Eight Schiff bases derived from various salicylaldehydes: phenol-imine and keto-amine forms, conformational disorder, and supramolecular assembly in one and two dimensions.

Structures are reported for eight Schiff bases derived from various salicylaldehydes: five are newly synthesized and re-investigations are reported for three previously reported structures, leading, in each case, to some revision of previous conclusions. In (E)-N-(3,4-dimethylisoxazol-5-yl)-4-[(2-hydroxybenzylidene)amino]benzenesulfonamide, CHNOS, (I), and (E)-4-[(5-bromo-2-hydroxy-3-methoxybenzylidene)amino]-N-(3,4-dimethylisoxazol-5-yl)benzenesulfonamide. CHBrNOS, (II), the isoxazole rings adopt different orientations relative to the rest of the molecules, despite the additional substituents in (II) being in the aryl ring remote from the isoxazole unit.

The crystal structure of ()-2-ethyl--(4-nitro-benzyl-idene)aniline: three-dimensional supra-molecular assembly mediated by C-H⋯O hydrogen bonds and nitro⋯π(arene) inter-actions.

In the mol-ecule of the title compound, CHNO, the 2-ethyl-phenyl group is disordered over two sets of atomic sites having occupancies of 0.515 (19) and 0.485 (19), and the dihedral angle between the two partial-occupancy aryl rings is 6(2)°.

Reinvestigation of the crystal structure of -(4-chloro-benzyl-idene)-2-hy-droxy-aniline: a three-dimensional structure containing O-H⋯N, O-H⋯O and C-H⋯π(arene) hydrogen bonds.

The mol-ecule of the title compound, CHClNO, (I), which contains an intra-molecular O-H⋯N hydrogen bond, is almost planar: the dihedral angle between the two aryl rings is only 3.31 (9)°. The mol-ecules of (I) are linked into sheets by two C-H⋯π(arene) hydrogen bonds and the sheets are linked into a three-dimensional structure by O-H⋯O hydrogen bonds.

Crystal structures of ()-1-{3-[(5-fluoro-2-hy-droxy-benzyl-idene)amino]-phen-yl}ethanone and of a fourth polymorph of ()-1-{3-[(2-hy-droxy-3-meth-oxy-benzyl-idene)amino]-phen-yl}ethanone.

In the mol-ecules of both ()-1-{3-[(5-fluoro-2-hy-droxy-benzyl-idene)amino]-phen-yl}ethanone, CHFNO, (I), and ()-1-{3-[(2-hy-droxy-3-meth-oxy-benzyl-idene)amino]-phen-yl}ethanone, CHNO, (II), which crystallizes with ' = 2 in space group 2, there are intra-molecular O-H⋯N hydrogen bonds, and the non-H atoms in each mol-ecule are essentially coplanar. In the crystal of (I), mol-ecules are linked by a single C-H⋯O hydrogen bond to form a (8) chain, whereas in the crystal of (II), mol-ecules are linked by three C-H⋯O hydrogen bonds to form sheets within which orthogonal (16) and (17) chains can be identified. Comparisons are made with some related structures.

Crystal structures of 2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3-benzo-thia-zol-3-ium benzoate and 2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3-benzo-thia-zol-3-ium picrate.

In both 2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3- benzo-thia-zol-3-ium benzoate, CHNS·CHO, (I), and 2-amino-4,4,7,7-tetra-methyl-4,5,6,7-tetra-hydro-1,3-benzo-thia-zol-3-ium picrate (2,4,6-tri-nitro-phenolate), CHNS·CHNO, (II), the cations are conformationally chiral as the six-membered rings adopt half-chair conformations, which are disordered over two sets of atomic sites giving approximately enanti-omeric disorder. For both cations, the bond lengths indicate delocalization of the positive charge comparable to that in an amidinium cation. The bond lengths in the picrate anion in (II) are consistent with extensive delocalization of the negative charge into the ring and onto the nitro groups, in two of which the O atoms are disordered over two sets of sites.