Complexes of zinc(II) with N-[2-(hydroxyalkyliminomethyl)phenyl]-4-methylbenzenesulfonamides: synthesis, structure, photoluminescence properties and biological activity

Article abstract of DOI:10.1016/j.poly.2018.01.020

The synthesis of a series of zinc(II) complexes with Schiff bases products of condensation of 2-tosylamonobenzaldehide with various aminoalcohols containing aliphatic spacers of a variable length (CH₂)_n (n = 2–6) was performed. All compounds were characterized with C, H, N elemental analysis, FT-IR, ¹H NMR, X-ray absorption spectroscopy, UV–Vis and photoluminescence data. The local atomic structures of complexes were determined by X-ray absorption spectroscopy from analysis of EXAFS and XANES of Zn K-edges. The electronic absorption spectra, photoluminescence, and biological activities of the complexes were investigated. The assignments of the experimental UV–Vis spectra of zinc(II) complexes have been carried out by Time-Dependent Density Functional Theory TD-DFT calculations.

Full text of DOI:10.1016/j.poly.2018.01.020

Accepted Manuscript
Complexes of zinc(II) with N-[2-(hydroxyalkyliminomethyl)phenyl]-4-meth-
ylbenzenesulfonamides: synthesis, structure, photoluminescence properties and
biological activity
A.S. Burlov, V.G. Vlasenko, Yu.V. Koshchienko, N.I. Makarova, A.A.
Zubenko, Yu.D. Drobin, G.S. Borodkin, A.V. Metelitsa, Ya.V. Zubavichus,
D.A. Garnovskii
PII:
S0277-5387(18)30050-0
https://doi.org/10.1016/j.poly.2018.01.020
POLY 13018
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
13 November 2017
20 January 2018
Please cite this article as: A.S. Burlov, V.G. Vlasenko, Yu.V. Koshchienko, N.I. Makarova, A.A. Zubenko, Yu.D.
Drobin, G.S. Borodkin, A.V. Metelitsa, Ya.V. Zubavichus, D.A. Garnovskii, Complexes of zinc(II) with N-[2-
(hydroxyalkyliminomethyl)phenyl]-4-methylbenzenesulfonamides: synthesis, structure, photoluminescence
properties and biological activity, Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.2018.01.020
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1
Complexes of zinc(II) with N-[2-(hydroxyalkyliminomethyl)phenyl]-4-
methylbenzenesulfonamides: synthesis, structure, photoluminescence
properties and biological activity
A. S. Burlova, V. G. Vlasenkob,*, Yu. V. Koshchienkoa, N. I. Makarovaa, A. A.
Zubenkoc, Yu. D. Drobinc, G. S. Borodkina, A. V. Metelitsaa, Ya. V. Zubavichusd,
D. A. Garnovskiie
aInstitute of Physical and Organic Chemistry of Southern Federal University, Stachki ave. 194/2,
Rostov-on-Don 344090, Russian Federation;
e-mail: anatoly.burlov@yandex.ru
bInstitute of Physics of Southern Federal University, Stachki ave. 194, Rostov-on-Don 344090,
Russian Federation
cNorth-Caucasian Zonal Scientific Research Veterinary Institute, Rostov highway, 0,
Novocherkassk 346421, Russian Federation
dNRC Kurchatov Institute, 1 Acad. Kurchatov Sq., Moscow 123182, Russian Federation
eSouthern Scientific Centre of Russian Academy of Sciences, Chekhova ave. 41, Rostov-on-Don
344006, Russian Federation
Keywords: Azomethines, Zinc complexes, UV-Vis spectra, Photoluminescence, TD-
DFT, Biological activity
A B S T R A C T
The synthesis of a series of zinc(II) complexes with Schiff bases products of
condensation of 2-tosylamonobenzaldehide with various aminoalcohols containing
aliphatic spacers of a variable length (CH2)n (n = 2-6) was performed. All
1
compounds were characterized with C, H, N elemental analysis, FT-IR, H NMR,
X-ray absorption spectroscopy, UV-vis and photoluminescence data. The local
atomic structures of complexes were determined by X-ray absorption spectroscopy
*Corresponding author
E-mail address: v_vlasenko@rambler.ru

2
from analysis of EXAFS and XANES of Zn K-edges. The electronic absorption
spectra, photoluminescence, and biological activities of the complexes were
investigated. The assignments of the experimental UV-vis spectra of zinc(II)
complexes have been carried out by Time-Dependent Density Functional Theory
TD-DFT calculations.
1. Introduction
Azomethine compounds are versatile molecules with a fortunate combination
of structural and chemical properties and have received much attention in research
both fundamental and application. Azomethines also constitute a very important
class of ligands in coordination chemistry due to their wide applications in the
synthesis of a large variety of transition metal complexes with diverse biological
activities such as antibacterial, antimicrobial properties [1, 2], exhibit antitumor [3-
9] and hypoglycemic [10, 11] activities. For example, water-soluble azomethine
derivatives of salicylic aldehyde and amino alcohols (2-aminoethanol and 3-amino-
1-propanol) are highly efficient and selective chemical sensors for zinc, which can
be used for fluorescent quantification of zinc ions in vitro and in vivo in various
biological objects in the presence of other metal ions [12].
The deliberate introduction of alcoholic groups into the peripheral part of
azomethine ligands is a convenient route to polynuclear complexes since a hydroxy
group is a versatile O-donor prone to the formation of multi-center bridging bonds
[13]. Crystal structures of many coordination compounds with hydroxyethyl (or
propyl)salicylaldimine ligands were reported [13-15]. When the alcoholic hydroxyl
group is not involved in the coordination, mononuclear structures are formed [14,
15]. Mean while, binuclear structures with bridging oxygen atoms of the aldehyde
fragments [13] and even tetrameric structures with bridging oxygen atoms of the
alcoholic groups were described [14].
Polynuclear transition metal complexes with azomethines are promising as
single-molecule magnets [16, 17] or at least as synthetically affordable models to

3
study exchange interactions between paramagnetic sites and to verify modern
theoretical approaches to the prediction of magnetic properties [18-20].
Complexes of zinc(II) of bi-, three-, and tetradentate azomethinic ligands
derived from 2-hydroxy-2-N-tosylaminobenzaldehydes and aliphatic, aromatic, or
heterocyclic amines are also efficient metal-containing luminophores. Due to their
photo- (PL) and electroluminescent (EL) properties, zinc complexes with
azomethinic ligands are a subject of numerous investigations as promising materials
for emissive (EML) or conductive (either hole HTL or electron ETL transport)
layers in the technology of OLEDs [21-27].
With this regard, the rational synthesis of novel zinc complexes with
azomethinic ligands featuring the coordination node ZnN4 and manifesting EL
properties and bioactivity is an important and urgent problem of contemporary
coordination chemistry.
The present paper is devoted to the synthesis of zinc complexes with
azomethinic
ligands
of
the
N-[2-(hydroxyalkyliminomethyl)phenyl]-4-
methylbenzenesulfonamide family, which bear a terminal hydroxyl function
separated from the imine group by an aliphatic spacer of a variable length (CH2)n
(n= 2-6). The presence of such a long and flexible spacer hinders the involvement of
the OH group in metal binding and favors the formation of the monomeric structure
with the ZnN4 core. Molecular structures, PL, and biological properties of the
synthesized complexes were studied. To the best of our knowledge, no closely
related substances have been described so far.
2. Experimental
2.1. Materials required and general methods
All solvents, zinc acetate dihydrate, 2-amino-1-ethanol, 3-amino-1-propanol,
4–amino-1-butanol, 5-amino-1-pentanol, 6-amino-1-hexanol were purchased from
Alfa Aesar and used as received.

4
C, H, N elemental analyses were carried out on a Carlo Erba TCM 480
apparatus using sulfanilamide as a reference. The metal content was determined
gravimetrically in the analytical laboratory of the Institute of Physical and Organic
Chemistry (SFU, Rostov-on-Don, Russia). Melting points were measured on a
Kofler table.
Infrared spectra were recorded on a Varian Excalibur-3100 FT-IR
spectrophotometer for powders of compounds 1a, 2a-e and solution-cast films of
free azomethine ligands 1b-e.
1H NMR spectra were measured on a Bruker Avance-600 (600 MHz)
spectrometer at ambient temperature in DMSO-d6 with the signal of residual 2H of
the solvent as the internal reference.
UV-vis spectra were registered on «Varian Cary 100» spectrophotometer.
Photoluminescent spectra were measured on a «Varian Cary Eclipse» fluorescence
spectrophotometer. DMSO of the spectrally pure grade from Sigma-Aldrich was
used as a solvent. All UV–vis and fluorescence spectra were recorded using
standard quartz cells with an optical path of 1 cm at room temperature at c = 4.0·10-5
M. Fluorescence quantum yields were determined using the method by Parker-Rice
[28] with a solution of quinine bisulfate in 0.1 N H2SO4 (φ = 0.52, λex = 365 nm) as
a standard luminophore [29].
2.2. Synthesis of free ligands
2.2.1.
The
general
method
for
the
synthesis
of
N-[2-
(hydroxyalkyliminomethyl)phenyl]-4-methylbenzenesulfonamides (1a-e)
A solution containing 2 mmol of respective amino alcohol (0.12 g of 2-
amino-1-ethanol for 1a, 0.15 g of 3-amino-1-propanol for 1b, 0.18 g of 4–amino-1-
butanol for 1c, 0.21 g of 5-amino-1-pentanol for 1d, or 0.23 g of 6-amino-1-hexanol
for 1e) in 5 mL of methanol was added to a solution of 0.55 g (2 mmol) of 2-(N-
tosylamino)benzaldehyde in 10 mL of benzene. The mixture was refluxed during 1
h. After that the solvent was distilled off on a rotary evaporator to dryness.

5
Safety. Benzene is a highly flammable and very toxic solvent. (Caution:
chronic toxicity, carcinogenicity, mutagenicity). Avoid breathing vapor and contact
with skin. Protective clothing and fume hood are required working in laboratory.
2.2.2. N-[2-[(Z)-2-Hydroxyethyliminomethyl]phenyl]-4-methylbenzenesulfonamide
(1a)
Yellow crystals, m.p. = 58-59 °C. Yield 0.61 g, 96%. Anal. Calc. for С16H18N2O3S:
C, 60.36; H, 5.70; N, 8.80. Found: C, 60.43; H, 5.78; N, 8.84%. IR spectrum,
selected bands, cm-1: 3321 ν(OH), 1651 ν(CH=N), 1337 νas(SO2), 1125, 1069
νs(SO2). 1H NMR, δ (ppm): 2.29 (s, 3H, CH3), 3.66-3.70 (m, 4H, CH2), 4.76 (s, 1H,
OH), 7.03-7.06 (m, 1H, CAr-H), 7.27-7.34 (m, 3H, CAr-H), 7.44-7.48 (m, 2H, CAr-
H), 7.66 (dd, 2H, 3J = 6.6 Hz, 4J = 1.8 Hz, CAr-H), 8.42 (s, 1H, CH=N), 12.74 (br.s,
1H, NH).
2.2.3. N-[2-[(Z)-3-Hydroxypropyliminomethyl]phenyl]-4-methylbenzenesulfonamide
(1b)
Yellow oil. Yield 0.62 g, 93%. Anal. Calc. for С17H20N2O3S: C, 61.42; H, 6.06; N,
8.43. Found: C, 61.33; H, 6.14; N, 8.53%. IR spectrum, selected bands, cm-1: 3410
ν(OH), 1650 ν(CH=N), 1336 νas(SO2), 1159 νs(SO2). 1H NMR, δ (ppm): 1.80 (q, 2H,
3J = 6.6 Hz, CH2), 2.29 (s, 3Н, CH3), 3.52 (br.s, 2H, CH2), 3.64-3.66 (m, 2H, CH2),
3
4.52 (s, 1H, OH), 7.05 (t, 1H, J = 7.5 Hz, CAr-H), 7.29-7.35 (m, 3H, CAr-H), 7.46
(dd, 2H, 3J = 7.8 Hz, 4J = 1.8 Hz, CAr-H), 7.62 (dd, 2H, 3J = 6.6 Hz, 4J = 1.8 Hz, CAr-
H), 8.45 (s, 1H, CH=N), 13.22 (br.s, 1H, NH).
2.2.4. N-[2-[(Z)-4-Hydroxybutyliminomethyl]phenyl]-4-methylbenzenesulfonamide
(1c)
Yellow oil. Yield 0.63 g, 91%. Anal. Calc. for С18H22N2O3S: C, 62.40; H, 6.40; N,
8.09. Found: C, 62.48; H, 6.34; N, 8.14%. IR spectrum, selected bands, cm-1: 3423
1
ν(OH), 1633 ν(CH=N), 1336 νas(SO2), 1155 νs(SO2). H NMR, δ (ppm): 1.52-1.55
3
(m, 2H, CH2), 1.69-1.71 (m, 2H, CH2), 2.28 (s, 3Н, CH3), 3.49 (q, 2H, J = 4.8 Hz,

6
3
CH2), 3.60-3.63 (m, 2H, CH2), 4.47 (br.s,1H, OH), 7.06 (t, 1H, J = 7.5 Hz, CAr-H),
3
3
7.30 (t, 2H, J = 8.6 Hz, CAr-H), 7.32-7.36 (m, 1H, CAr-H), 7.46 (dd, 1H, J = 7.6
Hz, 4J = 1.5 Hz, CAr-H), 7.50 (d, 1H, 3J = 8.3 Hz, CAr-H), 7.64-7.66 (m, 2H, CAr-H),
8.45 (s, 1H, CH=N), 13.35 (s, 1H, NH).
2.2.5. N-[2-[(Z)-5-Hydroxypentyliminomethyl]phenyl]-4-methylbenzenesulfonamide
(1d)
Yellow oil. Yield 0.66 g, 92%. Anal. Calc. for С19H24N2O3S: C, 63.31; H, 6.71; N,
7.77. Found: C, 63.33; H, 6.80; N, 7.74%. IR spectrum, selected bands, cm-1: 3409
ν(OH), 1633 ν(CH=N), 1338 νas(SO2), 1155, 1164 νs(SO2). 1H NMR, δ (ppm): 1.40-
1.42 (m, 2H, CH2), 1.46-1.50 (m, 2H, CH2), 1.64 (q, 2H, 3J = 7.3 Hz, CH2), 2.29 (s,
3Н, CH3), 3.40-3.42 (m, 2H, CH2), 3.58-3.60 (m, 2H, CH2), 4.35 (s, 1H, OH), 7.03-
7.06 (m, 1H, CAr-H), 7.29-7.35 (m, 3H, CAr-H), 7.45-7.47 (m, 2H, CAr-H), 7.61-7.63
(m, 2H, CAr-H), 8.45 (s, 1H, CH=N), 13.16 (br.s, 1H, NH).
2.2.6. N-[2-[(Z)-6-Hydroxyhexyliminomethyl]phenyl]-4-methylbenzenesulfonamide
(1e)
Yellow oil. Yield 0.69 g, 92%. Anal. Calc. for С20H26N2O3S: C, 64.14; H, 7.00; N,
7.48. Found: C, 64.23; H, 7.08; N, 7.54%. IR spectrum, selected bands, cm-1: 3408
ν(OH), 1634 ν(CH=N), 1337 νas(SO2), 1157, 1167 νs(SO2). 1H NMR, δ (ppm): 1.36-
1.45 (m, 6H, CH2), 1.63 (q, 2H, 3J = 7.7 Hz, CH2), 2.29 (s, 3Н, CH3), 3.39 (br.s, 2H,
CH2), 3.58-3.60 (m, 2H, CH2), 4.31 (s, 1H, OH), 7.04-7.06 (m, 1H, CAr-H), 7.29-
7.35 (m, 3H, CAr-H), 7.45-7.47 (m, 2H, CAr-H), 7.61 (s, 2H, CAr-H), 8.45 (s, 1H,
CH=N), 13.27 (br.s, 1H, NH).
2.3. Synthesis of complexes
2.3.1. The general procedure for the preparation of complexes 2a-e
A solution containing 2 mmol of appropriate amino alcohol (0.12 g of 2-
amino-1-ethanol for 2a, 0.15 g of 3-amino-1-propanol for 2b, 0.18 g of 4 – amino-1-

7
butanol for 2c, 0.21 g of 5-amino-1-pentanol for 2d, 0.23 g of 6-amino-1-hexanol
for 2e) in 10 mL of acetonitrile was added to a solution of 0.55 g (2 mmol) of 2-(N-
tosylamino)benzaldehyde in 20 mL of acetonitrile. The solution was refluxed during
1 h and then a hot solution of 0.22 g (1 mmol) of zinc acetate dihydrate in 10 mL of
methanol was added and the reaction mixture was refluxed again for 1 h. After
cooling to r.t., the precipitates of complexes formed (2a-e) were filtered off, washed
twice with hot methanol (10 mL) and dried in vacuo. All products were crystallized
from a dichloromethane-methanol 1:2 mixture.
2.3.2. Bis{N-[2-[(Z)-2-hydroxyethyliminomethyl]phenyl]-4-
methylbenzenesulfonamide}zinc(II) (2a)
Colorless crystals, m.p. > 260 °С. Yield 0.53 g, 75%. Anal. Calc. for
С32H34N4O6S2Zn: C, 54.89; H, 4.89; N, 8.00; Zn, 9.34. Found: C, 54.90; H, 4.95; N,
8.12; Zn, 9.45 %. IR spectrum, selected bands, cm-1: 3305 ν(OH), 1628 ν(CH=N),
1
1288 νas(SO2), 1135 νs(SO2). H NMR, δ (ppm): 2.24 (s, 6Н, CH3), 3.45 (br.s, 2H,
CH2), 3.54 (br.s, 4H, CH2), 4.12 (br.s, 2H, CH2), 5.00 (t, 2H, 3J = 5.4 Hz, OH), 6.86
(t, 2H, 3J = 7.9 Hz, CAr-H), 7.14 (d, 4H, 3J = 8.3 Hz, CAr-H), 7.19-7.22 (m, 2H, CAr-
H), 7.27 (d, 2H, 3J = 7.9 Hz, CAr-H), 7.50-7.52 (m, 2H, CAr-H), 7.92 (d, 4H, 3J = 8.3
Hz, CAr-H), 8.50 (s, 2H, CH=N).
2.3.3. Bis{N-[2-[(Z)-3-hydroxypropyliminomethyl]phenyl]-4-
methylbenzenesulfonamide}zinc(II) (2b)
Colorless crystals, m.p. > 260 °С. Yield 0.62 g, 85%. Anal. Calc. for
С34H38N4O6S2Zn: C, 56.08; H, 5.26; N, 7.69; Zn, 8.98. Found: C, 56.18; H, 5.31; N,
7.72; Zn, 9.01%. IR spectrum, selected bands, cm-1: 3356 ν(OH), 1628 ν(CH=N),
1
1288 νas(SO2), 1136 νs(SO2). H NMR, δ (ppm): 1.68 (br.s, 4H, CH2), 2.24 (s, 6Н,
CH3), 3.26-3.29 (m, 4H, CH2), 3.60 (br.s, 2H, CH2), 4.00 (br.s, 2H, CH2), 4.46 (t,
2H, 3J = 5.0 Hz, OH), 6.86 (t, 2H, 3J = 7.9 Hz, CAr-H), 7.13 (d, 4H, 3J = 8.2 Hz, CAr-
3
3
H), 7.19-7.22 (m, 2H, CAr-H), 7.27 (d, 2H, J = 8.5 Hz, CAr-H), 7.50 (dd, 2H, J =
7.8 Hz, 4J = 1.7 Hz, CAr-H), 7.88 (d, 4H, 3J = 8.3 Hz, CAr-H), 8.55 (s, 2H, CH=N).

8
2.3.4. Bis{N-[2-[(Z)-4-hydroxybutyliminomethyl]phenyl]-4-
methylbenzenesulfonamide}zinc(II) (2c)
Colorless crystals, m.p. > 260 °С. Yield 0.57 g, 75%. Anal. Calc. for
С36H42N4O6S2Zn: C, 57.17; H, 5.60; N, 7.41; Zn, 8.65. Found: C, 57.10; H, 5.65; N,
7.38; Zn, 8.71%.IR spectrum, selected bands, cm-1: 3339 ν(OH), 1633 ν(CH=N),
1288 νas(SO2), 1135 νs(SO2). 1H NMR, δ (ppm): 1.22-1.27 (m, 4H, CH2), 1.45-1.50
(m, 4H, CH2), 2.24 (s, 6Н, CH3), 3.08-3.18 (m, 4H, CH2), 3.40-3.47 (m, 2H, CH2),
4.04 (br.s, 2H, CH2), 4.25 (s, 2H, OH), 6.86 (t, 2H, 3J = 7.4 Hz, CAr-H), 7.15 (d, 4H,
3J = 8.0 Hz, CAr-H), 7.19-7.23 (m, 2H, CAr-H), 7.33 (d, 2H, 3J = 8.6 Hz, CAr-H), 7.49
3
4
3
(dd, 2H, J = 7.9 Hz, J = 1.7 Hz, CAr-H), 7.92 (d, 4H, J = 8.3 Hz, CAr-H), 8.54 (s,
2H, CH=N).
2.3.5. Bis{N-[2-[(Z)-5-hydroxypentyliminomethyl]phenyl]-4-
methylbenzenesulfonamide}zinc(II) (2d)
Colorless crystals, m.p. > 260 °С. Yield 0.59 g, 75%. Anal. Calc. for
С38H46N4O6S2Zn: C, 58.19; H, 5.91; N, 7.14; Zn, 8.34. Found: C, 58.29; H, 6.00; N,
7.28; Zn, 8.42%. IR spectrum, selected bands, cm-1: 3352 ν(OH), 1633 ν(CH=N),
1296 νas(SO2), 1135 νs(SO2). 1H NMR, δ (ppm): 1.06-1.14 (m, 8H, CH2), 1.43 (br.s,
3
4H, CH2), 2.24 (s, 6Н, CH3), 3.17 (q, 4H, J = 5.8 Hz, CH2), 3.40-3.45 (m, 2H,
3
3
CH2), 4.08 (br.s, 2H, CH2), 4.20 (t, 2H, J = 5.1 Hz, OH), 6.86 (t, 2H, J = 7.0 Hz,
CAr-H), 7.16 (d, 4H, 3J = 8.6 Hz, CAr-H), 7.20-7.23 (m, 2H, CAr-H), 7.34 (d, 2H, 3J =
8.5 Hz, CAr-H), 7.49 (dd, 2H, 3J = 7.9 Hz, 4J = 1.8 Hz, CAr-H), 7.94 (d, 4H, 3J = 8.3
Hz, CAr-H), 8.54 (s, 2H, CH=N).
2.3.6. Bis{N-[2-[(Z)-6-hydroxyhexyliminomethyl]phenyl]-4-
methylbenzenesulfonamide}zinc(II) (2e)
Colorless crystals, m.p. > 260 °С. Yield 0.63 g, 78%. Anal. Calc. for
С40H50N4O6S2Zn: C, 59.13; H, 6.20; N, 6.90; Zn, 8.05. Found: C, 59.20; H, 6.26; N,
6.95; Zn, 8.17%. IR spectrum, selected bands, cm-1: 3361 ν(OH), 1633 ν(CH=N),

9
1
1296 νas(SO2), 1136 νs(SO2). H NMR, δ (ppm):0.98-1.04 (m, 8H, CH2), 1.11-1.17
(m, 4H, CH2), 1.38-1.44 (m, 4H, CH2), 2.25 (s, 6Н, CH3), 3.19-3.23 (m, 4H, CH2),
3
3.41-3.45 (m, 2H, CH2), 4.10 (br.s, 2H, CH2), 4.20 (t, 2H, J = 5.2 Hz, OH), 6.85-
3
6.87 (m, 2H, CAr-H), 7.16 (d, 4H, J = 8.0 Hz, CAr-H), 7.21-7.24 (m, 2H, CAr-H),
7.36 (d, 2H, 3J = 8.3 Hz, CAr-H), 7.48 (dd, 2H, 3J = 7.9 Hz, 4J = 1.7 Hz, CAr-H), 7.95
(d,4H, 3J = 8.3 Hz, CAr-H), 8.55 (s, 2H, CH=N).
2.4. X-ray absorption spectroscopy
Zn K-edge EXAFS spectra for the complexes were recorded at the "Structural
Materials Science" beamline of the Kurchatov Synchrotron Radiation Source
(Moscow, Russia) [30] with the storage ring operating at electron energy of 2.5 GeV
and current of 80−100 mA. A Si(111) channel-cut monochromator was used for the
energy selection. All data were measured in the transmission mode. Sample
thicknesses corresponded to an absorption jump Δμx=0.5–1.0.
EXAFS data (χexp(k)) were analyzed using the IFEFFIT data analysis package
[31]. EXAFS data reduction used standard procedures for the pre-edge subtraction
and spline background removal. The radial pair distribution functions around the Zn
ions were obtained by the Fourier transformation (FT) of the k3-weighted absorption
function χexp(k) range of photoelectron wave numbers k = 2.4–13.0 Å–1. Structural
parameters including interatomic distances (Ri), coordination numbers (Ni) and
distance RMS deviations due to the thermal motion and disorder-induced static
deviations of atomic positions, also known as Debye–Waller factors (σ2) were found
by non-linear fitting of the theoretical spectra against the experimental ones.
2Ri
n

2
2i k2
Ni F (k)
2
k
(k)  S0
e
e
sin(2kR  i 
k )
, (1)

i
R 2
i
k
i1
i
The experimental data were simulated using theoretical photoelectron mean-
free-path (λ), photoelectron backscattering amplitude Fi(k) and phase functions
(formula 1) calculated using the FEFF7 program [32]. The amplitude reduction
2
factor due to extrinsic losses S0 and the edge energy shift E0 were calibrated by
fitting EXAFS data for spectra of reference compounds with known crystal

10
2
structures. The amplitude reductions factors S0 were found to be equal to 0.9 in all
cases.
The accuracy of the fits was estimated by the standard mean-square deviation
criterion (formula 2) (Q-factor),
ki exp(ki )  ki th (ki )2
m
w(k )


i
Q2 
(2)
i1
m
w(k )

ki exp(ki ) 2


i
i1
w(k
where
i ) is a weighting function, m is the number of experimental points.
2.5. Quantum-chemical calculations
The GAUSSIAN-03 program package [33] was used for DFT calculations.
Ground-state geometry of isolated molecules of the complexes under study was
optimized using the Becke's three-parameter exchange functional [34], Lee–Yang–
Parr correlation functional (B3LYP) [35] and standard split-valence polarized 6-
31G(d) basis set [36, 37]. The absence of imaginary frequencies in the normal mode
analysis ensured optimized geometry to be the true energy minimum, not a
transition state.
The simulationof UV-vis absorption spectra for these complexes was
performed within the Time-Dependent Density Functional Theory (TD-DFT)
formalism using the optimized geometry subject to solvent effects as predicted by
the standard polarizable continuum model (PCM) [38].
2.6. Antimicrobial activity assay
Antimicrobial properties of azomethines 1a-e and complexes 2a-e were
studied by means of two-fold serial dilutions in a liquid nutrient medium [39, 40].
Suspensions of bacterial cultures (2 mL) with a concentration of 5.0·105 microbial
cells per mL were mixed with equal amount of test substance solutions at variable
concentrations in special vials (which gave rise to a nominal two-fold decrease in
the bacteria concentration to 2.5105 per mL). Vials were kept in an incubator for

11
18 h at 37 °C. In parallel, vials containing nutrient medium and bacteria at a
concentration of 2.5105 per mL and only nutrient medium without bacteria were
incubated under identical conditions as positive control and negative control probes,
respectively. Standard strains of bacteria Staphylococcus aureus P-209 and
Escherichia coli 078 (field isolates from the collection of the Rostov regional
veterinary laboratory) were used for the antimicrobial activity tests. Activity of the
azomethines and zinc complexes was compared with that of a commercial antibiotic
sulfadimethoxine (chemically pure grade).
2.7. Antiprotozoal activity assay
Antiprotozoal activity was studied against infusoria Colpoda steinii (field
isolate from the collection of the laboratory of parasitology of the North-Caucasian
Zonal Scientific-Research Veterinary Institute, Russia) using a method described
elsewhere [41]. The tests were carried out in a 96-well microplate typically used for
the enzyme-linked immunosorbent assays (ELISA), 12 wells of the first row were
used. A 1:1 mixture of boiled tap and sterile distilled water was used as a medium.
Initially the substance being tested was dissolved in distilled water. Serial dilutions
of the test solutionswere prepared as follows:
Solution No.1: 5 mg of the substance under study was dissolved in 50 µL of
70% aqueous DMSO under stirring, then 5 mL of distilled water was carefully
added to give an apparent concentration of the probe 1000 µg/mL, 150 µL of the
prepared solution was placed into the well No.1 of the microplate.
Solutions No.2-12: 150 µL of 1:1 mixture of boiled tap and sterile distilled
water was placed into the wells No.2-12 of the microplate using an automated 8-
channel pipette. Then 150 µL of the solution No.1 was placed into the well No.2
under stirring. After complete mixing an aliquot of 150 µL of solution No.2 was
placed into the well No.3. A similar procedure was applied to all further wells. In
order to provide identical volumes of solutions in all the wells, 150 µL of the
solution was removed from the last well No.12. Aliquots of the Colpoda steinii
protozoa culture suspended in water preliminary incubated for 3 days (30 µL) were

12
added to all wells in such a way that no less than 10-15 active infusoria were
distinctly visible in the field-of-view of an optical microscope. The microplate was
covered with a lid and left at room temperature (20-22 °C) for 18-20 h.
Test results were controlled as follows: 30 µL of content of each well one-by-
one starting from the well No.12 was transferred onto a clean glass slide and
examined under an optical microscope at a magnification of 10×15 to check for the
presence of living protozoa. The minimum protistocidal concentration of a
substance under study corresponded to the first well encountered with no living
infusoria. In a similar way, the following control solutions were tested:
- blank medium (boiled water + distilled water) – 5 wells;
- DMSO (50 µL of 70% DMSO + 5 mL of distilled water serially diluted exactly as
in the case of the tested substances) – 12 wells;
-commercial antiprotozoal agent toltrazuril (2.5% solution serially diluted similarly
to the tested substances).
2.8. Fungistatic activity assay
Antifungal activity of the compounds was determined by the agar-diffusion
method according to the guideline [42] for fungi culture Penicillium italicum
Wehmer (1894) (field isolate, from the collection of micromycetes of the laboratory
of mycotoxicology of the North-Caucasian Zonal Scientific Research Veterinary
Institute, Russia). A commercial fungicide fundazol was used for comparison. An
aqueous solution of fundazol was placed on a disc of filter paper (ND-PMP-1 Paster
Central Research Institute of Epidemiology and Microbiology) in an amount of 15
µg per disc with a diameter of 8 mm.
3. Results and discussion
3.1. Synthesis and spectroscopic properties of azomethines as free ligands and their
derived zinc complexes

13
Azomethine compounds 1a-e (HL) were prepared by a condensation of a
benzene solution of 2-(N-tosylamino)benzaldehyde and an alcoholic solution of the
respective aminoalcohol (Scheme 1). All compounds are oil-like except for 1a (n=2)
that is a yellow crystalline powder.
CH3
CH3
CH3
(CH2)nOH
O
NH2(CH2)nOH
O
O
S
S
S
O
O
O
.
NH2(CH2)nOH
Zn(CH3COO)2 2H2O
N
N
NH
NH
Zn
CH3OH, C6H6, 
CH3OH, CH3CN, 
N
N
N
O
O
S
(CH2)nOH
O
HO(CH2)n
1a-e
2a-e
a (n=2); b (n=3); c (n=4); d (n=5); e (n=6)
H3C
Scheme 1. The synthesis of azomethines 1a-e and their zinc complexes 2a-e.
The structure and composition of azomethines 1a-e have been established
1
based on IR, H NMR, and elemental analysis data. The IR spectra of compounds
1a-e show intense bands at 3423-3321 cm-1, 1633-1651 cm-1, 1336-1338 cm-1, and
1155-1159 cm-1 attributed to stretching vibrations ν(OH), ν(CH=N), νas(SO2), and
νs(SO2), respectively. In the 1H NMR spectra of these compounds, signals of protons
of the OH, CH=N, and NH groups appear at 4.31-4.76 ppm, 8.42 - 8.45 ppm, and
12.74-13.35 ppm, respectively.
Zinc compounds 2a-e were obtained in situ in a reaction of 2-(N-
tosylamino)benzaldehyde, corresponding amino alcohol, and zinc acetate dihydrate
taken in a molar ratio of 2:2:1, without a dedicated step of free ligand isolation.
The zinc complexes 2a-e differ from each other by the number of methylene
units in the N-hydroxyalkyl fragment (HydAlk) of the ligand: 2a (n = 2), 2b (n = 3),
2c (n = 4), 2d (n = 5), 2e (n = 6). This spacer defines the distance between the
azomethine nitrogen atom certainly involved into the coordination with Zn and the
hydroxyl group that is also coordinatively active.

14
According to the elemental analysis, all complexes have are characterized by
the ZnL2 composition. In the IR spectra of complexes 2a-e, a broad vibration band
in the region of 3305-3361 cm-1 ν(ОН) is preserved, but its intensity is reduced as
compared to that in the respective free ligands 1a-e. The stretching vibration band
ν(СН=N) redshifts with respect to the free ligands to 1628-1634 cm-1. Similarly, the
asymmetric and symmetric stretching vibrations of the SO2 group redshift by
1
50 cm-1. In the H NMR spectra of complexes 2a-e, the signal of the tosylamino
proton (observed as a singlet at 12.74-13.35 ppm in free ligands) disappear, whereas
that of the imine proton (CH=N) shifts downfield to δ 8.52 – 8.56 ppm (instead of
8.42-8.45 ppm). The signal of the OH proton is preserved and appears at 4.20-5.00
ppm.
1
Such spectral observations of IR and H NMR spectra are indicative of the
formation of complexes with the {ZnN4} coordination core and ZnL2
stoichiometry, in which the azomethines act as bidentate chelate monoanionic
ligands, and the terminal hydroxyl group remains uncoordinated [23, 25, 43-47].
3.2. The X-ray absorption spectroscopy
Parameters of the local atomic structure of complexes 2a-e were determined
from the analysis of Zn K-edge EXAFS and XANES spectra. Figure 1a (left panel)
shows normalized XANES spectra and their first derivatives dμ/dE. For all
complexes 2a-e, the shapes of XANES spectra are similar and are characterized by
the absence of pre-edge peaks and intense features just above the absorption edges.
The pre-edge peak in XANES is caused mainly by quadrupole electronic transitions
1s → 3d involving atomic orbitals of the central metal atoms, which are formally
forbidden by the dipole selection rules. These peaks can gain some intensity to be
registered in spectra for low-symmetry coordination polyhedra of the metal ion due
to partial 4p-3d hybridization. But these arguments are not applicable to Zn(II)
derivatives, since it has a completely filled 3d-shell. First derivatives dμ/dE of Zn K-
edge absorption spectra for complexes 2a-e show a broad main maximum with a
complicated multiple-component structure due to the splitting of Zn 4p*-orbitals in

15
an asymmetric ligand field. A comparison of experimental XANES spectra with
those reported in the literature [48-50] implies the tetrahedral environment of zinc
ions in the complexes.
Quantitative characteristics of the nearest atomic environment of zinc ions in
the complexes 2a-e were obtained from the analysis of EXAFS spectra. MFT k3χ(k)
for complexes 2a-e are shown in Fig. 1b (right panel) and the best-fit parameters of
the local structure are listed in Table 1.
Figure 1.
For all compounds 2a-e, MFTs show a main peak at r = 1.63 Å due to the
photoelectron scattering on the first coordination sphere (CS), and much weaker
peaks of more distant coordination spheres.
The initial structural model of zinc environment in complexes 2a-e was
constructed using crystallographic data for similar complexes retrieved from the
Cambridge Structural Database. According to the non-linear fitting of EXAFS, the
first CS of Zn ions for all complexes consists of four N atoms at an average distance
of 2.03 Å (Table 1). The best-fit values of Debye-Waller factors (0.0031-0.0035 Å2)
for the first CS Zn-N are typical values for spectra of such complexes measured at
room temperature [48-50].
Table 1.
Thus Zn K-edge EXAFS and XANES data for the complexes 2a-e fully
support the suggestion of ZnL2 composition with only tosylamino and imine
nitrogen atoms involved into the coordination with Zn and hydroxy groups of
OH(CH2)n spacers (n= 2-6) remaining intact regardless of their length.
3.3. Electronic absorption spectra and photoluminescence of the zinc complexes

16
A comparative study of UV-vis and PL properties of the zinc complexes 2a-e
were performed at room temperature in DMSO solutions. The electronic absorption
spectra of 2a-e are shown in Fig. 2, essential optical characteristics are summarized
in Table. 2.
Table 2.
Figure 2.
UV-vis spectra of the complexes 2a-e in the spectral range from 265 to 400
nm are virtually identical along the whole series and show two main absorption
bands centered at 350 nm (ε = 11540-12890 M-1 cm-1) and 270 nm (ε = 21700-
25300 M-1 cm-1) with slightly different relative intensities (Table 2, Fig. 2). All
complexes 2a-e demonstrate bright blue fluorescence (Table 2, Fig. 3).
Figure 3.
Fluorescence maxima and fluorescence quantum yields fall into narrow
ranges λmax = 428 – 430 nm and φ=0.32-0.35, respectively, for all complexes 2a-e
(Table 2). The fluorescence excitation spectra of 2a-e fit well their absorption
spectra, indicating that their fluorescence was correctly assigned zinc complexes
ZnL2. (Table 2, Figure 4 ).
Figure 4.
The above data show that the optical properties of the complexes 2a-e are
formed by the coordination core that is common for all of them and are essentially
independent of the length of the (CH2)n spacer within the N-hydroxyalkyl
substituent.

17
Thus, the novel zinc complexes 2a-e shows highly efficient PL properties in
the blue spectral region, which makes them promising luminophores for the
fabrication of white-light OLEDs.
3.4. Interpretation of UV-vis spectra based on TD-DFT calculations
In order to assign bands observed in the experimental UV-vis spectra to
specific singlet-singlet electronic transitions spectral simulation within the TD-DFT
formalism was utilized. Theoretical calculations predicted very similar values of
electronic transition characteristics for all zinc complexes 2a-e indicating again that
the hydroxyalkyl radicals do not participate in the charge transfer processes
reflected in UV-vis spectra. Therefore, results of calculations are presented below
only for 2a, for other complexes the respective data can be found in Supplementary
Materials (Table S1-S5, Fig. S1-S5).
The theoretical UV-vis spectrum for 2a corresponds well to the experimental
one, as shown in Fig. 4. Energies (E), wavelengths (λcal), oscillator strengths (f), and
frontier molecular orbitals (FMO) involved for all important singlet-singlet
electronic transitions are compiled in Table 3. The theoretical spectrum was
constructed as a convolution of Gaussian peaks associated with each of the
electronic transitions taking into account their positions and oscillator strengths.
The long-wavelength part of the experimental UV-vis spectrum is formed by
a wide absorption band with a maximum at 353 nm. As expected for Zn(II)
complexes with the completely filled d-shell and further confirmed by the
calculation, no d-d intra shell transitions of Zn is involved. Instead, according to the
TD-DFT spectral simulations, the absorption maximum at 353 nm is formed by a
superposition of four transitions, viz., HOMO→LUMO, HOMO→LUMO+1,
HOMO-1→LUMO and HOMO-1→LUMO+1 with oscillator strengths f = 0.03-
0.12. The energy diagram of the FMOs and respective isosurfaces are shown Fig.5.
An analysis of atomic composition of these FMOs responsible for the
experimentally observed absorption band indicate that all of them HOMO and
HOMO-1 as well as LUMO and LUMO+1 are dominantly localized (up to 85-90 %)

18
at the iminomethylphenyl (ImPh) fragments of the two ligands within the complex
(Fig.5). As one can see, HOMO and HOMO-1 are of the bonding π character and
the respective electronic density is delocalized between the two ligands. Mean
while, LUMO and LUMO+1 are of the antibonding π* character but the electron
density is localized at either of the two ligands separately. There is also a minor
contribution of charge transfer from the tosyl (Ts) and hydroxyalkyl (HydAlk)
fragments. Thus, the experimentally observed band of UV-vis spectra at 353 nm is
due to a superposition of π → π* electronic transitions with a dominant ligand-to-
ligand charge transfer (LLCT) character. The same interpretation of UV-vis spectra
was obtained for all other zinc complexes (Table S1-S5, Fig. S1-S5).
Table 3.
Figure5.
3.5. Biological activity of the azomethines and zinc complexes
The protistocidal, antibacterial, and fungistatic activities of the azomethines
1а-е and zinc complexes 2a-e made here were studied. The test results are presented
in Table 4.
Table 4.
As it can be judged from Table 4, most promising results relate to the
protistocidal and bacteriostatic properties. The azomethines 1а-е have been shown
to have only protistocidal activity. Compounds 1а,с-е have the same activity as
toltrazuril, but azomethine 1b was twice less active than the commercial drug.
The some complexes 2 show a very high protistocidal activity against
Colpoda steinii. More specifically, the complex 2a is four times more active than
the commercial drug toltrazuril taken as a reference, and the complex 2d is nearly as
active as toltrazuril. The complexes 2a-e also show a pronounced bacteriostatic

19
activity against Staphylococcus aureus with the complex 2e being twice more active
than the commercial drug sulfadimethoxine taken as a reference.
Two out of five compounds of the series also demonstrate a fungistatic
activity against Penicillium italicum, however, it does not exceed that of the
commercial drug fundazol.
Therefore, some members of the zinc complexes with N-[2-
(hydroxyalkyliminomethyl)phenyl]-4-methylbenzenesulfonamide ligands show
higher fungistatic and protistocidal activities exceeding those of approved free
ligands and commercial drugs, which encourages the further search for compounds
with medicine-important bioactivity among this family.
Acknowledgements
The work was performed with the financial support of the Ministry of Education and
Science of the Russian Federation (the State assignment: project 4.5388.2017/8.9).
1
IR, UV-vis, PL, PLE, and H NMR spectra were measured using equipment of the
center for collective use "Molecular spectroscopy" at the SFU. X-ray absorption
spectra were measured at the Unique Scientific Facility Kurchatov Synchrotron
Radiation Source funded by the Ministry of education and science of the Russian
Federation (project RFMEFI61914X0002).

20
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Nikolaevskii, M.A. Kiskin, D.A. Garnovskii, A.L. Trigub, A.V. Metelitsa, Russ. J.
Gen. Chem. 87 (2017) 764.
[50] A.S. Burlov, V.G. Vlasenko, A.V. Dmitriev, V.V. Chesnokov, A.I. Uraev, D.A.
Garnovskii, Y.V. Zubavichus, A.L. Trigub, I.S. Vasilchenko, D.A. Lypenko, E.I.
Mal’tsev, T.V. Lifintseva, G.S. Borodkin, Synth. Metals. 203 (2015) 156.

24
Table 1. Parameters of the local structure around zinc ions in complexes 2a-e:
coordination numbers (N), interatomic distances (R), and Debye-Waller factors (σ2).
Q is the integral fit quality factor.
Sample
2a
N
4
4
4
4
4
R, Å
2.02
2.03
2.03
2.02
2.03
σ2, Å2
0.0035
0.0035
0.0032
0.0031
0.0032
CS
N
Q, %
1.5
N
1.7
2b
N
2.2
2c
N
2.4
2d
N
1.5
2e

25
Table 2. UV-vis and photoluminescence characteristics of 2a-e in DMSO at 293 K:
ε - molar extinction coefficient; φ- quantum yield of fluorescence.
Photoluminescence
Absorption
Compound
Excitation
Emission
λmax, nm (ε, M-1сm-1)
φ
λmax, nm
λmax,nm
353 (11540)
270 (23700)
353 (12320)
270 (25300)
353 (12890)
270 (25100)
353 (12340)
270 (21700)
353 (12680)
270 (25280)
350
350
350
350
350
430
430
430
429
428
0.32
0.34
0.35
0.35
0.32
2a
2b
2c
2d
2e

26
Table 3. Calculated wavelengths (λ), energies (E), oscillator strengths (f), involved
molecular orbitals and their contributions for different electronic transitions in 2a
according to TD-DFT calculations.
λcal, nm E, eV
Electronic transitions, (contribution, %)
f
Character
*
364.54 3.4012
0.081
HOMO  LUMO (90 %)
352.66
3.5157
(353)†
*
HOMO→ LUMO+1 (83)
0.117
*
*
345.65 3.5870
333.33 3.7195
HOMO-1 → LUMO (86)
HOMO-1 → LUMO+1 (90)
HOMO-1 → LUMO+3 (11)
HOMO → LUMO+2 (77)
HOMO-1 → LUMO+2 (18)
HOMO → LUMO+3 (71)
0.047
0.031
*
*
292.09 4.2448
290.27 4.2713
0.0001
0.0247
†
experimental value

27
Table 4. Fungistatic, protistocidal, and bacteriostatic activities of the free ligands
(1а-е) and zinc complexes (2a-e) in a comparison with relevant commercial drugs.
Penicillium italicum,
inhibition zone
Staphylococcus
aureus P-209,
µg/mL
Colpoda steinii,
Escherichia coli
Compound
µg/mL
078, µg/mL
diameter, mm
0
0
0
0
62.5
125
>500
>500
>500
>500
>500
>500
>500
>500
1a
1b
1c
1d
62.5
62.5
0
8.0
0
62.5
15.6
125
500
62.5
250
>500
>500
>500
>500
>500
>500
>500
250
1e
2a
500
2b
0
>500
125
2с
0
2d
10
31.25
2e
Sulfadime-
thoxine
Toltrazuril
Fundazol
-
-
62.5
62.5
-
62.5
-
-
-
-
-
22

28
a
b
Fig. 1. Zn K-edge XANES spectra for the zinc complexes 2a-e (a) represented as
μ(E) and dμ/dE (insets), MFT EXAFS χ(k)k3 for zinc complexes 2a-e, experiment -
solid line, best-fit theory - empty circles (b).

29
0.4
0.2
0.0
2a
2b
2c
2d
2e
300
350
400
450
Wavelength (nm)
Fig. 2. UV-vis spectra of compounds 2a-e in DMSO.