Ammonothermal Synthesis of Alkali N,N′-Bis(aminocarbonyl)phosphorodiamidates M[PO2(NHCONH2)2] (M = Na, K, Rb)

Compounds M[PO2(NHCONH2)2] with M = Na, K, and Rb, which are the salts of N,N′‐bis(aminocarbonyl)phosphorodiamidic acid, were synthesized by ammonolysis of the corresponding alkali biuretooxophosphates M[PO2(NH)3(CO)2] (M = Na, K, Rb) at 350 °C and 120–150 bar in an autoclave. The structures were solved by single‐crystal X‐ray diffraction and exhibit 3D frameworks in which N,N′‐bis(aminocarbonyl)phosphorodiamidate ions connect the corresponding alkali ions. The thermal behavior was investigated by combined thermogravimetric (TG) and differential thermal analysis (DTA) as well as temperature‐dependent powder X‐ray diffraction to evaluate applicability of the alkali N,N′‐bis(aminocarbonyl)phosphorodiamidates as precursors for the synthesis of CNP(O) networks. In this context, the concept of Le Chatelier's principle for the hindrance of premature decomposition by applying elevated pressure was examined. Ammonothermal treatment of biuretooxophosphates prevented decomposition of the precursor into phosphates and gaseous CNH(O) compounds at higher temperatures according to Le Chatelier's principle and yielded the hitherto unknown alkaliN,N′‐bis(aminocarbonyl)phosphorodiamidates M[PO2(NHCONH2)2] (M = Na, K, Rb).