Coordinated Sulfur and Selenium

It is very rare to find a six-membered chelate ring which is purely inorganic, but such is the case with the [Pt(Ss)3] anion. It is difficult to decide what process involving these inorganic rings (19) is responsible for 

A whole-molecule contortion involving a pseudo-eight-coordinate platinum(IV) transition state is suggested/ Novel fluxional rearrangements have been probed by nmr for new binuclear complexes of the type 

AG = 58.6 kJ mor applies to a process involving 60° pivoting of the cyclic ligand with respect to the platinum-sulfur bonds, which averages CH2 and CH3 environments. At higher temperatures scrambling by ligand dissociation and recombination is possible. 

This type of investigation has recently been extended to chromium and tungsten carbonyl derivatives of sulfur and selenium ligands of this class. °  

Complex Formation Involving Unsubstituted Metal Ions Unidentate Ligands and Solvent Exchange 

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One of the major differences between two-coordinated sulfur and selenium is the tendency of the latter to increase its coordination number, as can be seen from the fairly strong intermolecular interactions between selenium rings in the various crystal structures. The shortest intermolecular distance observed (335 pm in y-Se8) is 65 pm shorter than the van der Waals distance (400 pm) but still 101 pm longer than the single bond distance defined above. In the case of sulfur rings the shortest observed intermolecular contact (323 pm in Si0 (88) is 37 pm shorter than the van der Waals distance (360 pm) but 101 pm longer than the single bond in S8. 

Fig. 2. The unit cell contents of Se Si2 n as completed to show full molecules (c horizontal, b vertical). Atomic coordinates are according to Weiss and Bachtler f Of the four independent atomic sites two (2 and 4) are occupied by sulfur only while the other two (1 and 3) are occupied by both sulfur and selenium. The occupation factor of selenium in these sites is 25 %...

Sulfur and selenium dichlorides coordinate through the chalcogen atom to form complexes of the type [PdCl2(ECl2)2] (E = S, Se) and these have a trans square planar structure.15 Sulfur... 

Thia-6-selenaspiro[3,3]heptane with Cu(hfac)2 provided a new coordination product, [Cu(hfac)2]32SeSC5H8. This complex statistically mixes positions of the donor sulfur and selenium atoms to give an average axial Cu- S/Se contact at 2.892A <2005IC77>. The following complexes were synthesized [W(CO)5L ], [ W(CO)s 2L1],... 

The six-membered ring has a chairlike conformation and the Se—Se bond lengths vary between 229.2 and 237.0 pm. The longest bonds are those originating from the three-coordinated atoms, as has been observed for a number of related sulfur and selenium compounds, e.g., Se102+, S7I+, or S80. 

The first stereoselective selenenylation reactions were reported using the binaphthyl-based diselenide 16 as the reagent precursor.71-76 After that, several other diselenides have been prepared initial attempts used quite long syntheses to obtain these compounds, for example, the C2 symmetrical diselenides 1777-79 and 2380 and the mannose-derived diselenide 18.81-84 The ferrocenyl-based diselenide 1985-89 is using expensive starting materials and in 1995 more simple and easy accessible diselenides like 20 and 21 have been described in literature.90-93 Camphor-based diselenides such as 2294-98 have been prepared and, based on the success of diselenides 20 and 21, structural variants 2499,100 and diselenides with different coordinating heteroatoms such as sulfur and selenium 25101-108 and 26109 have been described recently. 

S). Similar compounds with bis(diphenylphoBphino)methane disulfide and the corresponding diselenide have also been prepared (Table X). These are the first examples of coordination of sulfur and selenium donors to actinide pentahalides and it will be interesting to see whether uranium pentahalides behave in a similar fashion since the analogous niobium(V) and tantalum(V) compounds are also known (43). 

This volume has been divided (arbitrarily) into seven chapters. Chapter 1 contains some interesting syntheses of sulfur- and selenium-containing coordination compounds and clusters including the synthesis of the [Fe4S4(SR)4]2 species which R. H. Holm so elegantly identified as models for active sites in nonheme iron proteins. Compounds formed from S22 and S52 are described. A convenient synthesis of CSe2 is reported. Several additional compounds relevant to biological sulfur chemistry are described. 

A review of the complexes of sulfur and tellurium in 1964 was followed by an extensive survey of the heavy chalcogen complexes in a comprehensive text on the chemistry of selenium, tellurium and polonium in 1966. The subject of coordination in organoselenium and organotellurium chemistry, together with the structural chemistry of complexes of selenium and tellurium with sulfur- and selenium-containing ligands, has received recent attention in... 

Treatment of uranium metal with PhEEPh (E=S, Se) in the presence of a catalytic amount of iodine in pyridine affords the monomeric, seven-coordinate U(IV) chalcogenolates, [U(EPh)4(py)3], which do not require stabilizing ancillary ligands [107]. Crystallographic characterization of the sulfur derivative showed a distorted pentagonal bipyramidal uranium center, an average U-S distance of 2.734(3) A, and an average U-N distance of 2.597(9) A. Spectroscopic comparison of the sulfur and selenium com-... 

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