Problems connected with the melting of NiII, CoII and MnII cyclo-tetraphosphates

Differential thermal analysis has been used to follow the process of melting of Ni^II, Co^II and Mn^II cyclo-tetraphosphates. The melting is congruent in a dry atmosphere, being non-congruent in the presence of small amounts of water vapour: the tetraphosphate cycles are split and further condensed to chains of higher linear phosphates. Their end groups (and hence their stability) are provided by water molecules present in the atmosphere. After cooling the products have a glassy amorphous form. By repeated heating they are changed back into the cyclo-tetraphosphates with crystalline character, and the water molecules are released.