The investigation of modification in structural flexibility and coordination modes in a solvent free β-diketone Cu(II) complex by crystal structure and DFT studies

Abstract

Coordination-driven self-assembly in inorganic complexes is a viable methodology to construct supramolecular coordination complexes. Crystal engineering of β-diketone Cu(II) coordination complexes can be achieved via the host–guest complexation method. The effect of metal–ligand interactions (coordination polyhedra) on the supramolecular framework has been analysed by crystal structure and computational studies. A new crystal form of a Cu(II) complex with 4,4,4-trifluoro-naphthyl butanedione has been identified and characterized using various spectroscopic techniques. X-ray diffraction studies unveiled that complex 1, [Cu(TFNB)2], crystallized in the monoclinic (P21/n) space group and its solvent-induced crystal forms, complex 2, [Cu(TFNB)2DMSO] (Database Identifier: IVAKIC), and complex 3, [Cu(TFNB)2DMF] (Database Identifier: ZOCHOR), which were reported earlier, are in the triclinic (P1¯) crystal system. The previously reported crystal forms (complexes 2 and 3) are examples of a single crystal coordinated solvent exchange (SCCSE) transformation. In complex 1, the β-diketone molecules are attached to the metal ion in an equatorial form with a perfect square planar geometry, whilst complexes 2 and 3 feature a slightly distorted square pyramidal geometry with chelated donor oxygen atoms of the β-diketone ligands in equatorial sites and the crystallizing DMSO and DMF solvents are apically coordinated to the metal centre, respectively. Interestingly, the oxygen donors of the β-diketone ligands in complex 1 are inclined in a trans configuration, whereas in the solvent-induced pseudopolymorphic forms of complexes 2 and 3, a cis configuration is observed. The variation in the supramolecular framework with the coordination geometry in different crystal forms is analysed using the crystal structures and compared with quantum computational (Hirshfeld surface, enrichment ratio, energy framework, NCI index model and DFT) results. Molecular docking analysis was performed for all the complexes against the SARS-CoV2 main protease to explore the structure–property relationship.