SOLID-STATE N-15 AND C-13 NMR-STUDY OF SEVERAL METAL 5,10,15,20-TETRAPHENYLPORPHYRIN COMPLEXES

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.