EPR AND ENDOR STUDY OF SELECTED PORPHYRIN-COPPER AND PHTHALOCYANINE-COPPER COMPLEXES

Electron paramagnetic resonance spectra and nitrogen ENDOR powder spectra have been obtained from copper complexes of tetraphenylporphyrin, meso-tetrakis(2-methylpyridinium-N-yl)porphyrin (ortho), meso-tetrakis(4-methylpyridinium-N-yl)porphyrin (para), and phthalocyanine at approximately 4 K. All four samples display axial symmetry. The three porphyrins have nearly identical g(x) and g(y) values (2.054, 2.055) but differ in their g, values (2.186, 2.209, 2.212). The copper phthalocyanine has axial components equal to 2.060 and a z component of 2.179. CuTPP has the largest axial component of the copper hyperfine tensor, 98.6 MHz compared with values from the other three samples of 80 MHz. The z component of the copper hyperfine tensor is closer in magnitude for CuTPP and copper phthalocyanine (631 and 637 MHz), while for the methylpyridyl species its value is 593 MHz (ortho) and 598 MHz (para). Through analysis of these data, the orientations of molecules contributing to each ENDOR spectrum are readily calculated. The magnitudes of the nitrogen hyperfine and quadrupolar tensors were determined through analysis of the angle-selected ENDOR spectra. The largest component of the nitrogen hyperfine tensor was found to lie along the Cu-N bond axis in each case.