight
Crystal size, mm
Crystal system
Space group
a, Å
0.52 × 0.34 × 0.20
Monoclinic
P21/c
0.55 × 0.32 × 0.20
Rhombic
P212121
9.080(2)
12.888(3)
20.501(4)
90
10.287(2)
11.897(2)
6.976(3)
90
b, Å
c, Å
α, deg
β, deg
γ, deg
100.79(3)
90
90
90
V, Å3
2356.7(9)
4
2077.6(6)
4
Z
dcalc, g⋅cm-3
µ, mm-1
1.428
1.503
1.087
1.449
F(000)
1028
948
Diffractometer
Temperature, K
Scanning region, θ
Range of reflection indices
Enraf-Nonius CAD-4
293(2)
Enraf-Nonius CAD-4
293(2)
1.88-25.16
-10 ≤ h ≤10
0 ≤ k ≤ 15
0 ≤ l ≤24
2.09-25.47
0 ≤ h ≤ 12
0 ≤ k ≤ 14
0 ≤ l ≤ 20
2199
Number
reflections measured
ndependent reflections (Rint)
refinement parameters
R1 [I ≥ 2σ(I)]
4466
4212 (0.013)
312
2199
244
0.0360
0.0242
wR2 (all reflections)
Quality on F2
0.1101
0.0682
0.978
0.895
Residual electron density (max/min), e.Å-3
0.654 / -0.468
0.407 / -0.184
1446

In the reactions of pyridine-containing formazans with metal chlorides at a ratio of 1 : 1, in place of the
supposed complexes of type 1a we isolated tetrazolium trichlorometallates 5a,b and 6a,b. For compounds 5a
and 6b monocrystals were successfully grown and were studied by X-ray structural analysis (Tables 1-3).
In the molecular structure of complex 5a it is possible to separate out four planar fragments, the
tetrazolium ring, the pyridine ring, and the two benzene rings (Fig. 1). The first two fragments are completely
coplanar, the angle between the mean-square planes is 6.3°. The two phenyl rings are twisted in different ways
relative to the phenyl–tetrazole bond. The angle of turn of the phenyl ring, including atoms C(7) through C(12)
,
was 77.0°, and for the second phenyl ring (atoms C(13) through C(18)) this angle was 36.9°. The noncoplanarity of
the phenyl rings with the central tetrazolium ring is linked, evidently, with the repulsion of the o-H atoms in the
theoretically possible conformation with a coplanar disposition of these rings. The structure of the five-
membered ring is analogous to data existing in the literature on the structure of tetrazolium cations [41-43]
(Tables 2, 3).
Fig. 1. Molecular structure of complex 5a. Projection on the plane of the tetrazolium ring.
The coordination of the cobalt atom is a tetrahedron elongated lengthwise at one apex (direction Co-N(1))
(Tables 2, 3), which is characteristic of analogous complexes of Co(II) [44-52]. The closest intermolecular
contact (2.769 Å) corresponds to interaction between the Cl(2) atom and the H-6 atom of the centrosymmetric
molecule (-x, 1-y, -z). In the asymmetric unit cell one molecule of solvated acetonitrile is found, which has no
short contacts with the molecules of the complex.
It is also possible to separate out four planar fragments in the molecule of complex 6b, analogous to
those considered for compound 5a. However in this case the pyridine ring is twisted significantly (19.8°)
in relation to the central ring. The angles of turn of the phenyl rings are 46.5° and 56.8°.
1447

Fig. 2. Molecular structure of complex 6b. Projection on the plane of the tetrazolium ring.
Fig. 3. Fragment of the crystal structure of complex 6b.
The N(5)…H-16 hydrogen bond is shown by dotted lines.
The coordination polyhedron of the copper atom is a heavily distorted tetrahedron (Tables 2 and 3),
which is characteristic of analogous complexes of copper(II) [53-56]. In difference to the structure of complex
5a short intermolecular contacts (2.583 Å) were observed in the crystal of the copper analog 6b between the
tetrazolium N(5) atom and the para hydrogen atom (H-16) of one of the phenyl rings of a neighboring molecule
TABLE 2. Some Bond Lengths (l) in Complexes 5a and 6b
l, Å
Bond
5a, M = Co
6b, M = Cu
С(1)–N(2)
N(2)–N(3)
N(3)–N(4)
N(4)–N(5)
N(5)–C(1)
N(1)–M
1.3404(3)
1.3040(3)
1.3331(3)
1.3093(3)
1.3319(3)
2.0551(4)
2.2585(5)
2.2453(5)
2.2316(5)
1.3310(2)
1.3036(2)
1.3424(2)
1.3029(2)
1.3290(2)
2.0317(3)
2.2139(3)
2.2328(4)
2.2131(3)
M–Cl(1)
M–Cl(2)
M–Cl(3)
1448

TABLE 3. Some Valence Angles (ω) in Complexes 5a and 6b
ω, deg
Angle
5a, M = Co
6b, M = Cu
C(1)–N(2)–N(3)
N(2)–N(3)–N(4)
N(3)–N(4)–N(5)
N(4)–N(5)–C(1)
N(5)–C(1)–N(2)
N(1)–M–Cl(1)
N(1)–M–Cl(2)
N(1)–M–Cl(3)
Cl(1)–M–Cl(2)
Cl(2)–M–Cl(3)
Cl(3)–M–Cl(1)
103.73(2)
110.08(2)
109.70(2)
103.95(2)
112.52(2)
104.01(2)
108.78(2)
102.56(2)
114.88(2)
112.09(2)
113.93(2)
103.73(2)
110.08(2)
109.70(2)
103.95(2)
112.52(2)
124.34(2)
99.33(1)
97.45(1)
103.90(1)
130.91(2)
103.71(1)
(-0.5 + x; 1.5 – y; -z). In its turn atom H-16 of the first molecule is linked to the N(5) atom of another neighboring
molecule (0.5 + x; 1.5 – y; -z). As a result endless chains of 6b molecules are formed in the crystal (Fig. 3),
disposed along the crystallographic a axis. Neighboring chains are linked by weak interactions (2.765 Å)
between the Cl(3) and H-6 atoms.
An electrochemical investigation by cyclic voltamperometry has been carried out to study the reactions
forming complexes 5 and 6 in more detail (Table 4). As is seen from Table 4, formazans 4 are oxidized in two
steps and reduced in one. The presence of a system of four nitrogen atoms and one carbon atom conjugated with
three aromatic rings leads to ready electrochemical formation of stable anionic and cationic particles. The
mechanism of oxidation of compounds of this class may be described by a fairly simple scheme [57].
.
Ph
H
+
Ph
H
Ph
N
N
N
N
N
N
N
N
N
– e
N
– e
+
R
R
R
N
– H+
N
Ph
Ph
Ph
Reduction of the tetrazolium cation occurs at -0.30 V according to [57]. Consequently, as is seen from
Fig. 4, a quasireversible peak is observed at potential -0.30 V after oxidation in a reversible cathodic scan.
Fig. 4. Cyclic voltamperogram of formazan 4b.
1449

Fig. 5. Cyclic voltamperogram of the tetrazolium salt.
For comparison we synthesized 2,3,5-triphenyltetrazolium chloride (7) [28] from 1,3,5-tetraphenyl-
formazan (4c).
On the electrochemical curves for salt 7 (Fig. 5) three peaks were observed, an anodic peak
corresponding to oxidation of chloride ion (Epox = 1.05 V), and two quasireversible reduction peaks (Ep1red = -0.49;
Ep1ox = -0.28), (Ep2red = -0.87; Ep2ox = -0.70 V).
TABLE 4. Oxidation and Reduction Potentials of Formazans and Their
Complexes according to Data of Cyclic Voltamperograms*
Oxidation
Epox, В***
Reduction
Compounds
E1/2ox, В**
-E1/2red, В**
-Epred, В***
4a
4b
4с
5a
0.93; 1.20 (1.14)
1.19; 1.46 (1.32)
0.87; 1.05 (0.86)
1.25 (0.33)
0.82 (0.76)
1.08 (0.5)
0.94 (0.6)
0.71 (1.85)
0.78 (1.3)
0.78 (0.73); 1.90
0.79 (0.68)
0.33 (0.20);
0.74 (0.64)
5b
6a
6b
1.23
0.30 (0.20);
0.84 (0.66)
0.57 (0.3);
1.45 (0.48)
0.65 (0.52);
1.06 (0.94); 1.50
0.33 (0.48);
0.74 (1.04)
0.37 (0.28);
0.79; 1.11 (1.18)
0.58 (0.4);
1.44 (0.4)
0.64 (0.52);
1.06 (0.94); 1.49
0.30 (0.22);
0.75 (0.58)
0.37 (0.23);
0.76 (0.68);
1.21 (1.12)
7
1.00 (0.5)
1.05 (0.91)
0.46 (0.7);
1.02 (1.04)
0.49 (0.28);
0.87 (0.70)
4a + CoCl3
4b + CoCl3
4a + CuCl2
1.06; 1.18 (1.03)
0.36 (0.15);
0.72 (0.60); 1.03
0.83; 1.03 (0.89);
1.36
0.37 (0.18);
0.71 (0.60); 1.00
1.03 (0.96);
1.61 (1.20)
0.32 (0.21);
0.75 (0.61);
1.27 (1.17)
4b + CuCl2
1.06 (0.97);
1.51 (1.27)
0.31 (0.23);
0.68 (0.51); 1.22
_______
* Solvent was DMF with added tetrabutylammonium tetrafluoraborate,
standard was saturated Ag/AgCl/KCl, platinum electrode.
** Number of electrons is given in parentheses.
*** Reversible peaks are given in parentheses.
1450

In the anodic region of the second peaks of the oxidation of the formazans, where oxidation of the
appropriate radical to tetrazolium cation occurs, no electrochemical processes were observed, except a peak for
the oxidation of chloride ion. In the cathodic region the previous cathodic peak was observed at a potential close
to -0.3 V. On reducing formazans, probably an anion radical is formed the negative charge on which is
distributed along all four nitrogen atoms.
The complexes of ligands 4 with cobalt(II) and copper(II) chlorides also demonstrate fairly simple
electrochemical curves (Figs. 6 and 7).
Fig. 6. Cyclic voltamperogram of complex 5a.
Fig. 7. Cyclic voltamperpgram of complex 5b.
On the electrochemical curves for cobalt complexes 5a,b at the single anodic stage, oxidation probably
occurs at the Co-Cl bond (the potential of the oxidation peaks of complexes 5a,b lie in the region for oxidation
of chloride ions). The potentials of the second reduction peaks of 5a,b coincide almost exactly with the
potentials of the sole reduction peak of the corresponding ligand. Formazans 4 are therefore generated after
transfer of the first electron to complexes 5a,b. Reduction of of the cation occurs at the very first cathodic stage
at low cathodic potentials with the addition of a hydrogen atom from the solvent to it.
Ph
Ph
N
N
N
N
N
N
+ 2e
H
+
R
R
N
H (solvent)
N
Ph
Ph
1451

For a detailed study of the process of forming complexes we carried out experiments with the aim of
obtaining complexes 5 and 6 in the electrochemical cell. Solutions of the appropriate ligands in DMF were
poured in with cobalt(II) and copper(II) chloride and maintained for 5 h at room temperature. The formation of
the corresponding complex was therefore noted by the appearance of a reduction peak for the tetrazolium cation
at -0.3 V. It has been established that tetrazolium cations are formed on interaction of compound 4 with copper
chloride (Fig. 8) and are not formed on interaction with cobalt chloride. This is evidently linked with the lower
oxidative ability of Co(II) (Epred = -0.90 V) in comparison with Cu(II) (Epred = 0.54 V).
Fig. 8. Cyclic voltamperogram of complex 6a.
The desired peak at -0.30 V was not observed on the first reduction curve of a mixture of formazans 4 with
cobalt(II) chloride. However, after the first cathodic record the potential in the anodic region is scanned and then the
cathodic once again, it is possible to observe a reduction peak at -0.40 V on the reduction curves. This peak is
observed both at a reverse potential after 0.3 V and also at a reverse in current at the point of 0.8 V. This peak
emerging once again may be attributed to reduction of the tetrazolium cation, reduction of Co3+ (originating on
oxidation of metallic cobalt deposited on the surface of the platinum electrode, Epox = 0.1 V), or reduction of complex
5a, which may be formed on reaction of ligand 4a with Co3+ (see below). The available data are unable to choose
unequivocally any of the proposed variants.
+
Ph
Ph
H
N
N
N
N
N
N
N
–
H
CoCl3
Co(II)Cl3
R
+
+
R
N
Ph
Ph
R
Ph
.
–
Ph
Ph
+Co(II)Cl3
N
+
N
N
N
N
+ CoCl3
– CoCl2
N
N
N
.
R
5
R
N
N
N
N
Ph
Ph
Ph
On replacing cobalt(II) chloride by cobalt(III) chloride in the electrochemical cell tetrazolium cation is
formed at once (Epred = -0.30 V) when pouring in a solution of salt and a solution of ligand. In this case the strength of
CoCl3 as an oxidizing agent proved to be sufficient so that oxidation of formazans occurred on mixing solutions of
the appropriate ligands and CoCl3 salts. It should be mentioned that the cobalt salt itself is reduced at this potential.
However the presence of the opposite oxidation peak (at -0.18 V), the absence of the anodic desorption peak for the
oxidation of the cobalt film on the surface of the platinum electrode, and the fact that the reverse pair of peaks are
absent on treating the Co(III) salt of compounds 5a,b, confirm our conclusion on the formation of complexes 5
according to the following mechanism.
1452

An analogous mechanism also describes the formation of metallocomplexes on reaction with copper(II)
chloride. But in this case the oxidation of formazan occurs initially on reduction of Cu(II) to Cu(I). The Cu(I) ion
formed is then oxidized to Cu(II) by oxidation of the air or electrochemically.
Compound 4c, containing no pyridine, does not react with cobalt(II) salt nor with CoCl3. This indicates that
the important step of the reaction forming tetrazolium salts is the step of complex-formation of metal with the
pyridine nitrogen atom.
On the basis of the data presented it is possible to draw the conclusion that the principal step of forming
tetrazolium cations is the one-electron oxidation of formazans by a suitable oxidizing agent. Metal ions [Cu(II)
or Co(II)] or an electrode surface may act in this way. Participation of air oxygen, oxidizing Co(II) to Co(III) and
Cu(I) to Cu(II), is a necessay step in carrying out this process in the chemical reaction.
EXPERIMENTAL
A check on the progress of reactions and the homogeneity of the compounds obtained was effected by TLC
on a bound silica gel layer (Silufol). The 1H NMR spectra were recorded on a Bruker-Avance (400 MHz) instrument
in CDCl3 (compounds 3a,b and 4a,b) and acetone-d6 (compound 7). The residual protons in deuterochloroform were
used as internal standard. Measurement of electrochemical oxidation and reduction potentials was carried out with the
aid of a PI-50-1.1 potentiostat, switched to program PR-8. Recording of cyclic voltamperograms and waves at the
rotating disk electrode was carried out on an automatic two-dimensional recorder. Tetrabutylammonium perchlorate
(highest purity, 99.8%, Fluka) served as base electrolyte. Electrolyte concentration = 0.05 M.
3-Pyridinecarbaldehyde Phenylhydrazone (3a). 3-Pyridinecarbaldehyde (3.0 g, 28.0 mmol) was added
dropwise to a solution of phenylhydrazine (2.80 g, 25.9 mmol) in pyridine (15 ml) with ice-cooling at such a rate that
the temperature of the mixture did not exceed 10°C. The mixture was then stirred at the same temperature for a
further 2 h. The mixture was evaporated to dryness in vacuum until disappearance of the odor of pyridine. The dry
residue was recrystallized from alcohol and dried in the air. Phenylhydrazone 3a (3.45 g, 61%) was obtained as
yellow crystals of mp 162.5°C (from ethanol). 1H NMR spectrum, δ, ppm (J, Hz): 8.79 (1H, s, H-α' Py); 8.53 (1H, d,
J = 4.3, H-α Py); 8.07 (1H, d, J = 8.0, H-γ Py); 7.85 (1H, s, NH); 7.68 (1H, s, CH=); 7.29-7,35 (3H, m, H-β Py, H-m
Ph); 7.12 (2H, d, J = 7.7, H-o Ph); 6.93 (1H, t, J = 7.3, H-p Ph). Found, %: C 72.84; H 5.53; N 21.17. C12H12N3.
Calculated, %: C 73.10; H 5.58; N 21.32.
4-Pyridinecarbaldehyde Phenylhydrazone (3b) was synthesized by a procedure analogous to that for
obtaining compound 3a, from phenylhydrazine (1.88 g, 17.4 mmol) and 4-pyridinecarbaldehyde (2.00 g, 18.7 mmol)
with a yield of 2.95 g (76%). Yellow powder of mp 179°C (from ethanol). 1H NMR spectrum, δ, ppm (J, Hz): 8.59
(2H, d, J = 3.0, H-α' Py); 8.13 (1H, br s, NH); 7.63 (1H, s, CH=); 7.53 (2H, d, J = 3.3, H-β Py); 7.33 (2H, t, J = 7.9,
H-m Ph); 7.17 (2H, d, J = 8.4, H-o Ph); 6.93 (1H, t, J = 7.4, H-p Ph). Found, %: C 73.16; H 5.36; N 21.38. C12H12N3.
Calculated, %: C 73.10; H 5.58; N 21.32.
1,5-Diphenyl-3-(3-pyridyl)formazan (4a). A diazonium salt solution was obtained first. For this ice (0.5 g)
was added to a solution of aniline (0.47 g, 5.08 mmol) in conc. HCl (1 ml) and the mixture was diazotized at <5°C by
adding dropwise a solution of NaNO2 (0.35 g, 5.1 mmol) in water (1 ml). Acetic acid (1 ml) was added to a solution
of hydrazone 3a (1.00 g, 5.1 mmol) in pyridine (8 ml) and methanol (4 ml) and the solution of diazonium salt was
added dropwise with vigorous stirring and cooling at such a rate that the temperature did not exceed 5°C. Constant
foaming was observed during the reaction. After the end of adding diazonium salt the mixture was stirred at 5°C for a
further 30 min. The mixture was then heated at 50-60°C for a short time and cooled to room temperature. Water (10
ml) was added to the mixture and 2 M NaOH solution was added dropwise with constant stirring to pH 9. The
resulting claret-colored viscous solid was filtered off, suspended in water (10 ml), and filtered off once again. The
operation was repeated a further 2 times. After drying in vacuum the solid was recrystallized from ether. Formazan
4a (0.78 g, 51%) was obtained as a dark claret powder of mp
169°C (from ether). 1H NMR
1453

spectrum, δ, ppm (J, Hz): 15.66 (1H, s, NH); 9.40 (1H, s, H-α' Py); 8.62 (1H, d, J = 4.6, H-α Py); 8.39 (1H, dd,
J = 8.3, J = 1.4, H-γ Py); 7.80 (4H, d t, J = 8.0. J = 1.1, H-o Ph); 7.55 (4H, tt, J = 7.5, J = 1.2, H-m Ph); 7.36-7.45
(1H, m, H-β Py); 7.33 (2H, t t, J = 7.8. J = 1.6, H-p Ph). Found, %: C 71.46; H 4.86; N 23.41. C18H15N5. Calculated,
%: C 71.76; H 4.98; N 23.26.
1,5-Diphenyl-3-(4-pyridyl)formazan (4b) was obtained analogously to the previous compound 4a from
hydrazone 3b (1.72 g, 8.73 mmol) and aniline (0.81 g, 9.00 mmol) as a dark claret powder. Yield was 1.00 g (38%)
of mp 192°C (from ether) (lit. mp 185-187°C [26]). 1H NMR spectrum, δ, ppm (J, Hz): 15.80 (1H, s, NH); 8.66 (2H,
d, J = 4.5, H-α Py); 8.03 (2H, d, J = 4.6, H-β Py); 7.72 (4H, d, J = 8.0, H-o Ph); 7.49 (4H, t, J = 7.8, H-m Ph); 7.34
(2H, t, J = 7.3, H-p Ph). Found, %: C 71.76; H 4.86; N 23.70. C18H15N5. Calculated, %: C 71.76; H 4.98; N 23.26,
1,3,5-Triphenylformazan (4c) was obtained analogously from benzaldehyde phenylhydrazone (1.72 g, 8.73
mmol) and aniline (0.81 g, 9.00 mmol) as a dark claret powder. Yield was 1.32 g (50%) of mp 176°C (from ether)
(lit. mp 175-176°C [58]).
2,3-Diphenyl-5-(3-pyridyl)tetrazolium Trichlorocobaltate(II).MeCN (5a). A solution of cobalt chloride
hexahydrate (24 mg, 0.100 mmol) in ethanol (4 ml) was slowly poured into a solution of formazan 4a (30 mg, 0.100
mmol) in acetonitrile (4 ml). After keeping in a closed vessel for 20 days dark blue crystals of complex 5a separated
from the blue solution. The crystals were washed with ether and air dried. Complex 5a (21 mg, 91%) was obtained
having mp 293°C. Found, %: C 47.30; H 3.25; N 16.51. C20H17Cl3CoN6. Calculated, %: C 47.38; 3.36; N 16.58.
Crystals of 5a were grown from an acetonitrile–ethanol mixture.
2,3-Diphenyl-5-(4-pyridyl)tetrazolium Trichlorocobaltate(II) (5b). Ethanol (2 ml) was added slowly to a
solution of formazan 4b (30 mg: 0.100 mmole) in methylene chloride (4 ml) in such a way that the ethanol formed a
uniform layer above the layer of formazan solution. A solution of cobalt chloride hexahydrate (24 mg, 0.100 mmol)
in ethanol (3 ml) was added to the ethanol layer and the whole was left for 14 days. On mixing the solutions dark red
needles with a green iridescence were precipitated. The needles were washed with ether and dried in the air. Complex
5b (20 mg, 87%) was obtained with mp 315°C. Found, %: C 46.46; H 2.63; N 15.02. C18H14Cl3CoN5. Calculated, %:
C 46.40; H 3.01; N 15.04.
2,3-Diphenyl-5-(3-pyridyl)tetrazolium Trichlorocuprate(II) (6a). Ethanol (3 ml) was added slowly to a
solution of formazan 4a (50 mg, 0.166 mmol) in methylene chloride (5 ml) in such a way that the ethanol formed a
uniform layer above the layer of formazan solution. A solution of copper chloride dihydrate (28 mg, 0.166 mmol) in
ethanol (4 ml) was added to the ethanol layer. After 7 days pink crystals grew at the separation boundary of the
solutions and the red solution of formazan changed to yellow. The crystals were filtered off, washed with water, and
dried in the air. Complex 6a (35 mg, 92%) was obtained as orange needles with mp 250-251°C. Found, %: C 45.46;
H 2.63; N 14.79. C16H14Cl3CuN5. Calculated, %: C 45.96; H 2.98; N 14.89.
2,3-Diphenyl-5-(4-pyridyl)tetrazolium Trichlorocuprate(II) (6b). Ethanol (3 ml) was added slowly to a
solution of formazan 4b (50 mg, 0.166 mmol) in methylene chloride (5 ml) in such a way that the ethanol formed a
uniform layer above the layer of formazan solution. A solution of copper chloride dihydrate (28 mg, 0.166 mmol) in
ethanol (4 ml) was added to the ethanol layer and after 7 days pink crystals grew at the separation boundary of the
solutions and the formazan solution changed from red to yellow. The crystals were filtered off, washed with ether,
and dried in the air. Complex 6b (33 mg, 84%) was obtained of mp 267-268oC. Found, %: C 46.05; H 2.99; N 14.80.
C18H14Cl3CuN5. Calculated, %: C 45.96; H 2.98; N 14.89. On evaporating the mother liquor in the air yellow
monocrystals suitable for X-ray structural analysis were obtained. Crystals of compound 6b were grown from a
methylene chloride–ethanol mixture.
2,3,5-Triphenyltetrazolium Chloride (7). Isoamyl nitrite (110 mg, 0.927 mmol) was added dropwise to
formazan 4c (100 mg, 0.333 mmol) in absolute chloroform (10 ml). A stream of dry gaseous HCl was passed through
the solution stirring constantly until the color of the solution did not change first from claret to blue-green and then to
reddish brown. The mixture was left to stand for several hours, after which HCl gas was passed for a
1454

further short time. The solution was evacuated in vacuum, the oily residue was dissolved in a little amount of
ethanol and two volumes of a chloroform-diethyl ether 1 : 1 mixture were added. A white flaky solid was
precipitated, which was filtered off, and dried in the air. Product 7 (44 mg, 40%) was obtained with mp 251-253°C
(lit. mp 242-243°C [40]). 1H NMR spectrum, δ, ppm (J, Hz): 8.35 (2H, d, J = 6.9, H-o Ph(C)); 8.24 (4H, d, J = 7.9,
H-o Ph(N)); 7.86 (2H, d, J = 7.1, H-m Ph(C)); 7.70-7.82 (7H, m, H-p Ph(C), H-m Ph(N), H-p Ph(N)).
REFERENCES
1.
J.-M. Lehn, Supramolecular Chemistry: Concepts and Prospects [Russian translation], Izdanie, Novosibirsk
(1995).
2.
3.
4.
C. Janiak, J. Chem. Soc., Dalton Trans., 2781 (2003).
V. Yu. Kukushkin and A. J. L. Pombeiro, Chem. Rev., 102, 1771 (2002).
M. N. Kopylovich, A. J. L. Pombeiro, A. Fischer, L. Kloo, and V. Yu. Kukushkin, Inorg. Chem., 42,
7239 (2003).
5.
V. D. Vreshch, A. N. Chernega, J. A. K. Howard, J. Sieler, and K. V. Domasevitch. J. Chem. Soc., Dalton
Trans., 1707 (2003).
6.
7.
8.
V. Yu. Kukushkin and A. J. L. Pombeiro, Inorg. Chim. Acta, 358, 1 (2005).
I. Hausser, D. Jerehel, and R. Kuhn, Chem. Ber., 82, 515 (1949).
B. I. Buzykin, G. N. Lipunova, L. P. Sysoeva, and L. I. Rusinova, Chemistry of Formazans [in Russian],
Nauka, Moscow (1992).
9.
10.
11.
12.
L. Hunter and C. Roberts, J. Chem. Soc., 820 (1941).
L. Hunter and C. Roberts, J. Chem. Soc., 823 (1941).
A. Siedle and L. Pignolet, Inorg. Chem., 19, 2052 (1980).
Kh. M. Severo, B. E. Zaitsev, V. I. Ivlieva, G. V. Avramenko, T. S. Kolodina, and B. I. Stepanov, Zh Neorg.
Khim., 29, 2314 (1984).
13.
A. S. Batsanov, Yu. T. Struchkov, Kh. M. Severo, B. E. Zaitsev, and V. I. Ivlieva, Zh. Neorg. Khim., 32,
93 (1987).
14.
15.
16.
17.
18.
19.
20.
H. Irving, J. B. Gill, and W. R. Cross, J. Chem. Soc., 2087 (1960).
D. J. Dale, J. Chem. Soc., A, 278 (1967).
I. N. Polyakova, Z. A. Starikova, O. P. Sulim, and G. N. Lipunova, Kristallogr., 37, 653 (1992).
C. Banciu, Rev. Roum. Chim., 44, 3 (1999).
K. Ohashi, K. Kurosawa, and K. Yamamoto, Bunseki Kagaku, 32, E361 (1983).
G. N. Lipunova, E. I. Krylov, N. P. Bednyagina, and V. A. Sharov, Zh. Obshch. Khim., 39, 1293 (1969).
I. I. Shevelina, L. P. Sidorova, V. N. Podchainova, and N. P. Bednyagina, Zh. Obshch. Khim., 42,
2546 (1972).
21.
22.
R. I. Ogloblina, N. P. Bednyagina, and A. D. Garnovskii, Zh. Obshch. Khim., 40, 367 (1970).
N. N. Gumileva, L. F. Lipatova, G. N. Lipunova, and N. P. Bednyagina, Khim. Geterotsikl. Soedin.,
774 (1974). [Chem. Heterocycl. Comp., 10, 671 (1974)].
23.
24.
N. N. Gumelina, G. N. Lipunova, N. P. Bednyagina, and S. L. Mertsalov, Zh. Org. Khim., 5, 1108 (1977).
N. P. Bedyagina and G. N. Lipunova, Khim. Geterotsikl. Soedin., 877 (1969). [Chem. Heterocycl. Comp., 5,
652 (1969)].
25.
A. D. Garnovskii, N. P. Bednyagina, L. I. Kuznetsova, V. T. Panyushkin, O. A. Osipov, R. I. Ogloblina, and
A. P. Novikova, Zh. Neorg. Khim., 14, 1576 (1969).
26.
27.
28.
29.
H. J. Cottrell, D. L. Pain, and R. Slack, J. Chem. Soc., 2968 (1954).
E. Suenaga, Yakugaku Zasshi, 79, 803 (1959); Chem. Abs., 21938 (1959).
W. Ried and H. Gick, Ann. Chimie (Paris), 581, 16 (1951).
J. N. Ashley, B. M. Davis, A. W. Nineham, and R. Slack, J. Chem. Soc., 3881 (1953).
1455

30.
31.
32.
33.
34.
35.
36.
A. Eibner and K. Hofmann, Chem. Ber., 3011 (1904).
W. Ried, Angew. Chem., 64, 391 (1952).
M. Seyhan, Chem. Ber., 646 (1955).
L. Mester, J. Am. Chem. Soc., 4301 (1955).
S. V. Shinkorenko, G. T. Pilyugin, and G. B. Finkel', Zh. Obshch. Khim., 42, 2551 (1972).
M. Seyhan and W. C. Fernelius, J. Am. Chem. Soc., 217 (1957),
E. S. Karavaeva, N. P. Bednyagina, T. A. Sharkova, and I. I. Mudretsova, Khim. Geterotsikl. Soedin.,
1420 (1975). [Chem. Heterocycl. Comp., 11, 1208 (1975)].
37.
K. Mukai, M. Matsubara, H. Hisatou, Y. Hosokoshi, K. Inoue, and N. Azuma, J. Phys. Chem.(B), 106,
8632 (2002).
38.
39.
40.
41.
42.
43.
44.
45.
M. Kishita, Y. Mito, and M. Kubo, Aust. J. Chem., 11, 309 (1958).
M. I. Ermakova, E. I. Krylov, and I. Ya. Postovskii, Zh. Obshch. Khim., 30, 849 (1960).
R. Price, J. Chem. Soc. A, 3378 (1971).
M. Predota, V. Petricek, Z. Zak, T. Glowiak, and J. Novotny, Acta Crystallogr,. C47, 738 (1991).
R. Luboradzki, W. Kozminski, and L. Stefaniak, J. Crystallogr. Spectrosc. Res., 23, 133 (1993).
R. Luboradzki, J. Lipkowski, W. Kozminski, and L. Stefaniak, J. Chem. Crystallogr., 25, 29 (1995).
V. M. Divjakovic, V. M. Leovac, B. Ribar, G. Argay, and A. Kalman, Acta Crystallogr. B, 38, 1738 (1982).
G. A. Bogdanovic, V. B. Medakovic, L. S. Vojinovic, V. I. Cesljevic, V. M. Leovac, A. Spasojevic-de Bire,
and S. D. Zaric, Polyhedron, 20, 2231 (2001).
46.
47.
M. Bloy, M. Kretschmann, S. Scholz, M. Teichert, and U. Diefenbach, Z. Anorg. Allg. Chem., 626,
1946 (2000).
Hao Xu, Jinyu Ji, Zhongzhi Wu, Jianzhong Zou, Zheng Xu, and Xiaozeng You, Polyhedron, 12,
2261 (1993).
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
Tian-Tian Pan and Duan-Jun Xu, Acta Crystallogr., E60, m56 (2004).
C. M. Armstrong. P. V. Bernhardt, Piao Chin, and D. R. Richardson, Eur. J. Inorg. Chem., 1145 (2003).
F. E. Hahn, D. Scharn, and T. Lugger, Z. Kristallogr.-New Cryst. Struct., 212, 472 (1997).
A. Skorska, B. J. Oleksyn, and J. Sliwinski, Enantiomer, 7, 295 (2002).
P. Pytel, B. J. Oleksyn, and J. Sliwinski, Enantiomer, 6, 201 (2001).
P. C. Healy, C. Pakawatchai, and A. H. White, Aust. J. Chem., 38, 669 (1985).
J. M. Savariault, J. Galy, J. M. Gutierrez-Zorilla, and P. Roman, J. Mol. Struct., 176, 313 (1988).
R. Clerac, F. A. Cotton, S. P. Jeffery, C. A. Murillo, and Xiaoping Wang, Dalton Trans., 3022 (2003).
A. V. Navlyuk, V. N. Davydov, and M. G. Mys’kiv, Koordin. Khim., 27, 917 (2001).
M. Lacan, I. Tabakovic, and Z. Cecovic, Tetrahedron, 30, 2991 (1974).
A. M. Mattson, C. O. Jensen, and R. A. Duther, J. Am. Chem. Soc., 70, 1284 (1948).
1456