Shifts in Specific Classes of Compound

Solvent dependent Cyclotristannane Naked cluster anion Naked cluster anion Naked cluster anion 

The sensitivity to quite minor conformational and configurational changes at sites relatively remote from the central atom (for example, in norbornyl compounds and the various cis and trans propenyl compounds precludes simple correlations 

The dominating effect here appears to be factors associated with the bulk and/or polarizability of the halogen, with iodides at lowest frequency, and the pattern in multiply substituted species indicating that effective electronegativity plays a relatively small part. This consideration applies also with other substituent atoms that have lone pairs (e.g., N, Se, etc.). 

Tin and lead do not display the same tendency to form this type of compound, but oxygen does tend to coordinate to already four-coordinate tin (and lead) with a concomitant substantial increase in metal-atom nuclear shielding. Thus tin NMR has been invaluable for the study of the autoassociation and complexation of many different tin compounds, the large differences in 5( Sn) permitting the relatively precise determination of thermodynamic parameters. For example, in n-BuSn(OR)3 (5( Sn) ranges from —322 at 20°C to —205 ppm at 135°C for R = 5ec-Bu as the tin 

Many polysilanes have been studied, and ( Si) has been correlated with a, / , and y effects and the extent of chain branching such effects have been used to deduce structures. Many di- and tri-tins have also been studied. The very low-frequency tin and lead chemical shifts in anionic metal-atom clusters could be due to massive diamagnetic circulation in an extended molecular-orbital system, and an extended molecular orbital interpretation can also be advanced to account for the extreme sensitivity of ( Sn) to changes in remote substituents in [(SnCl3) RhCl6 ] . Overall many Sn shifts in transition metal complexes have now been determined, but the distribution of values is such that detailed discussion is not appropriate at present. 

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