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

The lithium, barium, ammonium, and guanidinium salts of nitrosodicyanometha nide ([ONC(CN)(2)](-)), and the lithium, sodium, barium, ammonium, guanidin ium, 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(C N)(2)](2)(H2O), [NH4][O2NC(CN)(2)], and Ba[O2NC(CN)(2)](Cl)(H2O)(2), have a lso been characterized by single-crystal X-ray diffraction data. The struct ural 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[O 2NC(CN)(2)](Cl)(H2O)(2) are also nearly planar with average N-O bond distan ces of 1.258(2) and 1.252(5) Angstrom, respectively. In Ba[ONC(CN)(2)](2)(H 2O), the nitrosodicyanomethanide anion binds a single metal center through the nitrogen and oxygen atoms of the nitroso group while also binding two o ther metal centers through the cyano nitrogen atoms. In Ba[O2NC(CN)(2)](Cl) (H2O)(2), the nitrodicyanomethanide anion coordinates to the metal center o nly through the cyano nitrogen atoms. The thermal properties of the new com pounds together with those of the known sodium, potassium, and silver salts of nitrosodicyanomethanide and the potassium and silver salts of nitrodicy anomethanide are examined by differential scanning calorimetry (DSC). The D SC data reveal that the two series of compounds undergo exothermic decompos ition releasing 240-690 cal/g. The alkali metal, silver, and barium salts d ecompose at higher temperatures (>200 degrees C), whereas the nitrogenous c ationic salts decompose at lower temperatures, indicating that the thermal behavior of the two anions can be significantly altered by choosing appropr iate cations.