Polysulfide ligands bonding

Bicyclo(4.4.1 Jundecapentaene complexes with group VI B metals, 12 237 Bidentate ligands, reactions with tetracyano complexes containing oxo or nitrido ligands, 40 310-313 Bidentate oligopyridines, 30 72-73 Bidentate polysulfide complexes, bond lengths, 31 114... 

Molybdenum complexes of polysulfide ligands are reactive and, for example, readily make and break sulfur-carbon bonds, a property undoubtedly relevant to the involvement of Mo—S... 

Polysulfides of several metals can be prepared by reaction of the metals with excess sulfur in liquid NH3 (group IA metals) or by heating sulfur with the molten metal sulfide. The polysulfide ion binds to metals to form coordination compounds in which it is attached to the metal by both sulfur atoms (as a so-called bidentate ligand). One example is an unusual titanium complex containing the S52-ion that is produced by the following reaction (the use of h to denote the bonding mode of the cyclo-pentadienyl ion is explained in Chapter 16) ... 

Another factor in M-S bonding stability is the presence of S-S bonds. Calculations and fragmentary spectral studies indicate that the cr orbitals of S-S bonds are even lower in energy than those of S-H bonds (i.e., ct energies are lower in HjSj than in HjS). Thus disulfide ligands, and probably polysulfides in general, are better electron acceptors than sulfur itself. It is well known that transition metals form numerous compounds with polysulfides (Draganjac and Rauchfuss, 1985 Muller and Diemann, 1987). In many polysulfides (e.g., S/ ) there are also empty tt orbitals in addition to the empty ct orbitals, and these may also accept electron density from the metal. 

Acetylenes and ethene insert into the S—S bonds of metal polysulfides [M—S] to yield, with two exceptions (535 and 540), dithiolene and 1,2-ethanedithiolato ligands coordinated in a variety of bonding modes (Table VI). 

The poly sulfides are most stable in alkaline waters, and for 2S(aq) = 10 mol/kg they predominate over HS above pH 8 (Fig. 12.15). Polysulfide ions are soft ligands that can be expected to form strong complexes with soft or borderline soft metal cations however, stability data for such complexes are lacking. Organically bonded polysulfides are important constituents in the pore waters of modern sediments (Boulegue et al. 1982). 

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