Zinc complexes of 1-Propyl-2-(2-tosylaminophenyl)-5-aminobenzimidazole: Synthesis, structure, and luminescence properties

Article abstract of DOI:10.1134/S1070328414070070

1-Alkyl-2-(2-tosylaminophenyl)-5-aminobenzimidazole and related zinc complexes are synthesized. The structure of the complex with zinc pivalate is determined by X-ray diffraction analysis. The fluorescence with the anomalous Stokes shift of the benzimidaz

Full text of DOI:10.1134/S1070328414070070

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2014, Vol. 40, No. 7, pp. 468–472. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © S.A. Nikolaevskii, Yu.V. Koshchienko, A.V. Chernyshev, A.S. Burlov, A.S. Cheprasov, G.G. Aleksandrov, M.A. Kiskin, A.V. Metelitsa, 2014, published in
Koordinatsionnaya Khimiya, 2014, Vol. 40, No. 7, pp. 410–414.
Dedicated to the 80th Anniversary of the Kurnakov Institute of General and Inorganic Chemistry
Zinc Complexes of 1ꢀPropylꢀ2ꢀ(2ꢀTosylaminophenyl)ꢀ5ꢀ
Aminobenzimidazole: Synthesis, Structure,
and Luminescence Properties
S. A. Nikolaevskiia, b, *, Yu. V. Koshchienkoa, A. V. Chernysheva, A. S. Burlova, A. S. Cheprasova,
G. G. Aleksandrovb, M. A. Kiskinb, and A. V. Metelitsaa
a Research Institute of Physical and Organic Chemistry, Southern Federal University, RostovꢀonꢀDon, Russia
b Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
*eꢀmail: sanikolaevskiy@sfedu.ru
Received November 6, 2013
Abstract—1ꢀAlkylꢀ2ꢀ(2ꢀtosylaminophenyl)ꢀ5ꢀaminobenzimidazole and related zinc complexes are syntheꢀ
sized. The structure of the complex with zinc pivalate is determined by Xꢀray diffraction analysis. The fluoꢀ
rescence with the anomalous Stokes shift of the benzimidazole ligand system in solution is transformed into
the fluorescence with the normal Stokes shift upon complex formation due to blocking the mechanism of
intramolecular proton transfer in the excited state or upon the transition to the crystalline state formed by
zwitterionic forms that are generated due to the proton transfer from the sulfonamide group to the amino
group.
DOI: 10.1134/S1070328414070070
INTRODUCTION
EXPERIMENTAL
1ꢀPropylꢀ2ꢀ(2ꢀtosylaminophenyl)ꢀ5ꢀaminobenzꢀ
imidazole (HL2) and related zinc complexes were synꢀ
thesized according to the following scheme.
The phenomenon of exited state intramolecular
proton transfer (ESIPT) in systematic series of 2ꢀ(2ꢀ
hydroxyphenyl)azoles is being actively studied for
more than 40 years [1]. Interest in similar studies of
aminoazoles demonstrating the anomalous Stokes
shift due to the intramolecular proton transfer N–
Synthesis of 1ꢀpropylꢀ2ꢀ(2ꢀtosylaminophenyl)ꢀ5ꢀ
nitrobenzimidazole (HL1). A boiling solution of 2ꢀpropylꢀ
aminoꢀ5ꢀnitroaniline (1.17 g, 6 mmol) [11] in 50% acetic
acid (15 mL) was added by a hot solution of copper aceꢀ
tate (2.40 g, 12 mmol) in water (15 mL) and a hot soluꢀ
tion of 2ꢀtosylaminobenzaldehyde (1.65 g, 6 mmol) [12]
in glacial acetic acid (6 mL). The resulting reaction mixꢀ
ture was refluxed for 1 h and cooled. The precipitate
formed was filtered off, washed with water, and dried.
The obtained copper salt was suspended in glacial acetic
acid (10 mL) and treated with a solution of sodium thioꢀ
…
H N in the excited state has recently increased [2].
The high efficiency of using these systems as fluoresꢀ
cent probes for the detection of traces of Zn2+ and
other transition metal ions in solutions was also shown
[3–7].
The synthesis and studies of the structure and the
spectral and luminescence properties of 2ꢀ(2ꢀtosylꢀ
aminophenyl)benzimidazole have first been reported sulfate (1.90 g, 12 mmol) in water (5 mL). In 30 min, the
precipitate was filtered off, washed with water, and dried.
Then the precipitate was dissolved in chloroform and
passed through an alumina layer, and the solvent was disꢀ
tilled off. Yellow crystals (mp = 185–186°С) were
obtained by recrystallization from acetic acid. The yield
was 1.62 g (60%).
in [8]. The coordination compounds of transition
metals were later synthesized on the basis of this comꢀ
pound [9]. We proposed a unique method for the synꢀ
thesis of compounds of similar structures that made it
possible to introduce the nitro group into position 5 of
the benzimidazole system. Further this made it possiꢀ
ble to obtain 1ꢀalkylꢀ2ꢀ(2ꢀtosylaminophenyl)ꢀ5ꢀamiꢀ
nobenzimidazoles that demonstrate fluorescence with
the anomalous Stokes shift. Before our studies, there
were single publications on benzimidazoles bearing
substituents in position 5 [10].
For C23H22N4O4S
anal. calcd., %:
Found, %:
C, 61.32; H, 4.92;
C, 61.23; H, 5.01;
N, 12.44.
N, 12.51.
468

ZINC COMPLEXES
CH3
469
C3H7
N
CH3
CH3
N
NH2
N
Zn
A
O S O
A
O S O
N
O S O
HN
O S O
Zn
HN
N
O2N
H2N
H2N
N
N
N
[H]
Zn(A)
2
N
N
CH3
C3H7
(HL1)
C3H7
(HL2)
C3H7
(I)
Ia: A = CH3COO–
Ib: A = (CH3)(CH3)3CCOO–
Scheme 1.
IR,
(vibrations of benzimidazole ring), 1522 s
1334 v.s νas(SO2), 1166 v.s νs(SO2). 1H NMR (DMSOꢀ
d6), , ppm: 0.70 (3H, t, = 7.3 Hz, CH2CH2CH3), 10.15 (1H, br.s, NH).
1.56 (2H, q, = 7.4 Hz, CH2CH2CH3), 2.25 (3Н, s,
CAr–CH3), 3.97 (2H, t, = 7.5 Hz, CH2CH2CH3),
7.17 (2H, d, = 8.1 Hz, CAr–H), 7.32–7.55 (6H, m,
CAr–H), 7.91 (1H, d, = 9.0 Hz, CAr–H), 8.23 (1H,
dd, = 8.9 Hz, = 2.2 Hz, CAr–H), 8.59 (1H, d,
2.2 Hz, CAr–H), 10.07 (1H, s, NH).
ν
, cm–1: 3147
w
ν
(NH), 1618 w, 1 5 9 5 w, 1 5 7 7 w
6
.91–6.93 (3H, m, CAr–H), 7.15–7.25 (4H, m,
CAr⎯H), 7.39 (1H, d, = 8.1 Hz, CAr–H), 7.42 (1H, d,
= 7.8 Hz, CAr–H), 7.61 (1H, d, = 7.8 Hz, CAr–H),
ν
(NO2)
,
J
J
J
δ
J
J
Synthesis of bis(μ2ꢀ(1ꢀpropylꢀ2ꢀ(2ꢀtosylaminopheꢀ
nylꢀ N)ꢀ5ꢀaminobenzimidazolatoꢀ
2N,N')bis(acetato)ꢀ
)dizincII) (Iа, A = CH3COO–). A hot solution of
Zn(CH3COO)2 2H2O (92 mg, 0.5 mmol) in methaꢀ
J
κ
κ
J
κ
O
J
⋅
nol (6 mL) was poured to a hot solution of HL2
(210 mg, 0.5 mmol) in methanol (4 mL), and the mixꢀ
ture was refluxed for 2 h. The solution was evaporated
to a volume of 4 mL, and the formed precipitate was
filtered off, washed with methanol, and dried. Colorꢀ
less crystals (mp > 250°C) were obtained by recrystalꢀ
lization from acetonitrile. The yield was 158 mg
(58%).
J
J
J =
Synthesis of 1ꢀpropylꢀ2ꢀ(2ꢀtosylaminophenyl)ꢀ5ꢀ
aminobenzimidazole (HL2). A solution of polysulfides,
prepared of sodium sulfide nonahydrate (6.48 g,
27 mmol) and sulfur (0.87 g, 27 mmol) in water
(15 mL), was added to a solution of 1ꢀpropylꢀ2ꢀ(2ꢀ
tosylaminophenyl)ꢀ5ꢀnitrobenzimidazole (6.08 g,
13.5 mmol) in ethanol (50 mL). The mixture was
refluxed for 4 h. The alcohol layer was separated, and
the solvent was filtered off. The residue was dissolved
in 15% hydrochloric acid (90 mL) and filtered. The filꢀ
trate was treated with a 22% solution of ammonia to
pH 7. The formed precipitate was filtered off, washed
with water, and dried. Creamꢀcolored crystals (mp =
For C50H52N8O8S2Zn2
anal. calcd., %: C, 55.20;
Found, %: C, 55.09;
H, 4.82;
H, 4.92;
N, 10.30.
N, 10.39.
IR,
1629
1135 vs νs(SO2)
Synthesis of bis(μ2ꢀ(1ꢀpropylꢀ2ꢀ(2ꢀtosylaminopheꢀ
nylꢀ N)ꢀ5aminobenzimidatazolatoꢀ
2N,N')bis(pivalatoꢀ
)dizonc(II) (Ib, A = (CH3)3CCOO–). A hot soluꢀ
ν
, cm–1: 3373 w νas(NH2), 3247
(NH2), 1565 s (C=O), 1239 vs νas(SO2),
w νs(NH2),
w
δ
140–141°С) were obtained by recrystallization from
ethanol. The yield was 4.54 g (80%).
.
κ
κ
For C23H24N4O2S
κ
O
anal. calcd., %: C, 65.69;
Found, %: C, 65.59;
H, 5.75;
H, 5.82;
N, 13.32.
N, 13.39.
tion of [Zn((CH3)3CСOO)2]n (0.11 g, 0.4 mmol) [13]
in acetonitrile (8 mL) was poured to a hot solution of
HL2 (0.17 g, 0.4 mmol) in acetonitrile (7 mL), and the
IR,
3374
1164 vs νs(SO2). H NMR (DMSOꢀd6),
(3H, t, = 7.4 Hz, CН2CН2СH3), 1.64 (2H, q,
7.6 Hz, CН2CН2СH3), 2.27 (3Н, s, CAr–СН3), 3.67 orless crystals (mp > 250°C) were obtained by recrysꢀ
(2H, t, = 7.8 Hz, CН2CН2СH3), 4.84 (2H, br.s, tallization from acetonitrile. The yield was 310 mg
NН2), 6.71 (1H, dd, = 8.6 Hz, = 1.6 Hz, CAr–H), (66%).
ν
, cm–1: 3462
νs(NH2), 1629
w
νas(NH2), 3440
w
ν
(NH), mixture was stirred for 3 h at 60
concentrated under reduced pressure to a volume of
, ppm: 0.82 5 mL and cooled. The precipitate formed was filtered
off, washed with benzene and hexane, and dried. Colꢀ
°С. The solution was
w
w (NH2), 1335 vs νas(SO2),
δ
1
δ
J
J =
J
J
J
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
No. 7
2014

470
NIKOLAEVSKII et al.
bilization of the 2H polar resonance line in DMSOꢀd6
IR spectra were recorded on Varian Excalibur 3100
FTꢀIR and PerkinꢀElmer Spectrum 65 instruments in
KBr pellets.
Xꢀray diffraction analysis. Single crystals were
grown from an acetonitrile–ethanol (2 : 1) mixture.
.
Table 1. Crystallographic parameters and refinement deꢀ
tails for structure Ic
Parameter
formula
Value
Brutto
−
C61H77N10O10.5S2Zn2
1313.19
The compound crystallizes as a solvate Ib
2H2O 0.5C2H5OH ( ). An experimental material
was obtained on a Bruker Smart CCD ApexII diffracꢀ
tometer (Mo , graphite monochromator, scan
· 2CH3CN ·
FW;
·
Ic
T
, K
173(2)
K
ω
α
mode). The structure was solved by a direct method
and refined by least squares using the SHELXSꢀ97
[14] and SHELXLꢀ97 [15] program packages in the
anisotropic fullꢀmatrix approximation. Hydrogen
atoms were refined isotropically in the riding model.
The solvate alcohol molecule is disordered, and the
site occupancy of its atoms is 1/2. The main crystalloꢀ
graphic and experimental characteristics of comꢀ
pound Ic are presented in Table 1. Selected interꢀ
atomic spacings and bond angles are listed in Table 2.
The Cif file containing the full information on strucꢀ
ture Ic was deposited with the Cambridge Crystalloꢀ
graphic Data Centre (969846; deposit@ccdc.cam.
ac.uk or http://www.ccdc.cam.ac.uk).
λ
, Å
0.71073
Crystal system
Space group
Monoclinic
P21/c
a
, Å
, Å
11.4425(7)
27.000(2)
20.843(1)
97.121(1)
6389.7(7)
4
b
c
, Å
β
V
Z
, deg
, Å3
RESULTS AND DISCUSSION
ρcalcd, g/cm–3
, mm–1
Number of reflections/meaꢀ
1.365
The structure of coordination compound Ic in the
crystal state (Fig. 1) was unambiguously determined
by Xꢀray diffraction analysis. In complex Ib, two Zn
atoms are linked by two bridging 1ꢀpropylꢀ2ꢀ(2ꢀtosylꢀ
aminophenyl)ꢀ5ꢀaminobenzimidazole ligands. Each
ligand L is tridentateꢀchelating (3N). Each zinc atom
is supplemented to a distorted tetrahedral coordinaꢀ
tion by the monodentate pivalate group (Zn–O 1.928,
1.934(4) Å). A weak interaction between the Zn atoms
and the second oxygen atoms of the pivalate groups
μ
0.88
45352/14800/9373
sured/independent/with
I
> 2 (I)
σ
Rint
0.093
0.420/0.746
2.11–27.79
1.001
Tmin/max
…
(Zn O 2.748, 2.800(4) Å) should be mentioned.
θ
Range, deg
Goodnessꢀofꢀfit
R1 > 2 ))
wR2 > 2 ))
Residual electron density
The sixꢀmembered metallocycles ZnN2C3 are nonꢀ
…
planar and inflected along the N N line by 141.4(4)
°
and 145.9(3)°. Among other features of complex Ib
,
(
I
σ(I
0.079
one should mention its cis structure: noncrystalloꢀ
graphic symmetry С2. The pivalate groups are
…
(I
σ(I
0.192
arranged at one side from the Zn Zn line (torsion
angle OZnZnO is 35°). Figure 1 shows that the benꢀ
zene fragments of the ligands are almost in the
screened conformation: the dihedral angle between
their medium planes is 155.1°, and the value of one of
–1.012/1.550
(min/max),
/Å3
e
…
the short intramolecular С С contacts is 3.04 Å. The
For C56H64N8O8S2Zn2
anal. calcd., %: C, 57.39;
Found, %: C, 57.18;
Zn(1) and Zn(2) atoms are remote from each other by
6.902(1) Å. The O(2) and O(6) oxygen atoms of the
carboxy groups of the pivalate anions that are not
involved in coordination are at a distance of
4.682(8) Å.
H, 5.50;
H, 5.45;
N, 9.56.
N, 9.73.
, cm–1: 3366 w νas(NH2), 3245
(NH2), 1566 s (C=O), 1244 vs νas(SO2),
w νs(NH2),
The absorption spectrum of HL2 in acetonitrile
(Fig. 2) is characterized by the longꢀwavelength with a
ε
IR,
1630
1140 vs νs(SO2)
ν
w
δ
ν
maximum at 341 nm (
= 9350 L mol–1 cm–1). The
.
1H NMR spectra were recorded on a Varian Unityꢀ UV irradiation of the solution at the longꢀwavelength
300 instrument (300 MHz) in the mode of internal staꢀ absorption band induces an intense fluorescence with
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
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2014

ZINC COMPLEXES
471
Table 2. Selected interatomic spacings (Å) and bond angles
(deg) in complex Ib
the band maximum at 478 nm and a quantum yield of
0.18.
The anomalously high Stokes shift of fluorescence
being 8405 cm–1 is caused by the intramolecular proꢀ
ton transfer N–H N in the excited state to form a
Bond
d, Å
Bond
d, Å
…
quinoid tautometer that demonstrates the radiative
deactivation of the electron excitation energy. Comꢀ
pounds HL2 in the solid phase (crystalline powder)
also possess intense fluorescence (Fig. 3), but its maxꢀ
imum is hypsochromically shifted to 440 nm. In addiꢀ
tion, zinc complex Ib having fluorescence in the solid
phase (Fig. 3) is characterized by a broad band at 400–
600 nm with a maximum at 458 nm. The Stokes shift
estimated from the excitation spectra was 3940 and
4300 cm–1 for the fluorescence of complex Ib and
ligand HL2, respectively.
Zn(1)–N(1)
Zn(1)–N(2)
Zn(1)–N(8)
Zn(1)–O(1)
2.020(4) Zn(2)–N(5)
2.013(4) Zn(2)–N(7)
2.071(4) Zn(2)–N(4)
1.928(4) Zn(2)–O(5)
2.004(4)
2.023(4)
2.060(4)
1.934(4)
Angle
ω, deg
Angle
ω, deg
Evidently, a substantial decrease in the Stokes shift
of fluorescence is caused by blocking the mechanism
of intramolecular proton transfer N–H N due to
N(2)Zn(1)N(1)
93.52(16) N(5)Zn(2)N(7) 94.27(17)
…
the replacement of the sulfonamide proton by the
zinc ion. At the same time, the absence of ESIPT fluꢀ
orescence of ligand HL2 in the solid phase can be
caused by its existence in the crystalline state as zwitꢀ
terions formed due to the proton transfer from the sulꢀ
fonamide group to the more basic amino group in
position 5 of the benzimidazole fragment.
N(1)Zn(1)N(8) 112.09(18) N(5)Zn(2)N(4) 111.07(18)
O(1)Zn(1)N(8) 113.90(18) O(5)Zn(2)N(4) 105.96(17)
N(2)Zn(1)N(8) 109.31(17) N(7)Zn(2)N(4) 110.15(16)
O(1)Zn(1)N(1) 109.56(16) O(5)Zn(2)N(5) 109.35(17)
O(1)Zn(1)N(2) 116.77(17) O(5)Zn(2)N(7) 125.36(17)
ACKNOWLEDGMENTS
The Xꢀray diffraction analysis was carried out at the
Center of Collective Use of the Kurnakov Institute of
O(2)
O(1)
N(8)
O(6)
O(5)
N(4)
Zn(1)
O(3)
Zn(2)
O(7)
S(2)
N(2)
S(1)
N(1)
N(5)
N(7)
O(4)
N(3)
O(8)
N(6)
Fig. 1. Molecular structure of complex Ib (hydrogen atoms and solvate molecules are omitted, thermal ellipsoids with 30% probꢀ
ability).
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
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2014

472
NIKOLAEVSKII et al.
This work was supported by the federal target proꢀ
I/Imax
gram “Scientific and Scientific–Pedagogical Personꢀ
nel of Innovative Russia” for 2009–2013 (agreement
14.A18.21.1194).
1.0
0.8
0.6
0.4
0.2
0
2
1
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tra of compound HL and the fluorescence (
1
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2
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2
3) emission
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4
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Translated by E. Yablonskaya
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
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2014