Antipyrine and pyridine n-oxide complexes of iron(II)

Iron(II) complexes of 1-phenyl-2,3-dimethyl-5-pyrazolone (antipyrine, Apy) and pyridine N-oxide (PyO), having the formulae [Fe(Apy)6](ClO4)2, Fe(Apy)2Cl2, Fe(Apy)2Br2, Fe(Apy)4I2, [Fe(PyO)3Cl3]2 . 2H2O, [Fe(PyO)Cl2 . 2H2O]2, [Fe(PyO)3Br2]2 and [Fe(PyO)6]I2 have been prepared and characterized. [Fe(Apy)6](ClO4)2 in nitrobenzene and [Fe(PyO)6]I2 in acetonitrile behave as 1:2 electrolytes; Fe(Apy)4I2 shows considerable dissociation while Fe(Apy)2Cl2 and Fe(Apy)2Br2 are non-electrolytes and monomeric in nitrobenzene. [Fe(PyO)3Cl2]2 . 2H2O and [Fe(PyO)3Br2]2 in nitrobenzene and [Fe(PyO)Cl2 . 2H2O]2 in acetonitrile behave as non-electrolytes. All the complexes are spin-free. The i.r. spectra show that the oxygens of the CO and NO groups are the donors in the Apy and PyO complexes. A large decrease in the NO stretching frequency in [Fe(PyO)Cl2. 2H2O]2 suggests PyO acts as a bridge forming a binuclear complex. The chloro and the bromo complexes of Apy have been assigned pseudo tetrahedral structures while the rest of the complexes have octahedral or near octahedral configurations around the iron(II) on the basis of the magnetic moments and the electronic transitions.