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Acta Cryst. (2014). A70, C556
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Hydrogen bonds have been exhaustively investigated in order to understand their role in intermolecular interactions [1]. The importance of the hydrogen bonds follows from their particular role in the molecular association thanks to their variable strength and geometry. Indeed depending on the chemical nature of the donor/acceptor as well as on the physical parameters such as temperature and pressure, hydrogen bonds can give rise to directional and/or to hydrophilic like interactions which play a crucial role both in stabilizing static structures and in mediating dynamic biological processes. Among the hydrogen bonds the less common ones are the strongest (and shortest) ones, characterized by donor-acceptor interatomic distances shorter than 2.6 Å with D-H...A angle close to 180° [2]. Most of the short hydrogen bonds observed and reported so far are intramolecular interactions, nevertheless, both the bridging as well as the coordination of the metal ions by carboxylate groups and oxalate anions can provide the possibility of short interactions [3]. During the refinement of the structure of the potassium-monodeprotonated salt of 1,4-butodioxybis(4'-benzoic) acid it was observed a high electron density maxima over the mirror symmetry element. This electron density indicates a hydrogen atom doing an ultra short intermolecular hydrogen bond (2.4846(1) Å) between the deprotonated and non-deprotonated carboxylic acid groups. The seven fold coordinate potassium atom ties the organic moieties pushing the hydrogen atom closer to the deprotonated and negatively charged, carboxylate oxygen atom. The hydrogen atomic displacement parameter suggests, however, a possible positional disorder, which could be interpreted both as symmetrical O-H-O or asymmetrical O-H...O interaction.

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Acta Cryst. (2014). A70, C1252
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Valence tautomers are bi-stable functional molecular materials in which it is observed charge transference between redox active ligands and a metallic center followed by the change of spin of the metal. Valence tautomerism (VT) interconversion is entropically driven and induced by external stimuli such as irradiation by light and soft X-rays and/or changes in temperature and pressure. VT interconversion is also associated with remarkable variations in optical and magnetic properties and and can be modulated with slight chemical changes [1]. Typical examples of valence tautomers are coordination compounds of Co and o-dioxolenes ligands [2]. Crystals of the [Co(diox)(4-X-py)2], where diox = 3,5-di-t-butylcatecholate/3,5-di-t-butylsemiquinonate, X=CN/NO2, py= pyridine, were initially studied with respect to low spin (LS) to high spin (HS) thermo and photoinduced VT interconversion. It was reported that [Co(diox)(4-CN-py)2] crystals become HS-Co3+ at temperatures below 110 K with cooperative VT interconversion whereas [Co(diox)(4-NO2-py)2] crystals present non cooperative VT interconversion [3]. Toluene and benzene solvates of [Co(diox)(4-NO2-py)2 and [Co(diox)(4-CN-py)2 have been prepared to investigate further the solvation effects on the VT interconversion properties. Analysis of the single crystal X-ray diffraction data obtained during cooling and heating at temperatures ranging from 293 K to 90 K indicated that [Co(diox)(4-CN-py)2] toluene and benzene as well as [Co(diox)(4-NO2-py)2].toluene solvate crystals undergo into non cooperative VT interconversion. The [Co(diox)(4-NO2-py)2].benzene crystal show a highly cooperative VT interconversion with a pronounced hysteresis. Intermolecular interactions between inlayer [Co(diox)(4-X-py)2] molecules are responsible for the VT interconversion in all compounds, however the VT interconversion cooperativity seems to be related with the strength of the Car-H...Odiox interactions and with the correspondent Co-Co separation. Thus solvation plays a key role in the definition of the VT interconversion nature. Acknowledgments: FAPEMIG, CNPq and CAPES grant 10030-12-3.

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Acta Cryst. (2014). A70, C1257
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The search for new functional materials involves the development of bistable molecules exhibiting different electronic states with distinct properties at the ambient condition (temperature, pressure, illumination) of application. Coordination compounds, which present electron transfer between metal ion and an organic ligand associated with a change in electron multiplicity of the metal ion, are named valence tautomers(VT)[1]. The chemical equilibrium between two distinct electronic states in VT can be induced by temperature and pressure change as well as by soft X-ray and light irradiation. Thermodynamic and structural data highlighting the mechanisms of the valence tautomerism interconversion can be found in the literature for materials build up with cobalt and benzoquinones such as the 3,5-di-t-butyl-semiquinonate. However, to the best of our knowledge, there is no example of compounds showing VT build up with cobalt and naphthoquinones. In the present work 2-hydroxy-1,4-naphthoquinone (law) has been used as redox active ligands in the search for new VT compounds with cobalt. Three new coordination compounds of cobalt and 2-hydroxy-1,4-naphthoquinone (law), [Co(law)2(im)2], [Co(law)2(phen)] e [Co(law)2(bpy)] were synthesized and characterized by infrared (IR), UV-vis spectroscopy, electron paramagnetic resonance (EPR) and cyclic voltammetry. The three dimensional structures were determined using single crystal X-ray diffraction techniques. However, within the investigated temperature range neither X-ray diffraction nor EPR data showed the presence of VT in the materials, mainly due to the electrochemical properties of the 2-hydroxy-1,4-naphthoquinone. Nevertheless the structural features of the compounds as well as their supramolecular packing motifs suggest that naphthoquinones can be an alternative for the synthesis of compounds showing valence tautomerism[3].

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Acta Cryst. (2014). A70, C1258
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The design, synthesis and characterization of infinite one-, two- and three dimensional coordination polymers have attracted increasing attention in chemistry and material science research due to their potential applications as drug deliver, magnetic and optical sensors [1]. In particular, a series metal-organic frameworks MOFs - (a coordination polymer subclass) with different topological nets such as honey-comb, brick wall, ladder, herringbone, diamondoid and rectangular grids have been comprehensively discussed by Yaghi, Kitagawa and their co-workers [2] and it was observed that the type of metal ion and organic bridge ligand determines the dimensionality and the topology of the network. In this work we report a new 2D coordination polymer obtained by from ZnSO4.7H2O and 5-aminoisophtalic acid (5AIF), using the base diffusion method (DMSO as solvent). The crystal structure was determined from single crystal X-ray diffraction data collect in a Gemini-Oxford diffractometer. The Zn atom is tetrahedrally coordinated with two oxygen and one nitrogen from three different 5AIF molecules and one oxygen from DMSO molecules. The molecular packing indicates the formation of a 2D parallel to (010) forming hydrophilic cavities along [001]. The 2D network is stabilized by intermolecular hydrogen bonds involving the donor hydroxyl group (O3-H3) and the acceptor nitrogen atom (N1). The geometrical features of this new 2D coordination polymer were are all in agreement with similar fragments deposited in CSD [3].
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