New metal chelates of 5-amino-4-azopyrazoles: The crystal and molecular structure of bis{1-phenyl-3-methyl-4-(p-tolyl)azo-5-(p-carboxymethoxyphenyl) pyrazolamidato}copper(II)

Article abstract of DOI:10.1134/S0036023609040068

The reactions of 1,3-alkyl(aryl) derivatives of 5-amino-4-azopyrazoles (HL) with copper(2+) acetate afford metal chelates CuL₂. Complexes with the CuN₄ chromophore containing a substituted amino group (X = NR) as a donor, like their

Full text of DOI:10.1134/S0036023609040068

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2009, Vol. 54, No. 4, pp. 521–529. © Pleiades Publishing, Inc., 2009.
Original Russian Text © A.I. Uraev, O.Yu. Korshunov, A.L. Nivorozhkin, A.S. Antsyshkina, G.G. Sadikov, V.I. Nevodchikov, V.S. Sergienko, A.D. Garnovskii, 2009, published
in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 4, pp. 575–583.
COORDINATION
COMPOUNDS
New Metal Chelates of 5-Amino-4-Azopyrazoles:
The Crystal and Molecular Structure
of Bis{1-phenyl-3-methyl-4-(p-tolyl)azo-5-
(p-carboxymethoxyphenyl)pyrazolamidato}copper(II)
A. I. Uraeva, O. Yu. Korshunova, A. L. Nivorozhkina, A. S. Antsyshkinab, G. G. Sadikovb,
V. I. Nevodchikovc†, V. S. Sergienkob, and A. D. Garnovskiia
a Institute of Physical and Organic Chemistry, Southern Federal University,
pr. Stachki 194/2, Rostov-on-Don, 344090 Russia
E-mail: garn@ipoc.rnd.runnet.ru
b Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
E-mail: antas@igic.ras.ru
c Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences,
ul. Tropinina 49, Nizhni Novgorod, 603600 Russia
Received October 15, 2008
Abstract—The reactions of 1,3-alkyl(aryl) derivatives of 5-amino-4-azopyrazoles (HL) with copper(2+) ace-
tate afford metal chelates CuL2. Complexes with the CuN4 chromophore containing a substituted amino group
(X = NR) as a donor, like their azomethine analogues, have a pseudotetrahedral structure. Copper chelates with
X = NH are planar. The X-ray diffraction data and an additional hyperfine structure (ahfs) from 15N atoms of
the azo group in the labeled complexes provide evidence for the formation of six-membered metallocycles. The
coordination polyhedron in bis{1-phenyl-3-methyl-4-(p-tolyl)azo-5-(p-carboxymethoxyphenyl)pyrazolami-
dato}Cu(II) can be described as a pseudotetrahedron.
DOI: 10.1134/S0036023609040068
†
Studies of copper-containing non-heme protein ical and practical significance [9, 12, 14–16]
molecules, which play a key role in biochemical
processes associated with absorption of oxygen
from the atmosphere and in cell metabolism, have
stimulated investigations of copper chelates with
nitrogen-containing ligands aimed at modeling the
active sites of these metalloproteins and reactions
involving these compounds [1–4].
(Scheme 1).
Ar
Ar
α
β
N N
N N
6
6
D
B
R1
5
X
M/2
M/2
A
X
(II)
(I)
X = NR, O, S; R = H, Alk, Ar, Ts; R1 = H, Alk;
A = NR, O, S; B = D = CR2, N;
In addition, such complexes can be used as
pseudonucleases catalyzing chemical and photo-
chemical DNA cleavage [5–7]. Metal-containing
pseudonucleases have great potential in nucleic
acid chemistry and have found use as new structural
probes in protein studies and as therapeutic agents.
Ts = SO2C6H4-pMe; R2 = Alk, Ar
Scheme 1.
Earlier, we have reported the synthesis and results of
investigation of copper chelates of pyrazolaldiminate
with the N2X2 ligand environment (X = O, S, or Se) [21].
In the present study, we continued our research aimed at
revealing the influence of the nature of the donor atoms
in the pyrazole ligands on the structure and spectral
properties of copper complexes and at designing
new metal chelates with the MN4 coordination core
A special place among nitrogen-containing com-
plex compounds belongs to metal chelates with the
N4 ligand environment [8–20]. In the series of these
metal chelates, chelate compounds of aromatic (I)
and heterocyclic (II) Ó-substituted azo compounds
have attracted growing interest due to their theoret-
†
Deceased.
521

522
URAEV et al.
Table 1. Physicochemical characteristics of complexes IIIa–IIIg
Elemental analysis, found (calculated), %
No.
Electronic absorption spectra,
M.p., K
241
of compound
λ
max(nm) (ε, L mol–1 cm–1)
C
H
N
IIIa
IIIb
IIIc
IIId
69.4
5.0
17.6
625(2140),
840(1720),
1450(410)br
655(2100),
885(1825),
1460(425)br
620(2495),
865(1515),
1550(395)br
635(1655),
815(2085),
1590(480)br
370(41100),
600(1200)sh
370 (55260),
600(1170)sh
380(43190),
600 (980)
(69.8)
(5.2)
(17.2)
208
235
188
67.3
5.2
16.4
(67.5)
(5.2)
(15.9)
65.9
4.8
15.3
(65.7)
(4.6)
(15.3)
63.8
6.5
17.3
(63.4)
(6.6)
(17.7)
IIIe
IIIf
IIIg
160 (decomp.)
57.0
(56.8)
62.4
5.9
(5.9)
4.6
25.6
(25.9)
22.7
172
204
(62.7)
49.7
(4.7)
3.4
(22.3)
18.1
(50.1)
(3.6)
(18.6)
and synthesized copper chelates of type III lized from toluene. The yields were 70–80%. The ele-
mental analysis data and the melting points of the com-
plexes are given in Table 1.
(Scheme 2).
2R2
α
β
The 15N-labeled ligand was synthesized with the use
of 15N-enriched aniline.
N
N
Cu/2
N
X-ray
crystallography.
Complex
IIIc
X
N
1
(ë50ç44CuN10é4) was studied by X-ray diffraction.
Crystals are triclinic, a = 11.195(2), b = 13.937(4), c =
16.992(5) Å, α = 104.51(3)°, β = 108.75(3)°, γ =
1R
(IIIa–IIIg)
a: X = NC6H4OCH3-p, R1 = iso-Pr, R2 = Ph;
b: X = NC6H4OCH3-p, R1 = Ph, R2 = C6H4CH3-p;
c: X = NC6H4OOCH3-p, R1 = Ph, R2 = C6H4CH3-p;
d: X = NC6H11-cyclo, R1 = Ph, R2 = C6H4CH3-p;
e: X = NH, R1 = iso-Pr, R2 = Ph;
97.70(3)°, V = 2373.5(11) Å3, F(000) = 950, ρcalc.
1.277 g cm–3, µ = 0.515 cm–1, space group P1, Z = 2.
=
The intensities of 6283 reflections were measured
on an Enraf-Nonius CAD4 diffractometer (MoKα radi-
ation, graphite monochromator, θ/5/3ω scan mode,
f: X = NH, R1 = Ph, R2 = Ph;
g: X = NH, R1 = Ph, R2 = C6H4Br-p.
θmax = 22°). The structure was solved based on 4135
Scheme 2.
independent reflections by direct methods with the use
of the SHELXS86 program package [23]. Non-hydro-
gen atoms were refined anisotropically by the full-
matrix and block-diagonal least-squares methods based
on 1864 reflections with Fo ≥ 2σ(Fo). Hydrogen atoms
were positioned geometrically (C–H, 0.96 Å) and
refined with the common temperature factor Bj. The
final R values were R1 = 0.0460 and wR2 = 0.1200 based
on 1864 reflections; 588 parameters were refined; the hkl
index ranges were –11 ≤ h ≤ 9, –14 ≤ k ≤ 13, 0 ≤ l ≤ 17;
GOOF = 1.071; the residual electron densities were
∆ρmin = –0.302 and ∆ρmax = 0.326 Â Å–3. All calculations
EXPERIMENTAL
Synthesis. The aminoazo derivatives of pyrazole
used as ligands were synthesized according to proce-
dures described earlier [22].
Complexes IIIa–IIIg were synthesized by refluxing
an ethanolic solution containing the corresponding
ligand HL (20 mmol) and Cu(CH3COO)2 · H2O
(10 mmol) in the presence of EtONa (20 mmol) for
15 min. The precipitates that formed were recrystal-
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NEW METAL CHELATES OF 5-AMINO-4-AZOPYRAZOLES
523
Table 2. Bond lengths (d) and bond angles (ω) in the coor-
dination polyhedron of copper(II) in compound IIIc
were carried out with the use of the SHELXL93 pro-
gram package [24].
The bond lengths and bond angles in the coordina-
Bond
d, Å
Bond
d, Å
tion polyhedron of compound IIIc are listed in Table 2.
Cu(1)–N(4)
Cu(1)–N(4a)
1.931(9)
Cu(1)–N(5)
1.941(8)
1.956(8)
The crystallographic data were deposited with the
Cambridge Crystallographic Data Centre (CCDC
704367).
1.961(9) Cu(1)–N(5a)
ω, deg Angle
Angle
ω, deg
EPR spectra were recorded on a Bruker ER200D-
SRC spectrometer. The anisotropic spectra were mea-
sured in a toluene solution at 130 K; the isotropic spec-
tra, at 290 K. The EPR parameters were determined
directly from the spectra, except for the parameters A⊥,
which were calculated according to the standard equa-
tion Ai = A|| + 2A⊥/3.
The electronic absorption spectra were recorded on
a Schimadzu UV-3100 spectrophotometer in a chloro-
form solution.
N(4)Cu(1)N(5)
N(4)Cu(1)N(5a)
N(5)Cu(1)N(5a)
96.7(4) N(4)Cu(1)N(4a)
103.8(4) N(5)Cu(1)N(4a)
134.9(4) N(4a)Cu(1)N(5a)
127.6(4)
101.6(4)
96.9(4)
that complexes III have the composition CuL2
(Table 1).
According to the X-ray diffraction data, aminoazo
complex IIIc has a pseudotetrahedral structure, in
which the copper atom is coordinated by the deproto-
nated amine N atoms and the Nβ atoms of the azo
groups giving rise to two six-membered chelate rings
RESULTS AND DISCUSSION
1
(6,6) .
Chelates of Ó-aminoazo compounds of the aromatic
series I (R = H) have been known for many years [25,
26]. The suggestion that five-membered chelate rings I
can exist was made for the first time for this type of che-
late compounds (R = H, M = Co) [25], as opposed to
six-membered chelates I (X = O). This hypothesis was
not confirmed in other investigations [9, 10, 16, 27].
X-ray diffraction studies unambiguously established
that five- and six-membered chelate rings (5,6) are
simultaneously present in copper(2+) chelates of type I
(R = Ts) [28], whereas two six-membered chelate rings
are formed in nickel chelate compounds of type II (R =
H, Alk, or Ar) [22]. Different combinations of chelate
rings (5–5, 6–6, 5–6) are observed in palladium, plati-
num, and zinc complexes of type I (X = S) [9, 10, 28].
Hence, it was of interest to investigate the influence of
the nature of metal in complexing agents on the chelate-
ring size in coordination compounds with azo ligands.
The complex as a whole tends to have pseudosym-
metry ë2 (Fig. 1a). This tendency was observed in the
nickel compound with analogous ligands (IV) [22]
(Fig. 1b). Although there is a crystallographic twofold
axis in the unit cell of IV, the complex molecules are in
general positions. The atomic numbering scheme
reflects the presence of a pseudo twofold axis in com-
plex IV.
The nonequivalence of the ligands in compound IIIc
is evidenced by the fact that only one of these ligands
forms a short contact with the ligand of the adjacent
complex (through a center of symmetry), resulting in
the formation of a molecular dimer (Fig. 2) or the sim-
plest supermolecule consisting of two complexes [30].
The distance between the planes (3.465 Å) is typical of
these contacts. There are no closer contacts in the struc-
ture of IIIc (Fig. 3). It should be noted that complex IV,
given for comparison (Fig. 1b), does not form dimers in
the crystal structure, in spite of the fact that the crystal
symmetry (space group C2/c) is even higher than that in
the structure of IIIc. However, the nature ignores the
tendency of the complex to be symmetric.
Studies of nickel(2+) and copper(2+) complexes
based on Schiff bases of type II (N2S2) showed that the
annelation of certain heterocyclic fragments (for exam-
ple, of pyrazole) with chelate rings results in a substan-
tial weakening of the ligand field and, as a conse-
quence, in the pseudotetrahedral coordination of the
metal atoms without the involvement of sterically bulky
substituents in the ligands [29]. It was of interest to
examine the influence of the annelated pyrazole ring
and the nature of different donor atoms on the structure
and spectral properties of metal chelates by comparing
complexes of Schiff bases with the CuN2O(S)2 chro-
mophore and bis-chelates with azo ligands having the
N4-ligand environment.
The dihedral angle α between the CuN(4)N(5) and
CuN(4a)N(5a) planes in IIIc is 67.3°. Two bidentante
ligands are in trans positions. Both chelate rings are planar
within 0.01 Å. All four aryl substituents are rotated with
respect to adjacent rings. The dihedral angles are as follows:
C(3)N(5)C(10)C(11), 44.5°; C(3a)N(5a)C(10a)C(11a),
42.5°; C(5)C(4)N(1)C(3), 43.1°; C(5a)C(4a)N(1a)C(3a),
46.5°;
N(3)N(4)C(16)C(17),
45.6°;
and
N(3a)N(4a)C(16a)C(17a), 43.2°. The Cu–N(amide) bond
Based on the above goals, we synthesized and studied
copper chelates with azopyrazole ligands of type III.
These chelates were synthesized according to a proce-
dure described in [22]. The elemental analysis showed
1
The degree of distortion of coordination polyhedra with four ver-
tices is characterized by the dihedral angle between two three-
atom planes ML2 (a, scheme). The angle α in the ideal square is
0° and in the ideal tetrahedron, 90°.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 4 2009

524
URAEV et al.
(a)
(b)
N(3) N(2)
N(7)
N(6)
N(8)
C(20A)
C(21A)
C(20)
C(19A)
C(18A)
C(1)
C(4)
C(21)
C(21)
C(22)
C(19)
N(4)
C(17A)
N(1)
C(22A)
N(9)
Ni(1)
C(18)
N(4A)
C(16A)
C(16)
N(3A)
C(2A)
C(24)
N(4)
C(3OA)
C(1A)
N(3)
N(5)
C(17)
C(30)
N(10)
C(2)
C(1)
N(5A)
C(11)
C(3A)
C(11A)
N(5)
Cu(1)
C(3)
C(20)
C(37)
N(2A)
C(10)
C(13)
C(10A)
C(13A)
N(2)
C(5)
C(12)
N(1A)
C(12A)
O(2A)
C(4A)
N(1)
C(4)
C(15A)
C(15)
C(5A)
O(2)
C(24)
C(24A)
C(14A)
C(23A)
O(1A)
C(23)
C(14)
C(6)
C(7)
C(6A)
O(2)
O(1)
C(9)
C(9A)
O(1)
C(7A)
C(8)
C(8A)
Fig. 1. Complexes of type III: (a) the Cu complex and (b) the Ni complex. The regions of interligand π−π stacking interactions are
indicated by dashes. Hydrogen atoms are omitted.
lengths (Cu–N(5), 1.94(1) Å; Cu–N(5a), 1.96(1) Å) are
similar to the Cu–N(azo) bond lengths (Cu–N(4),
1.93(1) Å; Cu–N(4a), 1.95(1) Å). The Cu–N(azo) bond
lengths are typical of complexes with the CuN4 chro-
The Ni complex with X = NC6H4OCH3-n,
R2 = C6H4OCH3-p) (V), which belongs to the same iso-
ligand series as complex IIIb, is characterized by a tet-
rahedral structure of the coordination polyhedron (α =
mophore (1.93–1.96 Å) [7, 8, 17–20, 31], and these bonds 90.0(3)°) [22]. Consequently, the coordination units in
copper complexes III are much more flattened com-
pared to the coordination units in the nickel complexes
with Ó-aminoazo derivatives of pyrazole of type V. This
is similar to the situation observed for the copper (α =
55.9°) and nickel (α = 65.3°) chelates based on
N,N'-bis(2-tosylaminobenzylidene)-2-aminobenzylamine
[19]. An even more substantial flattening of the coordi-
nation core is observed in the copper and nickel com-
plexes with the N,N'-bis(2-tosylaminobenzylidene)-
1,2-diaminoethane ligand [33] (α is 41.1° and α = 15.1°
in the Cu and Ni complexes, respectively).
A flattening of the coordination core correlates with
the concept of interligand π−π stacking interactions
[34]. In our case, the stacking interactions are formed
between the aromatic rings of aryl substituents. In the
complexes under consideration, nonbonded secondary
interactions are different. This is reflected in the distor-
tion of the coordination core. In complex IIIc these
interactions are observed between different six-mem-
bered rings of different ligands and are doubled due to
the presence of the pseudosymmetry axis ë2 (Figs. 4a
and 4b). In alternative nickel complex IV, a single intra-
complex interaction is observed between the same rings
from different parts of the complex (Fig. 4c). The dis-
tances between the overlapping parts of the interacting
rings are 3.39 and 3.32 Å. The noncoplanar arrange-
ment of the planes is characterized by the dihedral
angles β of 17.3° and 25.3°, respectively. The
ë(20)···ë(37) distance (Fig. 4c) is 3.476 Å. The dihedral
angle β between the corresponding planes is 12.6°. As
are shorter than the corresponding bonds in oxygen-con-
taining azo complexes of copper (1.97–2.00 Å) [32]. The
corresponding linear parameters and the endocyclic angles
in both chelate rings of complex IIIc have similar values.
The parameters of the peripheral fragments of both ligands
are also equal within experimental error.
The dihedral angles α in the copper complexes based
on N,N'-bis(2-tosylaminobenzylidene)-2-aminobenzy-
lamine and N,N'-bis(2-tosylaminobenzylidene)-1,2-
diaminoethane, which are structurally similar to com-
pound IIIc, are 55.9° and 41.1°, respectively. The Cu–N
distances are in the range of 1.940–1.978 Å [19, 33].
As opposed to metal chelate IIIc, the coordination
polyhedra in the oxygen-containing analogues (X = O,
R1 = Ph, R2 = Ph or p-tert-BuC6H4) have planar structures
distorted to different degrees (the dihedral angles α are
18.4° and 22.7°, respectively) with the trans arrangement
of the oxygen donor atoms [32]. The coordination core in
the complex with the CuN2S2 chromophore (bis[4-
(benzyl)aldimino-3-methyl-1-phenyl-5-pyrazolethi-
olate)Cu(II)) has a somewhat more flattened pseudotetra-
hedral structure (α = 60.5°) as compared to complex IIIc
(X-ray diffraction data) with the cis arrangement of the
sulfur donor atoms [21]. The Cu–N(azomethine) bond
lengths are 1.982(3) Å. Two six-membered chelate rings
of this pyrazolaldiminate complex of copper, unlike the
chelate rings in complex IIIc, are folded along the N–S
line (the corresponding angle is 15.8°).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 4 2009

NEW METAL CHELATES OF 5-AMINO-4-AZOPYRAZOLES
525
can be seen from Fig. 1, the interactions in these two
complexes act in opposite directions, which accounts
for the flattening of the coordination polyhedron of Cu.
N(3A)
N(4A)
Cu(1)
The EPR parameters of the copper chelates under
study are given in Table 3. The anisotropic spectra
recorded in glassy matrices of the solvent (toluene) are
characteristic of axially symmetric copper complexes
having the d9 (x2 – y2) (g|| > g⊥) ground-state electronic
configuration (g|| > Ä||). The parameters g|| and Ä|| in the
series of complexes containing a substituted amino
group (IIIa–IIId) are typical of complexes with metals
having a tetrahedrally distorted coordination geometry,
although this distortion of structures is rather rarely
observed in this type of complex. The parameters g|| =
N(5)
N(4)
N(1)
N(2)
C(1)
N(3)
N(2A)
N(1A)
N(5A)
2.17–2.18 and Ä|| =100–160 × 10–4 cm–1 are similar to
the corresponding parameters for copper(II) hydra-
zoiminates of the glyoxal derivative of 2,3,4-pentatri-
one (g|| = 2.15–2.19 and Ä|| = 130–179 × 10–4 cm–1) [35],
bis[2,2'-bis(2-imidazolyl)biphenyl]Cu(II) perchlorate
(θ = 90°, g|| = 2.26, Ä|| = 130 × 10–4 cm–1) [36], copper
complexes based on tetraazomacrocyclic oxamide
Schiff bases (g|| =2.175, Ä|| = 164 × 10–4 cm–1) [37], and
copper β-aminovinyliminates (θ = 61.39°–63.68°, g|| =
C(7)
C(6)
C(5)
O(2)
C(8)
C(12)
O(1)
C(13)
C(9)
C(23)
C(4)
C(11)
N(2)
C(1)
N(1)
N(5)
C(3)
C(15) C(14)
C(10)
C(30)
2.182–2.214, Ä|| = 125–132 × 10–4 cm–1) [20]. The
C(2)
Cu(1)
N(4A)
N(3A)
nature of the substituents R1 and R2 has only a slight
effect on the EPR parameters.
N(3)
N(4)
C(16)
C(17)
N(5A)
C(22)
N(1A)
O(1A)
N(2A)
Numerous correlations between the degree of tetra-
hedral distortion of the chelate unit and the EPR param-
eters were suggested for four-coordinate copper che-
lates, including the linear correlations between g|| and
Ä||, g|| and the dihedral angle, and g|| and the structural
C(18)
C(19)
C(21)
O(2A)
Fig. 2. Two orthogonal projections of the molecular dimer
(or the supermolecule composed of two complexes) in the
structure of IIIc. Hydrogen atoms are omitted.
parameter 1/sin4β [36, 38–43]. In studies [31, 40], g||/Ä||
was used to approximately estimate the geometry of
four-coordinate copper complexes. It was shown that
the planar geometry of the chelate unit is more probable
for complexes characterized by g||/Ä|| in the range from
110 to 120, whereas g||/Ä|| in the range of 130–150 are
characteristic of slightly tetrahedrally distorted com-
pounds. The parameter g||/Ä|| in the range of 180–250 is
indicative of a substantial tetrahedralization of the
coordination polyhedra of metal atoms.
hyperfine structure due to the 15N nuclei was not
observed in the EPR spectra of this compound.
Complexes IIIe–IIIg containing the unsubstituted
amino group are characterized by smaller g||/Ä|| (139–
153) and substantial larger Ä|| (141–157 × 10–4 cm–1) as
compared with chelates IIIa–IIId (Table 3). This is evi-
dence that the coordination polyhedra in metal chelates
IIIe–IIIg are more planar. It should be noted that the
parameter g|| changes only slightly in the series of com-
The parameters g||/Ä|| for complexes IIIa–IIId given
in Table 2 are in the range of 173-218. Apparently, this
is an indication of a strong tetrahedral distortion of the
coordination cores in these compounds. A substantial plexes containing unsubstituted and substituted amino
increase in g||/Ä|| and a decrease in Ä|| (to 99 × 10–4 cm–1)
groups; i.e., there is no correlation between g|| and Ä||
and the degree of tetrahedral distortion proposed by
Edison for complexes with the ëuN2X2 chromophore
[45, 46]. However, the absolute values of Ä|| for com-
pounds IIIe–IIIg are smaller than those for the planar com-
plexes with the CuN4 chromophore (180–200 × 10–4 cm–1)
[14], which suggests that there are distortions in the
coordination unit. Changes in the EPR parameters of
the copper complexes with 2-amino-1-azonaphthalene
ligands show a similar tendency [47–49].
for complex IIId containing the cyclo-NC6H11 substitu-
ent are, apparently, attributed to a higher degree of tet-
rahedral distortion compared to that observed in the
structure of complex IIIc. For example, the parameters
g|| = 2.218 and Ä|| = 107 × 10–4 cm–1 were assigned to the
complex [bis(N,N-diphenyl-1,3-dimethyl-β-aminoimi-
nato)]Cu(II) (α = 68°) diluted with the isoligand zinc che-
late [14, 44]. Due to the low symmetry of complex IIIa
containing the 15Nβ-labeled azo group, an additional
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 4 2009

526
URAEV et al.
a
Cu(1)
c
0
b
Fig. 3. Packing of complexes IIIc in the unit cell. The shortest ë(1)···C(1) contacts (3.465 Å) in the molecular dimers are indicated
by dashed lines.
Table 3. EPR parameters of copper(II) complexes IIIa–IIIg
Complex
g||
g⊥
gi
A||, 10–4 cm–1 A⊥, 10–4 cm–1 Ai, 10–4 cm–1 A(N)a, 10–4 cm–1
g||/A||
IIIa
IIIb
IIIc
IIId
IIIe
IIIf
IIIg
2.172
2.168
2.171
2.178
2.184
2.158
2.174
2.053
2.065
2.069
2.065
2.059
2.063
2.058
125.3
116.7
116.2
99.9
0
41.5
38.5
36.4
33.3
62.8
61.8
69.5
173
186
187
218
150
153
139
2.099
2.103
2.103
2.101
2.095
2.096
0
7.3 (14N)
3.5
0
146.0
141.0
156.7
21.2
22.2
25.9
11.9 (14N)
17.0 (15N)
12.1 (14N)
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NEW METAL CHELATES OF 5-AMINO-4-AZOPYRAZOLES
527
(a)
(b)
(c)
O(2A)
O(1A)
C(23A)
C(13A)
O(2)
O(1)
Ni(1)
C(20A)
C(19A)
C(23)
C(13)
C(17A)
C(18A)
C(12)
C(20)
C(12A)
C(14A)
C(15A)
C(18)
C(17)
N(1)
N(6)
C(19)
C(14)
C(11)
C(11A)
C(10A)
C(21A)
C(16A)
C(16)
C(21)
C(15)
C(20)
C(37)
C(10)
C(22A)
N(4A)
N(4)
C(22)
N(5A)
N(5)
Cu(1)
Cu(1)
O(2)
O(1)
Fig. 4. Interligand π−π stacking interactions in (a, b) the Cu complexes and (c) the Ni complex (IV).
The fact that g|| for geometrically different com- band at 400 nm and appears as a smooth shoulder. A
high intensity of the bands assigned to d−d transitions
plexes have similar values can be attributed to compen-
compared to those observed for complexes with the
sation of two opposite tendencies. Thus, a high degree
of covalence of the Cu–NR bond compared to the Cu– CuN4 chromophore (ε = 100–300 L mol–1 cm–1) [37, 53,
NH bond leads to a decrease in g|| whereas tetrahedral
distortions result in an increase in g||.
54] is, apparently, attributed to the borrowing of the
intensity from the adjacent region associated with the
ligand-to-metal charge transfer (LMCT). The energies
of the d–d transitions in complexes III are somewhat
lower than those in typical square copper(II) complexes
(500–588 nm, in nitromethane) [41]. This fact can be
accounted for by a tetrahedral distortion of the CuN4
chromophore. In the spectra of tetrahedrally distorted
copper(II) complexes, the absorption band envelope
generally shifts to lower energies [40, 41]. For example,
the spectrum of the CuN4 chromophore with bipyridyl-
type ligands having angles similar to those in the regu-
lar tetrahedron show absorption at 1300–1200, 1000–
900, 660–800, and 625–670 nm [55–57]. The elec-
tronic absorption spectra of hydrazoneiminate cop-
per(II) complexes with methylglyoxal and 2,3,4-penta-
trione show an increase in the intensity of d−d-transi-
tion bands at 500–800 nm and a bathochromic shift of
The isotropic spectra of complex IIIf containing the
15
labeled N atom in the β position show the hyperfine
15
structure dut to the N nucleus, thus providing unam-
biguous evidence for the presence of six-membered
chelate rings and the coordination of copper by the Nβ
atom of the azo group. The hyperfine structure due to
the 14N nucleus is also resolved in some cases, generally
in isotropic spectra (Table 2). A decrease in the hyper-
fine coupling compared to that observed in the spectra
of the planar complexes with the CuN4 chromophore
are indicative of tetragonal distortions [14]. The param-
eters g|| observed in the spectra of compounds III are
smaller than those observed for tetracoordinated azo
(X = O, R1 = Ph, R2 = Ph) and pyrazolaldiminate com-
plexes with the CuN2O2 chromophore (g|| = 2.250 and
g|| =2.234) and are larger than those for sulfur-contain- the longest-wavelength d−d-transition band as the
length of the polymethylene bridge increases [35].
ing analogues (g|| = 2.121 and g|| = 2.106–2.153) [21, 50,
51]. These results reflect an increase in the nephelaux-
etic effect, an increase in the degree of covalence, and a
decrease in the electronegativity in the series N2O2 >
N4 > N2S2 [52].
The influence of tetrahedral distortions in com-
plexes IIIa–IIId compared to complexes IIIe–IIIg is
manifested in the shifts of the bands at 600 nm to the
red side (to 620–655 nm) accompanied by a change in
their intensity and the appearance of weak ligand-field
bands in the subinfrared region at 1400–1600 nm.
This structural situation is typical also of isoligand
nickel complexes [22]. Such complexes with X = NAlk
or NAr are pseudotetrahedral both in solution and in the
solid state. The complexes with X = NH are diamag-
netic and, consequently, square-planar.
The above-considered data show that the nature of
the amino group is a key factor determining the struc-
ture of the coordination polyhedron in the series of cop-
The EPR spectra of complexes III show absorption per and nickel complexes based on 1,3-alkyl(aryl)
bands associated, apparently, with overlapping of the derivatives of 5-amino-4-azopyrazoles. All metal che-
charge transfer bands assigned to N
Cu(II) and d−d lates containing a substituted amino group (X = NR) as
transitions at 600–800 nm (Table 1). The band at a donor have pseudotetrahedral structures regardless of
600 nm is shielded by an intense intraligand-transition the nature of the substituents R. Complexes containing
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 4 2009

528
URAEV et al.
16. A. D. Garnnovskii, A. I. Uraev, and V. I. Minkin,
the unsubstituted amino group X = NH are planar or
nearly planar in spite of the fact that the pyrazole frag-
ment annelated with the chelate ring facilitate the tetra-
hedralization. The nature of substituents at the nitrogen
atom of the pyrazole ring R1 and in the phenyl ring of
the amino component have only a slight effect on the
structure and spectral parameters of the complexes. All
metal chelates belonging to this series are characterized
by the presence of two six-membered chelate rings.
Arkivoc. 3, 29 (2004).
17. V. V. Grushin and W. J. Marshall, Adv. Synth. Catal. 346
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A. R. Kennedy, Inorg. Chim. Acta 359 (8), 2455 (2006).
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21. A. I. Uraev, A. L. Nivorozhkin, G. I. Bondarenko, et al.,
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ACKNOWLEDGMENTS
This study was supported by the Council for Grants
of the President of the Russian Federation for Support
of Young Scientists and Leading Scientific Schools
(grant nos. MK 3534.2007.3 and NSh -363.2008.3), the
Russian Foundation for Basic Research (project
no. 07-03-00710a), the Ministry of Education and Science
of the Russian Federation “Development of Research
Potential” (2006–2008) (project no. RNP-2.1.1.1875),
and the Program No. 8 of the Russian Academy of Sci-
ences.
22. A. L. Nivorozhkin, H. Toftlund, L. E. Nivorozhkin, et al.,
Trans. Met. Chem. 19 (3), 319 (1994).
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