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Preparation and study of some arsenic and antimony trisdithiocarbamates
J. inorg, nucl. Chem., 1973, Vol. 35, pp. 743-750.
Pergamon Press.
Printed in Great Britain
PREPARATION AND STUDY OF SOME ARSENIC AND ANTIMONY TRISDITHIOCARBAMATES G. E. M A N O U S S A K I S and C. A. TSIPIS Laboratory of Inorganic Chemistry, University of Thessaloniki, Greece
(Received29 March 1972) Abstract-Trisdithiocarbarnates of arsenic and antimony with pyrrolidine, piperidine, diisobutylamine and dibenzylamine have been prepared by directly mixing either AsCIa or SbCI3 with CS2 and the corresponding amine. A reasonable mechanism is proposed. The frequencies of bands in the electronic spectra depend on the electron releasing ability of amine groups and probably on steric hinderence effects. Interpretation of the spectroscopic results indicates a distorted octahedral stereochemistry. The distortion is attributed to the stereochemically active lone pair of electrons on the arsenic and antimony atoms.
INTRODUCTION
MANY papers on dithiocarbamate complexes of group V elements have been
published [ 1]. However, little attention has been paid to the influence of amine groups of dithiocarbamates on the C - N and C-S bonds and consequently on the electronic structure of these complexes. The type of amine group (-NR2) plays an important role in the behaviour of dithiocarbamates (dtc) as ligands. This paper deals with the preparation and study of eight trisdithiocarbamate (tdtc) complexes of arsenic and antimony, namely: As[SC(S)NC4Hs]3, tripyrrolidyl dithiocarbamate-arsine, (I), As[SC(S)NC~Hlo]3, tripiperidyldithiocarbamatearsine, (II), As[SC(S)N(C4H9)2]3, tris (diisobutyldithiocarbamate) arsine, (III), As[SC(S)N(CH2CoHs)z]a, tris (dibenzyldithiocarbamate) arsine, (IV), Sb[SC(S)NC4Hs]3, tripyrrolidyldithiocarbamate-stibine, (V), Sb[SC(S)NCsHlda, tripiperidyldithiocarbamate-stibine, (VI), Sb[SC(S)N(C4Hg)z]3, tris(diisobutyldithiocarbamate) stibine, (VII) and Sb[SC(S)N(CH2CoH~)2]a, tris(dibenzyldithiocarbamate) stibine, (VIII). The amines were selected according to their electron releasing ability, EXPERIMENTAL
Measurements The i.r. spectra, for Nujol mulls and chloroform solution, were recorded on a Beckman-IR 5A spectrophotometer. Proton N M R spectra were recorded on a Varian A60 A(60 Mc/sec) instrument in CDCI3 solution, using TMS as internal standard. The u.v. spectra were recorded on a Zeiss PMQ il spectrophotometer, with freshly prepared CHCI3 solutions. Molecular weights were determined using a Perkin-Elmer Molecular weight apparatus Model 115.
Preparation Analytical grade reagents were used without further purification. The preparations of tris(dithiocarbamate) arsines or stibines were done according to the following methods. In a three-necked flask equiped with a refluxed condenser, a mechanical stirrer and a dropper funnel, arsenic or antimony trichloride (= 20 m-mole) was mixed with carbon disulfide (--- 60 m-mole). 1. S. Lippard, Progress in Inorganic chemistry, Vol. 11, p. 252. John Wiley, London (1970). 743
744
G . E . M A N O U S S A K I S and C. A. TSIPIS
Carbon tetrachloride (= 150 ml) was used as solvent. To this mixture a.s61ution of amine (= 120 mmole) in 50 ml carbon tetrachlodde was added dropwise. The mixture" was refluxed with stirring for four hours and after cooling it was filtered. The precipitate, in the case of the diisobutyl- and dibenzyl-compounds, which are soluble in CC14, consisted of amine hydrochloddes. These were identified by comparison of their properties with those of authentic samples. The filtrate was concentrated and after the addition of methanol or petroleum ether trisdithiocarbamates were obtained. The products were recrystallized from a mixture of benzene and methanol. The insoluble pyrrolidyl- and pipeddyl- compounds precipitated with the amine hydrochlorides. The precipitate was dissolved in a small quantity of chloroform and reprecipitated by addition of carbon tetrachloride. The precipitate, after filtration, was treated with distilled water. The mixture was filtered again. The filtrate was concentrated and upon cooling gave amine hydrochlorides. The precipitates were washed thoroughly with distilled water to remove chlorides and recrystallized from a mixture of CCI4 and CHCIa and dried at 110°C. The recrystallized products were white to yellowish crystals. Analytical results are shown in Table 1. RESULTS AND DISCUSSION
Products IV, V, VI, VII and VIII are new compounds. The previously known compounds [2, 3], have now been prepared by this simpler method which is similar to the previously described [4, 5] direct reaction of metal chlorides, amines and CS2, instead of one of the usual methods of preparation of dithiocarbamate complexes either by reaction of sodium dithiocarbamate and metal chloride [6], or by an insertion reaction between the corresponding aminoderivative of metal and C S 2 [7]. There is evidence, even in the simultaneous mixing of metal chlorides, amine and carbon disulfide, that the corresponding aminoderivatives are produced and then an insertion reaction takes place. For example, the corresponding aminoderivatives of trisamino-stibine or arsine are produced first according to this general reaction MC13 + 6R2NH --~ M(NR2)3 + 3R2NH.HCI.
(1)
This is supported by the fact that reaction (1) is extremely exothermic, it usually takes place at very low temperature, - 8 0 ° C [8]. Consequently we can consider that the carbon of CS2 undergoes nucleophilic attack by the trisamino-arsine or -stibine product forming the aminoderivative (a), Fig. 1. Repetition of the sequence on the monodithio derivative (a) gives finally tris(dithiocarbamate) arsine or stibine. It is generally known that the dithiocarbamates can react as ligands according to the resonance forms of Fig. 2. In form (a), dithiocarbamate reacts as a unidentate ligand and in forms (b), (c) and (d) as a bidentate ligand. In the last cases one of the sulfur atoms behaves as an electron donor to the metal ion, so that a second bond, which is a coordination bond, is created between the As or Sb ion and the ligand. 2. L. Bourgois and J. Bolle, Mere. Services chim. Etat 34, 411 (1948); Chem. Abstr. 44, 5814 d (1950). 3. L. Malatesta, Gazz. chim. Ital. 69, 629 (1939). 4. G. Manoussalds and P. Karayannidis, J. inorg, nucl. Chem. 31, 2978 (1969). 5. G. Manoussakis and P. Karayannidis, lnorg, nucl. Chem. Lett. 6, 71 (1970). 6. G. Thorn and R. Lusdwig, The Dithiocarbamates andRelated Compounds. Elsevier, Amsterdam (1962). 7. G. Ortel, H. Malz and H. Holtschmidt, Chem. Bet. 97, 891 (1964). 8. K. Modritzer, Chem. Ber. 92, 2637 (1959).
Arsenic and antimony trisdithiocarbamates
¢q
O~
O~ ¢'4
0
745
O~ ¢',1
¢',1
~o o~
0
@
.~.
6-
@
I'-
O~
Z~
t'---
I"O~
N oo
<
f_
¢q
I"--
I~
¢-q
¢',1
I t'q ¢'4 eq
¢q t"q
I t"-
¢,q
cq
O~
O~ ,et
i
I
I
I
¢ q ¢.q
746
G . E . MANOUSSAKIS and C. A. TSIPIS
N~ S-.~_~ C ~ S
+
M--NR
z
R~N (a)
Fig. 1.
/s\ M
/
e
/s
C --N
s//
%
M
\R
s\
M
+ /R
/ SN~N'xC---N
C--N
M
\ R
--I
~ \ s"?"
(c)
M-As
\R (b)
/R
x, s / /
R
C--N
3" \s /
(o)
/
/
\R (d)
or Sb,R=CHzCH(CH3] z or CHzCeHsand RR=C
Fig. 2.
The electron donating capacity of the -NRe group in dithiocarbamates affects the electronic structure of the complexes and it appears to play an important role in the preference of one form over the others. Since increasing the electron releasing ability of -NR2 group forces more electron density on to the sulfur atom, via the ¢r system and, therefore, to the ion of As or Sb, it causes greater double bond character in O , N bond. This and, therefore, the contribution to one of the resonance forms (Fig. 2) is reflected in the shifting of v(C-N) to higher frequencies. The frequencies of relevant i.r. bands are listed in Table 2. All of the compounds show a set of bands in the region of 1400-1500 cm -1 which falls between the streching frequencies of C - N single bonds (1250-1350cm -1) and C - N double bonds (1640-1690 cm -1) and can be assigned to v(C=N). These frequencies are a characteristic feature of the dithiocarbamates and they seem to be sensitive to the substituents of As and Sb atoms. A shift to the higher frequency positions is expected to correspond to the electron releasing ability of the -NR2 group, but the observed shifts do not follow this order. This irregular behaviour may be due to a hinderence effect, since it is known that the frequency of absorption is influenced by the stereochemistry of the complex [9]. The bands observed around 1000 cm -1 have been associated with v(CS2)[10]. It is clear from Table 2 9. F.A. Cotton and T. T. Mague, lnorg. Chem. 3, 1402 (1964). 10. M. Honda, M. Komura, Y. Kawasaki, T. Tanaka and R. Okawara, J. inorg, nucl. Chem. 30, 3221 (1968).
Arsenic and antimony trisdithiocarbamates
747
Table 2. Infrared frequencies of dithiocarbamates of arsenic and antimony and their assignments (cm -1) , S
S
H Compound
II
v(C=N) stretch
v(N-C-S)
v(C=S)
v(-C-S)
1473 vs* 1449 vs
1186 s* 1166 s
1035 m* 1002 s 948 vs
916 m 830 m
1493 vs 1480 vs 1448 vs
1135 s l120s
1028w* 978 s 950m
893 s
1478 vs 1412 vs
1143 vs 1090vs
982 s
III
909s 875m 856m
1467 vs 1417 vs
1145 s 1078 s
968 s
IV
929m 878m
V
1460vs 1442 vs
l180m 1160 s
1035 w 996s 943 s
912m 827m
VI
1485 vs 1455 vs
1134 s 1115 s
1023m 974 s 950m
1485 vs 1428 vs
l152vs 1093 s
981s
VII
912m 880 m
1483 vs 1436 vs
1158 s 1083 s
995 s 942 m
888 m
VIII
I
II
889 s
*vs = very strong, s = strong, m = medium, w = weak.
the increased double bond character of C'-"N bond is associated with decreased double bond character of C---S bond. The u.v. spectral data for the dithiocarbamates are collected in Table 3. The intense band around 39 kK (Band I) for all the compounds is assigned to an "intramolecular charge transfer" according to model d (Fig. 2). This is in agreement with results for zinc diethyldithiocarbamate [l l]. J6rgensen[12] also attributes these bands to the inter-ligand ~'--->Tr*transition located mainly in the CS2 group. This theory is supported by other authors [13, 14]. As is shown from Table 3 (Band I) the position of these bands depends on the basic character of the -NR2 group. As the basic character of amine is increased a slight shift to higher frequencies is observed. This phenomenom reflects the polar character of the 11. 12. 13. 14.
H. P. Koch, J. chem. Soc. 401 (1949). C. K. JiSrgensen, J. inorg, nucl. Chem. 24, 1571 (1962). G. Nikolov, N. Jordanov and 1. Havezov, J. inorg. Chem. 33, 1059 ( 1971 ). M. L. Shankaranarayana and C. C. Patel, A cta chem. scand. 19, 113 (1965).
748
G . E . M A N O U S S A K I S and C. A. TS1PIS Table 3. Electronic spectral data for trisdithiocarbamates of arsenic and antimony Band II
Band I
Band III
Compound Vmax(kK) lOgemol Umax(kK) log emol Vmax(kK) log emot I
39.6
4.76
32"5 sh*
4.20
28.3 sh
3.43
II
39"0
4.77
32.2 sh
4-22
28.2 sh
3.41
III
38"9
4.78
32.2 sh
4.23
27.8 sh
3.34
IV
38"6
4.75
31.8 sh
4.24
27.5 sh
3.34
V
39.1
4.83
32"0 sh
4.15
27.5 sh
3"53
VI
38"5
4.84
31.8 sh
4.18
27.4 sh
3.53
VII
38"6
4.84
31.7 sh
4.19
27.4 sh
3"48
VIII
38"2
4.93
31"4 sh
4.25
27.2 sh
3-59
*sh = shoulder.
C=N bond. The u.v. data leads to the following spectrochemical series (concerning the amines of dithiocarbamates) pyrrolidine > piperidine = diisobutylamine > dibenzylamine. The spectra of Sb compounds are very similar to those of the corresponding As compounds. Bands I, II and III appear to undergo only a small shift to lower energies. The weak band in the 28 kK region is believed to arise from a charge transfer from zr orbitals on the central atom [15]. The signals of proton N M R spectra (Table 4) of the trisdithiocarbamates appeared to be shifting considerably to lower field in comparison to the signals of the corresponding protons of free amines. This shift may be due to partial
I_..
:,
Fig. 3. 15. G. Vigee and J. Selbin, J. inorg, nucl. Chem. 31, 3187 (1969).
N
Arsenic and antimony trisdithiocarbamates
749
Table 4. Proton NMR spectra of trisdithioearbamates of arsenic and antimony and corresponding free amines Amines of dithiocarbamates
Protons
,(ppm) in free amine
r(ppm) r(ppm) in arsenic in antimony compounds compounds
(a) (b) CHz--CH2 HN~ ~
(a) (b) >NH
7.14 (mu)* 8.34 (mu) 7'92 (s)*
6.12 (mu) 7.90 (mu)
6.12 (mu) 7-92 (mu)
(a) (b, c) >NH
7'23 (su)* 8.50 (s) 8"35 (s)
5.86 (su) 8.24 (s)
5.88 (su) 8.27 (s)
(a) (b) (c)
7.55 (d)* 8" 16 (m) 9-06 (d)
6.27 (d) 7.63 (m) 9.06 (d)
6.29 (d) 7.66 (m) 9.06 (d)
4"78 (s) 2.63 (s)
4"87 (s) 2.62 (s)
CHz-- H2 (a) (b) CH2--CH2 HN
/
\ (c) CHz
\
/
CH2--CH2 (a) (b) (c) CH2--CH(CH3)z / HN \
>NH
8.40 (s)
(a) (b) >NH
6.24 (s) 2.70 (su) 8-34 (s)
CH~--CH(CHa)2 (a) (b) CH2C6H~ HN
/
\ CH2CaH5
s = singlet, d = doublet, m = multiplet and u = unresolved.
deshielding of protons and should be more pronounced in the case of a bidentate dithiocarbamate ligand, because in bidentate coordination the electron drift of the nitrogen w-electrons on to the carbon atom is greater and, therefore, the deshielding of protons should be greater than in unidentate dithiocarbamate. This is in agreement with the suggestion of Nikolov et al. [16]. Only one sharp signal from the aromatic protons of the benzyl group is observed in the N M R spectrum of tris (dibenzyldithiocarbamate) arsine and stibine. This suggests that the two benzyl groups are almost equivalent. Generally we can assume that the dithiocarbamates in complexes with As and Sb act as bidentate ligands. However the no clear splitting of the C=S vibration in the i.r. spectra of some of the trisdithiocarbamates indicates the existence of non-equivalent dithiocarbamate bonding [17]. On the other hand the absence of the characteristic bands at 970-980, 10601065 and 1260-1265 cm -1 in the spectra of these compounds suggests there is little possibility of the presence of unidentate dithiocarbamato ligands [ 18, 19]. 16. 17. 18. 19.
G. Nikolov, N. Jordanov and J. Havezov, J. inorg, nucl. Chem. 33, 1055 (1971). F. Bonati and R, Ugo, Jnl organomet. Chem. 10, 257 (1967). M, L. Shankaranarayana and C. C. Patel, Spectrochim. Acta 21, 95 (1965). A. Domenicano, A. Vaciago, L. Zamboneli, P. L. Loader and L. M. Venanzi, Chem. Comm. 476 (1966).
750
G. E. M A N O U S S A K I S and C. A. TSIP1S
The absence of similar bands has been used by some authors to rule out unidentate dithiocarbamato ligands[1]. In addition, the increased double bond character of the C " N bond and decreased double bond character of the C=S bond (Table 2), is further evidence for the presence of bidentate dithiocarbamates. The presence of only a weak band in the u.v. spectra around 32 kK, does not support the presence of a pure bidentate ligand. From the above results and those in literature, especially from X-ray investigations [19, 21], it is concluded that in trisdithiocarbamates of arsenic and antimony one of the As-S or Sb-S bonds in each ligand is practically covalent and the other one is more ionic. The formal coordination number suggests octahedral coordination, but the presence of the stereochemically active lone pair of electrons of As and Sb leads to a distorted octahedral stereochemistry. This lone pair of electrons seems to be responsible for the difference in the ionic character of As-S bonds of one of the ligands and, therefore, the splitting of the i.r. bands and the existence of a weak absorption band at 32 kK. The molecular weight determinations indicate that the complexes are monomeric. 20. M. Colapietro, A. Domenicano, L. Scaramuzza and A. Vaciago, Chem. Comm. 302 (1968). 21. G. Gottardi, Z. Krist. 115, 451 (1961).
Pergamon Press.
Printed in Great Britain
PREPARATION AND STUDY OF SOME ARSENIC AND ANTIMONY TRISDITHIOCARBAMATES G. E. M A N O U S S A K I S and C. A. TSIPIS Laboratory of Inorganic Chemistry, University of Thessaloniki, Greece
(Received29 March 1972) Abstract-Trisdithiocarbarnates of arsenic and antimony with pyrrolidine, piperidine, diisobutylamine and dibenzylamine have been prepared by directly mixing either AsCIa or SbCI3 with CS2 and the corresponding amine. A reasonable mechanism is proposed. The frequencies of bands in the electronic spectra depend on the electron releasing ability of amine groups and probably on steric hinderence effects. Interpretation of the spectroscopic results indicates a distorted octahedral stereochemistry. The distortion is attributed to the stereochemically active lone pair of electrons on the arsenic and antimony atoms.
INTRODUCTION
MANY papers on dithiocarbamate complexes of group V elements have been
published [ 1]. However, little attention has been paid to the influence of amine groups of dithiocarbamates on the C - N and C-S bonds and consequently on the electronic structure of these complexes. The type of amine group (-NR2) plays an important role in the behaviour of dithiocarbamates (dtc) as ligands. This paper deals with the preparation and study of eight trisdithiocarbamate (tdtc) complexes of arsenic and antimony, namely: As[SC(S)NC4Hs]3, tripyrrolidyl dithiocarbamate-arsine, (I), As[SC(S)NC~Hlo]3, tripiperidyldithiocarbamatearsine, (II), As[SC(S)N(C4H9)2]3, tris (diisobutyldithiocarbamate) arsine, (III), As[SC(S)N(CH2CoHs)z]a, tris (dibenzyldithiocarbamate) arsine, (IV), Sb[SC(S)NC4Hs]3, tripyrrolidyldithiocarbamate-stibine, (V), Sb[SC(S)NCsHlda, tripiperidyldithiocarbamate-stibine, (VI), Sb[SC(S)N(C4Hg)z]3, tris(diisobutyldithiocarbamate) stibine, (VII) and Sb[SC(S)N(CH2CoH~)2]a, tris(dibenzyldithiocarbamate) stibine, (VIII). The amines were selected according to their electron releasing ability, EXPERIMENTAL
Measurements The i.r. spectra, for Nujol mulls and chloroform solution, were recorded on a Beckman-IR 5A spectrophotometer. Proton N M R spectra were recorded on a Varian A60 A(60 Mc/sec) instrument in CDCI3 solution, using TMS as internal standard. The u.v. spectra were recorded on a Zeiss PMQ il spectrophotometer, with freshly prepared CHCI3 solutions. Molecular weights were determined using a Perkin-Elmer Molecular weight apparatus Model 115.
Preparation Analytical grade reagents were used without further purification. The preparations of tris(dithiocarbamate) arsines or stibines were done according to the following methods. In a three-necked flask equiped with a refluxed condenser, a mechanical stirrer and a dropper funnel, arsenic or antimony trichloride (= 20 m-mole) was mixed with carbon disulfide (--- 60 m-mole). 1. S. Lippard, Progress in Inorganic chemistry, Vol. 11, p. 252. John Wiley, London (1970). 743
744
G . E . M A N O U S S A K I S and C. A. TSIPIS
Carbon tetrachloride (= 150 ml) was used as solvent. To this mixture a.s61ution of amine (= 120 mmole) in 50 ml carbon tetrachlodde was added dropwise. The mixture" was refluxed with stirring for four hours and after cooling it was filtered. The precipitate, in the case of the diisobutyl- and dibenzyl-compounds, which are soluble in CC14, consisted of amine hydrochloddes. These were identified by comparison of their properties with those of authentic samples. The filtrate was concentrated and after the addition of methanol or petroleum ether trisdithiocarbamates were obtained. The products were recrystallized from a mixture of benzene and methanol. The insoluble pyrrolidyl- and pipeddyl- compounds precipitated with the amine hydrochlorides. The precipitate was dissolved in a small quantity of chloroform and reprecipitated by addition of carbon tetrachloride. The precipitate, after filtration, was treated with distilled water. The mixture was filtered again. The filtrate was concentrated and upon cooling gave amine hydrochlorides. The precipitates were washed thoroughly with distilled water to remove chlorides and recrystallized from a mixture of CCI4 and CHCIa and dried at 110°C. The recrystallized products were white to yellowish crystals. Analytical results are shown in Table 1. RESULTS AND DISCUSSION
Products IV, V, VI, VII and VIII are new compounds. The previously known compounds [2, 3], have now been prepared by this simpler method which is similar to the previously described [4, 5] direct reaction of metal chlorides, amines and CS2, instead of one of the usual methods of preparation of dithiocarbamate complexes either by reaction of sodium dithiocarbamate and metal chloride [6], or by an insertion reaction between the corresponding aminoderivative of metal and C S 2 [7]. There is evidence, even in the simultaneous mixing of metal chlorides, amine and carbon disulfide, that the corresponding aminoderivatives are produced and then an insertion reaction takes place. For example, the corresponding aminoderivatives of trisamino-stibine or arsine are produced first according to this general reaction MC13 + 6R2NH --~ M(NR2)3 + 3R2NH.HCI.
(1)
This is supported by the fact that reaction (1) is extremely exothermic, it usually takes place at very low temperature, - 8 0 ° C [8]. Consequently we can consider that the carbon of CS2 undergoes nucleophilic attack by the trisamino-arsine or -stibine product forming the aminoderivative (a), Fig. 1. Repetition of the sequence on the monodithio derivative (a) gives finally tris(dithiocarbamate) arsine or stibine. It is generally known that the dithiocarbamates can react as ligands according to the resonance forms of Fig. 2. In form (a), dithiocarbamate reacts as a unidentate ligand and in forms (b), (c) and (d) as a bidentate ligand. In the last cases one of the sulfur atoms behaves as an electron donor to the metal ion, so that a second bond, which is a coordination bond, is created between the As or Sb ion and the ligand. 2. L. Bourgois and J. Bolle, Mere. Services chim. Etat 34, 411 (1948); Chem. Abstr. 44, 5814 d (1950). 3. L. Malatesta, Gazz. chim. Ital. 69, 629 (1939). 4. G. Manoussalds and P. Karayannidis, J. inorg, nucl. Chem. 31, 2978 (1969). 5. G. Manoussakis and P. Karayannidis, lnorg, nucl. Chem. Lett. 6, 71 (1970). 6. G. Thorn and R. Lusdwig, The Dithiocarbamates andRelated Compounds. Elsevier, Amsterdam (1962). 7. G. Ortel, H. Malz and H. Holtschmidt, Chem. Bet. 97, 891 (1964). 8. K. Modritzer, Chem. Ber. 92, 2637 (1959).
Arsenic and antimony trisdithiocarbamates
¢q
O~
O~ ¢'4
0
745
O~ ¢',1
¢',1
~o o~
0
@
.~.
6-
@
I'-
O~
Z~
t'---
I"O~
N oo
<
f_
¢q
I"--
I~
¢-q
¢',1
I t'q ¢'4 eq
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¢,q
cq
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O~ ,et
i
I
I
I
¢ q ¢.q
746
G . E . MANOUSSAKIS and C. A. TSIPIS
N~ S-.~_~ C ~ S
+
M--NR
z
R~N (a)
Fig. 1.
/s\ M
/
e
/s
C --N
s//
%
M
\R
s\
M
+ /R
/ SN~N'xC---N
C--N
M
\ R
--I
~ \ s"?"
(c)
M-As
\R (b)
/R
x, s / /
R
C--N
3" \s /
(o)
/
/
\R (d)
or Sb,R=CHzCH(CH3] z or CHzCeHsand RR=C
Fig. 2.
The electron donating capacity of the -NRe group in dithiocarbamates affects the electronic structure of the complexes and it appears to play an important role in the preference of one form over the others. Since increasing the electron releasing ability of -NR2 group forces more electron density on to the sulfur atom, via the ¢r system and, therefore, to the ion of As or Sb, it causes greater double bond character in O , N bond. This and, therefore, the contribution to one of the resonance forms (Fig. 2) is reflected in the shifting of v(C-N) to higher frequencies. The frequencies of relevant i.r. bands are listed in Table 2. All of the compounds show a set of bands in the region of 1400-1500 cm -1 which falls between the streching frequencies of C - N single bonds (1250-1350cm -1) and C - N double bonds (1640-1690 cm -1) and can be assigned to v(C=N). These frequencies are a characteristic feature of the dithiocarbamates and they seem to be sensitive to the substituents of As and Sb atoms. A shift to the higher frequency positions is expected to correspond to the electron releasing ability of the -NR2 group, but the observed shifts do not follow this order. This irregular behaviour may be due to a hinderence effect, since it is known that the frequency of absorption is influenced by the stereochemistry of the complex [9]. The bands observed around 1000 cm -1 have been associated with v(CS2)[10]. It is clear from Table 2 9. F.A. Cotton and T. T. Mague, lnorg. Chem. 3, 1402 (1964). 10. M. Honda, M. Komura, Y. Kawasaki, T. Tanaka and R. Okawara, J. inorg, nucl. Chem. 30, 3221 (1968).
Arsenic and antimony trisdithiocarbamates
747
Table 2. Infrared frequencies of dithiocarbamates of arsenic and antimony and their assignments (cm -1) , S
S
H Compound
II
v(C=N) stretch
v(N-C-S)
v(C=S)
v(-C-S)
1473 vs* 1449 vs
1186 s* 1166 s
1035 m* 1002 s 948 vs
916 m 830 m
1493 vs 1480 vs 1448 vs
1135 s l120s
1028w* 978 s 950m
893 s
1478 vs 1412 vs
1143 vs 1090vs
982 s
III
909s 875m 856m
1467 vs 1417 vs
1145 s 1078 s
968 s
IV
929m 878m
V
1460vs 1442 vs
l180m 1160 s
1035 w 996s 943 s
912m 827m
VI
1485 vs 1455 vs
1134 s 1115 s
1023m 974 s 950m
1485 vs 1428 vs
l152vs 1093 s
981s
VII
912m 880 m
1483 vs 1436 vs
1158 s 1083 s
995 s 942 m
888 m
VIII
I
II
889 s
*vs = very strong, s = strong, m = medium, w = weak.
the increased double bond character of C'-"N bond is associated with decreased double bond character of C---S bond. The u.v. spectral data for the dithiocarbamates are collected in Table 3. The intense band around 39 kK (Band I) for all the compounds is assigned to an "intramolecular charge transfer" according to model d (Fig. 2). This is in agreement with results for zinc diethyldithiocarbamate [l l]. J6rgensen[12] also attributes these bands to the inter-ligand ~'--->Tr*transition located mainly in the CS2 group. This theory is supported by other authors [13, 14]. As is shown from Table 3 (Band I) the position of these bands depends on the basic character of the -NR2 group. As the basic character of amine is increased a slight shift to higher frequencies is observed. This phenomenom reflects the polar character of the 11. 12. 13. 14.
H. P. Koch, J. chem. Soc. 401 (1949). C. K. JiSrgensen, J. inorg, nucl. Chem. 24, 1571 (1962). G. Nikolov, N. Jordanov and 1. Havezov, J. inorg. Chem. 33, 1059 ( 1971 ). M. L. Shankaranarayana and C. C. Patel, A cta chem. scand. 19, 113 (1965).
748
G . E . M A N O U S S A K I S and C. A. TS1PIS Table 3. Electronic spectral data for trisdithiocarbamates of arsenic and antimony Band II
Band I
Band III
Compound Vmax(kK) lOgemol Umax(kK) log emol Vmax(kK) log emot I
39.6
4.76
32"5 sh*
4.20
28.3 sh
3.43
II
39"0
4.77
32.2 sh
4-22
28.2 sh
3.41
III
38"9
4.78
32.2 sh
4.23
27.8 sh
3.34
IV
38"6
4.75
31.8 sh
4.24
27.5 sh
3.34
V
39.1
4.83
32"0 sh
4.15
27.5 sh
3"53
VI
38"5
4.84
31.8 sh
4.18
27.4 sh
3.53
VII
38"6
4.84
31.7 sh
4.19
27.4 sh
3"48
VIII
38"2
4.93
31"4 sh
4.25
27.2 sh
3-59
*sh = shoulder.
C=N bond. The u.v. data leads to the following spectrochemical series (concerning the amines of dithiocarbamates) pyrrolidine > piperidine = diisobutylamine > dibenzylamine. The spectra of Sb compounds are very similar to those of the corresponding As compounds. Bands I, II and III appear to undergo only a small shift to lower energies. The weak band in the 28 kK region is believed to arise from a charge transfer from zr orbitals on the central atom [15]. The signals of proton N M R spectra (Table 4) of the trisdithiocarbamates appeared to be shifting considerably to lower field in comparison to the signals of the corresponding protons of free amines. This shift may be due to partial
I_..
:,
Fig. 3. 15. G. Vigee and J. Selbin, J. inorg, nucl. Chem. 31, 3187 (1969).
N
Arsenic and antimony trisdithiocarbamates
749
Table 4. Proton NMR spectra of trisdithioearbamates of arsenic and antimony and corresponding free amines Amines of dithiocarbamates
Protons
,(ppm) in free amine
r(ppm) r(ppm) in arsenic in antimony compounds compounds
(a) (b) CHz--CH2 HN~ ~
(a) (b) >NH
7.14 (mu)* 8.34 (mu) 7'92 (s)*
6.12 (mu) 7.90 (mu)
6.12 (mu) 7-92 (mu)
(a) (b, c) >NH
7'23 (su)* 8.50 (s) 8"35 (s)
5.86 (su) 8.24 (s)
5.88 (su) 8.27 (s)
(a) (b) (c)
7.55 (d)* 8" 16 (m) 9-06 (d)
6.27 (d) 7.63 (m) 9.06 (d)
6.29 (d) 7.66 (m) 9.06 (d)
4"78 (s) 2.63 (s)
4"87 (s) 2.62 (s)
CHz-- H2 (a) (b) CH2--CH2 HN
/
\ (c) CHz
\
/
CH2--CH2 (a) (b) (c) CH2--CH(CH3)z / HN \
>NH
8.40 (s)
(a) (b) >NH
6.24 (s) 2.70 (su) 8-34 (s)
CH~--CH(CHa)2 (a) (b) CH2C6H~ HN
/
\ CH2CaH5
s = singlet, d = doublet, m = multiplet and u = unresolved.
deshielding of protons and should be more pronounced in the case of a bidentate dithiocarbamate ligand, because in bidentate coordination the electron drift of the nitrogen w-electrons on to the carbon atom is greater and, therefore, the deshielding of protons should be greater than in unidentate dithiocarbamate. This is in agreement with the suggestion of Nikolov et al. [16]. Only one sharp signal from the aromatic protons of the benzyl group is observed in the N M R spectrum of tris (dibenzyldithiocarbamate) arsine and stibine. This suggests that the two benzyl groups are almost equivalent. Generally we can assume that the dithiocarbamates in complexes with As and Sb act as bidentate ligands. However the no clear splitting of the C=S vibration in the i.r. spectra of some of the trisdithiocarbamates indicates the existence of non-equivalent dithiocarbamate bonding [17]. On the other hand the absence of the characteristic bands at 970-980, 10601065 and 1260-1265 cm -1 in the spectra of these compounds suggests there is little possibility of the presence of unidentate dithiocarbamato ligands [ 18, 19]. 16. 17. 18. 19.
G. Nikolov, N. Jordanov and J. Havezov, J. inorg, nucl. Chem. 33, 1055 (1971). F. Bonati and R, Ugo, Jnl organomet. Chem. 10, 257 (1967). M, L. Shankaranarayana and C. C. Patel, Spectrochim. Acta 21, 95 (1965). A. Domenicano, A. Vaciago, L. Zamboneli, P. L. Loader and L. M. Venanzi, Chem. Comm. 476 (1966).
750
G. E. M A N O U S S A K I S and C. A. TSIP1S
The absence of similar bands has been used by some authors to rule out unidentate dithiocarbamato ligands[1]. In addition, the increased double bond character of the C " N bond and decreased double bond character of the C=S bond (Table 2), is further evidence for the presence of bidentate dithiocarbamates. The presence of only a weak band in the u.v. spectra around 32 kK, does not support the presence of a pure bidentate ligand. From the above results and those in literature, especially from X-ray investigations [19, 21], it is concluded that in trisdithiocarbamates of arsenic and antimony one of the As-S or Sb-S bonds in each ligand is practically covalent and the other one is more ionic. The formal coordination number suggests octahedral coordination, but the presence of the stereochemically active lone pair of electrons of As and Sb leads to a distorted octahedral stereochemistry. This lone pair of electrons seems to be responsible for the difference in the ionic character of As-S bonds of one of the ligands and, therefore, the splitting of the i.r. bands and the existence of a weak absorption band at 32 kK. The molecular weight determinations indicate that the complexes are monomeric. 20. M. Colapietro, A. Domenicano, L. Scaramuzza and A. Vaciago, Chem. Comm. 302 (1968). 21. G. Gottardi, Z. Krist. 115, 451 (1961).