Anion complexes nickel dithiocarbamates

Nickel(II) complexes with either bidentate mononegative ligands, such as dithiocarbamates, phosphorodithioates and thiocarboxylates, or monodentate neutral and anionic ligands are generally square planar. Nickel(II) complexes with Se and Te donors are strictly similar to those with S donors. 

Substituted dithioformate anions as ligands R C(S)S are usually called dithiocarbamates (R = R2N), alkyl and aryl dithiocarbonates or xanthates (R = RO), alkyl and aryl trithiocar-bonates or thioxanthates (R = RS). Dithioacid anions (R = alkyl, aryl) have been rarely used as ligands of nickel(II) because of their instability. Structural properties of selected nickel(II) complexes with substituted dithioformate, dithiolene and related ligands are shown in Table 90. 

Similarly, nickel(ll) and copper(ll) transition metal dithiocarbamate ion-pair receptors 21, containing amide-and crown ether-recognition sites, bind alkali metal cations and various anions. The sandwich K+ complex of the nickel(ll) receptor cooperatively enhanced the binding of acetate anion, while the copper(ll) receptor electrochemi-cally can sense anions and cations via perturbation of the copper(n)/copper(m) dithiocarbamate redox couple <2002JSU89>. 

The crystal structure of bis(NN-di-isobutyldithiocarbamato)nickel(ii). [Ni(S2-CNBu 2)2], shows that nickel is approximately square planar and co-ordinated by two symmetric bidentate ligands (Ni—S = 2.20 A) the ligand symmetry approximates to 2- The reduction mechanism of a series of nickel(ii) dithiocarbamates has been investigated in DMSO at the mercury electrode it is claimed to involve a dissociation to a nickel species which is more easily reduced than the nickel(ii) dithiocarbamate. An e.p.r. study of the reversible electrochemical reduction of nickel(ii) diethyldithio-carbamates in the presence of 2,2 -bipyridyl show that a bipy radical anion is formed initially. Ligand alkylation occurs when ao -dibromo-o-xylene is added to bis-(NiV-diethyldithiocarbamato)nickel(ii). The electron-transfer properties of 16 nickel(ii) dithiocarbamate complexes have been studied in acetone at a platinum electrode. Their oxidation is difficult and irreversible the overall process is ... 

Related to this, a crown-ether containing nickel(II) bis(dithiocarbamate) complex 353 has been prepared (1471). As a multisite system, it is capable of exhibiting cooperative complexation of anion-cation pairs. Thus, a sixfold enhancement of the stability constant for acetate results when potassium is cobound at the crown-ether moiety in 353. 

Figure 195. Examples of anionic nickel(II) mono(dithiocarbamate) complexes.

Recently, Beer et al. (62) prepared the novel nickel(IV) complex 371, in which two metal centers are linked via three bis(dithiocarbamate) ligands, upon oxidation of the related macrocyclic complex 370 by 7/-bromosuccinimide (NBS) (Fig. 197). The nickel(IV) dication 371 binds both chloride and nitrate anions as shown by cathodic shifts of the Ni(IV)/Ni(III) wave of 70 and 15 mV, respectively. 

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