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  1. Yeap CS, Hemamalini M, Fun HK
    PMID: 21580347 DOI: 10.1107/S1600536810004526
    The title Schiff base compound, C(13)H(11)NO(5)S·3H(2)O, formed from sulfanilic acid and 2,4-dihydroxy-benzaldehyde, crystallized out as a zwitterion with the N atom protonated. The asymmetric unit consists of one 4-[(2,4-dihydroxy-benzyl-idene)ammonio]benzene-sulfonate and three water mol-ecules. The zwitterion exists in an E configuration with respect to the central C=N double bond. The two benzene rings of the mol-ecule are oriented at a dihedral angle of 27.33 (8)°. An intra-molecular N-H⋯O hydrogen bond stabilizes the mol-ecular structure. In the crystal, the zwitterions are linked into chains along [101] by inter-molecular O-H⋯O and N-H⋯O hydrogen bonds. The three water mol-ecules link these chains into a three-dimensional framework by additional inter-molecular O-H⋯O hydrogen bonds. A π⋯π inter-action [3.5485 (9) Å] further stabilizes the crystal structure.
  2. Yeap CS, Hemamalini M, Fun HK
    PMID: 21580598 DOI: 10.1107/S160053681000766X
    In the title Schiff base, C(17)H(14)Cl(4)N(2), the atoms of one of the 2,6-dichloro-benzyl-idene units and the central 1,2-diamino-propane grouping are disordered over two sets of sites in a 0.8838 (12):0.1162 (12) ratio. The dihedral angles between the ordered benzene ring and its disordered counterparts are 57.41 (12) and 54.8 (6)° for the major and minor disorder components, respectively. The crystal studied was a racemic twin, the refined ratio of the twin components being 0.37 (5):0.63 (5).
  3. Fun HK, Balasubramani K, Yeap CS
    PMID: 21583553 DOI: 10.1107/S1600536809026439
    In the title salt, 2C(5)H(8)N(3) (+)·C(4)H(4)O(4) (2-)·3H(2)O, the asymmetric unit contains a protonated 2,3-diamino-pyridinium cation, half of a succinate dianion (disposed about a centre of inversion), and one and a half water mol-ecules. One of the water mol-ecules is disordered over two sites with occupancies of 0.670 (17) and 0.330 (17). The other water mol-ecule has an occupancy of 0.5 (from refinement). The pyridine N atom of the 2,3-diamino-pyridine mol-ecule is protonated. The protonated N atom and one of the 2-amino H atoms are hydrogen bonded to the succinate anion through a pair of N-H⋯O hydrogen bonds, forming an R(2) (2)(8) ring motif. In the crystal, mol-ecules are consolidated into a three-dimensional network by N-H⋯O and O-H⋯O inter-actions.
  4. Yeap CS, Kia R, Fun HK
    PMID: 21201825 DOI: 10.1107/S1600536808027220
    The title Schiff base compound, C(23)H(30)N(2)O(2), has crystallographic twofold rotation symmetry. An intra-molecular O-H⋯N hydrogen bond forms a six-membered ring, producing an S(6) ring motif. The imino group is coplanar with the benzene ring. The two benzene rings are almost perpendicular to each other, making a dihedral angle of 87.38 (4)°. In the crystal structure, neighbouring mol-ecules are linked along the c axis by weak inter-molecular C-H⋯O hydrogen bonds and are further packed into columns along the b axis, forming sheets which are parallel to the bc plane.
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