Chiang Mai J. Sci. 2006; 33(3)
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Chiang Mai J. Sci. 2006; 33(3) : 357 - 362 www.science.cmu.ac.th/journal-science/josci.html Contributed Paper
Synthesis and Characterization of Dioxo-molybdenum (VI) Complexes of Some Dithiocarbamates. Didarul A. Chowdhury, Mohammad N. Uddin* and Abul K.M. L. Rahman Department of Chemistry, University of Chittagong, Chittagong-4331, Bangladesh. *Author for correspondence, e-mail:
[email protected] Received: 15 July 2005 Accepted: 10 February 2006.
ABSTRACT Some Dioxo-molybdenum(VI) complexes of the type MoO2(dtc) 2 have been prepared (where dtcH = is the uninegatively charged bidentate ligand of diamine-monodithiocarbamate).The prepared complexes are characterized by various physicochemical techniques. On the basis of analytical data, molar conductance, magnetic and spectral studies the molecular formula and structure of the complexes have been elucidated. Distorted octahedral geometry was proposed where oxygen atoms are in cis-position. Keywords: diamines, dioxomolybdenum(VI), distorted octahedral, dithiocarbamate. INTRODUCTION A large number of transition metal complexes with various aliphatic and aromatic dithiocarbamate ligands have been reported. Complexes with mono-dithiocarbamate (dtcH) also ligands (themselves) have practical application in agriculture and in medicine as fungicide and pesticides. Zhang W. et al. synthesized and characterized the bis-Zn(II) complexes of dibutyldithiocarbamate [1]. Dithiocarbamate complexes have been examined in organotin complexes of the type RnSn(dtc)4-n (n = 1- 4) [2]. Single-crystal X-ray structure have been recorded for dithiocarbamate metal compounds [M(R 2 dtc) 2 ][ M = Co, Ni, Pd] [3]. It is recognized that dithiocarbamate is capable of exhibiting monobasic bidentate ligand [4]. In organotin complexes it was established that dithiocar-bamate ligand coordinate in different mono, aniso and bidentate ways [5]. Most of the dithiocarbamates reported earlier were prepared from mono 1.
amines.Complexes of titanium(IV) containing mono-dithiocarbamate as a primary ligand derived from diamines have been reported where one NH 2-site remained unreacted [6-7]. Antimicrobial activity of dithiocarbamate and their titanium complexes have also been studied [8]. Moreover among the oxidation states of Mo, 6+ is stabilized through formation of the MoO22+. The aim of the work is to synthesize some new MoO2(dtc)2 type complexes as these are rare in literature. MATERIALS AND METHOD The diamines and sodium molybdate dihydrate were obtained from M/S E. Merck and BDH Chemicals respectively are 0thers were collected from Aldrich Chemicals Co. Ltd. Infrared spectra on KBr pelletes were recorded on a Shimadzu Infrared Spectrophotometer (model-470). Electronic spectra were run on a Shimadzu UV-Visible Spectrophotometer (model UV-160) using
2.
358
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1 cm cell. Melting points of both ligands and complexes were obtained with an electrothermal melting point apparatus. Conductivity was measured in DMSO (10-3M) solution with a Philips Conductivity Meter (model PW-9501). Magnetic moment was determined at room temperature by the Gouy method. The molybdenum content of the prepared complexes was done by complexometric titration method [9] after destruction of organic part of the complexes by the treatment with conc. H2SO4, conc. HNO3 and 70% HClO4. 2.1 Preparation of Ligands The white ethylene diamine-monoo dithiocarbamates (en-mono-dtcH; m.p.180 C), 1,3-propen diamine-mono-dithiocarbamate o (pn-mono-dtcH: m.p.200 C), N, N-dimethylethylene diamine-mono-dithiocarbamates (dme-en-mono-dtcH; m.p.135 o C), N, N-diethylethylene diamine-mono-dithiocaro bamates (dEt-en-mono-dtcH; m. p.142 C), Hexane-1,6-diamine-mono-dithiocarbamates o (Hda-mono-dtcH; m. p. 134 C) and tertiarydibutylethylene diamine-monodithiocarbamates(dBut-en-mono-dtcH; m. p. o 95 C) have been prepared by following the general procedure given below. Methanolic solution of amines(150 mmol in 40 cm3 methanol) taken in a beaker was cooled in ice-salt bath for 10 minutes. To this carbondisulphide(140 mmol; a bit less to
protect the possibility of formation of bisderivatives) was added drop wise over a period of 30 minutes with constant stirring when oily precipitate separated out. The white precipitate formed was allowed to stand for 5 hours in the bath for crystallization. The product was filtered on a buchner funnel under suction, washed with methanol and sucked dry. The product thus obtained was recrystallized from methanol and dried in vacuo over calcium chloride. 2.2 Preparation of Bis(acetylacetonato) Dioxo-molybdenum(VI), MoO2(acac)2 The starting material MoO2(acac)2 was prepared following the published procedure [10]. The compound was characterized by its metal analysis and characteristic IR and electronic spectral data. 2.3 Preparation of Complexes To a clear solution of the dtcH ligand (4 mmol) in a mixed solvent (60 cm3) of petroleum spirit (60-80 0C) and ethanol, MoO2(acac)2 (2 mmol) solution in the same solvent was added. The resulting mixture was refluxed for 1 hr. when the complexe precipitate was separated out. The product was filtered off, washed with ethanol and dried under vacuum over silica gel. Table 1 lists the prepared complexes of the type MoO2(dtc)2 along with their analytical data and some physical properties.
R R
N
S (CH2)n
NH
C
* S
MoO2
2
Figure 1. MoO2(dtc)2. Complexes: 1. R=H, n=2; 2. R=H, n=3; 3. R=CH3, n=2; 4. R=C2H5, n=2 5. R= H, n=6; 6. R= (CH3)3C- , n=2
violet
violet
violet
MoO2(pn-mono-dtc)2
MoO 2(dme-en-mono-dtc)2
MoO 2(dEt-en-mono-dtc)2
MoO2(Hda-mono-dtc)2
MoO 2(dBut-en-mono-dtc)2
2
3
4
5
6
75
75
80
85
60
>250
>250
>250
>250
>250
>250 (24.10)
13.90 (15.30)
19.40 (18.79)
18.10 (18.79)
20.60 (21.12)
21.80 (22.50)
23.60
% Mo
11.6
14.5
20.4
18.4
16.5
12.6
ΛM Ohm-1 cm2mol-1
Dia.
——
Dia.
—-
Dia.
Dia.
µeff B. M.
3160m
3240m
3160s
3180w
3160br
3200m
1500s
1540vs
1500s
1520vs
1505s
1505s
ν N-H ν C=N
1020vs
1020m
1020vs
1020w
1027w
1025m
ν C=S
930s
935m
930br
935s
907vs
940s 665m(ol)
ν M0=O
Infrared spectral data
Calculated values are given in parentheses. vs= very strong , s= strong, m= medium, w= weak, sh= shoulder, br= broad.
violet
Olive green 70
Dark
Colour %Yield M.P.0C
MoO2(en-mono-dtc)2 violet
Complexes
1
Sl. No.
Table 1. Analytical, spectral and some physical data of the complexes.
445s(keto) 665s(ol)
450m(keto) 665m(ol)
445s(keto) 670s(ol)
410m(keto) 700m(ol)
440w(keto) 683s(ol)
410s(keto)
ν Mo-S
350, 340, 299, 267, 253
350, 340, 298, 265, 250
350, 320sh, 299, 274, 257
360, 310, 297, 275, 248
350sh, 340, 298, 263, 251
347sh, 343, 299, 272, 257
Electronic Spectral bands (nm)
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2.4 Infrared Spectra A common feature in the IR spectra of all of the complexes is the appearance of stretching band around 1,500-1,520cm -1 corresponding tonC-N of the Et3dtc ligand [11]. All the examined complexes show bands in 1,500-1,450 cm -1 range which can be assigned to C-N bonds vibrations of the S2 C-NR2 and lie between nC=N (1,640-1,680 cm -1) and nC-N (1,250-1,350cm -1) range suggesting a considerable double bond character of the C-N bond in dtc group [1,5,12-15]. As double bond character is more pronounced in the complexes it can be concluded that ligand is coordinated via S, S atoms. The lack of SH bond at 2,550 cm-1 in complexes confirms such a mode of coordination [12]. The presence of a single strong band at around 1,000 cm-1 due to a νC-S mode in the spectra of complex is strongly indicative of bidentate behavior of the dithiocarbamate ligand in the complexes, otherwise a doublet(978, 959 cm-1) would be expected in the 1,000±70 region as in the case of monodentate coordination [1,5,13-15]. Bands νC=S at around 1,200 cm-1 and νC-S at around 780 cm -1 for ligands showed negative and positive shift, respectively in the spectra of complexes indicating the coordination of both S- atoms. In the spectra of both ligands (containing –NH2 group) and complexes, no significant change is observed for νN-H mode indicating non-involvement of amino nitrogen in coordination [6,7]. Complexes have distorted octahedral structure with cis-oxygen atoms, with stronger Mo=O, stretching bands in 900-930 cm-1 [16]. In the spectra of the complexes some new bands at 400-420 cm-1 and at 665-700 cm-1due to νMo-S (keto) and νMo-S(ol) stretching modes, respectively [5,12]. Selected bands of IR spectral data are given in Table 1. 2.5 Electronic Spectra The electronic spectra of the prepared complexes were recorded on nujul mull and observed bands are given in Table 1. There is
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no evidence of any d-d transitions over visible region suggesting 4d O electronic configuration of Molybdenum. The low energy bands ovserved around 400 nm may be assigned to a ligand to metal charge transfer [LMCT] transition due to the promotion of electron from the highest occupied ligand (donor) molecular orbital to the lowest unoccupied molybdenum orbital. The other high energy bands are due to intraligand π→π* and n→π* transitions. The colour of the complexes is due to charge transfer absorption tailing in from the ultraviolet. 2.6 Magnetic and Conductivity Measurements The diamagnetic behaviour of these complexes supports 4d0 electronic configuration consistent with 6+ oxidation state of the central molybdenum ion. The low molar conductance values (Table.1) of the complexes in DMSO solution(ca.10-3M) show them to be non-electrolytes supporting neutral MoO2L formulation of the compounds. CONCLUSION The dithiocarbamate (dtcH) possess a planar configuration with respect to the position of the donor atoms/ions. The analytical and some physical data of the prepared complexes support neutral MoO2 (dtc)2 stoichiometry. A six-coordinated and approximate octahedral structure is possible for the present prepared complexes. However, it is difficult to suggest the exact geometry for each compound without crystal structural evidences. 3.
O
O
S Mo
S
S S
Figure 2. Approximate octahedral structure
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Figure 3. IR Spectra of the ligand: (dBut-en-mono-dtc).
Figure 4. IR Spectra of the Complex: MoO2(dBut-en-mono-dtc). REFERENCES [1] Zhang W., Zhong Y., Tan M., Tang N. and Yu K., Synthesis and Structure of Bis(Dibutyldithiocarbamate)Zinc(II): Zn2[(n-Bu)2NCSS]4, Molecules, 2003; 8: 411-417. [2] Song X., Cahill C. and Eng G., The Crystal Structure of Tricyclohexyltin NN-Butyl Dithiocarbamate, Main Group Met. Chem., 2002; 25: 13-14.
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