Crystal structure of K<sub>0.75</sub>[Fe<sup>II</sup><sub>3.75</sub>Fe<sup>III</sup><sub>1.25</sub>(HPO<sub>3</sub>)<sub>6</sub>]·0.5H<sub>2</sub>O, an open-framework iron phosphite with mixed-valent Fe<sup>II</sup>/Fe<sup>III</sup>ions
Acta crystallographica. Section E, Crystallographic communications