Structural Characterization in Solution by NMR

The grid compounds described in this chapter exhibit limited solubility in most organic solvents but are sufficiently soluble in acetone-dg to record H NMR spectra and spectra in the majority of cases. In dmso-dg and acetonitrile-dj they decompose, releasing the free ligands. Evidence for the stability of the structures in acetone solutions, at least when the counter-anion has a low coordinating ability (PFfi-, BF,, trifiate, CIO4 ), is obtained from the spectra (a) The chemical shifts of 

Different behavior was found for the p-toluenesulfonate and chloride derivatives containing ligands derived from pyrimidine. This could be due to a competitive coordination of these anions against the heterocyclic ligands. For the chloride complexes, a clear resonance broadening is observed at room temperature. Considering the chemical shifts it must be accepted that the free ligand is the dominant species. 

For the Ag grids a slight broadening of the resonances is observed at low temperature, which can be attributed to a dynamic process, probably due to the marked tendency for decoordination of the silver complexes with N-donor ligands. 

A series ofcomplexes containing different counter-anions, BF4 , PFe , C1O4 and TfO, show very similar NMR chemical shifts, indicating that the cation-anion interactions are weak in solution. 

---