Synthesis and characterization of monothiocarbamates and monothioacetylacetonates of bismuth(III) and antimony(III)

Polyhedron Vol. 7, No. 6, pp. Printed in Great Britain

483487,

1988 0

0277%5387/88 S3.00+ .Xl 1988 Pergamon Press plc

SYNTHESIS AND CHARACTERIZATION OF MONOTHIOCARBAMATES AND MONOTHIOACETYLACETONATES OF BISMUTH(II1) AND ANTIMONY(II1) D. K. SRIVASTAVA, Department

of Chemistry,

R. P. SINGH

and V. D. GUPTA*

Faculty of Science, Banaras Varanasi-221 005, India

Hindu

University,

(Received 10 July 1987 ; accepted 13 October 1987) Abstract-Bismuth(II1) and antimony(II1) tris(monothiocarbamate), M(SOCNRZ)3 (where -NR2 = -N(CH2CH3)2 or -NC4H4), and bismuth(II1) tris(monothioacetylacetonate), Bi(CH3CSCHCOCH3)3, have been synthesized and studied. These have been characterized by elemental analyses, molecular weight measurement and, IR and NMR spectral analyses. PMR spectra of bismuth(II1) tris(diethylthiocarbamate), Bi[SOCN (CH2CH3)2]3, suggests a high temperature process that involves the rotation about the C-N bond in the 0SCN(CH2CH3)2 ligand.

Stereochemistry and configurational rearrangements of the metal tris-chelate complexes’ containing symmetrical ligands like P-diketones and dithiocarbamates have been examined in detail. Metal chelates derived from unsymmetrical sulphur ligands like monothio-/?-diketones and monothiocarbamates provide excellent systems to probe the origin of novel properties observed in the sulphur complexes. With this aim, we have undertaken a systematic investigation on these, and have recently reported the crystal and molecular structure of indium(II1) tris(monothiodibenzoylmethanate),2 and tin(IV) monothio-P-diketonates3 and pyrrolylthiocarbamates.4 The indium(II1) tris-chelate interestingly displays clustering of the sulphur atoms on the distorted octahedron. We report here the syntheses and characterization of a few tris complexes of bismuth and antimony, and variable temperature PMR spectra of Bi[SOCN(CH,CH,),],.

Preparation of bismuth(II1) tris(diethylthiocarbamute), Bi[SOCN(CHZCH3)2]3 and bismuth(II1) tris (pyrrolylthiocarbamate), Bi(SOCNC,H,), (Table 1)

EXPERIMENTAL Reactions were carried out under anhydrous conditions under a nitrogen atmosphere. Solvents were purified and dried by the standard methods.

*Author to whom correspondence

Diethylthiocarbamate’ and pyrrolylthiocarbamate637 were obtained as ammonium and potassium salts, respectively, by the literature procedures. Monothioacetylacetone8 was synthesized by the H2S method and converted into the sodium salt.’ Bismuth trichloride (H.P.C.) and antimony trichloride (B.D.H.) were purified by sublimation and distillation, respectively, before use. Bismuth was analysed gravimetrically as Bi,O, and antimony volumetrically by using potassium bromate. Sulphur was estimated by Messenger’s method and nitrogen by Kjeldahl’s method. Molecular weights of the complexes were determined cryoscopically in benzene. Infrared spectra were recorded as Nujol mulls using CsI plates in the range 4000-200 cm-’ on a Perkin-Elmer model 621. ‘H and 13C NMR spectra were recorded on a JEOL FX90Q spectrometer in CDC13 using TMS as an internal standard.

should be addressed.

Bismuth trichloride (0.99 g, 3.1 x lop3 mol in the case of diethyl- and 0.44 g, 1.3 x 1O-3 mol in the case of pyrrolylthiocarbamate) in methanol (- 15 cm’) was added dropwise with stirring to a methanol (- 30 cm3) solution of the salts of thiocarbamate (1.95 g. 9.3 x lop3 mol diethyl- and 483

D. K. SRIVASTAVA

484

Table

1. Analytical

rt

al.

and physical data for bismuth(III), antimony(II1) monothiocarbamates and monothioacetylacetone

tris complexes

of

Analyses (%) No. 1

Complex Bi[SOCN(CH,CH,),],

Colour

M.p. (O’C)

Yellow

90

2

Bi(SOCNC,H&

Yellow

165-166”

3

Sb[SOCN(CH2CH,),],

Yellow

94

4

Sb(SOCNC,H,),

Yellow

145-147

5

Bi(CH,CSCHCOCH,),

Yellow

125-127

M

S

33.3 (33.4) 34.7 (35.6) 23.2 (23.5) 23.8 (24.4) 37.5 (37.7)

15.4 (15.8) 15.9 (16.3) 18.3 (18.5) 18.8 (19.2) 17.3 (17.9)

N

MoleculaP weight 587 (607) 571 (587) 496 (518) 488 (500) 559 (544)

(Z) (Z) (X) (88::) -

“Calculated values in parentheses. ’ Decomposed. 0.70 g, 3.9 x 1o-3 mol pyrrolylthiocarbamate) maintained at 0°C under a nitrogen atmosphere. The reaction mixture was stirred for - 12 h at room temperature (28°C). From the mixture, volatile materials were removed and the products obtained were extracted with benzene. Removal of the solvent and crystallization from a dichloromethane/ n-hexane (1 : 1) mixture produced yellow crystalline solids. The products were dried at 0.1 mm Hg/- 3O”C/5 h. of antimony(II1) Preparation carbamate), Sb[SOCN(CH2CH3)J3

tris(diethyZthio(Table 1)

Into a stirred benzene solution (- 25 cm’) of the diethylammonium salt of diethylthiocarbamate (1 .O g, 7.2 x lop3 mol) maintained at - 10°C antimony trichloride (0.55 g, 2.4 x 10m3 mol) dissolved in benzene (- 15 ml) was added dropwise. The stirring was continued for - 12 h. The separated diethylammonium chloride was filtered out. The solvent was removed from the filtrate under reduced pressure and the product thus obtained was dried at 0.1 mm Hg/- 3O”C/- 6 h.

at 0.1 mm Hg/30”C/5 h and finally crystallized dichloromethane solution.

Preparation qf bismuth(II1) tris(monothioacetylacetonate), Bi(CH,CSCHCOCH,), (Table 1) To a stirred solution of bismuth trichloride (0.50 g, 1.5 x 10m3 mol) in methanol, the sodium salt of monothioacetylacetone (0.66 g, 4.5 x lop3 mol) dissolved in - 15 cm3 of methanol was added dropwise at 0°C. The reaction mixture was stirred at room temperature for 2 h. After complete removal of methanol the reaction product was treated with dichloromethane (- 20 cm”). Insoluble sodium chloride was filtered out and the solvent was removed from the filtrate under reduced pressure. The products were dried at 0.1 mm Hg/- 3O”C/4 h and finally crystallized from chloroform and ethanol. RESULTS

AND

DISCUSSION

Tris-complexes of bismuth(II1) and antimony(II1) with monothiocarbamates and monothioacetylacetone have been synthesized in good yields by the following reaction routes

Preparation of antimony(II1) tris(pyrrolylthiocarbamate), Sb(SOCNC,H,), (Table 1) A solution of antimony trichloride (0.50 g, 2.1 x lop3 mol) in dichloromethane (- 15 cm3) was added dropwise into a suspension of the potassium salt of pyrrolylthiocarbamate (1.09 g, 6.3 x 10P3 mol) in dichloromethane (- 30 cm’) with stirring under a nitrogen atmosphere. The reaction mixture was stirred for 12 h at ambient temperature. It was filtered to remove the separated potassium chloride and volatile materials were evaporated from the filtrate to obtain the solid product, which was dried

from

3 W-WH&NH~1+ [SOCN(CH,CH,),]

-

+ M[SOCN(CH,CH,),], + 3(CH,CH,),NH,Cl MCI, +

3KSOCNC4H4 -+ M(SOCNC,H,),

+ 3KCl

3NaCH3CSCHCOCH3 -+ M(CH3CSCHCOCH3)3 (where M = Sb or Bi).

+ 3NaCl

Monothiocarbamates

and monothioacetylacetonates

3THF (1568 cm-‘)‘j where the ligands are acting as bidentate. In a sulphur bonded unidentate pyrrolylthiocarbamate such as Ph$n(SOCNC,HJ whose crystal structure4 is known, the free v(C=O) is observed at a considerably higher frequency (1640 cm-‘). Another significant band is v(C-N) at N 1286 cm-‘. v(M-0)13 (4SCr500 cm-‘) and v(M--S)14 (38&390 cm-‘) vibrations can be seen in both diethyland pyrrolylthiocarbamate derivatives. ‘H NMR spectra of bismuth and antimony tris(diethylthiocarbamate) exhibit overlapping quartets and triplets respectively, due to methylene and methyl protons (Table 3), perhaps arising from the magnetic non-equivalence of the ethyl groups, due to partial double bond character in the C-N bond.” In order to get more insight, variable temperature PMR spectra of Bi[SOCN(CH2CH3)2]3 have been studied. Variable temperature PMR spectra of Bi[SOCN(CH2CH3),13 afford evidence for the distinct kinetic process involving hindered rotation around the C-N partial double bond in the diethylthiocarbamate ligand. Since the multiplet observed at 25°C is symmetrical in nature, it can be considered to arise due to the two overlapping triplets from the methyl protons of the same ligand moiety. Any non-equivalence of the spanning and equatorial ligands would amount to non-symmetrical multiplets. In this process by using the time averaged resonance of a simple triplet owing to the onset of rapid C-N bond rotation, the coalescence temperature was found to be 49°C (Fig. 1). Rotation about the C-N bond would exchange the ethyl groups between the sites adjacent to sulphur and the sites adjacent to oxygen. This nonequivalence is further reflected in its 13CNMR spectrum. At ambient temperature, the spectrum displays one signal for COS carbons and two resonances for methylene as well as methyl carbons. Thus on the basis of available evidence, a distorted

Monothiocarbamates and monothioacetylacetonates of bismuth(II1) and antimony(II1) are crystalline soluble in common organic solvents and monomeric in benzene. Sodium salts of dialkylthiocarbamates exhibit a very strong but broad band at 1507-1520 cm-’ assignable to highly coupled v(C=O) and v(C-N) vibrations.‘,” Bismuth(II1) and antimony(II1) tris(diethylthiocarbamate) show strong broad bands at 1545 and 1580 cm- ‘, respectively (Table 2), assignable to these coupled vibrations. The absorption at a comparatively higher frequency in the antimony derivative probably suggests a weaker Sb . . . 0 interaction in comparison to the bismuth analogue, this may be a consequence of the lone pair of electrons over antimony being more effective. The oxygens are perhaps strongly coordinated to bismuth or the marked change may arise due to the size effect. The point can only be settled after single crystal X-ray structure analysis. Notably in Fe[SOCN(CH,),],” whose crystal structure’* shows that the Fe-O and Fe-S bond lengths are equivalent to covalent bond distances, the v(C=O) absorption appears at 1540 cm-‘. In distinction to dialkylthiocarbamate, the potassium salt of aromatic thiocarbamates displays a sharp band at a higher frequency (1525-l 550 cm-‘) due to the v(Cu0) vibrations.6*7 This is consistent with the increased mercaptide character arising from the greater contribution by the canonical

form

1/

[\N-C”-

1

x0-

The IR spectra of the tris-

1

-

pyrrolylthiocarbamates of bismuth(II1) and antimony(II1) display a sharp v(C=O) absorption at 1582-85 cm-’ (Table 2). This absorption is at a somewhat higher frequency than that which has been found for the nickel complex, Ni,(SOCNC,H,),*

Table 2. Important

Sl. No. 1 2

3 4 5

485

IR bands” (cm-‘) of bismuth(II1) and antimony(II1) tris complexes of monothiocarbamates monothioacetylacetonate

Complex Bi[SOCN(CH,CH,)& Sb(SOCN(CH,CH,)J, Bi(SOCNC,H,), Sb(SOCNC,H,), Bi(CH,CSCHCOCH,),

v(C=o) v(C=N)

v(C-N)

v(C=C)

1545v

-

-

158Ovs 1582~~

1292s

-

1585~~

1280s

-

1600b

-

1500s

v(C=S)

S(COS)

W--O)

v(M-S)

942m

667m

508s

380s

943m 982m

663m 664m

508s 489m

385m 384m

975m

1210s

660m

480m

380m

-

490s

348s

n Spectra were recorded in the range 4000-200 cm-’ as Nujol mulls on CsI plates. ‘Bands due to purely the v(C=O) vibration.

and

“At 90 MHz. bSpectra were recorded in CDCl, with TMS as internal reference. ’ Centre of overlapping quartets. dCentre of overlapping triplets. eCentre of triplet.

CH3dO)

CH3-W

35.3 29.6

CH3 of (N)-CH2CH3 CH, of (N)-CH,CH,

13.8 13.5

*-

123.3

41.6

Assignments

(N)-CH,

(COS) (N)--CHz

173.1 46.4

13CNMR (ppm)” Bi(CH3CSCHCOCH3)3 C-(S) C-(O)

Assignments

Bi[SOCN(CH2CH,),],

3.19 0.99d -

-

7.25 6.23

6.33

3.39 2.18

@)--CH3

(SF=3

tL-H-NC,H, 8-H

(Nk-CHz (C)-CH,

Assignments

and monothioacetylacetonate

Bi(CH,CSCHCOCH,),

tris complexes of monothiocarbamates

‘H NMR(G)b Sb(SOCNC,H,), Sb[SOCN(CH,CH,),],

and antimony(II1)

195.6 167.2

-

7.34’ 6.26

Bi(SOCNC,H,),

-

-

3.41’ 1.25d

Bi[SOCN(CH,CH,),],

Table 3. ‘H and 13CNMR chemical shifts” of bismuth(III)

Monothiocarbamates

487

and monothioacetylacetonates

0-CH3 and methine protons (Table 3). The presence of only five resonances in the 13C NMR spectrum, furthermore suggests fairly high symmetry of the complex. With the available spectral evidence, bismuth(II1) tris(monothioacetylacetonate) may be considered to possess symmetrical cis(facia1) octahedral geometry. However, the presence of a lone pair of electrons on bismuth may bring about some distortion of the octahedron. It may be mentioned that in the 13C NMR spectrum, substantial downfield positions of CS (195.6 ppm) and CO (167.2 ppm) carbons (Table 3) are very indicative of the bidentate mode of the ligand. Attempts to prepare antimony(II1) tris(monothioacetylacetonate) were not successful due to the thermal instability of the complex. Repeated efforts to grow single crystals of all of the above described tris-chelate complexes by using various solvent combinations have been unsuccessful. Ackno&e&ement-We are Delhi for financial assistance.

thankful

to

CSIR,

New

REFERENCES

(8)

Fig. 1. Variable Bi[SOCN(CH,CH&

temperature PMR spectrum of (for simplicity only methyl signals have been shown).

cis(facia1) octahedral structure may be proposed for tris-thiocarbamates of bismuth and antimony. However, PMR spectra of metal tris(pyrrolylthiocarbamate) at ambient temperature give only two sets of triplets (Table 3) due to CI-and /?-protons of the ligand. of bismuth(II1) trisThe IR spectrum (monothioacetylacetonate), shows a lowering in the frequencies of v(C=O) (1600 cm-‘) and v(C-C) (1500 cm-‘) vibrations 15,16(Table 2) in comparison to the free ligand. This is consistent with the conjugated chelate ring structure having a higher degree of a-delocalization in the monothioacetylacetone moiety. In the far IR region two bands appearing at 490 and 390 cm-’ are considered to be due to stretching vibrations, (Bi-0)13 and (Bi-S)14 respectively. The PMR spectrum of Bi(CH&SCHCOCH3)3 shows only a single resonance each for S-CHJ,

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