Palladium(II) benzazolylformazanates: Synthesis, structure and optical properties

Article abstract of DOI:10.1134/S1070328409030099

The Pd(II) complexes of 1-aryl-5-benzazolyl- and 1,5- dibenzimidazolylformazans are synthesized and characterized by UV and IR spectroscopy, mass spectrometry, and magnetochemical studies. The complexes exhibit the intense absorption in the near-IR spectr

Full text of DOI:10.1134/S1070328409030099

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2009, Vol. 35, No. 3, pp. 215–221. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © G.N. Lipunova, Z.G. Rezinskikh, T.I. Maslakova, P.A. Slepukhin, I.G. Pervova, I.N. Lipunov, G.I. Sigeikin, 2009, published in Koordinatsionnaya
Khimiya, 2009, Vol. 35, No. 3, pp. 217–223.
Palladium(II) Benzazolylformazanates: Synthesis, Structure
and Optical Properties
G. N. Lipunovaa, Z. G. Rezinskikhb, T. I. Maslakovab, P. A. Slepukhinc,
I. G. Pervovab, I. N. Lipunovb, and G. I. Sigeikind
aUral State Technical University, Yekaterinburg, Russia
bUral State Forestry University, Yekaterinburg, Russia
cInstitute of Organic Synthesis, Ural Division, Russian Academy of Sciences, Yekaterinburg, Russia
dInterdepartmental Center for Analytical Research at the Presidium of the Russian Academy of Sciences,
Moscow, Russia
e-mail: family@k66.ru
Received April 7, 2008
Abstract—The Pd(II) complexes of 1-aryl-5-benzazolyl- and 1,5-dibenzimidazolylformazans are synthesized
and characterized by UV and IR spectroscopy, mass spectrometry, and magnetochemical studies. The complexes
exhibit the intense absorption in the near-IR spectral region (820–1020 nm). The interaction of the complexes with
amines leads to the transformation into binuclear palladium formazanates, which absorb at 620–680 nm and
whose structures were confirmed by X-ray diffraction analysis.
DOI: 10.1134/S1070328409030099
INTRODUCTION
of palladium chloride (0.0024 mol) in dimethylforma-
mide (DMF) (100 ml) was added to a solution of forma-
zan (0.002 mol) in acetone (50 ml) at ~50°ë. The result-
ing mixture was stirred for 30 min and evaporated to 10
ml. The precipitate that formed was filtered off, washed
with acetone, and dried. Palladium formazanates III and
V–VII (Table 1) were synthesized analogously.
The palladium complexes based on the dimercapto-
substituted derivatives are known [1] to absorb in the
near-IR spectral region and are used as IR-light filters.
However, the synthesis of ligands for these compounds is
associated with considerable difficulties. Therefore, the
search for new compounds absorbing in the near-IR
spectral region continues to be an urgent task.
The palladium complexes with such nitrogen-con-
taining ligands as 1,5-diaryl-3-R-formazans (R is the
aryl, cyano, and nitro group) were synthesized earlier
[2]. The structures of these complexes were studied, the
spectral data were obtained, and a dependence of the
position of the absorption bands in the electronic spectra
on the character of the R substituent was established. For
example, when R = aryl, the long-wavelength band shifts
to 790–810 nm.
It could be expected that the introduction of a hetero-
cyclic fragment into the formazan structure would elon-
gate the conjugated ligand chain and, as a consequence,
the band of the complex would further shift to the near-
IR region.
The purpose of this work is to synthesize the palla-
dium(II) complexes with 1-aryl-5-benzazolyl- and 1,5-
dibenzimidazolylformazans and to study their structures
and spectral characteristics.
Method B. A solution of formazan (0.0011 mol) in
toluene (25 ml) was added to a dilute hydrochloric acid
solution (100 ml) of palladium chloride (0.0015 mol).
After stirring for 2 h and keeping the solution for a day
at room temperature, the toluene layer was separated and
evaporated. The obtained precipitate of palladium(II)
formazanate was dried. The product was identical to that
synthesized by method A.
Palladium formazanates II and IV (Table 1) were
synthesized analogously.
Synthesis of dichloro-bis[1,3-diphenyl-5-(benzthia-
zol-2-yl)formazanate]dipalladium(II) (Ia). Several
drops of concentrated NH4OH were added to a yellow-
green solution of complex I (0.001 mol) in ethanol until
the blue color was obtained. The solution was evapo-
rated, and the regular blue crystals were used for X-ray
diffraction analysis (mp > 250°ë). Mass spectrum in
acetonitrile (electrospray): m/z (%): 998 (1.96), 994
(1.7), 499 (16.53), 498 (9.4), 497 (12.89), 496 (8.36),
494 (6.01).
EXPERIMENTAL
Elemental analysis was carried out on a PE2400SII
Synthesis of palladium(II) 1,3-diphenyl-5-(benz- automated CHN analyzer (PerkinElmer, United States).
thiazol-2-yl)formazanate (I). Method A. A hot solution The metal in the complexes was determined by express
215

216
LIPUNOVA et al.
Table 1. Yields, melting points, and elemental analysis data for the palladium(II) complexes*
L1–7
R1
Content (found/calculated), %
N (Cl)
Com-
plex
Yield, % Tm, °C
Het
R2
C
H
I
C6H5
C6H5
C6H5
2-COOHC6H4
72
56
>250
>250
48.9/48.3 3.0/2.8 14.4/14.1
50.3/49.9 2.8/2.6 14.1/13.9
II
N
2-OCH3C6H4 C6H5
III
IV
40
58
>250
>250
48.0/47.7 3.2/3.2 (6.2/6.7)
45.9/45.4 3.1/2.8 14.3/14.0
S
4-CH3C6H4
O
N
V
2-OCH3C6H4 4-N(CH3)2C6H4
80
>250
51.6/51.9 4.4/4.1 (8.0/7.8)
N
CH2C6H5
N
N
VI
CH3
65
60
>250
>250
54.8/54.7 4.3/4.2 17.7/17.1
42.4/41.8 4.0/3.0 24.1/24.8
N
N
CH2C6H5
CH2C6H5
N
N
VII
CH3
NH
NH
5
4
N
3
C
2
N
1
N
2
* L =
.
R
Het NH
R1
gravimetry using an equipment of the OAO Khimlabor- cal ionization under atmospheric pressure and
pribor (Klin, Moscow oblast, Russia).
electrospray with positive and negative ion detection.
Samples were injected into the mass spectrometer
through the chromatograph with an SPD-M10Avp diode
matrix using direct injection into the ion source. The field
desorption mass spectra for complexes I, III, and V–VII
were obtained on a MAT 311A instrument (Varian)
under the earlier described conditions [4].
The electronic absorption spectra of the samples were
measured with Specord UV-Vis and Model 26 detecting
two-beam spectrophotometers (Beckman) and using an
SF-256UVI instrument at a concentration in the solu-
tions of (1–5) × 10–5 mol/l.
The IR spectra of compounds I–VII were recorded
on a Specord 75IR spectrophotometer (KBr pellets and
suspensions in Nujol) at 400–4000 cm–1.
The magnetic characteristics of the compounds were
measured by the relative Faraday method at 293 K [3].
The studies of the palladium formazanates (com-
pounds I, Ia, II, and IV) by mass spectrometry were car-
X-Ray diffraction analysis. The crystals of com-
plex Ia (ë40ç28N10Cl2S2Pd2) as dark blue needles are
monoclinic: a = 23.119(5) Å, b = 16.3993(3) Å, c =
15.4966(9) Å, β = 125.767(13)°, V = 4767.3(11) Å3,
ρ
calcd = 1.567 g/cm3, Z = 4, space group C2/c.
The unit cell parameters and the set of experimental
ried out on an LCMS-2010 liquid chromatograph cou- data were measured in an Xcalibur 3 autodiffractometric
pled with a mass spectrometer (Shimadzu) using chemi- system equipped with a CCD detector at 295(2) K. The
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PALLADIUM(II) BENZAZOLYLFORMAZANATES
217
Table 2. Bond lengths and bond angles in structure Ia*
Bond d, Å Angle ω, deg
Pd(1)–Pd(1A) 3.1298(11) Pd(1A)Pd(1)Cl(1) 100.96(4)
completeness of the experiment (θ ≤ 28.30°) was 98.3%
(ω scan mode with an increment of 1° and an exposure
of 20 s per frame, crystal–detector distance 50 mm). The
experimental data were collected and edited and the unit
cell parameters were refined using the CrysAlis CCD
program [5].
Pd(1)–N(1)
Pd(1)–N(4)
Pd(1A)–N(5) 2.075(4) N(1)Pd(1)Cl(1)
Pd(1)–Cl(1) 2.3072(12) N(1)Pd(1)Pd(1A)
1.988(4) N(1)Pd(1)N(4)
2.024(4) N(1)Pd(1)N(5A)
80.80(16)
90.65(14)
174.98(12)
82.87(12)
119.4(4)
118.3(4)
114.8(4)
120.5(3)
123.7(5)
118.5(5)
114.0(4)
118.2(3)
116.8(5)
162.21(16)
94.41(12)
Structure Ia was solved by a direct method using the
SHELXS-97 [6] program package and refined using the
SHELXL-97 program package [6] by the least-squares
method in the anisotropic (isotropic approximation for
hydrogen atoms) approximation to R1 = 0.0446, wR2 =
0.0892 for 2566 reflections with F2 ≥ 2σ(F2). An absorp-
tion correction was applied analytically according to the
polyhedral crystal model [7].
The bond lengths and bond angles in structure Ia are
given in Table 2.
The coordinates of atoms and other parameters for
structure Ia were deposited with the Cambridge Struc-
tural Database (no. 695 480).
S(1)–C(2)
S(1)–C(3)
N(1)–N(2)
N(1)–C(2)
N(2)–C(1)
N(3)–C(1)
N(3)–N(4)
N(4)–C(15)
N(5)–C(2)
N(5)–C(8)
C(1)–C(9)
C(3)–C(4)
C(3)–C(8)
C(4)–C(5)
C(5)–C(6)
C(6)–C(7)
C(7)–C(8)
1.737(5) N(1)C(2)S(1)
1.747(5) N(1)N(2)C(1)
1.324(5) N(2)N(1)C(2)
1.369(5) N(2)N(1)-Pd(1)
1.327(6) N(2)C(1)N(3)
1.369(6) N(2)C(1)C(9)
1.275(5) N(3)N(4)C(15)
1.428(6) N(3)N(4)Pd(1)
1.296(5) N(3)C(1)C(9)
1.416(5) N(4)Pd(1)N(5A)
1.453(7) N(4)Pd(1)Cl(1)
1.384(6) N(4)Pd(1)Pd(1A) 120.39(11)
1.391(6) N(4)N(3)C(1) 123.7(4)
1.359(7) N(5A)Pd(1)Pd(1A) 73.44(10)
1.376(7) N(5A)Pd(1)Cl(1)
1.367(7) N(5)C(2)N(1)
1.382(6) N(5)C(2)S(1)
1.336(8) C(2)S(1)C(3)
1.383(8) C(2)N(1)Pd(1)
RESULTS AND DISCUSSION
93.55(9)
123.1(4)
117.5(4)
88.3(2)
The Pd(II) complexes based on 1-aryl-benzazolyl- and
1,5-dibenzimidazolylformazans (L1–7) were synthesized
by the reactions of benzazolylformazans with palla-
dium(II) chloride in a DMF solution (complexes I, III, C(9)–C(10)
and V–VII) or in a toluene–water two-phase system
(complexes I, II, and IV).
According to the elemental analysis data, compounds I
and III–VII have the composition Pd(L)Cl, and com-
plex II has the composition PdL', where L and L' are the
mono- and dianionic forms of the ligand, respectively
C(9)–C(14)
122.4(3)
109.5(4)
133.5(3)
114.5(4)
121.3(5)
128.5(4)
121.8(5)
117.9(5)
119.5(5)
120.4(5)
119.1(4)
126.4(4)
110.1(3)
116.9(3)
121.4(7)
121.0(6)
119.4(6)
118.9(9)
121.1(8)
C(11)–C(12) 1.382(11) C(2)N(5)C(8)
C(10)–C(11) 1.390(10) C(2)N(5)Pd(1A)
C(12)–C(13) 1.380(10) C(3)C(8)N(5)
C(13)–C(14) 1.378(9) C(4)C(3)C(8)
C(15)–C(16) 1.371(7) C(4)C(3)S(1)
(Table 1). The studies by mass spectrometry show that C(15)–C(20) 1.382(7) C(4)C(5)C(6)
the synthesized complexes correspond to the above com-
positions and are detected in the mass spectrum as a
group of ions with the corresponding isotope distribu-
tions for the Pd and Cl atoms (polyisotopic peaks å+ and
(å + ç)+ with the 60–100% intensity) (Table 3).
The participation of the NH group of the initial for-
mazan molecule in complex formation is confirmed by
the absence of the absorption band corresponding to the
ν(NH) stretching vibrations at 3200–3500 cm–1 in the IR
spectra of compounds I and III–VII. The carboxy group
in compound II is also involved in the design of forma-
zanate II, which is indicated by the shift of the ν(ëé)
band to the low-frequency region (1630 cm–1) compared
to the free ligand (1690 cm–1).
Crystalline complexes I, III, and V–VII are diamag-
netic (µeff = 0 µB), which can be due to the square struc-
ture of the metallochelate unit.
The electronic absorption spectra of complexes I–VII
exhibit low-intense absorption bands in the visible region
(450–550 nm, 30–40% absorption) and more intense
bands in the near-IR region (820–1020 nm, absorption
>80%) (Table 3).
C(16)–C(17) 1.367(8) C(5)C(4)C(3)
C(17)–C(18) 1.333(11) C(6)C(7)C(8)
C(18)–C(19) 1.381(11) C(7)C(6)C(5)
C(19)–C(20) 1.375(9) C(7)C(8)C(3)
C(7)C(8)N(5)
C(8)C(3)S(1)
C(8)N(5)Pd(1A)
C(9)C(10)C(11)
C(10)C(9)C(1)
C(10)C(9)C(14)
C(12)C(11)C10
C(13)C(14)C(9)
C(13)C(12)C(11) 120.4(9)
C(14)C(9)C(1) 119.5(6)
C(14)C(13)C(12) 118.7(8)
C(15)N(4)Pd(1) 127.5(4)
C(16)C(15)C(20) 120.7(6)
C(16)C(15)N(4) 118.2(5)
C(17)C(16)C(15) 119.2(7)
C(17)C(18)C(19) 119.2(9)
C(18)C(17)C(16) 121.7(9)
C(19)C(20)C(15) 117.9(7)
C(20)C(15)N(4)
C(20)C(19)C(18) 121.2(8)
* Coordinates of the A atom: –x; y; 1/2 – z.
120.9(6)
The solvent exerts almost no effect on the position of
absorption bands. However, the character of the substit-
uents of the formazan group influences on the position of
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 35 No. 3 2009

218
LIPUNOVA et al.
Table 3. Data of electronic spectroscopy and mass spectrometry for the palladium(II) complexes
M+
Complex
Empirical formula
λχı, nm
found (m/z)
calculated (m/z)
I
C20H14N5SClPd
480, 820, 900 sh
495, 496, 497, 498, 499, 501, 503
504, 505, 506, 507, 508, 509, 510
498.3
II
C21H13N5SO2Pd
505.87
450, 900, 1000 sh
450, 830
III
IV
V
C21H17N5SOClPd
C19H14N5SOClPd
C30H28N7OClPd · 2H2O
C30H26N8ClPd · H2O
C16H14N8ClPd
525, 526, 527, 528, 529, 531, 533
499, 500, 501, 502, 503, 504, 505
641, 642, 643, 644, 645, 647, 649
636, 637, 638, 639, 640, 643, 645
456, 457, 458, 459, 460, 462, 464
529.4
502.3
644.5
640.5
460.3
840, 900 sh
550, 840, 900 sh
505, 810, 1020
460, 540, 820, 960
VI
VII
the long-wavelength band. The 1-(2-carboxyphenyl)- alcoholic solutions of these complexes resulted in the
3-phenyl-5-(benzthiazol-2-yl)formazan complex (II) color change from yellow-green to blue, the appearance of
and the complexes of symmetric 1,5-dibenzylbenzimi-
dazolyl- and 1,5-dibenzimidazolylformazans (VI and
VII) are characterized by the shift of this band to the
long-wavelength region compared to the complexes of
nonsymmetric formazans I and III–V (Table 3, Fig. 1).
a new absorption band at 620–680 nm, and the disappear-
ance of the absorption band at 820–1000 nm. The reaction
of palladium 1,3-diphenyl-5-(benzthiazol-2-yl)formazan-
ate (I) with pyridine leads to a gradual decrease in the
absorption band intensity in the near-IR region and the
appearance of absorption bands in the visible region with
a maximum at 630 nm (Fig. 2). In this case, the titration
pattern is characterized by one isosbestic point, indicating
that two types of the complexes are equilibrated in the
solution.A similar change in the color occurs immediately
upon the addition of a stronger base (ammonia) to a solu-
It was earlier shown [8] that the addition of amines to
solutions of nickel(II) formazanates absorbing in the
near-IR region resulted in changes in the electronic
absorption spectra: the absorption band at ~1000 nm dis-
appeared and the absorption intensity in the visible spec-
tral region increased.
tion of complex I. Palladium formazanate Ia with λmax
=
630 nm was isolated in the crystalline state. According to
We studied the interaction of the synthesized palla-
dium formazanates (complexes I, II, and IV) with amines. the X-ray diffraction data, compound Ia is the dichloro-
The addition of ammonia, pyridine, or ethylenediamine to bis[1,3-diphenyl-5-(benzthiazol-2-yl)formazanate]dipal-
A
A
0.25
1
2
0.4
0.3
0.2
0.1
0
0.20
0.15
0.10
0.05
0
1
3
2
400
600
800
1000
λ, nm
400
600
800
1000
λ, nm
Fig. 1. Electronic absorption spectra of complexes (1) I,
(2) VI, and (3) II.
Fig. 2. Electronic absorption spectra of compound I in
(1) ethanol and (2) with the addition of pyridine.
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PALLADIUM(II) BENZAZOLYLFORMAZANATES
219
C(18)
C(18A)
C(19)
C(20)
C(17)
C(16)
C(17A)
C(19A)
C(16A)
C(20A)
C(15)
C(15A)
N(4A)
Cl(1)
Cl(1A)
N(3)
N(4)
N(3A)
C(14)
Pd(1)
Pd(1A)
C(1)
N(1)
C(14A)
C(13)
C(12)
C(1A)
N(1A)
N(5)
C(9)
N(5A)
C(7A)
N(2)
C(13A)
C(12A)
C(2)
C(9A)
N(2A)
C(10)
C(2A)
C(8)
C(3)
C(10A)
S(1A)
C(11)
C(8A)
C(3A)
C(7)
S(1)
C(4)
C(6A)
C(11A)
C(6)
C(4A)
C(5A)
C(5)
Fig. 3. General view of molecule Ia.
ladium(II) binuclear complex Pd2Cl2L2, where L is the ligand planarity. The metalloformazan cycle exists in an
anionic formazan ligand (Fig. 3)
envelope conformation, which is not typical of conju-
gated chelate systems, and the dihedral angle between
the root-mean-square planes of the phenyl substituent at
the C(1) atom and the thiazole cycle of formazan is 35°.
The crystal packing of the binuclear molecules forms
tunnels (Fig. 4) occupied by the solvate ethanol mole-
cules. However, the orientation of the molecule of the lat-
ter was not established because of the strong thermal dis-
ordering of the atoms, and the solvate is included into the
refined model as a group of the oxygen atoms disordered
over several positions with site occupancies of 0.25–0.5.
This, very rough assumption results in violations of a
series of the calculated experimental parameters and
introduces an additional inaccuracy to the determination
of the atomic coordinates. However, these violations are
insignificant and do not basically change the observed
molecular structure. This is indicated, in particular, by
the satisfactory R factor value: R1 = 0.0446. Since we did
not aimed at achieving high accuracy of structural data as
the main task of the study, the obtained result can be
accepted satisfactory.
Cl
Cl
N
N
N
N
N
N
C
Pd Pd
C
N
N
N
N
S
S
(Ia)
Binuclear molecule Ia occupies the partial position in
the 2 axis. The Pd atom is coordinated to the vertices of
a distorted square pyramid with the second palladium
atom in the axial position. The base of the pyramid is
formed by the N(1) and N(4) atoms of the formazan frag-
ment of the first ligand L, the N(5A) atom of the benzthi-
azole fragment of the second ligand L, and the chlorine
atom forming the five- and six-membered metallocycles.
This coordination mode results in the strong distortion of
the angles of the square pyramid: in the deviation of the
axial vertex of the pyramid from the normal to the equa-
Based on the obtained spectral data and results of
studying the behavior of complexes I and III–VII
with amines, we can assume structure A for these
torial plane and the strong distortion of the formazan complexes. In structure A, formazan acts as a triden-
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 35 No. 3 2009

220
LIPUNOVA et al.
y
z
0
x
Fig. 4. Fragment of the crystal packing of molecules Ia.
tate ligand and the palladium atom enters into the form three Pd–N bonds (the chlorine atom occupies
composition of the five-membered metallocycles to the fourth coordination site).
N
X
R2
N
Cl
C
Cl
Cl
R2
N
N
N
N
Pd
N
N
N
N
C
R1
R1
C
Pd
Pd
X
N
N
N
N
R2
R1
X
N
(A)
(B)
The participation of the N(1) and N(4) atoms of the
Structure B retaining the Pd2Cl2 fragment with the
formazan group and the atom of the benzthiazole cycle haloid bridge characteristic of the palladium(II) com-
of 1-aryl-5-(benzthiazol-2-yl)formazans in coordination pounds is an alternative for complexes I and III–VII
with such metals as Ni(II), Co(II), and Fe(II) was con- [12]. This structure is favored by the low-intensity peaks
firmed earlier by the X-ray diffraction data [9–11].
in the mass spectra (m/z (%): 994 (2.7) for I and 1005
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PALLADIUM(II) BENZAZOLYLFORMAZANATES
221
(3.6) for III) corresponding to the Pd2Cl2L2 composi- sion about the structures of complexes I and III–VII can
tion. In this structure, formazan coordinates the Pd atom be made on the basis of the X-ray diffraction data.
only by the N(1) and N(5) atoms of the formazan chain.
Structure B with two five-membered and one six-
Comparing structuresA and B (using complex I as an membered metallocycles seems probable for palladium
example) with structure Ia (according to the X-ray dif- formazanate II. This structure resembles that described
fraction data), we should prefer structure B from which previously for [1-(2-carboxyphenyl)-3,5-diphenylfor-
the transformation into compound Ia can occur more mazanate](pyridine)palladium(II) (structure D con-
easily than from structure A. However, the final conclu- firmed by the X-ray diffraction data [13]).
O
O
O
O
C
O
C
N
C
Pd
C
Pd
C
O
N
S
N
C
N
N
N
N
N
Pd
N
N
N
N
N
S
N
N
2
(C)
(D)
(E)
The coordination site in structures C and D is the
same: (PdN3é). The only difference is that the N(1) and
N(5) atoms of the formazan group and the pyridine nitro-
gen atom are involved in coordination with palladium in
structure D, whereas the N(1) and N(4) atoms of the for-
mazan fragment and the benzthiazole nitrogen atom par-
ticipate in coordination in structure C.
REFERENCES
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ACKNOWLEDGMENTS
13. Balt, S., Klok, C., and Meuldijk, J., Acta Crystallogr., Sect.
C: Cryst. Struct. Commun., 1985, vol. 41, no. 4, p. 528.
This work was supported by the Russian Foundation
for Basic Research, project nos. 07-03-12050ofi and
08-03-13512ofi-ts.
14. Kalia, K.C., Kumar, A., and Singla, M., Indian J. Chem.,
Sect. A: Inorg., Bio-inorg., Phys., Theor. Anal. Chem.,
1981, vol. 20, p. 610.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 35 No. 3 2009