Nickel (II) and cobalt (II) complexes with bidentate nitrogen-sulfur donor pyrazole derivative ligands: Syntheses, characterization, X-ray structure, electrochemical studies, and antibacterial activity

Article abstract of DOI:10.1016/j.poly.2020.114423

The synthesis, characterization, antibacterial activity and cyclic voltammetry of bidentate N_,S donor pyrazole derivative ligands abbreviated as Na(EtNCSPz) (1), Na(PhNCSPz) (2), Na(PhNCSPz^me2) (3), Na(PhNCSPz^me3) (4) and their metal complexes with Ni(II) and Co(II) metal ions are reported, where Pz = pyrazole, Pz^me2 = 3,5-dimethylpyrazole and Pz^me3 = 3,4,5-trimethylpyrazole. All of the synthesized ligands and complexes have been characterized by physicochemical and spectroscopic methods and the crystal structures of [Ni(EtNCSPz)₂] (1a) and [Ni(PhNCSPz^Me3)₂] (4a) have been determined by X-ray diffraction analysis. The X-ray crystal structure of both the complexes describe a square planar coordination geometry. The electrochemical studies show that the synthesized complex is an electrochemically active species, furthermore, substitution electron donating groups on the ligands shift the reduction and oxidation potentials to negative values. Antibacterial activity results indicate these complexes possess high activity against gram-positive and gram-negative bacteria compare to the free ligands.

Full text of DOI:10.1016/j.poly.2020.114423

Journal Pre-proofs
Nickel (II) and cobalt (II) complexes with bidentate nitrogen- sulfur donor pyr-
azole derivative ligands: Syntheses, characterization, X-ray structure, electro-
chemical studies, and antibacterial activity
Behzad Soltani, Monireh Ghorbanpour, Christopher J. Ziegler, Mostafa Ebadi-
Nahari, Rahim Mohammad-Rezaei
PII:
S0277-5387(20)30080-2
DOI:
https://doi.org/10.1016/j.poly.2020.114423
POLY 114423
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
3 November 2019
23 January 2020
29 January 2020
Please cite this article as: B. Soltani, M. Ghorbanpour, C.J. Ziegler, M. Ebadi-Nahari, R. Mohammad-Rezaei, Nickel
(II) and cobalt (II) complexes with bidentate nitrogen- sulfur donor pyrazole derivative ligands: Syntheses,
characterization, X-ray structure, electrochemical studies, and antibacterial activity, Polyhedron (2020), doi: https://
doi.org/10.1016/j.poly.2020.114423
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1
2
3
Nickel (II) and cobalt (II) complexes with bidentate nitrogen- sulfur donor pyrazole
derivative ligands: Syntheses, characterization, X-ray structure, electrochemical
studies, and antibacterial activity
4
5
Behzad Soltani a,*, Monireh Ghorbanpour a, Christopher J. Ziegler b, Mostafa
6
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8
Ebadi-Nahari c and Rahim Mohammad-Rezaei a
aDepartment of Chemistry, Faculty of Science, Azarbaijan Shahid Madani University, Tabriz, Iran
bDepartment of Chemistry, University of Akron, Akron, Ohio44325, USA
9
cDepartment of Biology, Faculty of Basic Sciences, Azarbaijan Shahid Madani University, Tabriz,
Iran
10
11
12
*Corresponding author: Department of Chemistry, Faculty of Science, Azarbaijan Shahid Madani
University, Tabriz P.O.Box 53714-161, Iran. Behzad Soltani (Soltani@azaruniv.ac.ir).
13
14
Tel: 0098-413 5152576, Fax: 0098-413 4428804
15 Abstract
16 The synthesis, characterization, antibacterial activity and cyclic voltammetry of
17 bidentate N,S donor pyrazole derivative ligands abbreviated as Na(EtNCSPz) (1),
18 Na(PhNCSPz) (2), Na(PhNCSPzme2) (3), Na(PhNCSPzme3) (4) and their metal
19 complexes with Ni(II) and Co(II) metal ions are reported, where Pz = pyrazole, Pzme2
20 = 3,5-dimethylpyrazole and Pzme3 = 3,4,5-trimethylpyrazole. All of the synthesized
21 ligands and complexes have been characterized by physicochemical and
22 spectroscopic methods and the crystal structures of [Ni(EtNCSPz)2] (1a) and
23 [Ni(PhNCSPzMe3)2] (4a) have been determined by X-ray diffraction analysis. The

24 X-ray crystal structure of both the complexes describe a square planar coordination
25 geometry. The electrochemical studies show that the synthesized complex is an
26 electrochemically active species, furthermore, substitution electron donating groups
27 on the ligands shift the reduction and oxidation potentials to negative values.
28 Antibacterial activity results indicate these complexes possess high activity against
29 gram-positive and gram-negative bacteria compare to the free ligands.
30 Keywords: N,S donor pyrazole based ligand, Antimicrobial activity,
31 Electrochemistry, Crystal structure.
32 1. Introduction
33 Currently, finding compounds with a wide spectrum of biological activity represents
34 a very important aspect in biochemistry research [1, 2]. Coordination compounds
35 comprised of transition metals with multidentate ligands containing N and S
36 donor atoms and their versatile chelating ability with transition metal ions have
37 attracted significant interest because of the roles they play in diverse biological
38 systems and their usefulness for human use [3-6]. Recently, there has been an
39 important amount of progress in pyrazole- derived ligands because of the recognition
40 of the importance of this unit’s role in biological systems for anxiolytic [7],
41 antiangiogenesis [8], antitubercular [9], antitumor [10], anti-inflammatory [11],
42 antiparasitic [12], antiviral [13] and antimicrobial activities [14]. Pyrazoles are
43 heterocycles with a 5-membered ring of three C atoms and two N atoms and are

44 well-known N donor ligands with versatile coordination chemistry. These rings can
45 act as neutral/anionic monodentate or also as exo/endo-bidentate anionic ligands
46 [15]. Pyrazole and pyrazolate as ligands have been investigated to synthesize model
47 complexes that can mimic the active site of metalloenzymes which are known to
48 contain imidazole groups from histidine, bound to the metal center [16-18]. Nickel
49 and cobalt are transition metals with an appreciable affinity for O, N and S atoms.
50 Nickel is known to play a significant role in biology as a cofactor in a wide variety
51 of enzymes [19]. Urease is the nickel-containing enzyme and present in some
52 plants, eubacteria, archaebacteria, and fungi, catalyzes the hydrolysis of urea to
53 form ammonia and carbamate [20-22]. Cobalt is unique among trace metals that are
54 observed in the metabolism of all animals. Cobalt is a key component of cobalamin,
55 also known as vitamin B12, and is required for the synthesis of hemoglobin [23-25].
56 Inspired by the occurrence of N, S-coordinated nickel and cobalt ions as antibacterial
57 or antiviral agents and catalysts many organic reactions [26], some N, S-donor
58 ligands and their nickel complexes using a chelating Schiff base have been
59 synthesized and reported to show antimicrobial activity [27, 28]. There is a drastic
60 change in their biomimetic properties including therapeutic and pharmacological
61 effects, when drugs or bioorganic molecules are bound to metal ions. However,
62 essential metal ions and ligands have been found to show antitumor, antimicrobial
63 and cytotoxic activity [29-32]. Keeping in view medicinal and biological properties

64 of pyrazoles and the potential chemistry of transition metals, so it is very important
65 to join the chemistry of both moieties and designing metal based compounds with
66 excellent biological activity that could aggressively apply against resistant bacterial
67 species. When organic compound or drugs are bound to metal centers, there is drastic
68 change in their biomimetic activity and medicinal properties. The antimicrobial
69 activity of pyrazole based complexes depends not only on the pyrazole ring in
70 structure but also on the nature of the metal center and the celation effect [33-35].
71 For this accomplishment we report the synthesis and characterization of Co(II) and
72 Ni(II) complexes with N, S donor pyrazole derivative ligands. Also, electrochemical
73 behavior and antibacterial activities of complexes and ligands were investigated.
74 2. Experimental
75 2.1. Materials and methods
76 All of solvents and chemicals were purchased from Merck and solvents were dried
77 by standard procedures.
78 2.2. Instruments
79 FT-IR spectra were recorded in the solid-state on an FT-IR Bruker
80 spectrophotometer device in the 400-4000 cm-1 range and using a pressed KBr disk
81 with polystyrene as reference. 1H NMR spectra and 13C NMR spectra for the organic
82 ligands were collected at 400 MHz and 100 MHz on a Bruker spectrometer in CDCl3

83 and DMSO-d6 solution, respectively. The UV-Visible spectra of ligands and
84 complexes were recorded on the Scinco F-4010 UV/Vis spectrometer in the range
85 of 800-200 nm. Melting points were measured with a Stuart Scientific SMP1
86 apparatus. Antibacterial activity was determined by the disk diffusion method. [36]
87 Cyclic voltammetry experiments were performed using an Autolab PGSTAT-204
88 with a three electrode system containing Ag/AgCl wire as the electrode of reference,
89 a Pt electrode as the counter electrode and a glassy carbon electrode as the working
90 electrode. Elemental analysis (C.H.N) were done on Elementar Vario ELIII.
91 2.3. Synthesis of the ligands
92 2.3.1. Synthesis of 3,5- dimethyl pyrazole (PzMe2)
93 As described elsewhere [37], semicarbazide hydrochloride (0.1 g, 1 mmol), 2,4-
94 pentanedione (0.2 mL, 2 mmol) and water (10 mL) were refluxed for 3 h. The
95 reaction mixture was cooled for 30 min in the refrigerator. After three days
96 (dependent on the amount of solvent) white crystals started forming. The crystals
97 were filtered off, washed with distilled water, and air-dried at 25 °C. Yield: 0.08 g
98 (83%). 1H NMR (400 MHz, CDCl3, 297.4 K) δ (ppm): 2.0-2.2 (s, 6H, 3-H and 5-H
99 in Pz), 5.7 (s, 1H, 4-H in Pz), 11.4 (s, 1H, 2-H in Pz). 13C NMR (100 MHz, CDCl3,
100 297.4 K) δ (ppm): 17.70-17.73, 103.40, 144.80-144.82. FTIR (KBr, cm-1): 3203 (m,
101 ν N-H), 3132 (m, ν C-H, aromatic), 2943 (m, ν C-H, aliphatic), 1595 (s, ν C=N),

102 1484 (m, ν C=C), 1422 (m, ν CH3, bending), 1306 (s, ν N-H, bending), 1267 (w, ν
103 C-N), 1154 (m, ν C-H, bending), 854 (s, ν N-N). M.p: 97-99 oC.
104 2.3.2. Synthesis of 3,4,5-trimethylpyrazole (PzMe3)
105 Hydrazine hydrate (0.048 mL, 1 mmol) was added dropwise to the solution of 3-
106 methyl-2,4-pentanedione (0.11 mL, 1 mmol) in ethanol (15 mL), the reaction
107 mixture was refluxed for 1 h [38]. The yellow product was filtered off and dried in
108 vacuum over P2O5 for 24 h. Yield: 0.09 g (92%). 1H NMR (400 MHz, CDCl3, 297.4
109 K) δ (ppm): 1.9 (s, 6H, 3-H and 5-H in Pz), 2.1 (s, 3H, 4-H in Pz), 11.47 (s, 1H, 2-
110 H in Pz). 13C NMR (100 MHz, CDCl3, 297.4 K) δ (ppm): 7.71, 12.12-12.17, 116.21,
111 139.45. FTIR (KBr, cm-1): 3204 (m, ν N-H), 2921 (m, ν C-H, aliphatic), 1565 (s, ν
112 C=N),1526 (m, ν C=C), 1474-1448 (w, ν CH3, bending), 1414 (m, ν N-H, bending),
113 1297 (s, ν C-N), 1261 (m, ν C-C), 1208 (s, ν C-H, bending), 938 (m, ν N-N). M.p:
114 127-130 oC.
115 2.3.3. Synthesis of Na(EtNCSPz) (1)
116 As described earlier [39], pyrazole (0.068 g, 1 mmol) in 15 mL dry THF was treated
117 with solid NaH (60%, 0.0488 g, 1.2 mmol) under an argon atmosphere. After stirring
118 for 1 h, EtNCS (0.10 mL, 1.2 mmol) was added into the resulting suspension of NaPz
119 and the reaction mixture was refluxed for 6 h. After cooling, THF (10 mL) and n-
120 hexane (20 mL) was added to the reaction mixture. The resultant white

121 precipitate, was filtered, washed with n-hexane and cold ether and dried in vacuum
122 over P2O5. 1H NMR (400 MHz, DMSO-d6, 296.5 K) δ (ppm): 1.35 (t, 3H, 2-H in
123 Et), 2.6 – 2.89 (q, 1H, 2-H in Et), 6.32 (t, 1H, 4-H in Pz), 7.55 (d, 2H, 3-H and 5-H
13
124 in Pz). C NMR (100 MHz, DMSO-d6, 296.5 K) δ (ppm): 31.15, 40.79, 116.68,
125 128.42, 139.12, 172.36. Yield: 0.12 g (75%). FTIR (KBr, cm-1): 1589 (s, ν C=N),
126 1514 (m, ν C=C), 1372 (m, ν C-N, aliphatic), 1231 (m, ν C-N), 1165 (m, ν C-C),
127 705 (s, ν C-S). M.p: 220 oC (start of melting along with decomposition).
128 2.3.4. Synthesis of Na(PhNCSPz) (2)
129 Na(PhNCSPz) was prepared according to a modified literature procedure [40],
130 PhNCS (1.4 mL, 1.2 mmol) was added to a stirred solution of NaPz (0.009 g, 1
131 mmol) in THF and reaction refluxed for 6 h. The suspension was cooled, washed
132 with cold THF (10 mL) and n-hexane (20 mL) and dried in vacuum over P2O5. Yield:
133 0.17 g (81%). 1H NMR (400 MHz, DMSO-d6, 296.5 K) δ (ppm): 6.2 (t, J=1.6 Hz,
134 1H, 4-H in Pz), 6.8 (t, J=8 Hz, 1H, 4-H in Ph), 7.0 (d, J=13.2 Hz, 2H, 3-H or 5-H in
135 Pz), 7.2 (t, J=8 Hz, 2H, 3-H or 5-H in Ph), 7.4 (d, J=1.6 Hz, 2H, 2-H or 6-H in Ph).
136 13C NMR (100 MHz, DMSO-d6, 296.5 K) δ (ppm): 114.44, 121.66, 122.05, 124.64,
137 127.57, 129.08, 129.23, 144.66, 151.14, 167.71. FTIR (KBr, cm-1): 1557 (s, ν C=N),
138 1510 (m, ν C=C), 1390 (s, ν C-N, aliphatic), 1246 (m, ν C-N), 1189 (s, ν C-C), 700
139 (s, ν C-S). M.p: 250 oC (start of melting along with decomposition).
140 2.3.5. Synthesis of Na(PhNCSPzMe2) (3)

141 Na(PhNCSPzMe2) was synthesized using the same procedure as Na(PhNCSPz).
1
142 Yield: 0.19 g (78%). H NMR (400 MHz, DMSO-d6, 296.5 K) δ (ppm): 2.13 (b,
143 3H, 3-CH3 or 5-CH3 in PzMe2), 2.40 (b, 3H, 3-CH3 or 5-CH3 in PzMe2), 6.09 (s, 1H,
144 4-H in Pz), 6.79 (t, J=20 Hz 1H, 4-H in Ph), 7.0 (d, J=19.8 Hz, 2H, 2-H and 6-H in
13
145 Ph), 7.2 (t, 2H, 3-H and 5-H in Ph). C NMR (100 MHz, DMSO-d6, 296.5 K) δ
146 (ppm): 17.70-17.78, 110.73, 120.04, 120.32 126.74, 129.11, 130.23, 142.20, 143.92,
147 164.21. FTIR (KBr, cm-1): 1585 (s, ν C=N), 1512 (s, ν C=C), 1364 (m, ν C-N,
148 aliphatic), 1286 (m, ν C-N), 1173 (w, ν C-C), 716 (w, ν C-S). M.p: 300 oC (start of
149 melting along with decomposition).
150 2.3.6. Synthesis of Na(PhNCSPzMe3) (4)
151 This compound was prepared in a manner similar to the ligands mentioned above.
152 [41]. Yield: 0.22 g (82%). 1H NMR (400 MHz, DMSO-d6, 296.5 K) δ (ppm): 2.07
153 (b, 3H, 3-CH3 or 5-CH3 in PzMe3), 2.17 (b, 3H, 3-CH3 or 5-CH3 in PzMe3), 2.31 (b,
154 3H, 4-CH3 in PzMe3), 6.72 (t, J=18Hz, 1H, 4-H in Ph), 6.95 (d, J=17.7Hz, 2H, 2-H
155 and 6-H in Ph), 7.16 (t, 2H, 3-H and 5-H in Ph). 13C NMR (100 MHz, DMSO-d6,
156 296.5 K) δ (ppm): 15.12 - 15.23, 111.26, 121,65, 122.00, 125,00, 127.45, 129,02,
157 130.01, 144.00, 150.92, 168.70. FTIR (KBr, cm-1): 1634 (m, ν C=N), 1606 (m, ν
158 C=C), 1384 (m, ν C-N, aliphatic), 1322 (s, ν C-N), 1135 (w, ν C-C), 720 (s, ν C-S).
159 M.p: 300 oC (start of melting along with decomposition).

160 2.4. Synthesis of the complexes
161 A methanol solution from CoCl2.6H2O or NiCl2.6 H2O (1 mmol) and a methanol
162 solution of the ligands (1 mmol) were mixed with stirring for 24 h at room
163 temperature. The resulting precipitate was collected by vacuum filtration, and then
164 dried in vacuum over P2O5.
165 2.4.1. [Ni(EtNCSPz)2] (1a)
166 Orange crystals, Yield: 0.18 g (89%). FTIR (KBr, cm-1): 1591 (m, ν C=N, aromatic),
167 1557 (s, ν C=C, aromatic), 1319 (s, ν C-N, aliphatic), 1271 (w, ν C-N, aromatic),
168 1101 (w, ν C-C, aromatic), 1104 (s, ν C-H, bending), 933 (m, ν N-N), 685 (w, ν C-
169 S), 490 (m, ν Ni-N), 466 (w, ν Ni-S). Elem Anal. (%) Calcd for C12H16N6NiS2: C,
170 39.25; H, 4.39; N, 22.89; S, 17.46. Found: C, 39.13; H, 4.22; N, 23.02; S, 17.38. M.p
171 >300 oC (Dec.). The crystal structure of the complex 1a was determined by X-ray
172 crystallography.
173 2.4.2. [Co(EtNCSPz)2] (1b)
174 Red-brown precipitate, Yield: 0.18 g (87%). FTIR (KBr, cm-1): 1598 (m, ν C=N,
175 aromatic), 1560 (s, ν C=C, aromatic), 1310 (s, ν C-N, aliphatic), 1211 (m, ν C-N,
176 aromatic), 1144 (m, ν C-C, aromatic), 1099 (m, ν C-H, bending), 483 (w, ν N-N),
177 649 (m, ν C-S), 497 (w, ν Co-N), 459 (m, ν Co-S). Elem Anal. (%) Calcd for

178 C12H16N6CoS2: C, 39.23; H, 4.39; N, 22.87; S, 17.45. Found: C, 39.09; H, 4.24; N,
179 23.01; S, 17.50. M.p >300 oC (Dec.).
180
2.4.3. [Ni(PhNCSPz)2] (2a)
181 Yellowish-brown precipitate, Complex 2a was prepared according to a modified
182 literature procedure [41]. Yield: 0.20 g (78%). FTIR (KBr, cm-1): 1600 (s, ν C=N,
183 aromatic), 1479 (w, ν C=C, aromatic), 1398 (s, ν C-N, aliphatic), 1338 (s, ν C-N,
184 aromatic), 1289 (m, ν C-C, aromatic), 1097-1054 (s, ν C-H, bending), 940 (s, ν N-
185 N), 670 (w, ν C-S), 474 (m, ν Ni-N), 423 (m, ν Ni-S). Elem Anal. (%) Calcd for
186 C20H16N6NiS2: C, 51.85; H, 3.48; N, 18.14; S, 13.84. Found: C, 51.77; H, 3.47; N,
187 18.21; S, 13.69. M.p >300 oC (Dec.).
188 2.4.4. [Co(PhNCSPz)2] (2b)
189 Brown precipitate, Yield: 0.22 g (86%). FTIR (KBr, cm-1): 1581 (s, ν C=N,
190 aromatic), 1513 (w, ν C=C, aromatic), 1396 (s, ν C-N, aliphatic), 1262 (s, ν C-N,
191 aromatic), 1193 (s, ν C-C, aromatic), 1080 (m, ν C-H, bending), 949 (s, ν N-N), 669
192 (s, ν C-S), 484 (m, ν Co-N), 465 (m, ν Co-S). Elem Anal. (%) Calcd for
193 C20H16N6CoS2: C, 51.83; H, 3.47; N, 18.13; S, 13.83. Found: C, 52.01; H, 3.38; N,
194 18.09; S, 13.66. M.p >300 oC (Dec.).
195 2.4.5. [Ni(PhNCSPzMe2)2] (3a)

196 Red-brown crystals, Yield: 0.24 g (88%). FTIR (KBr, cm-1): 1695 (s, ν C=N,
197 aromatic), 1557 (m, ν C=C, aromatic), 1461 (s, ν CH3, bending), 1364 (m, ν C-N,
198 aliphatic), 1276 (m, ν C-N, aromatic), 1230 (w, ν C-C, aromatic), 1066 (m, ν C-H,
199 bending), 990 (w, ν N-N), 680 (s, ν C-S), 500 (m, ν Ni-N), 472 (m, ν Ni-S). Elem
200 Anal. (%) Calcd for C24H24N6NiS2: C, 55.50; H, 4.65; N, 16.18; S, 12.34. Found: C,
201 55.45; H, 4.71; N, 16.12; S, 13.05. M.p >300 oC (Dec.).
202
2.4.6. [Co(PhNCSPzMe2)2] (3b)
203 Dark brown precipitate, Yield: 0.19 g (70%). FTIR (KBr, cm-1): 1596 (s, ν C=N,
204 aromatic), 1561 (s, ν C=C, aromatic), 1497 (s, ν CH3, bending), 1302 (s, ν C-N,
205 aliphatic), 1272 (w, ν C-N, aromatic), 1024 (w, ν C-C, aromatic), 934 (m, ν C-H,
206 bending), 779 (m, ν N-N, bending), 678 (s, ν C-S), 491 (m, ν Co-N), 453 (m, ν Co-
207 S). Elem Anal. (%) Calcd for C24H24N6CoS2: C, 55.48; H, 4.65; N, 16.17; S, 12.34.
208 Found: C, 55.75; H, 4.44; N, 16.27; S, 12.42. M.p >300 oC (Dec.).
209 2.4.7. [Ni(PhNCSPzMe3)2] (4a)
210 Purple crystals, Yield: 0.27 g (90%). FTIR (KBr, cm-1): 1601 (m, ν C=N, aromatic),
211 1563 (s,ν C=C, aromatic), 1457 (s, ν CH3, bending), 1343 (m, ν C-N, aliphatic), 1286
212 (m, ν C-N, aromatic), 1145 (w, ν C-C, aromatic), 1018 (m, ν C-H, bending), 850 (w,
213 ν N-N), 672 (w, ν C-S), 500 (m, ν Ni-N), 470 (m, ν Ni-S). Elem Anal. (%) Calcd for
214 C26H28N6NiS2: C, 57.05; H, 5.15; N, 15.35; S, 11.71. Found: C, 57.11; H, 5.17; N,

215 15.62; S, 11.57. M.p >300 oC (Dec.). The crystal structure of the complex 4a was
216 determined by X-ray crystallography.
217
218
2.4.8. [Co(PhNCSPzMe3)2] (4b)
Brown precipitate, Yield: 0.22 g (75%). FTIR (KBr, cm-1): 1595 (s, ν C=N,
219 aromatic), 1562 (s,ν C=C, aromatic), 1429 (s, ν CH3, bending), 1319 (s, ν C-N,
220 aliphatic), 1069 (w, ν C-N, aromatic), 1125 (w, ν C-C, aromatic), 1021 (m, ν C-H,
221 bending), 872 (w, ν N-N), 689 (s, ν C-S),480 (w, ν Co-N), 452 (w, ν Co-S). Elem
222 Anal. (%) Calcd for C26H28N6CoS2: C, 57.02; H, 5.15; N, 15.34; S, 11.71. Found: C,
223 57.15; H, 5.22; N, 15.70; S, 11.26. M.p >300 oC (Dec.).
224 2.5. X-ray crystallography
225 X-ray intensity data were carried on a Bruker CCD-based diffractometer with dual
226 Cu/Mo ImuS microfocus optics (Cu Kα radiation, λ = 1.54178 Å, Mo Kα radiation,
227 λ = 0.71073 Å). Single crystals were mounted on a cryoloop by Paratone oil and
228 placed under nitrogen atmosphere at 100 K (Oxford Cryosystems). The detector was
229 placed at a distance of 5.00 cm from the crystal. The data were corrected for
230 absorption using the SADABS program [42]. The structures were refined by the
231 Bruker SHELXTL Software Package (Version 6.1) and solved using direct methods
232 until the final anisotropic full-matrix, least-squares refinement of F2 converged [43].

233 Crystallographic data, collection and structure refinements for the two complexes
234 are summarized in Table 1.
Table 1. Crystal data and structure refinement parameters for complexes 1a and 4a.
1a
4a
Empirical formula
Formula weight, g mol-1
Radiation
C12 H16 N6 Ni S2
367.14
C26 H28 N6 Ni S2
547.37
MoKα (λ = 0.71073 Å)
100
MoKα (λ = 0.71073 Å)
100
T, K
Crystal shape and color
Crystal size, mm
Crystal system
Space group
a, Å
Needle - orange
0.55×0.10×0.07
Monoclinic
P21/c
Plate- purple
0.40×0.26×0.18
Monoclinic
C2/c
11.282
7.9356
b, Å
4.061
11.5755
26.159
c, Å
18.582
β, deg
122.25
93.117
Volume, Å3
Z
720.0
2399.4
2
4
Density (calc.), g cm−3
Absorption coefficient, mm−1
F(000)
1.693
1.515
1.639
1.012
380.0
1144.0
2.32-26.86
3.12-27.18
Ꮎ range, deg
Index ranges
-14 ≤ h ≤ 14
-5 ≤ k ≤ 5
-23 ≤ l ≤ 23
-9 ≤ h ≤ 10
-10 ≤ k ≤ 14
-33 ≤ l ≤ 33
Independent reflections
Measured reflections
Reflections with I> 2σ(I)
Rint
1545
4910
1366
0.0344
0/98
2745
12065
2375
0.0358
0/162
restraints/parameters

Goodness of fit on F2
R[F2> 2σ(F2)]
2.109
1.059
0.0316
0.0696
0.859
0.0315
0.0763
0.504
wR(F2)
Max electron density/e·Å–3
Min electrondensity/e·Å–3
-0.364
-0.410
235
236 2.6. Antibacterial activity
237 The inhibition efficiencies of the synthesized ligands and complexes were tested in
238 vitro against S. enterica (ATCC14028) and B. subtilis (ATCC6633). The disk
239 diffusion method was used to determine the antimicrobial activity of compounds.
240 Dimethyl sulfoxide (DMSO) and Gentamicin were used as negative and positive
241 controls, respectively. The antibacterial activity was determined at a concentration
242 of 60 mM and their efficacy was assessed on Muller Hinton agar disks. All the
243 solutions were prepared in DMSO. The bacterial cultures were grown for 24 h at 37
244 °C in a broth medium and then, were diluted to 0.5 McFarland standards. A cotton
245 swab was dipped into this nutrient broth medium of the organism and was used to
246 streak the Mueller-Hinton agar medium for a lawn of growth. A sterile filter paper
247 disk of 6 mm diameter impregnated with 10 μL of ligands or complexes was
248 suspended in the sterile DMSO and placed on the surface of the agar. The plates
249 were incubated at 37 °C and then after an overnight, the inhibition zone was
250 determined by measuring the minimum dimensions of the zone of no bacterial

251 growth surrounding the disk. An average of three independent determination which
252 appeared around the disks was recorded.
253 3. Results and discussion
254 3.1. FT-IR spectral studies
255 To specify the mode of binding of the ligands N, S donor to the metal ions of
256 complexes, the FT-IR spectra of N, S donors ligands were compared with the spectra
257 of the complexes. In the FT-IR spectrum of the ligands removal of the ν(SCN) strong
258 band is observed in the range of 2100 cm-1 as compared with the PhNCS and EtNCS
259 spectrums. Also, the absence of the ν(N-H) strong band of pyrazole derivatives in
260 the 3200±50 cm-1 range is indicative of complex formation. Two strong aliphatic
261 peaks in the ranges of 1302-1398 and 649-716 cm-1, respectively, were assigned to
262 ν(C-N) and ν(C-S) vibrations; these represents the band of the PhNCS or EtNCS
263 groups on the pyrazole ring. After complexation, new bands in the region of 400-
264 500 cm-1 are assigned to ν(M-N) and ν(M-S) stretching vibrations. The shifts of other
265 bands of the complexes compared with the corresponding ligands indicates
266 coordination of the atoms N, S to the metal (Fig S12-25) [44-46].
267 3.2. NMR spectral studies of ligands
1
13
268 The ligands N, S donor have been characterized by H NMR and C NMR
269 spectroscopy to determine the number of protons and carbons, respectively (Fig S1-

270 8). In the 1H NMR spectrum of ligand 1, -CH group in position 4 pyrazole ring shows
271 its proton signal at δ 6.32 ppm (t, 1H). A characteristic proton signal at δ 7.55 ppm
272 (d, 2H) is assigned to –CH groups in the 3,5 position on the pyrazole ring. In
273 addition to this, signals in the region δ 1.35 ppm (t, 3H) and δ 2.6- 2.89 ppm (q, 2H)
274 are attributed to –CH3 and –CH2 of the ethyl group. In spectra of ligand 2, the triplet
275 and doublet at δ 6.2 and 7 ppm can be linked to the pyrazole –CH in the position 4
276 and position 3,5 of pyrazole ring, respectively. In the case of ligand 3, the signal
277 observed at δ 6.09 ppm (s, 1H) is attributed to the pyrazole –CH in position 4 and a
278 signal at δ 2.13-2.40 ppm (s, 6H) is ascribed to the –CH3 of pyrazole. Also, signals
1
279 in the region δ 6.79-7.2 ppm (m, 6H) are due to aromatic proton. The H NMR
280 spectra 4 ligand is similar to 3; the only difference observed being a methyl group at
281 δ 2.31 ppm. The 13C NMR spectrum of the ligands N, S donor, exhibits the signals
282 in the region δ 120-130 ppm corresponding to aromatic carbons.

283
284
285
286
Scheme. 1 Structure of ligands, Na(EtNCSPz) (1), Na(PhNCSPz) (2), Na(PhNCSPzMe2) (3) and
Na(PhNCSPzMe3) (4).
287 3.3. UV-Vis spectra analysis
288 Electronic spectra of ligands 1, 2, 3 and 4 and their Ni, Co complexes were measured
289 in DMSO in the range of 200-800 nm and their results were summarized in Table 2,
290 (Fig S9-11). The measured UV-Vis spectra for all compounds were compared with
291 each other, the results showed each group (ligands, Ni complexes and Co complexes)
292 behave the same in solution. As can be seen ligands show two absorption bands in
293 the range of 265-278 and 290-340 nm, that corresponding to π→π* and n→π*
294 transitions, respectively. The shifts of the Ni(II) and Co(II) complex bands is relative
295 to the ligands which confirms formation of complex. Furthermore, the UV-Vis
296 spectra of the complexes in the DMSO show a ligand to metal charge transfer band

297 (LMCT) in the region of ~340-490 nm. In the Co(II) complexes, a weak shoulder
298 band at 580-620 nm can be attributed to a d-d band, which is assigned as a 3A2g→3Eg
299 (ν1) transition in a square-planar geometry. Also the Ni(II) complexes exhibits
300 absorption bands at 440-460 and 530-590 nm that can be attributed to 1A1g→1A2g
1
301 (ν1) and A1g →1B2g (ν2) transitions for a square-planar geometry. The obtained
302 results from Uv-Vis studies and crystal structure data, confirm square-planar
303 geometrical environment for both of the Ni(II) complexes [47-50].
304
Table 2. Electronic spectra of ligands and metal complexes.
Compound
λabs/nm
1
2
3
4
267, 290
269, 293
271, 307
270, 302
1a
1b
2a
2b
3a
3b
4a
4b
269, 295, 360, 458, 584
265, 293, 400, 600
268, 295, 387, 458, 549
269, 289, 421, 605
270, 308, 390, 420,553
269, 310, 410, 593
270, 310, 382, 432, 535
274, 298, 415, 604
305
306 3.4. Crystal structure
307 3.4.1. Crystal structure of 1a and 4a
308 The molecular structure of complexes 1a and 4a are shown in Fig.1 and 2,
309 respectively. Selected lengths and angles listed in Table 3. The structures show that

310 both of the complexes are mononuclear and the ligand to metal ratio is 2:1. Nickel
311 atoms adopt a four-coordinate geometry with an N2S2 donor environment via the
312 nitrogen atom from the pyrazole ring and sulfur atom from the thiocyanate of each
313 ligand. The distortion and exact geometry around the metal center can be expressed
314 with the parameter τ4, that were calculated from the largest (α) and second-largest
315 (β) angles around the metal center [51].
316 τ4= 60 ― (α + β)
141
317 When τ4 = 0 geometry is similar to square planar, while if τ4 is close to 1 then the
318 geometry is similar to tetrahedral [52]. The calculated value for 1a and 4a are 0,
319 0.26, respectively, that confirming an ideal square planar geometry for 1a and a
320 distorted square planar geometry for complex 4a. The geometrical analysis
321 demonstrates significant π-π interactions in both of the complexes (Fig.3 and 4)

322
323
324
Fig. 1 Molecular structure plot of complex 1a.
325
326
327
Fig. 2 Molecular structure plot of complex 4a.

328
329
330
331
Fig. 3 π-π interactions in complex 1a.
332
333
Fig. 4 π-π interactions in complex 4a.
334
335
336
337

338
Table 3. Selected bond lengths (Å) and angles (°) for complexes 1a and 4a.
Bond lengths (Å)
1a
4a
Ni1- S1
Ni1- S1i
Ni1- N1
Ni1- N1i
2.171
2.171
1.851
1.851
Ni1- S1
Ni1- S1i
Ni1- N1
Ni1- N1i
2.177
2.177
1.871
1.871
Bond angles (°)
1a
4a
S1- Ni1- N1
S1- Ni1- S1i
S1- Ni1- N1i
N1- Ni1- S1i
N1- Ni1- N1i
S1i- Ni1- N1i
87.50
180.00
92.50
92.50
180.00
87.50
S1- Ni1- N1
S1- Ni1- S1i
S1- Ni1- N1i
N1- Ni1- S1i
N1- Ni1- N1i
S1i- Ni1- N1i
86.92
154.49
95.57
95.57
168.73
86.92
339
340 3.5. Antibacterial activity
341 The synthesized ligands, their cobalt(II) and nickle(II) complexes, DMSO and
342 gentamicin were screened separately for antibacterial activity against Gram- positive
343 (B. subtilis) and Gram-negative (S. enterica) bacteria. Antibacterial results are
344 shown in Table 4. The experimental results of antibacterial screening of ligands and
345 their metal complexes showed that this activity against bacterial strains has increased
346 in comparison with the free ligands. Positive control (gentamaisin) showed a
347 significant zone of inhibition in the ranging 30 and 29 mm against Gram-positive
348 and Gram-negative bacterias, respectively. The negative control (DMSO solvent)

349 and paper disk revealed no inhibitory effect against any of the tested
350 microorganisms. Ligands and complexes showed a zone of inhibition ranging from
351 12.33-27 mm against B. subtilis and 11-25 mm against S. enterica. Among the
352 complexes, the (1b) [Co(EtNCSPz)2] showed the highest zone of inhibition against
353 both of the bacteria strains. The antimicrobial activities of compounds are often
354 attributed to their lipophilicity, and can be explained on the basis of the chelation
355 theory. In coordination compounds with chelation of ligands to metal ions, the
356 polarization of the metal ions is reduced to a greater extent due to the partial sharing
357 of the positive charge of the metal ions and the overlapping of the ligand orbital with
358 donor group of ligands. Moreover, the delocalization of the π-electrons over the
359 whole chelate ring is increased and lipophilicity of the complexes is enhanced.
360 Increasing the lipophilicity factor of the metal complex causes the higher rate of
361 entry into the lipid layers of the bacterial membranes. Furthermore, other factors that
362 influenced by the coordination of ligands to metal ions such as dipole moment and
363 solubility may also be possible reasons for increasing antibacterial activity of the
364 free ligands upon the complexes [53]. The experimental results indicated that
365 antibacterial activities of the synthesized compounds against Gram-positive bacteria
366 were more effective than Gram-negative strains. This is probably related to the lack
367 of an outer membrane in the Gram-positive bacteria, which acts as a barrier for
368 penetration of compounds [54].

369
Table 4. Zone of inhibition of the synthesized ligands and complexes
Compounds Zone of inhibition (mm)
B. subtilis
S. enterica
13.00
12.66
12.00
11.00
24.66
25.00
23.00
22.00
22.00
20.00
18.00
19.00
29.00
6 (NZ)
6 (NZ)
1
15.33
16.33
13.66
12.33
26.00
27.00
25.66
25.33
23.00
23.00
21.00
21.33
30.00
6 (NZ)
6 (NZ)
2
3
4
1a
1b
2a
2b
3a
3b
4a
4b
Gentamicin
DMSO
Filter paper disk
370
371
NZ = No zone of inhibition; diameter of filter disk is 6 mm.
372 3.6. Electrochemical studies
373 Electrochemical behavior of the synthesized ligands and metal complexes was
374 investigated using cyclic voltammetry in DMSO containing 0.1 M supporting
375 electrolyte. Fig 5 represents the cyclic voltammograms of the ligand 1 and complex
376 1b. As can be seen in the figure, ligand 1 has one cathodic peak at about -800 mV
377 which can be attributed to the reduction of the ligand which similarly appear in 1b.

378 The cathodic and anodic peaks at about -460 and -180 mV with the formal potential
379 of -320 mV is attributed to the quasi-reversible (ΔE=280 mV) redox reaction of Co3+
380 + e-  Co2+ [55, 56]. The results show that the synthesized complex is
381 electrochemically an active species which could be used as a novel electrode
382 material for sensing and storage purposes. Similar studies for the nickel complexes
383 were done (not shown) with a quasi-reversible behavior (ΔE=300 mV) with the
384 formal potential of about -450 mV corresponding to the Ni(II)/Ni(I) couple. In order
385 to evaluate the effect of the substituted ligand on the electrochemical behavior, the
386 cyclic voltammograms of the complexes with different ligands were studied and the
387 results are summarized in Table 7. According to previous reports electron- donor
388 groups made the reduction of ligand more difficult and the reduction and oxidation
389 waves should be shifted to more negative values [57]. The results on Table 5 show
390 that upon substation of the ligands by the donor derivatives such as phenyl and
391 methyl groups, the cathodic and anodic peaks and also formal potentials were shifted
392 to negative values.

0.004
0.002
0
-0.002
-0.004
-0.006
-0.008
-0.01
1
1b
-1400
-900
-400
100
600
1100
E / mV
393
394
395
396
Fig.5 Cyclic voltammograms of compounds 1 and 1b using a glassy carbon electrode with tetrabuthyl
ammonium perchlorate as the supporting electrolyte in DMSO at room temperature with scan rate 100 mV
s-1.
397
398
Table 5. Cyclic voltammetric (scan rate= 100 mVs-1) data for compounds
Compund
Ec (mV)
-550
-460
-595
-507
-624
-537
-640
-550
Ea (mV)
-290
Ef (mV)
-420
-320
-460
-360
-487
-389
-505
-405
1a
1b
2a
2b
3a
3b
4a
4b
-180
-325
-213
-350
-241
-370
-260
399
400 4. Conclusion
401 In summary, N, S donor pyrazole based ligands and their Ni(II) and Co(II)
402 complexes were synthesized and characterized by spectroscopic and
403 crystallographic methods. Single crystal X-ray analysis and calculated τ4 parameter
404 of two synthesized nickel complexes indicated these complexes were four coordinate
405 with square planar geometries. In addition, ligands were coordinated to the metal

406 centers via the nitrogen atom of the pyrazole group and sulfur atom of isothiocyanate
407 group on the ligands. The result of antimicrobial investigation confirmed that
408 synthesized ligands and complexes are bioactive and showing good antibacterial
409 activity in compare with earlier similar investigated compounds and can be
410 promising candidate for further evaluations for antimicrobial applications. Also it
411 has also been proposed that the chelation of metal to ligand plays a vital role in
412 increasing of inhibition, metal complexes exhibite significantly enhanced
413 antibacterial activity against investigated strains in comparison to the free ligands.
414 On the other hand, the electrochemical behavior indicated that electron donor
415 derivatives on the ligands made the reduction of compounds more difficult and the
416 oxidation and reduction waves were shifted to more negative values.
417
418 Acknowledgments
419 We are most grateful to the University of Azarbaijan Shahid Madani for the generous
420 financial support of this research. X-ray crystallography experiments were
421 performed at the University of Akron. We thank them for their helpful collaboration.
422
423 Appendix A. Supplementary data
424 CCDC 1962457 and 1962892 contain the supplementary crystallographic data for
425 1a and 4a. These data can be obtained free of charge from The Cambridge
426 Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
427
428
429

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444
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446
447
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449
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452
453
454
455
456
457
458
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