Stable high energy density materials (HEDM) are of great interest to NASA. HEDM's are viewed as suitable fuel for the single stage launching of jets into orbit. Nitrogen-rich molecules and salts with high-energy properties are also considered "green fuels" as these materials release environmentally safe N2 gas as the major combustion product. Diazeniumdiolate (RN2O2-) and sydnone-N-oxide (RC2N2O2-) salts exhibit exothermic decomposition behavior similar to explosives such as trinitrotoluene (TNT), nitroglycerine (NG) and pentaerythritol tetranitrate (PETN). We have synthesized a series of aliphatic and aromatic compounds containing diazeniumdiolate and sydnone-N-oxide substituents. Nitrous acid nitrosation of N-alkylhydroxylamines yields mono diazenium-diolate products. Reactions of carboxylic esters with nitric oxide gas form both diazeniumdiolate and sydnone products. Similar reactions with aldoximes (RCH=NOH) yield α-oximinoalkanediazeniumdioalte salts (RC(N2O2K)=NOH). IR, UV-Vis and NMR spectroscopic techniques are employed for the characterization of the new products. Some of them are also characterized by crystallographic data. Thermal behavior is determined by differential scanning calorimetry. The data reveal that the thermal behavior of the salts can be tuned by the substitution of appropriate hydrocarbon substituents.