Solid State 15N and 13C NMR Study of Several Metal 5,10,15,20-Tetraphenylporphyrin Complexes

The principal values of both the 13C and 15N chemical shift tensors are reported for the Zn, Ni, and Mg 5,10,15,20-tetraphenylporphyrin (TPP) complexes. The principal values of the 15N chemical shift tensors were obtained from static powder patterns of 15N-enriched samples. Due to overlap between the powder patterns of the different carbons, the 13C values were obtained using the recently developed magic angle turning (MAT) 2D experiment on unenriched materials. The measured principal values are presented along with theoretical calculations of the chemical shift tensors and a discussion of the effects that the metal bonding has on the chemical shift tensors in these compounds. Both the isotropic chemical shift and the principal values of the 15N chemical shift tensor are nearly identical for the Mg and Zn complexes. The 15N isotropic chemical shift for the NiTPP, however, changes by nearly 80 ppm relative to the Mg and Zn values, with large changes observed in each of the three principal values. Calculations show that the differences between the 15N 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 13C chemical shift tensor components as the metal is changed.