An open-framework iron phosphate with large voids, exhibiting spin-crossover

A novel iron phosphate, [(C4N3H16)(C4N3H15)]5+-[Fe5F4(H2PO4)(HPO4)3(PO4)3]5–·H2O, consisting of a Fe–O/F–Fe network crosslinked by PO4 groups is shown to possess unusually large elliptical voids of 24 T atoms (T = Fe, P) and to exhibit a gradual low- to high-spin transformation.