Novel copper(II), cobalt(II) and nickel(II) complexes with 5-(4-oxo-4H-chromen-3-yl)-4,5-dihydro-1,3,4-thiadiazole-2-carboxamide: Synthesis, structure, spectroscopic studies

Article abstract of DOI:10.1016/j.poly.2017.10.027

A series of novel organic ligands, 5-(4-oxo-4H-chromen-3-yl)-4,5-dihydro-1,3,4-thiadiazole-2-carboxamide, which are the tautomeric forms of 2-oxo-2-(arylamino)-(2E)-2- [(4-hydroxy-2-oxo-2H-1-benzopyran-3-yl)-methyledene]ethanethioic acid hydrazides, have been synthesized from 3-formylchromone and oxamic acid thiohydrazides. Copper(II), cobalt(II) and nickel(II) complexes with 2-oxo-2-(arylamino)-(2E)-2-[(4-hydroxy-2-oxo-2H-1-benzopyran-3-yl)methyledene]ethanethioic acid hydrazides have been synthesized by the interaction of corresponding organic ligands with MCl₂ (M = Cu, Co, Ni). The crystal structure of a copper(II) complex with 5-(4-oxo-4H-chromen-3-yl)-N-phenyl-4,5-dihydro-1,3,4-thiadiazole-2-carboxamide has been solved by a single-crystal X-ray diffraction method. The copper(II) ions in complex molecule are coordinated by aldimine nitrogen atom, thiolate sulfur atom and the oxygen atom the pyrone ring keto-group as well as two bridged chloride anions in a distorted triangular bipyramidal geometry. The electrochemical investigations of synthesized ligands and complexes have been performed by cyclic voltammetry technique.

Full text of DOI:10.1016/j.poly.2017.10.027

Accepted Manuscript
Novel copper(II), cobalt(II) and nickel(II) complexes with 5-(4-oxo-4H-chro-
men-3-yl)-4,5-dihydro-1,3,4-thiadiazole-2-carboxamide: synthesis, structure,
spectroscopic studies
Ksenia A. Myannik, Vladimir N. Yarovenko, Elena K. Beloglazkina, Anna A.
Moiseeva, Mikhail M. Krayushkin
PII:
S0277-5387(17)30689-7
https://doi.org/10.1016/j.poly.2017.10.027
POLY 12891
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
18 July 2017
27 October 2017
Please cite this article as: K.A. Myannik, V.N. Yarovenko, E.K. Beloglazkina, A.A. Moiseeva, M.M. Krayushkin,
Novel copper(II), cobalt(II) and nickel(II) complexes with 5-(4-oxo-4H-chromen-3-yl)-4,5-dihydro-1,3,4-
thiadiazole-2-carboxamide: synthesis, structure, spectroscopic studies, Polyhedron (2017), doi: https://doi.org/
10.1016/j.poly.2017.10.027
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Dedicated to Prof. Marian Mikołajczyk on the occasion of his 80th birthday
Novel copper(II), cobalt(II) and nickel(II) complexes with 5-(4-oxo-4H-chromen-3-yl)-4,5-
dihydro-1,3,4-thiadiazole-2-carboxamide: synthesis, structure, spectroscopic studies
Ksenia A. Myannika, Vladimir N. Yarovenkoa, Elena K. Beloglazkinab*, Anna A. Moiseevab ,
Mikhail M. Krayushkina.
aN.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 119991
Russia
b M.V. Lomonosov Moscow State University, Chemistry Department, Moscow 119992, Russia
A series of novel organic ligands, 5-(4-oxo-4H-chromen-3-yl)-4,5-dihydro-1,3,4-thiadiazole-2-
carboxamide, which are the tautomeric forms of 2-oxo-2-(arylamino)-(2E)-2-[(4-hydroxy-2-oxo-
2H-1-benzopyran-3-yl)-methyledene]ethanethioic acid hydrazides, have been synthesized from
3-formylchromone and oxamic acid thiohydrazides. Copper(II), cobalt(II) and nickel(II)
complexes
with
2-oxo-2-(arylamino)-(2E)-2-[(4-hydroxy-2-oxo-2H-1-benzopyran-3-
yl)methyledene]ethanethioic acid hydrazides have been synthesized by the interaction of
corresponding organic ligands with MCl2 (M=Cu, Co, Ni). The crystal structure of a copper(II)
complex
with
5-(4-oxo-4H-chromen-3-yl)-N-phenyl-4,5-dihydro-1,3,4-thiadiazole-2-
carboxamide has been solved by a single-crystal X-ray diffraction method. The copper(II) ions in
complex molecule are coordinated by aldimine nitrogen atom, thiolate sulfur atom and the
oxygen atom the pyrone ring keto-group as well as two bridged chloride anions in a distorted
triangular bipyramidal geometry. The electrochemical investigations of synthesized ligands and
complexes have been performed by cyclic voltammetry technique.
Key words: Chromones, 1,3,4-Thiadiazole, Oxamic acid thiohydrazide, Coordination
compounds.
1. Introduction
Thiohydrazides of oxamic acids represent a wide synthetic interest as multifunctional
organic compounds with both electrophilic and nucleophilic atoms, and possessing variety of
biological properties [1,2]. Synthetic approaches basing on amide and thiohydrazide group of
monothiooxamides modifications are promising for obtaining a wide range of diverse
heterocyclic structure [3-6]. It is worth to note the tautomerism possibility of the product, leading
1

to the formation of 2, 3-dihydro- 1,3,4-thiadiazoIes or corresponding hydrazones, when
thioaroylhydrazides are treated with aldehydes or ketones [7, 8].
Although, thiohydrazides are an interesting class of tridentate ligands because of their
mixed hard–soft donor character and versatile coordination behavior. Only copper complex of
salycilic aldehyde hydrazone and pyridine [9], and range of thiosemicarbazone complex [10],
which can be considered as the analogs of the thiohydrazide oxamic acids were described
previously.
The chromone (4H-benzopyran-4-one) skeleton is a fragment of the important flavone
compounds, which occur naturally in plants and have potential beneficial effects for human
health [11]. The metal complexes of chromone derived thiosemicarbazones exhibit antimicrobial
[12], cytotoxic [13], antituberculostatic, anticancer, antioxidant [12] activities.
The hydrazone derived from the chromones are a perspective class of the organic
compounds as due to their possible biological activity, as the ligand for metal ions complexation.
In the present paper we report the synthesis and characterization of new 5-chromone-4,5-
dihydro-1,3,4-thiadiazoles and also the study of these compounds as ligands in the reactions with
copper(II), cobalt(II) and nickel(II) chloride.
2. Experimental
2.1. General
NMR spectra were recorded in deuterated solvents on spectrometers working at
300.13 MHz for 1H, 75.77 for 13C. Data are represented as follows: chemical shift,
multiplicity (s, singlet; d, doublet; t, triplet; m, multiplet), coupling constant in hertz (Hz),
integration, and assignment. Elemental analysis was performed on a Eurovector EA 3000
automated analyzer. Mass spectra were obtained on a mass spectrometer (70 eV) with direct
sample injection into the ion source. Highresolution mass spectra were obtained from a TOF
mass spectrometer with an ESI source. All chemicals and anhydrous solvents were purchased
from commercial sources and used without further purification. Silica column
chromatography was performed using silica gel 60 (70−230 mesh); TLC analysis was
conducted on silica gel 60 F254 plates. UV−vis spectra were recorded in 1.0 cm quartz
cuvettes. The experimental measurements were performed in the presence of air in DMSO
solutions. IR spectra were registered on a Bruker ALPHA spectrometer in KBr pellets.
Electrochemical studies were carried out on a PI-50-1.1 potentiostat. Glassy-carbon disk
(2 mm in diameter) was used as the working electrodes; a 0.05 M Bu4NClO4 solution in DMF
served as the supporting electrolyte; Ag/AgCl/KCl(sat.) was used as the reference electrode. All
measurements were carried out under argon; the samples were dissolved in the pre-deaerated
2

solvent. Dimethylformamide (high-purity grade) was purified by successive refluxing and
vacuum distillation over anhydrous CuSO4 and P2O5. РM3 calculation were performed by use
the HYPERCHEM software on PC. Geometry optimization of the molecules was carried out
with a gradient less than 0.01 kcal/mol as the convergence criterion.
X-ray diffraction: single crystals of 7a were obtained by the slow diffusion of diethyl
ether to ethanolic solution of CuCl2 and ligand 6a (1:1). Single crystal data for 7a were collected
on a Bruker APEX2 DUO diffractometer using graphite monochromated Mo Kα radiation (λ =
0.71073 Å) at 120 K. The structure was solved by direct method and refined by the full-matrix
least-squares against F2 in anisotropic approximation for non-hydrogen atoms. Hydrogen atoms
were placed geometrically and refined in isotropic approximation in riding model. Crystals are
monoclinic, space group C2/c, at 120 K: a = 14.8541(10) Å, b = 7.7072(5) Å, c = 29.621(2) Å,
3
3
α= 90°, β= 91.9116(13)°, γ = 90°, V = 3389.2 (4) Å , Z=4, D calc = 1.761 Mg/m , (MoK) =
1.596 mm-1, F(000) = 1816. CCDC 1575758 contain the supplementary crystallographic data,
which can be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
2.2. 5-(4-oxo-4H-chromen-3-yl)-4,5-dihydro-1,3,4-thiadiazole-2-carboxamide 6–18 (typical
procedure)
Compounds 1a-e [14-17], 2a-e and 3a-e [18-19] were synthesized according to literature
procedures. Solution of compounds 3 (1 mmol) in minimal amount of hot EtOH was added to
an equimolar amount of 5 in 10 ml of EtOH. The mixture was boiled for 8 h, and then the
precipitate was filtered, dried and recrystallized from EtOH. Spectral and HRMS data for 6a-
o are shown in Supplementary Materials.
2.3. Synthesis of coordination compounds 7a-z (typical procedure)
Concentrated solutions of ligand 6a-d, g-m (0.05 g) in 5 ml of EtOH and equimolar amount of
MCl2*6H2O (M = Co, Ni) or CuCl2 in 1–2 ml of EtOH were mixed at room temperature, boiled
for 1 h and stand to the complex precipitation. The forming solid was filtered off, washed by
small portions of Et2O and dried in air. Spectral and Elemental analysis data for 7a-z are shown
in Supplementary Materials.
3. Results and discussion
3.1. Synthesis of ligand and complexes
3

Hydrazones 6 were synthesized by the condensation reactions of 3-formylchromones 5,
obtaining by the Vilsmeier–Haack reaction from various 2-hydroxyacetophenones 4, and
previously described oxamic acid thiohydrazides 3 [18-19] (Scheme 1).
S
O
O
R
NH
S8
R
NH2 + ClCH2
C
ClCH2
1a-e
C
morpholine
NH R
N
O
Cl
O
2a-e
S
R
NH
H2N-NH2 . H2O
NH NH2
O
3a-e
O
O
O
O
N NH
O
R
3a-e
CHO
R1
R1
R1
CH3
EtOH
S
POCl3
DMF
HN
HN
t oC
R2
OH
R2
R2
O
O
4a-d
5a-d
N
N
H
O
R
R1
R2
S
O
6a-o, 40-80%
6a, R = Ph, R1 = H, R2 = H (69%); 6b, R = 4-F-C6H4, R2 = H, R1 = H (60%);
6c, R = Ph, R1 = H, R2 = OH (70%); 6d, R = Ph, R1 = Br, R2 = OH (70%);
6e, R = 4-F-C6H4, R1 = H, R2 = OH (65%); 6f, R = 4-F-C6H4, R2 = OH, R1 = Br (66%);
6g, R = Ph, R2 = H, R1 = F (52%); 6h, R = 4-F-C6H4, R2 = H, R1 = F (40%);
6i, R = 4-OMe-C6H4, R2 = OH, R1 = H (55%); 6j, R = 4-OMe-C6H4, R2 = OH, R1 =Br (62%);
6k, R = 4-OMe-C6H4, R2 = H, R1 = F (49%); 6l, R = 4-OMe-C6H4, R2 = H, R1 = H (46%);
6m, R = 2,5-(OMe)2-C6H3, R2 = H, R1 = H (49%); 6n, R = 2,5-(OMe)2-C6H3, R2 = H, R1 = F (60%);
6o, R = 3,5-Cl2-C6H3, R1 = H, R2 = H (69%);
Scheme 1. Synthesis of ligands 6a–o.
1
Note, that all of the compounds 6 basing on H and 13C NMR data exist in DMSO
solution as unexpected cyclic tautomeric form of 4H-chromen-3-yl-4,5-dihydro-1,3,4-
thiadiazole-4-carboxamides 6a-o. Our earlier salicylic aldehyde thiohydrazone study showed that
there are equilibrium mixture of two tautomers, linear A and cyclic B in solutions (Scheme 2)
[15]. Instead of the hydrazinyl proton, the thiadiazole singlet is observed at 6.5 ppm, which
indicates the presence of an intermolecular hydrogen bond (between HC-N proton and pyrone
keto-group). 13C NMR spectra exhibit signal C10 at 55-70 ppm and absence C=S in the range
180-200 ppm. Thus, it can be assumed that the equilibrium is shifted toward a cyclic form B for
4

compounds 6a-o in the solution. Trans-configuration of ligand linear form 6a was confirmed by
the X-ray data for its copper complex 7a (see below).
IR spectra of all synthesized ligands display absorption bands of C=O fragments in the
1650- 1700 cm-1 region, C=N and C-N in 1500–1660 cm-1 region of, N-N in 1020-1090cm-1
region. Normally the "pure" C=S stretching frequency would observed in the 1080-1230 cm.-l
range [16] in our case it doesn’t. Also this is an evidence of the cyclic form B existence in the
solid state.
R
S
NH
R
N
H
HN
N
H
HN
N
S
R'
O
R'
O
Scheme 2. Tautomeric equilibrium of thiohydrazones A and thiadiazoles B.
To obtain the coordination compounds, the solutions of ligands 6a-d, g-n in ethanol were
mixed with equimolar amount of CuCl2 or CoCl2*6H2O, or NiCl2*6H2O ethanolic solution, the
resulting mixture was reflux for 1 hour and than were standing to the solid precipitation.
Complexes 7a-z (Scheme 3) with (L-H)2M2Cl2 composition (M = Cu, Co, Ni) were obtained in
all cases («L» is the collective designation for organic ligands 6a-d, g-n). All complexes are
reasonably soluble in DMF or DMSO and stable in the atmospheric conditions for extended
period.
R1
N
N
H
N
O
MCl2
EtOH
M
O
S
6a-d, g-n
O
R2
Cl
O
Cl
R2
S
O
M
R1
O
N
N
H
N
7a-z, 50-80%
M = Cu (a,d, g, i, k, n, p, s, v, z)
Co (b, e, h, j, l, o, q, t, x)
Ni (c, f, m,r, u, y)
Scheme 3. Synthesis of coordination compounds 7a–z.
Organic ligands fragments in complexes 7 are in linear form A, which can be determined
on the basis of the significant shift of N-N bond absorption to the characteristic hydrazide 4
vibrations frequencies in the IR spectra of complexes. IR spectra of complexes 7a-z show also
the shift of C=N group absorption bands at 1620-1600 cm-1 compare to initial ligands which
5

confirms the metal ions coordination with the C=N nitrogen atoms. Also the vibration bands of
C=O bonds are shifted as a result of complexation. The absorption band of C=S group doesn’t
appear in the IR spectra of complexes.
The electronic absorption spectra of complexes show high-intensive chromene cycle π-π*
[17] transition bands in the range 260-270 nm (ε = 30000-5600 l mol-1 cm-1). The cobalt, copper
and nickel complex show three additional absorbtion bands in UV-vis spectra around 300 nm (ε
= 20000-36000 l mol-1cm-1), 340 nm (ε = 28000-48000 l mol-1cm-1) and 430 nm (ε = 10000-
20000 l mol-1cm-1 or two, a wide band around 300 nm (ε = 10000-30000 l mol-1cm-1) and 450
nm (ε = 10000-16000 l mol-1cm-1). These bands refer to π-π* transitions in the ligand molecules
[18]. The bands in the visible region are observed at 430-470 nm for all coordination
compounds. It is assigned 10-20 nm bathochromic shift for them comparing with ligand, what
can be ligand-to-metal charge-transfer transitions.
The ligands 6j-m, having the OMe substituent in the arylamide fragment, show a low
intensive n-π transition at 450 nm. Ligand 6j display a wide band 250-390 nm with two
shoulders and peak at 304 nm (ε = 10600 l mol-1cm-1). Its complexes have in their UV-vis
spectra the overlapping absorption bands around 260 nm (ε = 60000 l mol-1cm-1), 300 nm (ε =
58000 l mol-1cm-1), 350 nm (ε = 50000 l mol-1cm-1) and 440 nm (ε = 20000 l mol-1cm-1.
3.2. Molecular and crystal structure of complex 7a
Figure 1. Molecular structure of complex 7a.
Table 1. Bond lengths [Å ] and angles [°] for 7a
Bond lengths
Cu(1)-O(2)
Cu(1)-N(1)
d (Å)
1.968(2) O(2)-Cu(1)-N(1) 90.14(8) O(2)-Cu(1)-Cl(1)#1 87.10(6)
2.008(2) O(2)-Cu(1)-S(1) 175.14(6) N(1)-Cu(1)-Cl(1)#1 114.81(7)
Bond angles
ω(°)
Bond angles
ω(°)
6

Cu(1)-S(1)
2.2321(8) N(1)-Cu(1)-S(1)
85.32(7) S(1)-Cu(1)-Cl(1)#1
96.37(3)
Cu(1)-Cl(1)
Cu(1)-Cl(1)#1
Cl(1)-Cu(1)#1
2.3305(7) O(2)-Cu(1)-Cl(1) 90.70(6) Cl(1)-Cu(1)-Cl(1)#1 89.62(3)
2.6500(8) N(1)-Cu(1)-Cl(1) 155.56(7) Cu(1)-Cl(1)-Cu(1)#1 90.38(3)
2.6500(7) S(1)-Cu(1)-Cl(1) 92.72(3) C(10)-N(1)-N(2)
113.2(2)
The structure of complex 7a was established by X-ray diffraction. Crystallographic data
and refinement parameters for 7a are shown in Supplementary Materials; selected bond lengths
are given in Table 1. Molecular structure of compound 7a together with the atom-numbering
scheme is shown in Fig. 1. The crystals, available for structural investigation, were made by slow
diffusion of diethyl ether to ethanolic solution of CuCl2 and ligand 6a (1:1).
The coordination compound is symmetrical relative to the plane of metals and established
as binuclear complex L2Cu2Cl2, bounded through two chlorine atoms. The ligands are practically
coplanar and rotated 180 degrees to each other. The coordination geometry of the copper(II)
atoms is distorted triangular bipyramid. The metal atom is surrounded by two chloride anions,
aldimine nitrogen atom, sulfur atom of the thiolate group and keto-group of the pyrone ring. The
corresponding donor atoms and copper atom form two practically coplanar 5-and 6-membered
metallacycle. The arylamide fragment is slightly disordered. The plane formed by the atoms of
chlorine and copper is a distorted square almost perpendicular to the plane of the ligands, with a
deviation of 3.65 °
3.3. Electrochemistry
Some of the obtained ligands and complexes were studied by means of cyclic
voltammetry (CV) using a glass carbon (GC) electrode in DMF, to determine the potential
participation of compounds in oxidation-reduction processes. The potentials of electrochemical
oxidation and reduction are given in Table 2.
All investigated ligands undergo three-step reduction on GC electrode at potentials in the
range -0.93 - -2.04 V (the only exception is the compounds 6b, which undergo two-step
reduction, see Table). Most ligands are characterized by irreversibility of reduction steps, except
the phenol- containing compounds 6d, with a reversible reduction on the first step. Ligands
oxidation proceeds in two irreversible steps at the potentials 0.94 – 1.68 В (Table2, Fig.2).
The performed semi-empirical PM3 calculation for the ligands showed that their HOMO
are mainly localized on the arylamido-fragment. At the same time, the conjugated
chromonohydrazone system makes a significant contribution to the LUMO (Table 3). Based on
this results, we can assume that the oxidation potentials of the compounds 6a, b, d, g, l will be
7

mainly influenced by the substituents in the benzene ring, and the reduction potentials – by the
chromone fragment substituents.
The values of the measured oxidation and reduction potentials are confirmed by the
calculated data: thus, the values of the first oxidation potentials of the compounds. 6a, d, g,
having various chromone substituents and the same benzamide moiety, are within the range
0.95-1.12 V, i.e. differ by no more than 0.17 V. At the same time, for the compounds 6a, l and
6b with the substituents of different nature (donor and acceptor) in the arylamide fragment, the
first oxidation potentials differ considerably (in the range 0.92-1.17 V, the potential range is of
0.25 V). As expected, the donor substituents (OMe) of aromatic fragments facilitate oxidation,
and acceptor (F) impede it (Table 2).
On the CVA curves of copper complexes two additional quazy-reversibly one-electronic
peaks are observed in addition to the ligand peaks (Table and supplementary). These peaks are in
the less negative potential region then the first peak of the free ligand, and presumably
correspond to СuIIСuII  CuIСuII and СuICuII  СuIСuI transitions. The peaks of oxidative
desorbtion of metal copper from the electrode surface was not observed on the CVA reverse scan
after these peaks, this indicates the stability of the reduced forms of complexes (Fig.2 ,Table 2).
Oxidation of the copper-containing complexes proceeds irreversibly in two or three steps.
Apparently, the oxidation of the coordinated ligand fragment takes place, as the shape of the CV
curves and the potentials of the oxidation peaks slightly differ from the free ligands curves. The
shift of oxidation potentials of the complexes to the lower potentials is presumably due to
coordination with positively charged metal ion.
The cobalt-containing complexes 7e, 7b, and 7y (the first reduction peaks at Ered = -0.69;
-0.69; -0.83 V; and the second reduction peaks at Ered = -1.36; -1.36; -1.37 V respectively) and
nickel containing complex 7c are presumably reduced initially to the metal, then to the ligand in
accordance with the scheme L2Cl2CoIICoII  L2Cl2CoICoII  L(L-.)Cl2CoICoII .
Thus, in accordance with electrochemical behavior two types of cobalt and nickel
complexes can be distinguished: cobalt complexes of phenolic ligands 6a, reduced to the metal,
and other complexes, which are reduced to the metal at the first step, and to the coordinated
ligand fragment at the second .Oxidation of cobalt and nickel complexes, as well as oxidation of
copper complexes, apparently proceeds to the ligand fragment.
The semi-empirical calculation of the frontier orbitals for complexes shows that the
HOMO and the LUMO of the molecules, as well as ligand molecules, are mainly located on the
C=S fragment. However, while for Cu and Ni complexes the HOMO is also localized on the
metal atom, for Co complexes the contribution of metal atoms to the HOMO is much smaller
(Table 3), which makes preferable the electron to the coordinated ligand fragment.
8

Table 2. Electrochemical reduction potentials (ERed) and oxidation potentials (EOx) of the ligands
6a, b , d, g, l and their metal complexes measured relative to Ag|AgCl|KCl(sat.) by the CV
methods at a glassy-carbon electrode (DMF, 0.05 M Bu4NClO4, 200 mV s-1). The values after
the slash marks represent the peak potentials for the reverse CV scans.
Compound
Epred, V
E pox, V
-1.65
-1.80
-1.97
0.96
1.68
6a
N
NH
O
O
O
NH
S
-0.12/-0.08
-0.68/-0.54
-1.63
0.78
0.93
(6a -H)2Cu2Cl2 (complex7a)
(6a - H)2Co2Cl2 (complex7b)
-0.69
1.10
1.28
1.64
0.69
0.90
1.60
-1.36
-1.92
-0.81
(6a - H)2Ni2Cl2 (complex7c)
-1.40
- 1.94
6b
-1.78
-1.94
1.17
1.44
N
NH
O
O
O
NH
F
S
-0.19/-0.08
-0.75/-0.67
-1.71
0.82
0.96 1.09
(6b - H)2Cu2Cl2 (complex 7d)
-1.87
-0.69;
-1.36;
-1.92
1.09
(6b - H)2Co2Cl2 (complex 7e)
(6b - H)2Ni2Cl2 (complex 7f)
-0.76;
1.00;
9

-1.11;
1.32;
1.66
-1.40;
-1.88
-1.17/-1.11
-1.73/-1.57
-2.04
0.95
1.45
6d
N
NH
O
O
O
NH
Br
S
HO
-1.26/-1.18
-1.66
0.97
1.35
(6d-H)2Co2Cl2 (complex 7h)
-1.84
-1.47
1.12/-0.93
6g
-1.75
N
NH
O
O
O
NH
-1.97
F
S
0.31/0.39
-1.35/-1.20
-1.76
0.85/0.74
1.08
(6g - H)2Cu2Cl2 (complex 7i)
-2.14
-1.66
0.92
1.36
6l
-1.81
N
NH
O
O
O
NH
OMe
- 1.99
S
0.04/0.55
-0.52/-0.45
-1.52
1.04
1.45
(6l - H)2Cu2Cl2 (complex 7v)
-1.65
-1.90
-0.83
1.28
(6l - H)2Co2Cl2 (complex 7x)
(6l - H)2Ni2Cl2 (complex 7y)
-1.37
-1.76
-0.93
0.90
1.24
10

Table 3. HOMO and LUMO of ligand 6a and its copper complex 7a.
Compound
HOMO
LUMO
6a
7a
0.008
0.004
0
0.2
0.1
0
b
a
0.1
-0.004
-0.008
-0.012
0.08
0.06
0.04
0.02
0
-1200 -800 -400
0
400 800
-0.1
-0.2
-3000
-2000
-1000
0
1000
2000
-0.02
E, mV
-3000
-2000
-1000
0
1000
2000
E, mV
11

0.002
0.001
0
0.004
0
0.03
0.02
0.01
0
0.03
0.02
0.01
0
d
c
-0.004
-0.008
-0.012
-0.001
-0.002
-0.003
-0.004
-1600 -1200 -800 -400
0
-1600 -1200 -800 -400
0
-0.01
-0.02
-0.01
-0.02
-3000
-2000
-1000
0
1000
2000
-3000
-2000
-1000
0
1000
2000
E, mV
E, mV
Fig 2. Cyclic voltammograms of ligand 6b (a) and its copper complex 7d (b), cobalt complex 7e
(c), nickel complex 7f (d). DMF, 0.05 M Bu4NClO4, 10–3 M.
4. Conclusion
In the conclusion, a series of binuclear copper(II), cobalt(II) and nickel(II) complexes
with novel organic ligands 2-oxo-2-(arylamino)-(2E)-2-[(4-hydroxy-2-oxo-2H-1-benzopyran-3-
yl)-methyledene]ethanethioic acid hydrazides, forming as a result of 3-formylchromones and
oxamic acid thiohydrazides interaction, have been prepared by the reactions of metal chloride
with ligand in EtOH. The complexes have been characterized by IR, UV–vis spectroscopy and
cyclic voltammetry. Unexpected cyclic forms of the ligands, namely 5-(4-oxo-4H-chromen-3-
yl)-4,5-dihydro-1,3,4-thiadiazole-2-carboxamides, have been determined as preferable tautomers
in the solution and solid. The X-ray analysis of di-μ-chloro-bis-(((Z)-2-oxo-1-((E)-((4-oxo-4H-
chromen-3-yl)methyledene)hydrazono)-2-(phenylamino)ethyl)thio)dicopper(II)distorted
triangular bipyramid geometry with an OSNCl2 donor set.
Appendix A. Supplementary data
CCDC 1575758 contains the supplementary crystallographic data for 7a. These data can
be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgements
This study was supported by the Russian Science Foundation (grant # 14-50-00126).
12

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14

N
S
N
O
O
HN
N
R
N
O
O
R1
R2
M
MCl2
EtOH
O
S
O
HN
R
R1, R2
Cl
O
Cl
R1, R2
S
O
M
O
N
N
R
N
M = Cu, Co, Ni
A series of 5-(4-oxo-4H-chromen-3-yl)-4,5-dihydro-1,3,4-thiadiazole-2-carboxamide and
copper(II), cobalt(II) and nickel(II) complexes of their tautomers 2-oxo-2-(arylamino)-(2E)-2-
[(4-hydroxy-2-oxo-2H-1-benzopyran-3-yl)methyledene]ethanethioic acid hydrazides have been
synthesized.
15