Nuclear magnetic resonance spectra of some β-diketone complexes of group III and IV elements

Abstract

The chemical shifts of the CH and CH₃ protons in the nuclear magnetic resonance spectra of many neutral β-diketone complexes are shown to be sensitive to the electrical symmetry of the molecule. The effects are ascribed largely to intramolecular linear electric-field shifts and can be calculated from the dipole moment of the molecule. The signs of the shifts can be used in discussing the structure of the complexes; they confirm the cis configuration for titanium(IV), germanium(IV), and tin(IV) complexes of the type M(acac)₂Cl₂, and the existence of two C-bonded (acac) ligands in [Pt(acac)₃]^–. The large low-field shift of CH recently observed in [Si(acac)₃]⁺ is also ascribed to both first- and second-order electric-field shifts rather than to any marked benzenoid resonance in the β-diketone ring.