Three triorganotin derivatives of N,N′diphenylphosphorodiamidic acid and three further derivatives of N,N,N′,N′-tetraethylphosphorodiamidic acid have been prepared and characterised by spectroscopic methods. Soluble derivatives are assigned cyclic, oligomeric structures, while insoluble triphenyltin compounds are believed to be chain polymers. Variable-temperature 119Sn Mössbauerspectroscopy is used