Synthesis and thermal decomposition studies of new nitroso- and nitrodicyanomethanide salts

The lithium, barium, ammonium, and guanidinium salts of nitrosodicyanomethanide ([ONC(CN)(2)](-)), and the lithium, sodium, barium, ammonium, guanidinium, and hydrazinium salts of nitrodicyanomethanide ([O2NC(CN)(2)](-)) are synthesized and characterized by infrared, UV-vis and C-13 NMR spectroscopy, and elemental analysis. Four of them, namely, [NH4][ONC(CN)(2)], Ba[ONC(CN)(2)](2)(H2O), [NH4][O2NC(CN)(2)], and Ba[O2NC(CN)(2)](Cl)(H2O)(2), have also been characterized by single-crystal X-ray diffraction data. The structural data reveal that the two anions possess comparable structural features irrespective of the nature of the cation. The N-O bond distances in [NH4][ONC(CN)(2)] and Ba[ONC(CN)(2)](2)(H2O) are similar at 1.286(2) and 1.292(4) Angstrom, respectively, and the anion possesses a nearly planar geometry. Nitrodicyanomethanide anions in the crystals of [NH4][O2NC(CN)(2)] and Ba[O2NC(CN)(2)](Cl)(H2O)(2) are also nearly planar with average N-O bond distances of 1.258(2) and 1.252(5) Angstrom, respectively. In Ba[ONC(CN)(2)](2)(H2O), the nitrosodicyanomethanide anion binds a single metal center through the nitrogen and oxygen atoms of the nitroso group while also binding two other metal centers through the cyano nitrogen atoms. In Ba[O2NC(CN)(2)](Cl)(H2O)(2), the nitrodicyanomethanide anion coordinates to the metal center only through the cyano nitrogen atoms. The thermal properties of the new compounds together with those of the known sodium, potassium, and silver salts of nitrosodicyanomethanide and the potassium and silver salts of nitrodicyanomethanide are examined by differential scanning calorimetry (DSC). The DSC data reveal that the two series of compounds undergo exothermic decomposition releasing 240-690 cal/g. The alkali metal, silver, and barium salts decompose at higher temperatures (>200 degrees C), whereas the nitrogenous cationic salts decompose at lower temperatures, indicating that the thermal behavior of the two anions can be significantly altered by choosing appropriate cations.