The alpha2-polymorph of salicylideneaniline.

N-Salicylideneaniline (SA), C13H11NO, belongs to the large family of aromatic Schiff bases. It is of particular importance owing to its reversible photoreactivity. SA forms two photochromic polymorphs, both with two non-coplanar benzene rings. In addition, we have recently discovered a planar polymorph, named the beta-polymorph, which will be discussed in a subsequent paper. We report here the structure of the alpha2-polymorph in the orthorhombic crystal system. This compound exhibits a strong intramolecular O-H...N hydrogen bond and the dihedral angle between the two rings varies with temperature.

The interaction of 5-fluoroorotic acid with transition metals: synthesis and characterisation of Ni(II), Cu(II) and Zn(II) complexes.

5-Fluoroorotic acid (H(3)FOro) is a potent inhibitor for some metalloproteins such as dihydroorotase and dihydroorotate dehydrogenase and for thymidylate synthase (nonmetalloprotein) in the human malaria parasite Plasmodium falciparum. To study the coordination chemistry of H(3)Foro, the ammonium salt [NH(4)(+)][H(2)FOro(-)].1H(2)O (1) and the first coordination compounds of H(3)FOro with transition metals [Ni(HFOro(2-))(H(2)O)(4)].1H(2)O (2), [Cu(HFOro(2-))(NH(3))(H(2)O)](n) (3) and [Cu(3)(FOro(3-))(2)(NH(3))(6)(H(2)O)(2)] (4) have been synthesised and characterised by single-crystal X-ray diffraction, IR spectroscopy and by thermogravimetry. Three different coordination modes of 5-fluoroorotic acid have been established. In all cases the ligand is chelated to the metal via an amido-nitrogen and a carboxylate-oxygen but for (3), there is also a carboxylate oxygen from another HFOro(2-) ligand resulting in a polymeric structure and for (4), the second amido-nitrogen in the ororotic acid ring coordinates to give a trinuclear complex. The metal coordination polyhedra are octahedral in (2), square-pyramidal in (3) and square-planar and approximately square-pyramidal in (4). An octahedral coordination geometry including a N(1)/O(61)-chelating HFOro(2-) ligand with four aqua ligands is proposed for the Zn complex [Zn(HFOro(2-)) (H(2)O)(4)].0.5H(2)O (5), based on IR and thermogravimetric data. Extensive hydrogen bonded networks and some ring-ring stacking interactions are observed in each of the structures.

Platinum complexes of oxopurines: cis-bis(theophyllinato-N7)bis(triphenylphosphine)platinum(II) and cis-chloro(theobrominato-N1)bis(triphenylphosphine)platinum(II) ethanol hemisolvate.

The syntheses and structures of two mixed-ligand complexes of platinum(II) with deprotonated oxopurine bases and triphenylphosphine are reported, namely the theophyllinate complex cis-bis(1,2,3,6-tetrahydro-1,3-dimethylpurine-2,6-dionato-kappaN(7))bis(triphenylphosphine-kappaP)platinum(II), [Pt(C(7)H(7)N(4)O(2))(2)(C(18)H(15)P)(2)], (I), and the theobrominate complex cis-chloro(1,2,3,6-tetrahydro-3,7-dimethylpurine-2,6-dionato-kappaN(1))bis(triphenylphosphine-kappaP)platinum(II) ethanol hemisolvate, [PtCl(C(7)H(7)N(4)O(2))(C(18)H(15)P)(2)].0.5C(2)H(5)OH, (II). In (I), the coordination geometry of Pt is square planar, formed by the two coordinating N atoms of the theophyllinate anions in a cis arrangement and two P atoms from the triphenylphosphine groups. In (II), there are two crystallographically independent molecules. They both exhibit a square-planar coordination geometry around Pt involving one Cl atom, the coordinating N atom of the theobrominate anion and two P atoms from the triphenylphosphine groups. The two triphenylphosphine groups are arranged in a cis configuration in both structures. The heterocyclic rings are rotated with respect to the coordination plane of the metal by 82.99(8) and 88.09(8) degree in complex (I), and by 85.91(16) and 88.14(18) degree in complex (II). Both structures are stabilized by intramolecular stacking interactions involving the purine rings and the phenyl rings of adjacent triphenylphosphine moieties.