KPr(PO(3))(4).

Single crystals of the title compound, potassium praseodymium(III) polyphosphate, were obtained by solid-state reaction. The monoclinic non-centrosymmetric structure is isotypic with all other KLn(PO(3))(4) analogues from Ln = La to Er, inclusive. The crystal structure of these long-chain polyphosphates is built up from infinite crenelated polyphosphate chains of corner-sharing PO(4) tetra-hedra with a repeating unit of four tetra-hedra. These chains, running along [100], are arranged in a pseudo-tetra-gonal rod packing and are further linked by isolated PrO(8) square anti-prisms [Pr-O = 2.3787 (9)-2.5091 (8) Å], forming a three-dimensional framework. The K(+) ions reside in channels parallel to [010] and exhibit a highly distorted coordination sphere by eight O atoms at distances ranging from 2.7908 (9) to 3.1924 (11) Å.