X-ray crystal structure determination shows that the conformation of the diaminoguanidinium (DAG) cation ((NH{sub 2}NH){sub 2}C({double bond}NH{sub 2}){sup +}) is different in its salts with nitrate ion and with the conjugate base of 3-nitro-1,2,4-triazol-5-one (NTO). In both cases, the carbon atom and all five nitrogen atoms are coplanar. In the nitrate salt an S' configuration is found where one of the terminal NH{sub 2} groups is cis to the central C{double bond}NH{sub 2} bond and the other is trans. In the NTO salt a W' configuration is found where both of the terminal NH{sub 2} groups are cis to the central C{double bond}NH{sub 2} bond. The terminal NH{sub 2} groups are positioned in such a fashion that the hydrogens appear above and below the plane of the rest of the molecule and the lone pairs are directed toward the hydrogens of the C{double bond}NH{sub 2} moiety. Calculations suggest that the nitrate salt contains DAG in its lower energy form, while favorable electrostatic interactions lead to selective binding of the less stable W form of DAG with NTO.