A study of pyridyl nitrosyl iron(II) tetraphenyl 15N4-porphyrin. NO geometry and spin coupling to the pyrrole nitrogens

Spin coupling with pyrrole nitrogens and NO geometry in pyridyl-NO-Fe(II) tetraphenyl-15N4-porphyrin, examined with hyperfine sublevel correlation spectroscopy (HYSCORE), was studied because of renewed interest in diatomic molecule bound ferrous hemes, e.g. the physiologically important NO synthase. Dipolar coupling locates the effective electron spin position (0.109±0.008 nm from the ring center, 0.106±0.006 nm above the ring plane and projecting 37±2° from the nearest pyrrole nitrogen). The NO projection in an X-ray study of the 4-methyl piperidine complex is 38.6°. The negative pyrrole nitrogen spin densities induced by the NO obey a sinusoidal angular relationship.