Potassium salts of hypodiphosphoric acid.

The synthesis and crystal structures of a series of six crystalline potassium salts of hypodiphosphoric acid, H(4)P(2)O(6), are reported, namely potassium hydrogen phosphonophosphonate, K(+)·H(3)P(2)O(6)(-), (I), dipotassium dihydrogen hypodiphosphate monohydrate, 2K(+)·H(2)P(2)O(6)(2-)·H(2)O, (II), dipotassium dihydrogen hypodiphosphate dihydrate, 2K(+)·H(2)P(2)O(6)(2-)·2H(2)O, (III), pentapotassium hydrogen hypodiphosphate dihydrogen hypodiphosphate dihydrate, 5K(+)·HP(2)O(6)(3-)·H(2)P(2)O(6)(2-)·2H(2)O, (IV), tripotassium hydrogen hypodiphosphate tetrahydrate, 3K(+)·HP(2)O(6)(3-)·4H(2)O, (V), and tetrapotassium hypodiphosphate tetrahydrate, 4K(+)·P(2)O(6)(4-)·4H(2)O, (VI). All the hypodiphosphate anions, viz. H(3)P(2)O(6)(-), H(2)P(2)O(6)(2-), HP(2)O(6)(3-) and P(2)O(6)(4-), adopt a staggered conformation. The P-P bond lengths [2.1722 (7)-2.1892 (10) Å] do not depend on the basicity of the anion. The compounds are organized into different types of one-, two- or three-dimensional polymeric hydrogen-bonded networks, or simply exist in the form of isolated or dimeric units. The coordination numbers of the K(+) cations range from 6 to 9, and the cationic sublattices are polymeric one-, two- or three-dimensional networks, or isolated [KO(6)] or dimeric [K(2)O(12)] polyhedra.