Pyridine-containing nickel(II) bis-formazanates: Synthesis, structure, and electrochemical study

Article abstract of DOI:10.1007/s11172-006-0491-9

Five diamagnetic nickel(II) complexes with pyridine-containing formazans of composition 2L·M were synthesized by slow diffusion. X-ray diffraction study of three of these complexes demonstrated that the nickel atoms are coordinated by four nitrogen atoms of two ligands and are in a square-planar environment. The nickel atoms lie on inversion centers. The chelate six-membered rings Ni-N-N-C-N-N are nonplanar due to noncovalent repulsions between the closely arranged aryl groups. Data from NMR spectroscopy, electronic absorption spectroscopy, and electrochemistry (cyclic voltammetry and rotating disk electrode) show that all complexes have similar structures in solution.

Full text of DOI:10.1007/s11172-006-0491-9

Russian Chemical Bulletin, International Edition, Vol. 55, No. 10, pp. 1810—1818, October, 2006
1810
Pyridineꢀcontaining nickel(II) bisꢀformazanates:
synthesis, structure, and electrochemical study
b
a
a
N. A. Frolova,a S. Z. Vatsadze,a V. E. Zavodnik, R. D. Rakhimov, and N. V. Zyk
ꢀ
aDepartment of Chemistry, M. V. Lomonosov Moscow State University,
1 Leninskie Gory, 119992 Moscow, Russian Federation.
Fax: +7 (495) 932 8846. Eꢀmail: szv@org.chem.msu.ru
bL. Ya. Karpov Institute of Physical Chemistry,
10 ul. Vorontsovo Pole, 105064 Moscow, Russian Federation
Five diamagnetic nickel(II) complexes with pyridineꢀcontaining formazans of composition
2L•M were synthesized by slow diffusion. Xꢀray diffraction study of three of these complexes
demonstrated that the nickel atoms are coordinated by four nitrogen atoms of two ligands and
are in a squareꢀplanar environment. The nickel atoms lie on inversion centers. The chelate sixꢀ
membered rings Ni—N—N—C—N—N are nonplanar due to noncovalent repulsions between
the closely arranged aryl groups. Data from NMR spectroscopy, electronic absorption specꢀ
troscopy, and electrochemistry (cyclic voltammetry and rotating disk electrode) show that all
complexes have similar structures in solution.
Key words: formazans, formazanates, metalloligands, nickel complexes, cyclic voltammetry,
Xꢀray diffraction study, electronic absorption spectroscopy.
In the last third of the 20th century, supramolecular
with metal M2. Compounds, which can form chelates
with the central metal ion with retention of the donor
centers directed outward, are commonly used as the orꢀ
ganic component L.5—7
chemistry, which has been earlier the subject of a few
studies on selective complexing agents and molecular recꢀ
ognition, became a rapidly developing field of chemistry.1
Extensive studies have been carried out on the chemistry
of supramolecular polymers, i.e., highꢀmolecularꢀweight
compounds composed of repeated lowꢀmolecularꢀweight
fragments linked to each other by noncovalent interacꢀ
tions.2 Coordination polymers consisting of an organic
molecule and a metal atom/ion as two components, which
are linked to each other by a coordination bond, are conꢀ
sidered by many researchers as promising materials posꢀ
sessing the semiconducting, optical, and magnetic propꢀ
erties.3,4 These properties are largely determined by a virꢀ
tually infinite series of combinations of inorganic and
organic components of structural polymers. However, an
empirical search for such combinations becomes increasꢀ
ingly less advantageous and attractive.
Instead of methods based on the use of simple organic
ligands, procedures with the use of "complex" ligands inꢀ
cluding one or several metal atoms have gained increasing
acceptance. Complex ligands provide an approach to nuꢀ
merous structures containing at least two exodentate
groups, which can form additional coordination bonds.
We will refer to such compounds as metalloligands.
The formation of a coordination polymer with the use
of metalloligands as building blocks can be represented by
Scheme 1, which involves the synthesis of the metalloꢀ
ligand by the reaction of an organic component L with
metal M1 followed by the reaction of this metalloligand
Scheme 1
Formazans and their complexes are convenient subꢀ
strates for the construction of metalloligands due to the
presence of a potentially chelating chromophoric group
and the possibility of introducing electronꢀdonating subꢀ
stituents at positions 1, 3, and 5. The deprotonated form
of formazan, in which the negative charge is delocalized
throughout the conjugated chain, is generally involved in
complexation with metal salts to form sixꢀmembered metal
chelates A in which the hydrogen atom is replaced by
metal.8 Complexes with CoII, NiII, CuII, CdII, PdII,
and ZnII containing the MN4 coordination unit have been
synthesized by this method and characterized.9—18
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1745—1753, October, 2006.
1066ꢀ5285/06/5510ꢀ1810 © 2006 Springer Science+Business Media, Inc.

Nickel bisꢀformazanates
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 10, October, 2006
1811
As for the design of metalloligands, it should be noted
that formazans containing heterocyclic substituents (Het
are benzazoles,19—24 azoles,25 pyridines,26—29 quinoꢀ
lines,28—35 or pyrimidines36) were described in the literaꢀ
ture. Nevertheless, in spite of numerous known heteroarylꢀ
substituted formazans, these compounds have not been
used for the synthesis of metalloligands.
In the present study, we examined the formation of
nickelꢀcontaining metalloligands based on formazans
bearing the pyridine substituents at position 3 or 5
(Scheme 2). The resulting complexes were characterized
by Xꢀray diffraction, microanalysis, NMR spectroscopy,
and electronic absorption spectroscopy. In addition, the
electrochemical properties of these compounds were
studied.
plexes as single crystals immediately during the synthesis.
In particular, we succeeded for the first time in isolating
single crystals of nickel bisꢀtriphenylformazanate 2d,
which has been known for at least 65 years.9,10
We chose nickel acetate, chloride, perchlorate, and
nitrate as metalꢀcontaining components (see Scheme 2).
It should be noted that not all reactions of nickel salts
with formazans 1a—d produce bisꢀformazanates. For
ligand 1a, we succeeded in preparing bisꢀformazanate 2a
only by the reaction of this ligand with nickel acetate and
perchlorate. In the latter case, perchloric acid generated
in the exchange reaction interacts with the pyridine subꢀ
2+
stituent to form bisꢀpyridinium salt 2aH2 •2ClO4. In
turn, ligand 1b gives bisꢀformazanate 2b only with nickel
acetate. In other cases, the reactions of ligands 1a,b afford
complexes of unknown composition. The reaction of
ligand 1c with all the nickel salts used produced bisꢀ
formazanate 2c. Bisꢀformazanate 2d was prepared by the
reaction of ligand 1d with nickel acetate or chloride. Comꢀ
plex 2d has been synthesized earlier.9,10,38
Scheme 2
Nickel(II) bisꢀformazanates are known15 to be diaꢀ
1
magnetic. Hence, we studied complexes 2 by H NMR
2+
–
spectroscopy. Complexes 2aH2 •2ClO4 •2H2O and
2c,d were isolated from the reaction mixtures as single
crystals suitable for Xꢀray diffraction study.
The resulting complexes are insoluble in deuteroꢀ
chloroform. Hence, NMR studies were carried out in
DMSOꢀd6. The use of DMSOꢀd6 instead of deuteroꢀ
chloroform does not lead to substantial changes in the
spectra of the ligand, which was exemplified by the specꢀ
tra of ligand 1c. Hence, all characteristic spectroscopic
features of the complexes can be assigned to their specific
i. Slow diffusion, CH2Cl2 or MeCN, EtOH, 20 °C.
1, 2
R1
R2
X
–
a
b
c
d
3ꢀpy
4ꢀpy
Ph
Ph
Ph
3ꢀpy
Ph
OAc–, ClO4
OAc–
OAc–, Cl–, ClO4–, NO3
OAc–, Cl–
–
Ph
1
structural parameters. In the H NMR spectra of prodꢀ
Note. The reaction 1a + Ni(ClO4)2 produces the bisꢀpyridinium
ucts 2, signals at δ 14 belonging to the N—H protons of
the starting formazans are absent, which is indicative of
the presence of the deprotonated form of formazan in the
structures of the complexes. Like the spectra of the ligands,
2+
–
salt 2aH2 •2ClO4
.
To synthesize metalloligands, viz., nickelꢀbased bisꢀ
formazanates, we used formazans containing the pyridine
substituents in different positions of the main chain, such
as 3ꢀ(3ꢀpyridyl)ꢀ1,5ꢀdiphenylformazan (1a), 3ꢀ(4ꢀpyriꢀ
dyl)ꢀ1,5ꢀdiphenylformazan (1b), and 5ꢀ(3ꢀpyridyl)ꢀ1,3ꢀ
diphenylformazan (1c), as well as 1,3,5ꢀtriphenylformazan
containing no pyridine substituents (1d) as the reference
compound. Formazans 1a—d have been synthesized and
characterized earlier.26,28,29,37
Known methods for the preparation of bisꢀformazaꢀ
nates are based on rapid mixing of ethanolic or acetone
solutions of the ligand and a nickel salt at room temperaꢀ
ture16,19,25 or on heating.9,10,14,15,38 Single crystals suitꢀ
able for Xꢀray diffraction were grown by recrystallization
of the primary reaction products. We synthesized nickel
bisꢀformazanates by slow diffusion of an ethanolic soluꢀ
tion of a nickel salt into a solution of the ligand in CH2Cl2
or MеCN. This method is commonly used for the syntheꢀ
sis of supramolecular infinite ensembles.7 For the systems
under study, this approach allowed us to prepare comꢀ
2+
–
the spectra of complexes 2a, 2aH2 •2ClO4 and 2b,d
are characterized by the equivalence of the signals of the
phenyl substituents at the first and fifths atoms of the
formazan chain. However, this fact for the ligands is atꢀ
tributed to fast exchange of the acidic hydrogen atom,
whereas for the complexes, this is accounted for by the
fact that both phenyl groups are in the identical environꢀ
ment, due to which the signals for the protons of the
corresponding rings are equivalent.
For all complexes 2, there are particular changes in
the chemical shifts of protons compared to those obꢀ
served in the spectra of the ligands. The signals for the
protons of the aryl substituent at the third carbon atom of
the formazan chain remain unchanged (compounds
2+
–
2aH2 •2ClO4 and 2b) or are shifted only slightly (the
other compounds). The signals for the ortho protons of
the phenyl rings at the first and fifth nitrogen atoms of the
formazan chain are shifted downfield by 0.04 ppm (for

1812
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 10, October, 2006
Frolova et al.
Table 1. Data from electronic absorption spectroscopy for
formazans 1 and their complexes 2
0.2—0.4 ppm (these signals are observed at δ 7.12—7.15
for all complexes). Such shifts of the signals for the
meta and para protons can be attributed to the mutual
influence of the closely spaced aryl groups (see below).
The electronic absorption spectra of arylformazans 1
show21—24,34,36,39—44 characteristic bands in the visible
and nearꢀUV regions at 300 and 480 nm (Table 1). The
spectra of complexes 2 have additional bands at 360 and
660—760 nm compared to the absorption spectra of the
ligands. These bands are assigned to charge transfer from
the nickel ion to the ligand,16,17,20,21,45 which is responꢀ
sible for the black color of the complexes.
Compound
Solvent
EAS, λmax/nm (logε)
1a
MeOH
DMF
MeOH
MeOH
MeOH
MeOH
309 (4.23), 473 (3.90)
309 (4.40), 481 (4.15)
319 (4.23), 468 (3.95)
291 (4.37), 472 (3.95)
298 (4.27), 484 (3.98)
309 (4.48), 358 (4.42),
424 sh, 774 (3.17)
303 (4.24), 363 (4.02),
424 (3.79), 560 sh,
684 (3.18)
1b
1c
1d
2a
2+
–
2aH2 •2ClO4
DMF
The crystallographic data and other parameters for
2+
–
complexes 2aH2 •2ClO4 •2H2O and 2c,d are given in
Table 2. The molecular structures of these complexes and
selected geometric parameters are presented in Figs 1—3,
respectively.
2b
MeOH
281 (4.57), 335 (4.55),
365 (4.52), 404 (3.49),
749 (3.23), 770 (3.22)
309 (4.50), 357 sh,
436 (3.92), 658 (3.22)
305 (4.24), 357 sh,
437 (3.99)
2c
2d
DMF
DMF
According to the Xꢀray diffraction data, compounds
2+
–
2aH2 •2ClO4 •2H2O and 2c,d are complexes of comꢀ
position 2L•M. In all these structures, the nickel atoms
lie on inversion centers and are surrounded by four nitroꢀ
gen atoms. The coordination environment of the metal
atom is a planar square. Known monoligand nickel comꢀ
plexes with acyclic 1,5ꢀdiarylformazans are characterized
2+
complexes 2a and 2aH2 •2ClO4–, the downfield shift is
0.15 ppm). The signals for the meta and para protons of
these phenyl rings coalesce and are shifted upfield by
C(16)
C(17)
C(15)
C(18)
C(14)
C(13)
N(4)
C(3)
C(2)
C(4)
C(5)
N(3)
Ni
C(1)
C(6)
N(5)
O(1)
N (1)
N(2)
C(7)
H(5N)
O(2)
Cl
O(3)
C(12)
C(8)
C(9)
O(4)
C(11)
C(10)
2+
–
Fig. 1. Molecular structure of the complex 2aH2 •2ClO4 •2H2O projected onto the NiN4 plane. The solvate water molecules are
omitted. The intramolecular O(2)...H(5N) hydrogen bond is indicated by a dashed line. Selected bond lengths/Å: Ni—N(1),
1.874(4); Ni—N(3), 1.879(4); N(1)—N(2), 1.299(5); N(1)—C(7), 1.424(6); N(2)—C(1), 1.335(6); N(3)—N(4), 1.302(5);
N(3)—C(13), 1.424(6); N(4)—C(1), 1.336(6); C(1)—C(2), 1.467(6). Selected bond angles/deg: N(1a)—Ni—N(3), 95.63(16);
N(1)—Ni—N(3), 84.37(16); N(2)—N(1)—C(7), 114.6(4); N(2)—N(1)—Ni, 121.4(3); C(7)—N(1)—Ni, 123.3(3); N(1)—N(2)—C(1),
118.7(4); N(4)—N(3)—C(13), 115.0(4); N(4)—N(3)—Ni, 122.0(3); C(13)—N(3)—Ni, 122.4(3); N(3)—N(4)—C(1), 118.3(4);
N(2)—C(1)—N(4), 125.7(4); N(2)—C(1)—C(2), 116.3(4); N(4)—C(1)—C(2), 116.7(4).

Nickel bisꢀformazanates
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 10, October, 2006
1813
2+
–
Table 2. Xꢀray data collection and refinement statistics for complexes 2aH2 •2ClO4 •2H2O
and 2c,d
2+
–
Compound
2aH2 •2СlO4 •2Н2О
2c
2d
Molecular formula
Molecular weight
Crystal dimensions/mm
Crystal system
Space group
a/Å
b/Å
c/Å
α/deg
β/deg
C36H34Cl2N10NiO10
896.34
0.44×0.10×0.08
C36H28N10Ni
659.39
0.34×0.22×0.06
Triclinic
P–1
C38H30N8Ni
657.42
0.29×0.26×0.19
P–1
7.748(2)
10.934(2)
12.674(3)
101.53(3)
95.01(3)
104.83(3)
1006.1(4)
2
P–1
8.022(2)
10.820(2)
11.077(2)
113.45(3)
95.35(3)
111.63(3)
786.8(3)
2
7.993(2)
10.619(2)
10.996(2)
114.03(3)
94.91(3)
110.74(3)
767.8(3)
1
γ/deg
V/Å3
Z
dcalc/g cm–3
µ/mm–1
1.479
0.684
1.426
0.677
1.387
0.659
F(000)
462
342
342
T/К
293(2)
293(2)
293(2)
θ Scan range/deg
Ranges of indices
of reflections
1.66—25.17
–9 ≤ h ≤ 0,
–12 ≤ k ≤ 13,
–15 ≤ l ≤ 15
3898
2.11—25.47
0 ≤ h ≤ 9,
–12 ≤ k ≤ 12,
–13 ≤ l ≤ 13
3200
2.09—25.97
–9 ≤ h ≤ 0,
–12 ≤ k ≤ 13,
–13 ≤ l ≤ 13
3312
Number of measured
reflections
Number of independent
3606 (0.0284)
271
2848 (0.0157)
266
3077 (0.0245)
250
reflections (Rint
)
Number of parameters
in refinement
R1 (I ≥ 2σ(I ))
0.0554
0.1101
0.985
0.0302
0.0731
0.922
0.0250
0.0626
0.887
wR2 (based on all reflections)
Goodnessꢀofꢀfit on F 2
Residual electron
density (max/min)/e Å–3
CCDC refcode
1.128/–0.332
0.371/–0.305
0.263/–0.253
610465
610466
611500
by the planar chelate Ni—N(Ar)—N—C(Ar)—N—N(Ar)
ring.46,47 Bisꢀligand complexes of 1,5ꢀdiarylformazans can
have two different types of structures due to repulsions
between the aryl substituents. In one case, the metal cheꢀ
late rings are twisted about the C(3)—Ni—C(3) axis, the
chelate rings remaining planar, whereas the coordination
environment of the metal atom being tetrahedrally disꢀ
torted. This type was found in the structure of copper(II)
bisꢀformazanate.13 In another case, the squareꢀplanar enꢀ
vironment of the metal atom is retained, but the metal
chelate rings are distorted due to deviation of the metal
atom from the plane through four nitrogen atoms of the
chelate ring. Such structures are typical of divalent
nickel15,16 and palladium.11
the nickel atoms from the mean N4 planes in the comꢀ
pounds under study are given in Table 3. This table also
lists the dihedral angles between these planes and the
planes of the NiN4 rings.
As can be seen from Fig. 4, the aryl substituents at the
first and fifths nitrogen atoms of the formazan chain are
located at certain distances from each other. Analysis of
these distances (see Table 3) shows that the aryl groups of
the adjacent ligand molecules are linked to each other by
π—π interactions, which is also manifested in the 1H NMR
spectra.
In the molecular structure of complex 2c, the phenyl
rings at position 3 of the ligands are disordered due to a
twist about the C(1)—C(7) bond by an equal angle. The
position of the nitrogen atom in the pyridine ring is statisꢀ
tical, and this atom is disordered over two positions. One
of several possible orientations is shown in Fig. 2. The
phenyl rings at position 3 of the ligands in the molecular
Like the nickel complexes of 1,5ꢀdiarylformazans deꢀ
2+
–
scribed in the literature,15,16 complexes 2aH2 •2ClO4
•
•2H2O and 2c,d belong to the second structural type with
nonplanar metal chelate rings (Fig. 4). The deviations of

1814
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 10, October, 2006
Frolova et al.
C(11)
C(12)
C(10)
C(9)
C(8)
C(13)
N(2)
N(1)
C(2A)
C(1)
C(3A)
C(4)
Ni
C(7)
C(5A)
C(6A)
N(3)
N(4)
C(15)
C(14)
C(18)
C(19)
C(16)
N(5C)
Fig. 2. Molecular structure of complex 2c for one orientation of the phenyl and pyridine rings projected onto NiN4 the plane. Selected
bond lengths/Å: Ni—N(2), 1.8723(17); Ni—N(4), 1.8778(16); N(1)—N(2), 1.299(2); N(1)—C(7), 1.347(3); N(2)—C(8), 1.422(3);
N(3)—N(4), 1.296(2); N(3)—C(7), 1.331(3); N(4)—C(14), 1.421(3); C(1)—C(7), 1.483(3). Selected bond angles/deg:
N(2a)—Ni—N(4), 94.93(8); N(2)—Ni—N(4), 85.07(8); N(2)—N(1)—C(7), 119.37(16); N(1)—N(2)—C(8), 113.65(15);
N(1)—N(2)—Ni, 122.98(13); C(8)—N(2)—Ni, 122.93(12); N(4)—N(3)—C(7), 119.89(16); N(3)—N(4)—C(14), 113.47(15);
N(3)—N(4)—Ni, 123.02(13); C(14)—N(4)—Ni, 123.13(12); N(3)—C(7)—N(1), 124.71(17); N(3)—C(7)—C(1), 117.48(17);
N(1)—C(7)—C(1), 116.40(17).
Table 3. Distances and angles between selected fragments in the molecules of complexes
2+
–
2aH2 •2ClO4 •2H2O and 2c,d
2+
–
Parameter
2aH2 •2СlO4 •2Н2О
2с
2d
Dihedral angle between the N4
and NiN4 planes/deg
40.5
37.0
37.2
Deviation of the Ni atom from
the mean N4 planes/Å
0.904
0.208
0.832
0.198
0.831
0.198
Deviation of the C atom of the formazan
chain from the mean N4 planes/Å
Distance between the N4 planes/Å
Distance between the centroids of
the nearest Ph rings/Å
1.808
3.934(1)
1.664
3.774(1)
1.662
3.829(1)
Distance between the closest C atoms
of the nearest Ph rings/Å
3.101(1)
3.018(1)
3.034(1)
2+
–
structure of complex 2d, like those in the structure of
complex 2c, are disordered over two positions. One of
several possible orientations is shown in Fig. 3.
In the crystal structure of 2aH2 •2ClO4 •2H2O,
one of the oxygen atoms of the perchlorate anion (O(2))
is linked to the H(5N) atom by a strong hydrogen

Nickel bisꢀformazanates
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 10, October, 2006
1815
C(11)
C(12)
C(10)
C(13)
C(9)
C(8)
N(2)
C(3A)
C(4A)
N(1)
Ni
C(5)
C(1)
C(2)
N(3)
C(6A)
C(7A)
N(4)
C(14)
C(19)
C(15)
C(16)
C(18)
C(17)
Fig. 3. Molecular structure of complex 2d for one orientation of the phenyl rings projected onto the NiN4 plane. Selected bond
lengths/Å: Ni(1)—N(3), 1.8754(15); Ni(1)—N(1), 1.8776(14); N(1)—N(2), 1.3011(17); N(1)—C(8), 1.429(2); N(2)—C(1), 1.337(2);
N(3)—N(4), 1.2991(17); N(3)—C(14), 1.426(2); N(4)—C(1), 1.342(2); C(1)—C(2), 1.481(2). Selected bond angles/deg:
N(3)—Ni(1)—N(1a), 94.83(7); N(3)—Ni(1)—N(1), 85.17(7); N(2)—N(1)—C(8), 113.40(13); N(2)—N(1)—Ni(1), 122.91(11);
C(8)—N(1)—Ni(1), 123.36(10); N(1)—N(2)—C(1), 119.64(14); N(4)—N(3)—C(14), 113.61(13); N(4)—N(3)—Ni(1), 123.06(12);
C(14)—N(3)—Ni(1), 122.95(10); N(3)—N(4)—C(1), 119.30(14); N(2)—C(1)—N(4), 125.02(15); N(2)—C(1)—C(2), 117.05(15);
N(4)—C(1)—C(2), 116.56(15).
bond (O(2)...H(5N), 1.884 Å; O(2)...N(5), 2.844(7) Å;
O(2)...H(5N)—N(5), 159.5°).
The electrochemical properties of complexes 2 were
studied by cyclic voltammetry (CV) and at a rotating disk
electrode (RDE) (Fig. 5, Table 4).
As can be seen from these data, oxidation of the comꢀ
plexes occurs in one quasireversible step, except for irreꢀ
versible oxidation of compound 2b (the number of elecꢀ
trons transferred in each electrochemical step, which was
experimentally determined by comparing with the ferꢀ
rocene current, is in a range of 0.2—0.4 due, apparently,
to electrode passivation during electrochemical measureꢀ
ments). The resulting radical cations are unstable on the
time scale used (the lifetime <5 s), because we observed a
pair of related peaks in the reverse
cathodic sweep of the CV curve (see
Fig. 5, the reduction peak A and the
oxidation peak B). The potentials of
these peaks are exactly equal to the
reduction potential of 2,3,5ꢀtriꢀ
2+
–
phenyltetrazolium chloride (3),
Fig. 4. Molecular view of 2a in the structure of 2aH2 •2ClO4
•
which we have synthesized and studꢀ
ied by electrochemical methods earlier,37 and the oxidaꢀ
•2H2O along the line between the N(1) and N(3) atoms. The
H atoms, perchlorate anions, and water molecules are omitted.

1816
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 10, October, 2006
Frolova et al.
erties of the latter compounds earlier.37 Therefore, the
initial electronic changes upon both oxidation and reducꢀ
tion are concentrated at the conjugated system of four
nitrogen atoms of the formazan chain.
2 µA
B
To reveal the influence of protonation of the pyridine
nitrogen atoms on the electrochemical characteristics of
the complexes, we also studied the redox properties of the
–2
–1
0
1
E/V
2+
complex 2aH2 •2ClO4–. As can be seen from Table 4,
protonation of the pyridine nitrogen atoms does not
lead to changes in the electrochemical potentials. This
is evidence that the nature of the aryl substituents is of
little importance. The early reduction peak (–0.58 V,
see Table 4) is in the reduction region of the protons
of HClO4.48
To summarize, we synthesized and structurally charꢀ
acterized previously unknown nickel(II) complexes with
formazans containing the pyridine fragments at positions 1
or 3. Such compounds are promising building blocks for
the construction of complex infinite polyheterometallic
ensembles. Preliminary 1H NMR monitoring experiments
demonstrated that the reaction of metalloligand 2c with
silver(I) nitrate in DMSOꢀd6 produced new complexes.
The structures and properties of these complexes are the
subject of further investigations.
2a
C
D
3
A
Fig. 5. Cyclic voltammograms of complex 2a (solid line)
and compound (dashed line) (DMF, Bu4NBF4,
Ag/AgCl/KCl(sat.), 20 °C, Pt electrode).
3
Table 4. Electrochemical oxidation (E Ox) and reduction (ERed
potentials of compounds 2a—d measured by the CV method
(Ep is the peak potential) and at an RDE (E1/2 is the halfꢀwave
potential)a
)
Ox
Ox b
Red
Red c
Comꢀ
pound
E1/2
Ep
–E1/2
–Ep
V
2a
1.04
1.01
(–0.34, 0.89)
1.05
0.64
0.74 (0.63),
1.31 (1.23)
0.58,
0.76 (0.56),
1.36 (1.24)
0.74
Experimental
2+
–
2aH2 •2СlO4
0.98
0.24,
0.70
(–0.30, 0.96)
The course of the reactions and the purity of the resulting
compounds were controlled by TLC on a layer of silica gel
(Silufol) as the stationary phase. The 1H NMR spectra were
recorded in CDCl3 and DMSOꢀd6 on a BrukerꢀAvance instruꢀ
ment (400 MHz) with the use of signals of the residual protons
of the solvents as the internal standard. The electrochemical
oxidation and reduction potentials were measured on a PIꢀ50ꢀ1.1
potentiostat equipped with a PRꢀ8 programmer. The CV curves
and waves at an RDE were recorded on an XY recorder.
Tetrabutylammonium tetrafluoroborate of high purity grade
(99.8%, Fluka) was used as the supporting electrolyte. The conꢀ
centration of the electrolytes was 0.05 mol L–1. The electronic
absorption spectra in the visible and nearꢀUV regions were meaꢀ
sured on a Shimadzu UVꢀ2100 spectrophotometer.
2b
2c
2d
1.02
0.96
0.90,
1.04
(–0.32)
1.00
0.65
0.68
0.77
(0.65)
0.73 (0.68),
1.13 (1.03)
0.79 (0.72),
1.23 (1.04)
(–0.28, 0.94)
0.92
1.40 (–0.40, 0.87),
1.41
a DMF, Bu4NBF4, Ag/AgCl/KCl(sat.), 20 °C, a Pt electrode.
b The potentials of the reverse cathodic peaks are given in parenꢀ
theses.
c The potentials of the reverse anodic peaks are given in parenꢀ
theses.
Xꢀray diffraction study was carried out on an EnrafꢀNonius
CADꢀ4 diffractometers at 293 K (β filter, λ(MoꢀKα) =
0.71073 Å, θ/2θ scanning technique). The absorption correcꢀ
tion was applied based on the crystal shape. The structure
was solved by direct methods (SHELXꢀ97)49 and refined by
the fullꢀmatrix leastꢀsquares method against F 2 with anisotroꢀ
pic displacement parameters for all nonhydrogen atoms
(SHELXLꢀ97).50 All H atoms were located in difference
electron density maps and were not refined. The crystalloꢀ
graphic data and Xꢀray data collection and refinement statistics
for compounds 2aH2 •2ClO4 •2H2O, 2c, and 2d are given in
Table 2.
5ꢀ(3ꢀPyridyl)ꢀ1,3ꢀdiphenylformazan (1c) was synthesized acꢀ
cording to a known procedure29 as a darkꢀclaretꢀcolored powder
with a green tint, the yield was 65%, m.p. 175 °C (from diethyl
ether) (cf. lit. data29: m.p. 169 °C). Found (%): C, 71.46; H, 4.86;
tion potential of reduction product 3 (–0.49 and –0.28 V,
respectively).
Hence, oxidation of the compounds under study afꢀ
fords radical cations, which rather rapidly decompose to
give the tetrazolium cation and, apparently, a dimeric
product with the nickel—nickel bond (LNi—NiL). The
formation of dimeric (polymeric) products leads to
Ptꢀelectrode passivation, which apparently decreases the
observed anodic current.
The CV curves have two quasireversible reduction
peaks (see Fig. 5, the peaks C and D), whose potentials are
virtually equal to the reduction potentials of substituted
formazans 1. We have studied the electrochemical propꢀ
2+
-

Nickel bisꢀformazanates
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 10, October, 2006
1817
N, 23.41. C18H15N5. Calculated (%): C, 71.74; H, 5.02; N, 23.24.
1H NMR (CDCl3), δ: 15.35 (s, 1 H, NH); 8.82 (s, 1 H, α´ꢀHPy);
8.62 (d, 1 H, αꢀHPy, J = 3.9 Hz); 8.12 (d, 2 H, oꢀHPh(2), J =
(t, 2 H, mꢀHPh(1), J = 7.9 Hz); 7.10—7.24 (m, 3 H, pꢀHPh(2)
pꢀHPh(1), βꢀHPy).
,
Nickel(II) bis(1,3,5ꢀtriphenylformazanate) (2d) was syntheꢀ
sized from formazan 1d in CH2Cl2 and nickel acetate tetraꢀ
hydrate as black prismatic single crystals in 83% yield, m.p.
>300 °C. Complex 2d was also prepared from nickel chloride
hexahydrate and a solution of formazan 1d in MeCN as a finely
7.1 Hz); 8.06 (d, 1 H, γꢀHPy, J = 8.0 Hz); 7.78 (d, 2 H, oꢀHPh(1)
J = 7.6 Hz); 7.51 (t, 2 H, mꢀHPh(2), J = 7.7 Hz); 7.46 (t, 2 H,
mꢀHPh(1), J = 7.4 Hz); 7.34—7.43 (m, 3 H, pꢀHPh(2), pꢀHPh(1)
,
,
1
βꢀHPy). H NMR (DMSOꢀd6), δ: 13.59 (s, 1 H, NH); 8.99 (d,
1 H, α´ꢀHPy, J = 2.4 Hz); 8.41 (dd, 1 H, αꢀHPy, J1 = 4.8 Hz,
J2 = 1.5 Hz); 8.12 (ddd, 1 H, γꢀHPy, J1 = 8.1 Hz, J2 = 3.6 Hz,
J3 = 1.2 Hz); 7.95 (d, 2 H, oꢀHPh(2), J = 6.6 Hz); 7.93 (d, 2 H,
oꢀHPh(1), J = 6.9 Hz); 7.55 (t, 2 H, mꢀHPh(2), J = 7.5 Hz);
7.38—7.51 (m, 5 H, mꢀHPh(1), pꢀHPh(2), pꢀHPh(1), βꢀHPy).
Synthesis of complexes 2 (slow diffusion). Ethanol (3 mL)
was very slowly added to a solution of formazan 1 (0.166 mmol)
in MeCN or CH2Cl2 (4 mL) until stratification was achieved.
A solution of a nickel salt (0.083 mmol) in EtOH (5 mL) was
slowly added to the ethanolic layer. The reaction solution was
kept for 25 days. The resulting crystals or powder were separated
from the mother liquor, washed with diethyl ether, and dried
in air.
1
crystalline powder in 40% yield. H NMR (DMSOꢀd6, 50 °C),
δ: 8.11 (d, 2 H, oꢀHPh(2), J = 8.0 Hz); 7.75 (d, 4 H, oꢀHPh(1), J =
7.6 Hz); 7.60 (t, 2 H, mꢀHPh(2), J = 7.5 Hz); 7.48 (t, 1 H,
pꢀHPh(2), J = 7.1 Hz); 7.17 (t, 4 H, mꢀHPh(1), J = 7.3 Hz); 7.11
(t, 2 H, pꢀHPh(1), J = 7.0 Hz).
We thank the Florida State University (Tallahassee,
USA) for help in performing NMR studies.
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 06ꢀ03ꢀ
33077).
References
Nickel(II) bis[3ꢀ(3ꢀpyridyl)ꢀ1,5ꢀdiphenylformazanate] (2a)
was synthesized from a solution of formazan 1a in MeCN and
nickel acetate tetrahydrate; the yield was 86%, a black crystalꢀ
line powder, m.p. >320 °C. Found (%): C, 65.15; H, 4.46;
N, 21.00. C36H28N10Ni. Calculated (%): C, 65.37; H, 4.57;
N, 21.18. 1H NMR (DMSOꢀd6, 20 °C), δ: 9.24 (br.s, 1 H,
α´ꢀHPy); 8.66 (br.s, 1 H, αꢀHPy); 8.38 (br.s, 1 H, γꢀHPy); 7.82
(br.s, 4 H, oꢀHPh); 7.61 (br.s, 1 H, βꢀHPy); 7.12 (br.s, 6 H,
mꢀHPh, pꢀHPh).
1. J.ꢀM. Lehn, Supramolecular Chemistry, VCH, Weinheim,
1995.
2. L. Brunsveed, B. J. B. Folmer, E. W. Meijer, and R. P.
Sijbesma, Chem. Rev., 2001, 101, 4071.
3. C. Janiak, J. Chem. Soc., Dalton Trans., 2003, 2781.
4. S. Kitagawa, R. Kitaura, and S. Noro, Angew. Chem., Int.
Ed. Engl., 2004, 43, 2334.
Nickel(II) bis[3ꢀ(3ꢀpyridyl)ꢀ1,5ꢀdiphenylformazanate] diꢀ
5. V. D. Vreshch, A. N. Chernega, J. A. K. Howard, J. Sieler,
and K. V. Domasevitch, J. Chem. Soc., Dalton Trans.,
2003, 1707.
6. V. D. Vreshch, A. B. Lysenko, A. N. Chernega, J. A. K.
Howard, H. Krautscheid, J. Sieler, and K. V. Domasevitch,
J. Chem. Soc., Dalton Trans., 2004, 2899.
2+
–
hydroperchlorate dihydrate (2aH2 •2ClO4 •2H2O) was synꢀ
thesized from a solution of formazan 1a in CH2Cl2 and nickel
perchlorate hexahydrate as lustrous black prismatic crystals in
21% yield. The melting point was not measured and microanalyꢀ
sis was not carried out because the complex is dangerously exꢀ
plosive. 1H NMR (DMSOꢀd6, 20 °C), δ: 9.34 (br.s, 1 H, α´ꢀHPy);
8.79 (br.d, 1 H, αꢀHPy, J = 4.6 Hz); 8.70 (br.s, 1 H, γꢀHPy); 7.93
(br.d, 1 H, βꢀHPy, J = 7.3 Hz); 7.85 (br.d, 4 H, oꢀHPh, J =
7.5 Hz); 7.11—7.23 (m, 6 H, mꢀHPh, pꢀHPh).
Nickel(II) bis[3ꢀ(4ꢀpyridyl)ꢀ1,5ꢀdiphenylformazanate] (2b)
was synthesized from a solution of formazan 1b in MeCN and
nickel acetate tetrahydrate; the yield was 70%, a blackꢀbrown
crystalline powder, m.p. 293 °C. Found (%): C, 65.15; H, 4.46;
N, 21.00. C36H28N10Ni. Calculated (%): C, 64.90; H, 4.53;
N, 20.89. 1H NMR (DMSOꢀd6, 20 °C), δ: 8.71 (br.s, 2 H,
αꢀHPy); 8.00 (br.s, 2 H, βꢀHPy); 7.76 (br.s, 4 H, oꢀHPh); 7.13
(br.s, 6 H, mꢀHPh, pꢀHPh).
7. S. Noro, H. Miyasaka, S. Kitagawa, T. Wada, T. Okubo,
M. Yamashita, and T. Mitani, Inorg. Chem., 2005, 44, 133.
8. B. I. Buzykin, G. N. Lipunova, L. P. Sysoeva, and L. I.
Rusinova, Khimiya formazanov [Chemistry of Formazans],
Nauka, Moscow, 1992, 376 pp. (in Russian).
9. L. Hunter and B. Roberts, J. Chem. Soc., 1941, 820.
10. L. Hunter and B. Roberts, J. Chem. Soc., 1941, 823.
11. A. R. Siedle and L. H. Pignolet, Inorg. Chem., 1980, 19, 2052.
12. Kh. M. Severo, B. E. Zaitsev, V. I. Ivlieva, G. V. Avramenko,
T. S. Kolodina, and B. I. Stepanov, Zh. Neorg. Khim., 1984,
29, 2314 [J. Inorg. Chem. USSR, 1984, 29 (Engl. Transl.)].
13. A. S. Batsanov, Yu. T. Struchkov, Kh. M. Severo, B. E.
Zaitsev, and V. I. Ivlieva, Zh. Neorg. Khim., 1987, 32, 93
[J. Inorg. Chem. USSR, 1987, 32 (Engl. Transl.)].
14. H. Irving, J. B. Gill, and W. R. Cross, J. Chem. Soc.,
1960, 2087.
Nickel(II) bis[5ꢀ(3ꢀpyridyl)ꢀ1,3ꢀdiphenylformazanate] (2c)
was synthesized from a solution of formazan 1c in MeCN and
nickel perchlorate hexahydrate as lustrous black crystals in 44%
yield, m.p. >360 °C. Complex 2c was synthesized analogously
from nickel chloride hexahydrate as lustrous black crystals
(76% yield) and from nickel acetate tetrahydrate as a blackꢀ
brown powder (91% yield). Complex 2c was also prepared from
nickel nitrate hexahydrate and a solution of formazan 1c in
CH2Cl2 as lustrous black crystals in 61% yield. Found (%):
C, 65.29; H, 4.47; N, 21.05. C36H28N10Ni. Calculated (%):
15. D. Dale, J. Chem. Soc. A, 1967, 278.
16. I. N. Polyakova, Z. A. Starikova, O. P. Sulim, and G. N.
Lipunova, Kristallografiya, 1992, 37, 653 [Crystallogr. Repts,
1992, 37 (Engl. Transl.)].
17. A. C. Banciu, Rev. Roum. Chim., 1999, 44, 3.
18. K. Ohashi, K. Kurosawa, and K. Yamamoto, Bunseki
Kagaku, 1983, 32, E361.
1
C, 65.55; H, 4.25; N, 21.24. H NMR (DMSOꢀd6, 50 °C), δ:
9.05 (s, 1 H, α´ꢀHPy); 8.26 (d, 1 H, αꢀHPy, J = 3.9 Hz); 8.11 (d,
2 H, oꢀHPh(2), J = 7.1 Hz); 8.03 (br.s, 1 H, γꢀHPy); 7.78 (d, 2 H,
oꢀHPh(1), J = 7.8 Hz); 7.61 (t, 2 H, mꢀHPh(2), J = 7.7 Hz); 7.50
19. G. N. Lipunova, E. I. Krylov, N. P. Bednyagina, and V. A.
Sharov, Zh. Obshch. Khim., 1969, 39, 1293 [J. Gen. Chem.
USSR, 1969, 39 (Engl. Transl.)].

1818
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 10, October, 2006
Frolova et al.
20. I. I. Shevelina, L. P. Sidorova, V. N. Podchainova, and
N. P. Bednyagina, Zh. Obshch. Khim., 1972, 42, 2546 [J. Gen.
Chem. USSR, 1972, 42 (Engl. Transl.)].
38. M. I. Ermakova, E. I. Krylov, and I. Ya. Postovskii,
Zh. Obshch. Khim., 1960, 30, 849 [J. Gen. Chem. USSR,
1960, 30 (Engl. Transl.)].
21. R. I. Ogloblina, N. P. Bednyagina, and A. D. Garnovskii,
Zh. Obshch. Khim., 1970, 40, 367 [J. Gen. Chem. USSR,
1970, 40 (Engl. Transl.)].
39. R. I. Ogloblina, N. P. Bednyagina, and N. N. Gumelina,
Khim. Geterotsikl. Soedin., 1972, 8, 393 [Chem. Heterocycl.
Compd., 1972, 8 (Engl. Transl.)].
22. N. N. Gumelina, L. F. Lipatova, G. N. Lipunova, and N. P.
Bednyagina, Khim. Geterotsikl. Soedin., 1974, 10, 774 [Chem.
Heterocycl. Compd., 1974, 10 (Engl. Transl.)].
23. N. N. Gumelina, G. N. Lipunova, N. P. Bednyagina, and
S. L. Mertsalov, Zh. Org. Khim., 1977, 13, 1108 [J. Org.
Chem. USSR, 1977, 13 (Engl. Transl.)].
24. N. P. Bednyagina and G. N. Lipunova, Khim. Geterotsikl.
Soedin., 1969, 5, 877 [Chem. Heterocycl. Compd., 1969, 5
(Engl. Transl.)].
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., 1969, 14, 1576 [J. Inorg. Chem.
USSR, 1969, 14 (Engl. Transl.)].
26. H. J. Cottrell, D. L. Pain, and R. Slack, J. Chem. Soc.,
1954, 2968.
27. E. Suenaga, Yakugaku Zasshi, 1959, 79, 803; Chem. Abstr.,
1959, 21938.
28. W. Ried and H. Gick, Ann. Chim. (Paris), 1951, 581, 16.
29. J. N. Ashley, B. D. Davis, A. W. Nineham, and R. Slack,
J. Chem. Soc., 1953, 3881.
30. A. Eibner and K. Hofmann, Chem. Ber., 1904, 3011.
31. W. Ried, Angew. Chem., 1952, 64, 391.
32. M. Seyhan, Chem. Ber., 1955, 646.
40. G. N. Lipunova, L. V. Rodnenko, N. P. Bednyagina, I. I.
Mudretsova, and N. V. Marina, Khim. Geterotsikl. Soedin.,
1976, 12, 4498 [Chem. Heterocycl. Compd., 1976, 12 (Engl.
Transl.)].
41. V. M. Ostrovskii, V. M. Dziomko, and T. E. Zhukova,
Zh. Obshch. Khim., 1976, 47, 2351 [J. Gen. Chem. USSR,
1976, 47 (Engl. Transl.)].
42. N. N. Gumelina, V. N. Kostylev, G. N. Lipunova, and N. P.
Bednyagina, Zh. Prikl. Spektrosk., 1975, 22, 941 [J. Appl.
Spectr., 1975, 22 (Engl. Transl.)].
43. G. N. Lipunova, N. N. Gumelina, L. V. Kourova, and N. P.
Bednyagina, Khim. Geterotsikl. Soedin., 1977, 13, 460 [Chem.
Heterocycl. Compd., 1977, 13 (Engl. Transl.)].
44. G. V. Avramenko and B. I. Stepanov, Zh. Obshch. Khim.,
1974, 44, 1298 [J. Gen. Chem. USSR, 1974, 44 (Engl.
Transl.)].
45. L. F. Dubinina, V. N. Podchainova, and Yu. A. Sedov,
Koord. Khim., 1977, 3, 1564 [Sov. J. Coord. Chem., 1977, 3
(Engl. Transl.)].
46. J. Meuldijk, W. E. Renkema, A. M. van Herk, and C. H.
Stam, Acta Crystallogr., Sect. C., 1983, 39, 1536.
47. W. E. Renkema, C. N. Lute, and C. H. Stam, Acta
Crystallogr., Sect. B, 1979, 35, 75.
33. L. Mester, J. Am. Chem. Soc., 1955, 77, 4301.
34. S. V. Shinkorenko, G. T. Pilyugin, and G. B. Finkel´,
Zh. Obshch. Khim., 1972, 42, 2551 [J. Gen. Chem. USSR,
1972, 42 (Engl. Transl.)].
35. M. Seyhan and W. C. Fernelius, J. Am. Chem. Soc., 1957,
79, 217.
48. J. F. Coetzee and I. M. Kolthoff, J. Am. Chem. Soc., 1957,
79, 6110.
49. G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467.
50. G. M. Sheldrick, SHELXLꢀ97. Program for the Refinement of
Crystal Structures, University of Göttingen, Göttingen (Gerꢀ
many), 1997.
36. E. S. Karavaeva, N. P. Bednyagina, T. A. Sharkova, and I. I.
Mudretsova, Khim. Geterotsikl. Soedin., 1975, 11, 1420 [Chem.
Heterocycl. Compd., 1975, 11 (Engl. Transl.)].
37. N. A. Frolova, S. Z. Vatsadze, A. I. Stash, R. D. Rakhimov,
and N. V. Zyk, Khim. Geterotsikl. Soedin., 2006, No. 11
[Chem. Heterocycl. Compd., 2006 (Engl. Transl.)].
Received July 13, 2006;
in revised form August 23, 2006