Copper xanthate structures

The structure of the methylxanthate analogue, (Ph3P)2Cu(S2COMe), is also known and this essentially adopts the same structure as described above (127). The remaining copper xanthate structures are mixed-metal species. 

A wide range of structural motifs are found for the copper-triad xanthates, ranging from monomeric species to layer structures. This variety of structures can be ascribed to the flexible coordination modes adopted by the xanthate ligands in this group, in particular for the copper and silver xanthates. However, there is a dearth of binary xanthate structures with only two available for copper and one each for silver and gold. The paucity of data can be ascribed directly to the inability to obtain suitable crystals for structure determination. Phosphine adducts are known for all three elements of this group and in the case of both copper and silver, mixed-metal species are also known. 

Water soluble derivatives of cellulose have also been made through the formation of sodium cellulose xanthate (Cell-O-CS Na ) ( 12) and copper amine complexes (that is, the cuprammonlum process) ( X3). Both these derivatives require regeneration of the Insoluble cellulose structure at the time of membrane formation. Strong salt and acid solutions are used to precipitate the soluble derivatives and simultaneously recover the cellulose structure. Residues of xanthate or cuprammonlum salt decomposition must subsequently be washed out of the resulting membrane. 

Earlier structural studies of carbohydrates by CD involved introduction of suitable chromophores into the sugar molecule thereby affording derivatives which exibit Cotton effects. These include, among others, xanthates (4-8) or azides (9). Later it was found that some metal ions (10), i.e. copper (11,13), vanadate (14), chromium (15), molybdate (16-22), nickel (23) or cobalt (24,25) ions form complexes with carbohydrates, which show appreciable Cotton effects. 

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