Oxidation states transition metal dithiocarbamates

In contrast to the transition elements, the main group element dithiocarbamates often have asymmetrical metal-sulfur bonds due to the lack of pn-dnMOs. In theses compounds the metal-sulfur interaction. High oxidation states for these dithiocarbamates are only found when high electron density is brought upon the metal by er-donating groups. For instance, (54) exists whereas (55) does not.73... 

Other extraction agents such as dithizone, diethyl dithiocarbamates, and 8-hydroxy-quinoline (oxine) are also useful as chelating agents and extract several metals including transition metals, alkali and alkaline metals. The dithizone can extract up to 20 elements and these complexes behave the same and there is no additional advantage of using one over the other. The compound 8-hydroxyquinoline will form stable complexes with Al, Ca, Sr and Mg at pH 8.0 these metals form unstable complexes with APDC. At carefully controlled pH the oxidation states of metals may also separated, e.g. Fe[II] and Fe[III], The stmcture of 8-hydroxyquinoline is ... 

Transition metal dithiocarbamate complexes were probably first prepared in 1907 by Delepine (2) and over the following century, dithiocarbamate complexes of all the transition elements have been prepared and in a wide range of different oxidation states (Table 1). Perhaps most impressive is their ability to stabilize molybdenum in seven oxidation states ranging from - -6 to 0 (Fig. 24). 

In many complexes, mixed oxidation states for the transition metals are found. Complex (41) is a diamagnetic compound with the actual composition (42).68 Copper dithiocarbamates are synthesized not only with copper in the oxidation states I, II or III but also with the metal in mixed oxidation states III and I (43, 44, 45), II and I (46, 47) and even III and I [48, 49).56 Complex (50), which has two isomeric structures a and / , has Ru either in a trapped oxidation state II,in or in a delocalized oxidation state of 2.5. The /J-isomer is the most stable.69 Slow, controlled potential electrochemical oxidation of (51) yields (52), in which the metal has a trapped oxidation state II,HI.70... 

The ligand field strength of the ligands is between that of the dithiocarbamates and water.49 IR studies show characteristic bands near 1250, 1100, 1020 and 550 cm-1.93 The contribution of the resonance form (85) in transition metal complexes is less than that of the analogous structure in the dithiocarbamates.60 The electron density on the metal is not very high, which accounts for the fact that abnormal high oxidation states are exceptional and a strong interaction of bases with the square planar nickel (and some other metal) xanthates is found.94... 

Dithiocarbamates can bind to between one and four transition metal atoms in a variety of different ways as illustrated in Fig. 27. By far, tbe most common of these is tbe simple chelating mode A. Here, the two metal sulfur interactions are approximately equal and the ligand can be considered as a net four-electron donor. (For electron-counting purposes it is often considered as a three-electron donor radical.) This mode of bonding is found for all the transition metals in all accessible oxidation states. 

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