Crystal structures of the barium salts of isonitroso- and of NN′-dimethyl-isonitroso-malonamide

The structures of (I) 2Ba[NH₂·CO·C(NO)·CO·NH₂] ₂·7H₂O, and (II) Ba[MeNH·CO·C(NO)·CO·NHMe]₂ have been determined by X-ray (heavy-atom) methods from diffractometer data and refined by least squares to R 0.10 and 0.038 respectively. Crystals of (I) are tetragonal, space group P4₁2₁2,a = 10.718(3), c = 51.12 (3) Å, Z = 8. Crystals of (II) are trigonal, space group R3, a = 10.966(2) Å, α = 73.34(2) °. Z = 3. (I) comprises pairs of barium atoms 4.763 Å apart and bridged in an infinite polymeric array in the ab plane by the ligands, the resulting layers normal to c being hydrogen-bonded by interleaving water molecules. The barium atoms are nine- and ten-co-ordinated by an assortment of ligand nitrogen and oxygen atoms and water molecules. (II) comprises centro-symmetric triads of barium atoms disposed in the three-fold axis [Ba ⋯ Ba, 4.2414(7) Å] and bridged by the oxygen atoms of the ligands, the centrosymmetric barium being six-co-ordinate, and the others nine-co-ordinate. A three-dimensional polymer is formed by oxygen bridges.