• charge density distribution;
  • density functional calculations;
  • lithium;
  • hypodiphosphate

Tetralithium hypodiphosphate hexahydrate, Li4P2O6·6H2O, forms a highly symmetrical crystal structure, where hypodiphosphate anions have inline image (D3d) symmetry. Analysis of the charge distribution (experimental and theoretically calculated) shows that the charges of the P atoms are lower than in phosphates and phosphonates, whereas the O charges are similar. Values of both ρc and ∇2ρc suggest that the P—P bond is a weak covalent one, while the P—O one is polarized covalent, with topological parameters similar to those of P—O bonds in phosphates or phosphonates. Theoretical calculations show that the hypodiphosphate anion is relatively insensitive to its coordination environment; this is brought about by the vicinity of cationic P atoms. The localization and delocalization indices have been computed and discussed.