Cover illustration: The molecular structure of (Ph3PI)I5, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. See Pritchard & Moreland [Acta Cryst. (2006), C62, o656-o658].
The title isotypic orthorhombic aliovalent KTP isomorphs contain octahedrally coordinated Cr3+ or Fe3+ and Nb5+ cations in cis–trans-arranged chains; these are linked by PO4 anions into a framework containing cavities in which K+ cations are located.