Six-coordinated Fe(II) complex ions [FeL3](2+) (L = en, amp, bpy, dmbpy, phen, and dmphen), prepared in a supercage of zeolite Y, were characterized by UV-vis, XRD, Mossbauer spectroscopy, and IR. The UV-vis spectra and XRD patterns of the zeolite encapsulating the Fe(II) complex ions show that [Fe(en)(3)](2+), [Fe(amp)(3)](2+), [Fe(bpy)(3)](2+), and [Fe(phen)(3)](2+) are formed in the zeolite supercage. The Mossbauer spectra of [Fe(bpy)(3)](2+) and [Fe(phen)(3)](2+) in the supercage gave extraordinarily large values of the quadrupole splitting for low-spin Fe(II) species, indicating that these complex ions in a supercage are distorted by a strong steric interaction with the zeolite lattice. The IR spectra of [Fe(bpy)(3)](2+) and [Fe(phen)(3)](2+) in the supercage as well as their Mossbauer results reveal that the complex ion is located in the supercage; (i) the 3-fold axis of the complex is parallel to that of the supercage, (ii) each of the three bidentate-ligand molecules in the complex faces to the 12-membered ring of the supercage, and (iii) the complex is twisted around its 3-fold axis toward a trigonal prism.