Synthesis and structure of diaquabis(nicotinamide-κ<i>O</i>)bis(nitrato-κ² <i>O</i>,<i>O</i>′)calcium(II)

The title complex, [Ca(NO 3 ) 2 (C 6 H 6 N 2 O) 2 (H 2 O) 2 ], crystallizes with an eight-coordinate Ca 2+ ion in a distorted trigonal–dodecahedral coordination environment. The metal ion is coordinated to two nicotinamide ligands via their carbonyl O atoms, two bidentate nitrate anions and two water molecules. The nicotinamide ligands adopt a nearly trans geometry, while the nitrate anions and aqua ligands are arranged in a pseudo- trans fashion. In the crystal, a three-dimensional supramolecular framework is constructed through N—H...O and O—H...O hydrogen bonds involving water, nitrate, and nicotinamide functional groups, reinforced by offset π–π stacking interactions between nearly parallel pyridine rings [centroid-to-centroid distance = 3.783 (2) Å]. A Hirshfeld surface analysis revealed that the intermolecular interactions are dominated by O...H/H...O (42.3%) and H...H (26.2%) contacts, corresponding to classical hydrogen bonding and van der Waals forces, respectively.

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