Spectroscopic properties, crystal structure, Hirshfeld surface analysis and DFT study of a new Cu(II) complex based on quinazolinone O,N, O-donor ligand

A quinazolinone-based Schiff base ligand 3-[(2-hydroxy-5-methoxybenzylidene)amino]-2-(2-hydroxy-5methoxyphenyl)-2,3-dihydroquinazolin-4-one (L1) and its new mononuclear copper(II) complex [Cu(L1)Cl (H2O)] (1) were synthesised and fully characterised by various spectroscopic techniques (NMR, FTIR, UV-Vis) and single-crystal X-ray diffraction study. The aspherical model of the crystal structure of the ligand L1 as well as of the copper(II) complex 1 was refined by the Hirshfeld Atom Refinement method. The crystal structure of the copper(II) complex shows the existence of a substitution disorder at the position of the water molecule, which represents two different complex molecules [Cu(L1)Cl(H2O)] (1a) and [Cu(L1)Cl] (1b) with different coordination polyhedra around the copper atom. The majority of the mononuclear complex [Cu(L1)Cl(H2O)] (1a) in the crystal structure contains a coordinated water molecule, but the minority in the crystal structure contains a mononuclear complex [Cu(L1)Cl] (1b) and a water molecule is outside the coordination sphere around the copper atom. The crystal structure of complex 1 showed a penta-coordinated (1a) or tetra-coordinated (1b) Cu atom in the shape of a tetragonal pyramid (1a) or square planar (1b) formed by a chloride atom in the equatorial plane, and a Schiff base bound as an O,N,O-tridentate ligand, and an additional water molecule in the axial position (only 1a). A detailed analysis of the intermolecular interactions was investigated using threedimensional 3D Hirshfeld surfaces and their associated two-dimensional 2D fingerprint plots. Hirshfeld surface analysis was performed for both crystal structures. Furthermore, theoretical DFT analysis has been performed in order to interpret the experimental data. In order to obtain high quality DFT data, we present here a new basis set B1MH, which is an extension of the LanL2DZ basis with incorporated polarisation and diffusion functions for heavy atoms (C, N, O, Cl and Cu) and added ECPs for Cl and Cu atoms. The presented B1MH basis set allowed us to obtain better theoretical results than those previously published.