The low-tempetature fluorination of the n = 2 Ruddlesden-Popper phase La2SrCr2O7 yields La2SrCr2O7F2 via a topochemical fluorine insertion reaction. The structure conserving nature of the fluorination, reaction means that the chromium centers Of the initial oxide phase retain an octahedral coordination environment in the fluorinated product, resulting in a material containing an extended array of apex-linked Cr4+O6 units. Typically materials containing networks of octahedrally coordinated Cr4+ centers can only be prepared at high pressure; thus, the preparation of La2SrCr2O7F2 demonstrates that low-temperature topochemical reactions offer an alternative synthesis route to materials of this type. Neutron diffraction, magnetization, and mu+SR data indicate that La2SrCr2O7F2 undergoes a transition to an antiferromagnetic state below TN approximate to 440 K. The structure-property relations of this phase and other Cr4+ oxide phases are discussed.