Iterative lineshape fitting of MAS NMR spectra: A tool to investigate homonuclear J coupling in isolated spin pairs

Possibilities and limitations of iterative lineshape fitting procedures of MAS NhlR spectra of isolated homonuclear spin pairs, aiming at determinatio n of magnitudes and orientations of the various interaction tensors, are ex plored. Requirements regarding experimental MAS NMR spectra as well as simu lation and fitting procedures are discussed. Our examples chosen are the is olated P-31 spin pairs in solid Na4P2O7. 10H(2)O, (1), and Cd(NO3)(2). 2PPh (3), (2). In both cases the two P-31 chemical shielding tensors in the mole cular unit are related by C-2 symmetry, and determination of the orientatio ns of these two tensors in the molecular frame is possible. In addition, as pects of homonuclear J coupling will be addressed. For 1, both magnitude an d sign of (2)J(iso)(P-31, P-31) (J(iso) = -19.5 +/- 2.5 Hz) are obtained; f or 2, (J(iso) = +139 +/- 3 Hz) anisotropy of J with an orientation of the J -coupling tensor collinear, or nearly collinear, with the dipolar coupling tensor can be excluded, while absence or presence of anisotropy of J with a ny other relative orientation of the J-coupling tensor cannot be determined . (C) 1998 Academic Press.