Crystal structures of zinc(II) complexes with ß-hydroxypyridinecarboxylate ligands: examples of structure-directing effects used in inorganic crystal engineering.

The coordination properties of four hydroxypyridinecarboxylates, designed for the treatment of iron-overloading conditions as bidentate O,O'-donor ligands, have been studied with ZnII in the solid state. The coordination compounds [Zn(A1)2(H2O)2] (1), [Zn(A2)2(H2O)] (2), [Zn(A3)2(H2O)]·2H2O (3) and [Zn2(B1)4(H2O)2]·4H2O (4), where the ligands are 1-methyl-4-oxidopyridinium-3-carboxylate (A1, C7H6NO3), 1,6-dimethyl-4-oxidopyridinium-3-carboxylate (A2, C8H8NO3), 1,5-dimethyl-4-oxido-pyridinium-3-carboxylate (A3, C8H8NO3) and 1-methyl-3-oxidopyridinium-4-carboxylate (B1, C7H6NO3), have been synthesized and analysed by single-crystal X-ray diffraction. The ligands were chosen to probe (i) the electronic effects of inverting the positions of the O-atom donor groups (i.e. A1 versus B1) and (ii) the electronic and steric effects of the addition of a second methyl group in different positions on the pyridine ring. Two axially coordinated water molecules resulting in a six-coordinated symmetrical octahedron complement the bis-ligand complex of A1. Ligands A2 and A3 form five-coordinated trigonal bipyramidal complexes with one additional water molecule in the coordination sphere, which is a rarely reported geometry for ZnII complexes. Ligand B1 shows a dimeric structure, where the two Zn2+ dications have slightly distorted octahedral geometry and the pyridinolate O atom of the neighbouring complex bridges them. The coordination spheres of the Zn2+ dications and the supramolecular structures are discussed in detail. The packing arrangements of 1-3 are similar, having alternating hydrophilic and hydrophobic layers, however the similarity is broken in 4. The obtained coordination geometries are compared with their previously determined CuII analogues. The study of the individual complexes is complemented with a comprehensive analysis of ZnII complexes with oxygen donor ligands with data from the Cambridge Structural Database.

Structural characterization of allomelanin from black oat.

The brown to black coloration found in plants is due to the melanins, which have been relatively poorly investigated among the plant pigments. The aim of this work was to study the dark pigment extracted from the black oat hull with respect to composition and structure. Ultraviolet-visible (UV-Vis) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) and Fourier transform infrared (FT-IR) spectroscopy were applied for the characterization of the pigment. UV-Vis spectroscopy revealed that the extracted material displays a broadband, structureless absorption profile a common feature of melanins. MALDI-TOF MS measurements demonstrated that oat melanin is a homopolymer built up from p-coumaric acid and consists mainly of low molecular weight (527-1499 Da) oligomers of 3-9 monomer units. The tetramer oligomer proved to be dominant. The results of the FT-IR analysis indicated that oat melanin is a fully conjugated aromatic system containing tetrasubstituted aromatic rings linked by CC coupling. The in vitro preparation of melanin from p-coumaric acid by horseradish peroxidase was performed for comparison. The resulting polymer consisted of oligomers of 4-9 monomer units similarly to those in oat melanin. However, the building blocks proved to be connected to each other via COC linkages in contrast with the CC linkages in oat melanin.

Crystal structure of levomepromazine maleate.

The asymmetric unit of the title salt, C19H25N2OS(+)·C4H3O4 (-) [systematic name: (S)-3-(2-meth-oxy-pheno-thia-zin-10-yl)-N,N,2-tri-methyl-propanaminium hydrogen maleate], comprises two (S)-levomepromazine cations and two hydrogen maleate anions. The conformations of the two cations are similar. The major difference relates to the orientation of the meth-oxy substituent at the pheno-thia-zine ring system. The crystal components form a three-dimensional supra-molecular network via N-H⋯O, C-H⋯O and C-H⋯π inter-actions. A comparison of the conformations of the levomepromazine cations with those of the neutral mol-ecule and similar protonated mol-ecules reveals significant conformational flexibility of the pheno-thia-zine ring system and the substituent at the pheno-thia-zine N atom.

Crystal structure of diethyl 3-(3-chloro-phen-yl)-2,2-di-cyano-cyclo-propane-1,1-di-carboxyl-ate.

In the racemic title compound, C17H15ClN2O4, which has been synthesized and the crystal structure of the solvent-free mol-ecule determined, the angle between the planes of the benzene and cyclo-propane rings is 54.29 (10)°. The mol-ecular conformation is stabilized by two weak intra-molecular C-H⋯Ocarbox-yl inter-actions. In the crystal, C-H⋯O hydrogen bonds form centrosymmetric cyclic R 2 (2)(10) dimers which are linked into chain substructures extending along c. Further C-H⋯Nnitrile hydrogen bonding, including a centrosymmetric cyclic R 2 (2)(14) association, link the chain substructures, forming a two-dimensional layered structure extending across the approximate ab plane. No significant π-π or halogen-halogen inter-molecular inter-actions are present in the crystal.

Crystal structure of diethyl 2-acet-oxy-2-[3-(4-nitro-phen-yl)-3-oxo-1-phenyl-prop-yl]malonate.

In the racemic title compound, C24H25NO9, the dihedral angle between the planes of the two benzene-ring systems is 80.16 (6)°, while the side-chain conformation is stabilized by a methyl-ene-carboxyl C-H⋯O hydrogen bond. Weak inter-molecular C-H⋯O hydrogen bonds form inversion dimers [graph set R 2 (2)(16)] which are linked into chains extending along a. Further C-H⋯O hydrogen bonding extends the structure along b through cyclic R 2 (2)(10) motifs. Although no π-π aromatic ring inter-actions are present in the structure, C-H⋯π ring inter-actions across c generate an overall three-dimensional supra-molecular structure.