Structure, Bonding, and Spectroscopy

In contrast to the CO molecule, the CS and CSe molecules are not stable. Carbon monosulfide polymerizes, sometimes explosively, above 113 K. However, both CS and CSe form complexes in which they show themselves as stable ligands (Table 2.30). 

It is assumed that in (diphos)2(CO) WCSW(CO)s there is a thiocarbonyl group bonded to tungsten atoms through the carbon and sulfur atoms W —C —S —W. 

In contrast to the carbonyl group, this is possible because ligands containing sulfur as a donor atom are soft bases and may form quite stable bonds with soft acids, in this case with the tungsten atom. Such bridges also occur in [(diphos)2(CO) WCSAgSCW(CO)(diphos)2] BF4. 

The vibrational v(CSe) bands occur in the 1060-1140 cmrange and are very intense. The free CSe molecule has a v(CSe) frequency of 1036 cmwhich has been obtained by extrapolation from the electronic spectrum of CSe. The C NMR chemical shifts for metal thiocarbonyl complexes are large. The C NMR signals for CS groups occur in the range 310-340 ppm C NMR signals for carbene complexes also occur in the same range. 

The mass spectra of thiocarbonyl complexes resemble those of carbonyl complexes the fragmentation patterns are similar. 

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Interest continues to be shown in acyclic phosphazenes (phosphazo derivatives, phosphine imines, phosphoranimines). Reviews include a comprehensive survey of the chemistry (synthesis, structure, bonding and spectroscopy) of transition metal complexes of phosphoranimines, a survey of recent uses of Ph2P(=NSiMe3)NSiMej as a precursor to transition metal... 

In the previous chapter, we saw that molecular geometry was a consequence of the tradeoff between electronic effects (the electron-electron repulsions that result from the Pauli principle) and steric effects (the nuclear-nuclear repulsions between the ligands on the central atom). In this chapter, we are concerned with the determination of molecular symmetry. While molecular geometry is concerned with the shapes of molecules, molecular symmetry has to do with the spatial relationships between atoms in molecules. As we shall see, it is the three-dimensional shape of a molecule that dictates its molecular symmetry and we can use a mathematical description of symmetry properties, known as group theory, to describe the structure, bonding, and spectroscopy of molecules. 

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