M. Strohmeier et al., SOLID-STATE N-15 AND C-13 NMR-STUDY OF SEVERAL METAL 5,10,15,20-TETRAPHENYLPORPHYRIN COMPLEXES, Journal of the American Chemical Society, 119(30), 1997, pp. 7114-7120
The principal values of both the C-13 and N-15 chemical shift tensors
are reported for the Zn, Ni, and Mg 5,10,15,20-tetraphenylporphyrin (T
PP) complexes. The principal values of the N-15 chemical shift tensors
were obtained from static powder patterns of N-15-enriched samples. D
ue to overlap between the powder patterns of the different carbons, th
e C-13 values were obtained using the recently developed magic angle t
urning (MAT) 2D experiment on unenriched materials. The measured princ
ipal values are presented along with theoretical calculations of the c
hemical shift tensors and a discussion of the effects that the metal b
onding has on the chemical shift tensors in these compounds. Both the
isotropic chemical shift and the principal values of the N-15 chemical
shift tensor are nearly identical for the Mg and Zn complexes. The N-
15 isotropic chemical shift for the NiTPP, however, changes by nearly
80 ppm relative to the Mg and Zn values, with large changes observed i
n each of the three principal values. Calculations show that the diffe
rences between the N-15 chemical shifts are almost entirely determined
by the metal-nitrogen separation. In addition, both the experimental
data and the calculations show only very minor differences in the C-13
chemical shift tensor components as the metal is changed.