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      https://www.ias.ac.in/article/fulltext/jcsc/119/01/0011-0020

    • Keywords

       

      4-Nitrobenzoate; imidazole; supramolecular; monodentate; H-bonding interactions; bifurcated donor; bifurcated acceptor; 𝜋-𝜋 interactions.

    • Abstract

       

      The reaction of hydrated magnesium or calcium 4-nitrobenzoate (4-nba) generated in situ, with imidazole (Im) results in the formation of the complexes [Mg(H2O)2(Im)2(4-nba)2] 1 and [Ca(H2O)3(Im)(4-nba)2]$\cdot$Im 2, which exhibit the same metal:4-nba:Im ratio but different degrees of hydration. Complex 1 crystallizes in the triclinic $P_{\bar{i}}$ space group and the Mg atom is located on an inversion centre, while 2 crystallizes in the monoclinic $P2_1/c$ space group and all atoms are located in general positions. In 1 the Im ligands, which are trans to each other, are coordinated to Mg, while 2 contains coordinated as well as free Im. The monodentate 4-nba ligands are disposed trans to each other in 1, while they adopt a cis orientation in 2 resulting in different supramolecular structures. Complex 1 exhibits two types of H-bonding interactions namely O-H𝛬O and N-H𝛬O, while in 2 three varieties of H-bond, viz. O-H𝛬O, N-H𝛬O and O-H𝛬N are observed. The Im ligand functions as a bifurcated H-bond donor in 1 while the O atom of the nitro group functions as a H-bond acceptor. In contrast, the nitro group in 2 is not involved in any H-bonding interactions. The free Im in 2 functions as a bifurcated acceptor and forms an extended chain linking adjacent complex molecules. The chains thus formed are further cross-linked with the aid of H-donor bonds from both the free as well as the coordinated Im. Both 1 and 2 exhibit 𝜋-𝜋 stacking interactions. Complex 1 is thermally more stable as compared to 2, and both complexes can be dehydrated to the corresponding anhydrous complexes by heating at 140 and 100°C respectively. At elevated temperatures, both the complexes can be pyrolysed to the corresponding oxide. The anhydrous complexes can be rehydrated to obtain the starting hydrated materials.

    • Author Affiliations

       

      Bikshandarkoil R Srinivasan1 Jyoti V Sawant1 Pallepogu Raghavaiah1

      1. Department of Chemistry, Goa University, Goa 403 206
    • Dates

       
  • Journal of Chemical Sciences | News

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