Indirect coupling to quadrupolar nuclei: observation of 1J(105Pd,31P) in one- and two-dimensional 31P CP/MAS spectra

High-resolution solid-state 31P cross-polarization magic angle spinning (CP/MAS) spectra of a series of Pd(II) complexes were obtained. All of these spectra exhibit low-intensity satellite peaks flanking the main resonances which are assigned to originate from a combination of direct (D) and indirect (J) spin-spin coupling between the 31P and the 105Pd spins. The parameter 1J(105Pd,31P) is found to be sensitive to the nature of the ligand in a trans position and thus of great value in assigning the configuration, i.e. cis or trans, in square-planar complexes of Pd(II). A linear relationship between 1J(105Pd,31P) and 1J(195Pt,31P) in analogous Pd(II) and Pt(II) complexes is suggested, the latter parameter being a factor of ca 14 larger. Two-dimensional exchange spectroscopy proved valuable in resolving overlapping resonances and relating pairs of inequivalent 31P spins within the same complex and spreading their satellite manifolds into two dimensions. These two spectral features are unrelated, being due to dipolar coupling among the phosphorus spins in the former and finite lifetimes of the spin states of the 105Pd isotope in the latter case.