Polymorphism and isomorphism in trans-bis(2,5-diiodopyridine)dihalocopper(ii) complexes: theoretical and crystallographic studies?

New Journal of Chemistry Pub Date: 2022-09-09 DOI: 10.1039/D2NJ03373A

Abstract

Two polymorphs of each of the complexes, [Cu(25dIpy)2Cl2] and [Cu(25dIpy)2Br2], (where 25dIpy = 2,5-diiodopyridine) were prepared and characterized by single crystal and powder X-ray diffraction methods. The two polymorphs of [Cu(25dIpy)2Cl2] are conformational polymorphs, whereas, the polymorphs of [Cu(25dIpy)2Br2] are packing polymorphs. The formation of the conformational polymorphs is due to the rotation around the Cu–N bond, which results in the formation of two geometries: (a) syn-geometry; the iodine atoms located in the position 2 of each pyridine ring are oriented in the same direction and (b) anti-geometry: the two iodine atoms are oriented in opposite directions. The above geometrical conformers of [Cu(25dIpy)2Cl2] are stabilized by C–H?Cl hydrogen bonding interactions in the syn-geometry and by Cu?I interactions in the anti-geometry). The conformational polymorphs have different optical properties; syn-[Cu(25dIpy)2Cl2] is green, whereas, anti-[Cu(25dIpy)2Cl2] is brown. The two backing polymorphs of [Cu(25dIpy)2Br2] complex are brown. The molecular structures of the two packing polymorphs are almost identical, while, their supramolecular structures differ significantly; the topologies of C2–I2?Br halogen bonding interactions are similar in both polymorphs while that of C5–I5?Br halogen bonding interactions are not. The role of the solvent and temperature on the formation of the different polymorphs was investigated. The supramolecular structures of the different polymorphs were rationalized based on C–I?X halogen bonding interactions. The crystallographic results were supported by density functional theory (DFT) calculations and by analyzing the topology of the electron density using the quantum theory of atoms in molecules (QTAIM). The kinetics of the rotation process (syn-anti interconversion) were studied using the QST2 method.

Graphical abstract: Polymorphism and isomorphism in trans-bis(2,5-diiodopyridine)dihalocopper(ii) complexes: theoretical and crystallographic studies
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