Electronic, magnetic, and structural characterization of the five-coordinate, high-spin iron(II) nitrato complex [Fe(TpivPP)(NO 3)]^-

The preparation and characterization of the five-coordinate iron(II) porphyrinate derivative [Fe(TpivPP)(NO3)]- (TpivPP = picket-fence porphyrin) is described. Structural and magnetic susceptibility data support a high-spin state (S = 2) assignment for this species. The anionic axial nitrate ligand is O-bound, through a single O atom, with an Fe-O bond length of 2.069(4) Å. The planar nitrate ligand bisects a N p-Fe-Np angle. The average Fe-Np bond length is 2.070(16) Å. The Fe atom is located 0.49 Å out of the 24-atom mean porphyrin plane toward the nitrate ligand. From solid-state Mössbauer data, the isomer shift of 0.98 mm/s at 77 K is entirely consistent with high-spin iron(II). However the quadrupole splitting of 3.59 mm/s at 77 K is unusually high for iron(II), S = 2 systems but within the range of other five-coordinate high-spin ferrous complexes with a single anionic axial ligand. Crystal data for [K(222)]-[Fe(TpivPP)(NO3)]·C6H5Cl: a = 17.888 (5) Å, b = 21.500 (10) Å, c = 22.514 (11) Å, β = 100.32 (3)°, monoclinic, space group P21/n, V = 8519 Å3, Z = 4. © 2006 American Chemical Society.