Calcium coordination compounds of dipicolinic and quinolinic acids: synthesis, characterization, crystal structures and DFT studies
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Date
2022
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Abstract
<jats:title>Abstract</jats:title>
<jats:p>In the past two decades various N-heterocyclic carboxylate coordination compounds have been synthesized with intriguing architectures and potential applications as functional materials. In this regard, two novel calcium coordination compounds [Ca(2,6-Hpdc)<jats:sub>2</jats:sub>(H<jats:sub>2</jats:sub>O)<jats:sub>2</jats:sub>] <jats:bold>1</jats:bold> and [Ca<jats:sub>2</jats:sub>(2,3-pdc)<jats:sub>2</jats:sub>(H<jats:sub>2</jats:sub>O)<jats:sub>6</jats:sub>]<jats:sub>n</jats:sub> <jats:bold>2</jats:bold> (where 2,6-H<jats:sub>2</jats:sub>pdc = 2,6-pyridinedicarboxylic acid and 2,3-H<jats:sub>2</jats:sub>pdc = 2,3-pyridinedicarboxylic acid) were grown at room temperature. The compounds were characterized using elemental analysis, Fourier Transform infrared (FT-IR) spectroscopy, thermogravimetric analysis, powder X-ray diffraction and single crystal X-ray crystallographic analysis. Compounds <jats:bold>1</jats:bold> and <jats:bold>2</jats:bold> crystallize in orthorhombic space group <jats:italic>Pccn</jats:italic> and monoclinic space group <jats:italic>Pc</jats:italic>, respectively. The structures of both compounds are stabilized by a network of hydrogen bonds arising from coordinated water molecules and carboxylate groups. Computational analysis revealed that compound <jats:bold>1</jats:bold> has a large energy gap (9.221 eV) suggesting high excitation energies and chemical hardness making it a better electron acceptor while compound <jats:bold>2</jats:bold> displayed a smaller energy gap (5.156 eV) which is indicative of a softer molecule with better polarizability and reactivity.</jats:p>