Synthesis, crystal structure, bioactivities of Ni(II), Cu(II), Co(II) and Pd(II) complexes with unsymmetrical thioether donor Schiff base: Phosphine free Pd(II) complex catalyzed Suzuki reaction

Article abstract of DOI:10.1016/j.poly.2015.05.020

A series of new Ni(II), Cu(II), Co(II) and Pd(II) complexes were synthesized from the reaction of thioether containing Schiff base ligand with corresponding metal salts by a simple environmentally benign procedure. The molecular formulae of ligand and their complexes are (C₂₁H₁₉NO₂S)₂,1, [Ni(C₂₁H₁₈NO₂S)₂]·CH₃OH·H₂O,2, [M(C₂₁H₁₈NO₂S)₂] (3 and 4), where (M = Cu(II) and Co(II)) and [Pd(C₂₁H₁₈NO₂SCl)](5). All complexes were characterized by elemental analysis, FT-IR, UV–Vis spectroscopy and single crystal X-ray diffraction analysis. The ligand was characterized by same techniques and with ¹H NMR spectroscopy. X-ray diffraction study reveals that copper complex adopts square planar geometry by coordinating via deprotonated hydroxyl oxygen, azomethine nitrogen of ligand to the copper centre and sulfur atoms remain unligated. As expected, nickel complex acquired a distorted octahedral geometry coordinating via deprotonated hydroxyl oxygen, azomethine nitrogen and thioether sulfur atoms of ligands. Interestingly, one water and one methanol molecule are attached at the out sphere of the nickel complex. Suzuki reaction was carried out in open atmospheric conditions using palladium complex as catalyst. The significant features of the palladium complex catalyzed reaction are good yield, simple workup procedure, easy purification and easy recovery technique of the catalyst. The reported palladium complex is phosphine free, air stable, moisture insensitive. The ligand and complexes show very good biological activities against Mycobacterium abscessus, Bacillus subtilis, Staphylococcus aureus, Proteus vulgaris, Mycobacterium smegmatis and Escherichia coli.

Full text of DOI:10.1016/j.poly.2015.05.020

Accepted Manuscript
Synthesis, crystal structure, bioactivities of Ni(II), Cu(II), Co(II) and Pd(II)
complexes with unsymmetrical thioether donor Schiff base: Phosphine free
Pd(II) complex catalyzed Suzuki reaction
Mukul Kalita, Kashyap Jyoti Tamuli, Pranjit Barman, Bipul Sarma, Reshita
Baruah, Hari Prasanna Deka Boruah
PII:
S0277-5387(15)00262-4
DOI:
http://dx.doi.org/10.1016/j.poly.2015.05.020
POLY 11319
Reference:
To appear in:
Polyhedron
Received Date:
Accepted Date:
27 February 2015
1 May 2015
Please cite this article as: M. Kalita, K.J. Tamuli, P. Barman, B. Sarma, R. Baruah, H.P. Deka Boruah, Synthesis,
crystal structure, bioactivities of Ni(II), Cu(II), Co(II) and Pd(II) complexes with unsymmetrical thioether donor
Schiff base: Phosphine free Pd(II) complex catalyzed Suzuki reaction, Polyhedron (2015), doi: http://dx.doi.org/
1
0.1016/j.poly.2015.05.020
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Synthesis, crystal structure, bioactivities of Ni(II), Cu(II), Co(II) and
Pd(II) complexes with unsymmetrical thioether donor Schiff base:
Phosphine free Pd(II) complex catalyzed Suzuki reaction
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a
a
a*
b
c
Mukul Kalita , Kashyap Jyoti Tamuli , Pranjit Barman , Bipul Sarma , Reshita Baruah ,
c
Hari Prasanna Deka Boruah
a
Department of Chemistry, National Institute of Technology, Silchar 788010, Assam, India
b
Department of Chemical Sciences, Tezpur University, Tezpur 784028, Assam, India
c
Biotechnology Division, CSIR-North East Institute of Science and Technology, Jorhat, 785006,
Assam, India
E-mail: mukulkalita88@gmail.com (M. Kalita), kashyap1309@gmail.com (K. J. Tamuli)
barmanpranjit@yahoo.co.in (P. Barman), bcsarma@tezu.ernet.in (B. Sarma),
reshitabaruah@yahoo.com (R. Baruah), hpdekaboruah@yahoo.com (H.P. Deka Boruah)
Abstract
A series of new Ni(II), Cu(II), Co(II) and Pd(II) complexes were synthesized from the reaction
of thioether containing Schiff base ligand with corresponding metal salts by a simple
environmentally benign procedure. The molecular formulae of ligand and their complexes are
C H NO S) ,1, [Ni(C H NO S) ].CH OH.H O,2, [M(C H NO S) ] (3 & 4), where
21
19
2
2
21 18
2
2
3
2
21 18
2
2
(
M=Cu(II) and Co(II)) and [Pd(C H NO SCl)](5). All complexes were characterized by
21 18 2
_
____________
Corresponding author. Tel.: +91 9435374128
E-mail address: barmanpranjit@yahoo.co.in (P. Barman)
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elemental analysis, FT-IR, UV-Visible spectroscopy and single crystal X-ray diffraction
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analysis. The ligand was characterized by same techniques and with HNMR spectroscopy. X
ray diffraction study reveals that copper complex adopts square planar geometry by coordinating
via deprotonated hydroxyl oxygen, azomethine nitrogen of ligand to the copper centre and sulfur
atoms remain unligated. As expected, nickel complex acquired a distorted octahedral geometry
coordinating via deprotonated hydroxyl oxygen, azomethine nitrogen and thioether sulphur
atoms of ligands. Interestingly, one water and one methanol molecule are attached at the out
sphere of the nickel complex. Suzuki reaction was carried out in open atmospheric conditions
using palladium complex as catalyst. The significant features of the palladium complex catalyzed
reaction are good yield, simple workup procedure, easy purification and easy recovery technique
of the catalyst. The reported palladium complex is phosphine free, air stable, moisture
insensitive. The ligand and complexes show very good biological activities against
Mycobacterium abscessus, Bacillus subtilis, Staphylococcus aureus, Proteus vulgaris,
Mycobacterium smegmatis and Escherichia coli.
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Keywords: Thioether; Crystal structure; Schiff Base; Phosphine free ligand; Suzuki reaction;
Bioactivity
Introduction
In recent years, interest in coordination chemistry of Schiff base ligand with ONS donating sites
have increased due to capabilities of forming stable complexes [1] and have a wide range of
antifungal [2], antibacterial [3, 4], anticancer properties [5]. The combination of thioether with
imine moiety escalates such properties [6]. So, attempts to design model complexes which can
possibly mimic such activity with reported biologically active compounds. Nickel with N/S
coordinating sphere is present in several metalloenzymes and this property encourages in
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synthesizing N/S coordinated nickel complexes [7]. Incorporation of thioether atom in copper
complex is important due to presence of N/S atoms in most copper containing mettaloenzymes.
Cobalt complexes with thioether are also interesting as they can mimic the role of sulfur donor
site around cobalt in enzyme like nitrile hydratase [8]. Apart from biological activities they gain
interest in varied catalytic activities due to their deep involvement in organic synthesis with
several ligand systems [9]. There have been different notable examples on activity of Schiff base
complexes in heterogeneous as well as homogeneous catalysis [6, 10, 11, 12, 13, 14, 15, 16].
Palladium complex catalyzed Heck reaction, Suzuki reaction etc. are important tool for
construction of aryl-carbon bond [17]. However, phosphine containing palladium complexes
failed to catalyze C-C coupling raection with aryl chlorides [18]. Now a days, researchers are
given interest in simpler, faster, cheaper and more efficient methodologies for such coupling
reactions [19].
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The present article deals with the synthesis of tridentate N-(4-metoxy phenol)-2-
methyliden-2-benzylthiophenyl amine HL, ligand and its Ni(II), Cu(II), Co(II) and Pd(II)
complexes of composition [NiL ].CH OH.H O,2, [CuL ] 3 [CoL ] 4, and [PdLCl],5. The
2
3
2
2 ,
,
2 ,
complex formations have been authenticated by X-ray diffraction studies, UV-Visible
spectroscopy and elemental analyses. The ligand formation was confirmed by same techniques
1
and HNMR spectroscopy. The synthesized phosphine free palladium complex shows excellent
catalytic activities towards Suzuki reaction under mild conditions. All compounds show
considerable antibacterial and antifungal properties Mycobacterium abscessus, Bacillus subtilis,
Staphylococcus aureus, Proteus vulgaris, Mycobacterium smegmatis and Escherichia coli.
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. Experimental
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.1. Physical measurement
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Nickel acetate tetrahydrate (Merck), copper nitrate trihydrate (Merck), cobalt sulphate
heptahydrate (Merck), 2-hydroxy-5-methoxy benzaldehyde (Alfa Aeser), sodium
tetrachloropalladate (Alfa Aeser) were used as obtained. 2-(benzylthio) aniline was prepared
according to literature method [20]. Elemental analyses were recorded on Perkin-Elmer Model
2
40C elemental analyzer. Electrical conductivities were measured on CM-180 Conductivity
meter (Elico India). Electronic spectra were measured on Cary 100 Bio UV-Visible
spectrophotometer. Magnetic susceptibilities were measured on conventional Gouy balance
using freshly prepared Hg[Co(NCS) ] as calibrant by Magway MSB MK1 Magnetic
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susceptibility balance, Sherwood Scientific, Cambridge, UK. Infrared spectra of the ligand and
complexes were recorded on IR-affinity-I FTIR Spectrometer SHIMADZU as KBr Pellet.
1
Melting points were recorded on a Veego melting point apparatus and were uncorrected. The H
NMR spectrum was recorded on a Bruker 400 DRX spectrometer in CDCl solution, using TMS
3
as the internal standard. All other reagents and solvents used were of commercially grade and
employed as received or purified by standard methods prior to use. All reactions were carried out
at open atmosphere.
2
.2. Preparation of N-(4-metoxy phenol)-2-methyliden-2-benzylthiophenyl amine (1)
In a simple procedure, 2-hydroxy-5-methoxy benzaldehyde (0.1 mL, 1 mmol) was added drop
wise with continuous stirring to a 30 ml ethanolic solution of 2-(Benzylthio) aniline (0.215 g, 1
mmol). The solution was stirred for another 30 minutes and the color of the solution changes to
orange yellow. The solution was kept in freezing condition for 6 hours. The orange yellow
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crystalline product formed was filtered off, washed several times with 25% ethanol-water
-2
solution to remove the impurities and dried in vacuum (10 torr) (Purity was checked by TLC).
o
-1
Yield 89.2%. M.P. 180 C. IR (KBr pellet, cm ): 3413(m), 1695(s), 1604(s), 1429(s), 1109(s),
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35(s). H NMR (CDCl , 400 MHz): δ 13.70 (1H, s, OH), 8.41 (1H, s, CH=N), 7.08-7.32 (13 H,
3
-1
-
m, Ar-H), 4.11 (3H, s, OCH ) and 3.81 (2H, s, CH ). UV-Vis [DCM, λmax, nm(ε max, Lmol cm
3
2
1
)
]: 259 (37881), 396 (26385). Anal. Calc. for C H NO S, M.W.: 349.45, C, 72.18; H, 5.48; N,
21 19 2
4.01; S, 9.18. Found: C, 72.09; H, 5.40; N, 3.92; S, 9.05 %. The reaction scheme for synthesis of
ligand is shown in Scheme 1.
H CO
3
CHO
OH
NH2
OH
Ethanol
S
+
N
RT 30 Minutes
H CO
S
3
Scheme 1: Synthesis of ligand
2
.3. Preparation of [NiL ].CH OH.H O complex (2)
2 3 2
In a simple procedure, the ligand, 1 (0.698g, 2 mmol) was dissolved in boiling methanol (30 mL)
followed by addition of 2 mmol methanolic (10 ml) NaOH solution. Then a methanolic solution
(30 ml) of nickel acetate tetrahydrate (0.248g, 1 mmol) was added drop wise to above solution
with continuous stirring. The solution was stirred for 30 minutes. The color of the solution
changed to brown-black. Then the solution was kept undisturbed for 3 days. The black-brown
needle like crystals suitable for single crystal X-ray diffraction study formed was filtered off,
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washed with 25% methanol-water solution for several times to remove the impurities and dried
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under vacuum (10 torr) (Purity was checked by TLC). Yield 69.8%. MP 286 C. IR (KBr,cm ):
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929(s), 1734(s), 1591(s), 1456(s), 1149(s), 1011(s), 680(s), 582(m). UV-Vis [DCM, λmax, nm(ε
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max, Lmol cm )]: 273 (35798), 308 (26741), 501 (8120). Anal. Calc. for C H N NiO S ,
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6 2
M.W.: 805.63, C, 64.11; H, 5.25; N, 3.48; S, 7.96. Found: C, 64.01; H, 5.14; N, 3.23; S, 7.84 %.
.4. Preparation of [CuL ] complex (3)
2
2
The preparation of complex 3 follows the same procedure as that of 2 except that copper nitrate
trihydrate (0.241g 1 mmol) was used. The resulting solution was kept undisturbed for 24 hours
after color changes to bluish black. The bluish black needle like crystals suitable for single
crystal X-ray diffraction study formed was filtered off, washed with 25% methanol-water
-2
solution for several times to remove the impurities and dried under vacuum (10 torr) (Purity was
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-1
checked by TLC). Yield 70.6 %. MP 246 C. IR (KBr,cm ): 2983(s), 1734(s), 1593(s), 1465(s),
-1
-1
1
255(s), 756(s), 663(m), 567(m). UV-Vis [DCM, λmax, nm(ε max, Lmol cm )]: 272 (35009), 445
(7402), 503 (6763). Anal. Calc. for C H CuN O S , M.W.: 760.42, C, 66.34; H, 4.77; N, 3.68;
4
2
36
2
4 2
S, 8.43. Found: C, 66.21; H, 4.69; N, 3.56; S, 8.38%.
2
.5. Preparation of [CoL ] complex (4)
2
The preparation of complex 4 follows the same procedure as that of 3 except that cobalt sulphate
heptahydrate (0.281g 1 mmol) was used. The resulting solution was kept undisturbed for 2 days
after color changes to black. Black micro crystals were collected by filtration and washed with
25% methanol-water solution for several times to remove the impurities and dried under vacuum
-2
o
_1
(
10 torr) (Purity was checked by TLC). Yield 64.7%. MP 239 C. IR (KBr,cm ): 2918(s),
1729(m), 1589(s), 1456(s), 1153(m), 1031(m), 752(s), 686(s). UV-Vis [DCM, λmax, nm(ε max
,
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Lmol cm )]: 275 (38726), 306 (29820), 506 (7391). Anal. Calc. for C H CoN O S , M.W.:
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55.81, C, 66.74; H, 4.80; N, 3.71; S, 8.48. Found: C, 66.61; H, 4.69; N, 3.67; S, 8.42%.
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.6. Preparation of [PdLCl] complex (5)
Sodium tetrachloropalladate (250 mg, 0.85 mmol) is dissolved in 15 ml ethanol. It was added
drop wise to a boiling ethanolic solution (15 ml) of ligand, HL (258 mg, 0.81 mmol). The
0
solution was stirred in water bath at 90 c for 1 hour. The color of the solution changed to bright
red. The resulting solution was kept undisturbed for 1 hour. The red micro crystals were
collected by filtration and washed with 25% ethanol-water solution for several times to remove
-2
the impurities and dried under vacuum (10 torr) (Purity was checked by TLC). Yield 83.2%.
0
-1
MP: above 300 C. IR (KBr,cm ): 3290(m), 2990(m), 1710(m), 1630(s), 1439(s), 1140(s),
-1
-1
1
4
040(s), 725(s), 651(s). UV-Vis [DCM, λmax, nm(ε max, Lmol cm )]: 264 (32473), 328 (28398),
95 (5466). Anal. Calc. for C H ClNO PdS, M.W. 490.31 C, 51.44; H, 3.70; N, 2.86; S, 6.54.
2
1
18
2
Found: C, 51.32; H, 3.61; N, 2.77; S, 6.43 %. The reaction scheme for the synthesis of metal
complexes is shown in Scheme 2.
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H CO
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S
CoCl .4H O
Methanol
2
2
Cu(CH3COO)2. H2O
1(HL)
Methanol
RT 30 Min
&
RT 30 Min
NiCl .6H O
2
2
H CO
3
H CO
3
Ethanol
RT- 1 Hr
Na PdCl
2
4
N
M
N
N
O
S
S
O
M
S
S
O
H CO
O
3
N
O
2
3 & 4
OCH3
Pd Cl
N
OCH3
S
5
Scheme 2: Synthesis of metal complexes
2
.7. General experimental procedure for the Suzuki reaction:
A mixture of aryl boronic acid (3.5 mmol), aryl halide (3.5 mmol), the palladium complex (0.001
mmol) and potassium carbonate (8.0 mmol) in methanol (10 ml) were heated to reflux for 24
hours. After evaporation of solvent, the residue was poured into water and extracted with diethyl
ether. The ether solution was dried over Na SO to remove trace water content and filtered. The
2
4
ether solution was passed through silica column (60–120 mesh) and catalyst remains trapped.
After extraction of desired compound, catalyst was extracted using dichloromethane. Pure
product was obtained upon evaporation of the ether. The yields of the products were determined.
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5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
2
.8 Antibacterial activity analysis:
The antibacterial assay was performed against test pathogens Mycobacterium abscessus, Bacillus
subtilis, Staplylococcus aureus, Proteus vulgaris, Mycobacterium smegmatis and Escherichia
coli by adopting agar diffusion assay method [21]. The presence of inhibition zone (in mm)
around the well was observed. All bacterias were cultured in Mueller Hinton broth (MHB) at 37
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
o
C for 24 h. Experiments were carried out in a laminar flow by strictly maintaining aseptic
conditions. 100 µL of fresh inoculum from each culture was added on the plates and spread using
sterilized spreader. Wells were punctured on freshly spread bacterial culture on MHA. A stock
solution of 10 mg/ml of each compound was prepared in DMF solvent and each compound (20
µg) was added to the wells. Four wells were bored on each plate, each filled with same
compound and two plates for each test compound were taken. All the plates were incubated at
o
3
7 C for 24 h. Growth inhibition of test organisms was measured with standard scale, the mean
values of inhibition zones were taken and the data were compared with standard drug kanamycin
acid sulphate.
2.9. X-ray data collections, crystal structure solutions and refinement:
Single-crystal X-ray Diffraction data collections for compound 2 and 3 at 296 K were performed
with Mo Kα radiation (λ=0.71073Å) using a Bruker Smart Apex II CCD diffractometer equipped
with graphite monochromator. The SMART [22] software was used for data collection and also
for indexing the reflections and determining the unit cell parameters. Collected data were
integrated using SAINT [22] software. The structures were solved by direct methods and refined
by full-matrix least-square methods using SHELXTL [23] software. Absorption corrections were
done by multi-scan method (SADABS) [22]. All the non-H atoms were refined in the anisotropic
9

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
2
approximation against F of all reflections. The H-atoms were placed at their calculated positions
and refined in the isotropic approximations. Details of crystal analysis, data collection and
structure refinement data are summarized in Table 1. The same atom numbering scheme was
adopted for every structure to simplify further structural description.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
1
0

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
Table 1: Crystal structure refinement details for the two complexes 2 and 3.
Compound
Nickel complex
Copper complex
CCDC entry no.
Empirical formula
Formula weight
T (K)
1020519
C43 H42 N2 Ni O6 S2
805.60
1020520
C42 H36 Cu N2 O4 S2
760.40
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
296(2) K
296(2)
λ (Ǻ)
0.71073 Å
0.71073
Crystal system
Space group
Unit cell dimensions
a (Ǻ)
Orthorhombic
Orthorhombic
Pbca
Pca (1)
2
21.1584 (7) Å
11.3032 (3) Å
15.9419(6) Å
90°
90°
90°
20.4740 (6) Å
7.5475 (2) Å
22.2830 (6) Å
90°
90°
90°
b (Ǻ)
c (Ǻ)
o
α ( )
o
β ( )
o
γ ( )
V (Ǻ )
3
3
3
3
4
812.6 (2) Å
3443.34(16) Å
4
1.467 g/cc
Z
3
Dcalc (Mg/m )
μ (mm )
1.404 g/cc
0.670 mm
-1
-1
-1
0.804 mm
F (0 0 0)
Crystal size (mm )
θ range for data collection ( )
Index ranges
1
0
688
.32 x 0.21 x 0.16 mm
1580
3
3
3
0.31 x 0.18 x 0.12 mm
1.83 to 26.28°.
-25 ≤ h ≤ 20
-9 ≤ k ≤ 9
-23 ≤ l ≤ 27
14235
o
2.31 to 20.55°
25 ≤ h ≤ 26
-13 ≤ k ≤ 13
11 ≤ l ≤ 19
5941
5151 [R(int) = 0.0707]
00.0 %
-
-
1
Reflections collected
Independent reflections (Rint)
3485 [R(int) = 0.0447]
98.3 %
Completeness (%)
1
Absorption correction
Semi-empirical from
equivalents
Semi-empirical from
equivalents
Max and min transmission
Refinement method
0
.9003 and 0.8141
0.9710 and 0.5904
Full-matrix least-squares on
F
Full-matrix least-squares
on F
2
2
Data/restraints/parameters
Goodness-of-fit on F
5151 / 0 / 502
3485 / 0 / 233
1.113
2
1
.004
Final R indices [I>2ζ(I)]
R indices (all data)
R1=0.0430, wR2=0.0828 R1 = 0.0382, wR2 = 0.1050
R1=0.0596, wR2=0.0912 R1 = 0.0502, wR2 = 0.1210
1
1

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
3
3
. Results and discussion
.1 Characterization
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
3.1.1. H NMR spectrum of ligand (1)
1
The H NMR (400 MHz) spectrum of ligand (HL) 1 was recorded in CDCl in the range 0-15
3
1
(ppm). The H NMR spectrum shows signal as singlet δ 13.70 ppm downfield for phenolic
proton. Another singlet appears at δ 8.41 ppm due to benzilidemine proton (CH=N). The
multiplet, singlet and singlet appear at δ 7.08-7.32, δ 4.11 and δ 3.81 ppm for aromatic (Ar—H),
methoxy proton and benzylic protons (CH ) respectively.
2
3
.1.2. Infrared spectroscopy
The ligand exhibits characteristics ν(O—H), ν(C=C), ν(C—S), ν(C=N) bands at 3413, 1604,
-1
1429, 735 cm respectively. The absence of ν(O—H) band in all metal complexes indicates the
-1
deportation of ligand. The appearance of a band for ν(C=N) in the range of 1600-1589 cm
-1
which shows a shifting to the lower frequencies by 7-5 cm compared to ligand (HL) suggesting
the complexion of ligand with metal atom through nitrogen atom. Moreover, in complexes
-1
phenolic ν(C—O) stretching is shifted by 20-32 cm towards lower wave numbers compared to
ligand indicating coordination of the phenolic oxygen to the metal ion [24]. The metal complexes
-1
show bands in the range 750-756 cm for ν(C—S) band shifted to higher frequencies compared
-1
to ligand confirmed the M—S bond [25]. The new band for complexes in the range 651-680 cm
tentatively assigned coordination with oxygen atom [24]. Metal sulfur stretching frequencies
-1
occur in the (480± 210 cm ) range but are often difficult to detect as they tend to be weak and
quite broad [9].
1
2

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
3
.1.3. Electronic spectroscopy
The electronic spectra of ligand and complexes are recorded in dichloromethane medium. The
bands for ligand, 1 at 259 nm and 396 nm due to n-π* transition of the imine moiety and π-π*
transition of phenyl rings respectively [26]. Nickel(II) complex, 2 shows two peaks in 273 nm
and 308 nm which are due to n—π*, π—π* transitions respectively. The presence of only one
band in 500-800 nm region in the electronic spectrum of nickel(II) complex shows evidence of
octahedral coordination [27]. The intense band at 501 nm in spectrum of nickel(II) complex is
probably combination of a d-d transition and S-Ni charge transfer band [28]. The electronic
spectrum of copper(II) complex, 3 shows bands at 267 nm and 427nm suggesting n—π*, π—π*
transitions respectively. In copper(II) complex the d-d transition cannot be observed as it is
obscured by strong charge transfer transition [29]. The appearance of band at 509 nm show the
evidence of square based geometry around Cu(II) centre [30, 31]. Again, the Cobalt(II) complex,
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
4
shows bands at 275 nm and 306 nm due to n—π*, π—π* transitions respectively. The low
energy absorption for cobalt(II) complex is appeared around 506 nm due to due to a MLCT
transition [32]. It is interesting to observe that palladium(II) complex, 5 shows a low energy band
in the range 502 nm and a structured band within the range 330 nm for MLCT transitions [33,
3
3
4].
.1.4. Molar conductivity
The molar conductivity of complexes is taken in acetonitrile medium. The values of complexes
2
-1
2
, 3, 4 and 5 are 25.9, 20.7, 33.4 and 39.7 s cm mol respectively. The molar conductivity
2
-1
values in the range 20.7-39.7 s cm mol confirm non-electrolytes nature of complexes [35].
1
3

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
3
.1.5. Magnetic measurement
The magnetic moment (µ ) for nickel complex, 2 was found to be 2.79 BM. This value is quite
eff
8
good agreement to the spin only value of 2.83 BM for d system with O symmetry. Copper
h
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
9
complex, 3 show 1.69 BM and confirmed d configuration with square planar geometry [36].
The magnetic moment of the cobalt complex, 4 is 5.17 BM. This value almost closes with high
spin octahedral cobalt(II) complex [37].
3.2. X-ray crystallography
3
.2.1. Structure description of nickel complex, 2
The molecular structure of Nickel complex, 2 shows octahedral geometry (Figure 1). The
complex is a six coordinated centrosymmetrical mononuclear complex. It crystallizes in the
orthorhombic space group Pca (1). Interestingly, one methanol and one water molecule resides in
2
the asymmetric unit. The methanol and water molecules are hydrogen bonded to the phenolic
oxygen atoms of each of the coordinated ligand molecules. Nickel atom is in axially distorted
octahedron condition. The equatorial plane is satisfied by two thioether atoms and two hydroxyl
oxygen atoms. The two imine nitrogen atoms are remained in axial position. The Ni—O
distances are 2.000(3) Å, 2.007(3) Å. Whereas Ni—S distances are 2.433(14) Å, 2.476(13) Å.
Ni—N distances are 2.035(4) Å, 2.035(4) Å [9]. The bite angles are O2—Ni1—O1 (88.74(12) ˚),
O1—Ni1—S2 (95.33(10) ˚), S2—Ni1—S1 (82.92(4) ˚), O2—Ni1—S1 (93.39(9) ˚). The bond
angles N2—Ni1—N1 (175.35(16) ˚) indicates distortion from ideal octahedral geometry. Some
selected bond lengths and bond angles are summarized in Table 2.
1
4

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
Figure: 1 Molecular structure of the nickel complex, 2 shown with 35 % probability ellipsoids.
3
.2.2. Structure description of copper complex, 3
Copper complex, 3 adopts square planar geometry. The perspective view of the crystal structure
is shown in Figure 2. An approximately square planar geometry is formed around Cu atom by
two deprotonated hydroxyl nitrogen atoms and two imine nitrogen atoms. However, two sulfur
atoms are remained unligated. This may be due to soft nature of sulfur atoms. Moreover, most
copper complexes interested to form tetradentate complexes. Bulkiness of the ligand also favored
in this regard. The bond angles O1—Cu1—N1, O1—Cu1—N1, O1—Cu1—N1, O1—Cu1—N1
are 87.86(7) ˚, 92.14(7) ˚, 92.13(7) ˚, 87.87(7) ˚. The significant discrepancies in bond angles
1
5

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
show the deviation from square planar geometry. The bond lengths Cu1—O1, Cu1—O1, Cu1—
N1, Cu1—N1 are 1.8716(17) Å, 1.8717(17) Å, 2.0137(19) Å, 2.0137(19) Å respectively [38].
Some selected bond lengths and bond angles are summarized in Table 3.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
Figure: 2 Molecular structure of copper complex, 3 shown with 35 % probability ellipsoids
3
.2.3. Hydrogen bonding in nickel and copper complexes (2 & 3)
The hydrogen bonds along with equivalent positions are summarized in Table 4. The water and
methanol molecules in nickel complex are connected by O—H…O interactions forming one
dimensional chain along c-axis (Figure 3). 1D chain is connected by C—H…O and C—H… π
interactions between host molecules that fulfill the crystal packing (Figure 4). In copper
complex, molecules are stacked via C—H… π and C—H…O interactions along b-axis (Figure
1
6

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
5
). Columnar stacks are connected by C—H…O interactions that complete the 3D packing
(Figure 6).
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
Figure: 3 Water and methanol connected through O—H…O interactions in nickel complex, 2.
Figure: 4 C—H…O and C—H… π interactions in nickel complex, 2.
1
7

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
Figure: 5 C—H… π and C—H…O interactions in copper complex, 3.
Figure: 6 C—H…O interactions in copper complex, 3.
1
8

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
Table 2: Selected bond lengths (Å) and bond angles (˚) for 2
Bond length
Ni1—O2
Ni1—O1
Ni1—N2
Ni1—N1
Ni1—S2
Ni1—S1
O1—C1
O4—C43
N1—C7
N1—C8
N2—C27
N2—C28
S1—C13
S1—C14
S2—C33
S2—C34
Bond angle
2.000(3)
2.007(3)
2.035(4)
2.035(4)
2.433(14)
2.476(13)
1.309(5)
1.274(8)
1.309(5)
1.399(5)
1.294(6)
1.427(5)
1.772(4)
1.830(5)
1.785(5)
1.834(5)
O2—Ni1—O1
O2—Ni1—N2
O1—Ni1—N2
O2—Ni1—N1
O1—Ni1—N1
N2—Ni1—N1
O2—Ni1—S2
O1—Ni1—S2
N2—Ni1—S2
N1—Ni1—S2
O2—-Ni1—S1
S1—Ni1—S1
N2—Ni1—S1
N1—Ni1—S1
S2—Ni1—S1
88.74(12)
90.59(14)
94.38(14)
91.94(14)
89.58(14)
175.35(16)
173.63(10)
95.33(10)
84.23(12)
92.98(11)
93.39(9)
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
171.18(10)
94.03(11)
81.91(11)
82.92(4)
Table 3: Selected bond lengths (Å) and bond angles (˚) for 3
Bond length
Cu1—O1
Cu1—N1
S1—C14
S1—C15
O2—C4
O2—C7
O1—C1
N1—C8
N1—C9
Bond angle
1.871(17)
2.013(19)
1.775(2)
1.830(3)
1.385(3)
1.428(3)
1.319(3)
1.306(3)
1.441(3)
O1—Cu1—O1
O1—Cu1—N1
N1—Cu1—N1
C14—S1—C15
C4—O2—C7
C1—O1—Cu1
C8—N1—C9
C8—N1—Cu1
C9—N1—Cu1
N1—C8—C6
180.0
87.86(7)
180.0(5)
97.92(11)
116.45(18)
130.64(16)
114.8(2)
123.97(17)
121.01(15)
126.8(2)
1
9

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
Table 4: Hydrogen bond geometries.
H Bond
D-H(Å) d (Å)
Nickel complex, 2
1.67 2.646 (6) 171
D (Å)
Angle (°) Equivalent positions
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
O5‒ H5A∙∙∙O1
O6‒ H6A∙∙∙O5
O6‒ H6B∙∙∙O3
C11‒ H11∙∙∙O2
C14‒ H14B∙∙∙O6
C36‒ H35A∙∙∙O5
0.98
0.98
0.98
1.08
1.08
1.08
1/2+x,1-y,z
-
1.90
1.94
2.38
2.28
2.38
2.859(6)
2.856(6)
3.408(5)
3.356(6)
3.445(6)
163
155
158
173
166
1/2-x,y,1/2+z
1/2+x,1-y,z
1/2-x,y,-1/2+z
-1/2+x,1-y,z
Copper complex, 3
C11‒ H11∙∙∙O2
1.08
1.08
2.42
2.45
3.405 (6) 150
3.477 (4) 158
-x,1/2+y,1/2-z
-x,1-y,-z
C15‒ H15B∙∙∙O1
3.3. Palladium complex catalyzed phosphine free Suzuki reaction
Suzuki reaction is most important palladium catalyzed C–C coupling reaction in organic
synthesis. In this case, phosphine moiety containing palladium complex are widely used. But,
most palladium complexes of phosphine ligands are air and moisture sensitive and therefore P—
C bond decomposition occurs at elevated temperature which poisons the metal, leading to
decomposition of the catalyst and affects in conversion and selectivity of Suzuki reaction [39].
The reported thioether containing palladium complex is thermally stable and insensitive to
oxygen and moisture. The apparent stability of present complex has led to precise mode of
action. A few works has been reported with thioether containing palladium catalyzed Suzuki
reaction. The synthesized palladium complex show very good catalytic activity towards Suzuki
reaction (Scheme 3). We have tried for the ability of the catalyst for optimization of coupling
2
0

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
reaction between iodobenzene and phenylboronic acid with different amounts of the catalyst,
solvents, bases and at different temperatures (65, 85 and 100 ◦C) (Table 5). The effect of bases
(
Et N, Na CO and K CO ), solvents (nonpolar, protic and aprotic) and catalyst amount are
3 2 3 2 3
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
summarized (Table 6). Among the bases, K CO was found to be the most effective. Our
2
3
investigation show methanol is found to be best choice. 1 mol% of palladium complex gave the
o
optimum results using methanol as solvent and 65 C as the reaction temperature. Thus, the
optimum conditions are: iodobenzene (1 mmol), phenylboronic acid (1.1 mmol), palladium
complex (1 mol %) methanol (2 mL), K CO (2 mmol) and 65◦C as the reaction temperature.
2
3
Adopting the optimized reaction condition coupling reactions of various substituted aryl halides
and phenylboronic acids were carried out using 1 mol% palladium complex as catalyst at 65◦C
(Table 7). Most of the reactions completed in 24–34 hours with moderate to excellent yields.
The yields vary with the substrates having either electron-donating groups or electron-
withdrawing groups. Under optimized conditions, phenyl iodide and bromide were reacted
efficiently with phenylboronic acid (Table 7). Both electron-withdrawing and releasing groups
with phenylboronic acid afforded the corresponding products with high yields (Table 7). It was
found that present catalyst exhibited higher conversions and yields [40].
Pd Complex
+
(HO) B
2
R
R
I
o
K2CO3, MeOH, 24 hrs, 65 C
Scheme 3: Palladium complex catalyzed Suzuki reaction
2
1

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
Table 5: Optimization of the reaction conditions for the Suzuki reaction of iodobenzene with
phenylboronic acid
o
Entry
Solvent
DMF
DMF
Base
Temp ( C) Time(hrs) Conversion
1
2
3
4
5
6
7
8
9
Et N
100
100
100
85
24
24
24
24
24
24
24
24
24
0
3
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
Na CO3
48
64
0
2
DMF
K CO3
2
CH
CN
Et N
3
3
CH CN
Na CO3
85
85
65
58
68
0
3
2
CH CN
K CO3
3
2
Methanol
Methanol
Methanol
Et N
3
Na CO3
65
65
77
92
2
K CO3
2
Table 6: Optimization of the catalyst concentration on the reaction of iodobenzene with
phenylboronic acid
Entry Cat (mol %)
Time(hrs)
Conversion
1
2
3
4
5
6
None
0.1
0.2
0.3
0.4
34
32
30
28
26
24
0
55
64
73
84
92
0.5
2
2

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
[
xyz]
Table 7: Suzuki reaction with the catalyst [PdLCl]
Reaction
time
(Hours)
Melting
point( C)
Isolated
yield
Aryl halide
Boronic acid
Product
o
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
I
(HO) B
24
68-70
84-87
92
2
O
O
I
I
(HO) B
2
26
90
O
O
O
O
2
8
85-89
89
88
(
HO) B
2
F
F
F
F
I
(HO) B
F
F
2
30
100-102
Br
Br
(
HO) B
2
30
32
68-70
84-87
90
87
O
O
(HO) B
2
O
O
O
O
Br
Br
33
34
85-89
83
81
(
HO) B
2
F
F
F
F
(HO) B
F
F
2
100-102
x
y
z
Solvent= Methanol, Base=K CO , Time=24-34 hrs
2
3
3
.4. Antibacterial activities of compounds:
Antibacterial activities of the ligand and complexes are evaluated by adopting the literature
method [21] and compared with standard drug kanamycin acid sulphate [41]. Individually 10
mg/ml of ligand and complexes in DMF are tested qualititavely for vitro antibacterial activities
2
3

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
against the gram positive and gram negative bacterias using disc diffusion assay. The ligand and
complexes exhibit activity against all bacterias. DMF do not exhibit any antibacterial properties.
The biological activities of compounds depend on metal atom, geometry of the complex, charge
of the metal ion, chelate effect of the ligand. The results are shown in Table 8. It is observed that
ligand is more active against Mycobacterium abscessus and palladium complex show very good
activity against Bacillus subtilis, Staphylococcus saureus, Proteus vulgaris, Mycobacterium
smegmatis and Escherichia coli. The bacterial activity follow the order
Pd(II)>Cu(II)>Ni(II)>ligand. The increasing activity may be explained by Tweedy’s chelation
theory [42]. Chelation decreases the polarity of the metal center by neutralizing partial positive
charge of metal ion and delocalization of pi electron within the chelate ring. Chelation increases
the lipophilic nature of metal centre. As a result, hydrophobic nature and liposolubility of the
complex increases and favors permeability through the lipid layers of the cell membrane. It
enhances the up taking/entrancing tendency. Hence antimicrobial activity of the testing
compounds [43]. Accordingly, the antimicrobial activity of the complexes increases lipophilic
nature which deactivates enzymes responsible for respiration processes and other cellular
enzymes also. These are important in various metabolic pathways of micro-organisms.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
Table 8: Antibacterial activity of ligand and complexes
Zone of
a
inhibition (cm)
Compounds Concentration Bacillus Staphylococcus Proteus Escherichia Mycobacterium Mycobacterium
(µg/ml)
subtilis
aureus
vulgaris
coli
smegmatis
abscessus
Ligand(1)
NiL (2)
CuL (3)
10
10
10
10
1.6
1.7
1.8
1.9
0.6
0.7
0.6
0.9
1.9
1.2
1.7
1.9
1.7
1.4
1.6
1.8
1.5
1
1.3
1.9
2
1.4
1.1
1.8
2
2
PdLCl(5)
Kanamycin
10
1.15
1.32
1.28
1.29
—
—
a
Kanamycin (20 µg/well) was used as positive reference, synthesized compounds (20 µg /well).
2
4

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
4
. Conclusion
A new sterically and electronically tunable mixed hydroxyl-imine-thioether tridentate ligand and
its four mononuclear Ni(II), Cu(II), Co(II), Pd(II) complexes were prepared. These were
characterized by physio-chemical analysis. Single crystal X-ray diffraction data, elemental
analyses and electronic spectra revealed slightly distorted octahedral arrangement for complex 2
and slightly distorted square planar geometry for complex 3. The phosphine free palladium
complex show very good catalytic activity towards and Suzuki reaction. All compounds show
very good antibacterial activity.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
Acknowledgments:
Authors thank SAIF IIT Bombay, Tezpur University Tezpur and IIT Guwahati for spectral and
analytical data. Authors also thank Director of NIT, Silchar for financial assistance (M. K.)
Appendix A. Supplementary data
1
It contains H NMR, FT-IR and UV-Visible spectra of compounds 1-5, which can be found via
the ―supplementary data‖ section of this article’s webpage. CCDC 1020519 and 1020520
contain the supplementary crystallographic data for nickel complex, 2 and copper complex, 3.
These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html
or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
2
5

1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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