Dithiocarbamato

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. 

In Aceton/Tetrabutylammoniumperchlorat wird Bis-[dithiocarbamato]-ruthenium(III) an Platin (-0,5 V) zum Bis- dithiocarbamato]-ruthenium(II) reduziert4. Tris-[2,2 -bi-py-ridyl]-ruthenium(II) kann bei -1,42 Volt sclektiv zum entsprechenden Ruthenium(I)-, bei —1,65 zum Ruthenium(0)-Komplex reduziert werden5. 

Auf ahnliche Weise erhalt man aus Tris-[diathyl-dithiocarbamato]-nickel(IV) bei -0,4 V in Acetonitril/Tetraathylammoniumperchlorat das Bis-[diathyl-dithiocarbamato -nik-kel(II)6. 

Reaction with one mole of base produces the dithiocarbamato anion, L (XXIII). 

The simultaneous observation of the two EPR spectra has been reported in particular for several tris(dithiocarbamato)iron(III) complexes [Fe(R2NC(S)S)3] where R = cyclohexyl [143], hydroxyethyl [144], and n-butyl [145, 146]. In addition, a considerable number of iron(III) complexes of the type [Fe" -N402] has been found which show EPR spectra of both the HS and LS isomers. These comprise [Fe(X-SalEen)2] Y2 where X-SalEen is the Schiff-base ligand obtained by condensation of X-substituted salicylaldehyde and IV-ethylethylenediamine [147] and similar compounds [100, 148, 149, 150, 151]. For the cobalt(II) complex [Co(terpy)2] (004)2, it is not completely clear whether the two observed EPR spectra are due to HS and LS states related by a spin-state transformation [152]. 

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... 

Among the polyatomic ligands the dithiocarbamato ligand can stabilise high oxidation states of the transition metals in its complexes. like all 1,1-dithioates the a-donation and TT-back-donation of the sulfur atoms is assumed to be of the same order of magnitude. 

The special feature of the dithiocarbamato ligand is an additional 7r-electron flow from the nitrogen atom to the sulfur atoms via a planar delocalised rr-orbital system. The net effect is a strong electron donation, resulting in a high electron density on the metal. )... 

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). 

Titanium and zirconium dithiocarbamates are prepared with the metal in the oxidation state + 4, whereas the hafnium dithiocarbamato chemistry is unknown. 

The Zr(IV) dithiocarbamato chemistry is restricted to the complexes Zr(R2rfrc)4 until now 4,5). The properties of these compounds are similar to those of Ti(R2C rc)4. Although no X-ray studies are performed, it is likely that these compounds are iso-structural. 

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. 

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