The
n = 3 Ruddlesden-Popper phase Sr
3LaFe
1.5Co
1.5O
10± is capable of sustaining O contents as low as O
7.5 with a mean metal oxidation state of +2 and three coordination at the central site in the trilayer of originally octahedral transition metal sites. The shortening of the axial bonds to the flanking octahedral layers stabilizes the low oxidation state and consequent unusual low coordination number of the Fe
2+ and Co
2+ cations within the extended structure.