The Synthesis of Hypodiphosphoric Acid and Derivatives with P-P Bond, including Esters and Diphosphine Dioxides: A Review

The synthesis of hypodiphosphoric acid and its related compounds began in 1877, but no summary of the synthetic efforts has been reported. This review includes published papers related to the molecules containing the >P(=O)-P(=O)< fragment, which notably resembles the structure of the >P(=O)-O-P(=O)< moiety, the essential building block of many important molecules found in nature and in the field of medicinal chemistry. This review covers the strategies related to the synthesis of hypodiphosphoric acid (former name hypophosphoric acid), its ester form, and diphosphine dioxides. Finally, some properties and applications of these structures studied during this period are presented.

Oxyanion clusters with antielectrostatic hydrogen bonding (AEHB) in tetraalkylammonium hypodiphosphates

Organic–inorganic salts of hypodiphosphoric acid with tetraalkylammonium cations have been synthesized and characterized by X-ray crystallography and IR spectroscopy.

Crystal structure of catena-poly[[tetra-aqua-magnesium]-μ-(di-hydrogen hypodiphosphato)-κ(2) O:O']

[Mg(H₂P₂O₆)(H₂O)₄] is the first alkaline earth hypodiphosphate to be structurally determined. It consists of (H₂P₂O₆)²⁻ anions that are bridged by Mg²⁺ cations into a chain structure. Water mol­ecules complete the octa­hedral coordination sphere of the metal and built up a three-dimensional hydrogen-bonding network.

The crystal structure of the title compound, [Mg(H₂P₂O₆)(H₂O)₄]_n, is built up from (H₂P₂O₆)²⁻ anions bridging Mg²⁺ cations into chains extending parallel to [011]. The Mg²⁺ ion is located on an inversion centre and is octa­hedrally coordinated by the O atoms of two (H₂P₂O₆)²⁻ anions and four water mol­ecules. The centrosymmetric (H₂P₂O₆)²⁻ anion has a staggered conformation whereby the tetra­valent phospho­rus atom is surrounded tetra­hedrally by three O atoms and by one symmetry-related P atom. A three-dimensional O—H⋯O hydrogen-bonded network of medium strength involving the P—OH group of the anion and the water mol­ecules is present.