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, a = 4.3686 (4), b = 9.404 (2), c = 10.742 (1) Å, α = 83.54 (1), β = 80.386 (9), γ = 79.93 (1)°, V = 426.8 (1) Å 3 , Z = 2, D x = 1.62 g cm −3 . Biguanidinium bis-dinitramide, (BIGH 2 )(DN) 2 , monoclinic, C 2/ c , a = 11.892 (2), b = 8.131 (1), c = 13.038 (2) Å, β = 115.79 (1)°, V = 1135.1 (3) Å 3 , Z = 4, D x = 1.84 g cm −3 . Biguanidinium bis-dinitramide monohydrate, (BIGH 2 )(DN) 2 .H 2 O, orthorhombic, P 2 1 2 1 2 1 , a = 6.4201 (6), b = 13.408 (1), c = 14.584 (2) Å, V = 1255.4 (4) Å 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°. 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 Å.
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Martín et al. (1997) studied this question.