The encapsulation of transition metal ions by hexa-amine ligands of the sarcophagine type permits their electronic and spectroscopic properties to be studied in a magnetically dilute and kinetically inert environment. In particular, the saturated nature of the amine yields a cryptand of the innocent kind so that the ligand field absorption of the metal containing cages is not obscured by intense charge transfer bands. This paper presents the results of magnetic, vis-UV spectroscopic and NMR measurements on a series of hexa-aza Werner complexes of encapsulated divalent iron performed over a range of temperature. The data reveal that both low-spin and high-spin isomers of the iron(II) cages coexist in solution. The temperature dependence of the physical parameters is characteristic of a spin equilibrium between molecular states of 1A1g and 5T2g origin.