1Department of Applied Chemistry, ISM Dhanbad-826004, India
2Department of Chemistry, SDJ PG College, Azamgarh, UP
Corresponding author: yadav_drmahendra@yahoo.com
ABSTRACT:
Molybdenum and tungsten complexes of the type M2O4L2(H2O)2, where M = Mo(V), W(V), LH = N-nicotinoyl-N¢-2-thiophenethiocarbohydrazide (H2NTTH), have been synthesized and characterized by using elemental analysis, magnetic susceptibility measurements, infrared spectra, 1HNMR, 13CNMR,ESR.and X-ray spectroscopic studies. Molar conductance measurements in DMF show non-ionic behaviour of all the complexes. Magnetic susceptibility measurements indicate diamagnetic nature of the complexes. Although the complexes are ESR inactive, +V oxidation state of metal ions in octahedral geometry has been suggested on the basis of electronic spectral studies. IR and electronic spectral studies indicate dinuclear - type of complexes with M2O42+ moiety. IR spectral data suggest monoanionic bidentate mode of bonding for the ligand. The 1H NMR and 13C NMR spectra are found to be in good agreement with the proposed stoichiometry. X-ray powder diffraction of the complexes exhibit amorphous nature of the complexes.
KEYWORDS: molybdenum , tungsten, thiocarbohydrazide complexes.
The expansion of research in the coordination chemistry of nitrogen-sulfur donor ligands such as substituted thiosemicarbazides1, thiosemicarbazones2-5 and dithiocarbazates 6 during the recent years has been due to their remarkable antineoplastic activity against a variety of tumors 7 in addition to their appreciable antifungal 8 and antibacterial 9 activities. However, relatively few papers have been reported regarding the synthetic and structural aspects of molybdenum and tungsten complexes of a closely related class of ligands, namely the N-substituted thiohydrazides 10-14. Recently, organometallic compounds 15 and metal complexes16-21 have attained a prominent place as corrosion inhibitors in acid and neutral media, as very small dose is required for very high inhibition efficiency. Keeping in view the mentioned importance of the complexes it was planned to undertake the synthesis and characterization of the molybdenum and tungsten complexes of N-nicotinoyl-N¢-2-thiophenethiocarbohydrazide (H2NTTH) (Fig.1), having oxygen, nitrogen and sulfur as potential donors.
This ligand is expected to form addition complexes without loss of a proton, and deprotonated complexes by loss of one or both the hydrazinic proton(s).
Figure 1: H2NTTH
MATERIALS AND METHODS:
Starting materials:
All the chemicals used were of analytical grade. Ammonium polysulphide22 and carboxymethyl-2-thiophenedithioate 23 were prepared by literature methods.
Preparation of N-nicotinoyl-N¢-2-thiophenethiocarbohydrazide (H2 NTTH):
N-nicotinoyl-N¢-2-thiophenethiocarbohydrazide (H2 NTTH) was prepared by mixing solutions of nicotinic acid hydrazide (20 mmol) and carboxymethyl-2-thiophenedithioate (20 mmol) each dissolved separately in 50 mL of 0.5 N NaOH and allowing the mixture to stand at room temperature for 2 hrs. The product precipitated by adding dilute AcOH dropwise to the above ice-cold mixture, was filtered off, washed with H2O, dried and recrystallized from EtOH.
Synthesis of Molybdenum Complex of N-nicotinoyl -N¢-thiophenethiocarbohydrazide:
The molybdenum complex of N-nicotinoyl-N¢-2-thiophenethiocarbohydrazide (H2 NTTH) was prepared by mixing hot acidified aqueous solution (50mL) of sodium molybdate (, 2mmol) and ethanolic solution (50mL) of N-2-thiophenoyl- N¢-thiobenzhydrazide (2mmol) and digesting the mixture on a water bath for ~1½ hours. The precipitate obtained was filtered, washed with hot water followed by diethyl ether and dried in vacuum, yield 85%.
Preparation of tungsten complex of N-nicotinoyl -N¢-thiophenethiocarbohydrazide:
The complex was synthesized by digesting a mixture of the ethanolic solution (50mL) of N-nicotinoyl-N¢-2-thiophenethiocarbohydrazide (H2 NTTH) (2mmol) and acidified aqueous sodium tungstate (2mmol) solution(50mL) on the water bath for 1½ hours. The resulting brown complex was filtered, washed with hot water, ethanol and diethyl ether and finally dried in vacuum, yield 82%.
Instrumentation:
Complexes were analysed for their metal content, following a standard procedure 24 by decomposing the complexes with a mixture of HNO3 and HCl followed by H2SO4. Sulphur was determined as barium sulfate 24. Carbon, hydrogen and nitrogen were estimated on a EA 1108 CHN Elemental Analyzer. Magnetic susceptibility measurements were made at room temperature on a Cahn-Faraday balance using Hg [Co (NCS)4 ] as calibrant. Electronic spectra were recorded on a CARY-2390 U.V.-Visible Spectrophotometer as Nujol mulls 25. IR Spectra were recorded in the 4000-400 cm-1 region (KBr disc) on a JA SCO FT/FR-5300 spectrophotometer. The 1H and 13C NMR spectra were obtained in DMSO-D6 on a JEOL FX-300Q FT/NMR spectrometer using TMS as internal reference. ESR spectra were recorded on a X-band spectrometer model EPR-112 using DPPH as a <g> marker. The electrical conductivity of the pressed pellets of the complexes was obtained by a conventional two-probe method in the 303-383 K range with contact made on the pellet surfaces using graphite paint. The weight loss by heating the complexes upto 1200C was found to be almost negligible, however, heating further in the range 120-1600C resulted in weight loss corresponding to two water molecules. Loss in weight in this range of temperature indicates coordinated water molecules.
RESULTS AND DISCUSSION:
Analysis of the Complexes:
( H2TTBH)
-2-thiophenoyl- N¢-thiobenzhydrazide
( H2TTBH)
The analytical data of the
synthesized complexes are given in Table 1, together with some of their properties. The complexes, having 1:1 (metal:
ligand) stoichiometry, are formed by loss of one protons from the ligand
generating R¢-C(S)=N-NH-C(O)-R. Both the complexes
decompose above 2000C and are insoluble in H2O, EtOH and
MeOH but are soluble in coordinating solvents such as DMSO and DMF. The weight
loss by heating the complexes upto 1200C was found to be almost
negligible, however, heating further in the range 120-1600C resulted
in weight loss corresponding to two water molecules. Loss in weight in this
range of temperature indicates coordinated water molecules. The molar
conductance values of the complexes in DMF show the non-ionic behavior of both
the complexes. X-ray powder photographs of the complexes exhibit just a
diffused broad band which indicates their amorphous nature. As indicated by
analytical data the complexes of the type M2O4L2(H2O)2
[where M=Mo, W; L = HNTTH] are formed. The formation of the ligand is
represented by the following equations:
(C4H3S)CSSCH2COOH + (C5H4N)CONHNH2 C4H3OCSNHNHCOC5H4N + HSCH2CO2H
Magnetic Susceptibility Studies:
All the complexes exhibit diamagnetism instead of showing magnetic moment of 1.73 BM as expected for Mo(V) and W(V) complexes, which is in agreement with the proposed dinuclear structure for the complexes.
Electronic Spectral Studies:
The electronic spectra of the
molybdenum and tungsten complexes of (H2 NTTH) exhibit
two bands around 14000 and 18500 cm-1, which may be assigned to 2B2
® 2E and 2B2
® 2B1 transitions 26
respectively, characteristic of six coordinated molybdenum (V) complexes. In
the spectra of the complexes an additional band is found nearly at 22500 cm-1
which may be ascribed to the presence of the Mo2O42+
core 27. Thus the findings of electronic spectra are in conformity
with those of magnetic susceptibility measurements showing dimeric nature of
the complexes (Table 2).
Table 1: Analytical data and general behaviour of complexes
|
Complex |
Found (calculated) |
Molar conductance of 10-3 M solution in DMF (ohm-1 mol-1 cm2) |
||||
|
Metal |
Carbon |
Hydrogen |
Nitrogen |
Sulphur |
||
|
(H2 NTTH) C11H9N3S2O |
- |
49.25 (50.19) |
3.16 (3.42) |
15.45 (15.97) |
24.28 (24.33) |
- |
|
[Mo2O4(H NTTH)2 (H2O)2] Mo2C22H20N6S4O4 |
25.22 (25.53) |
34.88 (35.11) |
2.62 (2.66) |
11.02 (11.17) |
16.93 (17.02) |
0.06 |
|
[W2O4(H NTTH)2 (H2O)2] W2C22H20N6S4O4 |
39.44 (39.66) |
28.56 (28.45) |
2.15 (2.16) |
8.98 (9.05) |
13.86 (13.79) |
0.03 |
Table 2 : Electronic spectral bands (cm-1) and their assignments
|
Complex |
Bands (cm-1) |
Assignments |
|
[Mo2O4(H NTTH)2 (H2O)2]
|
14030 18520 22540 |
2B2 ® 2E 2B2 ® 2B1 |
|
[W2O4(H NTTH)2 (H2O)2]
|
14520 18630 22020 |
2B2 ® 2E 2B2 ® 2B1 |
ESR Spectral Studies:
ESR spectral studies show that all the complexes were ESR inactive indicating the dinuclear structure of the complexes27.
NMR spectra:
The 1H NMR data (Table 3) of H2NTTH shows two signal at d 10.98 and 11.24ppm due to the presence of two NH protons which disappear on D2O exchange. Thiophene ring protons appear as three separate multiplets at d 6.70 (t, 1H), 7.20 (d, 1H) and 7.40 (s, 1H) ppm and the pyridine ring protons appear as separate multiplets at 7.58-9.22 ppm.. One of the NH signal is absent from the 1H NMR spectrum of the molybdenum complex suggesting loss of one of the NH protons via thioenolization. The thiophene ring protons show three separate signals at d 6.60 (s, 1H), 7.13 (d, 1H) and 7.38 (d, 1H) ppm and the pyridine ring protons are observed at d 7.54-9.12 ppm.
The 13C NMR spectrum of H2NTTH (Table 4) shows eleven signals, of which two signals at d 182 and 163 ppm are due to the C=S and C=O carbons, respectively. The spectrum of H2NTTH (Table3.4) show the chemical shifts for the pyridine and thiophene ring carbons at: (d, ppm) C2,6, 152, 148 C3, 135; C4,5, 128, 123; C¢2, 150, C¢3, 117, C¢4, 113 and C¢5, 146.
The 13C NMR spectrum of molybdenum complex (Table 4) also shows eleven signals. The chemical shifts for the ring carbons are: (d, ppm) C2,6, 151, 148; C3, 135, C4,5, 131, 123; C¢2, 148; C¢3, 116, C¢4, 112; C¢5, 144. The signal at d 163ppm in the ligand remains unchanged in molybdenum complex indicating noninvolvement of C=O in bonding. The signal due to C=S in ligand shows downfield shifts in the molybdenum complex indicating involvement of C=S in bonding.
IR spectra:
The important IR spectral bands and their assignments are given in Table 5. The spectrum of free H2NTTH shows bands at 3255 and 3120 cm-1 due to n(NH). The bands at 1660, 1420, 1330, 1025 and 840 cm-1 are assigned to n(C=O), thioamide I, thioamide II, n(N-N) and n(C=S) modes, respectively. In the IR spectra of the molybdenum and tungsten complexes bands at 3255 and 840 cm-1 in the ligand due to n(NH) and n(C=S) modes are absent but two new bands appear at 1580-1620 and 710 cm-1 due to n(N=C) and n(C-S) modes, respectively, suggesting removal of one of the -NH protons via thioenolization and bonding of the resulting thiolato sulfur takes place with the metal ion. Furthermore, the thioamide I, thioamide II and n(N-N) bands at 1420, 1330 and 1025 cm-1, respectively, in the free hydrazide undergo a positive shift of 40-50, 35-65 and 15-45 cm-1, respectively, in the complexes28,29 suggesting involvement of these groups as bonding sites. These observations show the involvement of thiolato sulfur and one of the hydrazinic nitrogens in bonding. The band corresponding to n(C=O) in the ligand remains almost unchanged in the spectra of the complexes indicating non-involvement of C=O group in complex formation. The spectra of the hydrated complexes exhibit a broad band in the region (3500-3700 cm-1) ascribed to n(OH) and another band at 850 cm-1 due to rocking mode of OH group. The presence of the latter band indicates coordinated nature of water molecules. These bands, as expected, are completely absent in the ligands as well as in the corresponding anhydrous complexes.
The spectra of molybdenum complexes show three characteristic bands approximately at 950, 740 and 480 cm-1 due to n(M = Ot) , nas(Mo-Ob-Mo) and ns(Mo-Ob-Mo) respectively. The occurrence of these bands leads to the conclusion that molybdenum is present in the complexes as Mo2O42+, moiety 27.Tungsten complexes also exhibit the above three modes at 960, 760 and 500 cm-1 respectively. The spectra of the complexes are characterized by M-N and M-S stretching vibration at ~540 cm-1 30.Thus, H2NTTH acts as a uninegative bidentate ligand.
Table 3 : 1H NMR spectral data (d, ppm)
|
Compound |
Pyridine ring |
Thiophene ring |
NH |
||
|
H¢3 |
H¢4 |
H¢5 |
|||
|
H2NTTH |
7.58-9.22 (4H) |
6.70 ( 1H) |
7.20 (1H) |
7.40 (1H) |
10.98(1H) 11.24(1H) |
|
[Mo2O4(H NTTH)2 (H2O)2] |
7.54-9.12 (4H) |
6.60 (1H) |
7.13(1H) |
7.38 (1H) |
11.02(1H) |
Table 4 : 13C NMR spectral data (d, ppm)
|
Compound |
>C=S |
C3 |
C2,6 |
C4,5 |
C¢2 |
C¢3 |
C¢4 |
C¢5 |
C=O |
|
H2NTTH |
182 |
135 |
152,148 |
128,132 |
150 |
117 |
113 |
146 |
163 |
|
[Mo2O4(H NTTH)2 (H2O)2] |
172 |
135 |
151,148 |
131,123 |
148 |
116 |
112 |
144 |
162 |
Table 5 : Important
IR spectral data (cm-1) and their assignments
|
Complex |
n (OH) |
n (NH) |
thioamide I (bNH+nCN) |
thioamide II (nCN+bNH) |
thioamide IV n(C=S)/ n(C-S) |
n (C=O) |
n(N-N) |
n (M=Ot) |
n(M-Ob-M) |
n(M-N) n(M-S) |
|
H2INTTH |
|
3255, 3120 |
1420 |
1330 |
840 |
1660 |
1025 |
- |
- |
- |
|
[Mo2O4(HNTTH)2 (H2O)2] |
3500 |
3120 |
1460 |
1365 |
710 |
1655 |
1040 |
950 |
740 480 |
550, 560 |
|
[W2O4(HNTTH)2 (H2O)2] |
3600 |
3120 |
1470 |
1395 |
720, 820 |
1650 |
1070 |
960 |
760,500 |
540, 520 |
Based on chemical composition, general behaviour and physico-chemical studies discussed above, it is suggested that the ligands used for synthesis of complexes in this section act as uninegative bidentate. The tentative structure proposed for the complexes is given below –
Fig. 2: Proposed structure of the complexes
Where, M= Mo(V), W(V) and R= C5H4N R`= C4H3S
CONCLUSIONS:
Based on various studies carried out, some important findings of the present work are:
1. The magnetic and electronic spectral studies suggest that the ligand act as uninegative bidentate ligand and both the complexes show distorted octahedral geometry
2. The infrared spectral studies of the complexes suggest that the bonding occurs through the thiolato sulfur and one of the hydrazinic nitrogen.
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Received on 24.10.2011 Modified on 10.11.2011
Accepted on 20.11.2011 © AJRC All right reserved
Asian J. Research Chem. 5(1): January 2012; Page 79-82