Synthesis, characterization and biomedical activities of molybdenum complexes of tridentate Schiff base ligands. Crystal and molecular structure of [MoO2(L10)(DMSO)] and [MoO2(L11)(DMSO)]

Synthesis, characterization and biomedical activities of molybdenum

complexes of tridentate Schiff base ligands. Crystal and molecular

1

0

11

structure of [MoO (L )(DMSO)] and [MoO (L )(DMSO)]

2

[a]

Sukla Rakshit , Debashis Palit , Saroj K. S. Hazari , Saswata Rabi , Tapashi G.

[a]*

[b]

Roy , Falk Olbrich , Dieter Rehder

[

a]

b]

Department of Chemistry, University of Chittagong, Chittagong-4331, Bangladesh

Department of Chemistry, University of Hamburg, Germany

*

Corresponding Author: tapashir57@gmail.com

Abstract

The molybdenum complexes of different Schiff base ligands have drawn remarkable attention

due to their different biological and analytical activities. Several molybdenum complexes of

1

11

different Schiff base ligands, L to L derived from dithiocarbazate, have been synthesized by the

reaction of the ligands with molybdenum(VI)acetylacetonate. The complexes were characterized

1

on the basis of IR, H NMR and electronic spectral analyses, along with elemental,

magnetochemical and conductometric data. All the complexes are diamagnetic and non-

electrolytes in DMF solution. The molecular structures of two complexes were confirmed by X-

ray crystallographic studies. Antibacterial and antifungal characteristics of the concerned

compounds were investigated against different gram-positive and gram negative bacteria, and

against fungi, respectively. Most of the complexes show good activity against fungi and bacteria;

in some cases, the complexes were more active than the standard medications Nystatin and

Ampicilin respectively.

Keywords: Antibacterial agent; Antifungal agent; Molybdenum; Spectral analysis; X-ray

crystallography

1

. Introduction

The coordination chemistry of molybdenum(VI) has assumed special importance due to its

biochemical significance [1-3] as well as for the involvement of Mo(VI) compounds as catalysts

in several industrial processes, such as epoxidation of olefins [4], olefin metathesis [5] and

isomerisation of allylic alcohols [6]. The discovery of the presence of ONS donors in the

coordination sphere the Mo(VI) centre of oxotransferase enzymes, such asxanthine oxidase,

DMSO reductase [7,8] and others, led to the synthesis and exploration of the oxotransfer ability

of a number of model complexes that mimic the oxotransferase activity of molybdoenzymes [9].

1

2

-

Oxotransferases catalyze oxidative and reductive oxygen (O ) transfer reactions and play an

important role in the global metabolism of elements like nitrogen, carbon, sulfur and arsenic.

These studies also led to the belief that the presence of the sulfur donor is essential for the

oxotransfer activity of such systems.

-

2

Dithiocarbazate (NH NHCS

) and its substituted derivatives have been investigated as ligands

for a long time [10-13]. These compounds have received much attention for further studies

because i) they provide an interesting series of ligands whose properties can be greatly modified

by introducing different organic substituent, thereby causing a variation of the ultimate donor

properties, ii) the interaction of these donors with metal ions gives rise to complexes of different

geometries and properties, and iii) these complexes are potentially biologically active. The

present study focuses on the synthesis, characterization and biological studies of

molybdenum(VI) complexes of tridentate Schiff base ligands derived from dithiocarbazate.

2. Results and Discussion

In model studies of molybdenum complexes, the selection of the ligand is of substantial

importance. Earlier work [14-15], including rate and activation parameter data, indicated that at

least one sulfur atom is essential for the resulting complex to be suitable for the kind of model

studies described herein. Considering extended X-ray absorption fine structure (EXAFS) results,

we thought that it is appropriate to concentrate on ONS ligands, also to avoid the formation of the

biologically irrelevant )-oxido-molybdenum(V) dimer in the course of the reaction. In this study,

1

11

eleven Schiff base ligands (L - L ) with ONS donor sets have been synthesized [10-13], the

names and structures of which are provided in Table-S1. The general reaction Schemes 1 and 2

for the synthesis of the ligands and complexes can be represented as follows:

ꢇ

ꢀ

ꢁ

ꢀ

ꢀꢁ

ꢄ

ꢆ

ꢂꢁ

ꢆꢁ

ꢀ

ꢇꢀꢁ ꢀ ꢁ

ꢈ ꢉ ꢊ

ꢇ

ꢂꢁ

ꢋ

ꢁ ꢆ ꢆꢁ

ꢈ

ꢀ

ꢇꢀꢁ ꢀ ꢁ

ꢈ ꢉ ꢊ

ꢋꢁꢈꢂ

ꢅ

ꢃ

ꢅ

ꢃ

ꢄ

2 5 2

[X = H, Cl, Br, OMe, OEt; Y = N(C H ) , H; Z = NO2, Br, Cl, H]

Scheme 1

2

Scheme 2

Almost all of the molybdenum complexes prepared were orange in color, except for a few which

were brown, golden-yellow or black (Table 1). The complexes showed a decomposition point

ataround 200 °C (Table 1).

2

.1. IR Spectra

The IR data (Table 2) of some of the complexes feature the presence of a broad band at about

-1

3

420 cm due to the /(OH) stretch, indicative of the presence of water either in the coordinated or

-

1

uncoordinated form. The Schiff bases exhibit a sharp strong band at 1620-1600 cm due to the

(C=N) stretching frequency. In case of the molybdenum complexes, this band is shifted by 5-25

/

-1

cm to low frequency, indicating the coordination of the azomethine nitrogen atom to the

-1

molybdenum ion [16]. Medium to strong bands at about 1294-1250 cm for the free ligands are

-

1

assigned to /(C-O) (phenolic) which undergo a shift of 5-20 cm to low frequency in the case of the

molybdenum complexes [17]. In some cases, this band weakens in intensity for the complex. This

suggests that the phenolic oxygen atom also coordinates to the molybdenum ion. No appreciable

-1

change is observed in the position of the band at about 1090-1030 cm , which is assigned to the

(N-N) stretch in the case of the molybdenum complexes.

/

3

The IR spectra (Table 2) of the complexes exhibit two bands in the regions 980-950 and 850-900

-1

cm due to the /(sym)(O=Mo=O) and /(asym)(O=Mo=O) stretches, respectively, the reported range

-

1

-1

being /(sym) = 892-964 cm and /(asym) = 840-925 cm for the majority of

dioxidomolybdenum(VI) complexes [18]. These bands are absent in the free ligand, thus proving

the formation of the dioxidomolybdenum complexes. These IR data are also indicative of the

2

+

2+

presence of a cis-MoO

(O=Mo=O) band due to the asymmetric stretch. The MoO

groups due to optimal utilization of the d-orbitals for chemical bonding. A medium strong band at

moiety, as the trans-MoO

2

moiety would show only one IR-active

2

+

/

moiety prefers to form cis-dioxido

-

1

about 520-560 cm for the molybdenum complexes is assigned to the /(Mo-N) stretching mode

-

1

[

19]. This band is absent in the free ligands. A weak band in the range 420-440 cm is due to the

molybdenum-sulfur stretching frequency [20]. Thus, from the above discussion, it is clear that the

2

+

ligands are attached to the molybdenum atom of the MoO

moiety via the azomethine nitrogen,

phenolic oxygen and thiolato sulfur atoms; the ligands are thus acting as tridentate dinegative

ligands.

1

.2. H NMR Spectra

2

The NMR spectra of the complexes (Table 3) account for all the protons of the ligands in the

complexes except for the phenolic proton and the thiol sulfur proton, which are lost during

complex formation, thus evidencing coordination via the phenolic oxygen and thiolato sulfur

atoms of the ligand. Multiplet peaks in the range ꢌ 7-9 ppm are due to the phenyl protons of the

salicylaldehyde and benzyl moieties. The range is large because different substituents are

attached to the phenyl group. A singlet in the range ꢌ 8-9 ppm is due to the azomethine proton of

the ligand [21]. The peak of the –SCH

2

proton appears in the range ꢌ 3.3-4.2 ppm. These peaks

2

5

are common for all of the complexes. The complexes [MoO

2

(L )(H

2

O)] and [Mo(O )(L )], where

2

a methoxy group is present in the ligand moiety, show a separate peak in the NMR spectra at ꢌ

3

.3 ppm [21]. The complex [MoO

for the –CH

peaks for –CH

attached to the complex, and in fact proves coordination of CH

2 3

(L )(CH CH

2

OH)]⋅H

2

O shows two separate peaks at ꢌ 3.1 ppm

protons) [23]. This type of separate

protons is found in all complexes where the CH CH OH molecule is

CH OH (stemming from the

(

2

protons) [22] and ꢌ 1.3 ppm (for the –CH

3

and –CH

2

3

2

3

2

solvent) to the molybdenum ion. Many molybdenum complexes found in the literature are

comparable, i.e. associated with the solvent molecule. The other peaks found in some spectra are

due to H

2

O present in the complex and/or to a contaminant in DMSO-d [24].

6

4

2.3. Molar Conductance and Magnetochemical Data

The molar conductance data indicate that all the compounds are non-electrolytes in DMF, while

the magnetic susceptibility data reveal that all compounds are diamagnetic (Table 1).

2.4. Electronic Spectra

The spectra were taken in dimethylsulfoxide (DMSO) and show only one peak at 320-330 nm

Table 3). A band in this region may be attributed to a ligand-to-metal charge transfer or to an

(

intraligand transition. The absence of bands due to d-d transitions in the range 650-420 nm in the

spectra of these complexes supports the presence of the molybdenum(VI) ion [25].

From all of the data, we can deduce two different types of structures for the above complexes,

viz. a polymeric and a monomeric one. In either case, Mo is in an octahedral coordination sphere;

Figs. 1 (a) and 1(b).

Fig. 1

1(a)

1(b)

From the above structure it is clear that some complexes have a polymeric structure without a

solvent molecule, while other complexes have a solvent molecule (ethanol) attached, within the

normal octahedral structure of the molybdenum complex. This statement is supported by the

1

crystal structure of the complexes. A derivative of [MoO

2

(L )(H

2

O)] crystallized as [(cis-

1

MoO

2

L )()-O)(cis-MoOL (OH

2

)]^CHCl from chloroform, and had been studied by X-ray

3

10

crystallography [26]. The detailed crystallographic analyses of [MoO

2

(L )(C

2

H OH)] and

5

1

10

11

[MoO

2

(L )(C

2

H

5

OH)], recrystallized as [MoO

2

(L )(DMSO)] and [MoO

2

(L )(DMSO)] from

DMSO, are discussed in sections 2.5 and 2.6.

5

1

0

2

.5. Crystal structure and relevant data of the complex [MoO (L )(DMSO)]

1

0

The molecular structure and atom numbering scheme for [MoO

2

(L )(DMSO)] are shown in Fig 2

and selected atomic distances and angles are provided in Table 5. The Mo1 atom features in a cis

2

+

[MoO

2

]

core, to which is also bonded a dinegative tridentate S-benzyl-3-(2-hydroxy-3,5-

dichlorophenyl)-methylene-dithiocarbazate ligand via sulfur, oxygen and nitrogen donors, and a

DMSO molecule to complete the octahedral coordination geometry. In the structure of the

complex, the molybdenum atom is octahedrally surrounded by two terminal oxido ligands (the

oxygen atoms O1 and O2), by the phenolic oxygen O3, imine nitrogen N2 and sulfur S2 atoms

belonging to the ligand, and finally by the oxygen atom O4 from the coordinated DMSO. The

values of the Mo=O bonds, 1.7075(9) and 1.7082(9) Å, are common for cis-MoO complexes.

2

The ligand forms one six- and one five-membered chelate ring with the central Mo ion. The Mo-

O3, Mo-N2 and Mo-S2 bond lengths are 1.9283(8), 2.3189(10) and 2.4528(3) Å, respectively.

The Mo-O4 bond length is 2.2431(9) Å.

1

0

Fig.-2G Structure of [MoO L DMSO]

2

1

2

.6. Crystal structure and the relevant data of the complex [MoO (L )(DMSO)]

11

The molecular structure and atom numbering scheme for [MoO

2

(L )(DMSO)] are shown in Fig.

3

and selected atomic distances and angles are provided in Table 6. In the ORTEP plot of the

complex, the molybdenum atom is octahedrally surrounded by two terminal oxido-ligands, O1

and O2, the phenolic oxygen O4, imine nitrogen N2 and sulfur S2 atoms belonging to the ligand,

and finally by the oxygen O3 atom from the coordinated DMSO molecule. The values of the

6

Mo=O bonds, ranging from 1.672(13) and 1.689(14) Å, are usual for cis-MoO complexes. The

2

ligand forms one six- and one five-membered chelate ring with the Mo atom. The Mo-O4 and

Mo-N2 bond lengths are 1.946(13) and 2.293(13) Å respectively. The Mo-O3 bond length is

2.241(15) Å.

1

Fig.-3G Structure of [MoO (L )(DMSO)

2

3

. Biomedical Studies

.1. Antifungal Studies

From Table 7, it is clear that all the five fungi under investigation were very sensitive towards all

of the test compounds. Among these, Fusarium equiseti and Colletotrichum corchori were the

most sensitive ones. These growths were 100% inhibited by application of almost all the test

compounds, but with time, the parent inhibition of the mycelial growth decreased for some

compounds, while for other compounds it remained constant. As a general trend for almost all of

the compounds, the sensitivity of the fungi decreased with time. The test compounds exhibited

moderate effectiveness against the other fungi. Table 4 shows that Curvularia lunata was less

sensitive in comparison to the other fungi for most of the compounds. The data (Tables S4 and

S3) reveal that the ligands are more potent antifungal agents than the corresponding complexes.

This observation corresponds to that seen for some other cases [27]. However, the observation is

in contrast with other transition metal complexes of different Schiff base ligands. Comparing the

7

activity of the complexes with the standard fungicide Nystatin revealed that almost all of the

compounds showed a more pronounced activity than Nystatin.

3.2. Antibacterial Studies

All of the synthesized molybdenum complexes have been screened for their antibacterial activity

against selected Gram positive and Gram negative bacteria. The results are summarized in Tables

8

and 9. During the study of the zone of inhibition of Gram positive bacteria (Table 8), it was

found that most of the metal complexes show some activity against the bacteria under

5

investigation, although other compounds are inactive. Among the complexes, [MoO

2

(L )] (23

6

mm) and [MoO

2

(L )] (20 mm) showed a remarkable zone of inhibition against Bacillus

megaterium, clearly more extended than in the case of the antibiotic Ampicillin (15mm). Nearly

all of the molybdenum complexes in fact showed very good inhibition zones against all of the

Gram positive bacteria, and are thus comparable with Ampicillin. The results for the antibacterial

activity of the metal complexes against Gram negative bacteria (Table 9) are almost the same as

in the case of Gram positive bacteria, except for two of the bacterial strains (Vibrio cholerae and

1

Escherichia coli). In accordance with the data for Gram positive bacteria, the ligand H

2

L (Table

S4) was found to be very effective against all the Gram negative bacteria except Escherichia coli.

4

Individually, [MoO

2

(L )] showed the most extended zone of inhibition against Salmonella typhi

6

(

20 mm, Ampicillin 25 mm), while [MoO

2

(L )] was particularly effective in the inhibition

against Salmonella paratyphi (21 mm, Ampicillin 12 mm) and Pseudomonas species (20 mm,

Ampicillin 19 mm). One interesting observation from Table 9 is that, in some cases, the zone of

inhibition increases with time, which is not found in case of gram positive bacteria.

It is observed that the molybdenum complexes are more effective against Gram positive than

Gram negative bacteria when comparing the data of the zones of inhibition for the Gram positive

and Gram negative bacteria. In many cases, more extended zones of inhibition than in the case of

Ampicillin have been observed, and in almost all cases, our compounds were comparable to

Ampicillin. However, the data (Tables 5, 6, S4 and S5) reveal that the antibacterial activity of

most of the complexes is almost the same as that of the ligands. In some cases, the ligands are

even more potent, while in other cases the complexes are more potent. So no definite trend could

be deduced, and further studies are thus warranted with analogous series.

8

4

. Experimental

.1. Materials and method

All chemicals were of analytical grade (Sigma Aldrich) or equivalent grades and were used

without further purification. The solvents were of reagent grade and dried according to literature

procedures. Dioxido-bis(acetylacetonato)molybdenum(VI) (MoO

2

(acac) ) was obtained from

2

commercial sources. UV-visible spectra were recorded on a Shimadzu UV-visible

spectrophotometer in pure DMSO. Conductance measurements were carried out on a conductivity

bridge Hanna instrument HI-8820 in pure DMF. Magnetic measurements were performed on a

Gouy Balance which was calibrated using Hg[Co(NCS) ]. IR spectra were recorded on a

4

Shimadzu IR 20 spectrophotometer as KBr disks. Microanalyses of the complexes were carried

out on a C, N, H analyser at the Institute of Inorganic and Applied Chemistry, University of

1

Hamburg, Germany. H NMR spectra were recorded in DMSO with a 400 MHz Bruker DPX-400

spectrometer using TMS as internal standard at the BCSIR Laboratory, Dhaka, Bangladesh.

4

.2. Synthesis of the tridentate ligands and their molybdenum complexes derived from

S-benzyldithiocarbazate

4

.2.1. Synthesis of the ligands of S-benzyldithiocarbazate (H L)

2

The ligands were prepared by condensation of hydrazine with carbondisulfide in alkaline medium

to form the S-alkylmercaptocarbonylhydrazines, followed by condensation with the aldehyde or

ketone to the hydrazonate.

4.2.2. Preparation of the molybdenum complexes of the ligands derived from

S-benzyldithiocarbazate

Dioxido-bis(acetylacetonato)molybdenum(VI) [MoO

2

(acac) ] (3.27 g, 10 mmol) was dissolved in

2

hot ethanol and then added to a hot ethanolic solution (20 mL) of the respective ligands in a ratio

of 1:1. The solution was then refluxed for 8 to 12 hours on a water bath. After reducing the

volume of the refluxed solution, a dark coloured crystalline product appeared from the solution.

The crystalline product was then filtered and washed with ethanol several times. The product was

then recrystallized from chloroform and dried in a vacuum desiccator over silica gel.

9

For, [MoO

2

(L

1

)(H

2

O)] Calcd (%) for C15

H

14

N

2

O

4

2

S Mo: C 40.36, H 3.16, N 6.28; found: C

4

0.32, H 3.10, N 6.25.

2

For, [MoO

2

(L )(H

2

O)] Calcd (%) for C16

H

16

N

2

O

5

2

S Mo: C 40.34, H 3.39, N 5.88; found: C

4

0.30, H 3.34, N 5.85.

3

For, [MoO

2

(L )(C

2

H

5

OH)]. H

2

O, Calcd (%) for C17

H

24

N

2

O

6

S

2

MoN : C 39.85, H 4.72, N

2

5

.47; found: C 39.82, H 4.70, N 5.44.

4

For, [MoO

2

(L )] Calcd (%) for C15

H

13

N

2

O

3

S MoBr: C 35.38, H 2.57, N 5.50; found: C

2

3

5.35, H 2.55, N 5.48.

5

[

MoO

2

(L )] Calcd (%) for C15

H

15

N

3

O

6

2

S Mo: C 36.52, H 3.06, N 8.52; found: C 36.48, H

3

.04, N 8.50.

6

For, [MoO

2

(L )] Calcd (%) for C15

H

13

N

2

O

3

S MoCl: C 38.76, H 2.82, N 6.03; found: C

2

3

8.74, H 2.80, N 6.01.

7

For, [MoO

2

(L )(C

2

H

5

OH)]. H

2

O, Calcd (%) for C17

H

18

N

2

O

5

2

S MoBr: C 35.80, H 3.18, N

4

.91; found: C 35.78, H 3.15, N 4.88.

8

For, [MoO2(L )(C

2

H

5 2

OH)].H O, Calcd. (%) for C17

H

19

N

3

O

7

2

S Mo: C 33.08, H 3.10, N 6.81;

Found: C 33.05, H 6.78, N 6.79.

9

For, [MoO

2

(L )(C

2

5

H OH)], Calcd (%) for C17

H

16

N O

2 4

2

S MoBrCl: C 34.74, H 2.74, N 4.77;

found: C 34.72, H 2.70, N 4.75.

1

0

For, [MoO

2

(L )(C

2

H

5

OH)]Calcd (%) for C17

H

16

N O

2 4

S

2

MoCl : C 32.76, H 2.59, N 4.50;

2

Found: C 32.72, H 2.55, N 4.48.

1

For, [MoO

2

(L )(C

2 5

H OH)], Calcd (%) for C21

H N

27 3

O

4

2

S Mo: C 46.24, H 4.99, N 7.70;

found: C 46.20, H 4.95, N 7.65.

4.4. X-ray Single Crystal Structure Analysis

10

During recrystallization from DMSO, the complexes [MoO

2

(L )(C

)L DMSO]

OH molecule by DMSO.The datasets for the

2

H

5

OH)] and

1

10

[

MoO

2

(L )(C

2 5

H OH)]

crystallized

as

orange

[Mo(O

2

and brown

1

[

2

(L )(DMSO)], by replacement of the C

H

2 5

10

compounds were collected with Mo-K

α

radiation, using a graphite monochromator, and ω-scans at

100 K. An empirical absorption correction was carried out with the program SADABS [28]. All

structures were solved with direct methods (SHELXS-97) [29] and refined with full-matrix least-

2

squares on F

o

, using the program SHELXL-2013 [30]. All non-hydrogen atoms were refined

with anisotropic temperature factors. Hydrogen atoms were calculated in idealized positions using

a riding model with isotropic temperature factors. For the molecular graphics and publication

materials, the program package SHELXTL-PLUS (PC v5.03) [31] was used.

4

.5. Biological Studies

.5.1. Antibacterial activities

Antibacterial activities of the ligands and their complexes against selected gram-positive and

gram-negative bacteria were investigated by the disc diffusion method. Paper discs (6 mm in

diameter) and Petri plates (70 mm in diameter) were used throughout the experiment. Pour plates

were made with sterilized melted nutrient agar NA (45 °C) and after solidification of the pour

plates, the test organisms (suspension in DMSO) were separately spread uniformly over the plates

with sterilized glass rods. The paper discs, after soaking with test chemicals (1% in DMSO), were

placed at the centre of the inoculated pour plate. A control plate was also maintained in each case

with DMSO. The plates were first kept for four hours at low temperature (4 °C) and the test

chemicals diffused from the disc to the surrounding medium in this time. The plates were then

incubated at (35±2) °C for growth of test organisms and were observed at 24 and 48 hour

intervals. The activity was expressed in terms of the zone of inhibition in mm. The test was

repeated three times at a 24 hour interval for statistical analysis

4

.5.2. Antifungal activities

The in vitro antifungal activities of the complexes against selected phytopathogenic fungi were

assessed by the poisoned food technique. Potato Dextrose Agar (PDA) was used as a growth

medium. Dimethylsulfoxide (DMSO) was used as the solvent to prepare solutions of the

molybdenum complexes. The solutions were then mixed with the sterilized PDA so as to

maintain the concentrations of the compounds at 0.01 % (ca. 3 µM). 20 ml of these solutions

were each poured into a Petri dish. After the medium had solidified, a 5 mm mycelial disc of each

fungus was placed in the centre of each assay plate, along with a control. The linear growth of the

fungus was measured in mm after five days of incubation at 25 ± 2 °C.

11

Table 1. Some physical and analytical data of molybdenum complexes

Colour

Melting

point

Conductance in

DMF

)

eff

Complex

-1

2

-1

(

°C)

(ohm cm mol )

00

1

[

MoO

2

(L )(H

2

O)]

Orange

Black

214

210

110

218

216

210

220

198

220

184

200

Diamagnetic

2

(L )(H

00

3

(L )(C

2

H

5

OH)]. H

2

O Orange

Orange

4

(L )]

5

(L )]

Orange

6

(L )]

Orange

7

(L )(C

2

H

5

H

5

H

5

OH)]. H

OH)]

2

O Orange

8

2

(L )(C

2

9

(L )(C

Golden yellow

1

0

(L )(C

2

H

5

OH)]

Brown

1

(L )(C

2

H

5

12

-1

Table 2.Selected IR absorption bands (cm ) of the molybdenum complexes

Ligand/Complex

ν

(Mo-S)

(OH)

(C=N)

(C-O)

(N-N)

(O=Mo=O)

Sym)

(O=Mo=O)

(Asym)

(Mo-N)

(

1

[MoO

MoO

2

(L )(H

2

O)]

1598st

1253s

1222s

1018s

1029s

977s

906s

875ms

873ms

540ms 414w

563ms 426w

2

[

2

(L )(H

2

3420 1596st

br

3

st

[

MoO

2

(L )(C

2

H

5

OH)].

3404 1589st

br

1261

1083s

975s

856sm

565ms 453w

H O

4

[MoO

2

(L )]

1596st 1253ms

1022s

1068sm

1024s

981s

968st

952s

983s

842s

906st

833st

893ms

540ms 447w

522ms 439w

547ms 420w

543ms 418w

5

(L )]

1568s

1598st

1267s

1207s

1213s

6

(L )]

7

(L )(C

2

H

5

OH)].

3422 1583st

br

3420 1598st

H O

2

8

[MoO

2

(L )(C

2

5

1294s

1099st

964s

852ms

509ms 420w

H O

2

br

9

[MoO

2

(L )(C

2

H

5

OH)]

1589st

1591st

1213s

1211s

1608s 1271sm

1085s

1076s

983s

987s

981s

867ms

896s

862sm

545ms 414w

549ms 428w

563ms 428w

1

0

(L )(C

2

H

5

OH)]

1

(L )(C

2

5

13

1

Table 3. H NMR (ꢀ, ppm) and electronic spectral (nm) data of the molybdenum

complexes

Complex

Phenyl

proton

7.2-7.5

7.0-7.4

6.9-7.4

Azomethine

proton

!SCH₂!

proton

4.2

Other peaks

(

max

1

[

MoO

2

(L )(H

(L )(C

2

O)]

7.7

8.9

320

326

2

3.8

4.0

3.3(-OCH

3

)

3

2

H

5

OH)]. H

2

O

3.1(-CH

.3(-CH

2

-)

1

3

4

[

MoO

2

(L )]

(L )(C

6.9-8.0

7.2-8.5

6.9-7.9

7.2-8.0

8.9

9.2.

8.9

9.0

3.3

3.9

3.3

3.4

5

3.3(-OCH

3

337

323

329

6

7

2

H

5

H

5

H

5

OH)]. H

OH)]

2

O

3.1(-CH

.2(-CH

3.1(-CH

.0(-CH

3.6(-CH

.2(-CH

3.3(-CH

.0(-CH

3.1(-CH

.1(-CH

2

3

2

3

2

3

2

3

2

3

-)

1

8

[

MoO

2

(L )(C

2

7.0-8.8

7.2-7.8

7.2-7.9

6.1-7.4

9.2

8.7

9.0

8.6

3.4

3.7

3.4

4.3

322

328

325

1

9

(L )(C

1

10

(L )(C

2

H

5

OH)]

1

11

(L )(C

2

H

5

1

14

1

0

11

Table 4. Crystal data of [MoO

2

(L )(DMSO)]and [Mo(O

2

)(L )DMSO]

1

0

11

[

C

MoO

2

(L )(DMSO)]

MoN

[Mo(O )(L )(DMSO)]

2

empirical formula

formula weight

crystal habit, color

crystal system

space group

a (F)

17

H16Cl

2

O

4

S

3

C

21

H

3

27MoN O

S

4 3

575.34

577.57

plate, brown

Monoclinic

block, orange

Triclinic

P-1

P2

1

7.6964(4)

8.1821(4)

17.3440(8)

96.654(1)

98.015(1)

91.684(1)

1073.09(9)

2

1.781

1.179

576

0.50×0.36 × 0.29

24386

6149

8.054(4)

6.903(3)

21.508(9)

90

93.945(5)

90

1192.9(9)

2

1.608

0.846

592

0.24 x 0.05 x 0.02

10278

b (F)

c (F)

o

ꢍ ( )

o

!

"

( )

o

( )

3

volume (F )

Z

3

density, calc. (Mg/m )

absorption coefficient (mm )

-

1

F(000)

crystal size (mm )

3

reflections collected

independent reflections

index ranges

5158

-10<=h<=10, -11<=k<=11,

24<=l<=24

-10<=h<=10, -8<=k<=8,

-27<=l<=26

-

number of parameters

goodness-of-fit on F

281

0.999

295

1.091

2

final R indices [I 1 2ꢎ(I)]

R1= 0.0172, wR2=0.0460

R1= 0.0176, wR2=0.0463

R1 = 0.0843, wR2 = 0.1981

R1 = 0.1148, wR2 = 0.2178

1.540 and -1.152

R indices [all data]

largest difference peak and 0.512 and -0.494

-

3

hole (e F )

15

10

Table G5 Selected Bond lengths [Å] and angles [°] for [MoO

Bond Length Bond Angle

O2-Mo-O1

2

(L )DMSO]

Mo-O1

Mo-O2

Mo-O3

Mo-O4

Mo-N2

Mo-S2

1.7082(9)

1.7075(9)

1.9283(8)

2.2431(9)

2.3189(10)

2.4528(3)

104.22(4)

99.20(4)

88.95(3)

93.75(3)

88.84(4)

79.20(3)

O1-Mo-O3

O1-Mo-N2

O1-Mo-S2

O2-Mo-O4

O3-Mo-O4

11

Table -6G Selected bond lengths [F] and angles [°] for [MoO

2

(L )DMSO]

Bond Length Bond Angle

Mo-O1

Mo-O2

Mo-O3

Mo-O4

Mo-N2

Mo-S2

1.688(14) O1-Mo-O2

1.696(16) O2-Mo-O4

2.241(15) O2-Mo-N2

1.946(13) O2-Mo-S2

104.5(7)

98.40(7)

91.50(6)

96.50(5)

84.70(7)

91.20(5)

2.293(15)

2.446(5)

O1-Mo-O3

O1-Mo-S2

16

Table 7: Antifungal activity of the molybdenum complexes

Complexes (100 )gdw/mL

% Inhibition of mycelial growth after 48 and 72 hours of incubation

PDA)

Macrophomina

phaseolina

Alternaria

alternata

Fusarium

equiseti

Colletotrichum

corchori

Curvularia

lunata

4

8h

72h

48h

72h

48h

72h

48h

72h

48h

72h

1

[

MoO

2

(L )(H

2

O)]

70

44

70

84

90

80

70

84

70

76

60

64

60

70

80

60

70

50

100

57

100

57

65

71

42

71

57

85

47

42

100

88

100

77

71

100

71

42

71

81

62

53

81

100

81

62

81

68

37

81

70

68

21

37

68

100

53

06

37

21

0

2

(L )(H

2

O)]

3

(L )(C

2

H

5

OH)]. H

2

O

100

85

42

4

(L )]

100

66

100

85

100

71

5

(L )]

85

6

(L )]

85

66

100

85

7

(L )(C

2

H

5

OH)]. H

5

OH)]. H

5

OH)]

2

O

85

100

45

88

8

(L )(C

2

85

88

71

9

(L )(C

100

94

88

100

71

1

0

(L )(C

2

H

5

OH)]

88

100

28

1

(L )(C

H

2 5

77

88

37

Nystatin

51

41

PDA= Potato dextrose agar medium used for the culture medium for antifungal tests.[dw = dry weight]

17

Table 8: Antibacterial activity of molybdenum complexes against Gram positive bacteria

Complexes (100)gdw/disc)

Zone of inhibition in mm after 24 and 48 hours of incubation

Bacillus

cereus

Bacillus

subtilis

Staphylococcus

aureus

Bacillus megaterium

2

4h

48h

24h

48h

24h

48h

24h

48h

1

[

MoO

2

(L )(H

2

O)]

15

12

15

10

8

15

12

15

10

8

18

15

0

18

15

0

15

8

15

8

2

(L )(H

2

O)]

15

2

15

8

3

(L )(C

2

H

5

OH)]. H

2

O

4

(L )]

5

MoO2 (L )]

0

13

0

13

0

23

20

0

23

20

0

6

MoO

2

(L )]

15

5

15

5

7

(L )(C

2

H

5

OH)]. H

2

O

0

8

(L )(C

2

5

OH)]. H

2

5

0

9

MoO2(L )(C

2

H

5

OH)]

8

15

0

15

0

10

13

10

15

10

13

10

15

1

0

MoO

2

(L )(C

2

H

5

0

1

(L )(C

2

H

5

10

16

10

16

0

2

Ampicillin

16

17

20

22

18

Table 9: Antibacterial activity of molybdenum complexes against Gram negative bacteria

Complexes Zone of inhibition in mm after 24 and 48 hours of incubation

100)g

dw/disc)

(

Escherichia

coli

Vibrio

Salmonella Salmonella Pseudomona

typhi paratyphi species

Shigella

sonnei

Shigella

cholerae

dysenteriae

2

4h

48h 24h 48h 24h 48h 24h

48h 24h

48h

24h 48h 24h

48h

1

[

MoO

2

L H

2

O]

0

8

0

8

0

15

20

13

15

0

16

20

14

15

0

15

12

8

15

13

8

15

20

15

5

15

17

15

20

15

6

18

15

0

19

15

0

15

10

5

15

16

15

10

5

2

L H

2

3

L C

2

H

5

OH]. H

2

O

0

4

L ]

0

5

L ]

0

6

L ]

0

20

10

5

21

11

10

5

0

7

L C

2

H

5

OH]. H

OH]

2

O

0

5

8

L C

H

5

2

0

15

0

15

0

13

0

13

0

9

L C

H

5

0

10

8

11

9

0

1

0

L C

2

H

5

OH]

0

8

12

10

12

10

13

8

0

1

L C

2

H

5

0

5

6

10

19

10

20

0

Ampicillin

28

24

25

24

13

14

‘dw’ means dry weight

Appendix A. Supplementary data

CCDC 745141 and 1453808 contain the supplementary crystallographic data for

1

0

11

[

MoO(L )(DMSO)] and [Mo(O )(L )DMSO]. These data can be obtained free of charge

2

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)

1

223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.

Acknowledgments

We gratefully acknowledge the University Grants Commission, Bangladesh for awarding a

fellowship to Sukla Rakshit, Department of Chemistry, University of Chittagong, Bangladesh.

19

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[

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[

5

[

8.

ꢀ

21

Scheme-1

Synthesis of the ligands from S-benzyldithiocarbazate

Scheme-2

Preparation of the molybdenum complexes of the ligands

Figure-1

1

(a)Polymeric structure of molybdenum complexes 1(b) Monomeric structure of the

molybdenum complexes ꢀ

Figure-2

1

0

Structure of [MoO

2

(L )(DMSO)]

Figure-3

1

Structure of [MoO

ꢀ

2

(L )(DMSO)ꢀ

ꢀ

22

Synthesis, characterization and biomedical activities of molybdenum

complexes of tridentate Schiff base ligands. Crystal and molecular structure

1

of [MoO (L )(DMSO)] and [MoO (L )(DMSO)]

0

11

2

[

a]

[a]

Sukla Rakshit , Debashis Palit , Saroj K. S. Hazari , Saswata Rabi , Tapashi G. Roy , Falk

[a]

[a]*

[

Olbrich , Dieter Rehder

b]

[b]

[

a]

b]

Department of Chemistry, University of Chittagong, Chittagong-4331, Bangladesh

Department of Chemistry, University of Hamburg, Germany

*

Corresponding Author: tapashir57@gmail.com

Different Schiff base ligands and their molybdenum complexes have been prepared. The complexes were

characterized by using a multitude of analytical methods. Biomedical activities of the compounds were

also studied. The structures of two compounds were confirmed by X-ray crystallography.

1

0

11

[MoO (L )(DMSO)]

2

[

MoO (L )(DMSO)]

2

Article Doi

Synthesis, characterization and biomedical activities of molybdenum complexes of tridentate Schiff base ligands. Crystal and molecular structure of [MoO2(L10)(DMSO)] and [MoO2(L11)(DMSO)]

DOI: 10.1016/j.poly.2016.05.053

Source and publish data:

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Article abstract of DOI:10.1016/j.poly.2016.05.053

Full text of DOI:10.1016/j.poly.2016.05.053

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