Synthesis, crystal structures, antimicrobial activities, and DFT calculations of two new azido nickel(II) complexes

Article abstract of DOI:10.1080/00958972.2014.936859

Two new complexes, [Ni(HL¹)(N₃)(μ _1,1N₃)]₂ (1) [HL¹: NC ₅H₄CH₃C=NNH (C=O) NH₂] and [Ni(L²)N₃] (2) [HL²: NC₅H ₄HC=N NH(C=S)NH₂], have been synthesized by reaction of Ni(OAC)₂·4H₂O and sodium azide with HL¹ and HL² and characterized by elemental analysis, FT-IR, and UV-vis spectral studies. Single-crystal X-ray diffraction reveals that 1 is dinuclear with nickel(II) in an octahedral environment of NNO donors of HL¹, two nitrogens of azide bridges and one nitrogen of terminal azide; 2 is mononuclear containing nickel(II) in a distorted square-planar environment of NNS donors of HL² and one terminal azide. The structures of 1 and 2 have been optimized by density functional theory. The results of antimicrobial activities of ligands, 1 and 2 demonstrated that HL² and 2 have good antimicrobial activity in contrast with HL¹ and 1, related to the presence of sulfur donor in HL². 2014

Full text of DOI:10.1080/00958972.2014.936859

This article was downloaded by: [B. SHAABANI]
On: 04 August 2014, At: 12:32
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Coordination Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gcoo20
Synthesis, crystal structures,
antimicrobial activities, and DFT
calculations of two new azido nickel(II)
complexes
a
a
b
Behrouz Shaabani , Ali Akbar Khandar , Michal Dusek , Michaela
b
c
d
Pojarova , Miguel Anxo Maestro , Rabindranath Mukherjee &
a
Farzaneh Mahmoudi
a
Faculty of Chemistry, Department of Inorganic Chemistry, Tabriz
University, Tabriz, Iran
b
Institute of Physics of the ASCR, v.v.i., Prague, Czech Republic
Click for updates
c
Departamento de Química Fundamental, Universidade da
Coruña, Acoruña, Spain
d
Department of Chemistry, Indian Institute of Technology Kanpur,
Kanpur, India
Accepted author version posted online: 30 Jun 2014.Published
online: 31 Jul 2014.
To cite this article: Behrouz Shaabani, Ali Akbar Khandar, Michal Dusek, Michaela Pojarova, Miguel
Anxo Maestro, Rabindranath Mukherjee & Farzaneh Mahmoudi (2014) Synthesis, crystal structures,
antimicrobial activities, and DFT calculations of two new azido nickel(II) complexes, Journal of
Coordination Chemistry, 67:12, 2096-2109, DOI: 10.1080/00958972.2014.936859
To link to this article: http://dx.doi.org/10.1080/00958972.2014.936859
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“
Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or

howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Journal of Coordination Chemistry, 2014
Vol. 67, No. 12, 2096–2109, http://dx.doi.org/10.1080/00958972.2014.936859
Synthesis, crystal structures, antimicrobial activities, and
DFT calculations of two new azido nickel(II) complexes
BEHROUZ SHAABANI*†, ALI AKBAR KHANDAR†, MICHAL DUSEK‡,
MICHAELA POJAROVA‡, MIGUEL ANXO MAESTRO§,
RABINDRANATH MUKHERJEE¶ and FARZANEH MAHMOUDI†
†
Faculty of Chemistry, Department of Inorganic Chemistry, Tabriz University, Tabriz, Iran
Institute of Physics of the ASCR, v.v.i., Prague, Czech Republic
Departamento de Química Fundamental, Universidade da Coruña, Acoruña, Spain
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, India
‡
§
¶
(Received 30 September 2013; accepted 18 May 2014)
1
2
Structure and labeling diagram for [Ni(HL )(N
3
)(µ1,1
N
3
)]
2
(1).
3
View of the presence of intermolecular H-bonds in [Ni(L )(N )] (2).
1
1
Two new complexes, [Ni(HL )(N
3
)(μ1,1
N
3
)]
2
(1) [HL : NC
5
H
4
CH
3
C=NNH (C=O) NH
2
] and [Ni
2
2
(
L )N
3
] (2) [HL : NC
5 4 2
1 2
H HC=N NH(C=S)NH ], have been synthesized by reaction of Ni
(
OAC)
2
·4H O and sodium azide with HL and HL and characterized by elemental analysis, FT-IR,
2
and UV–vis spectral studies. Single-crystal X-ray diffraction reveals that 1 is dinuclear with nickel
1
(
II) in an octahedral environment of NNO donors of HL , two nitrogens of azide bridges and one
nitrogen of terminal azide; 2 is mononuclear containing nickel(II) in a distorted square-planar envi-
2
ronment of NNS donors of HL and one terminal azide. The structures of 1 and 2 have been opti-
mized by density functional theory. The results of antimicrobial activities of ligands, 1 and 2
2
1
demonstrated that HL and 2 have good antimicrobial activity in contrast with HL and 1, related to
2
the presence of sulfur donor in HL .
Keywords: Semicarbazone and thiosemicarbazone Schiff base; Azido ligand; Nickel(II) complex;
X-ray structure; Antimicrobial activity
*
Corresponding author. Email: shaabani@tabrizu.ac.ir
©
2014 Taylor & Francis

Azido nickel(II) complexes
2097
1. Introduction
Schiff bases have played a key role as chelating ligands in main group and transition metal
coordination chemistry, due to their ease of synthesis and their structural versatility associ-
ated with diverse applications [1–5]. Schiff bases are important intermediates for synthesis
of some bioactive compounds [6–8]. Semi and thiosemicarbazones are of interest because
of their chemistry and potentially beneficial biological, antitumor, antibacterial, antiviral,
and antimalarial, activities [9–18]. Semi and thiosemicarbazones belong to the family of
Schiff bases which can coordinate to the metal either as neutral or deprotonated ligands
through two or three donors [11, 15, 19, 20]. Pseudohalides can form bridging complexes
−
−
−
with transition metals where N , NCS , NCO coordinate in end-to-end and end-on bridg-
3
ing modes. Azide is a versatile bridging ligand that can link metal ions in μ-1,1, μ-1,3
,
μ-1,1,3, and other modes, and ferromagnetic and antiferromagnetic interactions can be medi-
ated through different modes [21–30]. We herein report the synthesis, characterization, and
X-ray crystal structure of two azido nickel(II) complexes based on semi and thiosemicarba-
zone Schiff base ligands. Antimicrobial activities of ligands and complexes are reported.
2
2
. Experimental
.1. Materials and general methods
All chemicals and solvents were of reagent grade and used as received from Merck or
Fluka. Microanalyses were carried out using a Heraeus CHN–O– Rapid analyzer. Melting
points were measured on an Electrothermal 9100 apparatus and are uncorrected. Infrared
(
4
IR) spectra were recorded on a FT-IR Spectrometer Bruker Tensor 27 from 4000 to
00 cm using KBr pellets. Electronic spectra were recorded on a Shimadzu UV-1650 PC
−
1
spectrophotometer at 300 K in DMSO.
2
2
.2. Synthesis of Schiff base ligands
.2.1. Methyl 2-pyridyl ketone semicarbazone (HL ). As seen in scheme 1, HL
1
1
[
11–14] was prepared by condensation of methyl 2-pyridyl ketone with semicarbazide
hydrochloride. 0.8 g (7 mM) of semicarbazide hydrochloride was added to a solution of
methyl 2-pyridyl ketone (0.85 mL, 7 mM) in 20 mL of methanol in a round-bottom flask
under continuous stirring. The mixture was refluxed for 5 h to produce a white suspension.
The final reaction mixture was filtered off and the filtrate was kept at room temperature for
1
0 h. The resulting white precipitate (m.p. 206 °C) was filtered off, washed with methanol,
and dried in air. Yield: 1.30 g (5 mM, 80%), Anal. Calcd for C H N O: C, 44.72; H, 4.66;
8
10 4
1
Scheme 1. Reaction for the synthesis of HL .

2
098
B. Shaabani et al.
−
1
N, 26.08. Found: C, 44.65; H, 4.56; N, 26.08. Characteristic IR absorptions (cm ): 3431m,
ν(NH ); 3192m, ν(NH); 1578s, ν(C=N); 1105s, ν(NN); 1685s, ν(C=O).
2
2
2
2
[
.2.2. Pyridine 2-carbaldehyde thiosemicarbazone (HL ). The chemical scheme of HL
2
15, 16] is shown in scheme 2. For synthesis of HL , hot ethanolic solution of thiosemicar-
bazide (0.8 g, 7 mM) and ethanolic solution of pyridine-2-carbaldehyde (0.85 mL, 7 mM)
were mixed in the presence of a few drops of concentrated HCl with constant stirring. This
mixture was refluxed at 100 °C for 5 h. The reaction mass on cooling gave cream-colored
crystals, which were filtered off, washed with ethanol, and dried in air (yield: 1.40 g (87%),
m.p. 185 °C). Anal. Calcd for C H N S: C, 30.01; H, 2.85; N, 20.01. Found: C, 30.23; H,
7
8 4
−
1
2
1
.98; N, 20.32. Characteristic IR absorptions (cm ): 3424m, ν(NH ); 3185m, ν(NH);
604s, ν(C=N); 1112s, ν(N N); 844s, 1246s, ν(C=S).
2
_
Caution! Metal azido compounds are potentially explosive. Only a small amount of mate-
rial should be prepared and should be handled with prudence.
2
2
.3. Synthesis of complexes
1
.3.1. [Ni(HL )(N )(μ N )] (1). Synthesis of complexes in the form of crystalline mate-
3
1,1 3 2
rial was performed by slow diffusion in an H-shaped tube already described [31–34]. In this
method, methyl 2-pyridyl ketone semicarbazone (0.2 mM) was placed in one arm of a
branched tube and Ni(OAC) ·4H O (0.4 mM) and sodium azide (1.2 mM) in the other.
2
2
Methanol was carefully added to fill both arms, the tube sealed and the ligand-containing
arm immersed in a bath at 60 °C while the other was at ambient temperature. After three
days, light-green crystals had deposited in the cooler arm, which were filtered off, washed
with acetone and ether, and air dried; yield: 30%, decomposed at 160 °C. Anal. Calcd for
C H N Ni O : C, 30.02; H, 3.21; N, 43.73. Found: C, 29.91; H, 3.11; N, 43.62. Charac-
1
6
20 20
2 2
−
1
teristic IR absorptions (cm ): 3412m, ν(NH ); 3162m, ν(NH); 1591s, ν(C=N); 1189s,
ν(NN); 1666s, ν(C=O); 2061s, ν(N ).
2
−
3
2
2
.3.2. [Ni(L )(N )] (2). For synthesis of 2, 0.2 mM HL, 0.8 mM Ni(OAC) ·4H O, and
3
2
2
1
.2 mM sodium azide in methanol were used. After two days, dark brown crystals (decom-
posed at 150 °C) had formed which were isolated, filtered off, washed with acetone and
diethyl ether, and dried in air. Yield: 0.12 g (30%). Anal. Calcd for C H N NiS: C, 30.01; H,
7
7 7
−
1
2
3
.50; N, 35.01. Found: C, 30.23; H, 2.76; N, 35.25. Characteristic IR absorptions (cm ):
453,3411m, ν(NH ); 3189m, ν(C=N); 1168s, ν(N N); 809m, ν(C=S); 2052s, ν(N ).
_
−
2
3
2
.4. X-ray crystallography
1
X-ray diffraction data of [Ni(HL )(μ N )(N )] (1) were collected at 163 K with a
1
,1
3
3 2
four-circle diffractometer (Gemini of Oxford Diffraction, Ltd) using a sealed X-ray tube
2
Scheme 2. Reaction for the synthesis of HL .

Azido nickel(II) complexes
2099
Table 1. Crystal data and structure refinement parameters for 1 and 2.
1
2
Chemical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
C
16
H
20
N
20Ni
2
O
2
C
7 7 7
H N NiS
641.90
164 K
Monoclinic
P2 /c
11.1326(3)
14.2647(3)
8.4223(2)
90
279.96
100 K
Monoclinic
P2 /n
3.853(2)
16.766(3)
15.325(4)
90
1
1
β (°)
γ (°)
Volume (Å )
Z
ρ calculated (g cm
μ (mm
106.904(3)
90
1279.70(6)
2
1.666
1.531
90.108(5)
90
990.0(6)
4
1.878
2.151
3
−
3
)
−1
)
T
min, Tmax
0.723, 0.896
24.710
0.753, 0.879
28.400
θ max (°)
Final R indices [I > 2σ(I)]
Final R indices (all data)
S
0.0209(2001)
0.0522(2166)
1.032
0.0462(2002)
0.1840(2418)
1.146
with MoKα graphite-monochromated radiation (0.7107 Å). The diffracted beam was
detected with the Atlas charge-coupled device (CCD) detector. Standard data collection
strategy of Crysalis [35] was used for data collection. The crystal structures were solved by
SHELXS-97 and refined with SHELXL-97. The materials for publication were prepared by
using publCIF.
2
For [Ni(L )(N )] (2), a suitable single crystal was mounted on a Hampton Research Cryo-
3
Loop with the help of a Stemi 2000 stereomicroscope equipped with Carl Zeiss lenses. Data
were collected on a Bruker X8 Kappa APEX II CCD area-detector diffractometer (Mo Kα
graphite-monochromated radiation, 0.71073 Å) controlled by the APEX2 software package
and equipped with an Oxford Cryosystems Series 700 cryostream monitored remotely using
the software interface Cryopad. Images were processed using the software package SAINT,
and data were corrected for absorption by the multi-scan semi-empirical method
implemented in SADABS. The structures were solved by direct methods implemented in
2
SHELXS-97 and refined from successive full-matrix least-squares cycles on F using
SHELXL-97. All non-hydrogen atoms were successfully refined using anisotropic
displacement parameters, including those from crystallization solvent molecules (water and
n-hexane).
Crystallographic data and details of the data collection and structure refinements of 1 and
2
are listed in table 1.
2
.5. Antimicrobial activity
The free ligands and metal complexes were screened for antimicrobial activities against the
bacteria (Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Erwinia carotovora) and
fungi (Candida kefyr, Candida krusei, Aspergillus niger) by the disk diffusion method as
Gram negative, Gram positive, and fungal organisms, respectively. The culture media (Miller
Hinton agar for bacteria, Sabouraud dextrose agar for fungi) were poured into sterile plates
and micro-organisms were introduced on the surface of agar plates individually. Blank sterile
disks of 6.4 mm diameter were soaked in a known concentration of the test compounds.

2
100
B. Shaabani et al.
Then the soaked disks were implanted on the surface of the plates. A blank disk was soaked
in DMSO and implanted as negative control on each plate along with the standard drugs.
The plates were incubated at 37 °C (24 h) and 27 °C (48 h) for bacterial and fungal strains,
respectively. The MIC for each tested substance was determined by macroscopic observation
of microbial growth. It corresponds well with the lowest concentration of the tested substance
where microbial growth was clearly inhibited.
2.6. Computational details
The geometry of 1 and 2 has been optimized by using the B3LYP density functional model
36, 37]. In these calculations, we used the 3-21G* basis set for carbon and hydrogen
[
atoms, whereas the 6-31G* basis set was used for nitrogens. For nickel atoms, the
LanL2DZ valence and effective core potential functions were used [38, 39]. All DFT calcu-
lations were performed using the Gaussian 98 R-A.9 package [40]. X-ray structures were
used as input geometries when available.
3
3
. Results and discussion
.1. IR spectra
IR spectral bands of ligands, 1 and 2 are presented in table 2. Formations of Schiff bases
−
1
1
2
have been confirmed by sharp bands at 1578 and 1604 cm , respectively, for HL and HL ,
−
1
1
indicating presence of an imine functionality. The band at 1685 cm in HL has significant
−
1
contribution from C=O stretching vibration. A medium band at 3192 cm is assigned to
ν(N–H) of semicarbazone. Most semicarbazone ligands reveal keto–enol tautomerism in
coordination to metal ions, coordinating as neutral or deprotonated forms [11, 13]. In 1, the
−
1
presence of a band at 3192 cm corresponding to ν(N–H) vibration indicates the HL is coor-
−
1
dinated in the keto form. Observation of a band at 1666 cm related to C=O stretch supports
2
the keto form [20] of the HL in 1. HL can exhibit thione–thiol tautomerism since it contains
a thioamide–NH–C=S group. The ν(S–H) band at 2565 cm is absent in IR spectra of
ligand [10]. On coordination of the azomethine nitrogen, the ν(C=N) at 1578 and 1604 cm
−1
−
1
−
1
shifts to 1591 and 1638 cm for 1 and 2 [20]. The spectra of 1 and 2 exhibit a systematic
−
1
shift in the position of ν(N–N) bands at 1189 and 1168 cm for 1 and 2, respectively, due to
increase in bond strength, which again confirms coordination of azomethine nitrogen to
−1
2
nickel(II) [13, 41, 42]. The band at 844 cm for ν(C=S) in HL is shifted to lower
wavenumber 809 cm for 2, which indicates coordination via sulfur of thiosemicarbazone
−
1
−
1
Table 2. IR spectra (cm ) assignment for ligands, 1, and 2.
Compound
ν
NH2
ν
NH
νC=O or νC=S
ν
C=N
ν
N–N
ν
N3
1
HL
HL
1
2
3431
3424
3412
3411
3192
3185
3162
–
1685
844
1666
809
1578
1604
1591
1638
1105
1112
1189
1168
–
–
2
2061
2052

Azido nickel(II) complexes
2101
1 2
Figure 1. The electronic absorption spectra of HL and 1 (a), HL and 2 (b).
−1
[
10]. Complexes 1 and 2 exhibit strong bands at 2061 and 2052 cm corresponding to
ν(N ) of the coordinating azide [24–26, 42, 43].
3
3
.2. Electronic spectra
As shown in figure 1, electronic spectra of ligands show absorption maxima at 260 and
1
2
2
95 nm for HL and 255 and 350 nm for HL , attributed to intra-ligand π→π* transitions of
the pyridine ring and azomethine group and also a sharp band at 300 nm attributed to
2
n→π* transition of imine group for HL [13, 14]. Spectra of the complexes show two dif-
ferent CT bands at 265 and 304 nm for 1 and 260 and 310 nm for 2. In spectra of the com-
plexes, bands for pyridine and azomethine chromophore shift the π→π* transition to lower
frequencies, indicating that the pyridine and imine nitrogens were involved in coordination
[
13]. As spectra of the free ligands have no CT bands from 350 to 430 nm, the CT bands at
3
85 nm for 1 and 380 nm for 2 are associated to LMCT →d [14, 24, 44, 45]. The pres-
N3
ence of intense π→π* and LMCTN/S/N3→d transitions causes the lower energy d–d bands to
appear as weak shoulders, bringing about difficulty in assignment of bands.
3
3
.3. Crystal structures
.3.1. Structure of [Ni(HL )(N )(μ N )] (1). A perspective view of 1 is displayed in
1
3
1,1 3 2
figure 2. Complex 1 crystallizes in the monoclinic system with space group P2 /c. The crys-
1
tal data and structure refinement are summarized in table 1. Its structure contains a six-coor-
dinate dinickel complex, in which the two Ni(II) ions are bridged by two azides. The
bridging azides are in end-on modes. Each Ni(II) in the dinickel core is further bound by
tridentate HL and by a terminal nitrogen of azide. Both nickel centers have distorted octahe-
dral geometry. The apical positions are occupied by two nitrogens; N1 from the azide
bridge in EO mode [Ni1–N1 is 2.1288(14) Å] and N4 from the terminal azido [Ni1–N4 is
2
.0695(14) Å] with N1–Ni1–N4 angle of 169.56(6)° (for more information about the bond
lengths and angles see table 3). The equatorial plane is formed by two nitrogens and one
oxygen from chelating HL (N9, N10 and O1) and one nitrogen from the other azide bridge
in EO mode (N1). The average Ni–N bond length in the basal plane is 2.036 Å.

2
102
B. Shaabani et al.
1
Figure 2. Structure and labeling diagram for [Ni(HL )(N
3
)(μ1,1N
3
)]
2
(1).
Table 3. Selected bond lengths (Å) and angles (°) for 1 (experimental data belong to the solid phase, whereas the
calculated data correspond to the isolated molecule in a gas phase).
Bond lengths (Å)
Bond angles (°)
Experimental
Calculated
Experimental
Calculated
Ni1–Ni1
Ni1–N1
Ni1–N1a
Ni1–N4
Ni1–N9
Ni1–N10
Ni1–O1
N1–N2
N2–N3
N4–N5
N5–N6
3.186(6)
2.9815
1.9113
1.9227
1.9033
1.8921
2.3796
2.2316
1.2501
1.1434
1.2178
1.1497
2.0555(14)
2.1288(14)
2.0695(14)
1.9952(14)
2.0700(15)
2.1034(12)
1.209(2)
1.149(2)
1.191(2)
1.150(2)
N9–Ni1–N1
N9–Ni1–N4
N9–Ni1–N10
N9–Ni1–O1
N1–Ni1–N4
N1–Ni1–O1
N1–Ni1–N1
N4–Ni–N1
172.92(6)
93.19(6)
78.45(6)
78.06(5)
91.14(6)
96.51(5)
80.84(6)
169.56(6)
178.65(19)
178.3(2)
15.0991
87.0649
77.5724
72.7743
92.0723
88.2234
79.6191
175.3289
169.0727
171.7268
N3–N2–N1
N6–N5–N4
Selected bond parameters observed in 1 are listed in table 3. The Ni–Nazido–Ni–Nazido rings
are planar and the Ni1–Nazido–Ni1 bond angle is 99.16(6)°, which falls in the range of pub-
lished Ni–azide–Ni angles in similar compounds [41, 47–51]. The end-on azide bridges are
essentially linear with angles N1–N2–N3 178.65(19)° and show asymmetric N–N distances
of 1.209(2)/1.149(2) Å. The terminal azides are quasi-linear with N4–N5–N6 of 178.3(2)°
and show asymmetric N–N distances of 1.191(2)/ 1.150(2) Å. The terminal azides are

Azido nickel(II) complexes
2103
coordinated trans to each other and the N4–Ni1⋯Ni1–N4 torsion angle is 180°. Two
2
+
neighboring bridged Ni ions give a binuclear unit in which the bond lengths of Ni1–N1
are 2.0555(14) and 2.1288(14) Å. The Ni1⋯Ni1 separation in the dimer is 3.186(6) Å.
These values lie in the typical range for double EO azido-bridging nickel(II) complexes
(3.155–3.449 Å) [47–52] (For more information see table 4). The nitrogens of the semicar-
bazone and azido ligands are involved in intermolecular H-bonding interaction with adja-
cent dinuclear units. The hydrogen bonds N1⋯H1–N7 (N1⋯H1 distance 2.291 Å, N1H1N7
angle 154.81°) and N4⋯H1–N8 (N1⋯H1 distance 2.026 Å, N1H1N7 angle is 164.01°)
expand the structure of 1 in 2-D.
2
3
.3.2. Structure of [Ni(L )(N3)] (2). Complex 2 crystallizes in the monoclinic system with
space group P2 /n. The molecular structure and atom numbering scheme of 2 are depicted in
1
figure 3. The crystal data and structure refinement are summarized in table 1. Single X-ray
crystal analysis reveals a mononuclear complex with coordination number four for 2.
Table 4. Structural properties of 1 and selected di-μ1,1 azide bridged nickel(II) complexes.
Ni⋯Ni
Complex
Ni–N–Ni (˚)
(Å)
Ni–N(bridging) (Å)
Ref.
[27]
[
Ni
(
2
(pbdiim)
O)
(biq)
(dmbpy)
4
(μ-1,1-N
3
)
2
]·2(N
3
)·6
102.96(13)
3.345(3)
2.138(2), 2.138(2)
H
2
[
[
[
[
M
M
Ni
Ni
2
2
(μ1,1-N
(μ1,1-N
(μ1,1-N (N
3
)
2
Cl
2
]
104.86(17)
105.1(3)
105.20(8)
3.241(1)
3.276(2)
3.294(1)
3.155(2)
2.028(3), 2.060(4)
2.068(7), 2.060(6)
2.068(1), 2.078(2)
2.061, 2.108, 2.13,
2.061
2.150(6), 2.144(6)
2.086(8), 2.088(9)
2.085(2), 2.184(2)
2.1288(14), 2.0555(14)
[46]
[46]
[46]
[46]
2
2
3 2 3 2
) (N ) ]
2
(biq)
2
3
)
2
3
)
2
]
1
2
(L )(N
3
)
4
]
98.36(2), 97.66
(
3)
2
[
[
[
[
Ni
Ni
2
(L )(N
3
)
4
]·CH
3
CN
(N
(N
)]
101.7(2)
99.7(4)
100.0(10)
99.16(6)
3.329(1)
3.191(4)
3.222(3)
3.186(6)
[49]
[50]
[50]
Present
work
3
2
(L )
2
(μ1,1-N
3
)
2
3
)
2
]
4
Ni2(L )
2
(μ1,1-N
3
)
2
3
)
2
]
Ni(HL)(μ1,1
N
3
)(N
3
2
1
Notes: [pbdiim: 2-(2′-pyridyl)benzo[1,2-d:4,5-d′]diimidazole], [biq: 2,2′-biquinoline], [dmbpy: 6,6′-dimethyl-2,2′-bipyridine], (L
2
Schiff base ligand made from the reaction of 2 M of 2-benzoyl pyridine and 1 M of triethylenetetramine), [L : prepared from the
reaction of 2-benzoylpyridine with N,N0-bis-(3-aminopropyl) ethylenediamine in the 2 : 1 M ratio], [L : N,N-bis(2-pyridylmethyl)
3
4
amine], [L : N-(2-pyridylmethyl)-N0,N0-diethylethylenediamine].
2
Figure 3. Structure and labeling diagram for [Ni(L )(N
3
)] (2).

2
104
B. Shaabani et al.
The mononuclear unit consists of a Schiff base ligand and a terminal azide. The coordination
geometry of Ni(II) is square planar with Ni(II) in the plane made by a pyridyl nitrogen (N1),
an azomethine nitrogen (N2), and thioamide sulfur S(1) of the thiosemicarbazone ligand and
a nitrogen from azide (N5). Ni(II) ion is 0.038 Å from the average plane formed by
N1N2S1N5 in the complex. HL is a tridentate ligand with NNS donors and is deprotonated.
It coordinates to Ni(II) in thiol form, also confirmed by the IR spectral data. By considering
the bond lengths around Ni(II), Ni1–N1; 1.937(4) Å, Ni1–N2; 1.857(4) Å, Ni1–N5; 1.887(4)
Å (for more information about the bond lengths and angles see table 5), similar and in the
range 1.857–1.937 Å. The Ni1–S1 (2.1526(14) Å) bond length is longer than the Ni–N
bonds, in agreement with those previously reported [11–13]. The C(7)–S(1) bond length in
the complex is 1.757(4) Å, similar to those found in related thiosemicarbazone complexes in
the thiol form in the solid state, such as 1.76(1) Å in [Ni(dmtsc)] and 1.715(4) Å in [Ni(ats-
c)]·0.5EtOH] where Hatsc is pyridyl methyl ketone thiosemicarbazone and H2dmtsc is 2,6-
diacetylpyridine bis(4N-morpholyl thiosemicarbazone)] [11], 1.74(1) Å in [Cu(NCS)(L)]
[
[
where HL is pyridine-2-carbaldehyde thiosemicarbazone[ [12], and 1.735(4) Å in
MnL [·H O [where HL is pyridine-2-carbaldehyde N(4)-p-methoxyphenyl thiosemicarba-
2
2
zone] [13]. The chelate bite angles in the two five-membered rings are also close [N1–Ni1–
N2; 83.66(16)° and N2–Ni1–S1; 86.37(12)°]. The terminal azide shows asymmetric N–N
distances of 1.209(5)/1.154(5) Å and the azide is quasi-linear with N5–N6–N7; 173.9(4)°.
The Ni–Nazide distance is 1.887(4) Å for Ni–N(5), similar with those reported for similar
structures in the literature [11, 41]. The nitrogen groups of the thiosemicarbazone and azide
are involved in intermolecular H-bonds with the adjacent units (for more information see
table 6). The N4–H4A⋯N3 and N4–H4B⋯N7 are two H-bonds which expand the structure
in two directions (see figure 4). Also, the presence of a C–H⋯S link between C(3) and S(1)
is also remarkable. In the complex, the H⋯S distances is 2.909 Å and the C3H3⋯S1 angle is
Table 5. Selected bond lengths (Å) and angles (°) for 2 (experimental data belong to the solid phase, whereas the
calculated data correspond to the isolated molecule in a gas-phase).
Bond lengths (Å)
Bond angles (°)
Experimental
Calculated
Experimental
Calculated
Ni1–N1
Ni1–N2
Ni1–S1
Ni1–N5
S1–C7
N3–N2
N6–N5
N7–N6
N3–C7
N2–C6
N4–H4A
N4–H4B
1.937(4)
1.857(4)
2.1526(14)
1.887(4)
1.757(4)
1.371(5)
1.209(5)
1.154(5)
1.330(6)
1.315(6)
0.8600
1.9358
1.8562
2.1526
1.8863
1.7587
1.3711
1.2101
1.1531
1.3287
1.3143
0.8595
0.8612
N2–Ni1–N5
N2–Ni1–N1
N5–Ni1–N1
N2–Ni1–S1
N5–Ni1–S1
N1–Ni1–S1
C7–S1–Ni1
N3–N2–Ni1
N6–N5–Ni1
N7–N6–N5
176.35(16)
83.66(16)
92.94(16)
86.37(12)
96.95(12)
169.67(12)
95.93(15)
125.0(3)
176.3527
83.6972
92.9194
86.3858
96.9257
169.7156
95.9072
124.9698
127.0120
174.0745
126.9(3)
173.9(4)
0.8600
Table 6. Selected hydrogen bonding parameters in 2.
D–H⋯A
D–H (Å)
H⋯A (Å)
D⋯A (Å)
D–H⋯A (°)
N4–H4A⋯N3
N4–H4B⋯N7
0.860
0.861
2.119
2.632
2.960
3.230
165.68
127.59

Azido nickel(II) complexes
2105
Figure 4. View of presence of N4–H4A⋯N3 intermolecular H-bonds in 2.
1
(
31.39°; the values suggest strong interactions within this class of weak noncovalent contacts
figure 5). A search for π⋯π stacking interactions in the complex revealed that interplanar
distance between HL rings is 3.853 Å, similar to the separation of 3.738(3) Å in [MnL [·H O
2
2
[with HL pyridine-2-carbaldehyde N(4)-p-methoxy phenyl thiosemicarbazone] [13]. Parallel
arrays of the planes of the aromatic moieties in the complex indicate that these interactions
are of the slipped face-to-face stacking types. The interplanar distance of 3.853 Å between
Figure 5. View of presence of the C–H⋯S linkage between the C(3) and S(1) atoms in 2.

2
106
B. Shaabani et al.
aromatic rings in the complex is normal for π⋯π stacking interactions [53–55]. Also there is
a strong C–H⋯π stacking interaction C3–H3⋯π, with a separation of 3.531 Å between the
hydrogen of the pyridyl ring with the pyridyl ring of the adjacent unit.
3
.4. Antimicrobial screening
The ligands, 1, and 2 were tested for their effect on certain bacteria and fungi, and the
1
results are given in table 7. MIC values reveal that HL has weak biological activity but
2
HL with the sulfur donor has better results. The complexes showed enhanced antimicrobial
activities against bacteria and fungi than free ligands. The increased activity of the metal
chelates can be explained on the basis of chelation theory [1, 8, 11–14, 56–58] and block-
ing the metal binding sites on enzymes of micro-organisms [56–60]. Comparing MIC val-
ues for complexes reveal that 2 has better results than 1, in agreement with the results of
previous research that thiosemicarbazone complexes have better antimicrobial activity than
semicarbazone complexes [11–16].
3
.5. DFT calculations
The structural parameters calculated by the DFT method are listed in tables 3 and 5. The
experimental data belong to the solid phase, whereas the calculated data correspond to the
isolated molecule in a gas-phase, the parameters only slightly differ from each other. As a
result, the calculated geometrical parameters represent a good approximation. The computed
IR frequencies are listed in table 8 together with the experimentally determined frequencies.
Both calculated and experimental frequencies are in agreement. Also, the value of the energy
separation between the highest occupied molecular orbital (HOMO) and the lowest unoccu-
pied molecular orbital (LUMO) was calculated. Figure 6(a) and (b) show the HOMO and
LUMO for 1 and 2, respectively. The HOMO–LUMO energy gap could be regarded as the
quantitative index in evaluating the sensitivity of energetic complexes with similar geometric
structure. The lower the energy gap, the more sensitive the energetic complex is. The energy
gap of 1 and 2 with azido ligands are 2.65 and 3.49 eV. These are in agreement with the fact
that the metallic azide is widely used as initiator due to its high sensitivity [61, 62]. Judged
1
2
−1
Table 7. The antimicrobial activity of HL , HL , 1, and 2 (MIC in μg mL ).
Bacillus
subtilis
Staphylococcus Escherichia Erwinia
Candida Candida
Aspergillus
niger
Compound
aureus
coli
carotovora
kefyr
krusei
1
HL
625
312
625
154
4
1250
625
625
154
8
1250
625
625
312
8
1250
312
625
312
8
625
312
625
312
–
625
312
625
312
–
1250
625
1250
312
–
2
HL
1
2
*
Gentamicin
Amphotricin
B
*
–
–
–
–
4
4
16
DMSO
–
–
–
–
–
–
–
*
−1
Gentamicin is used as the standard. MIC (μg mL ) minimum inhibitory concentration, i.e. the lowest concentration to completely
inhibit the bacterial growth.
*
−1
Amphotricin B is used as the standard. MIC (μg mL ) minimum inhibitory concentration, i.e. the lowest concentration to com-
pletely inhibit the fungal growth.

Azido nickel(II) complexes
2107
−
1
−1
Table 8. Experimental FT-IR (cm ) data for 1 and 2 with the theoretical IR (cm ) data obtained from DFT cal-
culations.
Compound
ν
NH2
ν
NH
νC=O or νC=S
ν
C=N
ν
N–N
ν
N3
1
Experimental
Calculated
2
3412
3532
3162
3574
1666
1709
1591
1586
1189
1207
2061
2080
Experimental
Calculated
3411
3760
–
–
809
722
1638
1613
1168
1055
2052
2027
Figure 6. Frontier molecular orbitals for 1 (a) and 2 (b).
by the difference of 0.84 of energy gap between 1 and 2, 1 is a more sensitive explosive
than 2.
4
. Conclusion
1
2
Two new complexes of nickel(II), [Ni(HL )(N )(μ N )] (1) and [Ni(L )(N )] (2), have
3
1,1
3
2
3
been synthesized by slow diffusion in an H-shaped tube. Comparison of the IR spectra of
1
1
2
HL and 1 indicates HL is a neutral ligand, chelated to nickel(II) in keto form; for HL
2
and 2, HL is deprotonated and chelated to the nickel(II) centers in thiol form. Calculated
structural parameters and IR spectra for 1 and 2 are in agreement with the crystal structure.
Complexes 1 and 2 were structurally characterized by single-crystal X-ray diffraction and
the results indicate dinuclear units bridged with azide for 1 and mononuclear 2. In 1, each
1
Ni(II) in the dinickel core is further bound by tridentate HL , two bridging azides and a ter-
minal azide. Both nickel centers have distorted octahedral geometry. For mononuclear 2, Ni
2
(
II) is bound by tridentate HL and a terminal azide with square-planar geometry.

2
108
B. Shaabani et al.
2
1
Antimicrobial activities demonstrate that HL has better results than HL and 2 has better
antimicrobial activities than 1 due to sulfur donors of thiosemicarbazone. The DFT
calculations for 1 and 2 demonstrate that both calculated and experimental frequencies are
in agreement. Judged by 0.84 energy gap between 1 and 2, 1 would be a more sensitive
explosive than 2.
Supplementary material
Crystallographic data (excluding structure factors) for all the structures reported in this
paper have been deposited with the Cambridge Crystallographic Data Center as supplemen-
tary publication Nos. CCDC 901690 and 889344 for 1 and 2. Copies of these data can be
obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 2EZ,
UK; Fax: (+44) 1223 336033, or online via www.ccdc.cam.ac.uk/data_request/cif or by
emailing data_request@ccdc.cam.ac.uk.
Acknowledgements
We are grateful to Tabriz University of Research council for the financial support of this
research. We also acknowledge the project Praemium Academiae of the Academy of Sci-
ences of the Czech Republic. We are thankful to Departamento de Química Fundamental,
Universidade da Coruña of Spain and Department of Chemistry, Indian Institute of Technol-
ogy Kanpur, for kindly helping.
References
[
[
1] G.G. Mohamed, M.A. Zayed, S.M. Abdallah. J. Mol. Struct., 979, 62 (2010).
2] C. Maxim, T.D. Pasatoiu, V.Ch. Kravtsov, S. Shova, C.A. Muryn, R.E.P. Winpenny, F. Tuna, M. Andruh.
Inorg. Chim. Acta, 361, 3903 (2008).
[
3] S. Nayak, P. Gamez, B. Kozlevcˇar, A. Pevec, O. Roubeau, S. Dehnen, J. Reedijk. Polyhedron, 29, 2291
(
2010).
[
[
[
[
4] G.G. Mohamed, M.M. Omar, A.A. Ibrahim. Spectrochim. Acta Part A, 75, 678 (2010).
5] S. Meghdadi, M. Amirnasr, K. Mereiter, H. Molaee, A. Amiri. Polyhedron, 30, 1651 (2011).
6] S. Baluja, A. Solanki, N. Kachhadia. J. Iran. Chem. Soc., 3, 312 (2006).
7] T. Rosu, E. Pahontu, C. Maxim, R. Georgescu, N. Stanica, G.L. Almajan, A. Gulea. Polyhedron, 29, 757
(
2010).
[
[
8] N. Raman, S. Sobha, A. Thamaraichelvan. Spectrochim. Acta Part A, 78, 888 (2011).
9] J.G. Tojal, J.L. Pizarro, A. García-Orad, A.R. Pérez-Sanz, M. Ugalde, A.A. Díaz, J.L. Serra, M.I. Arriortua, T.
Rojod. J. Inorg. Biochem., 86, 627 (2001).
[
[
[
10] E. Viñuelas-Zahínos, F. Luna-Giles, P. Torres-García, M.C. Fernández-Calderón. Eur. J. Med. Chem., 46, 150
2011).
11] N.Ch. Kasuga, K. Sekino, Ch. Koumo, N. Shimada, M. Ishikawa, K. Nomiya. J. Inorg. Biochem., 84, 55
2001).
12] N.Ch. Kasuga, K. Sekino, M. Ishikawa, A. Honda, M. Yokoyama, S. Nakano, N. Shimada, Ch. Koumo, K.
Nomiya. J. Inorg. Biochem., 96, 298 (2003).
(
(
[
[
13] N.Ch. Kasuga, K. Onodera, S. Nakano, K. Hayashi, K. Nomiya. J. Inorg. Biochem., 100, 1176 (2006).
14] B. Shaabani, A.A. Khandar, F. Mahmoudi, M.A. Maestro, L. Cunha-Silva, S.S. Balula. Polyhedron, 57, 118
(
2013).
[
[
[
15] J. Garcia-Tojal, L. Lezama, J.L. Pizarro, M. Insausti, M.I. Arriortu, T. Rojo. Polyhedron, 18, 3703 (1999).
16] H. Elo. Z. Naturforsch., 62c, 498 (2007).
17] A. Karakucuk-Iyidogan, D. Tasdemir, E.E. Oruc-Emre, J. Balzarini. Eur. J. Med. Chem., 46, 5616 (2011).

Azido nickel(II) complexes
2109
[
[
[
[
[
18] S. Chandra, A. Kumar. Spectrochim. Acta Part A, 68, 1410 (2007).
19] V.M. Leovac, L. Bjelica, L. Jovanovic. Polyhedron, 4, 233 (1985).
20] T.A. Reena, E.B. Seena, M.R. Prathapachandra Kurup. Polyhedron, 27, 1825 (2008).
21] B.-L. Liu, H.-P. Xiao, E.N. Nfor, Y. Song, X.-Z. You. Inorg. Chem. Commun., 12, 8 (2009).
22] A. Ray, G.M. Rosair, G. Pilet, B. Dede, C.J. Gómez-García, S. Signorella, S. Bellú, S. Mitra. Inorg. Chim.
Acta, 375, 20 (2011).
[23] A.M. Madalan, M. Noltemeyer, M. Neculai, H.W. Roesky, M. Schmidtmann, A. Müller, Y. Journaux, M.
Andruh. Inorg. Chim. Acta, 359, 459 (2006).
[24] Ch. Adhikary, D. Mal, K.-I. Okamoto, S. Chaudhuri, S. Koner. Polyhedron, 25, 2191 (2006).
[25] W.-W. Sun, X.-B. Qian, Ch.-Y. Tian, E.-Q. Gao. Inorg. Chim. Acta, 362, 2744 (2009).
[26] F.A. Mautner, A. Egger, B. Sodin, M.A.S. Goher, M.A.M. Abu-Youssef, A. Massoud, A. Escuer, R. Vicente.
J. Mol. Struct., 969, 192 (2010).
[
[
27] S. Shit, P. Talukder, J. Chakraborty, G. Pilet, M.S. El Fallah, J. Ribas, S. Mitra. Polyhedron, 26, 1357 (2007).
28] X.-L. Yu, W.-S. You, X. Guo, L.-C. Zhang, Y. Xu, Z.-G. Sun, R. Clérac. Inorg. Chem. Commun., 10, 1335
(
2007).
[
29] A. Ray, G.M. Rosair, G. Pilet, B. Dede, C.J. Gómez-García, S. Signorella, S. Bellú, S. Mitra. Inorg. Chim.
Acta, 375, 20 (2011).
[
[
[
[
[
[
[
[
[
[
30] A. Dehno Khalaji, H. Stoekli-Evans. Polyhedron, 28, 3769 (2009).
31] A.A. Soudi, A.H. White. Aust. J. Chem., 49, 1029 (1996).
32] F. Marandi, B. Mirtamizdoust, A.A. Soudi, H.-K. Fun. Inorg. Chem. Commun., 10, 174 (2007).
33] G. Mahmoudi, A. Morsali. Inorg. Chim. Acta, 362, 3238 (2009).
34] B. Shaabani, A.A. Khandar, M. Dusek, M. Pojarova, F. Mahmoudi. Inorg. Chim. Acta, 394, 563 (2013).
35] Agilent. CrysAlis PRO, Agilent Technologies UK Ltd, Yarnton (2010).
36] A.D. Becke. J. Chem. Phys., 98, 5648 (1993).
37] C. Lee, W. Yang, R.G. Parr. Phys. Rev. B, 37, 785 (1988).
38] P.J. Hay, W.R. Wadt. J. Chem. Phys., 82, 270 (1985).
39] A description of the basis sets and theory level used in this work can be found in the following: J.B.
Foresman, A.E. Frisch. Exploring Chemistry with Electronic Structure Methods, 2nd Edn, Gaussian Inc.,
Pittsburgh, PA (1996).
[
40] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Roob, GAUSSIAN 98, Revision A.9, Gaussian
Inc., Pittsburgh, PA (1998).
[
41] S. Deoghoria, S. Sain, M. Soler, W.T. Wong, G. Christou, S.K. Bera, S.K. Chandra. Polyhedron, 22, 261
(
2003).
[
[
[
[
[
[
[
[
42] V. Philip, V. Suni, M.R. Prathapachandra Kurup, M. Nethaji. Polyhedron, 23, 1225 (2004).
43] B. Machura, A. Switlicka, I. Nawrot, J. Mrozin ski, K. Michalik. Polyhedron, 30, 2815 (2011).
44] P. Mukherjee, O. Sengupta, M.G.B. Drew, A. Ghosh. Inorg. Chim. Acta, 362, 3285 (2009).
45] Zh.-H Zhang, X.-H. Bu, Zh.-H. Ma, W.-M. Bu, Y. Tang, Q.-H. Zhao. Polyhedron, 19, 1559 (2000).
46] P. Chaudhuri, T. Weyhermtiller, E. Bill, K. Wieghardt. Inorg. Chim. Acta, 252, 196 (1996).
47] X.-J. Lin, Zh. Shen, Y. Song, H.-J. Xu, Y.-Zh. Li, X.-Z. You. Inorg. Chim. Acta, 358, 1963 (2005).
48] H.-Zh. Kou, Sh. Hishiya, O. Sato. Inorg. Chim. Acta, 361, 2396 (2008).
49] S. Sain, S. Bid, A. Usman, H.-K. Fun, G. Aromí, X. Solans, S.K. Chandra. Inorg. Chim. Acta, 358, 3364
(
2005).
[
[
50] S. Sarkar, A. Mondal, A. Banerjee, D. Chopra, J. Ribas, K.K. Rajak. Polyhedron, 25, 2285 (2006).
51] S. Sarkar, A. Mondal, M.S. El Fallah, J. Ribas, D. Chopra, H. Stoeckli-Evans, K.K. Rajak. Polyhedron, 25,
28 (2006).
[
[
[
[
52] P.T. Kissinger, W.R. Heineman. J. Chem. Educ., 60, 702 (1983).
53] F. Marandi, P. McArdle, B. Mirtamizdoust, A.A. Soudi. J. Coord. Chem., 60, 891 (2007).
54] C.A. Hunter, J.K.M. Sanders. J. Am. Chem. Soc., 112, 5525 (1990).
55] J.C. Collings, K.P. Roscoe, E.G. Robins, A.S. Batsanov, L.M. Stimson, J.A.K. Howard, S.J. Clark, T.B.
Marder. New J. Chem., 26, 1740 (2002).
[
[
[
[
56] N.P. Priya. Int. J. Appl. Biol. Pharm. Tech., 2, 538 (2011).
57] A.A. Nejo, G.A. Kolawole, A.O. Nejo. J. Coord. Chem., 63, 4398 (2010).
58] L. Mishra, V.K. Singh. Indian J. Chem., 32A, 446 (1993).
59] R.J. Carlin, A.J. van Duyeneveldt. Magnetic Properties of Transition Metal Compounds, Springer Verlag,
New York (1977).
[
60] G. Chastanet, B. Le Guennic, C. Aronica, G. Pilet, D. Luneau, M.-L. Bonnet, V. Robert. Inorg. Chim. Acta,
361, 3847 (2008).
[
[
61] B. Tang, J.-H. Ye, X.-H. Ju. Int. Scholarly Res. Network ISRN Org. Chem., 2011, 1 (2011).
62] B. Shaabani, B. Mirtamizdoust, M. Shadman, H.-K. Fun. Z. Anorg. Allg. Chem., 635, 2642 (2009).