Mercury, dithiocarbamate complexes

The electrochemistry of [Hg(S2CNR2)2] at mercury electrodes has been probed, with dithiocarbamate exchange occurring upon reduction (163, 607, 1891). Interestingly, two reversible one-electron oxidation processes are observed and this is believed to be associated with the oxidation of the mercury electrode producing cationic multinuclear mercury dithiocarbamate complexes... 

Shih and Carr [277,278] showed that metal complexes of bis(/ -butyl-2-naphthyl-methyldithiocarbamate) are thermodynamically stable and chemically inert and that the nickel(II), iron(III), copper(II) and mercury (II) complexes of this dithiocarbamate can be separated by high performance liquid chromatography and detected with a variable wavelength detector. 

Many dithiocarbamate complexes of zinc, silver, cadmium or mercury improve emulsion stability, including bis(dibenzyldithiocarbamato)-zinc(II) or -cadmium(II) and silver(I) diethyldi-thiocarbamate. Cadmium salts, mixed with citric acid or tartaric acid and added to the emulsion, are reported to be effective. Mercury(II) complexes of ethylenediaminetetraacetic acid (EDTA) and related ligands and of solubilized thiols such as (4) can be used. Other coordination compounds reported include EDTA and related ligand complexes of Co and Mn, mixtures of Co salts with penicillamine (5) and macrocyclic complexes of Ag such as (6). The latter compounds may be used in diffusion transfer systems in which transferred maximum densities are stabilized. 

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 ... 

Labuda, J. and Vanickova, M. (1988). Anodic stripping voltammetry with mercury electrodes in extracts of Cd, Pb, Tl and In diethyl-dithiocarbamate complexes and analysis of mixtures. Anal. Chim. Acta, 208, 219-230. 

The structural chemistry of some metal dithiocarbamates, i.e. systematics, coordination modes, crystal packing, and supramolecular self-assembly patterns of nickel, zinc, cadmium, mercury, organotin, and tellurium, complexes has been thoroughly analyzed and discussed in detail. Supramolecular self-assembly frequently occurs in non-transition heavier soft metal dithiocarbamates. Thus, lead(II), bismuth(III) zinc, cadmium, and (organo)mercury dithiocarbamates are associated through M- S secondary bonds, to form either dimeric supermolecules or chain-like supramolecular arrays. The arsenic(III) and antimony(III) dithiocarbamates are... 

The mechanism of 1 1 complex formation between palladium(II) and catechol and 4-methylcatechol has been studied in acidic media, and the rate of 1 1 (and 1 2) complex formation between silver(II) and several diols is an order of magnitude higher in basic solution than in acidic. The kinetics of formation and dissociation of the complex between cop-per(II) and cryptand (2,2,1) in aqueous DMSO have been measured and the dissociation rate constant, in particular, found to be strongly dependent upon water concentration. The kinetics of the formation of the zinc(II) and mercury(II) complexes of 2-methyl-2-(2-pyridyl)thiazolidine have been measured, as they have for the metal exchange reaction between Cu " and the nitrilotriacetate complexes of cobalt(II) and lead(II). Two pathways are observed for ligand transfer between Ni(II), Cu(II), Zn(II), Cd(II), Pb(II) and Hg(II) and their dithiocarbamate complexes in DMSO the first involves dissociation of the ligand from the complex followed by substitution at the metal ion, while the second involves direct electrophilic attack by the metal ion on the dithiocarbamate complex. As expected, the relative importance of the pathways depends on the stability of the complex and the lability and electrophilic character of the metal ion. 

It is not clear when dithiocarbamates were first prepared, but certainly they have been known for at least 150 years, since as early as 1850 Debus reported the synthesis of dithiocarbamic acids (1). The first synthesis of a transition metal dithiocarbamate complex is also unclear, however, in a seminal paper in 1907, Delepine (2) reported on the synthesis of a range of aliphatic dithiocarbamates and also the salts of di-iTo-butyldithiocarbamate with transition metals including chromium, molybdenum, iron, manganese, cobalt, nickel, copper, zinc, platinum, cadmium, mercury, silver, and gold. He also noted that while dithiocarbamate salts of the alkali and alkali earth elements were water soluble, those of the transition metals and also the p-block metals and lanthanides were precipitated from water, to give salts soluble in ether and chloroform, and even in some cases, in benzene and carbon disulfide. 

By using electrochemical methods, Bond and Schultz (606) also derived a considerable number of stability constants (P2) for mercury bis(dithiocarbamate) complexes in water (Eq. 48). They found no correlation between them and the Taft substituent constants for the dithiocarbamate substituents. There is, however, a linear correlation between log p2 and the molecular weight (Mw) of the complexes, which can be represented by the empirical equation log P2 = 29.95 + 0.03301... 

Bond and Scholz (606) calculated thermodynamic data for solid mercury bis(dithiocarbamate) complexes mechanically attached to the surface of a paraffin-impregnated graphite electrode. Two-electron reduction generates mercury and the soluble dithiocarbamate anions in a chemically reversible couple during the second and subsequent scans. The formal potential of the reaction has been measured, which enables the calculation of conventional stability constants (P2) for 17 mercury complexes, and a previously unrecognized correlation between log p2 and molecular weight is found (see Section III.G). 

In a very recent contribution, Lai and Tiekink (235) isolated the mercury-chloride complex [HgCl(ri -S2CNEt2)(l,10-phen )] (500) from the reaction of [Hg(S2CNEt2)2] and 1,10-phen, which is presumed to result from the loss of a dithiocarbamate and chloride abstraction from the chloroform solvent. An X-ray crystal structure shows that the dithiocarbamate binds in a monodentate fashion, allowing the mercury center to adopt a highly distorted tetrahedral coordination geometry. 

Figure 277. Examples of heterometallic mercury-molybdenum dithiocarbamate complexes...

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