Synthesis, spectroscopy, structures and antimicrobial activity of mixed-ligand zinc(ii) complexes of 5-nitro-salicylaldehyde thiosemicarbazones

Article abstract of DOI:10.1039/c5nj02822a

A series of new complexes of zinc(ii) with 5-nitro-salicylaldehyde-N¹-substituted thiosemicarbazones {5-NO₂-C₆H₄(2-OH)-C²(H)=N³-N²H-C¹(=S)-N¹HR; H₂

Full text of DOI:10.1039/c5nj02822a

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Full paper
Synthesis, spectroscopy, structures and antimicrobial
activity of mixed-Ligand zinc(II) complexes with 5-nitro-
†
salicylaldehyde thiosemicarbazones
a
a
b
b
Shikha Indoria , Tarlok S. Lobana* , Henna Sood , Daljit S. Arora , Geeta
a
c
Hundal , Jerry P. Jasinski
1
A series of new complexes of zinc(II) with 5ꢀnitroꢀsalicylaldehydeꢀN ꢀsubstituted
2
3
2
1
1
1
thiosemicarbazones {5ꢀNO ꢀC H (2ꢀOH)ꢀC (H)=N –N H–C (=S)–N HR; H L ꢀNHR, R = H,
2
6
4
2
Me, Et, Ph: respective thioꢀligands} using bipyridines/phenanthrolines (L′) as coꢀligands have
been synthesized and characterized using elemental analysis, infrared, NMR, electronic
absorption and fluorescence spectrocopy and single crystal Xꢀray crystallography. Thioꢀligands
2
ꢀ
3
coordinate to the metal center as diꢀanions (O,N,SꢀLꢀNHR) in their complexes, [Zn(κ ꢀO,N,Sꢀ
2
LꢀNHR)(κ ꢀN,NꢀL′)] {R, (N, NꢀL′): H, bipy 1, phen, 2; Me, bipy 3, phen 4; Et, bipy 5, phen, 6;
Ph, bipy, 7, phen 8}. The geometries complexes comprise three categories: distorted trigonal
bipyramidal (1ꢀmolecule II, 5, 7); distorted square pyramidal (4, 6 and 8ꢀmolecule II) and
geometry in between square pyramidal and trigonal bipyramidal (1ꢀmolecule I, 8ꢀ molecule II).
These zinc(II) complexes have shown significant antimicrobial activity against Staphylococcus
aureus (MTCC740), methicillin resistant Staphylococcus aureus (MRSA), Klebsiella
pneumoniae (MTCC109), Shigella flexneri (MTCC1457), Selmonella typhimurium (MTCC741)
and Candida albicans (MTCC227). The activity against MRSA and S. aureus is significant
development in antimicrobial investigations visꢀàꢀvis lack of activity of gentamicin against
MRSA, or low antimicrobial activity against S. aureus as per literature reports. All complexes are
active against K. pneumoniae and S. typhimurium while complexes reported in literature were
found to be inactive. Complexes tested were found to be cytotoxic to microorganisms
(bactericidal/fungicidal).
1

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DOI: 10.1039/C5NJ02822A
a
Department of Chemistry, Guru Nanak Dev University, Amritsar – 143 005, India.
Eꢀmail: tarlokslobana@yahoo.co.in; Fax: +91ꢀ183ꢀ2258820.
b
Department of Microbiology, Guru Nanak Dev University, Amritsarꢀ143 005, India.
c
Department of Chemistry, Keene State College, Keene NH 03435ꢀ2001, USA.
†
Electronic supplementary information (ESI) available. CCDC 1427481ꢀ1427485 (1, 4, 5, 6 and
),1427480 (8). The data can be obtained free of charge from The Cambridge Crystallographic
7
Data via www.ccdc.cam.ac.uk /data_request/cif. For ESI and crystallographic data in CIF or
other electronic format see DOI:
1
Introduction
Among the biometals (Cu, Ni, Zn, Co), zinc metal is cofactor in a number of enzymes such as
zinc proteinases, carbonic anhydrases, histone deacetylases, alcohol dehydrogenases, alkaline
phosphatases and aminopeptidases, which are involved in various metabolic processes of plants,
1
ꢀ11
animals, viruses and bacteria.
Zinc proteinases enzyme in various viruses and Gram
positive/Gram negative pathogenic bacteria split the host’s protein into small fragments and
1
ꢀ3
hence increasing the number of microbial cells results in enhancement of cell growth. In order
to stem this microbial growth, there is need to use organic reagents or compounds which can
encapsulate zinc(II) located in the active site of enzymes. These compounds can act as
6
, 10, 12ꢀ14
pharmaceuticals (potential inhibitors).
complexes of thiosemicarbazones (structure I) have demonstrated antimicrobial,
It is interesting to mention here that zinc(II)
1
5ꢀ18
anticancer
1
9ꢀ26
27, 28
(antitumour, antiproliferation, cytotoxicity)
and antioxidant activity.
The antimicrobial
1
2
15
activity was observed when R at C atom of thiosemicarbazone was 2ꢀ thiopheneyl,
1
6,18
17
17
2
3
4
acetylpyridine,
furan, 2ꢀacetylꢀbutyrolactone with R being H or methyl and NR R being
NH NHR (R = Me, Et, Pr, Ph etc.). However, complexes reported in literature displayed low
2
,
antimicrobial activity and also minimum inhibitory concenterations (MIC) were relatively very
1
5ꢀ18
high.
S
R1
1
C
2
NH
2
C
3
N
1
3 4
R2
N R R
Structure I
2

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In view of our interest in antimicrobial activity of metal complexes with
2
9, 30
thiosemicarbazones,
here in this paper, we are reporting synthesis, spectroscopy, structures
1
and antimicrobial activity of zinc(II) complexes of 5ꢀnitroꢀsalicylaldehydeꢀN ꢀsubstitued
thiosemicarbazones (R= H, Me, Et, Ph, Chart 1) with 2, 2′ꢀbipyridine and 1,10 –phenanthroline
as coꢀligands. The antimicrobial activity is investigated against various Gram positive bacteria
such as Staphylococcus aureus (MTCC740), methicillin resistant Staphylococcus aureus
(
MRSA), Gram negative bacteria, Shigella flexneri (MTCC1457), Klebsiella pneumoniae
MTCC109), S. typhimurium (MTCC741) and yeast, Candida albicans (MTCC227). It may be
(
noted that there are only few reports of biological activity of Zn(II) complexes with
2
5, 26
salicylaldehyde thiosemicarbazones.
14
11
13 12
1
5
10
9
16
7
OH
C2
S
N
N
8
6
H
N3 N2 C1
5
3
2, 2' bipyridine (bipy)
X
4
1
13
12
N HR
H
14
1
1
1
5
1
1
0
X = MeO, NO ; R = H, Me, Et, Ph
2
9
6
N
N
1, 10-phenanthroline (phen)
Chart 1. Salicylaldehyde thiosemicarbazones and co-ligands.
2
Results and discussion
2.1 Synthesis and spectroscopy
1
Chart lists complexes of zinc(II) with 5ꢀnitroꢀsalicylaldehydeꢀN ꢀsubstituted
2
thiosemicarbazones. In the formation of these complexes, the acetate anions of zinc salt remove
2
OH and N H protons and thus the thioꢀligands coordinate to Zn(II) as O,N,Sꢀ terdentate dianions.
Each of the coꢀligands, namely, bipy and phen occupy the two coordination sites leading to the
formation of five coordinated complexes (1ꢀ8). The stoichiometry of the complexes can be
3
2
represented by the general formula, [Zn(κ ꢀO,N,SꢀLꢀNHR)(κ ꢀN,NꢀL′) {R, (N,NꢀL′): H, bipy 1,
phen 2; Me, bipy 3, phen 4; Et, bipy 5, phen 6; Ph, bipy 7, phen 8}. Complexes are soluble in
dimethyl sulfoxide and partially soluble in dichloromethane, methanol and acetonitrile. The IR
2
spectra of complexes reveal the absence of ν(O−H) and v(N −H) bands and thus these thioꢀ
2
ꢀ
ligands (H LꢀNHR, R= H, Me, Et, Ph) coordinate as dianions (LꢀNHR) . Further, the diagnostic
2
3

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ꢀ1
ꢀ1
ν(CꢀS) bands of the free ligands (1012–1042 cm ) shift to low energy region, 829–850 cm in
complexes and this large shift suggests that the neutral thioꢀligands have changed into anionic
1
1
1
ligands during coordination to the metal ion. The ν(N −H) bands of –C (=S)–N HR moiety
ꢀ1
appear in the range, 3345ꢀ 3417 cm in complexes (for more details see experimental and
supplementary). Various proton signals due to the thioꢀligands and bipy/phen coꢀligands are
2
listed in the experimental section. The diagnostic OH and N H proton NMR signals disappeared
2
in complexes {cf. free ligands, δ(OH) = 11.45ꢀ11.89 and δ(N H) = 8.57ꢀ10.31 ppm, see
supplementary}, and it supported that the thioꢀligands were coordinating as anions.
1
4
11
1
3 12
N
S
15
10
9
N
O
bipy
1
6
N
1
N
H, H L-NH2 1, 2
R =
2
Zn
, 3, 5, 7
Me, H L-NMe 3, 4
2
Et, H L-NEt 5, 6
13
12
2
C
N3
Ph, H L-NPh 7, 8
2
14
11
1
O N
2
N HR
N2
1
5
10
CH
phen
9
1
6
N
N
1- 8
2
, 4, 6, 8
Chart 2. List of complexes synthesized.
ꢀ4
The electronic absorption spectra of complexes (10 molar solution) are shown in Figs. 1 and
2, which display absorption bands in the UV−visible region. Broadly, the absorption occurs in
two regions: 250ꢀ300 nm, assigned to π→π* transitions and 300ꢀ500 nm, assigned to n→π*
transitions, of the azomethine group (C=N)/thiouride group (C=S) of thioꢀligands and the MLCT
3
1
transitions involving metal to π* orbitals of bipy/ phen ligands. Complexes exhibit fluorescence
in the range 370ꢀ580 nm with λmax at 428ꢀ441 nm corresponding to the excitation wavelength, λ
=
300 nm (Fig. 3). The origin of fluorescence appears to be linked to {Zn(N,NꢀL’} moiety (N, Nꢀ
3
0
L’ = bipy, phen) involving intraꢀligand transitions.
4

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Fig. 1. Electronic absorption spectra of bipy complexes, 1, 3, 5 and 7.
Fig. 2. Electronic absorption spectra of phen complexes, 2, 4, 6 and 8.
Fig. 3 Fluorescence spectra complexes 1ꢀ8.
5

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2.2 Description of crystal structures
The molecular structures of complexes 1, 4ꢀ6, 7 and 8 (except 2 and 3) have been obtained.
Crystals of complexes 1, 4, 6, 7 and 8 are triclinic with space groups P while the crystals of
ī
complex 4 are monoclinic with space group C2/c. Crystal data are given in Table 1 while
important bond parameters are placed in Table 2.
3
2
Bipy complexes (1, 5 and 7). The crystal structure of complex, [Zn(κ ꢀO,N,SꢀLꢀNH )(κ ꢀN,Nꢀ
2
bipy)] 1, reveals the presence of two independent molecules, namely, molecule ꢀI and moleculeꢀ
II (Figs. 4 and 5). In moleculeꢀI, O3, N4, S of thioꢀligand and N1(eq) atom of bipy occupy the
square basal plane while the N2(ax) nitrogen atom of bipy occupies the axial site. It is added here
that distortion value of coordination polyhedron, τ = (βꢀα)/60 is evaluated by the two largest
bond angles (α, β) in five coordination geometry (τ = 1 for ideal trigonal bipyramid and 0 for
3
2
square pyramidal environment). The largest bond angles in the basal plane, namely, N4(thioꢀ
ligand)ꢀZn1ꢀN1(eq) (166.79(9)º) and O3ꢀZn1ꢀS1 (152.77(6)º) give a τ value of 0.233 which
suggests that geometry around zinc(II) of molecule ꢀ I is distorted square pyramidal. In molecule
ꢀ
II, the atoms O6, N10, S2 of thioꢀligand and N8(eq) atom of bipy occupy the square basal plane
while the N7(ax) nitrogen atom of bipy occupies the axial site. The largest angles in the basal
plane, namely, N10(thioꢀligand)ꢀZn2ꢀN8(eq) (173.74(8)º) and O6ꢀZn2ꢀS2 (146.57(6)º) give a τ value
of 0.453 which suggests that the geometry around zinc(II) of moleculeꢀ II is distorted square
pyramidal. In moleculeꢀ I, N(1) atom of bipy occupies equatorial site, while second nitrogen,
N(2) of bipy is axial. In contrast, the equivalent nitrogen N(7) now occupies axial site in
moleculeꢀ II, while second nitrogen, N(8), shifts to the equatorial site.
6

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N1
N2
N8
O
N7
S
C
Zn
Zn
N
O
S
NH2
N
NH2
C
N
O N
2
CH
O N
2
CH
N
Molecule I
Molecule II
Fig. 4 A structural view of molecules I and II of complex 1.
3
2
Crystal structure of complex, [Zn(κ ꢀO,N,SꢀLꢀNHEt)(κ ꢀN,Nꢀbipy)] 5 (Fig. 6), shows that
O1, N3, S atoms of thioꢀligand and N1 and N2 atoms of bipy are coordinated to zinc(II). The τ
value of 0.653 suggests that the geometry around zinc(II) is more close to a trigonal bipyramidal
geometry. This suggests that N3(thioꢀligand) and N1(ax) atoms occupy the axial site {(N1ꢀZn1ꢀN3 =
172.94(6)º} while O1, S1 and N2(eq) atoms occupy the equatorial plane {N2ꢀZn1ꢀS1 = 115.12(4);
3
N2ꢀZn1ꢀO1 = 110.75(6); O1ꢀZn1ꢀS1 = 133.79(5)º}. The bonding pattern of complex, [Zn(κ ꢀ
2
O,N,SꢀLꢀNHPh)(κ ꢀN,Nꢀbipy)] 7 (Fig. 7) is similar to that of complex 5. The N5
and
(thioꢀligand)
N1(ax) atoms occupy the axial site {(N5ꢀZn1ꢀN1 = 172.56(7)º} while O3, S1 and N2(eq) atoms
occupy the equatorial plane {N2ꢀZn1ꢀS1 = 113.81(5); N2ꢀZn1ꢀO1 = 107.31(7); O1ꢀZn1ꢀS1 =
138.57(5)}. The major difference in the two structures lies in the bond parameters in the
equatorial plane. This affects τ parameter which is 0.567 somewhat less than that of complex 5.
In brief, it is concluded that both 5 and 7 have distorted trigonal bipyramidal geometry.
7

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3
2
Fig. 5 Molecular structure of complex, [Zn(κ ꢀO, N, SꢀLꢀNH )(κ ꢀN,Nꢀbipy)] 1.
2
3
2
Fig. 6 Molecular structure of complex, [Zn(κ ꢀO, N, SꢀLꢀNHEt)(κ ꢀN,Nꢀbipy)] 5.
8

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3
2
Fig. 7 Molecular structure of complex, [Zn(κ ꢀO,N,SꢀLꢀNHPh)(κ ꢀN,Nꢀbipy)] 7
3
2
Phen complexes (4, 6 and 8). The crystal structure of complex, [Zn(κ ꢀO,N,SꢀLꢀNHMe)(κ ꢀ
N,Nꢀphen)] 4 reveals that O1, N3, S atoms of thioꢀligand and N1 and N2 nitrogen atoms of phen
coꢀligand are coordinated to zinc(II) (Fig. 8). The largest bond angles, namely, N4(thioꢀligand)ꢀZn1ꢀ
N1(eq) (177.66(7)º) and O1ꢀZn1ꢀS1 (149.04(5)º) give a τ value of 0.477 which suggests that the
geometry around zinc(II) is distorted square pyramidal. Here O1, N3, S atoms of thioꢀligand and
N1(eq) atom of phen ligand occupy square basal plane {N(1)ꢀ Zn(1)ꢀS(1) = 96.94(5); O(1)ꢀZn(1)ꢀ
N(1) = 91.58(6); N(4)ꢀ Zn(1)ꢀS(1) = 83.01(5); O(1)ꢀ Zn(1)ꢀN(4) = 89.63(6)º}, while N2(ax) atom
of phen ligand occupies the axial site. The bite angle, {N(2)– Zn(1)–N(1) = 77.67(7)º}, is the
3
2
shortest angle. The crystal structure of complex, [Zn(κ ꢀO, N, SꢀLꢀNHEt)(κ ꢀN,Nꢀphen)]⋅CH CN
3
6
, shows that the trans bond angles, namely, N4(thioꢀligand)ꢀZn1ꢀN1(eq), 159.1(2)º and O1ꢀZn1ꢀS1,
149.04(5)º give a τ value of 0.08. This suggests that that O1, N4, S1 and N1 atoms are at the
corners of a square plane and zinc atom is bulging outside the plane as shown in Figs. 9 and 10.
9

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The axial site is occupied by the N(2) donor atom of phen ligand. The geometry of complex 6 is
pseudo square pyramidal. Complex 6 contains coꢀcrystallized acetonitrile in the crystal. The
3
2
crystal structure of complex, [Zn(κ ꢀO,N,SꢀLꢀNHPh)(κ ꢀN,Nꢀphen)] 8 (Fig. 11) reveals the
presence of two independent molecules: molecule ꢀ I and molecule ꢀ II. In moleculeꢀ I, O1, N4,
S1 atoms of thioꢀligand and N1(ax) and N2(eq) nitrogen atoms of phen coꢀligand are coordinated
to zinc(II). Both molecules I and II have distorted square pyramidal geometry (τ = 0.453 for
moleculeꢀI and 0.331 for moleculeꢀII). Complex 8 contains coꢀcrystallized dichloromethane in
the crystal.
3
2
Fig. 8 Molecular structure of complex [Zn(κ ꢀO, N, SꢀLꢀNHMe)(κ ꢀN,Nꢀphen)] 4.
1
0

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N2
N1
O N
2
O
Zn
S
HC
N
C
N
NHEt
Fig. 9. A stuctural view of complex 6
3
2
Fig. 10 Molecular structure of complex [Zn(κ ꢀO, N, SꢀLꢀNHEt)(κ ꢀN,Nꢀphen)]⋅CH CN 6.
3
1
1

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3
2
Fig. 11 Molecular structure of complex [Zn(κ ꢀO,N,SꢀLꢀNHPh)(κ ꢀN,Nꢀphen)]⋅0.5CH Cl 8.
2
2
The bond lengths of complexes are similar with minor differences as shown in Table 2. In
these complexes, the Zn−Neq distances (2.058(2) ꢀ 2.1267(18)Ǻ) are shorter than the ZnꢀNax
bond distances (2.115(7)ꢀ 2.185(2) Ǻ) related to the coꢀligands bipy/phen. Further, Zn−N(thioꢀ
bond distances (2.067(6)ꢀ2.0920(18) Ǻ) are shorter than the Zn−Neq and ZnꢀNax bond
ligand)
distances as cited above. The ZnꢀS and ZnꢀO bond distances lie in the range, 2.3233(7)ꢀ2.384(2)
and 1.9679(16)ꢀ2.035(7) Ǻ respectively. It is pertinent to note that the bond distances and bond
angles of complexes whose Xꢀray structures have been determined are comparable with those of
1
analogous zinc(II) complexes reported with the thioꢀligands, salicyaldehydeꢀN ꢀsubstituted
2
2,33
1
25,34,35
thiosemicarbazones,
2, 4 dihydroxyꢀbenzalehyde ꢀN ꢀ substituted thiosemicarbazones
2
6
and 3, 5ꢀdiiodoꢀ2ꢀhydroxyꢀbenzaldehydeꢀNHPh thiosemicarbazones (Chart 3). As an example,
τ value of complex 7 (τ = 0.567) is comparable to τ value (0.54) of analogous complex, [Zn(O,
3
22
N , SꢀL)(N,Nꢀbipy)] (Chart 3 for ligand L, here, X, X = H, H; R= Ph) reported in literature.
3
Similarly, various bond distances of complex 7 {ZnꢀO, ZnꢀS, ZnꢀN , ZnꢀN (bipy) and Znꢀ
ax
3
N (bipy)} are similar to that of the reported complex, [Zn(O, N , SꢀL)(N,Nꢀbipy)] {ZnꢀO
eq
3
1
.958(5), ZnꢀS 2.3435(19), ZnꢀN 2.098(5), ZnꢀN (bipy) 2.1645(5), ZnꢀN (bipy) 2.0975(5)
ax
eq
2
2
Ǻ}.
1
2

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1
N HR
H
N2
C
N3
C
O
N
X'
X
H C
3
CH3
CH3
S
N
N
N
N
N
O
H C
3
Zn
[22, 25, 26,34]
[33]
L
S
N3
2
2
33
X, X' = H, H; R = Ph , allyl
3
4
25, 35
X, X' = OH, H; R = H , Ph
N
N
[35]
X, X' = I, I; R = Ph26
Chart 3. Zinc(II) complexes with salicylaldehyde thiosemicarbazones reported in literature.22, 25, 26, 33-35
Table 1 Crystallographic data for complexes 1, 4ꢀ8.
1
4
5
Empirical formula
M
C H N O SZn⋅0.25 C H N O Zn
C H N O SZn
20 18 6 3
18
14
6
3
21 16
6
3
CH OH
3
467.81
497.86
487.86
296(2)
T(K)
296(2)
296(2)
Crystal system
Space group
Triclinic
Triclinic
Monoclinic
C2/c
P
ī
P ī
Unit cell dimensions
a(Å)
b(Å)
c(Å)
α(°)
β(°)
γ(°)
10.550(3)
12.969(4)
14.219(4)
6.0475(6)
22.2366(8)
12.0486(5)
17.9814(6)
ꢀ
12.1271(11)
14.1409(15)
86.254(3)
103.147(14)
92.137(16)
98.310(15)
82.737(4)
114.9940(12)
ꢀ
81.271(3)
1
3

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3
V(Å )
1869.5(10)
1015.71(17)
4366.4(3)
Z
1
2
8
ꢀ
3
Dcalcd(g cm )
1.662
1.462
954
1.628
1.351
508
1.484
1.255
2000
25703
6523,
ꢀ
1
ꢀ
(mm )
F(000)
Reflections collected
Unique reflections
25644
7552,
16500
4993,
(
R = 0.0667)
(R = 0.0387)
(R = 0.0263)
int
int
int
Data/restraints/ parameters 7552/ 5/550
4993/0/290
3818
6523/1/ 284
4739
Reflens.with [I>2σ(I)]
6538
R Indices
R1
0.0422
0.1205
0.0365
0.0334
0.0844
WR2
0.0885
Largest diff. Peak and hole 0.983 and
0.326 and
0.535 and
ꢀ3
ꢀ3
ꢀ3
ꢀ0.666e. Å
ꢀ0.300 e.Å
ꢀ0.319 e. Å
6
7
8
Empirical formula
C
24
H
21
N
7
O
3
SZn
C
24
H
18
N
6
O
3
SZn
C H N O SZn⋅
2
6
18
6
3
0
.5CH Cl
2 2
M
552.94
100(2)
535.87
173(2)
602.38
296(2)
T(K)
Crystal system
Space group
Triclinic
Triclinic
Triclinic
P
ī
P
ī
P ī
Unit cell dimensions
a(Å)
b(Å)
c(Å)
α(°)
β(°)
γ(°)
7.9317(14)
11.671(2)
14.471(3)
111.165(9)
91.581(10)
102.581(9)
9.7377(13)
11.906(4)
15.107(6)
16.009(5)
10.8604(12)
11.9599(15)
67.510(11)
76.142(11)
76.077(11)
65.288(15)
73.741(17)
73.112(17)
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3
V(Å )
1210.9(4)
1118.9(3)
2
2461.1(15)
Z
2
2
ꢀ
3
Dcalcd(g cm )
1.516
1.142
568
1.591
2.749
548
1.626
1.236
1228
16505
8262,
ꢀ
1
ꢀ
(mm )
F(000)
Reflections collected
Unique reflections
15934
4562,
6935
4215,
(
R = 0.0693)
(R = 0.0350)
(R = 0.0675)
int
int
int
Data/restraints/ parameters 4562 / 3/ 330
4215 / 0/ 316
8262 / 0 / 679
Reflens.with [I>2σ(I)]
3520
3884
4845
R Indices
R1
0.0875
0.2298
0.0388
0.1169
WR2
0.1045
0.3046
Largest diff. Peak and hole 2.169 and
0.555 and
2.117 and
ꢀ3
ꢀ3
ꢀ3
ꢀ3.079 e. Å
ꢀ0.735 e. Å
ꢀ0.476e. Å
Table 2 Important bond distances (Å) and bond angles (°) in complexes 1, 4ꢀ8.
3
2
3
2
Bipy complexes [Zn(κ ꢀO,N,SꢀLꢀNHR)(κ ꢀN,N)]
Phen complexes [Zn(κ ꢀO,N,SꢀLꢀNHR)(κ ꢀN,N)]
1
(molecules
5
7
4
6
8(molecules I and
II)
I and II)
I
I
Zn –O
2.0181(18) , 1.9840(14)
1.9679(16)
2.0920(18)
2.3233(7)
2.1238(18)
1.9958(15) 1.976(6)
2.0703(17) 2.112(7)
1.994(9) ,
II
II
1.9923(18)
2.035(7)
I
I
Zn–N
Zn–S
2.089(2) ,
2.0891(14)
2.092(7) ,
II
II
2.107(2)
2.067(6)
I
I
2.3504(10) , 2.3370(6)
2.3385(7)
2.356(2)
2.360(3) ,
II
II
2.3587(10)
2.384(2)
I
I
Zn–Neq
2.107(2) ,
2.1094(15)
2.1267(18) 2.114(6)
2.085(8) ,
II
II
2.058(2)
2.089(9)
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5

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I
I
Zn–Nax
OꢀZnꢀN
NꢀZnꢀS
OꢀZnꢀS
2.127(2) ,
2.1270(14)
87.81(5)
81.75(4)
133.79(5)
172.94(6)
96.80(6)
77.19(6)
2.1326(18)
89.18(7)
81.77(5)
138.57(5)
172.56(7)
96.17(7)
76.77(7)
0.567
2.1606(17) 2.166(7)
2.147(6) ,
II
II
2.185(2)
2.115(7)
I
I
88.37(8) ,
89.63(6)
83.01(5)
149.04(5)
177.66(7)
100.18(7)
77.67(7)
0.477
87.3(2)
88.4(3) ,
II
II
88.67(8)
87.2(3)
I
I
82.64(6) ,
81.82(19)
82.1(2) ,
II
II
81.44(6)
82.07(19)
I
I
152.77(6) ,
153.77(19)
159.1(2)
121.8(3)
79.1(2)
149.6(2) ,
II
II
1
46.57(6)
152.1(2)
I
I
NꢀZnꢀ Neq 166.79(9) ,
176.8(4) ,
II
II
1
73.74(8)
172.0(3)
I
I
NꢀZnꢀNax 114.89(8) ,
103.1(3) ,
II
II
1
02.59(8)
109.8(3)
I
I
N ꢀZnꢀ
eq
78.33(8) ,
78.5(3) ,
II
II
Nax
77.17(9)
78.1(3)
τ value
0.233, 0.453 0.653
0.089
0.453, 0.331
N= N(thioꢀligand);
Nax= N(axial); Neq = N(equatorial); I = Molecule 1, II = Molecule 2
2.3 Importance and discussion of biological data
Various infections, namely, gastrointestinal tract infections, urinary tract infections,
3
6
respiratory tract infections and skin infections are caused by different microorganisms such
as S. aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Klebsiella
pneumoniae, Selmonella typhimurium, Shigella flexneri, Penicillium citrinum, C.albicans,
Aspergillus niger, Candida guilliermondii, Candida parapsilosis and Cryptococcus neoformans
etc. A series of antibiotic drugs, namely, aminoglycoside, dalfopristin, teicoplanin, linezolid,
methicillin, gentamicin, kanamycin, neomycin, streptomycin fluconazole and amphotericin are
used for the treatment of these microbial infections. Many of the microorganisms have developed
37ꢀ41
resistance to several antibiotics due to the development of resistant mutants.
The increasing
drug resistant bacteria cause various noscomial infections and among these; methicillin resistant
4
2, 43
Staphylococcus aureus is one of the most frequent noscomial pathogen.
This shows that
1
6

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there is critical need to develop new antimicrobial agents for difficult to treat multidrug resistant
microorganisms and thus invited the search for new antimicrobial agents.
Table 3 lists biological data for antimicrobial activities of zinc(II) complexes with 5ꢀnitro ꢀ
1
3
2
salicylaldehydeꢀN ꢀsubstituted thiosemicarbazones, [Zn(κ ꢀO,N,SꢀLꢀNHR)(κ ꢀN,NꢀL′)] 1ꢀ8
Chart 2, H LꢀNHR = H LꢀNH , H LꢀNHMe, H LꢀNHEt, H LꢀNHPh}. The antimicrobial
{
2
2
2
2
2
2
activity of Zn(II) complexes is higher than that of free thioꢀligands. In respect of MRSA,
complexes 2, 3, 5ꢀ8 have shown highest antimicrobial activity ranging from 24ꢀ25 mm zone of
inhibition (zoi). It is an interesting observation as the commercially available Gentamicin is
inactive against this bacterial strain. As regards Staphylococcus aureus, most of complexes
exhibited antimicrobial activity in the range, 30ꢀ35 mm zoi, which is higher than that shown by
Gentamicin (25 mm zoi). In case of Klebsiella pneumoniae, complex 8 showed activity (30 mm
zoi) comparable to that of Gentamicin (32 mm zoi). Other complexes showed lower activity. All
complexes have shown activity against Shigella flexneri either close to or higher (15ꢀ25 mm zoi)
than that of Gentamicin (17 mm zoi). As regards activity against Selmonella typhimurium, most
of complexes exhibited antimicrobial activity in the range, 24ꢀ28 mm zoi, which is higher than
that shown by Gentamicin (20 mm zoi). In case of Candida albicans, complex 8 showed
comparable activity (30 mm zoi) to that of Amphotericin (34 mm zoi). Other complexes showed
lower activity.
In literature only few Zn(II) complexes of thiosemicrabazones have been studied for their
antimicrobial activity, which are summarized as follows: Thiopheneꢀ2ꢀcarbaldehyde
thiosemicarbazone complex, namely, [Zn(SꢀHL) Cl ], showed antimicrobial activity against
2
2
15
C.albicans with zoi = 17 mm; 2ꢀacetylpyridine thiosemicarbazone complexes, [Zn(N, N, Sꢀ
HL) ] showed activity against S. aureus with MIC = 125 ꢀg/mL and against C. albicans with
2
MIC = 65 ꢀg/mL; other complexes of this ligand, namely, [ZnCl (N, N, SꢀHL)] and [Zn(OSO )(
2
3
N, N, SꢀHL)(H O)] were active against S. aureus with MIC of 250 ꢀg/mL and showed no
2
16
activity against C.albicans; complexes of 2ꢀfuranaldehyde and 2ꢀacetylꢀγꢀbutyrolactone
thiosemicarbazone, namely, [Zn(N, SꢀL) ] and [Zn(N, SꢀL)Cl ], showed antimicrobial activity
2
2
against MRSA, S. aureus and C. albicans with MIC >200 ꢀg/mL, but were inactive against K.
1
7
pneumoniae and S. typhimurium.
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In comparison to above literature reports, the antimicrobial activity of zinc(II) complexes
under investigation is much higher, which is briefly summarized below. Zn(II) complexes, 2, 3,
5ꢀ8 showed comparatively very good antimicrobial activity against MRSA with MIC = 50
1
7
ꢀ
g/mL than that reported in literature. Interestingly, complexes 2, 3, 5ꢀ8 are highly active
1
6
against S. aureus with MIC of only 0.5 ꢀg/mL visꢀàꢀvis that in the literature report. As regards
the activity against K. pneumoniae and S. typhimurium, most of the complexes showed good
antimicrobial activity with MIC of 50ꢀ250 ꢀg/mL (3, 5, 6, 7) and 10ꢀ50 ꢀg/mL (1, 3, 5ꢀ8)
1
7
respectively, while complexes reported in literature were found to be inactive.
Zinc(II)
complexes also show good activity against resistant bacterial strain Sh. flexneri with MIC
broadly in the range, 50ꢀ750ꢀg/mL, but there is no report in literature for comparison purpose. In
case of C.albicans, complexes 3, 5ꢀ8 showed antifungal activity with MIC of 10ꢀ50 ꢀg/mL and
1
7
this activity is much higher than the activity shown by complexes reported in literature. Higher
antimicrobial activity may be attributed to the fact that the use of polypyridyl heterocyclic bases
4
4ꢀ47
increases lipophilicity,
which enhances the cell membrane penetrating ability. The cause of
inhibitory action of complexes can be due to their interaction with enzyme prosthetic group in
4
8, 49
microbial cells which inhibit the replication of DNA.
a,b,c
Table 3. Biological data for complexes 1ꢀ8
f
g
h
i
j
k
Ligands/complexes
MRSA S. aureus
K.
S.
Sh.
C
pneumoniae
typhumirium Flexenri albicans
[
Zn(LꢀNH )(bipy)] (1)
18
30
17
24
17
17
2
[
[
[
[
[
[
[
Zn(LꢀNHMe)(bipy)] (3)
Zn(LꢀNHEt)( bipy)] (5)
Zn(LꢀNHPh)( bipy)] (7)
24
25
26
24
15
25
26
35
33
35
35
24
35
35
24
25
21
18
15
24
15
8
27
28
25
27
20
28
27
18
16
15
20
15
18
25
25
24
22
18
15
25
30
Zn(LꢀNH )( phen)] (2)
2
Zn(LꢀNHMe)( phen)] (4)
Zn(LꢀNHEt)( phen)] (6)
Zn(LꢀNHPh)( phen)] (8)
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ꢀ
H L NH
13
11
14
14
12
10
15
13
13
N.A
N.A
10
N.A
10
13
12
14
2
2
H LꢀNHMe
2
H LꢀNHEt
N.A
2
H LꢀNHPh
15
15
25
15
32
11
20
N.A
17
15
ꢀ
2
Gentamicin
N.A
Amphotericin
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
34
a)
b)
All measurements are in mm diameter of the inhibition zone (N.A indicates no activity); The
c)
standard deviation varied in the range 0ꢀ1 based on three readings; Studies were made in dmso;
d,e)
f)
g)
Commercially available antiꢀmicrobial agents. Methiciilin resistant Staphylococcus aureus,
h)
i)
j)
Staphylococcus aureus, Klebsiella pneumoniae, Selmonella typhimurium, Shigella flexneri,
k)
Candida albicans , Gentamicin acts as positive control against bacteria (S. aureus, K.pneumoniae
1, S. flexneri , S.typhimurium) and Amphotericin acts as positive control against yeast (Candida
albicans).
Table 4. Minimum Inhibitory concentration (MIC in ꢀg/mL) of zinc(II) complexes 1ꢀ8.
Complexes
MRSA
S. aureus K. pneumoniae S.typhumirium
S. flexenri
C. albicans
Complex 1
750
10
750
50
750
750
Complex 3
Complex 5
Complex 7
Complex 2
Complex 4
Complex 6
Complex 8
50
0.5
0.5
0.5
0.5
50
50
10
10
50
10
250
10
10
750
750
750
250
1000
750
50
50
50
50
50
50
250
750
1000
50
50
50
750
1000
50
1000
50
0.5
0.5
50
1000
10
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1
For time kill studies, complexes 5ꢀ8 with Et/Ph substituents at N atom of
thiosemicarbazones under study have been selected. The selection is based on the observation
that the antimicrobial activity of complexes is found to vary in general in the order, R= Ph > Et ≥
Me > H. On the basis of 1 x MIC of these complexes obtained for different microorganisms they
were subjected to viable cell count studies. From time kill studies done by viable cell count
method (Figs. 12ꢀ15), it is revealed that all the four Zn(II) complexes tested showed potent
microbicidal activity against most of the microorganisms used. Complexes 5 and 6 with ethyl
1
substitution at N ꢀatom (Figs. 12, 13) completely killed S. aureus during 2 to 4 h of incubation.
Similarly these complexes showed 100% killing of S. typhimurium, MRSA and C. albicans
during 4 to 6 h of incubation and likewise K. pneumoniae was completely killed during 6 to 8 h
of incubation. In view of low zoi (16 ꢀ 18 mm), complexes 5 and 6 took longer time against
Shigella flexneri for nearly complete killing (∼ 98%, 24 h of incubation.
2
0

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3
2
Fig. 12. Time kill graph of complex, [Zn(κ ꢀO,N,SꢀLꢀNHEt)(κ ꢀN,Nꢀbipy)] 5.
2
1

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3
2
Fig. 13. Time kill graph of complex, [Zn(κ ꢀO,N,SꢀLꢀNHEt)(κ ꢀN,Nꢀphen)] 6.
1
Likewise as regards the activity of complexes 7 and 8 with phenyl substitution at N atom
Figs. 14, 15), both these complexes showed potent microbicidal activity against S. aureus which
(
was completely killed at 2 h of incubation. The microbicidal activity of compound 7 against K.
pneumoniae was found to be high (completely killed at 10 h of incubation, zoi 21 mm) as
compare to that of compound 8 (completely killed at 24 h of incubation, zoi 15 mm). Further Sh.
flexneri was found to be variably sensitive to both the compounds: about 11.25% viable cells
were seen in case of compound 7 even after 24 hrs of incubation whereas compound 8
completely killed S. flexneri at 8 h. Complexes 7 and 8 completely killed C. albicans during 8 h
and 4 h of incubation respectively. MRSA was completely killed during 6 h of incubation by
both the complexes 7 and 8 and likewise S. typhimurium was completely killed during 8 h of
incubation (Figs. 14, 15) . Further, complexes 5ꢀ8 were tested for cellular toxicity testing using
sheep blood cells. It has been observed that the viability of living cells is found to be low and
hence cellular toxicity of these complexes is high.
2
2

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3
2
Fig. 14. Time kill graph of complex, [Zn(κ ꢀO,N,SꢀLꢀNHPh)(κ ꢀN,Nꢀbipy)] 7.
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3

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3
2
Fig. 15. Time kill graph of complex, [Zn(κ ꢀO,N,SꢀLꢀNHPh)(κ ꢀN,Nꢀphen)] 8.
3
Conclusions
1
3
Zinc(II) complexes with 5ꢀnitroꢀsalicylaldehydeꢀN ꢀsubstituted thiosemicarbazones, [Zn(κ ꢀ
2
O,N,SꢀLꢀNHR)(κ ꢀN,NꢀL′)] (R = H, Me, Et, Ph, H; L′ = bipy/phen) 1ꢀ8 have distorted trigonal
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bipyramidal geometry (1ꢀmolecule II, 5, 7), distorted square pyramidal geometry (4, 6 and 8ꢀ
molecule II) and geometry in between square pyramidal and trigonal bipyramidal (1ꢀmolecule I,
8ꢀ molecule II). This structural difference may be due to the combined effect of substituents at
1
N ꢀ nitrogen and nature of coꢀligands, bipy and phen. Complexes have shown significant
antimicrobial activity against MRSA, S. aureus, K. pneumoniae, Sh. flexneri, S. typhimurium and
C. albicans. The activity against MRSA as well as that against S.aureus are significant
developments in antimicrobial investigations visꢀàꢀvis lack of activity of Gentamicin against
MRSA or low antimicrobial activity against S.aureus as per literature reports. All complexes are
active against K. pneumoniae and S. typhimurium, while complexes reported in literature were
found to be inactive. Zinc(II) complexes also showed good activity against resistant bacterial
strain Sh. flexneri, but there is no report in literature for comparison purpose. Higher
antimicrobial activity of these complexes may be attributed to the increase in lipophilicity due to
presence of bipy and phen coꢀligands with increase in ability to penetrate the cell membrane. The
cause of inhibitory action of complexes may be due to their interaction with enzyme prosthetic
group in microbial cells which inhibit the replication of DNA. Time kill/cellular toxicity studies
of complexes have revealed that they are cytotoxic to microorganisms (bactericidal/fungicidal)
and living cells. This work makes significant contribution in the use of zinc(II)
thiosemicarbazone complexes as efficient antimicrobial agents, hitherto unreported with this
class of ligands.
4
Experimental section
4
.1. Materials and Methods
Zinc(II) acetate noculums Zn(OAc) ·2H O, thiosemicarbazide, Nꢀmethyl thiosemicarbazide,
Nꢀethyl thiosemicarbazide, Nꢀphenyl thiosemicarbazide, 5ꢀnitroꢀsalicylaldehyde, 2,2ꢀbipyridine
ꢀ
2
2
(
bipy) and 1,10ꢀphenanthroline (phen) were procured from Aldrich Sigma Ltd. The thioꢀligands
H LꢀNH , H LꢀNme, H LꢀNEt, H LꢀNPh, Chart 1) were synthesized according to reported
(
2
2
2
2
2
5
0, 51
procedures.
(See Supplementary). Elemental analysis C, H, and N were carried out with a
thermoelectron FLASHEA1112 analyzer. The melting points were determined with a
Gallenkamp electrically heated apparatus. The IR spectra of compounds were recorded in 4000 –
ꢀ1
4
50 cm region with a Perkin Elmer FTꢀIR Spectrometer by making their KBr pellets. The UVꢀ
2
5

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ꢀ3
ꢀ4
visible spectra of compounds (10 ꢀ10 M) were recorded in dimethyl sulfoxide (dmso) with the
ꢀ4
help of a UVꢀ1601 PC Shimadzu spectrophotometer. Fluorescence spectra of complexes (10
1
M) were recorded with a Varian Cary Eclipse Fluorescence spectrophotometer. The H NMR
spectra were recorded on Bruker Avance 500MHz NMR spectrometer in CDCl ꢀdmso mixture
3
(9:1) with TMS as the internal reference.
4.2. Synthesis of complexes.
3
2
[
Zn(κ ꢀO,N,SꢀLꢀNH )(κ ꢀN, Nꢀbipy)]⋅MeOH
1
. To a pale yellow solution of thioꢀligand,
2
H LꢀNH (0.027 g, 0.11 mmol) in acetonitrile (10 mL) was added white solid Zn(OAc) ·2H O
2
2
2
2
(0.025 g, 0.11 mmol). The reaction mixture was stirred for 15 minutes which yielded white
precipitate and to these white precipitate, solution of bipyridine coꢀligand (0.017g, 0.11 mmol)
in dichloromethane and methanol (10 mL, 1:1 v/v) was added . The contents were again stirred
for 15 min and a clear orange solution formed was allowed to evaporate at room temperature
which yielded an orange compound (Yield. 0.036 g, 70%, M. p. 235ꢀ236 °C). Elemental analysis
calculated (%) for C H N O SZn⋅MeOH: C 46.40; H 3.66; N 17.09; S 6.51; Found: C 45.14; H
1
8
14
6
3
1
3
.45; N 17.36; S 6.63 %. IR (KBr): ν(N –H) 3548s, 3320s; ν(C–H) 3189s, 3069w, 3018w,
931w; ν(C=N) + ν(C=C) + δ(N−H) 1600s, ν(N=O) 1549m; δ(C−H) 1481s, 1423m; 1372m;
2
δ(N=O) 1309s; 1246m, 1195w, 1143m, 1109m, 1052m, 1018m, 954m, 906w, ν(C–S) 846 s;
ꢀ1
8
00m, 760s, 726s, 680m, 658s, 612s, 509 w, 457w, 423w cm . UV/vis (dmso) λ
/nm, ε /L
max
ꢀ1
ꢀ1
ꢀ4
3
4
4
mol cm : [10 M] 421 (8.39 x 10 ); 381(1.47 x 10 ), 284(1.41 x 10 ). Fluorescence spectrum:
ex
em
1
(
λmax = 300 nm; λmax = 433 nm). H NMR (δ, ppm; CDCl : dmso; 9:1): δ = 8.91 (2H, s,
3
9
16
2
11
14
4
7
C H
+ C H ); 8.55 (3H, m, C H+ C H
+ C H ), , 8.12 (4H, m, C H + C H), 7.99
bipy
bipy
bipy bipy
12
13
10
15
1
(
2H, s, C H
+ C H ), 7.84 (2H, s, C H
+ C H ), 7.71 (1H, d, N H), 6.45 (1H, s,
bipy
bipy
bipy bipy
6
C H) ppm. Complexes 2ꢀ8 were prepared by a similar method.
3
2
Zn(κ ꢀO,N,SꢀLꢀNH )(κ ꢀN, Nꢀphen)] 2. Orange compound (Yield. 0.039 g, 72%, M.p. 200ꢀ
2
2
6
3
1
01 °C). Elemental analysis calculated (%) for C H N O SZn: C 49.65; H 2.92; N 17.37; S
20
14
6
3
1
.63; Found: C 49.39; H 2.71; N 17.18; S 6.41 %. IR (KBr): ν(N –H ) 3547, 3317 br; ν(C–H)
2
066 w, 2926w, 2853w; ν(C=N) + ν(C=C) + δ(N−H) 1600s; ν(N=O) 1549s; δ(C−H) 1521w,
482s, 1426 m; 1371 s, δ(N=O) 1309s; 1242w, 1192w, 1141w, 1097w, 1041s, 951w; ν(C–S)
2
6

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ꢀ1
ꢀ1
ꢀ1
8
50s; 800 w, 727m, 654w, 610w, 503w, 453w cm . UV/vis (dmso) λ /nm, ε /L mol cm :
max
ꢀ4
3
4
4
4
[
10 M] 420 (8.03 x 10 ), 373 (1.20 x 10 ), 257 (1.33x10 ), 285 (1.73 x 10 ). Fluorescence
em
ex
1
spectrum: (λmax = 426 nm; λmax = 300 nm). H NMR (δ, ppm; CDCl : dmso; 9:1): δ = 8.95
3
9
16
2
11
14
4
7
(
2H, s, C H
+ C H ); 8.55 (3H, m, C H+ C H
+ C H ), , 8.10 (3H, t, C H + C H),
phen
phen
phen
phen
10
1
2
13
1
15
7
.96 (2H, s, C H
+ C H ), 7.78 (1H, s, N H), 7.60 (2H, m, C H
+ C Hphen), 6.41(1H,
phen
phen
phen
6
s, C H) ppm.
3
2
[
Zn(κ ꢀO,N,SꢀLꢀNHMe)(κ ꢀN,Nꢀbipy)] 3. Orange crystals (Yield. 0.037 g, 69%, M.p. 188ꢀ
1
6
3
1
90°C). Elemental analysis calculated (%) for C H N O SZn: C 48.16; H 3.40; N 17.74; S
19 16 6 3
1
.77; Found: C 48.03; H 3.51; N 17.65; S 6.74 %. IR (KBr): ν(N –H) 3397sb; ν(C–H) 3104w,
064s, 2940m, 2851w; ν(C=N) + ν(C=C) + δ(N−H) 1651w, 1600s; ν(N=O) 1549s; δ(C−H)
493s, 1476s, 1437m, 1403m; 1370m; δ(N=O) 1302s; 1246m, 1183m, 1104m, 1065m, 1019m,
ꢀ
964m, 941w, 906w; ν(C–S) 829s; 766s, 733 s, 682m, 649s, 609s, 513w, 486w, 457w, 400w cm
1
ꢀ1
ꢀ1
ꢀ4
3
4
.
UV/vis (dmso) λmax /nm, ε /L mol cm : [10 M] 425 (8.03 x 10 ), 387 (1.47 x 10 ), 281
4
em
ex
1
(
1.72 x 10 ). Fluorescence spectrum: (λmax = 434 nm; λmax = 300 nm). H NMR (δ, ppm;
9
16
2
12
CDCl : dmso; 9:1): δ = 8.65 (2H, s, C H + C H ); 8.52 (H, d, C H), 8.40 (2H, s, C H
+
3
bipy
bipy
bipy
13
4
7
1
11
14
C H ), 8.13 (H, s, C H+C H), 7.86 (1H, s, N H), 7.69 (2H, m, C H + C Hbipy), 7.61 (3H,
bipy
bipy
10
15
1
6
1
m, C H + C H + N H), 6.50(1H, s, C H), 3.48 (3H, d, CH N )) ppm.
bipy
bipy
3
3
2
[
Zn(κ ꢀO,N,SꢀLꢀNHMe)(κ ꢀN,Nꢀphen)] 4. Orange compound (Yield. 0.039 g, 70%, M.p.
1
93ꢀ194 °C). Elemental analysis calculated (%) for C H N O SZn: C 50.66; H 3.24; N 16.88;
21 16 6 3
1
S 6.44; Found: C 50.49; H 3.12; N 16.91; S 6.33 %. IR (KBr): ν(N –H) 3404s; ν(C–H) 3056m,
2
981m, 2925w, 2838w; ν(C=N) + ν(C=C) + δ(NꢀH) 1596s; ν(N=O) 1559m; 1516m, δ(CꢀH)
478s, 1429s; 1367w; δ(N=O) 1311s; 1242m, 1187m, 1137w, 1100s, 1031m, 944w, 919m;
1
–
1
ꢀ1
ꢀ1
ν(C–S) 845s; 720s, 646m, 602 m, 497m, 441m cm . UV/vis (dmso) λ
/nm, ε /L mol cm :
max
ꢀ4
3
4
4
4
[
10 M] 426 (9.26 x 10 ), 387 (1.75 x 10 ), 295 (1.23 x 10 ), 265 (2.69 x10 ). Fluorescence
em
ex
1
spectrum : (λmax = 433 nm; λmax = 300 nm). H NMR (δ, ppm; CDCl : dmso; 9:1): δ = 9.20
3
9
16
11
14
12
13
(
2H, s, C H
+ C H ), 8.97 (2H, s, C H
+ C H ), 8.58 (2H, C H
+ C Hphen),
phen
phen
phen
phen
phen
2
4
7
1
10
8
.41 (1H, d, C H), 8.06 (2H, m, C H+C H), 7.81(1H, m, N H), 7.68 (2H, m, C H
+
phen
15
6
1
C H ), 6.48 (1H, s, C H), 3.47 (3H, d, CH N )) ppm.
phen
3
2
7

New Journal of Chemistry
Page 28 of 36
View Article Online
DOI: 10.1039/C5NJ02822A
3
2
[
Zn(κ ꢀO,N,SꢀLꢀNHEt)(κ ꢀN, Nꢀbipy) 5. Orange crystals (Yield. 0.040 g, 71%, m.p. 183ꢀ
1
6
3
85 °C). Elemental analysis calculated (%) for C H N O SZn: C 49.24; H 3.69; N 17.23, S
20
18
6
3
1
.57; Found: C 48.95; H 3.66; N 17.06, S 6.63 %. IR (KBr): ν(N –H) 3345 br, ν(C–H) 3107w,
066w, 2970 w, 2925 w, 2868w ; ν(C=N) + ν(C=C) + δ(N−H) 1648m, 1600s; ν(N=O) 1551m;
δ(C−H) 1481s, 1437m; δ(N=O) 1313s; 1242w, 1194w, 1150w, 1097m, 1046w, 1021w, 956m;
–
1
ν(C–S) 837w; 767w, 729m, 686m, 648m, 609w, 508w, 448w, 416w cm . UV/vis (dmso) λ
max
ꢀ1
ꢀ1
ꢀ4
3
4
4
/
nm, ε /L mol cm : [10 M] 430 (9.64 x 10 ), 388 (1.73 x 10 ), 275 (1.29 x 10 ). Fluorescence
em
ex
1
spectrum: (λmax = 437 nm; λmax = 300 nm). H NMR (δ, ppm; CDCl : dmso; 9:1): δ = 8.46
3
9
16
2
4
7
12
(
2H, s, C H + C H ); 8.33 (H, d, C H), 8.13 (H, d, C H+C H), 7.99 (3H, m, C H
+
bipy
bipy
bipy
13
1
11
14
10
15
C H + N H), 7.67 (2H, d, C H + C H ), 7.42 (2H, s, C H + C Hbipy), 6.26 (1H, s,
bipy
bipy
bipy
bipy
6
1
3
C H), 3.31 (2H, m, N (CH ), 1.03 (3H, m, CH ) ppm.
2
3
2
[
Zn(κ ꢀO,N,SꢀLꢀNHEt)(κ ꢀN,Nꢀphen)] 6. Orange crystals (Yield. 0.044 g, 75%, M.p.
1
6
2
95ꢀ197°C). Elemental analysis calculated (%) for C H N O SZn: C 51.62; H 3.54; N 16.42; S
2
2
18
6
3
1
.26; Found: C 51.39; H 3.57; N 16.53; S 6.19 %. %. IR (KBr): ν(N –H) 3359s; ν(C–H) 3060 br,
974 br, 2923 w, 2870 w; ν(C=N) + ν(C=C) + δ(N−H) 1651m, 1593s; ν(N=O) 1547s; 1513s;
δ(CꢀH) 1485s, 1423s; δ(N=O) 1307s; 1249m, 1186s, 1186m, 1146 m, 1100s, 1049w, 1014w,
–
1
ꢀ1
9
56w; ν(C–S) 848s; 762w, 734s, 647w, 510w, 429w cm . UV/vis (dmso) λ /nm, ε /L mol
max
ꢀ1
ꢀ4
3
4
4
4
cm : [10 M] 428 (8.69 x 10 ), 386 (1.45 x 10 ), 287 (1.21 x 10 ), 257 (2.17 x 10 ).
em
ex
9
16
Fluorescence spectrum: (λmax = 437 nm; λmax = 300 nm). δ = 8.79 (2H, s, C H
+ C Hphen),
phen
2
11
14
4
7
12
8
.43 (3H, d, C H+ C H
+ C H ), 7.87 (2H, m, C H+C H), 7.75(3H, m, C H
+
phen
phen
phen
1
3
1
10
15
6
1
C H
+ N H), 7.68 (2H, m, C H
+ C H ), 6.20 (1H, s, C H), 3.31 (2H, m, N (CH ),
phen
phen phen 2
3
1
.03 (3H, m, CH ) ppm.
3
2
[
Zn(κ ꢀO,N,SꢀLꢀNHPh)(κ ꢀN,Nꢀbipy)] 7. Orange crystals (Yield. 0.045 g, 74%, M.p. 223ꢀ
2
5
3
1
6
25 °C). Elemental analysis calculated (%) for C H N O SZn: C 53.79; H 3.24; N 15.68;S
24
18
6
3
1
.98; Found: C 53.42; H 3.12; N 15.32; S 6.10 %. IR (KBr): ν(N –H) 3342br; ν(C–H) 3100w,
066w, 2960w, 2858w; ν(C=N) + ν(C=C) + δ(N−H) 1650m, 1600s; ν(N=O) 1550s; δ(CꢀH)
491s, 1432s; δ(N=O) 1316s; 1241m, 1175s, 1100s, 1025w, 933w; ν(C–S) 833s; 767w, 725s,
–1
ꢀ1
ꢀ1
ꢀ4
4
42m, 483m, 408m cm . UV/vis (dmso) λ /nm, ε /L mol cm : [10 M] 428 (2.07 x 10 ), 376
max
2
8

Page 29 of 36
New Journal of Chemistry
View Article Online
DOI: 10.1039/C5NJ02822A
4
4
em
max
ex
1
(
1.92 x 10 ), 284 (1.58 x 10 ). Fluorescence spectrum: (λ
= 444 nm; λmax = 300 nm). H
9
16
2
NMR (δ, ppm; CDCl ): δ = 9.47 (2H, s, C H + C H ), 8.81 (1H, s, C H), 8.56 (2H, d
3
bipy
bipy
12
13
11
14
4
7
1
,
C H + C H ), 8.28 (2H, d, C H + C H , 8.22 (2H, s, C H + C H), 8.06 (1H, sb, N
bipy
bipy
bipy
bipy)
1
0
15
H+ C H + C H ), 7.55 (2H, d, mꢀH ), 7.17(2H, m, mꢀH 6.89 (1H, m, pꢀH ), 6.38 (1H,
bipy
bipy
ph
ph),
ph
6
d, C H) ppm.
3
2
[
Zn(κ ꢀO,N,SꢀLꢀNHPh)(κ ꢀN,Nꢀphen)].CH Cl 8. Orange crystals (Yield. 0.048 g, 76%),
2
2
m.p. 218ꢀ220°C. Elemental analysis calculated (%) for C H N O SZn⋅CH Cl : C 50.28; H
2
6
18
6
3
2
2
1
3
.10; N 13.04; S 4.97; Found: C 49.87; H 3.62; N 12.93; S 4.58 %. IR (KBr): ν(N –H) 3343br;
ν(C–H) 3064w, 3000w, 2920br; ν(C=N) + ν(C=C) + δ(N−H 1598s; ν(N=O) 1546s; 1546m,
518m; δ(C−H) 1489s, 1426s; 1369w; δ(N=O) 1312s; 1238m, 1181m, 1130m, 1107s, 953; ν(C–
1
–
1
ꢀ
S) 844s, 753w, 725s, 691w, 639w, 594w, 502w, 416w cm . UV/vis (dmso) λ
/nm, ε /L mol
max
4
1
ꢀ1
ꢀ4
4
4
4
cm : [10 M] 428 (2.35 x 10 ), 367(1.91 x 10 ), 294(1.24 x 10 ), 271(2.64 x 10 ). Fluorescence
em
ex
1
9
spectrum: (λmax = 441 nm; λ = 300 nm). H NMR (δ, ppm; CDCl ): δ = 9.47 (2H, s, C H
3
phen
16
2
11
14
12
+
C H ), 9.03 (1H, s, C H), 8.85 (2H, d, C H
+ C H ), 8.47 (2H, d, C H
phen
+
phen
phen
phen
1
3
4
7
1
10
15
C H
, 8.26 (2H, s, C H + C H), 8.06 (1H, m, N H), 7.99 (2H, m, C H
+ C Hphen), 7.86
phen)
phen
6
(
2H, d, mꢀH ), 7.70 (2H, m, oꢀH 7.17 (1H, m, pꢀH ), 6.38 (1H, d, C H) ppm.
ph
ph),
ph
4.3. Crystal structure determination
A single crystal was mounted on a glass fiber and used for data collection with a Bruker Apex
(
II) CCD diffractometer (1,296(2), 6, 100(2) K; 4, 5 and 8, 296(2) K) and with a Agilent Eos
(Gemini) (7; 173(2) K) equipped with graphite monochromated MoꢀKα (λ = 0.71073 Å for 1,4ꢀ
6
and 8) and CuꢀKα (λ = 1.54178 for 7). The data recorded for compounds were processed with
Bruker APEX II CCD (1, 4ꢀ6 and 8) or CrysAlisPro (7) (data collection) and Bruker SAINT
5
2
RED (1, 4ꢀ6 and 8) or CrysAlisPro RED (7) (cell refinement and data reduction). The
5
3
structures were solved by direct methods using the program SHELXT (compound 1),
5
4
55
56ꢀ58
SHELXSꢀ97
(compounds 4 and 6), SIRꢀ92
(compound 5 and 8), or Superflip
2
54
(
compound 7), refined by fullꢀmatrix leastꢀsquares techniques against F using SHELXLꢀ97
5
4
(
compounds 1, 4ꢀ6, 7 and 8) and molecular graphics from SHELXTL (1, 4ꢀ6 and 8) or OLEX
5
9
2
(7). The data were corrected for absorption using SADABS (1, 4ꢀ6 and 8) or spherical
2
9