Abstract
Possibilities and limitations of iterative lineshape fitting procedures of MAS NMR spectra of isolated homonuclear spin pairs, aiming at determination of magnitudes and orientations of the various interaction tensors, are explored. Requirements regarding experimental MAS NMR spectra as well as simulation and fitting procedures are discussed. Our examples chosen are the isolated31P spin pairs in solid Na4P2O7· 10H2O, (1), and Cd(NO3)2· 2PPh3, (2). In both cases the two31P chemical shielding tensors in the molecular unit are related byC2symmetry, and determination of the orientations of these two tensors in the molecular frame is possible. In addition, aspects of homonuclearJcoupling will be addressed. For 1, both magnitude and sign of2Jiso(31P,31P) (Jiso= −19.5 ± 2.5 Hz) are obtained; for 2, (Jiso= +139 ± 3 Hz) anisotropy ofJwith an orientation of theJ-coupling tensor collinear, or nearly collinear, with the dipolar coupling tensor can be excluded, while absence or presence of anisotropy ofJwith any other relative orientation of theJ-coupling tensor cannot be determined.
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