[Preparation and structural study of NH(4)Gd(PO(3))(4) and NH(4)GdP(4)O(12)].

Ammonium gadolinium polyphosphate, NH(4)Gd(PO(3))(4), (I), and ammonium gadolinium cyclotetraphosphate, NH(4)GdP(4)O(12), (II), were synthesized by flux growth with excess (NH(4))(2)HPO(4). In (I), the PO(4) tetrahedra share vertices to produce corrugated ribbons along the c direction, while in (II) they form P(4)O(12) rings arranged in layers perpendicular to the c axis. In both structures, isolated GdO(8) polyhedra link the phosphate anions into a three-dimensional framework with channels containing the NH(4)(+) cations. The Gd and N atoms are located in general positions in (I) and on twofold axes in (II).