Chemistry

Problem

Magnetite, Fe

_3

_4

, can be described as an inverse spinel in which O

^{2-}

ions form a close-packed lattice and the Fe

^{2+}

and Fe

^{3+}

cations occupy tetrahedral (4-coordinate) and octahedral (6-coordinate) interstices. Given the ionic radii Fe

^{2+}\!: 78\,\text{pm}

and Fe

^{3+}\!: 65\,\text{pm}

, which distribution of cations is most likely to maximize lattice stability? a) Fe

^{2+}

in all tetrahedral sites; Fe

^{3+}

in all octahedral sites b) Fe

^{3+}

in all tetrahedral sites; Fe

^{2+}

equally in octahedral and tetrahedral sites c) Fe

^{2+}

in octahedral sites; Fe

^{3+}

distributed between tetrahedral and octahedral sites d) Fe

^{2+}

in tetrahedral sites; Fe

^{3+}

equally divided between tetrahedral and octahedral sites