Ni(II)-tetrahedral complexes: Characterization, antimicrobial properties, theoretical studies and a new family of charge-transfer transitions

Article abstract of DOI:10.1016/j.saa.2012.12.078

A new amine containing selenium and their five imine, (SeSchX)(X: -H, F, Cl, Br, CH₃), and Ni (II) complexes, [Ni(SeSchX)(H₂O) ₂]Cl/[Ni(SeSchCl)(H₂O)Cl], were synthesized. The compounds were characterized by means of elemental analyses, ¹³C and ¹H NMR (for imine), FT-IR, UV-Visible spectroscopy, TGA/DTA and elemental analyses. [Ni(SeSchCl)(H₂O)Cl] complex from Ni(II) complexes changes color from yellow to orange in the range pH 5-7. [Ni(SeSchCl)(H₂O)Cl] complex has ligand-to-metal charge-transfer (LMCT) transitions in the basic medium. Excitation characteristics and energetic of [Ni(SeSchCl)(H₂O)Cl] complex, examined via TD-DFT calculations, reveals transitions of LMCT and π → π^* character that matches the experimental values. [Ni(SeSchCl)(H₂O)Cl] complex showed the highest antibacterial activity when compared to other complexes reported in this work.

Full text of DOI:10.1016/j.saa.2012.12.078

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 60–67
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Ni(II)-tetrahedral complexes: Characterization, antimicrobial properties,
theoretical studies and a new family of charge-transfer transitions
a
b
Nurßsen Sarı a, , Songül Çig˘dem Sßahin , Hatice Ög˘ütcü , Yavuz Dede a,1, Soydan Yalcin a,
⇑
Aliye Altundasß a, Kadir Dog˘anay a
a Gazi University, Faculty of Science, Department of Chemistry, 06500 Ankara, Turkey
b Ahi Evran University, Faculty of Arts and Science, Department of Biology, Kırßsehir, Turkey
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
Five new Schiff bases involving Selenium [(SeSchX)(X: -H, F, Cl, Br, CH3)] and Ni(II) complexes ([Ni(SeS-
chX)(H2O)2]Cl/[Ni(SeSchCl)(H2O)Cl]) are synthesized and characterized. [Ni(SeSchCl)(H2O)Cl] complex
exhibits metal-centered color-changing in between pH 5–7 and is a more potent bactericide than other
complexes.
"
Novel Ni(II)-tetrahedral complex
with selenium ligand has been
synthesized by means of template
method and characterized.
[Ni(SeSchCl)(H2O)Cl] complex shows
different properties of synthesized
Ni(II) complexes.
This complex changes color from
yellow to orange in the range pH 5–
7.
"
"
"
[Ni(SeSchCl)(H2O)Cl] complex is
more potent bactericides than all of
the substances synthesized.
a r t i c l e i n f o
a b s t r a c t
Article history:
A new amine containing selenium and their five imine, (SeSchX)(X: -H, F, Cl, Br, CH3), and Ni (II) com-
plexes, [Ni(SeSchX)(H2O)2]Cl/[Ni(SeSchCl)(H2O)Cl], were synthesized. The compounds were character-
ized by means of elemental analyses, 13C and 1H NMR (for imine), FT-IR, UV–Visible spectroscopy,
TGA/DTA and elemental analyses. [Ni(SeSchCl)(H2O)Cl] complex from Ni(II) complexes changes color
from yellow to orange in the range pH 5–7. [Ni(SeSchCl)(H2O)Cl] complex has ligand-to-metal charge-
transfer (LMCT) transitions in the basic medium. Excitation characteristics and energetic of
[Ni(SeSchCl)(H2O)Cl] complex, examined via TD-DFT calculations, reveals transitions of LMCT and
Received 25 September 2012
Received in revised form 14 December 2012
Accepted 17 December 2012
Available online 4 January 2013
Keywords:
Charge-transfer transitions
Cyclic seven-membered ring
DFT
Amine containing selenium
Antimicrobial properties
p
?
pꢀ character that matches the experimental values. [Ni(SeSchCl)(H2O)Cl] complex showed the
highest antibacterial activity when compared to other complexes reported in this work.
Ó 2013 Elsevier B.V. All rights reserved.
Introduction
The coordination chemistry of transition metal complexes with
azomethine ligands has been widely studied, partly due to the use
of such compounds as antibacterial drugs in the field of medicine
[1]. In particular, titanium (IV), platinum (II) and silver (I) com-
plexes have been used in the treatment of numerous diseases [2–
⇑
Corresponding author. Tel./fax: +90 3122021157.
E-mail addresses: nursens@gazi.edu.tr (N. Sarı), dede@gazi.edu.tr (Y. Dede).
For theoretical studies. Tel./fax: +90 3122021386.
1
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.12.078

N. Sarı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 60–67
61
4]. Researchers have become increasingly interested in the coordi-
nation chemistry of nickel complexes as models for the active sites
in nickel containing enzymes [5]. Nickel (II)-azomethine com-
plexes have attracted attention in recent years due to their well-
defined spectroscopic, photochemical and electrochemical proper-
ties [6–8]. Complexes of Nickel (II) can be prepared in various con-
formational structures, each having an extensive number of
examples. This is probably the reason whereby Ni(II) is one of
the most spectroscopically studied metal ions.
Molecules involving selenium are still efficient and encouraged
in medicinal chemistry due to the structural features are retained
and softer atom which can be served as hydrogen-bond acceptor
or electron donor [9]. Selenium compounds were found playing
important roles in protecting the heart, preventing cancer and car-
diovascular diseases [10]. Because selenium functions as an antiox-
[Ni(Se-SchCl)(H2O)Cl] complex showed different property then
other Ni (II) complexes. This complex was observed color change
depends on pH. Ligands or complexes that change color have at-
tracted a great deal of interest because of their useful photochem-
ical properties and potential applications in many fields, such as
chemosensors [15], photocatalysts and light-emitting diodes
(LEDs) [16]. In this study, [Ni(Se-SchCl)(H2O)Cl] complex showed
change color in different pH unlike from other synthesized Ni(II)-
tetrahedral complexes. So, we decided to study electronic spectra
of [Ni(Se-SchCl)(H2O)Cl] complex. Furthermore calculated spin
densities the triplet ground states for all Ni (II) complexes bear
two unpaired electrons residing in Ni d-based orbital.
Experimental section
idant works in conjunction with vitamin
E
[11]. Selenium
Materials and physical measurements
containing compounds have gained attention as potential a antiox-
idants for preventing some metal ions mediated oxidative damage.
Therefore, systematic investigation of molecules containing sele-
nium is very important for bioinorganic area [12]. So, it would be
interesting to investigate the structural and antimicrobial proper-
ties of complexes including selenium and Nickel (II) ion.
Here we report the synthesis, characterization, antimicrobial
properties of new azomethine (Schiff bases) and their Ni (II) com-
plexes (Scheme 1). Motivated by the presence of heterocyclic se-
ven-membered rings in numerous biologically active natural
products and pharmaceuticals (such as tuberostemonine), a new
amine 2-Amino-5,6,7,8-tetrahydro-4H-cyclohepta[b]selenophene-
3-carbonitrile (1) was synthesized using the Gewald methods
[13,14]. Then, its five Schiff bases (2) prepared from the reaction
of 2-aminocycloheptaselenophene-3-carbonitrile and salicylalde-
hyde derivatives and their Ni (II) complexes (3) were synthesized
by means of condensation and template method, respectively.
All chemicals used in the study were reagent grade and were
purified when it was necessary. The aldehydes (salicylaldehyde,
5-fluorosalicylaldehyde, 3-chloro-5-fluorosalicylaldehyde, 3-bro-
mo-5-fluorosalicylaldehyde and 5-fluoro-3-methylsalicylalde-
hyde), cycloheptanone, selenium and morpholine were purchased
from Sigma–Aldrich. Elemental analyses were performed with a
LECO-CHNS-9320 instrument. Metal contents were determined
by using a Philips PU 9285 atomic absorption instrument. 1H and
13C NMR spectra were recorded with a Bruker DPX-300 MHz and
100 MHz using TMS as an internal standard and CDCl3 as solvent.
Electronic spectra were recorded on a UV-1800 ENG240V spectro-
photometer in ethanol. IR spectra were recorded on a Mattson-
5000 FTIR instrument in KBr pellets. Melting points were deter-
mined with
a Barnstead-Electrothermal-9200 melting point
apparatus. The molar conductivities were measured with an inoLab
Cond 730 conductivity meter (10ꢁ3 mol Lꢁ1 in DMF solution). The
Scheme 1. The Synthetic route of Ni(II) complexes.

62
N. Sarı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 60–67
TGA curves were obtained on General V4.1C Du Pont 2000 between
30 and 900 °C at a heating rate of 10 °C minꢁ1 in nitrogen atmo-
sphere. Magnetic measurements were performed with a Sherwood
Scientific magnetic susceptibility balance (Model No: MK 1) at
21 °C with Hg[Co(NCS)4] as a calibra.
the test solutions. The plates were incubated for 24 h at 37 °C. On
completion of the incubation period, the mean value obtained from
the two holes was used to calculate the zone of growth inhibition
of each sample. Bacterial subcultures and fungus were tested for
resistance to five antibiotics (produced by Oxoid Ltd., Basingstoke,
UK): ampicillin (preventing the growth of gram-negative bacteria),
nystatin (binding to sterols in the fungal cellular membrane, alter-
ing the permeability and allowing leakage of the cellular contents),
kanamycin (used in molecular biology as agent to isolate bacteria),
sulphamethoxazol (bacteriostatic antibacterial agent that inter-
feres with folic acid synthesis in susceptible bacteria), amoxycillin
(b-lactam antibiotic used to treat bacterial infections caused by
susceptible microorganisms).
Synthesis
Synthesis of 2-amino-5,6,7,8-tetrahydro-4H-
cyclohepta[b]selenophene-3-carbonitrile, (1), [Se-NH2]
2-Aminoselenophene-3-carbonitrile (1) was prepared according
to the procedure described by Gewald [14,17]. To the stirred solu-
tion of 5.61 g (0.05 mol) cycloheptanone, 3.30 g (0.05 mol) malon-
onitrile, and 3.95 g (0.05 mol) of selenium in 50 ml anhydrous
ethanol, 4.36 g (0.05 mol) of morpholine was added drop wise at
room temperature. Then the reaction was refluxed for 48 h. After
the reaction mixture was poured into the ice-water. The resulting
solid was collected and recrystallized from ethanol (m.p.: 125–
127 °C, 71% yield).
Studies of spectroscopy under different pH for [Ni(Se-SchCl)(H2O)Cl]
[Ni(Se-SchCl)(H2O)Cl] complex was dissolved in DMF (10 mL,
1 ꢂ 10ꢁ3 M) at room temperature. Buffer solution pH 10, 7, 5, 4
and 0.01 M standard HCl solution were purchased from Sigma–Al-
drich. Buffers dissolved in water (1 mL) were added dropwise to
the solution of 1 ꢂ 10ꢁ3 M [Ni(Se-SchCl)(H2O)Cl] complex. It was
then stirred and color was obtained as follows (Fig. 1).
Synthesis of imine compounds: general procedure, (2), ([Se-SchH], [Se-
SchF], [Se-SchCl], [Se-SchBr], [Se-SchCH3])
A
mixture of aldehyde (0.443 g, 0.308 g, 0.344 g, 0.442 g,
0.268 g, 0.022 mol, respectively, salicylaldehyde, 5-fluorosalicylal-
dehyde, 3-chloro-5-fluorosalicylaldehyde, 3-bromo-5-fluorosali-
cylaldehyde and 5-fluoro-3-methylsalicylaldehyde) and 2-
Aminoselenophene-3-carbonitrile compound (0.536 g of [Se-
NH2], 0.022 mol) in 20 ml of ethanol was refluxed for 2 h and then
cooled at room temperature. The precipitated solid was collected,
washed with cold ethanol, and recrystallized from ethanol. All
imine compounds were prepared by using the same procedure.
Computational method
UB3LYP/LANLDZ level of theory is employed throughout all cal-
culations. Geometries of all species are fully optimized and con-
firmed for having no imaginary frequencies, thus verifying the
authenticity of global minima. TD-DFT calculations utilize the
polarizable continuum model (PCM). A dielectric medium of
e
= 36.6 is used, instead of the experimental DMF (e = 38.3). Com-
plexes VII-X are experimentally observed whereas IX’ is modeled
to provide insight on suggested MLCl(OH2) structure instead of
ML(OH2)2. All calculations were performed using Gaussian 03 pro-
gram suite [19].
Template method for Ni (II) complexes, (3)
Ni (II) complexes were prepared by following a general method:
A solution of 1 (0.119 g, 5 ꢂ 10ꢁ4 mol) and aldehyde (0.061 g,
0.070 g, 0.078 g, 0.100 g, 0.068 g, 5 ꢂ 10ꢁ4 mol; respectively, sali-
cylaldehyde, 5-fluorosalicylaldehyde, 3-chloro-5-fluorosalicylalde-
Results and discussion
hyde,
3-bromo-5-fluorosalicylaldehyde
and
5-fluoro-3-
methylsalicylaldehyde) are dissolved in 1,10,2,20-tetrachloro-ethan
(25 mL). The solution refluxed for 2 h. The solution was stirred mag-
netically and heated NiCl2ꢃ6H2O (0.12 g, 5 ꢂ 10ꢁ4 mol) dissolved in
methanol (5 mL) was added dropwise to the solution of the amine–
aldehyde mixture. The reaction mixture was, after refluxing for 2 h,
concentrated through evaporation until half of the volume [18].
After keeping it another 2 days, the solid complexes formed were
collected by filtration and then dried in a desiccator over CaCl2.
Analytical data and some of the physical properties of the Schiff
bases and their complexes are summarized in Table 1. The com-
plexes are only soluble in DMF and DMSO, but insoluble in organic
solvents like C2H5OH, CCl4 and benzene. The molar conductance
values of the four Ni (II) complexes are found to be 12.97–
14.79 l
S/cm in 10ꢁ3 M DMF solutions were indicated the 1:1 elec-
trolytic nature of the compounds [18]. [Ni(Se-SchCl)(H2O)Cl] com-
plex were nonelectrolytic.
½NiðSe-SchXÞðH2OÞ ꢄCl $ ½NiðSe-SchXÞðH2OÞ ꢄþ þ Clꢁ
X
Detection of antimicrobial activity
2
2
: -H; -F; -Br; -CH3
The bacterial subcultures chosen were Listeria monocytogenes
4b ATCC19115, Staphylococcus aureus ATCC25923, Escherichia coli
ATCC1280, Salmonella typhi H NCTC-901.8394, Brucella abortus
(A.99, UK-1995) RSKK03026, Staphylococcus epidermis sp., Micro-
coccus luteus ATCC9341, Shigella dysenteria type 10 NCTC 9351,
Pseudomonas putida sp., Bacillus cereus RSKK-863. An antifungal
susceptibility test was used by Candida albicans Y-1200-NIH, To-
kyo. The ligands and the complexes were tested for their antimi-
crobial activity by the well-diffusion method. Each ligand and
complex were kept dry at room temperature and dissolved
½NiðSe-SchClÞðH2OÞClꢄ $ ½NiðSe-SchClÞðH2OÞClꢄ
IR, UV–Visible and NMR spectra of ligands
Table 2 summarizes the main IR and UV–Visible bands of the
azomethine (Schiff bases) and their Ni(II) complexes. 2-Aminose-
lenophene-3-carbonitrile ([Se-NH2]) spectra show three medium
broad band in the region 3228–3433 cmꢁ1 and another band at
(0.25
l
g/mL) in DMF. DMF was used as solvent and also for control.
2197 cmꢁ1, assigned to the
tNH2 and tCN groups, respectively
It was found to have no antimicrobial activity against any of the
tested organisms. 1% (v/v) of 24 h broth culture containing 106
CFU/mL was placed in sterile Petri dishes. Mueller- Hinton Agar
(MHA) (15 mL) kept at 45 °C was then poured into the Petri dishes
and allowed to solidity. Then 6 mm diameter wells were punched
carefully by using a sterile cork borer and were entirely filled with
[20]. The IR showed the disappearance of the NH2 bands together
with the presence of CH@N band. IR bands of azomethines in the
1553–1567 cmꢁ1, 3387–3467 cmꢁ1, 2197–2225/1601–1651 cmꢁ1
regions are characteristic of
respectively [18,20]. The bands in the 2857–2917 cmꢁ1 and
3058–2979 cmꢁ1 regions may, respectively, ascribe to
CHaliphatic
t(CH@N), t(OH), and t(CN)/t(Se-C),
t

N. Sarı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 60–67
63
Fig. 1. UV–Visible spectra and color change imaging of [Ni(Se-SchCl)(H2O)Cl] in between pH = 2–10.
Table 1
Analytical data and some of the physical properties of synthesized molecules.
Compound
Chemical formula, Mw
Color
l
eff, BM
Elemental analysis Found (calculated) %
C
H
N
Ni
[Se-NH2]
C10H12N2Se
(238.96)
Brown
50.77
(50.21)
59.44
(59.48)
56.56
(56.51)
53.93
(54.04)
47.96
(47.86)
59.01
(58.15)
43.45
(44.72)
42.89
(43.11)
43.40
(43.32)
37.45
(38.24)
41.33
(42.01)
4.36
(5.02)
4.12
(4.66)
3.76
(4.15)
3.53
(3.97)
3.16
(3.55)
4.49
(4.20)
3.99
(4.16)
3.88
(3.59)
3.20
(3.18)
3.64
(3.18)
4.33
(3.70)
12.32
(11.71)
8.14
(8.16)
7.82
(7.76)
7.39
(7.42)
6.61
(6.64)
7.69
(7.84)
6.36
(6.13)
6.06
(5.91)
6.00
117–118
Cream
172–174
Yellow
221–223
Yellow
232–234
Yellow
243–245
Brown
201–203
Green
2.72
Clear green
2.97
Green
3.74
[Se-SchH]
C
17H16N2SeO
(342.96)
17H15N2SeOF
(360.95)
17H15N2SeOCl
(377,46)
17H15N2SeOBr
(421.86)
17H15N2SeOCH3
[Se-SchF]
C
[Se-SchCl]
C
[Se-SchBr]
C
[Se-SchMe]
C
(356.96)
C17H19N2SeO2ClNi
(456.10), 288
C17H17N2SeO2FClNi
(473.20), 256
C17H15N2SeOCl2Ni
(470.96), 280
C17H17N2SeO2BrClNi
(533.36), 273
C18H18N2SeOClNi
(485.5), 235
[Ni(SeSchH)(H2O)2]Cl
[Ni(SeSchF)(H2O)2]Cl
[Ni(SeSchCl)(H2O)Cl]
[Ni(SeSchBr)(H2O)2]Cl
[Ni(SeSchMe)(H2O)2]ClꢃH2O
13.70
(12.71)
12.40
(12.26)
12.30
(12.32)
10.74
(10.87)
12.30
(11.95)
(5.94)
5.20
(5.25)
5.58
Green
2.69
Green
2.31
(5.76)
and
t
CHaromatic vibrations [17]. The 1H NMR spectrum of 2-Ami-
and t(ACH@N) vibrations [22,23]. A shift at t(CN) bands is not
noselenophene-3-carbonitrile, recorded in CDCl3 showed the fol-
lowing signals: -NH2 proton at 4.80 ppm (t, 2H), aa0(cyclo) proton
at 2.56–2.67 ppm (m, 4H), bb0(cyclo) proton at 1.60–1.68 ppm (m,
4H), c(cyclo) proton at 1.77–1.87 ppm (d, 2H). The 1H NMR spectrum
of the ligands shows the following signals: = aa0(cyclo) proton at
2.76–2.91 ppm (s, 4H), bb0(cyclo) at 1.60–1.75 ppm (s, 4H), c(cyclo)
proton at 1.86–1.93 ppm (d, 2H) phenyl as multiplet at 6.18–
6.98 ppm (m, 4H or 3H), ACH@NA at 8.23–8.30 ppm (s, 2H) and
the peak at 11.85–11.90 ppm (s, 1H) is attributable to the phenolic
AOH group present in the aldehyde moiety. The 13C NMR spectra
data of the Schiff bases (Table 3) are in accordance with the pro-
posed structures. The electronic spectra of the Schiff bases in
DMSO show bands ca. 420 nm are attributed to the azomethine
seen in the complexes, lending further support to the suggestion
that the atoms N in the ACN do not coordinate with the metal
ion [18] (Scheme 1(3)). The azomethine in the IR spectra of the
complexes are in the 1574–1609 cmꢁ1 range, somewhat lower
than observed for the free ligands. These indicate that the azome-
thine nitrogen is coordinated to metal ion [18,21]. Assignment of
the proposed coordination sites is further supported by the appear-
ance of medium bands at 420–455 cmꢁ1 which could be attributed
to mMAN respectively. In addition, the Nickel (II) complex shows a
band at 483–490 cm–1 attributed to NAO frequency.
The electronic absorption spectra of the Ni (II) complexes were
recorded at 298 K. The absorption region, band assignment and the
proposed geometry of the complexes are given in Table 2. The elec-
tronic spectra of the Ni (II) complexes shows two d–d bands at ca.
690 and 380 nm, respectively, the position of which is indicative of
n ? pꢀ
transition. The bands at higher energies (253–
398 nm) are associated with the benzene
(CH@N)
p ? r ?
pꢀ and rꢀ tran-
sition [20,21].
tetrahedral stereochemistry, assigned to 3T1(F) ? 3T2, (
m
2) and
3T1(F) ? 3A2, (
m
3) transitions. More intense bands in the d-d elec-
tronic spectra and high magnetic moment values support a tetra-
hedral configuration for the Ni (II) complexes [18].
IR, UV–Visible spectra, thermal analyses (TGA/DTA) and magnetic
susceptibilities of Nickel(II) complexes
The TGA curves of the Ni (II) complexes are similar in the 50–
400 °C range; the loss in weight is equivalent to degradation of
the complexes. A weight loss (ca. 4.0%) between 55 and 155 °C
for the [Ni(Se-SchMe)(H2O)2]ClꢃH2O complex is assigned to the loss
The IR assignments for the important bands of the complexes
are given in Table 2. The bands in the 2217–2225 cmꢁ1 and
1574–1609 cmꢁ1 region may be, respectively, ascribed to
t(CN)

64
N. Sarı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 60–67
Table 2
Important IR vibration frequencies (cmꢁ1) and UV–Visible spectrum values (nm) of synthesized molecules.
Compound
m
(OAH)
m
(CACN)
m
(SeAC)
m(CAH)aliphatic
m(CAH)aromatic
m(NH2)asym, sym m(CH@N) m(MAO), m(MAN) kmax (e)
n ? pꢀ(CAN) p
?
pꢀ
d ? d
(C@N)
[Se-NH2]
–
2922–2837
–
3433, 3336, 3228
–
–
–
1567
-
-
1562
–
–
1553
–
–
1556
–
261 (3580)
266 (3399)
298 (3875)
288–415 (3800–3900),
420–446 (3529–3413)
2197
1624
3467
2214
1601
3455
2219
1632
3461
2225
1638
3444
2225
1651
3387
2219
1620
3426
2217
1602
3433
2218
1602
3433
2224
1602
3405
2225
1623
[Se-SchH]
2917–2849
3064
[Se-SchF]
2922–2854
3064
263 (3055), 302 (3342),
400 (3926), 441 (3441)
[Se-SchCl]
2917–2846
3063–2993
256 (2758), 306 (1256)
417 (2728), 436 (3800)
[Se-SchBr]
2922–2849
3058–2990
253 (2707), 304 (1262)
417 (2328)
[Se-SchMe]
2917–2849
3058–2979
–
260 (2912), 308 (3854)
398 (3214), 441 (3546)
1567
[Ni(SeSchH)(H2O)2]Cl
[Ni(SeSchF)(H2O)2]Cl
[Ni(SeSchCl)(H2O)Cl]
[Ni(SeSchBr)(H2O)2]Cl
2916–2846
Overlap
–
401 (2216); 406 (2314)
549 (2,27)
1581
434/490
–
1574
434/490
1560
441/483
2923–2853
Overlap
295(1307); 407 (1989)
606(987)
2916–2846
2993–3063
292 (2216); 408 (2314)
536 (227)
2923–2846
Overlap
1609
420/490
290 (972); 407(2496)
598 (4,86)
[Ni(SeSchMe)(H2O)2]ClꢃH2O 3384
2916–2846
overlap
1581
455/490
295 (908); 408 (2107)
544 (12,94)
2217
1602
Table 3
1H NMR and 13C NMR spectral data in ppm (CDCl3) of amine and azomethines.
Comp
1H NMR
13C NMR
ANH2/AOH
1, 10
2, 20
HC@N
HC@N
ArAC1-10
[Se-NH2]
4.80/–
–
8.3
8.20
8.20
8.23
8.24
2.56–2.67
2.77–2.91
2.79–2.88
2.77–2.91
2.76–2.90
2.76–2.91
1.60–1.68
1.7
1.65–1.74
1.65–1.74
1.65–1.75
1.7
–
27.97,26.38,31.92,128.24,93.68
[Se-SchH]
[Se-SchF]
[Se-SchCl]
[Se-SchBr]
[Se-SchMe]
–/11.90
–/11.85
–/11.85
–/11.9
–/11.9
161.16
159.59
159.39
159.29
161.10
31.98,26.86,30.00, 142.60,112.72,161.02, 118.47,132.58,132.58,134.36
32.53,26.83,30.00, 143.53, 113.43, 154.13, 118.25, 118.15, 118.97, 121.40
32.53, 26.83,30.01,143.63, 113.52, 124.25 119.19,119.28, 131.26, 134.00
31.95, 26.83,30.01,143.63, 111.08, 119.92 115.49,119.68, 134.30, 136.76
31.98, 26.87,29.99,142.36, 112.47, 128.75 118.11,117.46, 132.41, 135.46
CN
(1)
X
(2)
(2)
(8)
(4)
(4)
(5)
X: -H, -F, -Cl, -Br, -CH3
(3)
(9)
N CH
Se(6)
(7)
(1)
HO
of hydrated water. For other the Ni (II) complexes, the first weight
loss (8.5–9%) in the 50–200 °C range may be accounted for in terms
of the loss of coordinated water [24]. The exothermic peaks lying at
ca. 200–350 °C for all of the complexes were due to melting. This is
followed by broad and stronger exothermic peaks, corresponding
to decomposition of the complexes. The residues at the end of
the decomposition for all of the complexes were found to be
NiCl2 + SeCO3 + residues (Table 4).
ited varying degree of inhibitory effects on the growth of different
tested strains (Table 5). All the compounds were active against Br.
abortus except [Ni(Se-SchBr)]. Br. abortus is a gram-negative bacte-
rium that causes premature abortion of a cattle fetus. What makes
this bacterium so dangerous is that it can be transferred from an
animal to a human host. In humans, this disease causes both acute
and chronic symptoms, but can be treated with antibiotics. This re-
search indicates that Schiff bases of 2-Aminoselenophene-3-carbo-
nitrile and their Ni (II) complexes are active against Br. abortus
(Table 5). Synthesized Schiff bases were inactive against S.typhi
H, whereas their complexes were active except [Ni(Se-SchBr)]. In
general, the metal complexes are more potent bactericides than
the ligand. This enhancement in activity may be explained on the
basis of chelation theory [25]. Chelation reduces the polarity of
the metal ion. Hence, a complex has lipophilic character, and in-
Biological activity of Schiff bases and their complexes
The ligands and their Ni (II) complexes were screened for anti-
microbial activity in DMF solvent as a control substance. The com-
pounds were tested with the same concentrations in DMF solution
(0.08 lg/mL). All the synthesized compounds and antibiotic exhib-

N. Sarı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 60–67
65
Table 4
TGA results of Ni (II) complexes.
Compound
Thermally decomposed
Ti
T1/2
Tf
Loss of mass at 900 °C (wt.%)
Residue formulae Found (calculated) %
[Ni(Se-SchH)(H2O)2]Cl
[Ni(Se-SchF)(H2O)2]Cl
[Ni(Se-SchCl)(H2O)Cl]
[Ni(Se-SchBr)(H2O)2]Cl
[Ni(SeSchMe)(H2O)]ClꢃH2O
50
70
80
44
1/2NiCl2 + C + 1/2NiO + SeCO3
56 (57.7)
1/2NiCl2 + 1/2NiF2 + SeCO3
68 (68.5)
NiCl2 + SeO + C
51 (50.1)
1/2NiCl2 + 4C + 1/2NiBr2 + SeCO3
69 (69.8)
1/2NiCl2 + 3C + 1/2NiCO3 + SeCO3
62 (61.3)
150
65
160
85
180
90
35
39
31
38
155
175
160
190
200
155
55
Ti: temperature of inital degradation; T1/2: temperature of half degradation.
Tf: temperature of finally degradation.
Table 5
Antimicrobial activity of studied molecules (0.25
lg/ml) and standard reagents (diameter of zone inhibition (mm)).
Schiff bases
Ni(II) complexes
DMF control
1
2
3
4
5
6
7
8
9
10
11
Sh.dys. typ 10
P. putida
S. typhi H
Br. Abortus
L. monocytogenes 4b
B. cereus
S. aureus
S. epidermis
M. luteus
E. coli
C. albicans
–
–
–
–
–
–
7
–
–
–
–
12
15
–
15
–
–
13
–
12
–
–
–
10.5
–
–
–
10
–
–
13.5
–
–
–
6.5
7
10
–
–
12
–
14
–
–
–
–
11
14.5
–
15
10
–
13
–
–
–
–
8
11
-
11
15
–
–
–
–
–
18
14
16
–
–
12
–
15
16
15
21
12
14
12
14
13
–
14
15
16
14
–
15
–
–
–
13
–
–
–
–
–
–
Gram (+)
13
14
15
–
15
-
14
15
15
–
–
–
–
–
–
–
–
–
–
–
Gram (ꢁ)
17
16
12.5
12.5
–
–
–
–
19
Antifungal
20
Positive control
K30
SXT25
AMP10
AMC30
S. aureus
P. putida
E. coli
S. typhi H
Br. abortus
C. albicans
–
–
–
–
20
25
24
30
30
–
14
18
8
15
–
25
18
10
14
–
20
17
11
19
–
–
–
–
–
–
SXT25, Sulphamethoxazol, 25 lg;
AMP10, Ampicillin 10
lg;
NYS100, Nystatin 100
lg;
SCF, Sulbactam (30 lg)
NYS100
(1) (Se-NH2), (2) (Se-SchH), (3) (Se-SchF), (4) (Se-SchCl), (5) (Se-SchBr), (6) (SeSch-CH3), (7) [Ni(Se-SchH)], (8) [Ni(Se-SchF)], (9) [Ni(Se-SchCl)], (10) [Ni(Se-SchBr)], (11) [Ni(Se-
SchMe)].
Fig. 2. Imaging of the couple work of antimicrobial affect of (Se-SchCl) (1) and [Ni(Se-SchCl)(H2O)Cl] complexes (2) against P. putida (A), M. luteus (B), C. albicans (C).
Table 6
creases the interaction between the metal ion and the lipid is fa-
Transmittances of the [Ni(Se-SchCl)(H2O)Cl] complexes in between pH = 2–10.
vored. This lead to the breakdown of the permeability barrier of
pH
Color
Wavenumber (nm), absorbans
the cell, resulting in interference with the normal cellular pro-
cesses [26]. [Ni(Se-SchCl)] complexes were observed to be the
most active against Sh.dys. typ 10 (Fig. 2). It was interesting to note
that methyl and chlorine groups in the metal chelates had an im-
pact on the bactericidal activity. Furthermore, the antibacterial
activity of these compounds was also compared with five commer-
cial antibiotics, namely Sulfamethoxazol, Ampicillin, Nystatin and
p
?
pꢀ
n?pꢀ
LMCT
2
4
5
7
Lemon-yellow
Lemon-yellow
Orange
Red
Dark-red
307 (1.35)
306 (1.05)
309 (0.63)
310 (0.65)
311 (1.02)
416 (3.35)
417 (2.59)
416 (1.97)
416 (0.99)
415 (1.02)
–
–
–
510 (1.19)
504 (0.62)
10

66
N. Sarı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 60–67
Fig. 3. (A) Selected bond lengths (Å) for IX. Hydrogens are omitted for clarity, except for the one involved in hydrogen bonding. (B) Simulated TD-DFT spectrum for IX. LMCT
and
pꢀ character dominates the transitions.
p
?
bonding interaction between nitrile and water for the more stable
conformer (Fig. 3A). Two conformers differ in the y-axis orientation
Table 7
Ligand environment and mulliken atomic spin densities on Ni(II)-center of complexes
studied in this work.
of the nitrile group and interconvert via change of the dihedral
x.
Common features of the emission process are reproduced and
assignments are in good agreement with the available data
(Fig. 3B). Calculated spin densities given in Table 7 shows that
the triplet ground states for all Ni (II) complexes bear two unpaired
electrons residing in Ni d-based orbitals, consistent with the para-
magnetic character observed experimentally.
Species Complex
X1 X2 qNi
VII
VIII
IX
[Ni(SeSchH)(H2O)2]Cl H2O H 1.63
[Ni(SeSchF)(H2O)2]Cl H2O F 1.62
[Ni(SeSchCl)(H2O)Cl] Cl Cl 1.63
[Ni(SeSchBr)(H2O)2]Cl H2O Br 1.62
[Ni(SeSchCl)(H2O)2]Cl H2O Cl 1.62
X
IX0
The interesting observation of failure to obtain [Ni(SeSchCl)-
(H2O)2] (IX0) well agrees with the computed thermodynamic
stability difference between the Ni-chloro and Ni-aqua complexes
IX0 ! IX þ H2O
D
Erxn ¼ ꢁ111 kcal=mol
ð1Þ
Sulbactam. It was seen that the synthesized compounds were
effective as the antibiotics mentioned.
Conclusions
The spectral studies for [Ni(Se-SchCl)(H2O)Cl] complexes in between
pH = 2–10
Coordination structures of Ni (II) complexes have been deter-
mined by spectral analyses. All of Ni (II) complexes have tetrahe-
dral structure. The superior bactericide [Ni(Se-SchCl)(H2O)Cl] (IX)
exhibits pH-dependent color and has [ML(OH2)Cl] coordination
unlike the rest. Structural and electronic properties of all com-
plexes were further studied computationally. Thermodynamic sta-
bility of IX relative to its hypothetical analog [ML(OH2)2]Cl(IX0) well
correlates with the experiment. TD-DFT spectra featured transi-
As shown in Table 6, the spectral studies were carried out at
room temperature in the wavelength region of 340–700 nm. The
absorption spectra of the [Ni(Se-SchCl)(H2O)Cl] complexes under
different pH are as shown that Fig. 2. [Ni(Se-SchCl)(H2O)Cl] com-
plexes can change its color from yellow to dark red along with
the pH value decreasing. Between pH = 5 and pH = 7, [Ni(Se-
SchCl)(H2O)Cl] complexes gave rise to color change from yellow2
to red in DMF which was clearly visible to the naked eye (Fig. 1B).
tions mainly of LMCT and
p ? p character, and also closely
matched the experimental values. We believe that, this novel bac-
tericide, Ni(SeSchCl)(H2O)Cl], can find practical applications in
chemical, environmental and biological systems.
Theoretical assessment, calculated UV-spectrum and thermodynamic
details of tetrahedral Ni(II) complexes
Acknowledgment
This work was supported by the Gazi University Research Fund
(Project number: 05/2010-74).
All complexes exhibit triplet ground state that lie 10–14 kcal/
mol below the singlet. Singlet complexes assume the square planar
geometry, whereas triplets are tetrahedral. IX has two conformers
that lie 2.5 kcal/mol apart, which is attributable to the hydrogen
Appendix A. Supplementary material
2
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2012.12.078.
For interpretation of color in Fig. 2, the reader is referred to the web version of
this article.

N. Sarı et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 60–67
67
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