Dithiocarbamato complexes

This simple explanation accounts quite well for a variety of dithiocarbamato complexes of iron(III) whose magnetic moments rise gradually from about 2.3 BM (corresponding to low-spin d ) at very low temperatures to > 4BM (corresponding to roughly equal populations in the two states) above room temperature. 

An interesting example is the iron(III) dimethyldithiocarbamato complex [181] [Fe((CH3)2NC(S)S)3] where the unit cell amounts to 44.4 per Fe atom or 26.7 cm mol This value is somewhat higher than the AF° values of Table 16. It should be noted, however, that the dithiocarbamato complex is of [Fe Sg] type, whereas the iron(III) complexes in Table 16 are examples of the type [Fe -N4.02]. As far as cobalt(II) is concerned, for the complex [Co(nnp)(NCS)2] where nnp = AT-[(diphenylphosphino)ethyl]-JV -diethylethyl-enediamine [182, 183], the volume change has been obtained as 21.5 per Co atom or 13.0cm mol S whereas for [Co(terpy)2]l2 2H20 [132] where terpy = 2,2, 2"-terpyridine, the corresponding results are 33.7 A per Co atom or 20.3 cm moP Again this value is higher than the AV° value for the closely related [Co(terpy)2]Cl2 complex of Table 16. 

Group VIII Transition Metal Dithiocarbamato Complexes.97... 

Infrared evidence supports the suggestion that the lone pair of the nitrogen atom in the dithiocarbamato complex becomes progressively more important for the donation of electrons the higher the oxidation state of the metal. 

In view of this, it is not surprising that dithiocarbamato compounds with copper in the oxidation state + 3 are stable instead it must be regarded as unexpected that Cu(I) dithiocarbamato complexes exist. The latter complexes are not simply monomeric, but they are tetrameric metal cluster compounds. Obviously, the stability must be attributed to the metal-metal bond rather than to the stabilising effect of the ligand. 

In all other dithiocarbamato complexes in which the metal has a low oxidation state the existence of this type of compounds is due to other, low-oxidation-number stabilising ligands e.g. NO" in (NO)2Fe(Et2C rc)2 and CO in (CO)4pe(Et2(ifc). 

In dithiocarbamato complexes such an ambiguity can only occur when at least two dithiocarbamato ligands are bonded to a metal. In that case the question arises whether the compound is a bis (dithiocarbamato) or a thiuram disulfide complex. In these two types of complexes the oxidation number of the metal differs 2 units. 

With a few exceptions, only the binary dithiocarbamato complexes of the transition metals and those of group lib are included, leaving it to the reader, to determine what has to be considered as usual or unusual. 

For a more complete survey of the dithiocarbamato chemistry up to 1969 the reader is referred to the reviews of Coucouvanis (2) and Eisenberg (2a). The investigations about the fluxionalityof the octahedral dithiocarbamato complexes are not covered in this article, as they were reviewed recently by Pignolet (3). 

V(IV) complexes with the formula V(R2C fc)4 (R = Me, Et) were studied by Bradley et al. 11,12, 4, 5). The ethyl complex (5) is thermally unstable and air-sensitive. The thermal instability accounts for the formation of the vanadium tris(dithio-carbamate). The tetrakis(dithiocarbamato) complex is isomorphous with 4)... 

All known Nb(V) dithiocarbamato complexes are prepared by the reaction of NbX5 and Na(Et2iitc), the nature and the number of products being dependent on the stoichiometry of the reacting species, the solvent, and the temperature 16,17). 

Interesting compounds are [Cr(R4rinfrared spectra indicate that these complexes are not Cr(V) dithiocarbamato complexes but rather Cr(III) compounds with coordinated thiuram disulfide. As will be shown, thiuram disulfide can oxidise Cu, Ag and Au to M(II) and M(III) dithiocarbamato complexes. The Cr(III)-thiuram disulfide combination seems to be stable, just like the thiuram disulfide combination with Zn, Cd, and Hg. 

The oxidation states + 4 and + 5 are known for tungsten in its dithiocarbamato complexes. 

Apart from the bis(dithiocarbamato) complexes a tris(dithiocarbamato) complex of Mn(II), Mn[(CH2)46 tc]3, is known. Although isolation of this type of complex failed so far (45), electrochemical characterisation was possible (43). 

Binary rhenium dithiocarbamato complexes are prepared with the metal in the oxidation state -I- 3, + 4 and + 5. 

At present only one Re(IV) dithiocarbamato complex has been described, a paramagnetic octahedral compound Cl2Re(Et2C tc) (59). Obviously, the reported formula is in error. 

Of the oxidation states -f 2, + 3 and + 4, found for the metal in cobalt dithiocarbamato complexes, -H 3 is the most stable. 

In nickel dithiocarbamato complexes the metal can have the formal oxidation state + 2, +3 and +4. 

For palladium and platinum, dithiocarbamato complexes with the metal in the oxidation state of -H 2 and -i- 4 are known. 

Table 2. Types of copper dithiocarbamato complexes found so far ) ...

Attempts to oxidise silver dithiocarbamato complexes with halogens to compounds with the metal in higher oxidation states obviously failed. By addition of iodine to a solution of [Ag(Bu2 fc)]g in CHQ3, an insoluble product is formed with the composition rjA% S> X2dtc) 141). With other alkyl groups similar complexes are obtained. Investigations about the nature of this type of compounds are in progress. 

The common oxidation states for gold in the dithiocarbamato complexes are + 1 and + 3. Like for the silver compounds the oxidation state + 2 is observed in diluted liquid and solid solutions only. 

Au(JII) dithiocarbamato complexes exist, analogous to the copper compounds, in two types, ionic [Au(R2ionic species Br2 Au(R2C tc) in addition, Au(602 0)3 has been reported. 

In dithiocarbamato complexes of these elements the metal has, without exception, the oxidation state + 2, and the compounds are of the type M(R2C tc)2 only (2). 

The literature dealing with EPR studies of transition metal dithiocarbamato complexes is extensive. Interesting results were obtained about the interaction of copper compounds with various solvents 165,166,167,168) and about dimer formation of Cu(R2frozen solutions, 133,169) whereas extensive EPR studies about other transition metal dithiocarbamato complexes are reported as well 170,5,171, 37). As the measurements of the planar systems are most suitable for comparison with theoretical studies, we shall pay attention to the results of these investigations on Cu(II), Ag(II) and Au(II). 

In Table 4 typical values are given for the isomer shift (IS) and the quadrupole splitting (QS) of dithiocarbamato complexes with iron in various formal oxidation states. 

Many dithiocarbamato complexes have been studied with voltametric techniques. Comparison of data, however, is often difficult because different solvents and reference electrodes have been used. The solvent and the reference electrodes used in recent studies of Martin as. (43, 68, 162, acetone and an Ag/AgCl, 0.1 M LiCl electrode) and those in our work (34, 37, 56, 150,163, CH2CI2 and a saturated calomel electrode) give results sufficiently close to make a general discussion of the data possible. 

The dependency of 2 on oxidation and reduction of tris(dithiocarbamato) and bis(dithiocarbamato) complexes is illustrated in Fig. 10. The great stability of the andd compounds viz. Cr(R2 c)3 and Co(R2tiic)3 both to oxidation and reduction is remarkable. A similar trend is present in recently published data 191) of the bipy complexes M(bipy)3, M(bipy)3 and M(bipy)3. Maxima in redox stability are found for M = Fe(II), Cr(0) and V(— 1), respectively, which all have configuration. For the few bis(dithiocarbamato) complexes known, the stability of the Ni(II) complexes is greater than for the d Cu(II) complexes. 

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