Transition Metal Complexes of Vitamin B6 Related Compounds. 2. Synthesis and Properties of Several Iron(III) Complexes of Pyridoxylideneglycine and 5'-phosphopyridoxylideneglycine

Iron(III) complexes of pyridoxylideneglycine and 5'-phosphopyridoxylideneglycine have been prepared and their electronic and structureal properties investigated. The compounds are the essentially monomeric five-coordinate complexes, Fe(PLgly)(H ₂ O)X, where PLgly is the pyridoxylideneglycine Schiff-base dianion and X is Cl, Br, or OAc and Fe(PlPgly)(H ₂ O)(OAc), where PLPgly is 5'-phosphopyridoxylideneglycine. Infrared spectra indicate that PLgly and PLPgly are coordinated to iron(III) through their azomethine nitrogen, phenolic oxygen, and carbpxylic oxygen donor atoms. These spectra also indicate the presence of coordinated water. The complexes are predominantly high-spin with magnetic moments which decrease from ca. 5.8 µ _B at room temperature to ca. 5.40 µ _B at 120 K. This behavior is explained in terms of weak intermolecular anti-ferromagnetic coupling. Mössbauer effect spectral parameters for these compounds are consistent with five-coordinate iron(III) but do not eliminate the possibility of weak bonding at the sixth coordination site. The chemical isomer shifts are in the range of 0.40-0.50 mm/s (relative to natural αiron foil) and the quadrupole interactions are ca. 0.70 mm/s. The magnetically perturbed Mössbauer spectrum of Fe(PLgly)(H ₂ O)Cl obtained at 6 Tesla and 4.2 K indicates a large asymmetry parameter and an internal hyperfine field which is the same as the applied field. These compounds exhibit several intense charge-transfer and intraligand absorption bands and, as a result, only a single d-d band is observed at ca. 11000 cm ^-1 .