Energetic materials: The preparation and structural characterization of three biguanidinium dinitramides

Three biguanidinium salts of the energetic dinitramide anion have been prepared and structurally characterized from room-temperature X-ray diffraction data. Biguanidinium mono-dinitramide, (BIGH)(DN), triclinic, <P(1)over bar>, a = 4.3686(4), b = 9.404(2), c = 10.742(1) Angstrom, alpha = 83.54(1), beta = 80.386(9), gamma = 79.93(1)degrees, V = 426.8 (1) Angstrom(3), Z = 2, D-x = 1.62 g cm(-3). Biguanidinium bis-dinitramide, (BIGH(2))(DN)(2), monoclinic, C2/c, a = 11.892(2), b = 8.131(1), c = 13.038(2) Angstrom, beta = 115.79(1)degrees, V = 1135.1(3) Angstrom(3), Z = 4, D-x = 1.84 g cm(-3). Biguanidinium bis-dinitramide monohydrate, (BIGH(2))(DN)(2) . H2O, orthorhombic, P2(1)2(1)2(1), a = 6.4201(6), b = 13.408(1), c = 14.584(2) Angstrom, V = 1255.4(4) Angstrom(3), Z = 4, D-x = 1.76 g cm(-3). All three structures are characterized by extensive hydrogen bonding. Both the mono- and diprotontated cations consist of two planar halves twisted with respect to each other. The dinitramide anion has a surprisingly variable and asymmetric structure. The two halves of the anion are twisted with respect to each other; however, the twist varies from 5.1 to 28.9 degrees. In addition, the two ends of the anion have significantly different geometries, e.g. the 'equivalent' N-N bond lengths differ by up to 0.045 Angstrom.